Geotechnical Engineering Report...Geotechnical Engineering Report Prepared for Vermont Agency of Transportation 1 National Life Drive Montpelier, Vermont 5633-5001 July 2013 CHA Project

Geotechnical Engineering Report

Prepared for

Vermont Agency of Transportation

1 National Life Drive Montpelier, Vermont 5633-5001

July 2013 CHA Project No. 23825.4000.32000

III Winners Circle, Albany, NY 12205-0269 www.chacompanies.com

Bridge Replacement PIN 10C216

BHF 0241(38) Bethel, Vermont

Bridge Replacement BHF 0241(38)

- ii - Bethel, Vermont

TABLE OF CONTENTS

SECTION PAGE NUMBER

1.0 INTRODUCTION............................................................................................................. 1

1.1 Purpose and Scope of Services ....................................................................................... 1 1.2 Site History ..................................................................................................................... 1 1.3 Project Description ......................................................................................................... 2 1.4 Project Authorization ..................................................................................................... 3

2.0 SUBSURFACE INVESTIGATION ................................................................................ 4

2.1 Investigation ................................................................................................................... 4 2.2 Laboratory Testing ......................................................................................................... 5

3.0 SUBSURFACE CONDITIONS ....................................................................................... 7

3.1 Regional Geology ........................................................................................................... 7 3.2 Subsurface Stratigraphy ................................................................................................. 7 3.3 Groundwater Observations ............................................................................................. 9

4.0 EVALUATION AND RECOMMENDATIONS .......................................................... 10

4.1 Permanent Bridge Structure ......................................................................................... 10 4.2 Temporary Bridge Structure ......................................................................................... 11 4.3 Driven Piles .................................................................................................................. 11 4.4 Spread Footings ............................................................................................................ 13

4.4.1 Strength Limit Design ................................................................................... 14 4.4.2 Service Limit Design ..................................................................................... 14

4.5 Drilled Shafts ................................................................................................................ 14 4.6 Lateral Earth Pressures ................................................................................................. 17 4.7 Seismic Site Classification and Design Parameters ..................................................... 18

5.0 CONSTRUCTION CONSIDERATIONS .................................................................... 19

5.1 Rock Removal .............................................................................................................. 19

5.2 Subgrade Preparation ................................................................................................... 20 5.3 Subgrade Protection ..................................................................................................... 21

5.4 Engineered Fill ............................................................................................................. 21 5.5 Control of Water ........................................................................................................... 22 5.6 Temporary Excavations ................................................................................................ 22

6.0 CLOSURE ....................................................................................................................... 23


- iii - Bethel, Vermont

TABLES

Table 1: Laboratory Analysis Samples .......................................................................................... 6

Table 2: Permanent Bridge Structure Foundation Types ............................................................. 10

Table 3: Temporary Bridge Structure Foundation Types ............................................................ 11

Table 4: Nominal H-Pile Capacities at North Abutment ............................................................. 12

Table 5: Factored Bearing Resistance – Strength Limit Design .................................................. 14

Table 6: Drilled Shaft Embedment Lengths (from Factored Resistance) .................................... 15

Table 7: Granular Backfill Soil Parameters for Earth Pressure Coefficients ................................ 17

Table 8: Seismic Design Site Coefficients ................................................................................... 18

Table 9: Ground Vibration Limits for Newly Placed Concrete .................................................... 19

APPENDICES

Appendix A: Figures

Appendix B: Site Photographs

Appendix C: Excerpts from 1928 Record Drawings

Appendix D: Boring Logs

Appendix E: Laboratory Test Results


- 1 - Bethel, Vermont

1.0 INTRODUCTION

1.1 Purpose and Scope of Services

This report summarizes the results of the geotechnical investigation performed by CHA for

the Vermont Agency of Transportation (VTrans) for the replacement of Bridge 38 over Gilead

Brook in Bethel, Vermont. The bridge has a north-south alignment and carries VT State

Route 12 between Bethel and Randolph. This work is part of VTrans BHF 0241 (38), PIN

10C216.

The primary objectives of this investigation were to evaluate subsurface conditions at the

proposed abutment and pier locations for the permanent replacement bridge, and a temporary

bridge to be used during construction, and provide geotechnical recommendations for

foundation design and construction of the permanent bridge.

1.2 Site History

Bridge 38 was constructed over Gilead Brook to serve as a replacement of the bridge that

washed away in the historic flooding of 1927. Realignment of VT Route 12 took place at this

time resulting in approach fills up to about 20 feet at the south abutment and 35 feet at the

north abutment. Construction drawings from 1928 were provided by VTrans.

The 1928 replacement bridge is founded on three piers and two abutments. The piers are

denoted, north to south, as Pier No. 1 through Pier No. 3. The north abutment is Abutment

No. 1 and the south abutment is Abutment No. 2. The drawings indicate that Pier No. 3 and

Abutment No. 2 foundations were constructed with spread footings on the bedrock surface.

Pier No. 1, Pier No. 2 and Abutment No. 1 foundations were constructed with timber piles

with a minimum bearing capacity of 15 tons. The elevation data on the drawings is assumed

to have been used with a local datum reference. Copies of sheets related to the bridge

foundations are included in Appendix C.

During Tropical Storm Irene flooding in 2011 and/or previous storm events, the center pier,

Pier No. 2, shifted thereby reducing the pier’s support to the bridge deck. In addition, the



bridge superstructure is structurally deficient for current HL-93 loadings, and strengthening of

the current members is not economically feasible. Therefore, complete bridge replacement is

proposed.

1.3 Project Description

This project consists of replacing the existing 320-foot long, three span bridge with a two or

three span structure. At the time of this report, a three span structure is favored based on

CHA’s bridge design group’s Alignment and Structure Study report submitted to VTrans in

May 2013 and recommendations outlined in this report are based on that configuration,

including preliminary static loading of the substructure elements.

The north end of the bridge is located approximately 0.2 mile south of the VT Route 12 and

Gilead Brook Road intersection. The southern end of the bridge is bounded by the

intersection with Spring Hollow Road. The Site Location Map is included as Figure 1 in

Appendix A. Photos of the site are included in Appendix B.

In addition to replacement of the existing structure, a temporary bridge will be installed

approximately 90 feet east of the existing bridge alignment to convey VT Route 12 traffic

during construction. The temporary bridge configuration is currently undetermined but

borings were taken to allow for abutment and/ or pier support at brook level or on the top of

stream bank.

Bedrock outcrops are visible at the toe of the southern abutment embankment at

approximately the streambed level. Based on comparison to record drawings, the streambed

and embankments have been severely eroded since construction in 1928. Fresh scarps on

both the north and south embankments and downed trees indicate that the 2011 Tropical

Storm Irene flooding was a significant erosion event.



1.4 Project Authorization

CHA performed our services in accordance with our proposal number X36216 dated February

26, 2013. VTrans authorized the work as part of Contract Number PS0178 in a letter dated

April 10, 2013.



2.0 SUBSURFACE INVESTIGATION

2.1 Investigation

Borings were advanced over 10 work days between May 8 and May 21, 2013 to depths

meeting VTrans refusal criteria for bridge structures of either 10 feet of rock core or 30 feet

into soil with N greater than 100 blows per foot (bpf). Borings B-1, B-7, B-7A, B-11 and B-

12 were advanced within VT Route 12. Borings B-2 through B-6, B-8 through B-10 and B-

10A were advanced within the Gilead Brook streambed in the areas of the proposed piers and

abutments.

The approximate boring locations, as determined by taking ties to existing features, are shown

on Figure 2: Boring Location Plan included in Appendix A. The ground surface elevations at

the boring locations indicated on the logs were interpolated from the survey information

provided to CHA from Vermont Survey in October 2012. The locations and elevations of the

borings should be considered accurate only to the degree implied by the method used to

determine them.

A CHA geotechnical engineer observed the borings to ensure that proper drilling techniques

were used. They also prepared boring logs based upon visual observation of the soil samples

and drilling action. A copy of the boring logs is included in Appendix D. Additional

information regarding the sample descriptions is included on the Legend to Subsurface Logs

included in Appendix D.

CHA retained New Hampshire Boring, Inc. of Londonderry, New Hampshire to advance the

borings. The borings were performed by an ATV-mounted drill rig advancing 3-, 4- or 5-

inch-inside-diameter flush joint casing. The drillers performed Standard Penetration Tests

(SPT) using a split spoon sampler with an approximately 140-pound safety hammer at the

depths noted on the borings logs in general accordance with AASHTO T 206: Standard

Method of Test for Penetration Test and Split-Barrel Sampling of Soils. Additional

information regarding the soil sampling procedures is included on the Legend to Subsurface

Logs included in Appendix D.



An NX size core barrel was used to collect bedrock samples from all borings with the

exception of B-7A, B-11 and B-12. The Rock Quality Designation (RQD) values were then

determined in the field for the bedrock core samples. Additional information regarding the

rock core sampling procedures and sample descriptions is included on the Legend to

Subsurface Logs included in Appendix D.

Boring B-7 was abandoned prior to VTrans refusal requirements due to broken casing in the

bottom of the boring and the exploration was offset to B-7A. Boring B-7A was terminated at

a depth of 25 feet into material with SPT N-values greater than 100 blows per foot. Borings

B-11 and B-12 were advanced for purposes of sampling the subbase and subgrade materials

beneath the asphalt pavement on VT Route 12 and sampled with a 3-inch split spoon sampler.

Upon completion, the boreholes were backfilled with soil cuttings. The borings advanced

within VT Route 12 were patched at the ground surface with bituminous cold patch.

2.2 Laboratory Testing

Eleven soil samples representative of the soil layers observed were submitted to the VTrans

soil lab for the tests indicated in Table 1. The tests were performed in general accordance

with the following standard test methods:

AASHTO T-265: Laboratory Determination of Moisture Content of Soils,

AASHTO T-88: Particle Size Analysis of Soils, and

AASHTO T-90: Determining the Plastic Limit and Plasticity Index of Soils.

A copy of the laboratory test report is included in Appendix E and the data is included on the

boring logs in Appendix D.



Table 1: Laboratory Analysis Samples

Boring Depth (ft) Strata AASHTO T-88

AASHTO T-90

N/A Stream Grab Sample Sandy Gravel X

B-1 3 – 7 Fill X

B-1 13 – 15 Silt X X

B-4 2 – 4 Glacial Till X X

B-5 0 – 2 Sandy Gravel X

B-6 4 – 6 Glacial Till X

B-7 5 – 7 Fill X

B-7 9 – 11 Fill X

B-7 34 – 36 Glacial Till X X

B-7A 69 – 79 Glacial Till X X

B-12 1 – 3 Fill X



3.0 SUBSURFACE CONDITIONS

3.1 Regional Geology

CHA reviewed the following publications to assess the regional geologic conditions:

Doll, C.G., W. M. Cady, J. B. Thompson, and M. P. Billings (1970) “Surficial

Geologic Map of Vermont.” Vermont Geological Survey.

Ratcliffe, N.M., R.S. Stanley, M.H. Gale, P.J. Thompson, and G.J. Walsh (2011)

“Bedrock Geologic Map of Vermont,” U.S. Geological Survey Scientific

Investigations Map 3184.

According to the Surficial Geologic Map of Vermont, the bridge is likely located within

horizontally bedded deposits of gravel. Glacial till deposits are noted to the north and south.

It was anticipated that the natural soils above bedrock may contain numerous cobbles and

boulders due to the observed cobbles on the river banks and notes on the 1928 record

drawings.

According to the Bedrock Geologic Map of Vermont, conglomerate and conglomerate

quartzite bedrock cross the site from northwest to southeast and was anticipated to be the

predominate rock type at the permanent bridge. Quartz-muscovite phyllite and silicic

phyllite, and garnet-rich biotite-muscovite-quartz schist are located immediately northeast of

the site and may be the predominate rock type below the temporary bridge. Bedrock is

exposed at the toe of the southern stream bank.

3.2 Subsurface Stratigraphy

Subsurface conditions encountered in the borings are detailed and described on the boring

logs included in Appendix D of this report. Subsurface profiles along the alignments of the

proposed and temporary bridges are included as Figures 3 and 4 in Appendix A. Subsurface

conditions are generally described below.



Pavement – A 4- to 10-inch thick layer of asphalt pavement was encountered at the ground

surface in borings B-1, B-7, B-7A, B-11 and B-12.

