EXHIBIT_B-GEOTECH_REPORT.pdf

REPORT OF GEOTECHNICAL ENGINEERING EVALUATION

EROSION CONTROL COUNTERMEASURES WITHIN THE LITTLE WEKIVA RIVER

BETWEEN SR 436 AND SR 434

HURRICANE IAN EWP EROSION CONTROL PROJECTS

Altamonte Springs, Florida

CDM Smith Project No. 288044 GEC Project No. 5344G

Prepared for:

CDM Smith, Inc.

2301 Maitland Center Parkway, Suite 300 Maitland, Florida 32751

Prepared by:

Geotechnical and Environmental Consultants, Inc.

919 Lake Baldwin Lane Orlando, Florida 32814

September 10, 2024

September 10, 2024

CDM Smith, Inc.

2301 Maitland Center Parkway, Suite 300 Maitland, Florida 32751

Attention: Mr. Stephen P. Burwinkel, P.E.

Subject: Report of Geotechnical Engineering Evaluation

EROSION CONTROL COUNTERMEASURES WITHIN THE LITTLE WEKIVA RIVER

BETWEEN SR 436 AND SR 434

HURRICANE IAN EWP EROSION CONTROL PROJECTS

Altamonte Springs, Florida CDM Smith Project No. 288044 GEC Project No. 5344G

Dear Stephen:

Geotechnical and Environmental Consultants, Inc. (GEC) has completed our geotechnical engineering evaluation for the Hurricane Ian NRCS EWP Projects and prepared this report in accordance with our Proposal No. 11390G dated June 16, 2023. The purpose of this study was to explore soil and groundwater conditions along the identified erosion/washout/failure areas and to use the information obtained to provide geotechnical engineering recommendations for design and construction of the proposed erosion/washout repairs and erosion control improvements. This report describes our methodology, documents our field and laboratory test results and presents our recommendations regarding the geotechnical engineering aspects of the project.

GEC appreciates the opportunity to be of service to you on this project. If you have any questions concerning the contents of this report, or if we may be of further assistance, please contact us.

Sincerely, GEOTECHNICAL AND ENVIRONMENTAL CONSULTANTS, INC.

Ryan J. Petersen, E.I. Daniel C. Stanfill, P.E.

Engineer Intern Senior Geotechnical Engineer Florida License No. 42763

This Report has been digitally signed and sealed by Daniel C. Stanfill on the date adjacent to the seal. Printed copies of this document are not considered signed and sealed and the signature must be verified on any electronic copies.

GEC Project No. 5344G ii Report of Geotechnical Engineering Evaluation CDM Smith Project No. 288044 Erosion Control Countermeasures within the Little Wekiva River

TABLE OF CONTENTS

1.0 SITE LOCATION AND DESCRIPTION

2.0 PROJECT DESCRIPTION

3.0 NRCS SOIL SURVEY

4.0 POTENTIOMETRIC MAP DATA

5.0 SUBSURFACE EXPLORATION

6.0 LABORATORY TESTING

7.0 SUBSURFACE CONDITIONS

7.1 Subsurface Profile

7.2 Groundwater Levels

8.0 DESIGN RECOMMENDATIONS

8.1 Steel Sheet Pile

8.2 Concrete Endwall

8.3 Articulated Concrete Block Mattress Slope Stabilization

8.4 Gabion Baskets/Mattress

9.0 CONSTRUCTION RECOMMENDATIONS

9.1 General Site Preparation

9.2 Fill Selection, Placement and Compaction

9.3 Foundation Subgrade Preparation

9.4 Temporary Excavations

9.5 Noise and Vibration Monitoring

10.0 REPORT USE AND LIMITATIONS

FIGURES

Figures 1.1 – 1.7: USGS Quadrangle and NRCS Soil Survey Maps Figures 2.1 – 2.4: Site Locations with Boring and Muck Probe Results

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TABLES

Table 1: Summary of Ground Surface Elevations Table 2: Summary of NRCS Soil Survey Units Table 3: Summary of Potentiometric Surface of the Floridan Aquifer Table 4: Site Exploration Summary Table 5: Summary of Laboratory Testing Program Table 6: Soil Stratigraphy Table 7: Summary of Analyses for Sheet Pile Retaining Wall Table 8: Summary of Slope Stability Analyses for Sheet Pile Retaining Wall Table 9: Summary of Slope Stability Analyses for Cantilever Retaining Headwall Table 10: Summary of Slope Stability Analyses for ACB Mattress Slope Stabilization Table 11: Recommended Soil Parameters for Slope Stabilization Design ...................................... A Table 12: Gabion Basket External Stability Analyses Results ......................................................... B

APPENDIX

APPENDIX A FIELD EXPLORATION METHODS

A.1 Standard Penetration Test Borings A.2 Dynamic Cone Penetrometer A.3 Groundwater Measurement A.4 Manual Muck Probes

APPENDIX B DESIGN CALCULATIONS

Site No.1 Site No. 2 Site No. 3 Site No. 4

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1.0 SITE LOCATION AND DESCRIPTION

The project includes the design and construction of erosion/washout repairs and erosion control improvements at 4 sites in Seminole County along the Little Wekiva River which were impacted during Hurricane Ian. The 4 project site locations evaluated as part of the geotechnical study are depicted on Figures 1 to 2.4 in the Appendix and are summarized as follows:

• Site No. 1: This site is located along the Little Wekiva River in Altamonte Springs at the end of a drainage easement off Little Wekiva Circle between 727 and 729 Little Wekiva Circle. The site is located along the northern riverbank. There is an existing sheet pile wall that functions as a headwall for the drainage pipe located within the easement that is failing. The site begins at approximate station 16+30 and continues to station 16+85.

