EXHIBIT 21 GEOTECHNICAL BASELINE REPORT...2019/05/23 · Geotechnical Baseline Report Exhibit 21 Execution Version Hampton Roads Bridge-Tunnel Expansion Commonwealth of Virginia Project

Geotechnical Baseline Report Exhibit 21 Execution Version

Hampton Roads Bridge-Tunnel Expansion Commonwealth of Virginia Project No. 0064-M06-032 Virginia Department of Transportation

EXHIBIT 21

GEOTECHNICAL BASELINE REPORT

[See attached]

Virginia Department of Transportation

FINAL GEOTECHNICAL BASELINE REPORT

I‐64 HAMPTON ROADS BRIDGE‐TUNNEL

EXPANSION PROJECT

UNDER THE

VIRGINIA PUBLIC‐PRIVATE

TRANSPORTATION ACT OF 1995

(AS AMENDED)

STATE PROJECT NO. 0064‐M06‐032

FEDERAL PROJECT NO. [●]

ISSUANCE OF FINAL GBR:

NOVEMBER 28, 2018

Final Geotechnical Baseline Report November 28, 2018

Hampton Roads Bridge‐Tunnel Expansion Commonwealth of Virginia Project No. 0064‐M06‐032 i Virginia Department of Transportation

Table of Contents

1.0 Introduction ...................................................................................................................................... 1

1.1 Purpose and Scope ........................................................................................................................ 1

1.2 Project Elements Covered by GBR ................................................................................................ 1

1.3 Sources of Geotechnical Information ........................................................................................... 2

1.4 Stationing and Datum ................................................................................................................... 2

2.0 Project Description ............................................................................................................................ 4

3.0 Previous Construction Experience .................................................................................................... 5

3.1 Hampton Roads Project ................................................................................................................ 5

3.2 Second Hampton Roads Bridge‐Tunnel Crossing .......................................................................... 6

3.3 Other Projects ............................................................................................................................... 6

4.0 Ground Characterization ................................................................................................................... 7

4.1 Island Artificial Fill (af) ................................................................................................................... 8

4.2 Alluvial Marine Sediments ............................................................................................................ 9

4.2.1 Alluvial Marine Sediments – Coarse‐Grained (Qc) .............................................................. 10

4.2.2 Alluvial Marine Sediments – Fine‐Grained (Qf) .................................................................. 11

4.2.3 Alluvial Marine Sediments – Organic/Fat Clay (Qo) ............................................................ 12

4.3 Yorktown Formation (Tys, Tyf) .................................................................................................... 15

4.3.1 Yorktown Formation – Coarse‐Grained (Tys) ...................................................................... 15

4.3.2 Yorktown Formation – Predominantly Fine‐grained (Tyf) .................................................. 16

4.4 Eastover Formation (Tye) ............................................................................................................ 17

4.5 Groundwater ............................................................................................................................... 18

5.0 Design and Construction Considerations ........................................................................................ 25

5.1 Tunnel Approach Structures ....................................................................................................... 25

5.1.1 Stratigraphy ......................................................................................................................... 25

5.1.2 Obstructions ........................................................................................................................ 26

5.1.2.1 Rock Containment Dikes and Scour Protection ............................................................... 26

5.1.2.2 Temporary Works from Previous Construction ............................................................... 27

5.1.3 Groundwater Control .......................................................................................................... 28

5.1.4 Gas Conditions .................................................................................................................... 28

5.1.5 Soil pH ................................................................................................................................. 29

5.2 Bored Tunnel .............................................................................................................................. 29

5.2.1 Stratigraphy ......................................................................................................................... 29


Hampton Roads Bridge‐Tunnel Expansion Commonwealth of Virginia Project No. 0064‐M06‐032 ii Virginia Department of Transportation

5.2.2 Break‐in/out ........................................................................................................................ 30

5.2.3 Behavior of Soft Soils .......................................................................................................... 31

5.2.4 Obstructions ........................................................................................................................ 32

5.2.4.1 Rock Containment Dikes and Scour Protection ............................................................... 32

5.2.4.2 Temporary Works from Previous Construction ............................................................... 33

5.2.4.3 Unrecovered Equipment from Geotechnical Drilling Program ........................................ 34

5.2.4.4 Foundations for Survey Towers ....................................................................................... 35

5.2.5 Sticky Clay Behavior ............................................................................................................ 35

5.2.6 Cemented Sand and Shell Zones ......................................................................................... 36

5.2.7 Soil Abrasion Behavior ........................................................................................................ 36

5.2.8 Gas Conditions .................................................................................................................... 37

5.2.9 Soil pH ................................................................................................................................. 37

5.3.2 Obstructions ........................................................................................................................ 38

6.0 Instrumentation and Monitoring .................................................................................................... 39

7.0 Limitations ....................................................................................................................................... 40

8.0 References ...................................................................................................................................... 41

APPENDIX A ‐ Boring Location Plan and Baseline Subsurface Profile ......................................................... 43

APPENDIX B – Tunnelman’s Classification System ...................................................................................... 44

Tables Table 4.1 Baseline Values for Soil Index Properties and Shear Strength Table 4.2 Baseline Values for Soil Permeability and Compressibility Table 5.1 Location of Unrecovered Equipment from Geotechnical Drilling Program Table 5.2 Baseline Values for Soil Abrasivity Figures Figure 4.1 Baseline Subsurface Profile Figure 4.2 Range of Particle Size Distribution ‐ Island Artificial Fill Figure 4.3 Range of Particle Size Distribution‐Alluvial Marine Sediments–Coarse‐Grained Figure 4.4 Plasticity Chart for Alluvial Marine Sediments – Fine‐Grained

Figure 4.5 Undrained Shear Strength v. Elevation, Fine‐Grained Alluvial Marine Sediments Figure 4.6 Plasticity Chart for Alluvial Marine Sediments – Organic/Fat Clay Figure 4.7 Range of Particle Size Distribution ‐ Yorktown Formation – Coarse‐Grained Figure 4.8 Plasticity Chart for Yorktown Formation – Predominantly Fine‐Grained Figure 4.9 Range of Particle Size Distribution ‐Eastover Formation

Figure 5.1 Limits of Ground Improvement Required to Support TBM in Soft Soils Figure 5.2 Location of Unrecovered Equipment from Geotechnical Drilling Program Appendices Appendix A Appendix B

Boring Location Plan and Baseline Subsurface Profile Tunnelman’s Classification System


Hampton Roads Bridge‐Tunnel Expansion Page 1 Commonwealth of Virginia Project No. 0064‐M06‐032 Virginia Department of Transportation

1.0 Introduction

The purpose of this Geotechnical Baseline Report (GBR) is to establish contractual baselines

describing the anticipated ground conditions to be encountered during construction of the

following elements of the I‐64 Hampton Roads Bridge‐Tunnel Expansion (HRBT) project: the

Tunnel Improvements.

Capitalized terms used in this GBR but not otherwise defined herein shall have the meanings

given to such terms in the Comprehensive Agreement.

1.1 Purpose and Scope

The baselines established in this report shall be used by the Design‐Builders in proposal

preparation and will also be used to evaluate potential Differing Tunnel Improvements Site

Conditions encountered during construction. To evaluate design alternatives and approaches,

construction means and methods, selecting equipment, and developing construction plans,

Design‐Builders are required to read and consider the GBR, the Geotechnical Data Report (GDR),

and all other Request for Proposal (RFP) Documents in their entirety.

The geotechnical baseline conditions described in this report reflect the Department’s judgment

of anticipated subsurface conditions and ground behavior based on construction means and

methods commonly employed to complete the work indicated by the RFP Documents. In

establishing these baselines, the Department considered available geologic and geotechnical

data and construction experience in similar ground conditions. Actual conditions encountered in

the field are expected to be within the range of conditions discussed herein for purposes of

determining whether such conditions constitute Differing Tunnel Improvements Site Conditions

pursuant to Section 4.3.2 of the General Conditions of Contract. However, the geotechnical

baseline conditions presented in this report are not a warranty that these conditions will, in fact,

be encountered. Ground behavior will be influenced by, among other factors, the construction

sequence and methods employed by the Design‐Builder, as well as the Design‐Builder’s

equipment, materials and workmanship. The issuance of the baselines shall not relieve the

Design‐Builder of its responsibility for the adequacy of the subsurface investigation program with

respect to the design and alignment of the permanent works, the design and implementation of

construction means and methods and safety precautions and programs.

1.2 Project Elements Covered by GBR

This baseline report pertains only to the tunnel, the boat section and cut‐and‐cover tunnel

approach structures on the portal islands, and island expansions. This baseline report does not

represent conditions for other project construction elements, including the Roadway and Bridge

Improvements. The Department will not issue a GBR covering other project construction



activities. The baseline report does not represent environmental baseline conditions such as

contaminated or hazardous soils or other materials.

1.3 Sources of Geotechnical Information

Geotechnical Investigations have been performed in phases for this project, and the applicable

data for the tunnel and tunnel approach structures is presented in the following two

Geotechnical Data Reports, which are included as part of the Contract:

“Preliminary Geotechnical Data Report – Hampton Roads Bridge Tunnel – North and

South Islands”, prepared by ECS Mid‐Atlantic LLC and dated June 15, 2018.

“Geotechnical Data Report – Marine”, prepared by Jacobs Engineering and dated July

2018.

Additional geotechnical information from within and near the HRBT location can be found in the

historic reports, records and published references listed in Section 8.0. The additional

geotechnical information includes boring logs from the original HRBT tunnel construction in the

1950s and the construction of the second HRBT crossing in the 1970s. In addition to the

geotechnical information, an archaeological survey report (AECOM, 2017) includes the results of

geophysical investigations performed along the tunnel alignment. These reports, records and

published references listed in Section 8.0 are provided as Disclosed Information to the Contract.

1.4 Stationing and Datum

All stations referred to in this report are based on the stationing established for the second bridge

tunnel crossing in the 1970s, with the end of the northernmost tube at Station 862+57, and the

end of the southernmost tube at Station 931+54, as shown on Drawing S‐1 of the original plans

for Contract T‐2 (Commonwealth of Virginia, 1975).

The project datum for horizontal control is NAD83, and all elevations referred to in this report

are based on NAVD88.

1.5 Disclosed Information and Scope Validation on Portal Islands

The Disclosed Information included in the Comprehensive Agreement provides supplemental

data on subsurface conditions beyond the baselines described in this report, such as but not

limited to, the presence of utilities, building foundations, and other site improvements. Should

the Disclosed Information within the perimeters of the existing North and South Islands have a



material impact on the Design‐Builder’s means and methods, Article 2.2 of Part 4, General

Conditions of Contract relating to scope validation and identification of scope issues shall apply.



2.0 Project Description

The Project consists of improvements along approximately nine miles of the I‐64 corridor

between Settlers Landing Road in Hampton (Exit 267) and I‐564 in Norfolk (Exit 276). On land,

the Project will add a third lane to I‐64 in each direction, with a roadway section sufficient to

accommodate a part‐time median shoulder lane.

The Project will include a new bridge‐tunnel crossing of the Hampton Roads waterway,

approximately 3.5 miles long and generally parallel to the existing bridge‐tunnel crossings. The

new crossing will provide four additional lanes of traffic for a total of eight lanes of capacity across

the waterway.

The bridge‐tunnel section of the project includes the following main components:

A new approximate 3.5‐mile‐long bridge‐tunnel parallel to the existing bridge‐tunnels;

The tunnel may be constructed as either an immersed tube tunnel (ITT) or a bored tunnel,

designed to carry four lanes of eastbound traffic (the existing two‐lane eastbound tunnel

will be subsequently converted to carry westbound traffic, thereby providing four lanes

of westbound traffic);

Widening of the existing north and south portal islands to the west as required to

accommodate the new portals and approach structures for the parallel tunnel;

New trestle bridges connecting the mainland to each of the portal islands;

Repairs and improvements to the existing trestle bridges; and

Support systems, services and utilities for the new tunnel including but not limited to:

tunnel ventilation buildings; tunnel ventilation systems and equipment; tunnel and

approach lighting; power for lighting and other tunnel electrical needs; tunnel drainage;

fire detection and alarm; communications (phones and radio system); fire protection

systems; intrusion detection, supervisory control and data acquisition (SCADA) and

information technology systems (ITS).



3.0 Previous Construction Experience

The existing bridge‐tunnel was built in two separate projects: one in the 1950s and the second in

the 1970s. Both projects were built using ITT method of construction. In addition to the original

design and record drawings for both projects, several technical journal articles describe the

construction of the original and second crossings in some detail; these articles are included in the

list of references in Section 8.0 of this report. In addition, project documents included as

Supplemental Information to the contract contain several hundred photos taken during

construction of each project.