Fill – Granular fill was encountered below the pavement in the borings advanced in the

roadway to depths ranging from 9.5 feet at the southern abutment and 27.5 feet at the northern

abutment. Borings B-11 and B-12 were terminated in the fill at depths of 4.4 feet and 4.8

feet, respectively. The fill materials were fine to coarse sand with varying amounts of silt and

fine to coarse gravel. The fill was brown and visually described as moist. The SPT N-values

ranged between 11 and 29 blows per foot (bpf) indicating medium compact conditions.

Alluvial Deposits – Alluvial deposits were encountered at the ground surface in all borings

advanced within Gilead Brook to depths ranging from 2 to 3 feet. The deposits generally

consisted of fine to coarse sand with varying amounts of silt and fine to coarse gravel. The

deposits were brown to red and visually described as moist to wet. The SPT N-values ranged

between 14 and 28 bpf, indicating medium compact conditions.

Glacial Till – Glacial till was encountered beneath the fill and lacustrine deposits in borings

B-1, B-4, B-6, B-7, B-7A and B-10 to depths ranging between 10.5 and 84.5 feet at

termination of B-7A. The glacial till was fine to coarse sand and silt with varying amounts of

fine to coarse gravel. The glacial till was brown to gray and visually described as moist to

wet. The SPT N-values ranged from 15 to greater than 100 bpf, indicating medium compact

to very compact conditions.

Boulders and cobbles are likely embedded within the glacial till. Drilling refusal was

encountered in boring B-7 and during core sampling, 6 feet of boulder material was

recovered.

Quartzite – Quartzite was encountered below the glacial till in boring B-4 to a depth of 22

feet. The quartzite was light gray, medium hard, moderately weathered and had an RQD

value of 52% indicating fair rock quality conditions.



Phyllite – Phyllite bedrock was encountered beneath the glacial till or quartzite in all borings

to termination depths with the exception of B-7 and B-7A. The phyllite was gray to dark

gray, micaceous, soft to medium hard, slightly to severely weathered and had RQD values

ranging from 22 to 96% indicating very poor to excellent rock quality conditions. Several of

the core recoveries had large white quartz seams embedded within the sample.

3.3 Groundwater Observations

Groundwater was observed at elevation 666.1 feet in boring B-1 and at 662.0 feet in boring B-

7. Borings B-2 through B-6 and B-9 through B-10A were advanced within the Gilead Brook

streambed and the water level was observed to be within 1 foot of the ground surface.

The water depth of Gilead Brook ranged from less than 1 inch to approximately 12 inches at

the time of the investigation.

The boreholes were generally only open for a short time period during the drilling and clean-

up activities, and water was used as a drilling fluid. Also some of the soils at the site had high

fines content and produce water slowly. Therefore, groundwater level observations during

drilling operations may not represent static conditions. Seasonal factors such as temperature

and precipitation also affect groundwater levels. For this reason, long-term groundwater

levels may differ from those described in this report.



4.0 EVALUATION AND RECOMMENDATIONS

The following recommendations have been prepared based upon the guidelines presented in

the 2010 VTrans Structures Design Manual which is based upon the AASHTO 2010 LRFD

Bridge Design Specifications, 5th Edition. We understand that the preferred bridge alternative

identified by CHA in the Alignment and Structure Study, is a 3-span, continuous steel girder,

integral abutment bridge.

4.1 Permanent Bridge Structure

VTrans’ preferred abutment style for replacement bridges is integral abutment. Therefore, the

abutments will be founded on driven piles. Maximum 10-foot long wing walls will be

cantilevered off the abutments. The pier foundation support and self-supported wing wall

extension foundations, if more than 10-foot long wing walls are required based on final

roadway and alignment and embankment slopes, will be determined based on the encountered

subsurface condtions. Results of the subsurface investigation along the permanent bridge

alignment have been compiled into a visual representation of estimated stratigraphy, Figure 3

in Appendix A.

The following table outlines the recommended foundation type for each structure of the

permanent bridge:

Table 2: Permanent Bridge Structure Foundation Types

Structure Recommended Foundation Type South Abutment Integral Abutment / Driven Piles

South Abutment Wing Wall Extensions

Driven Piles or Spread Footings on Glacial Till

South Pier Spread Footing on Bedrock North Pier Cast-in-Place Drilled Shafts

North Abutment Integral Abutment / Driven Piles North Abutment Wing

Wall Extensions Driven Piles or Spread Footings on

Glacial Till



4.2 Temporary Bridge Structure

A temporary bridge will be constructed to direct traffic on VT Route 12 around the

construction site. The configuration of the temporary bridge has not been determined and

design of the temporary bridge will likely be the selected contractor’s responsibility. Results

of the subsurface investigation along the temporary bridge alignment have been compiled into

a visual representation of estimated stratigraphy, Figure 4 in Appendix A.

In general, the following table outlines feasible foundation types for the temporary bridge:

Table 3: Temporary Bridge Structure Foundation Types

Structure Recommended Foundation Type

South Side Spread Footing on Bedrock or Undisturbed Glacial Till

North Side Driven Piles to Bedrock or Undisturbed Glacial Till

4.3 Driven Piles

VTrans recommendations outline integral abutment configurations as the preferred foundation

type for new permanent bridge construction. CHA’s Alignment and Structure Study also

outline recommendations for integral abutment foundations. Therefore driven piles are

recommended for the permanent bridge integral abutments. Based on subsurface conditions,

the piles at the south abutment will likely encounter refusal on bedrock and the capacity will

be controlled by the structural strength of the steel. The piles at the north abutment will likely

obtain capacity in the glacial till.

In addition to the VTrans design manual, abutment foundation recommendations are based on

VTrans Integral Abutment Pile Design Guidelines, 2nd Edition, 2008 and AASHTO LRFD

Bridge Design Specifications, 5th Edition, 2010.

We recommend supporting the abutments on steel piles arranged with the weak axis parallel

to the bridge center line driven to bedrock at the south abutment and to refusal criteria within



the glacial till at the north abutment. Where driven to bedrock the pile capacity will be

controlled by the structural strength of the steel. Piles achieving capacity within the glacial

till will be controlled by soil conditions. Bedrock was encountered at elevation 656 feet in

boring B-1 at the south abutment, and was not encountered at boring termination of elevation

617 feet in B-7A at the north abutment.

Piles at the north abutment will have capacities outlined in Table 4 if bedrock is not

encountered during pile driving operations.

Table 4: Nominal H-Pile Capacities at North Abutment

Pile Size Nominal Unit Side Friction (kips/ft) Nominal Tip Resistance in Glacial Till (kips) Fill Material Glacial Till

HP10x57 1.75 2.76 200 HP12X74 2.11 3.33 290 HP14X102 2.50 3.94 420

A resistance factor ( ) of 0.65 shall be applied to the nominal resistances above for strength

limit design. This resistance factor assumes that pile dynamic testing with signal matching

and restrike testing is performed on at least two piles per abutment. A resistance factor ( ) of

1.0 shall be applied to the nominal resistances above for service limit design.

Based on VTrans criteria provided in Integral Abutment Bridge Design Guidelines section

10.2.2.3, the minimum pile length for an integral abutment structure using simplified analysis

techniques is 16 feet below scour depths to pile refusal, in addition to a minimum extension of

1 foot into the pile cap. Additionally, piles should be spaced greater than 5 feet-on-center so

as not to act as a pile group.

We anticipate pile lengths, based on preliminary loads and encountered subsurface conditions

will be about 30 feet and 60 feet at the south and north abutments, respectively. These lengths

are based on existing road grades being maintained. Final pile length estimates will be based

on final alignment of the replacement bridge.



Lateral analysis will be required of these piles once the bridge design is advanced past its

current preliminary stage. CHA will include this analysis in the bridge design scope of

services.

4.4 Spread Footings

The bedrock encountered in borings B-2 and B-3 is suitable for spread footings for the south

pier at the permanent bridge. Alluvial deposits and glacial till were encountered close to the

ground surface at the location of the north pier. These soils are likely susceptible to scour

conditions, so we expect deep foundations will be required at the north pier (See Section 4.6 –

Drilled Shafts).

If independently founded wing wall extensions are required at the north and south abutments,

spread footings are an option, founded on undisturbed glacial till. Fill associated with the

bridge approach at each embankment is not suitable for foundation support. Therefore,

consideration must be given to the location and proposed elevation of the footings to

determine if driven piles are more suitable.

Where spread footings are used, the footings should be founded on competent bedrock or at

least 5 feet below the ground surface when placed on soil for frost protection. Additional

depth may be required to meet scour protection criteria, as provided by others.

The existing fill and streambed materials are of variable strength and composition. If fill or

streambed materials are encountered at the proposed spread footing elevations, the material

should be removed so that permanent spread footings are bearing on competent bedrock.

The design groundwater level for the piers should be selected based upon the high water level

within the stream from the hydraulic design. The design groundwater level for the abutments

should be the higher of the high water level within the stream based on the hydraulic design,

or El. 665 feet based on the subsurface investigation.



4.4.1 Strength Limit Design

CHA has determined the factored bearing resistance for strength limit state design (qR) for

both spread footings on bedrock, and spread footings on glacial till. The factored bearing

resistance ( = 0.45) at the Strength Limit State for bedrock is 17 ksf.

The factored bearing resistance for spread footings of various widths founded on undisturbed

glacial till are included in Table 5. These values are based upon a water level at or above the

ground surface. A resistance factor ( ) of 0.45 has been included in the factored bearing

resistance values.

Table 5: Factored Bearing Resistance – Strength Limit Design

Footing Width (ft)

Factored Bearing Resistance (ksf)

10.0 7.9 12.0 8.0 14.0 8.0

When checking the sliding resistance, the factored friction factor of 0.63 for cast-in-place

concrete on bedrock. The factored friction factor includes a factor of = 0.9.

4.4.2 Service Limit Design

For service limit design for footings bearing on bedrock, CHA recommends a factored

bearing resistance ( 1.0) of 10 ksf to limit settlement to less than 1.0 inch.

For service limit design for footings bearing on undisturbed glacial till, CHA recommends a

factored bearing resistance ( 1.0) of 6 ksf to limit settlement to less than 1.0 inch.

4.5 Drilled Shafts

Drilled shaft foundations at the north pier of the permanent bridge should extend through the

alluvial wash and the glacial till to bear on bedrock. Predicted scour depths exceed the



thickness of overburden material on the bedrock in this location. Therefore the overburden

will not provide reliable frictional resistance for the pier foundation support. We recommend

socketing the drilled shafts into the bedrock surface to provide lateral support and reduce the

potential for sliding during large scour events.

The estimated drilled shaft embedment length is based on factored side friction capacities of

the shafts only. The tip bearing is not included in design considerations because it would

require a displacement of approximately 0.4 inches to mobilize the tip resistance. Table 6

outlines estimated total embedment depths based on the subsurface conditions and the total

service limit factored axial load anticipated on the north pier of approximately 2,400 kips.

The total embedment depth is the amount that must be obtained for the entire foundation

system, i.e. if the foundation system is a two-shaft configuration then the total embedment

depth is halved assuming equal distribution of the axial loading.

The nominal side friction resistance of the shaft for any diameter is 20.5 ksf. To compute the

Strength Limit and Service Limit embedment values, a factor of 0.55 and 1.0 have been

applied, respectively, to the nominal capacities of the piles.

Table 6: Drilled Shaft Embedment Lengths (from Factored Resistance)

Pile Diameter

Service Limit Strength Limit

Frictional Resistance

(kips/ft)

Minimum Total Embedment (1)

(ft)

Frictional Resistance

(kips/ft)

Minimum Total Embedment(1)

(ft) 3.0 192.8 12.5 106.0 22.7 3.5 224.9 10.7 123.7 19.5 4.0 257.1 9.4 141.4 17.1

(1) Based on preliminary axial loading of 2,400 kips

Concrete should be placed immediately after drilling and inspection are completed.

Inspection of drilled shafts should include recording the top and bottom elevations and a

visual examination for plumbness, alignment, and diameter.



It should be noted that cobbles and boulders were noted to be present throughout the glacial

till soils at various depths. Drilled shaft contractors should be made aware of the presence of

cobbles and boulders and the potential need to drill through these conditions at the depths

indicated on the boring logs. Contract documents should clearly define the contractor’s

responsibilities with respect to cobbles and boulders and include separate pay items, if

warranted, to account for these conditions.

