REVIEW OF SUBSURFACE INFORMATION 3 SOIL · PDF file20.04.2015 · Peer Review Report Of Seawall Stabilization Options Apollo Beach, Florida Langan Project Number 30017702 ... secondary

Peer Review Report Of Seawall Stabilization Options

Apollo Beach, Florida

Langan Project Number 30017702

20 April 2015

Page i of i

TABLE OF CONTENTS

INTRODUCTION 1

SITE DESCRIPTION 1

Overall Site Description 1

Mirabay Pilot Project Site Description 1

PILOT TEST SEAWALL STABILIZATION ALTERNATIVES 2

REVIEW OF SUBSURFACE INFORMATION 3

Generalized Subsurface Conditions 3

Landside Subsurface Materials 3

Waterside Subsurface Materials 3

Groundwater 3

SOIL PARAMETERS 4

SEAWALL STABILIZATION ALTERNATIVE EVALUATIONS 4

Baseline (Existing Conditions) and Analytical Approach 5

Option 1 (Rip-rap with Two Tieback Anchors) 5

Option 2 (Rip-rap Sheet Pile “Knee Wall”) 5

Option 3 (New Seawall) 5

Option 4 (Rip-rap Extended to a Length of 12 feet) 6

Modified Option 1 (Refined Rip-rap Configuration with Single Tie Back) 6

OTHER CONSIDERATIONS 6

Existing Tieback Anchor Condition 6

Preliminary Estimated Costs for Seawall Stabilization Options 7

Further Geotechnical Engineering Evaluation of Soil Parameters 7

Buffer Piers for Rip-rap Options 7

CONCLUSIONS AND SEAWALL ENGINEERING DESIGN IMPLEMENTATION 7

LIMITATIONS 7

TABLES

Table 1 – Summary of Soil Parameters Used for Seawall Options Analysis

Table 2 – Summary of Results for Seawall Stabilization Options

FIGURES

1 SITE AND VICINITY MAP

2 COMPARATIVE PROFILES- OPTION 1 AND OPTION 1-MODIFIED

APPENDICES

A INGENIUM’S SUMMARY REPORT DATED 25 SEPTEMBER 2014

B PILOT STUDY TEST SITES SELECTED SUBSURFACE PROFILES




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INTRODUCTION

Langan Engineering and Environmental Services, Inc. (Langan) has performed a peer review of

Ingenium, Inc.’s (Ingenium) “Mirabay Pilot Project Report”, dated 25 September 2014 for the

Harbor Bay Community Development District (CDD). The CDD encompasses the development

located in Apollo Beach, Florida and known as “Mirabay.” The pilot project conducted by

Ingenium was the first step in the CDD’s proposed seawall stabilization project for the Mirabay

community seawall. Our peer review of the pilot project was performed in accordance with the

“Agreement for Professional Engineering Services”, and Task 1 of Exhibit A, revised date 12

February 2015 between Langan and the CDD. The purposes of our peer review of Ingenium’s

pilot project was to 1) thoroughly review three seawall design options and their supporting

information, 2) review the geotechnical data used by Ingenium as well as that used in previous

studies performed by others, 3) review our previous seawall stabilization recommendations

provided in our 2013 expert witness report; 4) perform geotechnical engineering analysis to

evaluate each proposed seawall stabilization option presented by Ingenium as well as potential

modified options; and 5) preliminarily evaluate seawall stabilization option construction costs

and their practical application with respect to navigation and other potential issues.

The CDD provided us with Ingenium’s pilot project report and supporting calculations in order

to perform our review. A copy of Ingenium’s summary report is attached as Appendix A. We

were also provided geotechnical soil test data for the pilot test locations that included field

Cone Penetrations Tests (CPT) and laboratory Direct Shear Test results. The CPT tests were

performed by Direct Push Services, LLC. The Direct Shear Tests were performed by Tierra Inc.

We also reviewed previous geotechnical and seawall studies performed at Mirabay that were

used in preparation of our Geotechnical Expert Witness Report, dated 12 April 2013. That report

included a comprehensive review of the original seawall design and viable seawall stabilization

option.

We also performed a cursory reconnaissance of the site on 10 April 2015 to make specific

observations of the existing site conditions at pilot study test sites and the overall Mirabay

seawall.