There are also several other similar transportation tunnel projects in the vicinity of the Hampton

Roads Bridge‐Tunnel Expansion with similar construction methodologies and subsurface

conditions. Section 3.3 provides a list of those projects.

3.1 Hampton Roads Project

The original Hampton Roads Project was completed in 1957 and included construction of a two‐

lane bridge and tunnel connecting Norfolk, Virginia with Hampton, Virginia across the Hampton

Roads waterway. The tunnel has a length of 7,479 feet between portals and consists of 23 steel

immersed tube tunnel sections, each approximately 300 feet long. The tunnel sections were

placed in a dredged trench between two man‐made portal islands, while the tunnel approach

structures on the islands were built by cut and cover methods. Trestle bridge connections from

the portal islands to the mainland on both the north and south sides provide a total water

crossing length of approximately 3.5 miles.

The North Island was founded on sands and silty sands which provided a suitable foundation.

However, at the South Island location, up to 80 feet of normally consolidated clay and organic

layers overlying sandy soils were present, which were expected to cause settlement or stability

issues during island construction. To mitigate these issues, the soft layers were dredged out over

the width of the tunnel approach structures and vent buildings on the South Island with 2H:1V

slopes, and the excavation was then hydraulically backfilled with soils dredged from nearby areas.

This hydraulic fill consisted of poorly graded, fine sand, which was densified by vibro‐flotation.

The perimeter slopes of the islands are protected by rip rap and armor stone.

The tunnel approach structures on the islands were built by cut and cover methods with steel

sheeting or soldier pile and lagging with cross‐lot struts used for temporary support of

excavation. Dewatering systems were employed to build the cut and cover structures “in‐the‐

dry.” Ventilation buildings and other support facilities were constructed on the islands.



3.2 Second Hampton Roads Bridge‐Tunnel Crossing

The second Hampton Roads Bridge‐Tunnel Crossing was completed in 1975, and was built parallel

to, and 250 feet to the west of, the original tunnel. Similar to the original tunnel, it consists of a

6,900‐ft long two‐lane steel immersed tube tunnel between the two portal islands, which were

enlarged to accommodate the new tunnel and approach structures. Two additional trestle

bridges connect the islands with the mainland.

Design and construction of the South Island expansion faced similar issues to the original

construction. As opposed to over‐excavating the underlying normally consolidated clay and

organic layers, sand drains were installed through the clay and organics, and a surcharge was

placed to pre‐consolidate these layers prior to tunnel construction. An initial contract to build

the South Island expansion included placement of fill up to 25 feet higher than the finished island

elevation, as well as the installation of the sand drains and monitoring systems. The

consolidation of the clay layers achieved 90% consolidation approximately 15 months after

completion of the surcharge placement, with a maximum measured settlement under the

highest surcharge of approximately 13 feet.

A second contract included the removal of the South Island surcharge, the construction of the

North Island expansion, and the immersed tube tunnel. The tunnel approach structures were

again built by cut and cover methods using temporary support of excavation systems including

sheeting and soldier pile and lagging, however this time with tiebacks instead of cross‐lot struts.

Dewatering systems were again employed to build the cut and cover structures “in the dry”.

Follow‐on contracts included construction of the ventilation buildings and other facilities.

3.3 Other Projects

Other similar tunnel projects in the vicinity of the Hampton Roads Bridge‐Tunnel Expansion with

similar subsurface conditions include the following:

Midtown Tunnel;

Downtown Tunnel;

I‐664 Monitor‐Merrimack Memorial Bridge‐Tunnel; and

Chesapeake Bay Bridge and Tunnel (original Thimble Shoal Channel and

Chesapeake Channel tunnels constructed in the 1960s, as well as the Parallel

Thimble Shoal Tunnel, which is currently under construction).

Transportation tunnel projects completed in the vicinity to date were constructed exclusively

using the immersed tube tunneling method. The proposed Parallel Thimble Shoal Tunnel for the

Chesapeake Bay Bridge‐Tunnel crossing, which is expected to commence tunneling operations in

2019, will be constructed using the bored tunneling method.



4.0 Ground Characterization

The project site is located within the Coastal Plain of Virginia where the James River meets the

Chesapeake Bay. The Coastal Plain comprises a thick wedge of sediments underlain by

Precambrian to early Mesozoic basement bedrock at depths greater than 2,000 feet. The

majority of the sediments consist of late Jurassic and Cretaceous clays, sands and gravels which

were transported from the Appalachian Mountains and deposited in the Atlantic Ocean basin.

The subsurface materials anticipated to be encountered within the tunnel alignment overlie

these sediments, and comprise younger Tertiary and Quaternary layers that can generally be

classified into the following four geological strata, from youngest to oldest:

Island Artificial Fill (af)

Alluvial Marine Sediments (Qc, Qf, Qo)

Yorktown Formation (Tys, Tyf)

Eastover Formation (Tye)

The Yorktown and Eastover formations are fossiliferous marine sands and clays that were

deposited during interglacial highstands of the sea under similar conditions to the current site

environment. The Eastover is thought to be late Miocene‐aged, while the Yorktown is considered

to be early Pliocene‐aged. The Alluvial Marine Sediments are Quaternary aged, geologically

unconsolidated layers that were likely deposited during the Holocene and late Pleistocene

epochs.

Each stratum is discussed in the following sections of the report, and the baseline properties of

these layers are presented in Tables 4.1 and 4.2. A baseline subsurface profile projected along

the alignment of the second tunnel built in the 1970s is shown in Figure 4.1. In addition, in

Appendix A, the baseline subsurface profile is shown on full size sheets with the boring location

plan. This baseline profile is applicable for new tunnel alignments between the existing tunnels,

and for alignments up to 500 feet to the west of the second 1970s tunnel alignment. Although

the subsurface profile is drawn along the 1970s tunnel alignment, for clarity, the existing tunnel

structure and associated backfill materials are not included in the profile. The limits of existing

structures, and the associated dredging limits and backfill and scour protection materials are

shown on the record drawings (Commonwealth of Virginia, 1956, 1975). Qualifying statements

related to interpretation of the subsurface profile for different elements of the proposed

construction are presented in Sections 5.1.1, 5.2.1 and 5.3.1 of this report.

In Appendix B, the Tunnelman’s Classification System (after Heuer, 1974) is presented. This

classification system was developed to describe soft ground behavior during tunnel excavation



and each stratum that could be encountered in the bored tunnel alignment will be classified in

accordance with this system. Although this classification system was created before the

widespread use of pressurized‐face TBMs and therefore assumes an open‐face excavation

method, it is nevertheless useful for conveying how soils are anticipated to behave if not properly

controlled during tunneling or other excavation.

4.1 Island Artificial Fill (af)

The North Island and the South Island were constructed using hydraulically placed fill to a finished

surface elevation of approximately Elevation +11 feet. The hydraulic fill is predominantly

composed of clean fine sands and typically classifies in the Unified Soil Classification System

(USCS) as poorly graded sand (SP), silty sand (SM) and poorly graded sand with silt (SP‐SM).

Based on the mudline elevation shown on the drawings for the original tunnel construction

contracts, at the North Island, the artificial fill thickness varies between 20 and 25 feet, with the

base of the layer between Elevation ‐9 and ‐14 feet. At the South Island, the artificial fill thickness

to the west of the existing tunnels appears to vary between 33 and 48 feet below ground surface

with the base of the layer encountered between Elevations ‐22 and ‐37 feet. Although not

reflected by the most recent site investigations as documented in the GDRs, the fill thickness is

greater at locations beneath the original tunnels and tunnel approach structures constructed in

the 1950s, with the over‐excavation and replacement of the soft clay layers employed at that

time resulting in the fill extending to the top of the Yorktown formation, up to Elevation ‐105, as

shown in the 1950s record drawings and documented by Steuerman and Murphy (1957).

Over 13 feet of settlement was measured during construction of the South Island expansion in

the 1970s so it is reasonable that the fill thickness would be greater than for the North Island.

Based on analysis of the N60 SPT test results, the hydraulic fill is very loose to medium dense.

Grain size analyses were performed on several samples, and the range of particle size distribution

observed in the test samples from the recent geotechnical investigations is shown in Figure 4.2.

Baseline index and shear strength properties for this layer are provided in Table 4.1 and the range

for the hydraulic conductivity is included in Table 4.2. When encountered above the

groundwater level, this layer when unsupported and unimproved would classify in the

Tunnelman’s Classification System as “Running”, while below groundwater would classify as

“Flowing”.

Armor stone, rip rap, and crushed rock filter layers were placed around the island perimeters to

contain the hydraulic fill placement, and to provide scour protection. When the islands were

expanded in the 1970s construction, it is understood that the existing scour protection placed in



the 1950s was not removed but rather was buried under the new hydraulic fill; for example, a

note on Sheet 7 (of 127) of the record drawing set for Contract T‐2 (Commonwealth of Virginia,

1975) states: ”Existing rip rap and bedding along the entire west side of North Island to be

removed to El +7.0.”

Figure 4.2 Range of Particle Size Distribution ‐ Island Artificial Fill (af)

4.2 Alluvial Marine Sediments

Below the island fill, and below the mudline outside of the island footprints, a layer of alluvial

marine sediments is present, and consists of interlayered sands, inorganic and organic silts and

clays, and peat. Based on the properties of the materials in this layer, it can be sub‐divided into

the following three sub‐layers:

Alluvial Marine Sediments – Coarse‐Grained (Qc)

Alluvial Marine Sediments – Fine‐Grained (Qf)

Alluvial Marine Sediments – Organic/Fat Clay (Qo)

The distribution of these three sub‐layers is quite variable, particularly below the South Island.

The sub‐layers may be individually present or present in any combination. Furthermore, the

relative order of appearance of the sub‐layers, vertically, is also variable.

Gravel SandSilt or Clay

Coarse Fine Coarse Medium Fine

0

10

20

30

40

50

60

70

80

90

100

0.0010.0100.1001.00010.000100.000

Percent Finer

Particle Size (mm)

Maximum25% QuartileMedian75% QuartileMinimum

Hydrometer AnalysisUS Standard Sieve NumberUS Standard Sieve Size (inches)

#200#4 #10 #40 #80 #100



4.2.1 Alluvial Marine Sediments – Coarse‐Grained (Qc)

The coarse‐grained alluvial marine sediments were encountered below the fill of both islands and

below the mudline over most of the tunnel alignment. Below the North Island and north of

Station 878+00, the fine‐grained and organic/fat clay marine sediments were not encountered,

and the coarse‐grained deposits extend to the top of the Yorktown formation, which was

encountered between Elevations ‐85 and ‐32 feet. South of Station 878+00, the coarse‐grained

sediments vary between 5 and 30 feet thick and are typically encountered above the fine‐grained

alluvial marine sediment layers, but in some locations granular layers and lenses are also

encountered within and below the cohesive alluvial deposits. The coarse‐grained alluvial marine

sediments are very loose to dense, and generally classify in the USCS as poorly graded sand (SP),

silty sand (SM), and clayey sand (SC). Grain size analyses were performed on several samples,

and the range of particle size distribution observed in the test samples is shown in Figure 4.3.

Figure 4.3 Range of Particle Size Distribution‐Alluvial Marine Sediments–Coarse‐Grained (Qc)

Baseline index and shear strength properties for the Qc layer are provided in Table 4.1 and the

baseline hydraulic conductivity range is listed in Table 4.2. If left unsupported or not modified

with ground improvement, depending on the fines content and water pressure, this layer would

classify as “Fast Raveling” or “Flowing” in the Tunnelman’s Classification System, as detailed in

Appendix B.

Sand

FineMediumCoarseSilt or Clay

Gravel

Coarse Fine

0

10

20

30

40

50

60

70

80

90

100

0.0010.0100.1001.00010.000100.000

Percent Finer

Particle Size (mm)



#200#4 #10 #40 #80 #100



4.2.2 Alluvial Marine Sediments – Fine‐grained (Qf)

From approximately Station 878+00 to 945+00, the fine‐grained marine sediments were

encountered below the coarse‐grained marine sediments. The fine‐grained marine sediments

predominantly consist of lean clay (CL) and fat clay (CH). A plasticity chart showing the liquid

limit plotted versus the plasticity index for laboratory tests on this layer is shown in Figure 4.4.

The thickness of the Qf layer is quite variable, and it can be difficult to visually distinguish

between the underlying organic/fat clay sub‐layer (i.e. the Qo layer described below). However,

the distinction between the two sub‐layers is clear from laboratory test data.