It is the contractor’s responsibility to use drilling methods that will maintain a stable

excavation. The shafts will be constructed at the stream level so the contractor shall utilize

measures such as drilling slurry and/or steel casing to minimize potential groundwater

intrusion or base softening due to contact with water.

It is recommended that the concrete for the drilled shafts have a design slump of at least 7

inches in order to ensure concrete workability and plastic flow around the reinforcing cage,

avoid arching of the concrete upon withdrawal of the temporary casing (if used), and promote

uniform slurry (if used) displacement as the concrete is poured. Furthermore, a positive head

of concrete should be maintained above groundwater during the withdrawal of the casing.

Additional design and construction considerations regarding drilled shaft installation are as

follows:

The rebar cage for the shafts should be adequately sized to permit concrete to flow

around the cage. Clear spacing between all bars should be greater than five times the

diameter of the largest coarse aggregate.

The water/cement ratio should be no greater than 0.45 to improve strength and

durability, and low range water reducers should be used.

Concrete should be placed rapidly and continuously.

Concrete used to construct shafts in the wet should be placed using tremie methods to

minimize concrete segregation. The contractor must maintain the tremie pipe

discharge below the concrete level to minimize void development and drill slurry

encapsulation in the concrete mass as it is being placed.



These measures will preclude groundwater and soil contamination in the shaft concrete and

safeguard the integrity of the shafts.

4.6 Lateral Earth Pressures

The abutments should be designed to resist lateral pressures from the soil backfill and

surcharge loads. Load factors for earth pressures are provided in Table 3.4.1.2 of the

AASHTO LRFD Bridge Design Specifications.

Free standing wing walls or retaining walls also need to be designed to support the imposed

lateral pressures. Free standing walls restrained from movement should be designed to resist

at-rest earth pressures. Free standing walls which are free to rotate may be designed to resist

active earth pressures.

Table 7 provides lateral earth pressure coefficients for use in design. The values are based

upon a vertical back to the abutment wall and horizontal ground surface behind the wall.

Table 7: Granular Backfill Soil Parameters for Earth Pressure Coefficients

Parameter Value

Coefficient of Active Earth Pressure, Ka: 0.28

Coefficient of At-Rest Earth Pressure, Ko: 0.44

Coefficient of Passive Earth Pressure, Kp Minimum (Rankine Theory) Log-Spiral Theory (assuming / = 0.5)

3.5 6.3

Total Unit Weight, : 140 pcf

Buoyant Unit Weight, ’: 77.6 pcf

The movement required to mobilize the full active and passive pressure is a

function of the wall height and backfill type as discussed in C3.11.1 and C3.11.5.4

of the AASHTO LRFD Bridge Design Specifications. Rankine theory provides a

conservative pressure for free standing retaining walls. Based on current practice,

we recommend using the spiral theory for design of the abutments.



Appropriate earth pressures shall be included in the design of any support of

excavation or cofferdam system.

Appropriate temporary and permanent surcharge loads should be included in the

abutment and wing wall design.

The recommendations above are based on no hydrostatic pressures behind the

walls. Therefore, weep holes with an aggregate or prefabricated drainage layer

should be provided to drain water that may collect behind the walls.

4.7 Seismic Site Classification and Design Parameters

The permanent bridge north abutment and temporary bridge north abutment control the

seismic site classification for these structures. These structures are seismic class D. Each

bridge should be designed for the following seismic criteria:

Table 8: Seismic Design Site Coefficients

Parameter Value Mapped Spectral Response Acceleration for 0.2-Second Period (SS) (AASHTO 2010 Maps using USGS Mapping Tool)

0.172g

Mapped Spectral Response Acceleration for 1.0-Second Period (S1) (AASHTO 2010 Maps using USGS Mapping Tool)

0.049g

Mapped Peak Ground Acceleration (PGA) (AASHTO 2010 Maps using USGS Mapping Tool)

0.079g

Site Class (AASHTO, Table C3.10.3.1-1)

D

Site Coefficient Fa and Fpga (AASHTO, Table 3.4.2.3-1)

1.6

Site Coefficient Fv: (AASHTO, Table 3.4.2.3-2)

2.4



5.0 CONSTRUCTION CONSIDERATIONS

5.1 Rock Removal

Based on the information obtained during the subsurface investigations, rock removal may be

required during earthwork operations.

In the event several feet of bedrock must be removed or the rock is not rippable by an

excavator, controlled blasting may be an economical rock removal method. Based on

recommendations provided by the Bureau of Mines, publication RI-180, dated 1980, to limit

potential for blasting damage to nearby structures, blasting vibrations should be limited to:

Maximum peak particle velocity of 2 inches per second at frequencies greater than 40

Hertz (Hz);

Maximum peak particle velocity of 0.5 inches per second between frequencies of 3

and 10 Hz; and

As shown in Table 9 for newly placed concrete.

Table 9: Ground Vibration Limits for Newly Placed Concrete

Age of Concrete Maximum PPV in/s (mm/s)

Less than 3 days No blasting

After 3 days 1.0 (25)



The footings at the south pier for the permanent bridge likely to be founded on bedrock. The

bedrock elevations decrease across the site, going north and the bedrock surface may be

irregular. Figure 3 and Figure 4, in Appendix A, give the approximate elevation of bedrock

across the project site. Existing bedrock surfaces are currently sloped.



We recommend that a precondition survey be performed of all structures within 200 feet of

any location where blasting will be performed that are to remain as part of the proposed

development. Precondition surveys should be performed by an independent firm experienced

in this type of work.

5.2 Subgrade Preparation

Cobbles and boulders, if encountered, must be removed from within 12 inches below the

bottom of the foundations. The resulting excavation should be backfilled with compacted

Granular Backfill for Structures (VTrans Item 204.30) as described below. Large boulders

that cannot entirely be removed should be cut at least 12 inches beneath the subgrade.

The exposed subgrade should be proof compacted prior to placement of fill or concrete. The

proof compaction effort should be completed using a smooth drum roller with a minimum

static weight of at least 10 tons. The roller should operate in its vibratory mode and complete

at least 6 passes at a speed not exceeding 3 feet per second. The subgrade should be

compacted to a firm and unyielding condition. Areas that tend to “pump” or “weave” under

the passing roller should be undercut by at least 12 inches and the resulting excavation

backfilled with compacted Granular Backfill for Structures.

Where bedrock is encountered at the footing elevations, the footings should extend to sound,

clean bedrock. Size 8 rebar dowels at 4-foot center spacing may be required on smooth or

sloping bedrock to provide shear resistance in accordance with Section 10.2.3.3 of the VTrans

Structures Design Manual. Dowling is not required for rough bedrock subgrades prepared to

a 10H:1V slope or flatter (i.e., not river worn).

A geotechnical engineer should observe the exposed subgrades prior to fill and concrete

placement to verify that the exposed bearing materials are consistent with those described

herein and are suitable for the design soil bearing pressure. If soft or loose pockets are

encountered in the footing excavations, the soft or loose materials should be removed, and the

bottom of the footing should be placed at a lower elevation on firm soil, or the resulting

excavation should be backfilled with compacted Granular Backfill for Structures or crushed



stone wrapped in a filter fabric.

5.3 Subgrade Protection

If construction takes place during freezing weather, special measures should be taken to

prevent the subgrade from freezing. Such measures should include the use of heat blankets,

or excavating the final six inches of soil just before placing concrete. Footings should be

backfilled as soon as possible after footing construction. Soil used as backfill should be free

of frozen material, as should the ground on which it is placed.

Materials with high fines contents are typically difficult to handle when wet as they are

sensitive to moisture content variations. Subgrade support capacities may deteriorate when

such soils become wet and/or disturbed. The contractor should keep exposed subgrades

properly drained and free of ponded water. Subgrades should be protected from machine and

foot traffic to reduce disturbance.

5.4 Engineered Fill

Backfill adjacent to and around the pile caps foundations shall meet the requirements for

VTrans Granular Backfill for Structures, Item No. 204.30. Backfill greater than 3 feet away

from structures shall be either Granular Backfill for Structures or shall meet the requirements

for VTrans Granular Borrow, Item No. 703.04.

The backfill shall consist of sound, durable, non-plastic sand and gravel, free of stumps, roots,

other organics and any frozen or deleterious materials. The on-site soils generally do not

meet the requirements for Granular Backfill for Structures. The on-site granular

glaciolacustrine soils may meet the requirements for Granular Borrow and should be tested in

accordance with Sieve Analysis of Fine and Coarse Aggregates (AASHTO T-27) to

determine the suitability as Granular Borrow.

Granular Backfill for Structures and Granular Borrow shall be placed in loose lifts not

exceeding 8 inches in thickness and shall be compacted to at least 95 percent of the maximum



laboratory dry density as determined by the modified Proctor test (AASHTO T-180). Actual

lift thickness shall depend upon the type of compaction equipment used during construction.

5.5 Control of Water

To provide frost protection, the foundations will extend at least 4 feet below the bottom of the

stream bed. Therefore groundwater control procedures will be required during construction.

Project specifications shall require that the contractor maintain groundwater at a minimum

depth of 2 feet below the excavation bottom at all times to maintain stable conditions. It

should be the responsibility of the contractor to maintain dry conditions so that foundation

construction may be completed in the dry.

A cofferdam and stream diversion may be required for control of groundwater and support of

excavation. The presence of cobbles and boulders and the very dense till and shallow bedrock

may present difficulty in driving sheet piles. These systems should be designed and

constructed in accordance with the VTrans Standard Specifications for Construction.

5.6 Temporary Excavations

In general, all excavations should be performed in accordance with the Vermont Occupational

Safety and Health Administration (VOSHA) standards and other applicable State and Federal

regulations. In areas where sufficient sloping of excavation cuts is not possible, the

excavation should be shored, sheeted, and braced. A registered professional engineer

(licensed in the State of Vermont) should design these systems, as required by VOSHA.



6.0 CLOSURE

The geotechnical recommendations presented in this report are based, in part, on project and

subsurface information available at the time this report was prepared and in accordance with

generally accepted soil and foundation engineering practices. No other warranty, expressed

or implied, is made. Some variation of subsurface conditions may occur between locations

explored that may not become evident until construction. Depending on the nature and extent

of the variations, it may be necessary to re-evaluate the recommendations presented in this

report.

CHA does not accept responsibility for designs based upon our recommendations unless we

are engaged to review the final plans and specifications to determine whether any changes in

the project affect the validity of our recommendations and whether our recommendations

have been properly implemented in the design.

This report has been prepared solely for design purposes and shall not be incorporated by

reference or other means in the Contract Documents. If this report is included in the Contract

Documents, it shall be for information only. Earthwork specification clauses shall take

precedence.


Bethel, Vermont

APPENDIX A

FIGURES

Scale 1" = 2000' CHA File No:23825

Project Location Map

Vermont Route 12 Over Gilead Brook – Bridge No. 38 (Bethel)Bethel, Windsor County, VT

Randolph and Bethel USGS Quads

PROJECT LOCATION

50 FT050

SCALE

PROJECT NO.

DATE: 07/2013

23825

BETHEL, VERMONT

BETHEL BHF 0241(38)III Winners Circle. PO Box 5269 Albany, NY 12205-0269

www.chacompanies.comMain: (518) 453-4500 www.chacompanies.com

BORING LOCATION PLAN

FIGURE 2

3511

LastSaved

By:

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LEGEND

N

VT STATE PLANE GRID

False Northing: 0.0000False Easting: 1640416.6667Origin Latitude: 42°30’00.0000"NCentral Meridian: 72°30’00.0000"WUS Survey FootTransverse MercatorNAD83 Vermont State PlanesVT83

B-1

B-2

B-3

B-4

B-5

B-6B-7A

B-7

B-116

B-12

B-1

B-11

B-9

B-8

B-10

B-10A

B-116 APPROXIMATE BORING LOCATION, MAY 2012

APPROXIMATE BORING LOCATION, MAY 2013

OUTCROP

VISIBLE BEDROCK

DETOUR ALIGNMENT

CONSTRUCTION

PROPOSED

VT. ROUTE 1

2

GIL

EA

D

BR

OO

K

640

640

640

640

640

650

650

650

650

650

650

650

650

650

650

660

660

660

660

660

660

660

660

660

670

670

670

670

670

670

670

670

670

680

680

680 6

80

680

680

680

680

680

680

680

690

690

690

690

690

690

690

700

700

700

700 710

710

710

282+00

283+00

284+00

285+00

286+00

287+00

288+00

289+00

290+00

D 282+00

D 283+00D 28

4+00

D 28

5+00

D 28

6+00

D 28

7+00

D 28

8+00

D 28

9+00

D 29

0+00

CURVE D3

CURVE D4

STONE WALL

RICHARD A

. DAVISN/F

RICHARD A

. DAVISN/F

RICHARD A

. DAVISN/F

JEFFREY TOWNSEND

N/F

OLD CHRIS

T CHURCH

N/F

OHW


Bethel, Vermont

APPENDIX B

SITE PHOTOGRAPHS

Drilling B-1 at location of proposed south abutment, looking south.