Elevations given in this report are approximate and are in feet relative to the National Geodetic

Vertical Datum of 1929 (NGVD 29).

SITE DESCRIPTION

Overall Site Description

The Mirabay community development is at the east side of Tampa Bay and immediately west

of Tamiami Trail (U.S. Highway 41) in Apollo Beach, Florida. The development has been

substantially developed with residential homes, and includes approximately seven to eight

miles of seawall along the back of the properties. The back of the residential properties

adjacent to the seawalls consist of uplands with amenity structures (i.e. pool and pool decks,

screen houses and landscape walls).

Mirabay Pilot Project Site Description

The pilot study tests were performed by Ingenium at two vacant lots at the Mirabay

development in the summer of 2014. The selected sites for the pilot project were as follows:

5701 Tybee Island Drive (Lot 10) and




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5607 Seagrass Place (Lot 3).

The approximate locations of the pilot test lots are shown on Figure 1–Site and Vicinity Map.

The 5607 Seagrass Place site has approximately 72 feet of constructed seawall and the 5701

Tybee Island Drive site has approximately 100 feet of seawall. The three seawall stabilization

options that were part of the pilot study were constructed side-by-side at each pilot study test

site.

The existing seawalls refer to the originally designed seawalls with a reinforced concrete cap

and vinyl sheet piles. Anchor rods extend from the back of the seawall cap to below-grade

deadmen. Based on previous understanding of the original design and our discussions with

Ingenium and CDD, pool structures are located above existing deadmen at many locations.

The pilot project consisted of designing, constructing and testing three options for seawall

stabilization. A fourth seawall stabilization alternative, that was presented in Langan’s Expert

Witness Report, was also presented in Ingenium’s pilot study report, but was not constructed.

This alternative Option 4 consisted of placing rip-rap from the base of the seawall out to timber

docks (approximately 12 ft in horizontal length).

PILOT TEST SEAWALL STABILIZATION ALTERNATIVES

Ingenium designed, constructed and conducted full-scale tests on three seawall alternatives

described in their report as Options 1, 2 and 3.

Option 1 consisted of stabilizing the existing vinyl sheet pile wall with rip-rap placed on the

channel side, immediately adjacent to the seawall. The rip-rap extended a horizontal distance of

approximately 8 feet from the seawall to the back edge of timber dock piers. Based on profile

drawings of the alternatives provided by Ingenium, the top of the rip-rap at the seawall was at

approximate el +2 and was placed at an approximate 2 horizontal to 1 vertical (2H:1V) slope into

the canal. Waler beams were installed at approximately el +2.5 along the wall and secured with

additional tieback anchors (helical screw anchors).

Option 2 and Option 1 were constructed in a similar fashion. Option 2 had waler beams and

additional anchors installed through the existing wall. The rip-rap length was shortened from 8

feet in Option 1 to 4.5 feet for Option 2 by using a secondary vinyl sheet pile wall “knee wall”

installed to vertically retain the rip-rap. Although not specifically stated, we understand the

intended length of the PVC knee wall is approximately 10 ft. The top of the knee wall is at

about el +1 and the bottom of the knee wall is at about el -9. The tip of the knee wall sheet

piles wall were reportedly installed to depths 1 to 1.5 feet short of the “design depth” due to

refusal from hard/shelly/slightly cemented soils. Nevertheless, we understand the pilot test wall

systems were reportedly still stable at the time of their construction and testing. Similarly,

refusal resistance depths during vinyl sheet installation could vary, but based on our review of

the subsurface information at the site, intermittent cemented zones could be encountered in

the silty sand zones below the bottom of the canal.

Option 3 consisted of constructing a new seawall using fiberglass reinforced polymer (FRP)

sheet piles installed immediately in front of the existing PVC sheet pile wall. The new sheet pile

wall was installed with a vibratory hammer to a design depth of about 4 foot deeper than the

existing wall with sheet pile tip elevations at approximately el -10. The FRP sheets were




20 April 2015

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reportedly 16 feet long and were advanced to the termination depth without encountering

refusal. A new reinforced concrete cap was constructed in front of and enveloping the existing

cap to incorporate both the existing and new sheet pile walls.