Below the channel between Stations 878+00 and 928+00, the top of the fine‐grained Alluvial

Marine Sediment layer was encountered below the coarse‐grained marine sediments between

Elevations ‐45 and ‐90 feet and varied between a few feet to over 35 feet thick. Below the South

Island, between Stations 928+00 and 945+00, the top of the fine‐grained Alluvial Marine

Sediment layer was encountered between Elevation ‐25 and ‐50 feet, and was up to 30 feet thick.

Figure 4.4 Plasticity Chart for Alluvial Marine Sediments – Fine‐grained (Qf)

Extensive in situ shear strength testing was performed during the geotechnical investigation

programs, including CPT probes, field vane shear tests, and flat plate dilatometer tests. In

addition, an extensive laboratory testing program was performed. The results of these tests were

highly variable. Figure 4.5 shows the measured undrained shear strength from the various tests

versus elevation. The plot has been split between the results from the marine geotechnical

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60 70 80 90 100

Plasticity Index

Liquid Limit

Alluvial Marine Sediments ‐ Fine grained (Qf)

CL‐ML ML or OLMH or OH



program performed by Jacobs Engineering (Figure 4.5a) and the South Island geotechnical

investigation by ECS Mid‐Atlantic LLC (Figure 4.5b). The data in Figure 4.5 includes results from

both the Qf sub‐layer and the Qo sub‐layer.

On the South Island, between Stations 928+00 and 944+00, the 1970s tunnel construction placed

a surcharge up to 26 feet over the current island elevation, which pre‐consolidated this layer and

increased the shear strength below the island. The increase in strength is apparent from a

comparison of the field and laboratory test results between the two GDRs. Figure 4.5 shows the

overall range of the test results from the marine and South Island investigations, which

demonstrates the increased shear strength below the South Island. Typical ranges of shear

strength are also highlighted, which shows an increase in strength with depth. Two baseline

ranges of undrained shear strength are provided in Table 4.1; one for locations outside the South

Island surcharge from the 1970s construction, and the second for pre‐consolidated layers below

the South Island surcharge.

The consolidation properties of the Qf sub‐layer were investigated by performing pore pressure

dissipation tests during the CPT probing, and by an extensive laboratory test program consisting

of one‐dimensional consolidations tests. In addition, the South Island pre‐consolidation works

from the 1970s were instrumented and well‐documented (Kuesel et al, 1973), which effectively

provides a field load test of in situ compressibility properties.

Baseline index and shear strength properties for the Qf sub‐layer are provided in Table 4.1, and

the baseline range for parameters relating to compressibility of the layer is presented in Table

4.2. This layer would classify as “Squeezing” in the Tunnelman’s Classification System.

4.2.3 Alluvial Marine Sediments – Organic/Fat Clay (Qo)

Below the channel between Stations 878+00 and 906+00, the Alluvial Marine Sediment‐

Organic/Fat Clay layer was encountered between Elevations ‐60 and ‐110 feet, and generally

varied between 10 and 20 feet thick. Between Stations 906+00 and 928+00 the thickness

increased to approximately 50 feet. Below the northern section of the South Island, between

Stations 928+00 and 932+00, the layer is as much as 60 feet thick and between Station 932+00

and 942+00 decreases to about 20 feet thick.

The index properties and classification of this layer were quite variable; it was variously classified

as fat clay (CH), organic clay (OL), fat organic clay (OH) and peat (PT). A plasticity chart showing

the liquid limit plotted versus the plasticity index for laboratory tests on this layer is shown in

Figure 4.6.



Figure 4.5a Outside South Island Surcharge Area from 1970s Construction

Figure 4.5b: Below South Island Surcharge Area from 1970s Construction

Figure 4.5 Undrained Shear Strength v. Elevation, Fine‐Grained Alluvial Marine Sediments

(Note: The test results shown include both Qf and Qo sub‐layers )

‐160

‐140

‐120

‐100

‐80

‐60

‐40

‐20

0

0 500 1000 1500 2000 2500 3000 3500Eleva

tion (ft)

Su (psf) Marine

VST

UU Test

CU Test

DM Tests Marchetti

DM Tests Schmertman

Typical Range

‐160

‐140

‐120

‐100

‐80

‐60

‐40

‐20

0

0 500 1000 1500 2000 2500 3000 3500

Elev

ation (ft)

Su (psf) South Island

DM Tests Marchetti

DM Tests Schmertman

CU Tests

UU Tests

Typical Range



Figure 4.6 Plasticity Chart for Alluvial Marine Sediments – Organic/Fat Clay (Qo)

Extensive in situ and laboratory shear strength testing was also performed for this layer during

the geotechnical investigation programs, and the measured undrained shear strength versus

elevation from the various tests is shown in Figure 4.5. As discussed in the previous section of

the report, the plot has been split between the results from the marine geotechnical program

(Figure 4.5a) and the geotechnical investigation from the South Island (Figure 4.5b).

The consolidation properties of the Qo sub‐layer were also investigated by performing pore‐

pressure dissipation tests during the CPT probing, and by an extensive laboratory test program

consisting of one‐dimensional consolidations tests. As discussed in the previous section, the

South Island pre‐consolidation works from the 1970s were instrumented and well‐documented

(Kuesel et al, 1973), which effectively provides a field load test of in situ compressibility

properties.

Baseline index and shear strength properties for the Qo layer are provided in Table 4.1, and the

baseline range for parameters relating to compressibility of the layer is presented in Table 4.2.

This layer would classify as “Squeezing” in the Tunnelman’s Classification System, as detailed in

Appendix B.

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70 80 90 100

Plasticity Index

Liquid Limit

Alluvial Marine Sediments ‐ Organic/Highly Plastic Clay (Qo)




4.3 Yorktown Formation (Tys, Tyf)

The Yorktown Formation lies beneath the Alluvial Marine Sediments over the entire tunnel

alignment and can generally be distinguished by the change to a green to blue gray color. The

top of the formation was encountered between Elevations ‐32 and ‐52 feet below the North

Island, between Elevations ‐60 and ‐140 feet between the islands, and between Elevations ‐40

and ‐120 feet below the South Island. The Yorktown formation is predominantly a granular layer,

but throughout, there are numerous interbedded layers of fine‐grained deposits; it can therefore

be subdivided into the following two sub‐layers:

Yorktown Formation – Predominantly Coarse‐Grained (Tys)

Yorktown Formation – Predominantly Fine‐Grained (Tyf)

4.3.1 Yorktown Formation – Coarse‐Grained (Tys)

The coarse‐grained Yorktown formation layer generally consists of green to blue‐gray, over‐

consolidated, silty fine sand with varying amounts of fine‐grained fractions and marine shell

fragments, typically classified as silty sand (SM) or clayey sand (SC), and sometimes classified as

poorly‐graded sand (SP), well‐graded sand (SW), poorly‐graded gravel (GP) or well‐graded gravel

(GW). Based on analysis of the N60 SPT test results, the layer relative density varies from very

loose to very dense.

In several zones, the SPT test recorded “weight of rod” resistance at depths of over 100 feet

below the mudline, which was unexpected within this over‐consolidated layer; these SPT results

may not be truly representative of the in situ relative density and may have been caused by

sample disturbance in the difficult drilling conditions involving fine sand layers under high

hydrostatic pressures.

Grain size analyses were performed on several samples, and the range of particle size distribution

observed in the test samples is shown in Figure 4.7.

Baseline index and shear strength properties for the Tys layer are provided in Table 4.1 and the

baseline hydraulic conductivity range is listed in Table 4.2. When unsupported and unimproved,

and depending on the fines content and water pressure, this layer would classify as “Fast

Raveling” or “Flowing” in the Tunnelman’s Classification System, as detailed in Appendix B.



Figure 4.7 Range of Particle Size Distribution ‐ Yorktown Formation – Coarse‐Grained (Tys)

4.3.2 Yorktown Formation – Predominantly Fine‐grained (Tyf)

Fine‐grained layers comprising very stiff to hard sandy, shelly clays, were encountered at various

elevations within the Yorktown formation. These layers are more prevalent towards the base of

the formation, between Elevations ‐150 and ‐170 feet, where a 5 to 20 feet thick layer was

observed along most of the tunnel alignment. This layer generally classifies as either fat or lean

clay (CH or CL) with sand. A plasticity chart showing the liquid limit plotted versus the plasticity

index for laboratory tests on this layer is shown in Figure 4.8.

Baseline index and shear strength properties for the Tyf layer are provided in Table 4.1. This

layer would classify as “Squeezing” in the Tunnelman’s Classification System, as detailed in

Appendix B.



0

10

20

30

40

50

60

70

80

90

100

0.0010.0100.1001.00010.000100.000

Percent Finer

Particle Size (mm)



#200#4 #10 #40 #80 #100



Figure 4.8 Plasticity Chart for Yorktown Formation – Predominantly Fine‐Grained (Tyf)

4.4 Eastover Formation (Tye)

The Eastover formation underlies the Yorktown formation along the entire tunnel alignment and

was first encountered at elevations varying between Elevation ‐158 feet to Elevation ‐175. The

formation extended to Elevation ‐275 feet where the deeper borings were terminated. The

Eastover formation generally consists of green‐gray, over‐consolidated, fine to coarse sand with

varying amounts of fine‐grained material and marine shell fragments. The formation is

comprised of poorly graded sand (SP), silty sand (SM), clayey sand (SC) and poorly graded sand

with clay (SP‐SC). A dense marker bed consisting of cemented shell fragments and coarse sand

was encountered overlying the Eastover formation. Based on analysis of the N60 SPT test results,

the layer’s relative density varies from very loose to very dense.

In several zones, the SPT test recorded “weight of rod” resistance at depths of over 100 feet

below the mudline, which was unexpected within this over‐consolidated layer; these SPT results

may not be truly representative of the in situ relative density and may have been caused by

sample disturbance in the relatively difficult drilling conditions involving fine sand layers under

high hydrostatic pressures. Some SPT samples also encountered refusal within this layer which

is considered to be representative of denser, more cemented zones.

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60 70 80 90 100

Plasticity In

dex

Liquid Limit

Yorktown Formation ‐ Fine grained (Tyf)




Grain size analyses were performed on several samples, and the range of particle size

distribution observed in the test samples is shown in Figure 4.9.

Figure 4.9 Range of Particle Size Distribution ‐ Eastover Formation (Tye)

Baseline index and shear strength properties for the Tye layer are provided in Table 4.1. This

layer when unsupported and unimproved would classify as “Flowing” in the Tunnelman’s

Classification System, as detailed in Appendix B.

4.5 Groundwater

Groundwater levels at the site are based on tidal fluctuations and are expected to vary from

Elevation +4 feet at high tide to Elevation ‐1 feet at low tide.

Artesian groundwater conditions were not observed during the project geotechnical

investigation but have been reported present in the Yorktown and Eastover formations in the

technical literature (e.g. Hamilton and Larson, 1988).

For baseline purposes, the Design‐Builder shall consider that the groundwater pressure in all

subsurface layers may vary by ±5 feet from the hydrostatic pressure due to the ambient sea level

in the shipping channel.



0

10

20

30

40

50

60

70

80

90

100

0.0010.0100.1001.00010.000100.000

Percent Finer

Particle Size (mm)



#200#4 #10 #40 #80 #100



Notes:

1. The baseline values shown represent the range of material properties that the Design‐Builder must consider when selecting construction equipment and materials, means and methods, and evaluating the potential impacts of construction on existing structures. Soil properties for design of the temporary and permanent project elements shall be derived by the Design‐Builder in accordance with Section 24, Geotechnical ‐ Islands and Tunnels of the Technical Requirements of the Contract.

2. Baselines for artificial fill consider the hydraulically placed sand only; the baselines do not consider the oversized material (i.e. containment dikes material, scour protection material, etc.).

3. The first range of undrained shear strength is for locations outside the 1970s South Island surcharge area, while the second range is for pre‐consolidated layers below the South Island surcharge. The extents of the South Island surcharge area shall be defined to be as shown on Drawing No S‐6 of Contract T‐2 of the 1970s construction record drawings (Commonwealth of Virginia, 1975).

4. Cemented sand and shell layers up to 5 feet thick within the Yorktown and Eastover Formations may have unconfined compressive strength up to 1000 psi. 5. For the granular layers (af, Qc, Tys, and Tye), the baseline range of the layer’s particle size distribution shall be between the maximum and minimum limits shown on

Figures 4.2, 4.3, 4.7 and 4.9. 6. For table entries designated as “N/A”, a baseline range is not provided.