1.

Drilling B-3 at location of proposed south pier, looking east. Bedrock outcrops visible south of boring location.

2.

CHA#: 23825.4000.32000 May 2013

BHF 0241 (38)

VT Route 12 Bridge Replacement

Bethel, VT

3542

Oval

Drilling B-4 at location of proposed center pier, looking south.

3.

Drilling B-5 at location of proposed center pier, looking east.

4.

CHA#: 23825.4000.32000 May 2013

BHF 0241 (38)


Bethel, VT

Drilling B-8 at location of proposed south temporary abutment, looking south.

5.

Drilling B-10A at location of proposed north temporary abutment, looking east.

6.

CHA#: 23825.4000.32000 May 2013

BHF 0241 (38)


Bethel, VT

Typical streambed material.

7.

View of Gilead Brook under VT Route 12, looking south.

8.

CHA#: 23825.4000.32000 May 2013

BHF 0241 (38)


Bethel, VT

Bedrock outcrop at toe of south embankment.

9.

CHA#: 23825.4000.32000 May 2013

BHF 0241 (38)


Bethel, VT


Bethel, Vermont

APPENDIX C

EXCERPTS FROM 1928 RECORD DRAWINGS


Bethel, Vermont

APPENDIX D

BORING LOGS

R-1 100(58)

4.4

4.8

31.1

Not Sampled, Asphalt PavementA-1-a, SubbaseA-1-a, f.c. SAND, little f.c. gravel, trace silt, dense, brown, Moist, Rec. =1.2 ft, (FILL)

A-1-a, f.c. GRAVEL, AND f.c. SAND,trace silt, dense, brown, Moist,Rec. = 0.9 ft, (FILL)

A-1-b, f.c. SAND, little silt,little f.c. gravel, dense, brown, Moist, Rec. =0.8 ft, (FILL)

A-1-b, becomes medium dense, Rec. = 0.4 ft, (FILL)

A-1-a, f.c. GRAVEL, little f.c. sand, trace silt, dense, blk-brn, Wet, Rec.= 0.7 ft, (FILL)A-2-4, f. SAND, Some Silt, dense, Light brown, Moist

A-4Rec. = 1.6 ft

A-4, SILT, little f.c. sand, dense, gray, Wet

A-4

No Recovery, f.c. GRAVEL, Some f.c. Sand, little silt, dense, red-brn,Wet, Rec. = 0.0 ft, (GLACIAL TILL) No recovery with standard split spoon.Sample recovered with 3" split spoon barrel.

A-4

A-4, SILT,Some f.c. Sand, little f.c. sand, very dense, gray, Moist, Rec. =0.2 ft, (GLACIAL TILL) Spoon bouncing during sample advancement.Gravel fragments appeared to be weathered rock.

27.0 ft - 32.0 ft, Gray, Micaceous Phyllite, close fracture spacing. Mediumhard, Slightly weathered, NXDC, Fair RQD. White quartz seamsembedded within rock core recovery.

18-14-15-11(29)

10-12-14-10(26)

12-14-17-11(31)

8-10-7-7

(17)

9-8-18-8

(26)

5-5-8-6(13)

24-22-20-11(42)

50/3"(R)

53.9 36.2

11.9

9.9

88.1

SS

STATE OF VERMONTAGENCY OF TRANSPORTATION

MATERIALS & RESEARCH SECTIONSUBSURFACE INFORMATION

BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

5

10

15

20

25

Route 12 Bridge, Bethel, VT

Boring Crew: K. Owens, M. D'Ambrosio

Date Started: 5/08/13 Date Finished: 5/08/13

VTSPG NAD83:

Ground Elevation: 682.3 ft

Boring No.: B-01

Page No.: 1 of 2

Pin No.: 10C216

Checked By: K. Adnams

Date Depth(ft)

Notes

Notes:

Hammer Fall:Hammer Wt:I.D.:Type:

05/08/13 14.0 During drilling.

05/08/13 16.2 Boring completion.

Run

(Dip

deg

.)

CE = 1.0

Cor

e R

ec. %

(RQ

D %

)

Dri

ll R

ate

min

utes

/ft

Moi

stur

eC

onte

nt %

Rig: Acker AD II TruckHammer/Rod Type: Manual/NW

CLASSIFICATION OF MATERIALS(Description)

Station: 284+01.00

1.38 in140 lb.30 in.

WB4 in

300 lb.N.A.

Casing Sampler

Offset: 8L

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %

Groundwater ObservationsS

trat

a (1

)

1. Stratification lines represent approximate boundary between material types. Transition may be gradual.2. N Values have not been corrected for hammer energy. CE is the hammer energy correction factor.3. Water level readings have been made at times and under conditions stated. Fluctuations of groundwater may occur due to other factors than those present at the time

measurements were made.2010

CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13

Top of Bedrock @ 27.0 ft

R-1 94(84)

6.232.0 ft - 37.0 ft, Gray, Micaceous Phyllite, medium fracture spacing.Medium hard, Slightly weathered, NXDC, Good RQD

Hole stopped @ 37.0 ft

Remarks:Bony/gravelly drilling at 18.5'.

Roller bit refusal at 27'.

SS



BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

35

40

45

50

55




VTSPG NAD83:


Boring No.: B-01

Page No.: 2 of 2

Pin No.: 10C216


Date Depth(ft)

Notes

Notes:


05/08/13 14.0 During drilling.

05/08/13 16.2 Boring completion.

Run

(Dip

deg

.)

CE = 1.0

Cor

e R

ec. %

(RQ

D %

)

Dri

ll R

ate

min

utes

/ft

Moi

stur

eC

onte

nt %



Station: 284+01.00

1.38 in140 lb.30 in.

WB4 in

300 lb.N.A.

Casing Sampler

Offset: 8L

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %


trat

a (1

)



CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13

R-1

R-2

100(94)

80(67)

3.2

3.4

No Recovery, Advanced roller bit through river bed material to bedrocksurface.

No Recovery, Hard drilling at 2' interpreted as top of bedrock. Advancedrollerbit and casing to 3.5' to obtain rock core sample.

3.5 ft - 8.5 ft, Gray, Phyllite, medium fracture spacing. Medium hard,Slightly weathered, NXDC, Excellent RQD

8.5 ft - 13.5 ft, Gray, Phyllite, close fracture spacing. Medium hard,Moderately weathered, NXDC, Fair RQD. Weathered zone within samplerecovery from 9'-9.5'.


N/A



BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

5

10

15

20

25


Boring Crew: K. Owens, M. Misiasek


VTSPG NAD83:


Boring No.: B-02

Page No.: 1 of 1

Pin No.: 10C216


Date Depth(ft)

Notes

Notes:


05/17/13 0.0 Adv. in river.

Run

(Dip

deg

.)

CE = 1.0

Cor

e R

ec. %

(RQ

D %

)

Dri

ll R

ate

min

utes

/ft

Moi

stur

eC

onte

nt %

Rig: MOBILE B-53 TRACKHammer/Rod Type: Manual/NW


Station: 285+22.00

1.38 in140 lb.30 in.

WB3 in

300 lb.N.A.

Casing Sampler

Offset: 24R

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %


trat

a (1

)



CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13


R-1

R-2

64(25)

100(63)

5

6.8

No Recovery, Advanced roller bit through river bed material to bedrocksurface.

No Recovery, Hard drilling at 2' interpreted as top of bedrock. Advancedrollerbit and casing to 3.5 to obtain rock core sample.

3.5 ft - 8.5 ft, Gray, Phyllite, very close fracture spacing. Soft to mediumhard, Severely weathered, NXDC, Poor RQD. White quartz seamsembedded within rock core recovery.

8.5 ft - 13.5 ft, Gray, Phyllite, medium fracture spacing. Medium hard,Moderately weathered, NXDC, Fair RQD. White quartz seams embeddedwithin rock core recovery.


N/A



BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

5

10

15

20

25




VTSPG NAD83:


Boring No.: B-03

Page No.: 1 of 1

Pin No.: 10C216


Date Depth(ft)

Notes

Notes:


05/14/13 0.0 Adv. in river.

Run

(Dip

deg

.)

CE = 1.0

Cor

e R

ec. %

(RQ

D %

)

Dri

ll R

ate

min

utes

/ft

Moi

stur

eC

onte

nt %



Station: 285+21.00

1.38 in140 lb.30 in.

WB3 in

300 lb.N.A.

Casing Sampler

Offset: 23L

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %


trat

a (1

)



CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13


R-1

R-2

94(52)

100(66)

2.6

3.4

10.3

A-1-a, f.c. SAND, Some f.c. Gravel, trace silt, medium dense, brown,Wet, Rec. = 0.4 ft

A-2-4

A-2-4, f.c. GRAVEL,Some Silt,Some f.c. Sand, very dense, gray, Moist,Rec. = 0.9 ft, (GLACIAL TILL)

A-2-4, f.c. GRAVEL, Some Silt, very dense, Dark gray, Wet, Rec. = 0.1ft, (GLACIAL TILL)

No Recovery, Rec. = 0.0 ft, Spoon bouncing.

Not Sampled, Hard drilling at 15.5' interpreted as top of bedrock.Advanced rollerbit to 17' to obtain rock core sample.

17.0 ft - 22.0 ft, Gray, Quartzite, very close fracture spacing. Medium hard,Moderately weathered, NXDC, Fair RQD

22.0 ft - 27.0 ft, Dark gray, Phyllite, very close fracture spacing. Mediumhard, Moderately weathered, NXDC, Fair RQD


1-4-10-9

(14)

23-40-40-41(80)

100/4"(R)

50/0"(R)

33.5 33.2 33.3

SS



BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

5

10

15

20

25




VTSPG NAD83:


Boring No.: B-04

Page No.: 1 of 1

Pin No.: 10C216


Date Depth(ft)

Notes

Notes:


05/20/13 0.0 Adv. in river.

Run

(Dip

deg

.)

CE = 1.0

Cor

e R

ec. %

(RQ

D %

)

Dri

ll R

ate

min

utes

/ft

Moi

stur

eC

onte

nt %



Station: 285+99.00

1.38 in140 lb.30 in.

WB4 in

300 lb.N.A.

Casing Sampler

Offset: 14L

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %


trat

a (1

)



CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13


R-1

R-2

100(70)

100(70)

5.2

7.6

11.5A-2-4, f.c. GRAVEL, AND f.c. SAND, little silt, dense, red-brn, Wet,Rec. = 0.7 ft

No Recovery, Rec. = 0.0 ft

Not Sampled, Very hard drilling at 5.5 interpreted as top of bedrock.Advanced rollerbit and casing to 7.5 to obtain rock core sample.

7.5 ft - 12.5 ft, Gray, Micaceous Phyllite, very close fracture spacing. Softto medium hard, Moderately to severely weathered, NXDC, Fair RQD.White quartz seams embedded within rock core recovery.

12.5 ft - 17.5 ft, NXDC, Similar Rock. White quartz recovered in bottom2.5' of rock core sample.


11-14-14-14(28)

45-90(R)

46.8 35.5 17.7

SS



BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

5

10

15

20

25




VTSPG NAD83:


Boring No.: B-05

Page No.: 1 of 1

Pin No.: 10C216


Date Depth(ft)

Notes

Notes:


05/20/13 0.0 Adv. in river.

Run

(Dip

deg

.)

CE = 1.0

Cor

e R

ec. %

(RQ

D %

)

Dri

ll R

ate

min

utes

/ft

Moi

stur

eC

onte

nt %



Station: 286+01.00

1.38 in140 lb.30 in.

WB4 in

300 lb.N.A.

Casing Sampler

Offset: 19R

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %


trat

a (1

)



CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13


R-1

R-2

92(63)

80(68)

4.2

4

9.9

A-1-b, f.c. GRAVEL, AND f.c. SAND,little silt, medium dense, brown,Wet, Rec. = 0.4 ft

A-2-4, (GLACIAL TILL) Hard drilling at 2.5' interpreted as top of glacial till.