• Site No. 2: This site is located along the Little Wekiva River in Altamonte Springs at the end of a drainage easement between 703 and 705 Little Wekiva Road. The site is located along the eastern riverbank. The drainage pipe outfall is exposed, and an adjacent sheet pile wall is failing from erosion. The site begins at approximate station 30+55 and continues to station 30+95.

• Site No. 3: This site is located along the Little Wekiva River in Altamonte Springs at the end of a drainage easement between 523 and 525 San Sebastian Prado. The site is located along the southern riverbank. The riverbank has been eroded and is exposing a drainage pipe outfall. The site begins at approximate station 40+05 and continues to station 40+25.

• Site No. 4: This site is located along the Little Wekiva River in Altamonte Springs at the bridge crossing of the Seminole Wekiva Trail. The site is located along the eastern and western river banks. The existing gabion baskets, mattress and associated weir have been damaged. The site begins at approximate station 12+50 and continues to station 13+10.

GEC reviewed the United States Geological Survey (USGS) Forest City, Quadrangle maps, shown on Figure 1, and project topographic survey data obtained by CDM Smith at the project sites. A summary of the ground surface elevations at the project sites are included in the following table:

Table 1: Summary of Ground Surface Elevations

Site No.

Top Of Bank Ground Surface Elevation Range

(NAVD88)

Channel Bottom Ground Surface Elevation Range

(NAVD88)

1 +49 to +50 +36 to +37 2 +46 to +48 +34 to +35 3 +45 to +46 +32 to +34 4 +47 to +50 +37 to +40

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2.0 PROJECT DESCRIPTION

We understand the project includes the design and construction of erosion/washout repairs and erosion control improvements at the 4 sites discussed in Section 1.0. The following summarizes our review of the project plans and the proposed erosion control countermeasures:

• Site No. 1:

o Current plans (dated February 2024) show proposed improvements including replacement of the sheet pile wall beginning at station 16+40 and continuing to Station 16+70 with a wall top elevation of +49.0 and removal of the existing failed sheet pile wall. Preliminary plans also show regrading in front of the sheet pile wall to include a 1:2.5 (v:h) slope with rubble riprap.

• Site No. 2:

o Current plans (dated December 2023) show proposed improvements including the construction of a concrete headwall around the existing outfall pipe. Preliminary plans also show the wall approximately 34 feet long.

• Site No. 3:

o Current plans (dated December 2023) show proposed improvements including the placement of a 10 feet by 20 feet articulated concrete block (ACB) matting around the existing outfall pipe. Preliminary plans show the ACB matting being placed at a 1:1.5 (v:h) slope.

• Site No. 4:

o Current plans (dated December 2023) show proposed improvements including the removal and replacement of the damaged gabion baskets, mattress and weir structures.

If any of the above project information is incorrect, please notify us so that we can evaluate whether the changes in design affect our recommendations.

3.0 NRCS SOIL SURVEY

The Natural Resources Conservation Service (NRCS) Soil Survey of Seminole County, Florida was reviewed for near-surface soil and groundwater information. The NRCS Soil Survey map at each project site is shown on Figure 1. The soils in the vicinity of the project sites are summarized in Table 2.

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Table 2: Summary of NRCS Soil Survey Units

Soil Unit No. Soil Name

Depth (inches) Soil Description

Unified Classification

Symbol

Depth to Seasonal High Groundwater

(feet) Hydrologic

Group

28 Pompano fine sand, occasionally flooded 0 – 80 Fine sand, sand SP-SM, SP 0 – 1.0 A/D

34 Urban land, 0 to 2 percent slopes --- --- --- --- ---

In general, the soils depicted on NRCS soil survey map at the project sites are generally classified as fine sands (SP, SP-SM). The NRCS predicts seasonal high groundwater levels for these soil types to generally range from at the ground surface to 1 foot below the natural ground surface.

Urban Land refers to areas where most of the ground surface is covered by asphalt, concrete, buildings and other impervious surfaces that modify surface/subsurface drainage and obscure or alter the soils so that their identification is not possible. The depth to seasonal high groundwater level for this soil unit is typically dependent upon the functioning of existing drainage systems.

Information contained in the NRCS Soil Survey is very general and may be outdated. Therefore, it may not be reflective of actual soil and groundwater conditions, particularly if recent development in the site vicinity has modified soil conditions or surface/subsurface drainage. The information obtained from recent soil borings provides a better characterization of actual site conditions.

4.0 POTENTIOMETRIC MAP DATA

Artesian groundwater conditions can be predicted based on comparison of the Floridan aquifer potentiometric surface and ground surface elevations. A summary of the potentiometric surface elevation of the Floridan aquifer at the project sites based on review of the Florida Department of Environmental Protection (FDEP) web map entitled Upper Floridan Aquifer Potentiometric Surface Contours, September, 2019 (the most recent map available) is included in the following table:

Table 3: Summary of Potentiometric Surface of the Floridan Aquifer

Site No.

Approximate Potentiometric

Surface Elevation

(NAVD88)

Ground Surface Elevation Range

(NAVD88)

1 +48 +49 to +50 2 +48 +46 to +48

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Site No.

Approximate Potentiometric

Surface Elevation

(NAVD88)

Ground Surface Elevation Range

(NAVD88)

3 +48 +45 to +46 4 +48 +47 to +50

Since the potentiometric surface is within potential excavation depths when compared to existing ground surface at the sites, artesian flow conditions are possible if a confining layer is breached and should be anticipated.