Table 4.1 – Baseline Values for Soil Index Properties and Shear Strength

Stratum / Sub‐Layer Typical USCS

Classification

Total Unit Weight

Water Content

Liquid Limit

Plasticity Index

Effective Friction Angle (°)

Undrained Shear

Strength (psf)(pcf) (%) (%)

Baseline Range

Baseline Range

Baseline Range

Baseline Range

Baseline Range

Baseline Range

Island Artificial Fill (af)(2) SP, SM, SP‐SM 105‐125 N/A Non‐Plastic

N/A 30‐34 N/A


SP, SM, SC 105‐125 N/A Non‐Plastic

N/A 30‐40 N/A

Alluvial Marine Sediments – Fine‐Grained (Qf) CL, CH 100‐120 20‐60 30‐60 15‐30 N/A 225‐750(3) 525‐1400

Alluvial Marine Sediments ‐ Organic/Fat Clay (Qo)

OL, OH, CH, PT 90‐110 35‐75 30‐110 25‐60 N/A 125‐650 (3) 250‐1500

Yorktown Formation – Coarse‐Grained (Tys) SM, SC 115‐130 N/A Non‐Plastic

N/A 30‐42 N/A(4)

Yorktown Formation – Fine‐Grained (Tyf) CL, CH 110‐130 25‐40 30‐55 15‐40 N/A 750‐6000(4)

Eastover Formation (Tye) SP, SM, SP‐SC 120‐130 N/A Non‐Plastic

N/A 30‐42 N/A(4)



Notes: 1. The baseline values shown represent the range of material properties that the Design‐Builder must consider when selecting construction equipment and

materials, means and methods, and evaluating the potential impacts of construction on existing structures. Soil properties for design of the temporary and permanent project elements shall be derived by the Design‐Builder in accordance with Section 24, Geotechnical – Islands and Tunnels of the Technical Requirements of the Contract.

2. The first range of OCR is for locations outside the 1970s South Island surcharge area, while the second range is for pre‐consolidated layers below the South Island surcharge area. The extents of the South Island surcharge area shall be defined to be as shown on Drawing No S‐6 of Contract T‐2 of the 1970s construction record drawings (Commonwealth of Virginia, 1975).

3. Horizontal and vertical coefficient of consolidation shall be considered equal. The first range of Cv is representative for virgin compression, while the second range is for recompression.

4. For table entries designated as “N/A”, a baseline range is not provided.

Table 4.2 – Baseline Values for Soil Permeability and Compressibility

Stratum / Sub‐Layer Typical USCS

Classification

Hydraulic Conductivity

In Situ Void Ratio

Over Consolidation

Ratio (OCR)

Compression Index (Cc)

Recompress‐ ion Index

(Cr)

Coefficient of Secondary

Compression (Cα)

Coefficient of Consolidation(3)

(Cv)

(cm/sec) (cm2/sec)

Baseline Range

Baseline Range

Baseline Range

Baseline Range

Baseline Range

Baseline Range

Baseline Range

Island Artificial Fill (af) SP, SM, SP‐SM 10‐3‐ 10‐1 N/A N/A N/A N/A N/A N/A

Alluvial Marine Sediments ‐ Coarse Grained (Qc)

SP, SM, SC 10‐3 – 10‐1 N/A N/A N/A N/A N/A N/A

Alluvial Marine Sediments – Fine‐ Grained (Qf)

CL, CH 10‐7 to 10‐5 0.6‐1.0 1.0 – 1.5(2)

1.0 – 2.0 0.30‐0.50 0.02‐0.05 0.001‐0.005 0.003‐0.030(3) 0.001‐0.020

Alluvial Marine Sediments ‐ Organic/Fat Clay (Qo)

OL, OH, CH, PT 10‐7 to 10‐5 1.3‐2.0 1.0 – 1.5(2)

1.0 – 2.0 0.60‐1.00 0.05‐0.16 0.001‐0.010 0.001‐0.015(3) 0.0005‐0.010

Yorktown Formation – Coarse‐ Grained (Tys)

SM, SC 10‐3 – 10‐1 N/A N/A N/A N/A N/A N/A

Yorktown Formation ‐ Fine‐Grained (Tyf)

CL, CH N/A N/A N/A N/A N/A N/A N/A

Eastover Formation (Tye) SP, SM, SP‐SC N/A N/A N/A N/A N/A N/A N/A



Figure 4.1 – Baseline Subsurface Profile 1/4












5.0 Design and Construction Considerations

This section will discuss design and construction considerations as well as anticipated ground

behavior during construction of the Tunnel Improvements, including:

Below‐grade tunnel approach structures

Bored tunnel

Island expansions 5.1 Tunnel Approach Structures

It is anticipated that the below‐grade approach structure to the bored tunnel on both portal

islands will be similar to the existing boat sections and cut and cover tunnels. This will involve

installation of support of excavation systems, excavation to the design subgrade level, and

construction of the reinforced concrete structures.

5.1.1 Stratigraphy Figure 4.1 shows the baseline stratigraphy along the tunnel approaches based on the recent and

historic geotechnical information. For design and construction of the tunnel approach structures,

the interfaces between adjacent geological strata shown in the baseline profile are qualified by

the following statements:

North Island (Station 850+00 to 867+00):

The boundary shown between the Artificial Fill (af) and the Alluvial Marine Sediments

Coarse‐grained (Qc) is not baselined. The geotechnical properties of both materials are

similar. Obstructions, that may be encountered more frequently in the fill layer, are

addressed in Section 5.1.2 of this GBR; and

The boundary between the Alluvial Marine Sediments (Qc) and the Yorktown formation

(Tys) is baselined and may vary by ±5 feet from the boundary shown in Figure 4.1.

South Island (Station 924+00 to 945+00):

The boundary shown between the Artificial Fill (af) and the Alluvial Marine Sediments‐

Coarse‐grained (Qc) is not baselined. The geotechnical properties of both materials are

similar. Obstructions that may be encountered more frequently in the fill layer are

addressed in Section 5.1.2 of this GBR;



The boundary between the Alluvial Marine Sediments‐Coarse‐grained sub‐layer (Qc) and

the underlying Alluvial Marine Sediments‐Fine‐grained sub‐layer (Qf) is baselined and

may vary by ±5 feet from the boundary shown in Figure 4.1;

The boundary between the Alluvial Marine Sediments‐Fine‐grained sub‐layer (Qf) and the

underlying Alluvial Marine Sediments‐Organic/Fat Clay sub‐layer (Qo) is baselined and

may vary by ±5 feet from the boundary shown in Figure 4.1; and

The boundary between the Alluvial Marine Sediments (Qc, Qf, Qo) and the Yorktown

formation is baselined and may vary by ±5 feet from the boundary shown in Figure 4.1.

5.1.2 Obstructions

There are numerous potential obstructions that may affect the construction of the tunnel

approach structures and must be accounted for by the Design‐Builder both in the design and

selection of means and methods of construction. These obstructions fall into the following

categories and are discussed in the subsequent paragraphs:

Rock Containment Dikes and Scour Protection; and

Temporary Works from Previous Construction.

5.1.2.1 Rock Containment Dikes and Scour Protection As shown on the record drawings (Commonwealth of Virginia, 1956, 1975), the existing portal

islands were constructed using a series of containment dikes, which contain armor stone with

individual stone size varying up to a maximum dimension of 5 feet. Additionally, the portal

islands, as well as the existing tunnels, are covered with various layers of scour protection

including heavy rip rap, quarry run rock and gravel sized crushed rock. The materials that

comprise the containment dikes and the scour protection were obtained from intact, crystalline,

igneous or metamorphic rock sources. They could potentially cause obstructions to installation

of support of excavations systems, and cause handling difficulties requiring special lifting

equipment during mass excavation of the approaches.

These rip rap and stone layers were installed in both the 1950s and 1970s construction, and it is

understood that the original stone layers from the 1950s were buried when the islands were

expanded in the 1970s. The general location of the armor stone dikes and heavy rip rap

placements are shown on the record drawings (Commonwealth of Virginia, 1956, 1975) and

construction photographs included as Supplemental Information to the Contract.



It is also very likely that rip rap and stone layers were also placed, inadvertently or otherwise, in

areas not shown on the record drawings. In addition, numerous major storms have occurred

throughout the construction and operational history of the islands which have damaged the

stone protection of both islands. This has resulted in the deposition and possible burial of

random armor stone, construction materials and other miscellaneous debris within the limits of

the proposed temporary and permanent construction.

For baseline purposes, the Design‐Builder shall be prepared to encounter heavy rip rap and other

large stone layers as follows:

At the North Island, between Stations 850+00 and 867+00, the Design‐Builder may

encounter armor stone with individual stone size up to a maximum dimension of 5 feet

and weighing up to 10 tons anywhere above Elevation ‐25 feet. This applies over a width

of 500 feet to the east and 200 feet to the west of the second 1970s tunnel centerline.

At the South Island, between Stations 924+00 and 945+00, the Design‐Builder may

encounter armor stone with individual stone size up to a maximum dimension of 5 feet

and weighing up to 10 tons anywhere above Elevation ‐30 feet. This applies over a width

of 500 feet to the east and west of the second 1970s tunnel centerline.

The thickness of the various stone layers is shown on the record drawings

(Commonwealth of Virginia, 1956, 1975) and for baseline purposes may be encountered

in local areas up to twice the layer dimension shown on the drawings.

The Design‐Builder’s means and methods and bid price shall account for accommodating any rip

rap or stone layers encountered within the limits outlined in the previous three bulleted items.

Heavy rip rap or armor stone is not expected to be encountered outside of these limits.

5.1.2.2 Temporary Works from Previous Construction

Based on review of construction photographs, both the 1950s and 1970s construction employed

a combination of soldier pile and lagging and steel sheeting to support the tunnel approach

excavations. In the 1950s, cross lot struts were placed between the two walls, whereas tiebacks

were installed in the 1970s. To maintain a dry excavation, dewatering wells were also installed.

Dewatering wells were likely to be more numerous in the vicinity of where excavations were

deepest. Temporary piers supported on piles may also have been constructed around the

perimeter of the islands for off‐loading construction materials.



The Design‐Builder’s means and methods and bid price for the tunnel approach structures shall

account for encountering any of the following temporary works from previous construction:

Steel soldier pile and lagging or steel sheeting encountered up to 10 feet behind the face

of the current finished walls of the tunnel approaches, and up to 20 feet below the base

of the original excavation.

Tieback tendons encountered up to 65 feet behind the face of the finished walls, and up

to 20 feet below the full depth of the original excavation. Tieback tendons are baselined

to have been de‐tensioned;

Steel dewatering well screens may be encountered to Elevation ‐140 feet and may be

present within 50 feet of the periphery of the current approach structures. Dewatering

wells may or may not have been grouted or backfilled when abandoned.

5.1.3 Groundwater Control

The Design‐Builder shall not rely on any untreated in situ soil strata (or combination of soil strata)

to provide stability and/or groundwater cutoff for any excavation required for the tunnel

approach structures. The Design‐Builder shall consider that dewatering or ground treatment,

along with provision of sufficient penetration below the base of excavation with support of

excavation walls, will be required to provide stability and limit groundwater inflows into the

excavations.

5.1.4 Gas Conditions The geotechnical investigations did not find any evidence of the presence of gas in the deposits

that will be encountered during construction of the approach structures. However, the

occurrence of methane due to decay of organic matter is expected. Historic records indicate that

the organic layers present from Station 878+00 to 945+00 have previously been a source of gas.

It is understood that during installation of the sand drains on the South Island during the 1970s

construction, methane gas was encountered. The escaping gas was lit which fueled a flare that

burned for months. In addition, in a 1970s era boring for I‐64 on the Willoughby Spit, to the south

of the South Island, methane gas was encountered in the organic layer, which led to relocation

of a proposed bridge following an unsuccessful attempt to burn off the gas that lasted for three

months without a significant drop in pressure.

Therefore, during construction of the below grade tunnel approach structures on the South

Island, gas may be encountered during any construction activity that penetrates layers with

organic content.



5.1.5 Soil pH Soil pH testing was conducted on samples from all strata that will be encountered in the

tunneling. For baseline purposes, the Design‐Builder shall consider the soil pH value will range

between a minimum of 7.0 and a maximum of 11.0.

5.2 Bored Tunnel

This section describes anticipated subsurface conditions along the bored tunnel alignment

including soil stratigraphy, ground improvement required to stabilize very soft layers below the

TBM, potential obstructions, and various geotechnical‐related issues that could arise during

construction of the tunnel.

Section 23, Bored Tunnel of the Technical Requirements (TRs) of the Contract Documents

requires tunnel excavation methods that were established based on the need to control unstable

ground conditions. The minimum requirements include the use of a pressurized face Tunnel

Boring Machine (TBM) that can control groundwater and stabilize the tunnel face in the various

strata that will be encountered. This machine must be able to apply a positive pressure to the

tunnel face, resisting the earth and groundwater pressures to effectively control the ground and

groundwater inflows.