Ingenium performed full-scale field load tests for the three constructed alternatives to simulate

working loads induced by upland features. Approximately 6 foot high timber retaining walls

were constructed about 5 feet landside of the existing seawall. The upland timber retaining

walls were backfilled to their tops with sand to induce a surcharge load on the existing seawall.

Ingenium estimated that the applied load on the existing seawall induced by the 6 foot high

surcharge was about 25 percent greater than typical 4.75 foot high segmental block landscape

walls at Mirabay properties. Ingenium also attempted to induce fully saturated hydraulic loads

by discharging water into the surcharge areas and the ground surface areas between the back

of the existing seawall and timber retaining walls.

REVIEW OF SUBSURFACE INFORMATION

Generalized Subsurface Conditions

Numerous geotechnical borings, both landside and waterside of the existing seawall, were

previously performed by others and reviewed by Langan in preparation of our Expert Witness

Report. In addition, Standard Penetration Test (SPT) borings and Cone Penetration Test (CPT)

probes were performed by Ingenium at the Pilot Study Test sites. The site conditions at the

pilot test sites were generally similar to the subsurface conditions throughout the Mirabay

development. The subsurface profiles developed by Ingenium for the Pilot Test study areas are

shown in Appendix B. Based on subsurface data developed for the site by others, the

subsurface conditions at the pilot study sites and at Mirabay generally consist of the following

inferred soil strata which were used for the subsequent seawall analyses discussed in

subsequent sections of this report.

Landside Subsurface Materials

On the landside of the seawall, underlying grassed and vegetated areas, is loose sand that

extends to varying depths of approximately el -4 to el -6. This upper landside material is

described as fine to silty fine and slightly clayey sands. Underlying this material is a layer of

loose to medium dense silty fine sand that extends to approximate depths of el -10 to el -13.

The landside borings at the pilot study test sites terminated in a sandy clay or sand with some

shell stratum at a depth of approximately el -14.

Waterside Subsurface Materials

Based on the subsurface information from borings that were performed immediately waterside

of the existing seawalls, the channel bottom starts at approximate el 0 and consists of very

loose to loose silty/clayey fine sands to sandy/clayey silts, approximately 2 feet to 4 feet thick.

The materials below this consist of fine sands, sands with shell, or sandy clays and are

generally loose to medium dense. These materials extend to approximate elevations of el -13 to

el -17. Waterside borings at the Seagrass Place test site terminated at about el -17 at the top of

a limestone stratum.

Groundwater

Generally, the mean high groundwater has been reported at approximate el +1.5 and mean low

groundwater at el -0.5. Groundwater elevation will fluctuate with tidal flow and seasonal rainfall.




20 April 2015

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For the seawall analysis, groundwater was set at about the mean high ground water table (el

+1.46).

SOIL PARAMETERS

The geotechnical engineering soil parameters used for the seawall alternative design analyses

are representative of the loose sand subsurface conditions. The soil parameters were derived

from geotechnical soil classification and property references, and also Direct Shear laboratory

tests performed by Ingenium for the pilot test site. The soil parameters used for Ingenium’s

and Langan’s seawall analyses are summarized in Table 1.

The soil profiles used by Ingenium and Langan are generally similar representations of the

seawall landside loose soil conditions, the very soft canal bottom sediments and the underlying

denser sand strata. The upland sandy materials as well as the canal materials underlying the

canal bottom soft silts are generally described as silty and clayey fine sands with some shell in

locations. It is our experience that slightly silty and clayey fine sand materials have some

cohesion along with the soil friction angle. Based on the clayey and silty sand descriptions from

the borings and grain size analysis results of the upper landside materials at Tybee Island Drive,

Ingenium assigned cohesion (shear strength) values of 200 psf to 300 psf along with a friction

angle of 30 degrees for the passive (water) side material. This is significant shear strength for

sandy soils that would affect earth pressures modeled for the seawall analysis. Soils with slight

cohesion would reduce passive side (landside) earth pressures on the seawall and help to

increase wall stability.

Based on our review of the soil boring information for the Mirabay development, we slightly

modified the original soil properties to infer that the slightly silty clay fine sands that are

predominantly on the upland side of the seawalls have some cohesion. Hence, we assigned a

conservatively low cohesion value of 50 psf along with varying friction angles of 28 to 30

degrees to model those soils in our analysis.