Artesian conditions were not encountered in our soil borings. However, our drilling operations required the use of high-density drilling mud which could potentially obscure the effect of artesian conditions during drilling. The contractor should be prepared to handle artesian levels up to the approximate Potentiometric surface elevation listed in the table above for each site.

5.0 SUBSURFACE EXPLORATION

In addition to consulting published sources, GEC conducted an exploration of each project site to evaluate subsurface conditions. Our field exploration is summarized in Table 4. Please refer to Appendix A for a description of the field exploration methods used for this investigation.

Table 4: Site Exploration Summary

Site No. 1Exploration Method Quantity Boring

No.

Depth Explored

(feet) Figure

No.

SPT Borings 1 SPT1-2 40 2.1

Manual Probes 5 --- --- 2.1

SPT Borings 1 SPT2-1 30 2.2

Manual Probes 11 --- --- 2.2

SPT Boring 1 SPT3-1 30 2.3

Manual Probes 9 --- --- 2.3

SPT Borings 1 SPT4-1 45 2.4

DCP Test Borings 1 SPT4-2 5 2.4 Manual Probes 9 --- --- 2.4

1. SPT = Standard Penetration Test; DCP = Dynamic Cone Penetration

The locations of the field activities listed in Table 2 are shown on the site plans in Figures 2.1 to

2.4. These locations were estimated by using a handheld, sub-meter accuracy Global Positioning System (GPS) unit.

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6.0 LABORATORY TESTING

Selected soil samples retrieved from the borings were tested in accordance with Florida Standard Testing Methods (FM), American Association of State Highway Transportation Officials (AASHTO) testing methods and American Standard Testing Methods (ASTM). Our laboratory testing program is summarized on the following table:

Table 5: Summary of Laboratory Testing Program

Test Test No.

Grain Size Analysis AASHTO T88

Atterberg Limits AASHTO T89/90 Organic Content FM 1-T267

Natural Moisture Content AASHTO T265

The results of our laboratory tests are shown adjacent to the soil profiles on the Soil Boring Result sheets Figures 2.1 to 2.4 in the Appendix.

7.0 SUBSURFACE CONDITIONS

GEC’s field exploration was conducted from December 13, 2023 to December 19, 2023. The soil and groundwater conditions encountered are summarized in this section. Please refer to Figures

2.1 through 2.4 for a detailed description of the subsurface profile at each boring location shown on Figures 2.1 through 2.4. Manual muck probe results are depicted on Figures 2.1 through 2.4.

7.1 Subsurface Profile

The descriptions and stratum numbers used for the encountered soils are summarized as follows:

Table 6: Soil Stratigraphy

Stratum No.

Unified Classification

Soil Description

1 SP Light Brown Fine Sand 2 SP-SM Light Brown to Brown Fine Sand With Silt With Occasional Trace Rock

3 SM

Light Brown to Brown To Dark Brown Silty Fine Sand With Occasional Trace

Rock, Cemented Sand And Phosphate

4 SC, CL

Grey to Light Brown Clayey Fine Sand to Sandy Lean Clay With Occasional

Trace Rock And Cemented Sands 5 PT Dark Brown Mucky Fine Sand

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7.1.1 Site No. 1 Subsurface Conditions

In general, the boring performed at Site No. 1 (SPT1-2) encountered loose to medium dense fine sand (SP)(Stratum 1) to fine sand with silt (SP-SM)(Stratum 2) to a depth of 28 feet underlain by loose to medium dense silty fine sand (SM)(Stratum 4) to the maximum boring termination depth of 40 feet. A notable exception to this profile was 1 foot of surficial mucky fine sand (PT)(Stratum

5) that was encountered in this boring.

The manual probes performed in the Little Wekiva River encountered water depths ranging from

1.5 to 3.0 feet, no surficial muck and loose sand sediment ranging from 0.0 to 0.5 feet in thickness. Areas of surficial and buried rubble/rocks were encountered in the channel bottom at the site as depicted on Figure 2.1.

7.1.2 Site No. 2 Subsurface Conditions

In general, the boring performed at Site No. 2 (SPT2-1) encountered loose fine sand with silt (SP- SM)(Stratum 2) to a depth of 18.5 feet underlain by loose to clayey fine sand (SC)(Stratum 4) to the maximum boring termination depth of 30 feet. A notable exception to this profile was that the clayey fine sand layer became dense at a depth of 30 feet.

The manual muck probes performed in the Little Wekiva River encountered water depths ranging from 0.5 to 5.0 feet, no surficial muck and loose sand sediment ranging from 1.5 to 4.0 feet in thickness at the site as depicted on Figure 2.2.

7.1.3 Site No. 3 Subsurface Conditions

In general, the boring performed at Site No. 3 (SPT3-1) encountered loose to medium dense fine sand (SP)(Stratum 1) to fine sand with silt (SP-SM)(Stratum 2) to silty fine sand (SM)(Stratum 3) to the maximum boring termination depth of 30 feet.

The manual muck probes performed in the Little Wekiva River encountered water depths ranging from 1.0 to 4.0 feet, no surficial muck and loose sand sediment ranging from 0.0 to 2.5 feet in thickness. Areas of rubble/rocks were encountered in the channel bottom as depicted on Figure 2.3.

7.1.4 Site No. 4 Subsurface Conditions

In general, the borings performed at Site No. 4 (SPT4-1, SPT4-2) encountered medium dense fine sand (SP)(Stratum 1) to fine sand with silt (SP-SM)(Stratum 2) to the maximum boring termination depth of 45 feet. A notable exception to this profile was a layer of very loose clayey fine sand to

GEC Project No. 5344G 7 Report of Geotechnical Engineering Evaluation

Little Wekiva River sandy lean clay (SC, CL)(Stratum 4) encountered from depths ranging from 39 to 44 feet below the ground surface.