5.2.1 Stratigraphy Figure 4.1 shows the baseline stratigraphy along the tunnel alignment based on the recent and

historic geotechnical information. For design and construction of the bored tunnel by TBM, the

boundaries between adjacent geological strata shown in the baseline profile are qualified by the

following statements:

The boundary shown between the Artificial Island Fill (af) and the Alluvial Marine

Sediments‐Coarse‐grained (Qc) is not baselined. The geotechnical properties of both

materials are similar.

The boundary shown between the Alluvial Marine Sediments‐Coarse‐grained sub‐layer

(Qc) and the Alluvial Marine Sediments‐ Fine‐grained sub‐layer (Qf) is baselined and may

vary by ±5 feet.

The boundary shown between the Alluvial Marine Sediments‐Fine‐ grained sub‐layer (Qf)

and the Alluvial Marine Sediments‐ Organic/Fat Clay sub‐layer (Qo) is not baselined.



Except for the baseline for determining ground improvement limits provided in the next

bullet, the boundary shown between the Alluvial Marine Sediments (Qc, Qf, Qo) and the

Yorktown formation (Tys) is baselined and may vary by ±5 feet.

For determining ground improvement limits required by the contract, the boundary

shown between the Alluvial Marine Sediments (Qc, Qf, Qo) and the Yorktown formation

(Tys) is baselined and does not vary from the location shown in Figure 4.1.

The boundary shown between the two Yorktown formation sub‐layers (Tys, Tyf), and

between the Yorktown and the Eastover formations is not baselined. When tunneling in

the Yorktown (Tys, Tyf), or the Eastover (Tye) formations, the TBM excavation will include

very soft to hard cohesive deposits, very loose to very dense granular deposits, as well as

cemented sands and shell layers; the Design‐Builder shall be prepared to encounter the

full range of the materials defined in this GBR for the Yorktown and Eastover Formations

anywhere along the tunnel alignment below the Alluvial Marine Sediments stratum (Qc,

Qf, Qo).

The Design‐Builder shall anticipate unstable soil conditions (e.g., flowing soil as defined in

Appendix B) at any location along the tunnel alignment and accordingly must maintain a positive

face pressure at the heading at all times; therefore, methods to excavate the tunnel in a

controlled manner (i.e., match the muck removal rate from the excavation chamber to the

advance rate of the TBM while maintaining the desired pressure at the working face) will be

necessary to maintain stability and control of over‐excavation. Refer to TR Section 23, Bored

Tunnel for minimum TBM requirements and requirements for compressed air interventions. The

ground conditions along the entire alignment will not support free air interventions.

Although adjustments to TBM operating parameters (e.g., face pressures, type and volume of

soil conditioning) are to be expected with the mixed soil conditions to be encountered at the face

of the TBM, these adjustments will be more frequent within zones where soil groups with

distinctly different index or engineering characteristics are encountered. Changes in the behavior

of the excavated material (e.g. stickiness, abrasivity, strength, and hydraulic conductivity) will

also occur as the proportion of the different soil groups encountered at the face changes.

Therefore, continuous monitoring and adjustments of face pressures and conditioners will be

necessary when tunneling throughout.

5.2.2 Break‐in/out Ground improvement will be necessary to allow for a stable excavation during break‐out/break‐

in of the TBM from the tunnel approach structures at the portal islands (i.e. the soil at the break‐



out/break‐in locations will be neither stable nor impervious). TR Section 23, Bored Tunnel

specifies minimum requirements for the ground improvement.

5.2.3 Behavior of Soft Soils Between approximately Stations 877+50 and 945+50, and between approximately Elevations ‐50

and ‐130 feet, the Alluvial Marine Sediments‐Fine‐grained sub‐layer (Qf) and the underlying

Alluvial Marine Sediments‐Organic/Fat Clay sub‐layer (Qo) consist of very soft, inorganic and

organic silts and clays, and peat. Ground improvement will be required to strengthen these layers

to provide sufficient support to the TBM to maintain alignment and grade.

TR Section 23, Bored Tunnel requires that between Stations 877+50 and 945+50, whenever any

part of the tunnel below the springline is within the Alluvial Marine Sediments‐Fine‐grained sub‐

layer (Qf) or the Alluvial Marine Sediments‐Organic/Fat Clay sub‐layer (Qo), the Design‐Builder

shall provide ground improvement to the in situ soils in advance of tunneling. The horizontal and

vertical limits of the ground improvement required by Section 23 are shown in Figure 5.1.

Figure 5.1 ‐ Limits of Ground Improvement Required to Support TBM in Soft Soils

The Design‐Builder’s bid price for the required ground improvement should be based on the

baseline profile shown in Figures 4.1 as modified by the qualifying statements in Section 5.2.1.

Prior to performance of this ground improvement, TR Section 24, Geotechnical ‐ Islands and

Tunnels requires that a detailed geotechnical investigation be implemented to define the top and

bottom of the Qf and Qo sub‐layers.



The ground improvement method shall be selected by the Design‐Builder to be compatible with

their tunneling operations from the alternatives listed in TR Section 24, Geotechnical ‐ Islands

and Tunnels. Other ground improvement techniques may be considered as an Alternative

Technical Concept (ATC). The design and performance requirements of the ground improvement

is the responsibility of the Design‐Builder. The improved ground limits and characteristics shall

be able to support the TBM to maintain the Design‐Builder’s proposed tunnel alignment within

reasonable driving tolerances.

5.2.4 Obstructions

The geologic strata present along the tunnel alignment are not known to contain naturally

occurring boulders that could impede the progress of the TBM, and the Design‐Builder may

consider that boulders will not be encountered outside the limits defined herein for man‐made

obstructions. Nevertheless, as a safeguard, and as required by TR Section 23, Bored Tunnel, the

TBM shall be equipped to accommodate boulders.

There are numerous “man‐made” obstructions that may impede the progress of the TBM and

must be accounted for by the Design‐Builder both in the design and selection of means and

methods of construction. These obstructions fall into the following categories and are discussed

in the following paragraphs:

Rock Containment Dikes and Scour Protection;

Temporary Works and Miscellaneous Debris from Previous Construction;

Unrecovered Equipment from Geotechnical Drilling Program; and

Foundations for Survey Towers.

5.2.4.1 Rock Containment Dikes and Scour Protection Rock containment dikes and scour protection constructed in the 1950s and 1970s were described

in Section 5.1.2.1. With respect to TBM tunneling, for baseline purposes, the Design‐ Builder

shall be prepared to encounter heavy rip rap and stone layers as follows:

At the North Island, between Stations 850+00 and 867+00, the Design‐Builder may

encounter armor stone the same as the size and limits detailed in Section 5.1.2.1;

At the South Island, between Stations 924+00 and 945+00, the Design‐Builder may

encounter armor stone the same as the size and limits detailed in Section 5.1.2.1;

Between the two islands, from Station 867+00 to 924+00, the Design‐Builder may

encounter armor stone with a maximum dimension up to 5 feet and weighing up to 10

tons anywhere within 10 feet below the mudline shown on Figure 4.1;



Between the two islands, from Station 867+00 to 924+00, the Design‐Builder may

encounter scour protection, locking backfill, and other types of special fill materials within

the backfilled trenches of the existing tunnels, as shown on the record drawings

(Commonwealth of Virginia, 1956,1975). For baseline purposes, the backfilled trench

limits may vary up ±20 feet horizontally and ±5 feet vertically from the limits shown on

the record drawings; and

The thickness of the various stone layers is shown on the record drawings

(Commonwealth of Virginia, 1956, 1975) and for baseline purposes may be encountered

in local areas up to twice the layer dimension shown on the drawings.

The Design‐Builder’s means and methods, and bid price, for TBM tunneling shall account for

accommodating any rip rap or stone layers encountered within the limits outlined in the previous

four bulleted items. However, the Design‐Builder’s bid price may consider that heavy rip rap or

armor stone will not be encountered outside of these limits.

5.2.4.2 Temporary Works from Previous Construction Temporary works from previous construction in the 1950s and 1970s were described in Section

5.1.2.2.

The Design‐Builder’s means and methods and bid price for TBM tunneling shall account for

encountering any of the following temporary works:

Soldier pile and lagging or sheeting encountered up to 10 feet behind the face of the

current finished walls of the tunnel cut and cover approach structures, and up to 20 feet

below the base of the original excavation;

De‐tensioned tieback tendons may be encountered up to 65 feet behind the face of the

finished walls, and up to 20 feet below the full depth of the original excavation.

Steel dewatering well screens may be encountered to Elevation ‐140 feet and may be

present within 50 feet of the periphery of the current approach structures. The steel well

casings may or may not have been backfilled with grout or other material.

Miscellaneous debris from the previous construction may be present within the footprint

of the work. For example, a steel cable was encountered in a Shelby tube sample in Boring

17‐BH‐022‐OS at a depth between 15 and 20 feet below the mudline. For baseline

purposes, the Design‐Builder shall consider that miscellaneous construction debris may

be encountered within ±25 feet horizontally, and ±10 feet vertically from the limits of the

backfilled trench for the previous tunnels, as shown on the record drawings.



Timber, steel or concrete piles left‐in‐place from temporary piers may be present up to

50 feet from the perimeter of the islands (both 1950s and 1970s perimeters) and may

extend 10 feet below the top of the Yorktown Formation shown in Figure 4.1. For baseline

purposes, the Design‐Builder shall account for up to 4 such piles being encountered where

the tunnel alignment crosses the island perimeter (or former perimeter).

5.2.4.3 Unrecovered Equipment from Geotechnical Drilling Program During performance of the marine drilling program, equipment issues and failures led to pieces

of steel being left buried below the mudline at three test locations, as outlined below.

B‐018 After completion of the boring, a 40‐foot‐long section of 6‐inch casing

became de‐coupled during removal and was left in the borehole;

CPT‐034 After completion of the CPT probe, a 5‐foot‐long section of NQ casing became de‐coupled during removal and was left in the borehole; and

VST‐045 After completion of a vane shear test it was discovered that the connection

between the vane and the rods sheared off leaving the vane, a coupler,

and an extension rod in the borehole.

The surface coordinates and elevations of the buried equipment that could not be recovered is

detailed in Table 5.1 and shown in Figure 5.2. The coordinates should be considered to be

accurate within ±20 feet, and the elevation within ±30 feet.

Boring Northing Easting Elevation (ft NAVD88)

Description of Potential Obstruction

B‐018 36° 59’ 36.90773”N 76° 18’ 40.92049”W ‐76.2 to ‐116.2 6” Casing

CPT‐034 36° 59’ 30.56334”N 76° 18’ 40.06898”W ‐73.6 to ‐90.3 NQ Casing

VST‐045 36° 59’ 12.9209”N 76° 18’ 18.2663”W ‐81.7 to ‐83.7 Shear Vane

Table 5.1 ‐ Location of Unrecovered Equipment from Geotechnical Drilling Program



Figure 5.2 ‐ Location of Unrecovered Equipment from Geotechnical Drilling Program

The Design‐Builder’s means and methods, and bid price, shall account for encountering these

potential obstructions and removing as necessary. If encountered with the TBM, these items

may create obstructions to inhibit TBM advance and or damage to the TBM and require special

effort to remove them such as through interventions.

5.2.4.4 Foundations for Survey Towers Horizontal and vertical control for the existing tunnels was established with the aid of survey

towers located in the Hampton Roads waterway. While the superstructure of the towers was

removed, the piles and other foundation elements were abandoned in place. The general

locations of the survey towers, which have since been removed, are indicated on the original

drawings (Commonwealth of Virginia, 1956, 1975). The Design‐Builder’s means and methods,

and bid price, shall account for encountering the piled foundations of these structures within ten

feet of the locations indicated on the original drawings, and removing as necessary. If

encountered with the TBM, these items may create obstructions to inhibit TBM advance and or

damage to the TBM and require special effort to remove them such as through interventions.

5.2.5 Sticky Clay Behavior The TBM tunnel drive will encounter cohesive layers within the Alluvial Marine Sediments (Qc,

Qf, Qo) and the Yorktown (Tyf, Tys) and Eastover (Tye) formations. The TBM design and

implementation of soil conditioning shall consider the potential for sticky clay behavior.

Selection of the specific materials, means, and methods for soil conditioning is the sole

responsibility of the Design‐Builder. The Design‐Builder must continuously monitor and adjust



the conditioning process to ensure these materials, means, and methods are appropriate for the

ground conditions being encountered at the face. This will require constant supervision and well‐

defined working plans and instructions for all construction personnel involved in TBM operations.