The rip-rap material which, generally consist of varying size boulders, have significantly high

friction angles (40+ degrees). This material, placed on the waterside of the seawall, had a

friction angle of 40 degrees for the analyses.

SEAWALL STABILIZATION ALTERNATIVE EVALUATIONS

Ingenium and Langan used industry accepted software packages to create computer models of

the pilot study options. The software packages allows efficient modeling of complex seawall

configurations, while parametrically changing soil properties, surcharge loads, rip-rap geometry

and seawall embedment depths to test seawall stability. Ingenium analyzed their seawall

designs using “SupportIT, version 2.36”. Langan used “Shoring Suite 8” and the United States

Corps of Engineers “CWALSHT”, two separate software packages used for computing earth

pressures and checking the seawall design options. Surcharge loads were used for all analyses

computer models. Ingenium also tested varying heights of surcharge and water table to test

the sensitivity of their computer models.

For any seawall stabilization option selected, there will be constructability issues due to the

landside site constraints at fully developed lots. At most locations where seawall stabilization is

required, landscape walls and other amenity structures would likely inhibit landside

construction. Therefore, the majority of the construction would likely be performed using




20 April 2015

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equipment and materials staged waterside of the seawall on barges. Waterside constraints are

also present in the form of the existing boat docks. The waterside constraints would likely be

heightened when installing new sheets due to tight installation tolerances.

Baseline Condition (Existing Condition) and Analytical Approach

Ingenium and Langan modeled the baseline conditions at the pilot test sites. The baseline

condition considers the existing vinyl sheet pile wall as is, with no additional tieback anchor.

Our approach was to review Ingenium’s baseline conditions to verify the existing marginal wall

stability at the site, while qualitatively checking the soil parameters selected to run the baseline

computer models. Upon our verification of the baseline computer models, we proceeded to

perform analytical checks using consistent baseline soil parameters compatible to Ingenium’s.

We subsequently evaluated the design options relative to global stability, viability of

construction, navigation and preliminary cost to construct. We also modified the soil

parameters in certain instances to include slight apparent cohesion in the subsoils.

Option 1 (Rip-rap with Two Tieback Anchors)

For Option 1, Ingenium used an additional tieback anchor and waler system along with rip-rap

extending 8 feet into the canal. Using Ingenium’s soil parameters, we were able to verify that

the Option 1 alternative is relatively stable.

While the issue of navigability requires further review, this option, as compared to Options 2

and 3, is more likely to potentially create some navigation issues for situations where the stern

of boats with propellers are maneuvered on the inland side of the timber docks where rip-rap

material may extend to the back of the docks. It is also apparently the least costly option when

compared to Options 2 and 3.

Option 2 (Rip-Rap with Sheet Pile “Knee Wall”)

For Option 2, Ingenium used an additional tieback anchor and waler system along with a

secondary sheet pile wall (“knee wall”) used to vertically retain the rip-rap at a horizontal

distance of 4.5 feet from the seawall. Using Ingenium’s soil parameters, we were able to verify

that the Option 2 alternative is relatively stable.

This option partially addresses the potential navigation issues associated with Option 1 by

reducing the length of the rip-rap. However, based on our analysis of this system, the

secondary new sheet pile wall would need to be embedded to a tip about 7 ft below the mud

line with a factor of safety of about 1.3. This results in about a 10 ft long sheet. Deeper knee

wall sheets may be required at areas where weaker subsurface conditions could be

encountered.

Based on our preliminary cost analysis, Option 2 would be more expensive to construct than

Option 1. The increased cost to construct is associated with the material and installations costs

of the additional PVC sheet pile knee wall and waler/tieback system for the primary wall.

Option 3 (New Seawall)

Option 3 is the construction of a new fiberglass composite (FRP) sheet pile wall immediately in

front of the existing vinyl sheet wall. The new wall system, embedded to its design depth

(about four feet below the depth of the existing seawall), would provide a factor of safety of




20 April 2015

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about 1.9 relative to embedment. As such, it is relatively more stable than any of the other

options.

This option also eliminates navigation issues because there is no rip-rap placed at the base of

the seawall. No additional anchor rods would be necessary because the new sheets would be

tied into to existing pile cap and would utilize the existing tie-back system for support.