A-2-4, f.c. GRAVEL,Some Silt,Some f.c. Sand, very dense, gray, Wet,Rec. = 0.9 ft

A-2-4, Similar Soil, Rec. = 0.4 ft, (GLACIAL TILL)

A-1-b

A-1-b, f.c. GRAVEL, little silt, little f.c. sand, very dense, Dark gray,Wet, Rec. = 0.2 ft, (CWR)

16.0 ft - 17.5 ft, Hard drilling at 16' interpreted as top of bedrock.Advanced rollerbit to 17.5' to obtain rock core sample.

17.5 ft - 22.5 ft, Gray, Phyllite, close fracture spacing. Medium soft,Moderately weathered, NXDC, Fair RQD

22.5 ft - 27.5 ft, Gray, Phyllite, medium fracture spacing. Medium soft,Slightly weathered, NXDC, Fair RQD


7-7-10-8

(17)

27-30-47-46(77)

64-100/6"

(R)

100/6"(R)

38.8 31.5 29.7

SS



BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

5

10

15

20

25




VTSPG NAD83:


Boring No.: B-06

Page No.: 1 of 1

Pin No.: 10C216


Date Depth(ft)

Notes

Notes:


05/17/13 0.0 Adv. in river.

Run

(Dip

deg

.)

CE = 1.0

Cor

e R

ec. %

(RQ

D %

)

Dri

ll R

ate

min

utes

/ft

Moi

stur

eC

onte

nt %



Station: 286+45.00

1.38 in140 lb.30 in.

WB4 in

300 lb.N.A.

Casing Sampler

Offset: 31L

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %


trat

a (1

)



CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13


7.0

18.2

Not Sampled, Asphalt Pavement

Not Sampled, SubbaseA-1-b, f.c. GRAVEL, Some f.c. Sand, little silt, dense, brn-gry, Moist,Rec. = 1.1 ft, (FILL)

A-2-4, f.c. SAND, Some f.c. Gravel, little silt, dense, brown, Moist, Rec.= 1.2 ft, (FILL)

A-2-4, f.c. SAND,Some f.c. Gravel,little silt, medium dense, brown,Moist, Rec. = 0.6 ft, (FILL)

A-2-4, f.c. SAND,Some Silt,Some f.c. Gravel, loose, brown, Moist, Rec.= 1.7 ft, (FILL)

A-2-4, Rec. = 0.4 ft, becomes dense (FILL)

A-2-4, f.c. SAND, Some Silt, Some f.c. Gravel, medium dense, brown,Moist, Rec. = 0.8 ft, (FILL)

A-2-4, Rec. = 0.6 ft, grades to little silt (FILL)

A-4

A-4, SILT, Some f.m.c. Gravel, trace f.c. sand, medium dense, brown,Moist, Rec. = 1.0 ft, (GLACIAL TILL)

14-16-12-9(28)

8-7-6-4(13)

5-7-4-5(11)

5-4-6-3(10)

44(N/A)

9-9-8-7(17)

9-7-8-11

(15)

28-8-7-6

34.4

29.4

51.4

36.4

14.2

34.2

SS



BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

5

10

15

20

25




VTSPG NAD83:


Boring No.: B-07

Page No.: 1 of 3

Pin No.: 10C216


Date Depth(ft)

Notes

Notes:


05/10/13 39.2 Beg. of day.

Run

(Dip

deg

.)

CE = 1.0

Cor

e R

ec. %

(RQ

D %

)

Dri

ll R

ate

min

utes

/ft

Moi

stur

eC

onte

nt %



Station: 287+72.00

1.38 in140 lb.30 in.

WB4 in

300 lb.N.A.

Casing Sampler

Offset: 4R

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %


trat

a (1

)



CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13

R-1

R-2

100(62)

43(20)

9.2

8

21.6A-4, SILT, little f.c. sand, little f.c. gravel, medium dense, brown, Moist,Rec. = 1.1 ft, (GLACIAL TILL)

A-1-b, Increased drilling resistance at 38' interpreted as top of gravelglacial till.A-1-b, f.c. GRAVEL, Some f.c. Sand, little silt, dense, brn-gry, Moist,Rec. = 0.5 ft, (GLACIAL TILL)

No Recovery, Rec. = 0.0 ft, Spoon bouncing. Very hard drilling 44'-47.5'.

47.5 ft - 56.5 ft, Phyllite boulder recovered in samples R-1 and R-2.Glacial till recovered in bottom 4" of sample.NXDC

NXDC

A-4, SILT, little f.c. sand, little f.c. gravel, very dense, gray, Moist, Rec. =1.0 ft, (GLACIAL TILL)

A-4, Boring telescoped with 3" casing at 60'.

(15)

5-6-5-4(11)

18-21-18-12(39)

50/0"(R)

43-40-41-50(81)

16.6 18.6 64.8

SS



BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

35

40

45

50

55




VTSPG NAD83:


Boring No.: B-07

Page No.: 2 of 3

Pin No.: 10C216


Date Depth(ft)

Notes

Notes:


05/10/13 39.2 Beg. of day.

Run

(Dip

deg

.)

CE = 1.0

Cor

e R

ec. %

(RQ

D %

)

Dri

ll R

ate

min

utes

/ft

Moi

stur

eC

onte

nt %



Station: 287+72.00

1.38 in140 lb.30 in.

WB4 in

300 lb.N.A.

Casing Sampler

Offset: 4R

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %


trat

a (1

)



CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13

A-4, Similar Soil, Rec. = 0.1 ft, (GLACIAL TILL) Spoon bouncing.Hole stopped @ 61.6 ft

50/1"(R)

Remarks:Casing broke at 62', unable to advance boring. Boring abandoned and offset 6' north to B-7A.

SS



BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

65

70

75

80

85




VTSPG NAD83:


Boring No.: B-07

Page No.: 3 of 3

Pin No.: 10C216


Date Depth(ft)

Notes

Notes:


05/10/13 39.2 Beg. of day.

Run

(Dip

deg

.)

CE = 1.0

Cor

e R

ec. %

(RQ

D %

)

Dri

ll R

ate

min

utes

/ft

Moi

stur

eC

onte

nt %



Station: 287+72.00

1.38 in140 lb.30 in.

WB4 in

300 lb.N.A.

Casing Sampler

Offset: 4R

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %


trat

a (1

)



CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13

Not Sampled, Boring offset from B-7. Advanced to 49' without sampling.

SS



BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

5

10

15

20

25




VTSPG NAD83:


Boring No.: B-07A

Page No.: 1 of 3

Pin No.: 10C216


Date Depth(ft)

Notes

Notes:


05/15/13 None obs.

Run

(Dip

deg

.)

CE = 1.0

Cor

e R

ec. %

(RQ

D %

)

Dri

ll R

ate

min

utes

/ft

Moi

stur

eC

onte

nt %



Station: 287+77.00

1.38 in140 lb.30 in.

WB5 in

300 lb.N.A.

Casing Sampler

Offset: 4R

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %


trat

a (1

)



CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13

No Recovery, Rec. = 0.1 ft, (GLACIAL TILL) Coarse gravel and weatheredmaterial recovered in shoe of spoon. Boring telescoped with 4" casing todecrease water loss during drilling operations.

A-4, SILT, trace f.c. sand, medium dense, gray, Moist, Rec. = 0.4 ft,(GLACIAL TILL) Weathered boulder or cobble material recovered in shoeof spoon.

A-4, SILT, little f.c. sand, very dense, gray, Moist, Rec. = 0.2 ft,(GLACIAL TILL)

15-7-14-55(21)

6-2-14-22

(16)

65-91/6"

SS



BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

35

40

45

50

55




VTSPG NAD83:


Boring No.: B-07A

Page No.: 2 of 3

Pin No.: 10C216


Date Depth(ft)

Notes

Notes:


05/15/13 None obs.

Run

(Dip

deg

.)

CE = 1.0

Cor

e R

ec. %

(RQ

D %

)

Dri

ll R

ate

min

utes

/ft

Moi

stur

eC

onte

nt %



Station: 287+77.00

1.38 in140 lb.30 in.

WB5 in

300 lb.N.A.

Casing Sampler

Offset: 4R

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %


trat

a (1

)



CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13

R-1 0(0)

1

10.9

No Recovery, (GLACIAL TILL) Hard drilling conditions and spoon recoveryat 59' indicated possible bedrock surface. Lack of core recovery likely dueto sampling through glacial till material.NXDC

A-4, SILT, Some f.c. Sand, Some f.c. Gravel, very dense, Dark gray,Moist, Rec. = 0.3 ft, (GLACIAL TILL) Weathered boulder or cobblematerial recovered in sample.

A-4, Rec. = 0.3 ft, grades to little f.c. gravel (GLACIAL TILL)

A-4, Similar Soil, Rec. = 0.3 ft, (GLACIAL TILL)

A-4, Similar Soil, Rec. = 0.4 ft, (GLACIAL TILL)Hole stopped @ 84.5 ft

(R)

100/3"(R)

100/4"(R)

100/5"(R)

100/6"(R)

31.6 26.2 42.2

Remarks:Boring terminated prior to advancing boring to final split spoon sample due to burst water hose and traffic control scheduling.

SS



BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

65

70

75

80

85




VTSPG NAD83:


Boring No.: B-07A

Page No.: 3 of 3

Pin No.: 10C216


Date Depth(ft)

Notes

Notes:


05/15/13 None obs.

Run

(Dip

deg

.)

CE = 1.0

Cor

e R

ec. %

(RQ

D %

)

Dri

ll R

ate

min

utes

/ft

Moi

stur

eC

onte

nt %



Station: 287+77.00

1.38 in140 lb.30 in.

WB5 in

300 lb.N.A.

Casing Sampler

Offset: 4R

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %


trat

a (1

)



CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13

R-1

R-2

90(88)

100(96)

2.6

3.4

A-2-4, f.c. SAND, Some Silt, trace organics, very dense, brown, Wet,Rec. = 0.4 ft, Spoon bouncing at 1', interpreted as top of bedrock.Not Sampled, Advanced rollerbit and casing to 3' to obtain rock coresample.

3.0 ft - 8.0 ft, Dark gray, Phyllite, close fracture spacing. Medium hard,Slightly weathered, NXDC, Good RQD

8.0 ft - 13.0 ft, Dark gray, Phyllite, close fracture spacing. Medium hard,Slightly weathered, NXDC, Excellent RQD


2-50/6"(R)

SS



BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

5

10

15

20

25




VTSPG NAD83:


Boring No.: B-08

Page No.: 1 of 1

Pin No.: 10C216


Date Depth(ft)

Notes

Notes:


05/16/13 None obs.

Run

(Dip

deg

.)

CE = 1.0

Cor

e R

ec. %

(RQ

D %

)

Dri

ll R

ate

min

utes

/ft

Moi

stur

eC

onte

nt %



Station:

1.38 in140 lb.30 in.

WB4 in

300 lb.N.A.

Casing Sampler

Offset:

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %


trat

a (1

)



CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13


R-1

R-2

94(66)

80(22)

6.8

7.2

Not Sampled, Boring advanced directly adjacent to rock outcrop. Boringadvanced to top of bedrock without sampling.

Not Sampled, Hard drilling at 3' interpreted as top of bedrock. Advancedrollerbit and casing to 3.5' to obtain rock core sample.3.5 ft - 8.5 ft, Gray, Phyllite, very close fracture spacing. Soft to mediumhard, Moderately weathered, NXDC, Fair RQD. White quartz seamsembedded within rock core recovery.

8.5 ft - 13.5 ft, Gray, Phyllite, very close fracture spacing. Very soft to soft,Severely weathered, NXDC, Very poor RQD. Severely weathered portionof sample between 8.5'-9.5'.


SS



BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

5

10

15

20

25




VTSPG NAD83:


Boring No.: B-09

Page No.: 1 of 1

Pin No.: 10C216


Date Depth(ft)

Notes

Notes:


05/14/13 0.0 Adv. in river.

Run

(Dip

deg

.)

CE = 1.0

Cor

e R

ec. %

(RQ

D %

)

Dri

ll R

ate

min

utes

/ft

Moi

stur

eC

onte

nt %



Station: 285+18.00

1.38 in140 lb.30 in.

WB3 in

300 lb.N.A.