The manual muck probes performed in the Little Wekiva River encountered water depths ranging from 0.5 to 2.0 feet, no surficial muck and loose sand sediment ranging from 0.0 to 0.5 feet in thickness. The existing gabion mattress were encountered in the channel bottom as depicted on Figure 2.4.

7.2 Groundwater Levels

Groundwater was not encountered within the top 10 feet at the boring locations, which is indicated as “GNE” to 10 feet on the boring profile.

Groundwater levels can vary seasonally and with changes in subsurface conditions between boring locations. Alterations in surface and/or subsurface drainage brought about by site development can also affect groundwater levels. Change in the water elevation in the rivers/creek/canals will also affect groundwater levels.

8.0 DESIGN RECOMMENDATIONS

The conclusions and recommendations contained in this report are based in part on the data obtained from a limited number of soil samples and the groundwater measurements obtained from widely-spaced borings. The sampling methods used indicate subsurface conditions only at the specific boring locations where samples were obtained, only at the time they were obtained, and only to the depths penetrated. Borings cannot be relied upon to accurately reflect the variations that usually exist between boring locations and these variations may not become evident until construction.

If variations from the subsurface conditions described in this report do become evident during construction or if the project characteristics described in this report change, GEC should be retained to reevaluate this report’s conclusions and recommendations in light of such changes.

We also recommend that GEC be allowed to review the construction plans prior to bidding so that we can verify that our recommendations were properly interpreted.

8.1 Steel Sheet Pile

We understand that a sheet pile retaining wall is the proposed creekbank stabilization alternative for Site No. 1. GEC utilized the typical sheet pile wall geometry depicted on the cross sections from the project plans and the subsurface data obtained at the boring locations for evaluation of the global stability of the sheet pile wall supported creekbank.

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GEC utilized the program CWalsht (Version XX) to evaluate the sheet pile wall deflection. The soil parameters utilized in our analyses are summarized in Table 11 in the Appendix. The following table summarizes the calculated minimum factors of safety for global stability of the retaining wall:

Table 7: Summary of Analyses for Sheet Pile Retaining Wall

Site No. Station Limits

Sheet Pile Section Backslope

(V:H)

Exposed Wall Height

(ft) Embedment

(ft)

Maximum Deflection

(in)

Minimum Factor of Safety 1 16+40 to 16+70 PZ27 1:4 9.0 24 3.35 1.53

GEC utilized the FDOT approved software, GEO5 (Version 2023.77) – Retaining Wall, to evaluate the global stability of the sheet pile wall supported creekbank using soil parameters developed from our borings. The soil parameters utilized in our analyses are summarized in Table 11 in the Appendix. The following table summarizes the calculated minimum factors of safety for global stability of the retaining wall:

Table 8: Summary of Slope Stability Analyses for Sheet Pile Retaining Wall

Site No.

Slope Stabilization Alternative Station Limits

Backslope (V:H)

Exposed Wall Height

(ft) Embedment

(ft)

Minimum Factor of Safety 1 Sheet Pile Wall 16+40 to 16+70 1:4 9.0 24 2.37

Based on the results of our analyses the calculated minimum factors of safety for sheet pile wall design and global stability exceeded the minimum requirements of 1.5.

Weep holes should be placed above the normal high water elevation of the Little Wekiva River and should be evenly spaced on approximately 5-foot centers to prevent build-up of hydrostatic pressure behind the sheet pile walls. GEC assumed a weep hole elevation of +42 feet NAVD88.

Place filter fabric at all weep holes to prevent soil loss.

Due to the proximity of the proposed sheet pile retaining wall to adjacent residential structures there are concerns regarding both vibration and noise generated by driving the sheet pile wall sections. It is recommended that the pile driving method be limited to hydraulic press-in method as vibratory or impact hammers have the potential to generate noise and vibration levels exceeding acceptable tolerances for the adjacent residential structures and may result in structural damage to the residential buildings. A specialty hydraulic press-in sheet pile contractor

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Little Wekiva River should be consulted regarding the feasibility of installation considering the vertical and horizontal access limitations of the project site.

If the site is deemed inaccessible to the equipment utilized for hydraulic press-in other alternatives to limit vibrations and noise associated with the sheet pile installation include preforming of the pile holes. Reduced skin friction should be considered in the design of the sheet pile walls if preforming is specified as detailed in Table 11 in the Appendix. In addition, after installation of the sheet pile the preformed pile holes should be grouted from the bottom of the preform hole to the bottom of the drainage stone layer behind the sheet pile wall. Use grout that meets the requirements of FDOT Standard Specifications 455-40 to 455-42.

Additional recommendations for noise and vibration monitoring during construction are included in Section 9.0 of this Report.

8.2 Concrete Endwall

A concrete endwall is the proposed riverbank stabilization alternative for Site No. 2. GEC utilized the typical geometry depicted on the plans provided by CDM Smith and the subsurface data obtained at the boring locations.

GEC utilized the FDOT approved software, GEO5 (Version 2023.74) – Cantilever. This program implements the USA–LRFD design methodology and was utilized to analyze the proposed gabion baskets for overturning, slip/sliding, eccentricity, and bearing capacity. The analyses assumed only Strength I Limit State Load and Resistance Factors of the AASHTO LRFD Bridge Design Specifications.