The construction constraints previously discussed would be a concern for this option as well, in

particular because of the potential for vibrational impacts on upland structures from the sheet

pile installation. The constructability of Option 3 could vary throughout the site depending on

soil conditions (and the nature of upland structures) and will require further analysis. This

construction method and material costs would drive up the cost of construction. The cost to

construct Option 3 would be more expensive than Option 2.

Option 4 (Rip-rap Extended to a Length of 12 feet with Existing Tieback)

Option 4 is similar to the solution analyzed as part of our Expert Witness Report. This option

uses rip-rap extending 12 feet out from the existing face of the seawall. The top of the rip-rap

would be at el +2 at the wall would slope on a 4H:1V toward the canal.

Option 1-Modified (Modified Rip-Rap Configuration with Existing Tieback)

Langan also analyzed a potential modification to Option 1.1 When a small cohesion of the

silty/clayey sand is considered as part of the computer models, the stability of the seawall

options improve. Based on overall stability and costs, Option 1-Modified is a viable alternative.

The rip-rap was reconfigured for this modified option, with the top at el +3 against the wall and

a slope of about 2H:1V (8 ft wide) toward the canal. With this configuration of rip-rap and

considering slight cohesion in the design, the factor of safety improved sufficiently, without the

need for a supplemental tieback anchor. The primary advantages of this option are that it

maintains the 8 ft. width of the rip-rap into the canal (as compared to Option 1) and eliminates

the need for an additional tieback anchor and waler system. Hence, Option 1-Modified would

be less costly than the original Option 1. Accordingly, it is a better option than Options 1 and

4.

The comparative profiles of Option 1 and Option 1-Modified are shown on Figure 2. A

comparative summary of key parameters for selected analytical runs is presented in Table 2.

This summary is for Options 1, 2, 3, and Option 1-Modified, considering for varied soil

properties.

OTHER CONSIDERATIONS

Existing Tieback Anchor Condition

Ingenium observed some corrosion to existing tieback rods during construction of the pilot test

seawall alternative. The extent of and potential for corrosion of the existing steel bar tieback

anchors should be documented and evaluated. The condition of existing tieback anchors needs

to be evaluated to address potential corrosion and loss of section that could result in seawall

failures. The conditions of tieback anchors and deadmen should be observed at selected

1 Langan is also exploring potential design changes for Options 2 and 3 that may enhance the

effectiveness of those designs.




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properties throughout the Mirabay development in order to develop a meaningful global

assessment. This may result in the implementation of a periodic maintenance program.

Preliminary Estimated Costs for Seawall Stabilization Options

As previously indicated, preliminary cost assessments indicate that Option 1-Modified is the

most economically viable option. Option 2 would be the next highest cost and Option 3 would

be the highest cost. Options 2 and 3 have higher costs due to materials and installation. When

the final seawall stabilization options are designed, more detailed cost estimates will be

developed.

Further Geotechnical Engineering Evaluation of Soil Parameters

Langan will be performing a geotechnical confirmatory study of the subsurface conditions

throughout the Mirabay development. The purposes of the confirmation geotechnical

engineering study will be to verify the subsurface conditions encountered in borings done by

others and determine the variability with soil parameters critical for developing the final seawall

stabilization designs.

Buffer Piers for Rip-rap Options

To address navigation concerns posed by options that use rip-rap extending into the canals,

timber “buffer piers” could be installed at the base of the rip-rap as a potential hazard warning

and impede the progress of watercraft into rip-rap. This consideration for navigation issues

would obviously add cost to rip-rap alternatives if implemented.

CONCLUSIONS AND SEAWALL ENGINEERING DESIGN IMPLEMENTATION

Considering relative stability, constructability, preliminary costs for construction and potential

navigation issues, Option 1-Modified with a modified rip-rap configuration, is technically viable

and more economically attractive than Option 2 or Option 4. The Option 2 alternative is also

relatively stable while having a higher cost to construct than Option 1-Modified.