Casing Sampler

Offset: 4L

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %


trat

a (1

)



CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13


R-1

R-2

94(83)

94(93)

4

4.6

A-1-a, f.c. GRAVEL, Some f.c. Sand, trace silt, dense, red-brn, Moist,Rec. = 1.0 ft

A-2-4, Rec. = 0.6 ft

A-2-4, f.c. SAND,Some Silt,little f.c. gravel, very dense, gray, Moist,(GLACIAL TILL) Zones of weathered boulder or cobble fragments withinsample recovery.

A-2-4, Similar Soil, Rec. = 1.0 ft, (GLACIAL TILL)

Not Sampled, Very hard drilling at 10.5' interpreted as top of bedrock.Advanced rollerbit and casing to 13' to obtain rock core sample.

13.0 ft - 18.0 ft, Dark gray, Phyllite, medium fracture spacing. Mediumsoft, Slightly weathered, NXDC, Good RQD. White quartz seamsembedded within rock core recovery.

18.0 ft - 23.0 ft, NXDC, Similar Rock


7-13-18-15(31)

39-61-88

(149)

33-58-100/4"

(R)

SS



BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

5

10

15

20

25




VTSPG NAD83:


Boring No.: B-10

Page No.: 1 of 1

Pin No.: 10C216


Date Depth(ft)

Notes

Notes:


05/16/13 0.0 Adv. in river.

Run

(Dip

deg

.)

CE = 1.0

Cor

e R

ec. %

(RQ

D %

)

Dri

ll R

ate

min

utes

/ft

Moi

stur

eC

onte

nt %



Station: 286+35.00

1.38 in140 lb.30 in.

WB4 in

300 lb.N.A.

Casing Sampler

Offset: 35L

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %


trat

a (1

)



CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13


Not Sampled, Boring advanced without sampling to identify top of rock in vicinity of temporarybridge north pier.

Not Sampled, Hard drilling at 8' interpreted as top of bedrock. Advanced rollerbit to 9.5' toconfirm bedrock.


SS



BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

5

10

15

20

25




VTSPG NAD83:


Boring No.: B-10A

Page No.: 1 of 1

Pin No.: 10C216


Date Depth(ft)

Notes

Notes:


05/21/13 0.0 Adv. in river.

CE = 1.0

Moi

stur

eC

onte

nt %



Station: 286+18.00

1.38 in140 lb.30 in.

WB4 in

300 lb.N.A.

Casing Sampler

Offset: 18L

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %


trat

a (1

)



CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13


0.0 ft - 0.4 ft, Rollerbit through 4" Asphalt Pavement.A-1-b, f.c. GRAVEL, Some f.c. Sand, little silt,, brown, Moist, Rec. = 1.1 ft, Samplesadvanced with 3-inch spoon to aid in coarse material recovery.

A-1-b, f.c. SAND, Some f.c. Gravel, trace silt,, brn-gry, Moist, Rec. = 1.0 ft


(N/A)

(N/A)

3 INCH SPLIT BARREL



BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

5

10

15

20

25




VTSPG NAD83:


Boring No.: B-11

Page No.: 1 of 1

Pin No.: 10C216


Date Depth(ft)

Notes

Notes:


05/10/13 None obs.

CE = 1.0

Moi

stur

eC

onte

nt %



Station: 282+20.00

1.38 in140 lb.30 in.

WB4 in

300 lb.N.A.

Casing Sampler

Offset: 4R

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %


trat

a (1

)



CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13

5.8

0.0 ft - 0.8 ft, Roller bit through 10" of Asphalt Pavement.

A-1-b, f.c. GRAVEL, AND f.c. SAND, little silt,, brown, Moist, Rec. = 1.0 ft

A-1-b, Similar Soil, Rec. = 1.0 ft


(N/A)

(N/A)

46.0 41.1 12.9

3 INCH SPLIT BARREL



BORING LOG

BETHELBHF 0241(38)

Dep

th(f

t)

5

10

15

20

25




VTSPG NAD83:


Boring No.: B-12

Page No.: 1 of 1

Pin No.: 10C216


Date Depth(ft)

Notes

Notes:


05/10/13 None obs.

CE = 1.0

Moi

stur

eC

onte

nt %



Station: 288+35.00

1.38 in140 lb.30 in.

WB4 in

300 lb.N.A.

Casing Sampler

Offset: 6L

Blo

ws/

6"(N

Val

ue)

Gra

vel %

San

d %

Fin

es %


trat

a (1

)



CO

PY

238

25_B

HF

0241

_LO

GS

.GP

J V

ER

MO

NT

AO

T.G

DT

7/3

/13


Bethel, Vermont

APPENDIX E

LABORATORY TEST RESULTS

AGENCY OF TRANSPORTATION OFFICE MEMORANDUM

To: Doug Bonneau, P.E., Structures Project Manager

From: Taylor Waring, Geotechnical Engineer via Callie E. Ewald, P.E.,

Geotechnical Engineering Manager

Date: February 9th, 2018

Subject: Bethel BHF 0241(38) - Embankment Widening Settlement Analysis

1.0 INTRODUCTION

Upon a request from the designer, the Geotechnical Engineering Section has performed a

settlement analysis for the proposed embankment widening on the subject project. The

project includes the replacement of Bridge No. 38 on VT Route 12 in the town of Bethel,

Vermont. The new bridge is proposed on a shifted alignment which will require the

widening of the southern approach embankment by approximately 41 feet to the west.

Contained herein are the results of our analysis with corresponding recommendations.

2.0 ANALYSIS OF BORING LOGS

Based on the plan set dated August 31, 2017, the proposed embankment widening is

confined between STA 287+50 and STA 290+00. A series of borings were performed by

New Hampshire Boring, Inc. in May of 2013. The results of these borings were

summarized in a Geotechnical Engineering Report, prepared by CHA, in July of 2013. Two

borings locations were within the area of interest for this settlement study, B-07/07A and

B-12. Boring B-12 extended only to a depth of 4.8 feet below the existing pavement,

therefore provided little information. Borings B-07 and B-07A combined extended to a

depth of 84.5ft below the pavement surface. The maximum height of the existing

embankment is approximately 51ft, therefore the subsurface information provided in

borings B-07/07A extended to an adequate depth for our analysis. The results shown in

borings B-07 and B-07A were conservatively used to develop a soil profile for these

analyses.

Below the existing pavement, the borings reveal a medium dense sandy fill to a depth of

27.5 ft, below which a medium dense silty glacial till was observed to a depth of 58.7ft.

The in-situ material then transitions to a very dense glacial till with standard penetration

test (SPT) N-values reaching refusal. Groundwater was recorded at a depth of 39.2 feet in

Boring B-07 corresponding to a depth of 662.0 feet. No bedrock was encountered to depth

in the borings.

BETHEL BHF 0241(38) Page 2 of 3

Borings B-07/07A were located at approximately STA 287+70 therefore, the settlement

analysis was performed at STA 288+00, the closest relevant cross section provided in the

plan set. Stations 288+00 through 289+00 have similar geometry and total fill volumes,

therefore we believe that settlements predicted in our analysis of STA 288+00 will be

consistent over the major fill area.

4.0 ANALYSIS

The settlement analysis was performed using the geometry of STA 288+00 and the soil

profile summarized in section 2.0. The existing embankment soils were then divided into

layers, each with a thickness no greater than 10 feet. The soil layers analyzed are shown in

Table 1 on the following page. The embankment was then modeled in the program

Settle3D, developed by RocScience. The program was used to determine the magnitude of

total stress increase for the in-situ soils of the existing embankment and foundation strata.

These values for total stress increase were then used to compute immediate settlement of

each soil layer using Hough’s method (1959) as modified by AASHTO (2004 with 2006

interims). Settlements were computed at the point of maximum total stress increase, the

edge of the existing embankment, the center of the proposed fill and the outside edge of

the proposed fill.

Table 1: Embankment Soil Layers for Settlement Analysis

Depth

(ft)

Soil

Description

Unit Weight

(pcf)

Friction Angle, ϕ

(degrees)

0 – 0.8 Bituminous Asphalt

Pavement 150 -

0.8 – 3.0 Medium Dense

Gravel/Subbase 145 38


Sand 120 33


Silt 110 31

38.0 – 44.0 Dense

Gravel 135 36


Silt 110 32

58.7 – 84.5 Very Dense Silt (Glacial Till)

SPT Refusal, No Expected Settlement

3.0 RESULTS AND RECOMMENDATIONS

Based on the results of our analysis, we expect minor elastic settlement to take place both

within the soils of the existing embankment as well as the embankment foundation soils

due to the additional stress caused by the proposed fill. The magnitude of this settlement is


expected to vary slightly throughout the width of the fill. However, we anticipate this

settlement to take place during construction, gradually as the fill is placed.

The most recent plan set specifies the fill material to be 703.02 - Earth Borrow. The general

leniency in the earth borrow specification may allow the use of a fine grained or cohesive

soil to construct the embankment. Even with proper compaction, if a cohesive soil were

used in the construction of the embankment fill, both long-term consolidation settlement

of the fill material as well as slope stability would be of concern. Therefore, we recommend

that 703.01A – Granular Borrow be used as the fill material in place of the Earth Borrow.

The Granular Borrow gradation was developed such that the material will be able to drain

more freely than a material with higher fines, therefore alleviating any concern for

consolidation settlement.

We recommend that all fill materials be compacted to 95 percent of the maximum dry

density, in uniform 1-foot maximum lifts, compacted with vibratory rollers. Prior to

compaction, cobbles larger than 8 inches should be removed from the fill. Where hand-

guided equipment, such as a vibratory plate compactor, is used, the loose lift thickness shall

not exceed 6 inches. Cobbles larger than 4 inches should be removed from the fill prior to

compaction. We recommend addressing this compaction standard in the project special

provisions as the 2011 Vermont Standard Specifications for Construction only require 95

percent compaction within 2 feet of subgrade. It is also advised that the slope be grubbed

and all organics be removed prior to the placement of fill material.

We additionally recommend that the embankment widening be constructed in “steps” in

accordance with VTrans Standard Drawing B-5. This procedure will aid in proper

compaction and reduce the potential for a slip surface at the interface causing the new

embankment to “slide” down the slope. Should any cohesive soils be encountered during

construction that are not similar to those found in the boring evaluated, the geotechnical

engineer should be contacted for further evaluation.

4.0 CONCLUSIONS

If you have any questions or would like to discuss this report, please contact us by phone

at (802) 828-2561.

cc: David Peterson, Structures Project Engineer

Electronic Read File/MG

Project File/CEE

TJW

Z:\Highways\CMB\GeotechEngineering\Projects\Bethel BHF 0241(38)\Embankment Widening\REPORTS\Bethel BHF 0241(38) Preliminary Geotechnical Report_Final.pdf

AGENCY OF TRANSPORTATION OFFICE MEMORANDUM

To: Carolyn Carlson, P.E., Structures Project Manager

From: Eric Denardo, P.E., Geotechnical Engineer via Callie Ewald, P.E

Geotechnical Engineering Manager Date: January 11, 2019 Subject: Bethel BHF 0241(38) - Integral Abutment Recommendations 1.0 INTRODUCTION As requested, we have completed a geotechnical and geological analysis for the replacement of Bridge No. 38 over the Gilead Brook on VT Route 12 in Bethel, Vermont. This is an addendum to the previous geotechnical report submitted by CHA dated July 2013, which included boring logs and a summary of the preliminary subsurface investigation, and the geotechnical report submitted by the Geotechnical Engineering Section dated February 2018, which detailed anticipated settlements due to the proposed embankment widening. Contained herein are the results from our geotechnical and geological analyses and recommendations for pile supported integral abutments and piers founded on spread footings as determined using the 2017 AASHTO LRFD Bridge Design Specifications.

2.0 FIELD INVESTIGATION A field investigation was conducted between May 8 and 21, 2013. A report written by CHA dated July 2013 summarizes the subsurface investigation and findings. Information taken from the previous report was used to estimate the soil and rock parameters used in this analysis. 3.0 SOIL PROFILE The following soil strata have been identified based on our review of the boring logs and laboratory testing. It should be noted that groundwater elevations are subject to change. Because groundwater elevations can fluctuate seasonally and are affected by temperature and precipitation, groundwater may be encountered during construction when not previously noted in the logs. Abutment No. 1 - (B-01): The ground surface elevations at boring B-01, was approximately 682.3 feet(ft). Groundwater was measured during drilling on May 8, 2013 at a depth of 14 ft. A bottom of pile cap (BOC) elevation of 673.5 ft for Abutment No. 1 was provided by David Peterson in an email dated July 26, 2018.