The minimum design criteria for verification of overturning, slip/sliding, eccentricity, and bearing capacity and the minimum factor of safety for global stability required by LRFD are as follows:

• Overturning Resisting Moment (Mresisting) > Overturning Moment (Moverturning)

• Slip/Sliding Resisting Horz. Force (Hresisting) > Acting Horiz. Force (Hacting)

• Eccentricity Allowable Eccentricity (eallowable) > Max. Eccentricity €

• Bearing Capacity

• Global Stability

Factored Bearing Capacity of Soil (Rd) > Max. Stress (σfooting bottom) Factor of Safety > 1.3

The soil parameters utilized in the analyses are summarized on Table 11 in the Appendix. The following table summarizes the calculated minimum factors of safety for global stability of the retaining wall:

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Table 9: Summary of Slope Stability Analyses for Cantilever Retaining Headwall

Site No. Station Limits Wall Type

Wall Geometry Minimum Factor of Safety Toe Length

(ft) Heel Length

(ft) Key Depth

(ft)

2 30+60 to 30+95

FDOT Index 430-032

1.33 3.08 2 1.14

Modified FDOT Index 430-032

2 8 4 1.3

The results of our analyses are based on the geometry and soil parameters included in the Appendix for each critical section. If actual parameters vary from those assumed, GEC should be notified immediately to reevaluate this report’s conclusions and recommendations.

8.3 Articulated Concrete Block Mattress Slope Stabilization

We understand that articulated concrete block (ACB) mattress is the proposed slope stabilization alternatives for Site No. 3. GEC utilized the typical ACB mattress geometry depicted on the cross sections from the project plans and the subsurface data obtained at the boring locations for evaluation of the global stability of the stabilized slopes.

GEC utilized the FDOT approved software, GEO5 (Version 2023.56) – Slope Stability, to evaluate the global stability of the channel slope with the proposed slope stabilization using soil parameters developed from our borings. The soil parameters utilized in our analyses are summarized in Table 11 in the Appendix. The following table summarizes the calculated minimum factors of safety for global stability of the project slopes:

Table 10: Summary of Slope Stability Analyses for ACB Mattress Slope Stabilization

SIte No.

Slope Stabilization

Alternative Station Limits Slope (V:H)

Minimum Factor of Safety

Minimum Factor of Safety ≥ 1.3

Articulated

Concrete Block Mattress

14+13 to 14+23 1:1.5 1.39 Yes

Based on the results of our global stability analyses a maximum slope of 1:1.5 is recommended for installation of the ACB mattress for Site No. 3 in order to meet the recommended minimum factor of safety of 1.3. The results of our global stability analyses are included in the Appendix.

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Recommendations regarding general site preparation and fill placement and compaction are included in the subsections of Section 9 of this Report. The following are additional construction and design recommendations for the proposed rubble rip-rap / gabion mattress slope stabilization:

• A filter fabric should be placed between the ACB mattress and the granular backfill/in-situ soils to prevent soil migration.

• The ACB mattress should be installed per the manufacturers specification and be tied in at the top and toe of slope.

8.4 Gabion Baskets/Mattress

Gabion basket walls are the proposed riverbank stabilization alternative for Site No. 4. GEC utilized the typical gabion basket geometry depicted on the plans provided by CDM Smith and the subsurface data obtained at the boring locations.

GEC utilized the FDOT approved software, GEO5 (Version 2023.74) – Gabion. This program implements the USA–LRFD design methodology and was utilized to analyze the proposed gabion baskets for overturning, slip/sliding, eccentricity, and bearing capacity. The analyses assumed only Strength I Limit State Load and Resistance Factors of the AASHTO LRFD Bridge Design Specifications.

The minimum design criteria for verification of overturning, slip/sliding, eccentricity, and bearing capacity and the minimum factor of safety for global stability required by LRFD are as follows:

• Overturning Resisting Moment (Mresisting) > Overturning Moment (Moverturning)

• Slip/Sliding Resisting Horz. Force (Hresisting) > Acting Horiz. Force (Hacting)

• Eccentricity Allowable Eccentricity (eallowable) > Max. Eccentricity €

• Bearing Capacity

• Global Stability

Factored Bearing Capacity of Soil (Rd) > Max. Stress (σfooting bottom) Factor of Safety > 1.5

The geometry and limits of the proposed gabion baskets and the results of the analyses are summarized on Table 12 in the Appendix. The soil parameters utilized in the analyses are summarized on Table 11 in the Appendix.

The results of our analyses are based on the geometry and soil parameters included in the Appendix for each critical section. If actual parameters vary from those assumed, GEC should be notified immediately to reevaluate this report’s conclusions and recommendations.

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Recommendations regarding general site preparation, fill placement and compaction and foundation subgrade preparation are included in the subsections of Section 9 of this Report. The following are additional construction and design recommendations for the proposed gabion retaining walls:

• A filter fabric should be placed between the gabion basket retaining wall and the granular backfill/in-situ soils to prevent soil migration.

• Recommend placement of rip-rap, ACB mat or extension of the gabion basket mattress layer across the channel bottom to prevent scour and undermining of the gabion wall foundation material.

• We recommend the wall manufacturer review the gabion basket design parameters utilized in GEC’s analyses for conformance with the proposed gabion basket system provided by the manufacturer.

• Gabion rock, baskets and other miscellaneous components of installation should meet the requirements of FDOT Standard Specification 530-2.3.

9.0 CONSTRUCTION RECOMMENDATIONS

The following sections of this report include comments on issues related to the geotechnical aspects of the proposed construction. These recommendations are not intended to dictate construction methods or sequences. Instead, they are furnished as an aid to design professionals and to identify important construction issues related to foundation and earthwork plans and specifications. These recommendations may also be useful to personnel who observe construction activity.

Prospective contractors for this project should evaluate potential construction problems on the basis of their review of the contract documents, their own knowledge and experience in the local area, and on the basis of similar projects in other localities, taking into account their own proposed methods and procedures.