If the community desires no navigation issues along with a potentially more aesthetically

pleasing alternative, then Option 3 could be considered. Preliminary costs for Option 3 indicate

it may be several times more costly than Option 1-Modified. The constructability of Option 3

would need to be evaluated in detail. Potential construction site constraints caused by existing

upland improvements and canal docks may tend to complicate Option 3 compared to Option 1-

Modified. In addition, potential vibrational impact to existing structures would need to be

further studied before implementing Option 3.

The seawall construction alternatives evaluated for this report would help to minimize upland

settlement issues in areas adjacent to the back of existing seawalls. All of the proposed

options, if properly implemented, would help to confine and retain the loose soil conditions

adjacent to the existing seawall and may mitigate potential settlement caused by lateral

movement of soil in contact with the seawall.

LIMITATIONS

This is a peer review study of a report done by others. Langan will be developing more detailed

subsurface properties to be used in our final evaluation and design of the preferred stabilization

option. \\langan.com\data\MI\data7\300117702\Office Data\Reports\Geotechnical\Final PDFs\Final Peer Review Report 2015-04-20.docx

TABLES

TABLE 1

SUMMARY OF SOIL PROFILE USED FOR ANALYSIS

MIRABAY COMMUNITY DEVELOPMENT

APOLLO BEACH, FLORIDA

300117702

Soil

Description

Depth Range

(feet)

Friction

Angle

(degrees)

Cohesion

(psf)

Soil Unit

Weight (pcf)

Soil

Description

Depth Range

(feet)

Friction

Angle

(degrees)

Cohesion

(psf)

Soil Unit

Weight (pcf)

Loose SAND0 to 3 (Active Side);

28 0 100Loose fine

SAND

0 to 4.6 (Active

Side)28 to 30 50 100

Typical SAND 3 to 8 (Active Side) 30 0 105

Fine SAND 8 to 12 (Active Side) 35 0 115

Saturated fine

SAND, some

silt

4.6 to 12.5 (Active

Side)30 50 105

Silty fine

SAND

Greater than 12 (Active

and Passive Sides)35 0 120

Silty fine

SAND

Greater than 10

(Passive Side)35 50 120

Dark clayey

SILT6 to 12 (Passive Side) 25 0 90

Dark clayey

SILT

6 to 10 (Passive

Side)25 0 90

RIP RAP 4 to 6 (Passive Side) 40 0 130 RIP RAP3 to 6 (Passive

Side)40 0 130

Notes

(1) Soil profiles based on information from previous geotechnial engineering studies.

(2) Depth to top of soil layers on passive side of seawall vary depending on seawall and rip-rap option geometry.

(3) Langan modified soil profile based on evaluation of available subsurface information available at the time of this writing.

(4) The Ingenium soil profiles and soil properties are general representations of the pilot study test Seagrass Place site.

(5) Soil thicknesses and properties were varied and paremetrically studied as part of the analyses.

Not Used

Summary of Generalized Soil Profiles Used for Analyses

Ingenium Langan Modified Soil Properties

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TABLE 2

SUMMARY OF ANALYSES

MIRABAY COMMUNITY DEVELOPMENT

APOLLO BEACH, FLORIDA

300117702

FSMMAX

(ft-kip/ft)

Tieback 1

Force

(kips)

Tieback 2

Force

(kips)

FSMMAX

(ft-kip/ft)

Tieback 1

Force

(kips)

Tieback 2

Force

(kips)

FSMMAX

(ft-kip/ft)

Tieback 1

Force

(kips)

Tieback 2

Force

(kips)

Baseline (Exisiting

Condition)0.99 2.68 0.9 No tieback 0.99 3.94 1.3 No tieback 1.03 3.53 1.1 No tieback

Option 1 (Rip Rap) 1.03 0.17 0.2 0.7 1.16 1.63 0.3 1.3 1.35 1.19 0.2 1

Option 2 (Knee Wall)Not

Provided

Not

Provided

Not

Provided

Not

Provided

Not

AnalyzedNot Analyzed

Not

Analyzed

Not

Analyzed1.34 1.22 0.2 1

Option 3Not

Provided

Not

Provided

Not

Provided

Not

Provided

Not


Not

Analyzed

Not

Analyzed1.90 2.94 0.9 No tieback

Option 1 ModifiedNot

Provided

Not

Provided

Not

Provided

Not

Provided

Not


Not

Analyzed

Not

Analyzed1.38 1.12 0.4 No tieback

Notes:

(1) Ingenium used Support IT Software Version 2.36 to run their seawall stability analysis; Langan used Shoring Suite Version 8 for their analysis, along with CWALSHT Software.