Accordingly, baselines for soil stickiness potential are not provided herein. The Design‐Builder is

solely responsible for determining how the soils, given the baseline soil properties as defined in

Tables 4.1 will respond to the means and methods selected and implemented by the Design‐

Builder. Sticky clay behavior will not be considered grounds for a Differing Tunnel Improvements

Site Condition for layers encountered with properties within the baseline values included in Table

4.1.

5.2.6 Cemented Sand and Shell Zones The Yorktown (Tyf, Tys) and Eastover (Tye) formations contain cemented layers and shell beds

that are classified as very dense or hard. The design and operation of the TBM should consider

the occurrence of these layers.

An upper bound unconfined compressive strength for the Yorktown (Tyf, Tys) and Eastover (Tye)

formations as indicated in Table 4.1 shall be a baseline for consideration of the potential

resistance that very dense granular, hard cohesive, or cemented sands or shells will present to

excavation equipment for the TBM tools and forward thrusting of the TBM.

5.2.7 Soil Abrasion Behavior The abrasion potential of the various soil strata that may be encountered by bored tunneling was

investigated by means of soil abrasion testing using a method based on Nilsen et al (2007). The

results of the testing are provided in the GDRs (Jacobs Engineering, 2018, ECS Mid‐Atlantic LLC,

2018).

Baseline values of soil abrasion for various soil strata (i.e., natural soil, without conditioners) are

presented in Table 5.2. The baselines were developed based upon the soil abrasion test results

included in the GDRs. As per Jakobsen et al. (2013), a soil with an SAT™ less than or equal to 7 is

classified as a “low” abrasive material, a soil with an SAT™ between 7 and 22 is classified as a

“medium” abrasive material and a soil with an SAT™ of greater than or equal to 22 is classified

as being a “high” abrasive material. These qualifiers notwithstanding, it is the numerical values

of the SAT™ that are baselined.



Stratum USCS Classification

Soil Abrasion Test Value

Baseline Range

Island Artificial Fill (af) SP, SM, SP‐SM 20‐40


SP, SM, SC 30‐55

Alluvial Marine Sediments – Fine‐Grained (Qf)

CL, CH N/A

Alluvial Marine Sediments – Organic/Fat Clay (Qo)

OL, OH, CH, PT N/A

Yorktown Formation – Coarse‐Grained (Tys) SM, SC 30‐40

Yorktown Formation – Fine‐Grained (Tyf) CL, CH 35‐50

Eastover Formation (Tye) SP, SM, SP‐SC 25‐35

Table 5.2 – Baseline Values for Soil Abrasivity

5.2.8 Gas Conditions Historic records indicating that the organic layers have previously been a source of methane gas

were described in Section 5.1.4.

The classification of the underground work associated with the bored tunnel option in

accordance with OSHA regulations (i.e., 29 CFR 1926.800 Subpart S) is provided in TR Section 23,

Bored Tunnel.

5.2.9 Soil pH Soil pH testing was conducted on samples from all strata that will be encountered in the

tunneling. For baseline purposes, the Design‐Builder shall consider the soil pH value will range

between a minimum of 7.0 and a maximum of 11.0.



5.3 Island Expansions

Expansions of the existing North and South Islands may be required to provide portals for

horizontal tunnel alignments located to the west of the existing tunnels, and also to provide

sufficient cover for vertical alignments that would not allow the TBM to operate with existing

island grades.

5.3.1 Stratigraphy

Figure 4.1 shows the baseline stratigraphy below the islands based on the recent and historic

geotechnical information. For design and construction of the island expansions, the interfaces

between adjacent geological strata shown in the baseline profile are qualified by the statements

included in Section 5.1.1.

5.3.2 Obstructions

There are numerous potential obstructions that may affect the construction of the island

expansions and must be accounted for by the Design‐Builder both in the design and selection of

means and methods of construction. For design and construction of the island expansions the

potential impacts from obstructions shall be as presented in Section 5.1.2.



6.0 Instrumentation and Monitoring

The Contractor shall be responsible for the design, installation, monitoring, and data

interpretation of the Instrumentation and Monitoring program in accordance with the Technical

Requirements.



7.0 Limitations

The interpretations and assessments contained in this report are based upon the available

information from borings, in situ tests and laboratory tests. The geologic environment of the

Hampton Roads Bridge‐Tunnel Expansion project is complex, and as such, no amount of pre‐

construction information will convey as detailed an understanding as will exist during and

following excavation. The range of anticipated site and construction conditions presented in this

report is established as a baseline only to be used by all Bidders in preparing their bids, and by

the Department to evaluate claims relating to alleged Differing Tunnel Improvements Site

Conditions. The range of anticipated conditions was developed with the standard of care

commonly applied as the state of the practice in the profession. No warranty is included either

expressed or implied that the actual conditions encountered will conform exactly to the baseline

conditions described herein.



8.0 References

1. AECOM, “Hampton Roads Crossing Archaeological Survey Hampton And Norfolk,

Virginia”, July 2017

2. Commonwealth of Virginia, Department of Highways, “Hampton Roads Project ‐ Record

Drawings”, 1956.

3. Commonwealth of Virginia, Department of Highways “Hampton Roads Project – Second

Bridge‐Tunnel Crossing Contract T‐1, South Island ‐ Record Drawings”, 1975.

4. Commonwealth of Virginia, Department of Highways “Hampton Roads Project – Second

Bridge‐Tunnel Crossing Contract T‐2, North Island, Tunnel and Completion of South

Island‐ Record Drawings”, 1975.

5. ECS Mid‐Atlantic LLC, “Preliminary Geotechnical Data Report – Hampton Roads Bridge

Tunnel – North and South Islands”, June 15, 2018.

6. Grantz W, “Immersed Tunnel Settlements Part 2: Case Histories”, Tunneling and

Underground Space Technology. Vol 16, 2001 pp203‐210

7. Hamilton P, and Larson J, “Hydrogeology and Analysis of the Ground‐water Flow System

in the Coastal Plain of Southeastern Virginia”, United States Geological Survey, Water

Resource Investigation Report 87‐4240, (1988).

8. Heuer, R.E., (1974), Important Ground Parameters in Soft Ground Tunneling: Proceedings

of Specialty Conference on Subsurface Exploration for Underground Excavation and

Heavy Construction, ASCE.

9. Kuesel T., Schmidt B., and Rafaeli D., “Settlements and Strengthening Of Soft Clay

Accelerated By Sand Drains” Highway Research Record number 457, Soil Slopes and

Embankments, 1973.

10. Jacobs Engineering, “I‐64 Hampton Roads Bridge‐Tunnel Expansion Project, Geotechnical

Data Report – Marine”, July 2018

11. Jakobsen, P. D., Bruland, A., and Dahl, F., “Review and Assessment of the NTNU/SINTEF

Soil Abrasion Test (SAT™) for Determination of Abrasiveness of Soil and Soft Ground”,

Tunneling and Underground Space Technology 37, 2013, pp107‐114.

12. Nilsen, B., Dahl, F., Holzhäuser J., Raleigh P., “New Test Methodology for Estimating the

Abrasiveness of Soils for TBM Tunneling”, Proceedings of RETC Conference, 2007, pp104‐

116.

13. Rafaeli, D., “Design of the South Island for the Second Hampton Roads Crossing”, Spec.

Conf. on Performance of Earth and Earth‐Supported Structures, Proc. ASCE, Purdue Univ.,

Vol. 1, Part 1, 1972, pp. 361‐378.



14. Steuerman S, and Murphy G, “Foundation of the Hampton Roads Tunnel”, Proceedings of

the Fourth International Conference on Soils Mechanics and Foundation Engineering,

1957.

15. Thewes, M., “Adhesion of Clays During Tunnelling with Slurry Shields”, Dissertation,

vol.21, Berichte aus Bodenmechanik und Grundbau der Bergischen University Wuppertal,

Department of Civil Engineering, 1999.

16. Thewes, M. and Burger, W., “Clogging of TBM Drives in Clay – Identification and Mitigation of Risks”, Proceedings ITA‐AITES World Tunnel Congress, Istanbul, Turkey, 2005, pp. 737‐742


Hampton Roads Bridge‐Tunnel Expansion Commonwealth of Virginia Project No. 0064‐M06‐032 Virginia Department of Transportation

APPENDIX A ‐ Boring Location Plan and Baseline Subsurface Profile

17BH-101N 17BH-102N

17BH-103N 17BH-104N17BH-105N

B-113B-8B-9

B-10

B-12

B-11

B-1417-BH-012-OS17-BH-011-OS

17-BH-013-OS

17-BH-014-OS

17-BH-015-OS

ASPHFL

FL

SP

SM

SC

SM

CH

SC

SM

SM

29 13 26 22 15 17 12 1 5 4 27 36 24 44 11 9 10 4 11 7 6 14 12 11 16 10 11 5 11 7 7 17 14 8 8

10 22 33 11 11 31 41 40 33 41 36 8 3 7 9 7

11 96 14 7 8

30 6 5 5

50/3 9

15 14

ASPHFL

FL

SM

SM

SC

SM

17 15 18 17 8 5 4 4 25 27 38 22 24 21 23 21 8 10 15 6 10 6 11 28 6 20 9 8 3 10 9 11 13 17 9

FLFL

FL

SM

SM

SC

SM

SM

SP-SC

10 10 15 7 6 4 18 7 30 21 16 19 11 19 9 10 16 3 6 9 11 12 13 5 5 12 9 12 7 7 23 8 15 11 11 47 30 10 13 32 35 75 41 26 39 31 9 5 8

27 7

50/2 7 7 8 8 8 6 4 9

14 11 16 9

FL

FLFLFLSC

SC

SM

34 12 10 12 26 15 27 28 18 3 24 25 19 18 9 7 5 11 7 17 9 12 22 7 7 16 5 12 5 16 5 6 10 11

FL

FL

FL

SP

SC

SM

CL

SM

SM

CL

15 8 9 8 12 9 12 9 9 6 8 33 7 13 7 5 9 5 11 5 8 16 7 27 13 7 13 5 11 4 6 12 8 18 6 8 14 56 40 8

17 29 32 38 36 23 40 8 9 6 5 8 8

50/4 11 8 9 7 7 4 6

50/5 14 10 13

18 12 18 19 28 46 24 30 20 22 21 15 13 18 16 25 25 51

5/12"

10/12"

13/12" 38/12"

50/12" 25/12"

14/12" 12/12"

17/12"

29/12"

20/12"

12/12"

12/12"

25/12"

25/12"

14/12" 128/12"

58/12"

38/12"

63/12"

46/12"

52/12"

83/12"

38/12"

62/12" 59/12" 46/12" 19/12" 6/12"

16/12"

7/12"

15/12"

7/12"

40/12"

35/12"

41/12"

48/12" 14/12"

38/12"

42/12"

20/12"

15/12" 18/12"

26/12"

14/12"

85/12" 82/12"

111/12"

30/12"

50/12"

35/12" 150/12"

135/12"

114/12"

93/12"

85/12"

21/12"

7/12" 11/12" 9/12" 10/12"

38/12" 11/12" 10/12" 11/12" 21/12" 16/12" 27/12" 11/12" 11/12" 11/12" 18/12" 22/12" 19/12" 59/12" 38/12" 36/12" 36/12" 64/12" 44/12" 83/12" 67/12" 47/12"

66/12" 15/12" 19/12"

13 11/12" 14/12"

3/12" 5/12" 3/12"

12/12" 20/12" 2/12" 38/12" 32/12"

15/12" 10/12" 10/12" 13/12" 15/12" 10/12" 10/12" 10/12" 12/12" 12/12" 13/12"

100/11" 54/12" 16/12" 34/12" 68/12" 37/12" 60/12" 37/12" 34/12" 28/12" 35/12" 11/12" 9/12"

12/12" 19/12" 21/12" 100/8" 10/12" 14/12" 15/12" 13/12" 28/12" 24/12" 12/12" 10/12" 28/12" 20/12" 100/3" 19/12" 29/12" 20/12" 13/12" 100/7" 17/12"

21/12" 22/12"

8/12" 18/12" 27/12" 10/12" 10/12" 19/12" 32/12" 32/12" 11/12" 11/12" 13/12" 31/12" 31/12" 32/12" 39/12" 40/12" 40/12" 24/12" 56/12" 36/12" 69/12" 66/12" 42/12" 42/12" 62/12" 46/12"

25/12" 12/12" 14/12" 17/12" 27/12" 21/12" 28/12" 16/12" 14/12" 21/12" 132/12" 85/12"

23/12" 36/12" 64/12" 84/12" 61/12" 80/12" 70/12" 58/12" 71/12"

60/12"