9.1 General Site Preparation

Our recommendations regarding routine site preparation of the slope stabilization areas can be summarized as follows:

• Remove all concrete, asphalt, rubble, vegetation and organic topsoil, major root systems, buried utilities, sprinkler systems and other deleterious materials from beneath and to a minimum of 5 feet beyond the proposed structure limits.

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• Leave existing sheet pile walls in place to avoid disturbing subsurface soils. Cut off existing sheet pile wall a minimum of 2 feet below grade or foundation whichever is greater.

• Standard clearing, grubbing, and topsoil stripping procedures should be appropriate for the sites.

• Perform temporary dewatering as required to achieve proper site preparation, fill placement and compaction. Temporary diversion of the water flow in the river/creek/canal bottom will be required to facilitate installation of gabion walls and channel bottom erosion systems.

9.2 Fill Selection, Placement and Compaction

Soils encountered in the borings appear suitable for use as structural fill. We recommend that all fill be selected, placed and compacted as follows:

• Use fill material comprised of non-plastic sands with less than about 12% fines content.

The fill should not contain any significant amount of organic substances (less than 5% by weight) and should be substantially free from roots or other organic or deleterious materials.

• Our borings encountered sands with varying silt content (SP, SP-SM) which appear suitable for use as fill. Sands excavated above the water table may have to be wetted to attain the moisture content needed to achieve the required degree of compaction.

• Silty or clayey sands (SM, SC) may be exposed at the compaction surface during site preparation. These soils can be unstable during compaction if they contain excess moisture. The contractor should be prepared to manipulate the moisture content of unstable subgrade soils as necessary to achieve stability and compaction requirements.

• Place fill in level lifts no thicker than 12 inches. Thinner lifts may be needed to achieve compaction in the silty sands.

• Compact fill to a minimum of 95% of the soil's modified Proctor maximum dry density as determined by ASTM D-1557 for each lift of fill placed.

• Allow an Engineering Technician, working under the direction of a registered Geotechnical Engineer, to perform in-place density tests to verify that the recommended degree of compaction has been achieved.

• Provide fill slopes no steeper than 1.5 horizontal to 1 vertical.

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• Compact fill placed in utility trenches to the specifications stated above. However, in restricted working areas, compact fill with lightweight, hand-guided compaction equipment and limit lift thicknesses to a maximum of 6 inches.

• All excavations, including utility trenches, should comply with the recommendations included in the Temporary Excavations section of this report.

9.3 Foundation Subgrade Preparation

We recommend the following steps be taken during excavation and subgrade preparation associated with gabion wall construction:

• Excavate foundations in accordance with the recommendations presented in the Temporary Excavations section of this report.

• Compact subgrade soils to a depth of 12 inches below the bearing elevations to a minimum of 95% of the soil's modified Proctor maximum dry density as determined by

ASTM D-1557.

• Perform in-place density tests to verify foundation subgrade compaction.

• Allow a Geotechnical Engineer, or his representative, to observe footing excavation conditions prior to placement of reinforcing steel or concrete.

• On the basis of the Geotechnical Engineer's observations, remove any unsuitable material encountered in the foundation excavations and replace with sand selected and compacted in accordance with the Fill Selection, Placement and Compaction section of this report.

9.4 Temporary Excavations

The owner and the contractor should be familiar with local, state and federal safety regulations, including current Occupational Safety and Health Association (OSHA) excavation and trench safety standards. Construction site safety is the responsibility of the contractor. The contractor should also be responsible for the means, methods, techniques, sequences, and operations of the construction.

The contractor should be aware that slope height, slope inclination, and excavation depths (including utility trench excavations) should not exceed those specified in local, state, or federal safety regulations; e.g., OSHA Health and Safety Standards for Excavations, 29 CFR Part 1926.

OSHA regulations are strictly enforced and, if not followed, the owner, contractor, earthwork subcontractor or utility subcontractor could be liable for substantial penalties.

GEC Project No. 5344G 15 Report of Geotechnical Engineering Evaluation

Little Wekiva River

The soil encountered in the borings performed by GEC at this site is primarily sand with varying amounts of silt. We anticipate that OSHA will classify these materials as Type C. OSHA recommends a maximum temporary slope inclination of 1.5 horizontal to 1 vertical for this soil type. Soils encountered in the construction excavations may vary significantly across the site.

Our soil classifications are based on the materials encountered in widely-spaced borings. The contractor should verify that similar conditions exist throughout the proposed excavation area.

If different subsurface conditions are encountered at the time of construction, GEC should be contacted immediately to evaluate the conditions encountered.

9.5 Noise and Vibration Monitoring

Existing structures may be affected by vibrations caused by the sheet pile installation and construction of the proposed improvements. To evaluate the existing conditions of the structures, GEC recommends a full preconstruction survey of the adjacent residential structures be performed. This includes documenting and photographing existing cracks and irregularities and obtaining floor elevations at each structure. Prior to the installation of the sheet pile, vibration monitors should be installed. In addition, any cracks observed during the preconstruction survey should be outfitted with crack monitors. The crack monitors should be observed at regular intervals during the entire sheet pile installation. If movement is observed at any of the monitoring devices or vibrations exceed acceptable limits, all operations should stop and the engineer of record should be notified immediately.

10.0 REPORT USE AND LIMITATIONS

This section of the report presents important information regarding the proper use of this report, our investigative methods and the limitations of this study. The test data, conclusions and recommendations presented in this report should be reviewed and applied with these limitations in mind.