(2) Baseline conditions analysis uses generalized subsurface conditions at the pilot study test sites.

(3) No additional tiebacks are present at the baseline condition sites.

(4) For Option 2 Ingenium analyzed knee wall stability, not for overall system.

Ingenium - Mirabay Pilot Project Ingenium Reviewed by Langan Langan Modified Seawall Profile

Pilot Study Condition

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FIGURES

GOLF & SEA BOULEVARD

APOLLO BEACH UNIT SIXPLAT BOOK 37, PAGE 88

STR

EE

T X

LEIS

EY RO

AD

WETLAND

PRESERVATION

WETLANDAREA "L"DITCH

WETLANDIMPACTAREA "L"

STR

EE

T L

STR

EE

T K

STR

EE

T M

STREET LSTREET A

STR

EE

T R

WETLANDIMPACT 4(0.02 Ac.)




POND T-4DHW=6.6DLW=6.0NW=4.5

POND T-5DHW=6.4DLW=6.1NW=4.5POND T-6

DHW=6.9DLW=6.5NW=4.5

EXFILTRATIONT-3

EXFILTRATION

POND T-14

EXFILTRATIONPOND T-15


POND T-9A


POND T-9BDHW=6.9

DLW=6.0

NW=4.5

POND T-7DHW=6.7DLW=6.3NW=4.5


Filename: \\langan.com\data\MI\data7\300117702\cadd data - 300117702\sheetfiles\Figure 1 - Site Plan and Vicinity Map.dwg Date: 4/20/2015 Time: 10:58 User: nmojarena Style Table: Langan.stb Layout: FIG1

15150 N.W. 79th Court, Suite 200

Miami Lakes, FL 33016

T: 786.264.7200 F: 786.264.7201 www.langan.com

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15150 N.W. 79th Court, Suite 200

Miami Lakes, FL 33016

T: 786.264.7200 F: 786.264.7201 www.langan.com

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APPENDICES

APPENDIX A

INGENIUM REPORT DATED

25 SEPTEMBER 2014

MIRABAY PILOT PROJECT REPORT

9/25/2014 By: Ingenium, Inc./Carl A. Hazenberg, P.E.

Seawalls along the MiraBay canal system started experiencing problems shortly after construction. Following the issues, litigation took place from 2007 - 2013. As a result of the litigation, recommendations for rock rip rap solutions to stabilize the existing seawalls issues were offered. The goal of pilot project was to examine other possible seawall stabilization solutions for the MiraBay Community. Three solutions were designed, constructed, loaded, and measured for movement on two vacant properties, 5607 Seagrass Pl and 5701 Tybee Island Dr.

MiraBay Pilot Project Report

Page 1

MiraBay Pilot Project Report A S S E S S M E N T O F C O N S T R U C T E D O P T I O N S

Option #1

Involved the use of a pair of rectangular fiberglass wale beams to support the lower part of the existing vinyl

sheet pile. These wale beams were anchored back with a helical screw anchors, which were driven to a

distance sufficient to develop the required holding capacity. Anchor installation torques and pulling capacities

varied significantly due to the varying soil conditions. Rock rip rap was piled up at the base of the seawall to

provide additional stabilization. Maximum slope of the rip rap is 2 horizontal to 1 vertical and has a

horizontal impact of approximately 8 feet in front of the existing seawall.

Typical Section of Option #1


Page 2

Photo of Option #1 from Front

Option #2

Identical to Option #1, with the exception of a vinyl sheet pile “knee” wall. This was installed to intersect the

toe of the rip rap and reduce the horizontal impact waterside of the wall. Sheets were driven 1’ to 1.5’ short

of design depth due to refusal from hard soils. Despite this installation struggle, sufficient stability was still

achieved. Horizontal impact for this option is approximately 4.5 feet and would cause less conflict with water

craft than Option #1.