SM

CH

SC

SM

SC

SMSC

SM

CL

SMSMSMSMSMSC

SC/GCSC/CL

SM

SC

SM

SC

SMSC

WOH WOH WOH WOH WOH 2 WOH WOH WOH WOH 5

WOH

63 11

10 43 13 13 33 21

WOR 23 15 15 15 35 20 28 6

WOR WOR

50/5" WOH WOH

WOR 79

WOR

10 50/10"

22 8

4

SP

SMSM

CL/SCSM

CH

SM

SC

SM

SC

SMSP

SC

SM

SC

CH

SC-SM

SM

SC

SM

SC

CL

SC

WOR WOR WOR WOR WOR WOH WOH 9

25 12 12

WOH WOH

11 8

WOH 12

26 22 26 11 21 16 20 25 26 39 28 18

19 11

50/3

16 12

WOH WOR

9

9 WOR

11 10

SP-SM

SCSM

SC

SMSC

SM

CHCH

SC

SC-SM

SCSM

SC

SM

WOR WOR WOR 8 8 WOR WOR WOR WOR 11

16

9 4

8 11 9

11 14 9

26

10 14 16 19 15 23 27 23

WOR

WOR WOR WOR

5 WOR

WOR WOR WOH WOR WOR

10 6 3

19 37

50/1

ML

SM

SC

SP-SM

SM

CLSC

SC-SM

SC

21 18 10 2 8 3 7 13 15 5

13 8

12

15 15 15 49 43 8

13 18 27 23 33 34 22 30

WOR

9 8

WOR 21 9

6 7 5

9

7 12 5

50/6"

SM

SC

SM

CL

SC

CL

WOR WOR 8 5 5 25 13 45

8

6 15 10 48 52 12 25 23 24 21 29 28 32 11 5

WOH

50/6"

5 29 6 6 4 5 4

3 3 7

11 9

32

17BH-101N

17BH-102N

17BH-103N 17BH-104N 17BH-105N

B-8

B-9

B-10

B-11

B-12

B-13

B-14

17-BH-007-OS

B-113

17-BH-008-OS

17-BH-009-OS

17-BH-012-OS

17-BH-010-OS

17-BH-011-OS

17-BH-013-OS

17-BH-014-OS

17-BH-015-OS

PROFILEHOR. SCALE: 1"=100'VERT. SCALE: 1"=30'

PLANSCALE: 1"=100'

-260

-240

-220

-200

-180

-160

-140

-120

-100

-80

-60

-40

-20

0

20

40

-260

-240

-220

-200

-180

-160

-140

-120

-100

-80

-60

-40

-20

0

20

40

-280-280852+00 854+00 856+00 858+00 860+00 862+00 864+00 866+00 868+00 870+00 872+00 874+00 876+00850+00

Tys

Qc

af

Tyf

Tye

17BH-101N B-113

928+00 930+00 932+00 934+00 936+00 938+00 940+00 942+00 944+00

Legend

Tye - Eastover Formation; Predominantly Coarse-grained(SC, SM, SP, SC-SM, SP-SC with minor lenses of CL)

Tyf - Yorktown Formation; Predominantly Fine-grained(CH, mainly fat clay with some lenses of CL, MH and SC)

Tys - Yorktown Formation; Predominantly Coarse-grained(SM, SP-SM, SP, SW, GP, SC, SW-SM, SC-SM)

Qc - Alluvial Marine Sediments; PredominantlyCoarse-grained (SP, SC, SM, SP-SM)

Qf - Alluvial Marine Sediments; PredominantlyFine-grained (CL, CH)

Qo - Alluvial Marine Sediments; Organic/Fat Clay(OL, OH, CH, PT)

af - Coarse-grained fill material (Fill)(SP, SM, SP-SM)

Water

3. This baseline profile is applicable for new tunnel alignments between the existing tunnels, and foralignments up to 500 feet to the west of the second tunnel alignment.

4. Qualifying statements related to interpretation of the subsurface profile for different elements ofthe proposed construction are presented in Sections 5.1.1, 5.2.1 and 5.3.1 of this report.

946+00 948+00

Notes:

1. This baseline profile was developed by projecting borings on to the alignment of the second bridge-tunnel built in the1970s. For clarity, the existing tunnel structure and associated backfill materials are not included in the profile. Referto project record drawings for limits of existing structures, and the associated backfill and scour protection materials.

2. For clarity, some CPT's are not shown and some have been moved slightly from their projected location.

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Concrete Sidewalk

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Concrete Ledge

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Concrete Ledge

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B-111B-112B-15AB-15 B-15B B-16A B-17 B-18A B-19 B-2017-BH-016-OS17-BH-017-OS

17-BH-018-OS17-BH-019-OS 17-BH-020-OS

17-BH-021-OS

11 22 68 S

35 6

WOR

S WOR WOR

1 36 75 72 37

43 67 48

7 3 7

12 5

WOR

WOR

S WOR

WOR WOR

62 87 81 72 16 24 20 57

S 10/12" 9/12" 5/12"

10/12" 11/12" 17/12" 15/12" 17/12" 82/12"

150/12" 14/12" 27/12" 24/12" 26/12" 28/12" 42/12" 32/12" 41/12" 48/12"

25/12" 12/12" 14/12" 17/12" 27/12" 21/12" 28/12" 16/12" 14/12" 21/12" 132/12" 85/12"

23/12" 36/12" 64/12" 84/12" 61/12" 80/12" 70/12" 58/12" 71/12"

60/12"

WOP/12" 18/12" 5/12"

WOP/12" 6/12" 7/12"

52/12" 100/12" 22/12" 23/12" 30/12" 39/12" 70/12" 58/12" 29/12" 50/12" 19/12"

WOP/12" 7/12" 10/12" 6/12" 1/12"

20/12"

2/12"

2/12"

5/12" 16/12" 20/12" 13/12" 15/12" 58/12"

12/12" 8/12" 6/12" 8/12" 5/12" 2/12"

1/12"

2/12"

2/12"

40/12" 47/12" 31/12" 34/12" 61/12"

40/12" 36/12"

42/12" 14/12" 21/12" 20/12"

3/3" 1/12"

1/12"

2/12"

21/12" 38/12" 28/12" 33/12" 16/12" 18/12" 11/12"

S 9/12"

35/12" 38/12" 21/12" 1/12" WOP/6" WOP/12" WOP/12"

2/12"

3/12"

7/12"

17/12" 37/12" 20/12" 14/12" 18/12"

WOP/12" 6/12"

WOP/12" 8/12" S

S

10/12" 8/12"

11/12"

10/12" 23/12" 26/12" 26/12" 31/12" 21/12"

SP

CH

CH

CH

CH

SP-SM

SM

CL

SC-SM

SM

WOR 3 2 6 2 WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR

22 23 18 17 6

14 6

51 15 7 9

10 5

13 44 25

89/6

6 9

24 50/3"

SP-SM

CLSP-SMCL

CL

SC

SPSW

SMCH

SM

SC-SM

WOR 24 7 16 14 7 WOH WOR WOH

WOR WOR WOR WOR WOR

WOR

WOR WOH

22 32

WOR 61 27 35 49 29

WOR

5 7

85

7 8 5

WOR WOR

14 42 17 13

70/3"

CL

SMCH

CH

SP-SM

SP

SW

SC

SM

SC

CL

WOR WOR WOR WOR WOR WOH WOR

WOR WOR WOR WOR WOR WOR WOR WOR 13 WOR WOR WOR WOR 18 27

26 32 30

WOR WOR WOR

50/2"

7 50/5"

7 WOH

50/5"

WOR WOH WOR WOR WOR

10 WOR WOR

8

39

SP

SC

CL

CL

CLSCSM

SP-SM

CHSMSC-SM

SC

CL

WOR WOR WOR WOR WOR WOR 57 13 12 17 WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR

WOR 22 23 22 31

WOH 60/5"

50/5"

12 16 8

15 11

WOR WOR

7 12 14 8

17 18 31

9 21

SP

SC

SP-SM

SC-SM

SMSC

SM

SMCH

SC

SM

SC

CL

WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR 8 21 26

WOR 17

WOR 21 31 24 8

24 4

24 WOR WOR

48 20 86

WOR 13

WOR WOR WOR WOH

50/4" 15 11 11

WOH 14

WOR 21 27

SP

SC

CHSPCLSMSCSMCHSC

SWSMCHSCSMSC-SM

SC

SM

SC

WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR

12

4 2

34 30 28 36 6 7 4 6

50/6" 2

55 5 5

WOH 13

WOH 9

14 7

11 3

4

B-15 B-15A B-15B B-16A B-17 B-18A B-19B-20

B-111B-112

17-BH-020-OS

17-BH-016-OS

17-BH-017-OS

17-BH-018-OS

17-BH-019-OS 17-BH-021-OS


PLANSCALE: 1"=100'

-260

-240

-220

-200

-180

-160

-140

-120

-100

-80

-60

-40

-20

0

20

40

-260

-240

-220

-200

-180

-160

-140

-120

-100

-80

-60

-40

-20

0

20

40

-280-280876+00 878+00 880+00 882+00 884+00 886+00 888+00 890+00 892+00 894+00 896+00 898+00 900+00 902+00

Qc

Qf

Qf

Tys

Tyf

Qo

Qc

Tye

928+00 930+00 932+00 934+00 936+00 938+00 940+00 942+00 944+00

Legend








Water



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Notes:



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Asphalt

AutoCAD SHX Text

Concrete Sidewalk

AutoCAD SHX Text

I-64 EBL

AutoCAD SHX Text

Asphalt

AutoCAD SHX Text

Concrete Sidewalk

AutoCAD SHX Text

I-64 EBL

AutoCAD SHX Text

Asphalt

AutoCAD SHX Text

Concrete Sidewalk

AutoCAD SHX Text

Concrete Sidewalk

AutoCAD SHX Text

Concrete Ledge

AutoCAD SHX Text

Concrete Ledge

AutoCAD SHX Text

Concrete Ledge

AutoCAD SHX Text

Concrete Ledge

B-110B-21 B-22 B-23 B-24 B-2517-BH-022-OS17-BH-023-OS

17-BH-024-OS17-BH-025-OS

17-BH-026-OS

17-BH-027-OS

0

WOR WOR

WOR 0

WOR

WOR

WOR

18 23 18 25 54 37 28 34

118 11 40

WOP/12" WOP/12" WOP/12"

S

S

7/12" 4/12"

5/12"

3/12" 16/12" 21/12"

21/12" 14/12" 13/12" 27/12" 38/12"

S S

S

1/12"

6/12" 20/12" 18/12" 8/12"

23/12" 20/12" 38/12" 27/12" 28/12" 37/12"

22/12"

S S

12/12" 18/12"

1/12"

29/12" 19/12" 24/12" 6/12"

5/12" 6/12"

12/12" 48/12"

127/12"

5/12"

13/12" 1/12" 1/12" 1/12"

1/12"

1/12"

1/12"

11/12" 4/12"

2/12"

2/12"

73/12" 9/12"

19/12" 6/12" 25/12" 46/12" 65/12" 76/12"

25/12" 38/12"

S

S

S

1/12"

1/12"

14/12"

8/12"

2/12"

22/12" 22/12" 39/12" 35/12" 91/12" 38/12" 60/12" 53/12" 65/12"

CL

CH

CH

SMCLSC

CL

SC-SM

SM

CH

SC

CL

CH

WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR 30 WOR

WOR WOR WOR WOR

26 18 9

19 6 3 3

WOR WOH

50/2"

WOR

WOR WOR

5 10 9 8 7 6

20

SMCL

CH

SM

CH

CHCHSCSPCH

SW

SM

CH

SC

SM

SM

SM

WOR WOR WOR WOR WOR WOR WOR WOR WOR 9 WOR WOR WOR WOR WOH WOR

WOR

WOR 20

WOR

23 6

12 16 32 24 19 6

10 2 3

86 9 3

24 WOR

WOR

50/5"

11 26

28

GW

SM

SW

CL

CH

SP

CH

SC

SW

CL

SM

CHCH

SC

SC-SM

SC

34 9 15 26 7 7 6 5 2 7 15 19 11 17

WOR WOR WOR WOR WOR 6 WOR WOR WOR WOR WOR WOR WOR WOH 26

WOR WOR WOR WOR WOR

10 20 15 11 16 12 11 15 30 33 30 9

WOR WOR

22 21 13 5

12 7

11

50/4

SMSPMLSP

GW-GMSP-SM

SC

CL

CH

OH

SC

CH

CLSP

SM

CL

SC

SM

SC

SM

16 18 21 14 12 12 17 17 25 92 10 20 30 10 12 WOH WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR

26 22 48

WOR

WOR WOR

WOR WOR

11 17 20

WOH 12 58 28 4

WOR WOR WOR

11 50/5" WOR

7 WOR WOR

15 WOR WOH

13 20

CL

OH

CL

SPSC

SM

SW-SM

CH

SC

WOR WOR WOR WOR WOR WOR WOR WOR WOH WOH WOR WOH WOR WOH WOH 6 WOH WOH WOR WOR WOR 16 29

WOR WOR WOR WOR

36 27 19 37 16 21 21

18 15 14

WOR WOR

47 50/3"

21 17 9

13

WOR 11

SP-SM

OH

SC

CH

SC

CLCHSPSWGP

SM

CLSCCLSC

SM

WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR 6 4 24 2 WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR

12 5

17 27 10 21 41 41 35 27

WOR WOR WOR

9

47 5

15 15 7 7

13 13

15

B-21 B-22 B-23 B-24B-25

B-110

17-BH-025-OS

17-BH-022-OS

17-BH-023-OS

17-BH-024-OS

17-BH-026-OS


PLANSCALE: 1"=100'

-260

-240

-220

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-160

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-120

-100

-80

-60

-40

-20

0

20

40

-260

-240

-220

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-80

-60

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-20

0

20

40

-280-280902+00 904+00 906+00 908+00 910+00 912+00 914+00 916+00 918+00 920+00 922+00 924+00 926+00 928+00

QfQc

Qo

QfQc

Qf

Tys

Tye

Tyf

Qc

Qf

af

928+00 930+00 932+00 934+00 936+00 938+00 940+00 942+00 944+00

Legend








Water



946+00 948+00

Notes:



AutoCAD SHX Text

I-64 EBL

AutoCAD SHX Text

Asphalt

AutoCAD SHX Text

Concrete Sidewalk

AutoCAD SHX Text

I-64 EBL

AutoCAD SHX Text

Asphalt

AutoCAD SHX Text

Concrete Sidewalk

AutoCAD SHX Text

I-64 EBL

AutoCAD SHX Text

Asphalt

AutoCAD SHX Text

Concrete Sidewalk

AutoCAD SHX Text

Concrete Ledge

AutoCAD SHX Text

Concrete Ledge

AutoCAD SHX Text

Concrete Ledge

B-101B-102

B-103B-104B-105

B-10617BH-101S17BH-102S

17BH-104S 17BH-105S17BH-106S 17BH-108S17BH-110S

17BH-109S 17BH-112S17BH-113S

17BH-103S 17BH-107S 17BH-111SB-26 B-29B-30 B-31B-46 B-44B-45

WOH

WOH

WOH

WOH

WOH

4

5

5

7

25

33

34

65

49

WOR

11

10

WOR

5

3

3 3

1 2

3 5

WOR

5

53 23

48 31

20

31

13

22

3

7

10

2

2 2

4

WOH

6

5

WOH

31

16

43

61

123/3"

32

10

11

7

10

0

WOR

2

WOR

8

9 16

55

62

33

22

64

51

49

16

8

8

4

3

5

6

11

8

6

20

17

20

10

8

9

28

36

72

72

19

70

32

45

32

37

11

14

31

11

2

5

5

6

20

10

19

8

21

44

28

11

6

8

7

10

49

52

28

50

72

WOR

40 50

FL

FL

SP-SM

MLSMCLCH

OH

OHOH

SMOHPTSPSM

SM

MHCH

SM

SM

14 9 12 14 15 16 21 17 13 16 17 11 4 7 2 2 6 WOH 3 3 6 5 5 3 4 3 6 6 4 7 4 8 2 4 6 7 6 10 33 19 25 9

34 15 40 9 5

20 23 13 10 20 36 22 10 6 3 6 5

50/3'' 6

50/2'' 8 3 6

11 7 5

11 10

FLFLFL

SP

SMSPOHML

CHCHSMSM

7 14 13 9 5 16 11 17 24 17 10 14 15 17 8 7 13 10 9 6 11 12 12 12 5 5 4 5 5 8 7 6 6 6 11 30 13 23 14 16 50/3"

FLFLFLFLFL

FL

SCCHSECH

OH

CHCHSMSM

13 8 8 8 11 8 10 9 6 8 6 5 2 5 WOH 4 4 4 WOH 8 5 6 6 6 6 6 5 8 10 16 22 19 8 12 14

FL

FL

FLSMMLCLSMOLSM

SM

CH

SM

SM

SP

17 13 WOH WOH

2 WOH 2 4 4 12 8 3 3 2 3 9 6 8 9 18 8 7 12 6 13 7 7 8 13 8 9 6 7

11 7

20 16 12 9

16 11 11 19 33 29 24 9

12 5 4

50/1'' 11 12 6 5 8 8 6 8

11 20

FL

CL

CHCH

OH

MLSMSM

17 7 7 9 10 10 12 8 15 2 2 5 3 5 3 3 4 6 4 5 7 6 6 5 7 4 6 3 2 5 6 5 3 6 10 6 11 13 34 25 9 12 10 20 23 13 44

FL

FL

SCCLSMCHSC

SM

4

5 4 4 6 6 7 3 5 9

10 8 8 18 9 16 9 7 17 9 25 10

FL

CH

SC-SM

CL

OH

OHSMCLPTSM

SM

CHSC-SM

SM

SM

3 13 2 8 2 2 3 WOH

WOH 3 2 3

4 3 5 3 3 4 5 4 2 4 3 3 3 7 5 5 7 6 6 13 38 27

18 11 WOH 2 WOH 2 2 2 WOH 2 2 3 WOH 2 2 3 2 2 5 6 5 2 2 2 2 2 3 2 2 2 4 3 5 5

15 30 13 15 29 12 12 35 9 13 9

13 13 18 24 34 37 27 4 9

9 9 8

50/1'' 19 7 4

11 9 5

10 12 30

FL

FL

CHSM

CL

CL

SMSP-SM

FL

FLCHSMCLSM

OH

OH

SPSM

7 14 6 8 5 2 2 WOH 2 2 3 3 8 10 7 3 4 4 4 5 5 3 4 5 6 5 3 6 7 23 21 19 11

FLFL

FL

CL

SM

SM

SP-SM

SM

CHSC

SM

10 6 9 15 2 WOH 2 2 2 4 2 3 4 20 8 6 4 4 17 15 9 9 10 10 11 10 5 11 11 12 10 17 9 12

12 8

18 17 30 32 16 12 20 15 14 31 41 40 36 10 9 4 4

50/2'' 8 50/4''

FL

SP-S

M

CLOL

OH

OHOHSP

SM

CH

SM

SM

14 12 4 6 9 8 9 6 5 9 16 6 3 2 WOH 3 3 4 5 5 5 4 4 3 6 3 4 6 5 6 4 4 10 38 39 9 9

50/3'' 23 12 8

14 15 10 19 19 31 17 5

15 4 5

10 12 14 18 20 4 9 8 5 9 9

14

FLFL

FL

MHSP-SMCL

CL

SC

OH

SCSMSM

8 4 5 3 12 6 2 3 2 2 4 2 3 3 6 5 4 5 4 7 4 4 6 4 7 4 5 8 4 6 5 6 46 23 33 8

FL

CL

OH

SP

SM

CH

SM

SM

11 6 2 9 3 3 2 3 2 2 WOH

WOH 3 4 2 2 3 3 6 4 4 5 4 3 6 6 5 5 27 32 12 13 15

14 25 25 10 9

13 11 8

19 27 41 21 8 9

5 50/2''

7 50/4''

11 10 10 11 7 6 9

16 13

S 1/12" 1/12" 1/12"

1/12" 1/12" 1/12" 2/12" 2/12" 1/12" 1/12"

1/12"

27/12" 21/12" 36/12" 36/12" 32/12"

48/12" 37/12" 75/12" 39/12" 36/12" 35/12" 72/12" 63/12"

1/12" 3/12" 1/12" 1/12" 1/12" 1/12" 1/12" 1/12" 1/12" 3/12" 3/12" 3/12" 3/12"

66/12" 32/12"

44/12" 43/12" 17/12" 14/12"

102/12" 96/12" 82/12" 27/12" 43/12" 33/12" 30/12" 12/12" 14/12" 10/12" 16/12" 6/12" S 24/12"

150/12" S

14/12" 16/12"

S 10/12"

25/12" 22/12"

S 22/12" 16/12"

S

13/12"

S

S

S S

S 2/12"

2/12"

2/12"

13/12"

15/12"

25/12"

17/12"

36/12" 96/12" 66/12"

28/12"

51/12"

33/12"

34/12" 19/12"

93/12"

S

S

S

2/12"

5/12"

5 6 5/12"

10/12"

15/12"

16/12"

43/12" 39/12"

21/12"

43/12"

38/12"

36/12"

45/12"

51/12"

31/12"

51/12"

39/12"

38/12"

41/12"

48/12"

WOH/12"

WOH/12"

WOP/12"

2/12"

5/12"

S

1/12"

1/12"

7/12"

55/12"

20/12"

S

S

S

1/12"

1/12"

1/12"

2/12"

3/12"

5 11/12"

33/12"

30/12" 18/12"

29/12"

65/12"

4/12"

S

1/12"

1/12"

1/12"

2/12"

4/12"

3/12"

4/12"

4/12"

22/12"

18/12"

22/12"

SMCL

SC

SC

SC-SM

WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR WOR 14 18 10 13 17 10 22 57 11 24 12 26 11 19

18 15 16 14 12 11

WOH WOH WOR WOR

5 WOR WOR WOR

22

17-BH-032-OS

17BH-101S

17BH-102S

17BH-103S 17BH-104S

17BH-105S

17BH-106S

17BH-107S17BH-108S

17BH-109S 17BH-110S 17BH-111S 17BH-112S

17BH-113S

B-26

B-27

B-28

B-29

B-30

B-31

B-44B-101

B-102 B-103

B-104B-105

B-106

17BH-032-OS


PLANSCALE: 1"=100'

-260

-240

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-200

-180

-160

-140

-120

-100

-80

-60

-40

-20

0

20

40

-260

-240

-220

-200

-180

-160

-140

-120

-100

-80

-60

-40

-20

0

20

40

-280-280928+00 930+00 932+00 934+00 936+00 938+00 940+00 942+00 944+00

af

Qc

Qf

Qo

Qc

Tys

Tyf

Tye

Qf

Legend








Water



946+00 948+00

Notes:



AutoCAD SHX Text

Concrete Sidewalk

AutoCAD SHX Text

Asphalt

AutoCAD SHX Text

I-64 EBL

AutoCAD SHX Text

Concrete Ledge



APPENDIX B – Tunnelman’s Classification System



Tunnelman’s Classification System (After Heuer, 1974)

Classification Behavior Typical Soil Type

Firm

Heading can be advanced without initial support, and final lining can be constructed before ground starts to

Loess above water table; hard clay, marl, cemented sand and gravel when not highly overstressed.

Raveling

Slow Raveling

Chunks or flakes of material begin to drop out of the arch or walls sometime after the ground has been exposed, due to loosening or to overstress and “brittle” fracture (ground separates or breaks along distinct surfaces, opposed to squeezing ground). In fast raveling ground, the process starts within a few minutes, otherwise the ground is slow raveling

Residual soils or sand with small amounts of binder may be fast raveling below the water table, slow raveling above. Stiff fissured clays may be slow or fast raveling depending upon degree of overstress.

Fast Raveling

Squeezing

Ground squeezes or extrudes plastically into tunnel, without visible fracturing or loss of continuity, and without perceptible increase in water content. Ductile, plastic yield and flow due to overstress.

Ground with low frictional strength. Rate of squeeze depends on degree of overstress. Occurs at shallow to medium depth in clay of very soft to medium consistency. Stiff to hard clay under high cover may move in combination of raveling at execution surface and squeezing at depth behind surface.

Running

Cohesive Running

Granular materials without cohesion are unstable at a slope greater than their angle of repose. When exposed at steeper slopes they run like granulated sugar or dune sand until the slope flattens to the angle of repose.

Clean dry granular materials. Apparent cohesion in moist sand, or weak cementation in any granular soil may allow the material to stand for a brief period of raveling before it breaks down and runs. Such behavior is cohesive‐ raveling

Running

Flowing

A mixture of soil and water flows into the tunnel like a viscous fluid. The material can enter from the invert as well as the face, crown, and walls, and can flow for great distances,

Below the water table in silt, sand or gravel without enough clay content to give significant cohesion and plasticity. May also occur in sensitive clay when such material is disturbed.

Swelling

Ground absorbs water, increases in volume, and expands slowly into the tunnel.

Highly pre‐consolidated clay with plasticity index in excess of about 30, generally containing significant percentages of montmorillonite.