Subsurface Variability. The analyses and recommendations contained in this report are based in part on the data obtained from a limited number of soil samples and groundwater measurements obtained from widely-spaced borings. The sampling methods used indicate subsurface conditions only at the specific boring locations where samples were obtained, only at the time they were obtained, and only to the depths penetrated. Borings cannot be relied upon to accurately reflect the variations that usually exist between boring locations and these variations may not become evident until construction. Conditions at the boring locations can change over time. Groundwater levels fluctuate seasonally, and soil conditions can be altered by earthmoving operations.

GEC Project No. 5344G 16 Report of Geotechnical Engineering Evaluation

Little Wekiva River

Manual Probes. Manual muck probes were performed by pushing a slender metal rod into the surficial soil and evaluating the relative resistance of the soil to manual penetration. Highly organic soils, such as muck and/or peat, are characteristically very soft and will easily yield to the manual probe. Manual probes, however, cannot detect peat or muck layers which are present beneath layers of sand or dense soils which cannot be penetrated by the probe. The probes can also penetrate to some extent in very loose sands which may be present beneath peat or muck layers. No soil samples are obtained for visual examination or laboratory testing when using this exploratory technique. The soil type being penetrated is inferred solely by evaluating the relative resistance of the soil to penetration. These limitations can lead to some under-estimation or over-estimation of peat or muck layer thicknesses. The probe data presented in this report should be evaluated with these limitations in mind.

Soil Stratification. The depths and thicknesses of the subsurface strata indicated on the boring logs were interpolated between samples obtained at different depths in the borings. The actual transition between soil layers may be different than indicated. These stratification lines were used for our analytical purposes. Earthwork quantity estimates based on the results of the borings will vary from the actual quantities measured during construction.

Groundwater Measurements. Groundwater levels can vary seasonally and with changes in subsurface conditions between boring and/or piezometer locations. Alterations in surface and/or subsurface drainage brought about by site development can also affect groundwater levels. Therefore, groundwater depths measured at different times or at different locations on the site can be expected to vary from those measured by GEC during this investigation.

Groundwater Predictions. For purposes of this report, estimated seasonal high groundwater levels are defined as groundwater levels that are anticipated at the end of the wet season during a “normal rainfall” year under pre-development site conditions. We define a “normal rainfall” year as a year in which rainfall quantity and distribution were at or near historical averages.

Construction Variations. If variations from the subsurface conditions described in this report do become evident during construction, GEC should be retained to reevaluate this report's conclusions and recommendations, and modify the recommendations included in this report, if needed, in light of such changes.

Plans/Specifications Review. GEC should be provided with the construction plans and specifications prior to bidding so that we can verify that the recommendations presented in this report were correctly interpreted and incorporated into the plans and specifications. The recommendations in this report were not written in specification language and are not intended to be used verbatim as a part of the plans and specifications. This report should not be wholly incorporated into the project contract documents.

GEC Project No. 5344G 17 Report of Geotechnical Engineering Evaluation

Little Wekiva River

Design Changes. The conclusions or recommendations of this report should be disregarded if the nature, design, or location of the facilities is changed. If such changes are contemplated, GEC should be retained to review the new plans to assess the applicability of this report in light of the proposed changes.

Contamination Exclusion. The sole purpose of the borings performed by GEC at this site was to obtain indications of subsurface conditions as part of a geotechnical exploration program. GEC has not evaluated the site for the potential presence of contaminated soil or groundwater, nor have we subjected any soil samples to analysis for contaminants.

Report Reliance. GEC has prepared this report for the exclusive use of our client, CDM Smith, and The City of Altamonte Springs and for specific application to this project. GEC is not responsible for any third party’s interpretation or use of this report’s subsurface data, engineering analysis or recommendations without our written authorization.

Standard of Care. GEC has performed the services described in this report in a manner consistent with that level of care and skill ordinarily exercised by members of our profession currently practicing in Central Florida. No other representation is made or implied in this document.

GEC Project No. 5344G A Report of Geotechnical Engineering Evaluation

FIGURES

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T:\J5344G Altamonte Springs Little Wekiva River Repairs_CDM Smith\7 CADD Files\ArcGIS\5344G QUAD.mxd 2/1/2024

FIGURE

NO.LITTLE WEKIVA RIVER

EROSION CONTROL

USGS QUADRANGLE AND

NRCS SOIL SURVEY MAPS 1

919 LAKE BALDWIN LANE

ORLANDO, FL. 32814

DANIEL C. STANFILL, P.E.

P.E. LICENSE NUMBER 42763

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GEC Project No. 5344G A Report of Geotechnical Engineering Evaluation

TABLES

Table 11: Recommended Soil Parameters for Slope Stabilization Design

Table 11 Summary of Recommended Soil Parameters for Design

Erosion Control Countermeasures within Little Wekiva River GEC Project No. 5344G

Description

Friction Angle (deg)

Cohesion (psf)

Moist Unit Weight

(pcf)

Saturated Unit Weight

(pcf)

1Encountered Ground Water

Elevation

(NAVD88)

Estimated Seasonal High Groundwater

Elevation

(NAVD88)

Basket Fill Unit Weight

(pcf)

Basket Fill Friction Angle

(deg)

Nominal Bearing Capacity

(psf)

LRFD Bearing Capacity Factor

Factored Allowable

Bearing Capacity

(psf) 0 - 28 Loose Sand 29.5 0 100 105

28 - 40 Loose Silty Fine Sand 30 0 105 110 0 - 18 Loose Sand 29 0 100 105

18 - 27 Loose Clayey Sand 29 0 100 105 27 - 30 Dense Clayey Sand 32 0 110 115

3 40+14 to 40+24 SPT3-1 0 - 30 Loose sand 29 0 100 105 +35.2 --- --- --- --- --- --- 0 - 8 Loose Sand 29 0 100 105

8 - 39 Medium Dense Sand 33 0 115 120 39 - 44 Soft Clayey Sand 0 250 100 105 44 - 45 Loose to Medium Dense Sand 30 0 105 110

Notes:

1. Soil Borings did not encounter groundwater within the top 10 feet. Groundwater elevations recorded from top of water survey elevations from the project topographic information.