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Photo of Option #2 (front)

Option #3

This involved driving of new FRP sheet pile directly in front of existing vinyl sheet pile seawall. New concrete

cap was poured at the top to tie the new sheets in with the existing concrete cap and existing deadman

system. New sheet piles were driven approximately 0.5’ short of design penetration due to conflict of

vibratory hammer with existing concrete cap. In spite of this conflict and slightly shorter sheet, sufficient

stability was provided by the dense soils.



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Photo of Option #3

Option #4

A fourth option represents the proposed solution that resulted from past litigation. This option utilizes rock rip

rap placed in front of the existing vinyl sheet pile seawall. The option does not incorporate an earth anchor,

resulting in a larger rip rap footprint. Rock would be piled up at a greater elevation on the wall, and

encroach waterside approximately 12 feet.

Typical Section Option #4


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Observations during Construction

Variability of site soils and the presence of compacted

shell, presented unpredictability when driving of helical

earth anchors. Contractor overtorqued and broke

several anchor shafts while attempting to drive through

lenses of compacted shell. At Seagrass site, contractor

excavated to confirm the presence of shell layer where

anchors were breaking. At the Tybee location one of the

anchors had to be driven longer than the design length

due to very loose soil. Installation of the anchor system

proved to be the most difficult aspect of the project.

Future design and construction should require anchor

flexibility to account for these varying site conditions.

Photo of Helical Earth Anchor Installation

Furthermore, it is worth noting that existing tie-rods

showed signs of corrosion beyond three feet behind the

cap. This is unusual since most tie rods tend to corrode

immediately behind the cap due to greater presence of

oxygen at the ground surface. This may indicate that

soils present are chemically aggressive for typical steel.

However, no measurements were taken for section loss to

determine whether significant structural loss will occur

over the life of the structure.

Anchors, rods, and hardware installed on the pilot project

for options #1 and #2 were treated by a thermal

diffusion galvanization for superior corrosion protection.

Photo of corrosion on existing tie-rod

Loading of Seawall

Timber walls were constructed approximately 5’ behind

the existing seawall. The intent was to simulate segmental

block retaining walls present throughout the community.

These timber walls were filled with compacted sand and

built 6’ tall. This is 25% higher than the 4.75’ high

segmental block walls, and corresponds to a 25% greater

surcharge being applied to the seawall than typically

present. Next, water was pumped immediately within the

backfill areas of both the retaining and seawalls to induce

a full saturated hydraulic load. While impossible to know


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the exact hydraulic loading of the existing seawall throughout the community during heavy rain events, I

estimate the loading applied for the pilot project is 100% to 250% greater than the current seawall normally

experiences.

Also, due to lack of compaction of backfill and presence of voids, much of the water flowed parallel to the

seawall and flowed out at drainage(weep) holes of the seawall on the adjacent property.

Instrumentation

Inclinometers and surveying were performed along the two properties to measure movement along the

seawall. Initial baseline readings were taken prior to construction of the timber retaining wall. Subsequent

measurements for movement were taken after each hydraulic loading. In summary, all of the options

constructed for the pilot project showed little to no movement. The little movement noted in a few

inclinometers, were likely due to voids present in the backfill soils. Survey information along the concrete cap

and front of the sheet pile, showed no appreciable movement of the seawall and coincided with the results

obtained from the inclinometers.


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Photo of inclinometer installation Photo of inclinometers in place (blue)

Conclusion

The pilot project attempted to replicate the primary loading conditions of the existing seawall throughout the

community. However, due to size and variation present within the community, it is impossible to account for all

possible variables that impact the seawall. Therefore, it is vital that as sections of the seawall are stabilized

throughout the community as part of the master seawall stabilization project, that each of these potential

variables are recognized and considered for the implemented design. Nevertheless, construction of a taller

timber retaining wall (6 feet) applied a significant greater load than the segmental block wall of 4.75 feet.

Also, saturation of water behind the seawall and timber retaining wall applies loads far greater than of likely

hydraulic loads present on site. All three options constructed and measured in the field appear to be

acceptable in terms of sufficiency concerning structural capacity and movement.

APPENDIX B

PILOT TEST SITES

SUBSURFACE PROFILES

Documents

REVIEW OF SUBSURFACE INFORMATION 3 SOIL · PDF file20.04.2015 · Peer Review Report Of Seawall Stabilization Options Apollo Beach, Florida Langan Project Number 30017702 ... secondary