HUM MALSR FUGRO GEOTECHNICAL REPORT.pdf

Runway 18 Approach Lighting Project Report

Geotechnical Investigation | Houma, Louisiana

251305rpt | Version 2 | Final

June 14, 2024

Jacobs

251305rpt | VER 2 | Runway 18 Approach Lighting Project Report

Document Control

Document Information

Project Title Runway 18 Approach Lighting Project

Project Type Geotechnical Investigation

Document Type Report

Fugro Project No. 04.00251305

Fugro Document No. 251305rpt

Version Number 2

Version Status Final

Fugro Legal Entity Fugro USA Land, Inc.

Issuing Office Address 4233 Rhoda Drive, Baton Rouge, LA 70816

Client Information

Client Jacobs

Client Address 125 Broadway Avenue, Oak Ridge, TN 37830

Client Contact Ms. Gina Collette

Version History

VER Date Status Comments on Content Prepared

By

Checked

By

Approved

By

1 May 14, 2024 Draft For client review and comment VL MLS MLS

2 June 14, 2024 Final For client use VL/MLS MLS ERM

Project Team

Initials Name Role

VL Viet Le, E.I. Project Professional

PJC Peter J. Cole Project Manager

FM Farid Motamed Vice President

MLS Martin L. Skyrman Principal Engineer

ERM Eric R. Marx Vice President / Louisiana General Manager

Page ii of v

Contents

Executive Summary 1

1. Introduction 3

1.1 Project Description 3

1.2 Scope of Work 3

1.3 Applicability of Report 4

1.4 Variations in Subsurface Conditions 4

2. Field Exploration 5

2.1 General 5

2.2 Soil Sampling Methods 5

2.3 Short-Term Depth-to-Water Observations 6

2.4 Borehole Completion 6

3. Laboratory Testing 7

3.1 Classification Tests 7

3.2 Undrained Shear Strength Tests 7

3.3 One-Dimensional Incremental Consolidation Test 8

3.4 Corrosion Tests 8

4. General Site Conditions 9

4.1 Site Description 9

4.2 Subsurface Conditions 9

4.3 Depth-to-Water Conditions 10

4.4 Seismic Site Classification 10

5. Site Preparation 12

5.1 Site Drainage 12

5.2 Subgrade Preparation 12

5.3 Site Grading 13

5.4 Settlement Due to Site Grade Raise 13

5.4.1 Soil Compressibility Parameters 13

5.4.2 Computed Consolidation Settlement and Time Rate of Settlement 14

5.4.3 Variations in Settlement Analysis 15

5.5 Consolidation Settlement Monitoring 15

6. Soil Parameters for Engineering Design 16

6.1 Design Soil Properties - General 16

6.2 Design Soil Properties – HDD Utility Crossing 18

Page iii of v

7. Shallow Foundations 20

7.1 Foundation Depth 20

7.2 Allowable Bearing Pressure 20

7.3 Resistance to Uplift Loads 21

7.4 Resistance to Lateral Loads 21

7.5 Resistance to Overturning Moments 22

7.6 Estimated Settlement 22

7.7 Slabs-on-Grade 23

7.7.1 Subgrade Preparation 23

7.7.2 Grade Beams 23

7.7.3 Additional Slab-on-Grade Considerations 24

7.8 Coefficient of Subgrade Reaction 25

8. Deep Foundation Recommendations 27

8.1 Axial Capacity 27

8.2 Factors of Safety and Verification 27

8.3 Lateral Load Analysis 28

8.4 Group Effects 29

8.5 Estimated Settlement 29

9. Pavements 30

9.1 Subgrade Preparation 30

9.2 Drainage 30

9.3 Pavement Sections 30

9.4 Site Grade Raise Effects on Pavements 31

10. Soil Corrosion Potential 32

10.1 General 32

10.2 Laboratory Test Results 32

10.3 Corrosion of Buried Steel 32

10.4 Degradation of Concrete 33

11. Pile Installation Considerations 34

11.1 General 34

11.2 ACIP Pile Installations Considerations 34

11.2.1 Contractor Experience and Equipment 34

11.2.2 Grout Mix 34

11.2.3 Pile Installation and Monitoring 35

11.2.4 Reinforcing Steel Placement 35

11.2.5 Construction Sequence 36

11.2.6 Sonic Integrity Logging 36

Page iv of v

11.3 Driven Pile Installation Considerations 36

11.3.1 Pile Driving Specifications 36

11.3.2 Pile Driving Equipment 37

11.3.3 Driven Pile Installation 37

11.3.4 Pile Driving Records 38

12. Construction Considerations 39

12.1 Surface Water and Groundwater Control 39

12.2 Shallow Foundation Excavations 39

12.3 Fill Material and Placement Recommendations 40

12.3.1 Structural Sand Fill 40

12.3.2 Structural Clay Fill 40

12.3.3 Lime-Stabilized Clay Fill and Subgrade 41

12.3.4 General Fill 42

12.3.5 Flowable Fill 42

12.4 Quality Control and Field Testing 42

13. Geotechnical Design Review and Construction Monitoring 44

14. References 45

Tables in Main Text

Table 3.1: Summary of Tests Performed and Methods 7

Table 4.1: Summary of Groundwater Measurements 10

Table 5.1: Design Parameters for Area Settlement Analyses – MALSR Equipment Shelter 14