30+60 to 30+95 SPT2-1 --- ---+37.2 ---

1 12+60 to 13+55 SPT1-2 +38.8 ---

Site No. Station Boring No.

Depth

(ft)

Gabion Basket Design ParametersSoil Parameters Water Levels

0.45 22504 40+25 to 42+00 B4-1, B4-2 +38.8 --- 105 40 5000

Table 12: Gabion Basket External Stability Analyses Results

Table 12 Gabion Basket External Stability Analyses Results

Erosion Control Countermeasures within Little Wekiva River GEC Project No. 5344G

Description

Minimum Embedment

Depth

(ft) 1Layer No.

Width (ft)

Height (ft)

Offset

(ft) Overturning Slip/Sliding Eccentricity Bearing Capacity

4 3.0 3.0 1.5 3 4.5 3.0 1.5 2 6.0 3.0 1.5 1 7.5 3.0 1.5

Notes

1. Layers are numbered from the bottom gabion basket to the top.

Satisfactory Satisfactory Satisfactory Satisfactory Acceptable4 12+45 to 13+10 9 Concept 3.5

Site No.

Approximate Station Limits

Unsupported Wall Height

(ft)

Design Criteria Verification

Global Stability

Gabion Basket Geometry iii

APPENDIX A

FIELD EXPLORATION METHODS

A. FIELD EXPLORATION METHODS

A.1 Standard Penetration Test Borings

Standard Penetration Test (SPT) borings were drilled in general accordance with ASTM Standard D1586. The boreholes were advanced by the rotary wash method with bentonite-based mud used as the circulating fluid to help remove cuttings and stabilize the borehole. Casing was used as necessary to further stabilize the borehole and prevent loose surficial sands from raveling into the lower more stable portions of the borehole. GEC’s field crew obtained SPT samples continuously in the borings to a depth of 10 feet and at 5-foot depth intervals thereafter.

However, Borings SPT 1-2 and SPT 4-1 were hand augered the initial 6 feet to avoid damaging underground utilities. A GEC engineering technician supervised the drilling operation, and collected, examined and visually classified each sample. Representative samples were collected for further visual examination and classification in the GEC laboratory. SPT borings that penetrate the Hawthorn Group are grout-sealed upon completion.

A.2 Dynamic Cone Penetrometer

The Dynamic Cone Penetrometer (DCP) tests were performed in manual auger borings in general accordance with ”Dynamic Cone for Shallow In-Situ Penetration Testing,” Vane Shear and Cone Penetration Testing of In-Situ Soils, ASTM STP 399, 1966. The DCP tests were performed at 2-foot intervals until the boring termination depth was reached.

A.3 Groundwater Measurement

A GEC engineering technician measured the depth to groundwater in the boreholes at the time of drilling and again after approximately 24 hours. A manual auger boring was performed adjacent to SPT borings that were grout sealed upon completion to record the groundwater depth. Once the 24-hour groundwater measurement was recorded, the boreholes were then backfilled with soil cuttings to prevailing ground surface.

A.4 Manual Muck Probes

Manual muck probes were performed by pushing a slender metal rod into the surficial soil and evaluating the relative resistance of the soil to manual penetration. Highly organic soils, such as muck and/or peat, are characteristically very soft and will easily yield to the manual probe.

Manual probes, however, cannot detect peat or muck layers which are present beneath layers of sand or dense soils which cannot be penetrated by the probe. The probes can also penetrate to some extent in very loose sands which may be present beneath peat or muck layers. No soil samples are obtained for visual examination or laboratory testing when using this exploratory technique. The soil type being penetrated is inferred solely by evaluating the relative resistance of the soil to penetration. These limitations can lead to some under-estimation or over-estimation of peat or muck layer thicknesses. The probe data presented in this report should be evaluated with these limitations in mind.

APPENDIX B

DESIGN CALCULATIONS

Site No. 1

Untitled

PROGRAM CWALSHT-DESIGN/ANALYSIS OF ANCHORED OR CANTILEVER SHEET PILE WALLS

BY CLASSICAL METHODS

DATE: 30-JANUARY-2024 TIME: 9:49:05

* INPUT DATA *

I.--HEADING

'EROSION CONTROLL COUNTERMEASURES WITHIN LITTLE WEKIVA RIVER

'SITE 1

'GEC PROJECT NO. J5344G

II.--CONTROL

CANTILEVER WALL ANALYSIS

SAME FACTOR OF SAFETY APPLIED TO BOTH ACTIVE AND PASSIVE PRESSURES.

III.--WALL DATA

ELEVATION AT TOP OF WALL = 49.00 FT.

ELEVATION AT BOTTOM OF WALL = 16.00 FT.

WALL MODULUS OF ELASTACITY = 2.900E+07 PSI.

WALL MOMENT OF INERTIA = 184.20 IN^4.

IV.--SURFACE POINT DATA

IV.A.--RIGHTSIDE

DIST. FROM ELEVATION

WALL (FT) (FT)

0.00 49.00

4.00 50.00

50.00 50.00

IV.B.--LEFTSIDE

DIST. FROM ELEVATION

WALL (FT) (FT)

0.00 40.00

8.00 37.00

14.00 36.00

50.00…