Table 3.1: B-01 Soil Strata Elevation Below BOC

(ft) Soil/Strata Type

673.5 – 669.8 Dense Sand 669.8 – 655.3 Dense Gravelly Silt

>655.3 Medium Hard Phyllite Abutment No. 2 - (B-07 and B-07A): The ground surface elevations at borings B-07 and B-07A were approximately 701.2 and 701.5 ft, respectively. Groundwater measurements were taken before drilling in B-07 on May 10, 2013 at 39.2 ft. A BOC elevation of 691 ft for Abutment No. 2 was provided with the Geotechnical Services Request Form dated April 2,2018.

Table 3.2: B-07/B-07A Soil Strata Elevation Below BOC

(ft) Soil/Strata Type

691.0 – 673.7 Medium Dense Sand 673.7 – 663.2 Medium Dense Silt 663.2 – 657.2 Dense Gravel 657.2 – 644.7 Boulder 644.7 – 642.5 Medium Dense Silt 642.5 – 616.7 Very Dense Silt

A boulder was noted by the drillers during boring operations in B-07 starting at a depth of approximately 44 ft as noted in Table 3.2 above. 4.0 ANALYSIS

Developed by the Florida Bridge Software Institute, FB-Multipier, version 5.1, is a multi-aspect software that allows the user to analyze a bridge pier system in three dimensions. Its analysis factors in the subsurface strata, pile group including cap, and the structural capabilities of the pier system. For this integral abutment analysis, only the piles and cap were modeled.

4.1 Loads: Unfactored loads were provided by David Peterson with the Geotechnical Services Request Form dated April 2, 2018 and can be found in Table 4.1. Due to the addition of approximately 12.3 ft of fill material at Abutment No. 2 associated with the embankment widening, downdrag analyses were performed and a load was added to each pile in accordance with AASHTO 3.11.8 and described in more detail in Section 4.4 below. Our common practice, as outlined in the 2008 VTrans Integral Abutment Manual, is to apply vertical live and dead loading, as well as longitudinal effects from thermal deformations, braking, and rotation due to live loading. When analyzing a single abutment, FB-Pier does not consider the longitudinal and transverse stiffness provided by the entire bridge structure; it models the abutment or pier standing alone. Due to this as well as guidance from other states’ bridge manuals, it is


assumed that all wind and braking forces are to be resisted by the stiffness of the frame that is not accounted for in the analyses.

Table 4.1: Unfactored Abutment Loads

Type Load Type Value Superstructure Dead

Load DC 626.77 kips

Superstructure Super Dead Load DW 77.5 kips

Dead Load Rotation DC 2.587x10-3 Radians

Vehicular Live Load LL 225.06 kips Live Load Rotation LL 3.75x10-3 Radians Thermal Movement TU 0.92” Thermal Expansion

Rotation TU 6.516x10-3 Radians

Downdrag* DD 63.9 kips/pile *Applied at Abutment No. 2 only

The Abutments were only analyzed for the non-scour condition per Structures request, due to the shallow bedrock at Abutment No. 1, and distance of the abutments from the bankfull width based on the Hydraulics report prepared by CHA, dated November 2016. According to loads provided in Table 4.1 and AASHTO LRFD Table 3.4.1-1, Limit State Strength I was determined to be the governing load case for both abutments. As a result, a maximum factored axial load, 1.25 DC, 1.5 DW, and 1.75 LL, of 1294 kips and 2009 kips would be distributed over Abutment No. 1 and Abutment No. 2, respectively, resulting in a maximum axial load equal to 162 kips per pile and 251 kips per pile for an eight pile layout for Abutment No. 1 and Abutment No. 2, respectively. 4.2 Modeling: The models used the soil strata determined from borings B-01 for Abutment No. 1 and B-07 and B-07A for Abutment No. 2. The models were analyzed for strength and service loading combinations. Bottom of pile cap elevations of 673.5 ft and 691 ft were used in the analyses for Abutment No. 1 and No. 2, respectively. Due to the shallow bedrock encountered in the location of Abutment No. 1, the piles were modeled to best replicate conditions of pre-drilled holes in rock for the pile installment using a custom P-Y curve developed based on the type and strength of the rock as outlined in the RSPile Laterally Loaded Piles Manual.

4.2.1 Abutments: The abutments were modeled with 8 HP 12 x 84 piles with the middle six piles spaced at 47 inches on center and the end piles spaced at 45 inches on center. For Abutment No. 1 piles are assumed to be placed in predrilled holes and oriented for weak axis bending due to the shallow bedrock. For Abutment No. 2, the piles are assumed to be driven plumb and oriented for


strong axis bending. The piles are oriented for strong axis bending in order to provide resistance for the unbraced length in the second pile segment. Figures 4.1 and 4.2 below show the pile layouts for Abutment No. 1 and No. 2, respectively.

Figure 4.1: Abutment No. 1 Pile Layout

Figure 4.2: Abutment No. 2 Pile Layout

The soil parameters used in the analyses for Abutments No. 1 and No. 2 are shown in Tables 4.2 and 4.3, respectively. The rock parameters used for Abutment No. 1 are shown in Table 4.4. It should be noted that the torsional shear stress values are skin friction values for that given layer of soil or rock. The unconfined compressive strength (UCS) and modulus of elasticity, of the rock were not determined using the rock cores recovered. Therefore, the compressive strength, modulus of elasticity, and Poisson’s Ratio of the rock were assumed using values from similar rock previously tested and recorded in the Geotechnical Section’s UCS Master List. P-Y curves, which in this case are a measure of shaft resistance in rock when subjected to lateral loading, are the primary model of rock strength when designing piles drilled into rock. The rock encountered at the location of Abutment No. 1 was classified as medium hard, slightly weathered micaceous phyllite. The average RQD of the rock cores is 71% indicating fair rock.

Table 4.2 FB-Pier Analysis Soil Parameters – Abutment No. 1

Elevation (feet) Description

Friction Angle (deg.)

Unit Weight

(pcf)

Subgrade Modulus

(pci)

Shear Modulus

(ksi)

Torsional Shear

Stress (psf)

681.97 – 673.5 Granular

Backfill for Structures

34 140 225 2.17 340.5

673.5 – 669.8 Sand 37 120 225 2.23 725.4

669.8 – 665.3 Gravelly Silt 38 125 125 2.73 1286.8


Table 4.3 FB-Pier Analysis Soil Parameters – Abutment No. 2

Elevation (feet) Description

Friction Angle (deg.)

Unit Weight

(pcf)

Subgrade Modulus

(pci)

Shear Modulus

(ksi)

Torsional Shear

Stress (psf)

696.8 – 688.9 Granular Borrow 32 130 225 3.48 305.3

688.9 – 673.7 Gravelly Sand 33 120 90 1.39 1051.5

673.7 – 663.2 Silt 31 110 25 1.24 1384.7 663.2 – 657.2 Silty Gravel 36 135 60 2.94 2637.1 657.2 – 642.5 Silt 33 110 60 3.48 2225.3

642.5 – 600.7 Sandy

Gravelly Silt

38 130 125 3.48 4403.2

Table 4.4 FB-Pier Analysis Rock Parameters

Parameter Value Unconfined Compressive Strength (ksf) 701.6

Modulus of Elasticity (ksi) 5718 Poisson’s Ratio 0.20

Shear modulus (ksi) 2382.6

Abutment No. 1 was modeled based on the dimensions provided in the Geotechnical Request Form dated April 2, 2018 as 13.15 ft high, 3 ft thick, and 35 ft long pile cap. Several pile layouts and sizes were modeled. The final number and size of piles modeled were 8 HP 12 x 84 piles spaced at 47 inches(in) on center for the middle six piles and 45 in on center for the outer two piles. All piles are assumed to be drilled and installed plumb and oriented for weak-axis bending. The piles for Abutment No. 1 were modeled as 24 ft long pre-drilled holes measured from the bottom of the pile cap corresponding to a rock socket extending 5 feet below the shallowest rock encountered in the location of Abutment No. 1. Various models were created and analyzed to determine the best fit that replicated actual field conditions of the pre-drilled holes for the pile installment. The final model in FB-Pier was generated with a custom P-Y curve. FB Pier has an option to create a custom curve based on soil/rock resistance as a function of pile deflection. This was developed using the diameter of the pile and the UCS of the rock encountered. This method was used to model the 27 in diameter pre-drilled hole through soil and rock with a pile placed inside and then backfilled with sand. Similarly, Abutment No. 2 was modeled as having an 11.55 ft high, 3 ft thick, and 35 ft long pile cap with 8 HP 12 x 84 piles spaced at 47 in on center for the middle six piles and 45 in on center for the outer two piles. All piles are assumed to be driven plumb and oriented for strong-axis bending. The piles were modeled as 75 ft long piles measured from the bottom of the pile cap driven into the very dense sandy gravelly silt layer.

BETHEL BHF 0241(38) Page 6 of 12 5.0 RESULTS

5.1 Pile Stresses: The piles were checked for combined axial compression and flexure in the strong and weak axes using the requirements of AASHTO LRFD 6.9.2.2, 6.9.4.1, and 6.10.8.2. FB-Pier analyses were performed by applying an axial load, longitudinal displacement, and rotations at the top of each pile, corresponding to the bottom of pile cap elevation. Strength Load Case I and Service Load Case II were found to be the two controlling load combinations for both abutments The output from FB-Pier was used to calculate the factored structural and flexure pile resistance as well as the moment that would cause a plastic hinge in the pile, in accordance with the VTrans 2008 Integral Abutment Bridge Design Guidelines. A plastic hinge consistently formed in the top segment of the pile in the analyses run at both abutments. This occurred when the applied moments exceed the plastic moments of the piles. Analyses were then performed to ensure that a plastic hinge would not form in the second segment of the piles, which would overstress the piles and cause a failure. The second segment of the pile was considered to be between the two points of zero moment when a fixed head condition was modeled. The outputs from FB-Pier were in the weak and strong axes for Abutments No. 1 and No. 2, respectively. FB-Pier outputs as well as calculated values are displayed below in Table 5.1.

Table 5.1. FB-Pier Output for AASHTO Governing Strength Case

Abutment

Max. Applied Moment (kip-ft)

Plastic Moment*

(kip-ft)

2nd Pile Segment

Interaction

Factored Lateral Load (kips)

Unbraced Length (feet)

Fixity** (feet)

1 331 203 0.91 196 2.0 17.4 2 759 399 0.94 246 3.8 37.5

*Moment resulting in plastic hinge development. This moment becomes constant at pile head after pile begins to plastically deform. ** Measured from top of pile head

The factored lateral load provided in the table is the load applied to the top of the pile to achieve the required deflection multiplied by a load factor of 1.2. The final design for both abutments includes a total of 8 piles spaced at 47 in on center for the middle 6 piles and 45 in on center for the outer two piles, as shown in Figure 4.1 and Figure 4.2 for Abutment No. 1 and No. 2, respectively. The minimum pile size needed to satisfy design requirements was found to be HP 12 x 84 piles for both abutments. For Abutment No. 1, piles will be predrilled so that they are a minimum of 24 ft long and have a 5 ft minimum length rock socket. For Abutment No. 2, the piles should be driven to a minimum depth of 75 ft below the pile cap. For the strength limit state, the piles were found to be within the acceptable stress limits such that a plastic hinge did not form in the second segment leading to overstressing of the piles. For the service limit state, deflections were found to be 0.92 and 1.7 in for Abutments No.1 and No. 2, respectively, due to the applied thermal deflections.


5.2 Axial Capacity Analysis: For Abutment No. 2, to aid in estimating pile lengths, the minimum length needed to resist the factored design load based on dynamic testing needed to be calculated. This is assuming the pile could achieve sufficient resistance primarily in skin friction as bedrock was not encountered in the borings. With a factored load of 251 kips/pile and a resistance factor, φdyn = 0.65, a nominal axial pile resistance of 387 kips is required. Using the Nordlund method for cohesionless soils, unit skin friction values were calculated for each soil layer. Based on these values, the lengths of piles needed to resist the 387-kip load was calculated to be 55 ft, measured from the bottom of the pile cap. However, based on past experience with piles tending to “run,” meaning that if the piles do not take up in the denser layers of soil they may continue to drive and not achieve the required capacity at the expected length, in similar soil conditions, we recommend pile lengths of 75 feet be used for estimating and plan preparation purposes. The resistance factor of 0.65 requires a minimum of 2 dynamic tests performed per site condition, but no less than 2% of the production piles, during installation in accordance with Table 10.5.5.2.3-1 of the AASHTO LRFD code. Because the piles for Abutment No. 1 will be predrilled and seated with the impact hammer, two dynamic tests should be performed at Abutment No. 2. The remaining piles should be calibrated by wave equation analysis. 5.3 Pile Cap Design: The backwall can be designed as a horizontal beam resisting lateral earth pressures. The lateral earth pressure is generated by the movement of the abutment either into (passive earth pressure) or away from (active earth pressure) the soil mass. Passive earth pressure conditions may govern during the warmer months as the structure expands. Similarly, an active earth pressure condition may control during the colder months of the year as the superstructure contracts. Assuming distances of 13.15 and 11.55 ft from the bottom of the bridge seat to the bottom of the pile cap for Abutments No. 1 and No. 2, respectively, and the abutment experiencing all of the lateral movement, then the full passive pressure condition would be met. This would produce a passive earth pressure coefficient larger than an active earth pressure coefficient. Therefore, it is conservative to design for the full passive pressure condition at the abutments.

Equation 1: 𝐾𝐾𝑃𝑃 = 1+𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠1−𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠

Equation 2: 𝑊𝑊𝑃𝑃 = 1

2𝛾𝛾𝐻𝐻2𝐾𝐾𝑃𝑃

The passive earth pressure per unit length of backwall can be calculated by inserting the value of Kp, computed in Equation 1, into Equation 2. The backfill unit weight is assumed to be equal to 140 pcf with an internal friction angle of 34 degrees. Based on these assumptions and Equations 1 and 2, the total passive earth pressure per unit length of the backwall is calculated to be equal to 42.8 k/ft and 33.0 k/ft for Abutments No.1 and No.2, respectively.


5.4 Downdrag Analysis Negative skin friction, or downdrag, is considered when the relative settlement between the pile and soil equals or exceeds 0.4 inches according to AASHTO 3.11.8. The proposed roadway varies significantly in grade with the existing site and as a result will require large amounts of fill. The proposed roadway will require up to 12.3 ft of fill to be placed to widen the embankment at the centerline of Abutment No. 2. A settlement analysis was performed and anticipated settlements of up to 2.7 inches were calculated. Assuming the full downdrag condition is met, where the downward movement of the settling soil acts on the pile, an additional axial load should be modeled acting on each pile. The settlement will induce axial loads of 63.9 kips per HP 12 x 84 pile for Abutment No. 2. 5.5 Driving Resistances: Past experience suggests that the HP 12x84 piles analyzed in this report could be driven through the soils encountered by pile-driving equipment commonly used by contractors in the region. Section 10.7.8 of the AASHTO LRFD Bridge Design Specifications stipulates that the maximum tension and compression stresses allowed in the piles shall not exceed σ =0.9∗φda*fy. φda as defined in AASHTO LRFD 6.5.4.2 as 1.0, resulting in a maximum induced stress in the pile of 0.9*f y or 45 ksi for grade 50 (50 ksi) piles. However, wave equation analyses only verify that the piles can be driven to a factored resistance; the program is not able to determine the location and size of boulders. 5.6 Nominal Axial Pile Resistance: The nominal bearing resistance, RR, shall be factored using the resistance factors, Φdyn, in Table 10.5.5.2.3-1 of the AASHTO LRFD code. The factored resistance RR may be taken as RR = Φdyn * Rn. The resistance factor, Φdyn, which should be applied to these piles bearing in either soil or on rock to attain the factored resistance, is 0.65. The use of 0.65 requires a minimum of 2 dynamic tests performed during installation in accordance with Table 10.5.5.2.3-1 of the AASHTO LRFD code. The remaining piles should be calibrated by wave equation analysis. For the predrilled piles, a resistance factor of 0.7 should be used based on our standard practice and guidance from surrounding states. Given the loads provided in Tables 3.1, the nominal axial pile resistances, or resistances the piles should be driven to, are 231 kips and 387 kips for Abutments No.1 and No.2, respectively. 5.7 Piers: Due to shallow bedrock at the location of the piers, it is anticipated that they will be supported on spread footings on bedrock. As per section 10.5.5.1 of the 2017 AASHTO LRFD Bridge Design Specifications, a resistance factor of 1.0 should be applied to the unfactored bearing resistance for use in service limit state design. Service limit state design includes, but is not limited to, settlement and scour. Section 10.5.5.2.2 specifies that a resistance factor of 0.45 should be applied to the unfactored bearing resistance for use in strength limit state design for spread footings on rock.

Strength limit state design includes, but is not limited to, checks for bearing resistance, sliding, and constructability. Potential for overturning is limited by controlling the location of the resultant of the reaction forces (eccentricity). Eccentricity, e, shall be limited as follows:


Foundations on rock: |e| < 0.45b

Eccentricity should be considered for settlement and bearing resistance design of spread footings by using effective footing widths based on AASHTO Section 10.6.1.3.

The bedrock at the pier locations has fair to good rock quality designation. Classified as medium hard to medium soft, moderately to slightly weathered, Phyllite, AASHTO recommends a presumptive bearing resistance of 20 ksf per Table C10.6.2.6.1-1 for weathered or broken bedrock of any kind except highly argillaceous rock. Taken as the nominal bearing resistance, in combination with a resistance factor of 0.45 for spread footings on rock, per AASHTO 10.5.5.2.2-1, this yields a factored bearing resistance of 9 ksf. Settlement of the piers, with maximum allowable bearing pressures indicated and designed as recommended herein is anticipated to be negligible. Scour is not anticipated to be a concern if the piers are founded directly on bedrock. It is recommended that any incompetent, weathered, and fractured bedrock encountered during construction of the spread footings be removed until competent bedrock is encountered. During excavation, the Agency Geologist should inspect the bedrock to determine the amount and extent of excavation needed. If uneven bedrock contours are encountered, the concrete subfooting should be stepped along the existing bedrock in order to transfer the footing pressure directly to the bedrock.

5.7.1 Resistance Factors: Sections 10.5.2 and 10.5.3 of AASHTO outline all design states relevant to spread footing design and their respective resistance factors. Eccentricity should be considered for bearing resistance design of spread footings by using effective footing widths based on AASHTO Section 10.6.1.3. Table 5.2 shows the appropriate resistance factors for various design states.

Table 5.2 Resistance Factors for Design States

Design State Resistance Factor, φ Service (Scour) 1.0

Strength (Bearing Resistance) 0.45 Sliding 0.80

Additional sliding resistance can be accomplished by doweling the footing into bedrock.

6.0 RECOMMENDATIONS

6.1 Integral Abutment Foundations: Based on the change in elevation across the bridge and anticipated thermal movements, elasticized expanded polystyrene (EPS) and a geotextile separation fabric should be installed between the back of the concrete surfaces and the backfill material at both abutments. The EPS and geotextile should extend from below the approach slab to the bottom of the pile cap for each abutment. The minimum required thicknesses of the EPS are 1.83 and 2.1 feet for Abutments No. 1 and No. 2, respectively based on the anticipated movement at the abutments.


The special provision entitled ‘Geogrid-compressible inclusion’ used in the Waterbury IM 089-2(43) plan set can be referenced for use on this project. The following table provides a summary of the requirements for the piles at Abutments No. 1 and No. 2. The piles for Abutment No. 1 should meet the requirements for both minimum pile embedment and minimum pile embedment in bedrock.

Table 6.1: Summary of requirements of H-piles at each abutment

Requirement Abutment No. 1 Abutment No. 2 Pile Size HP 12x84 HP 12x84

Pile Orientation Weak axis Strong axis Minimum Pile Embedment* 24 feet 75 feet

Minimum Embedment into Competent Bedrock 5 feet N/A

Method of Installation Pre-bored and placed Driven pile Backfill Material Sand N/A

Nominal Axial Pile Resistance 231 kips 384 kips

*Total length of pile below bottom of pile cap, including rock socket at Abutment No. 1

The piles for Abutment No. 1 will be pre-bored and placed into position in rock sockets. For this reason, dynamic tests are not required. However, the pre-bored piles for Abutment No. 1 should be seated in the rock sockets with a pile driving hammer. Because no tests will be performed on Abutment No. 1, in order to use the bearing resistance factor of 0.65 for the piles at Abutment No. 2 as outlined in Section 5.6 of this report, two dynamic tests will need to be performed on the piles at Abutment No. 2.

6.2 Construction Considerations:

6.2.1 Cofferdams/Temporary Earthwork Support: The use of cofferdams may be necessary in order to support the excavations required for the abutments and piers. If required, the Contractor should be reminded that Section 208.06 of VTrans’ 2018 Standard Specifications for Construction indicates that “The Contractor shall prepare detailed plans and a schedule of operation for each cofferdam specified in the Contract” The design and structural details of the cofferdam shall be signed, stamped, and dated by a Professional Engineer (Structural or Civil) registered in the State of Vermont. 6.2.2 Construction Dewatering: Temporary construction dewatering may be required to construct the abutments. Temporary dewatering may also be necessary to limit disturbance to and maintain the integrity of the bearing surface. Temporary


dewatering can likely be accomplished by open pumping from shallow sumps, temporary ditches, and trenches within and around the excavation limits. Sumps should be provided with filters suitable to prevent pumping of fine-grained soil particles. The water trapped by the temporary dewatering controls should be discharged to settling basins or an approved filter “sock” so that the fine particles suspended in the discharge have adequate time to “settle out” prior to discharge. All effluent water, or discharge, should comply with all applicable permits and regulations. 6.2.3 Placement and Compaction of Soils: Fills should be placed systematically in horizontal layers not more than 12 in in thickness, prior to compaction. Cobbles larger than 8 in should be removed from the fill prior to placement. Compaction equipment should preferably consist of large, self-propelled vibratory rollers. Where hand-guided equipment is used, such as a small vibratory plate compactor, the loose lift thickness shall not exceed 6 in. Cobbles larger than 4 in should be removed from the fill prior to placement. Embankment fills should be compacted to a dry density of at least 95% of the maximum dry density determined in accordance with AASHTO T-99 per section 203.11 of the 2018 VTrans Standard Specifications for Construction. Granular Backfill for Structures, or other select materials placed within the roadway base section shall be compacted to a dry density of 95% of the maximum dry density determined in accordance with AASHTO T-99.

6.3 Design Parameters: Table 6.2 highlights the geotechnical design parameters of the foundation bearing soils as well as regularly specified aggregates. These values should be used when designing the substructure units. It is recommended that values of Ko be used for calculating earth pressures where the structure is not allowed to deflect longitudinally, away from or into the retained soil mass. Values for Ka should be utilized for an active earth pressure condition where the structure is moving away from the soil mass and Kp where the structure is moving toward the soil mass. The design earth pressure coefficients are based on horizontal surfaces (non-sloping backfill) and a vertical wall face.


Table 6.2 Engineering Properties for Construction and In-Situ Materials

703.01A - Granular Borrow

704.08 - Granular

Backfill for Structures

In-Situ Bedrock

Density (lb/ft3): 130 140 169

Internal Friction Angle, φ (degrees): 32 34 33

Coefficient of Friction, f - concrete cast againstsoil/rock: 0.50 0.55 0.7

- soil against formedconcrete 0.40 0.45 N/A

Active Earth Pressure Coefficient, Ka: 0.31 0.28

Passive Earth Pressure Coefficient, Kp: 3.25 3.54

At-Rest Earth Pressure Coefficient, Ko: 0.47 0.44

7.0 CONCLUSION

If any further analysis is needed or you would like to discuss this report, please contact us at (802) 828-2561. Final FB-Pier input files used in the analyses are located in the M:\Projects\10c216\MaterialsResearch\FB-Pier folder on the M/drive.

Abut 1 STR I 8 piles.in Abut 1 SER II 8 piles.in

Abut 2 STR I 8 piles.in Abut 2 SER II 8 piles.in

cc: David Peterson, Structures Project Engineer Electronic Read File/MG Project File/CEE END

Z:\Highways\CMB\GeotechEngineering\Projects\Bethel BHF 0241(38)\Integral Abutment\REPORTS\Bethel BHF 0241(38) Integral Abutment Recommendations.docx