Table 5.2: Estimated Settlement Due to Site Grade Raise 15

Table 6.1: Design Soil Parameters (based on Borings B-1 and B-3) 16

Table 6.2: Design Soil Parameters (based on Borings B-2, B-4, and B-5) 17

Table 6.3: Design Soil Parameters for HDD Utility Crossing (based on Borings B-1 and B-3) 18

Table 6.4: Design Soil Parameters for HDD Utility Crossing (based on Borings B-2, B-4, and B-5) 19

Table 7.1: Allowable Bearing Capacity Recommendations 21

Table 8.1: Lateral Load Resistance and Resulting Maximum Bending Moment (Borings B-1 and B-3) 28

Table 8.2: Lateral Load Resistance and Resulting Maximum Bending Moment (Borings B-2, B-4, and B-5)

Table 9.1 Pavement Section Recommendations 31

Table 10.1: Summary of Soil Corrosion Potential Results 32

Table 10.2: Corrosion Potential Based on Resistivity, pH, and Chloride Content 33

Table 10.3: Potential of Concrete Degradation Based on Sulfate Ion Concentration 33

Page v of v

Plates

Title Plate No.

Vicinity Map 1

Exploration Plan 2

Boring Logs 3 through 7

Boring Log Terms and Symbols 8a and 8b

Generalized Subsurface Profile 9

Computation of Bearing Pressures 10

Appendices

Appendix A Summary of Test Results

Appendix B Grain Size Curves

Appendix C Consolidation Test Curve

Appendix D Corrosion Test Results

Appendix E Ultimate Axial Capacity Curves

Abbreviations

FOS factor of safety

SPT standard penetration test

HDD horizontal directional drilling

Executive Summary

This report presents the results of a geotechnical engineering study performed for the Runway 18

Approach Lighting project located at the Houma-Terrebonne Airport (HUM) in Houma, Louisiana.

1. Our geotechnical investigation consisted of drilling five (5) soil borings to depths between 12 and 60 feet below existing site grades and performing one (1) concrete coring within the existing blast pad.

2. Subsurface conditions at the site vary along the project alignment. Soils encountered in the borings include soft to stiff lean and fat clays (CL, CH), very soft organic clay (OH), silt (ML), and loose to dense silty sand, poorly graded sand with silt, and clayey sand. Depth to groundwater in the borings, after a 15-minute waiting period, ranged between 3 and 5 feet below existing grades at the time of our field investigation.

3. Per the 2021 IBC and ASCE 7-16, Seismic Site Class of ‘E’ is considered appropriate for the design of foundations.

4. Site grade will be raised between approximately 6 and 8 feet at the planned MALSR equipment shelter location. We anticipate that a 6-month settlement waiting period following completion of grade raise will be incorporated into the construction schedule. Temporary surcharge loads and/or ground improvement

(e.g., wick drains) to accelerate settlements are not anticipated. Settlement monitoring should be performed during and after fill placement.

5. Lightly loaded equipment and structures may be supported on spread and strip footings.

Recommended allowable bearing pressures (FS = 3.0 for sustained loading conditions) for square spread footings and strip footings are 1,000 pounds per square foot (psf) and 850 psf, respectively. Footings should bear a minimum of 1 foot into native soils and at least 2 feet below lowest adjacent finish grade.

6. The slab-on-grade at the MALSR equipment shelter location should bear on structural sand fill.

Elsewhere on the project, slabs-on-grade should be underlain by at least 12 inches of structural clay fill.

The applied pressures beneath slabs-on-grade should be limited to 500 psf.

7. Moderate to heavily loaded structures should be supported on deep foundations. Recommendations for 12-inch square precast concrete piles and 12-inch diameter auger cast-in-place (ACIP) piles are included herein.

8. Light-duty flexible pavements for the planned access roads and maintenance areas should consist of a minimum 4 inches of asphalt concrete over 6 inches of crushed limestone aggregate base placed on prepared subgrade. Light-duty rigid pavements should consist of a minimum of 6 inches of reinforced

Portland cement concrete.

9. Due to shallow groundwater at the site, dewatering of foundation and utility excavations may be required depending on site groundwater levels at the time of construction.

This executive summary provides a brief presentation of some of the key recommendations of this report.

It is by no means intended to be a comprehensive or stand-alone representation of the findings of our study. The full text of the report and the attached appendices contain important information which the reader should use to come to more informed conclusions about the information presented herein.

1. Introduction

1.1 Project Description

Fugro understands that Jacobs is assisting the Federal Aviation Administration (FAA) in the design and construction of new airport lighting structures located in Terrebonne Parish, Louisiana. A Vicinity Map is included on Plate 1. Fugro performed the scope of services described in detail below in general accordance with the provided Request for Proposal: Geotechnical

Investigative Services for the Runway 18 Approach Lighting project located at the Houma-

Terrebonne Airport (HUM).

Based on the information provided by Jacobs, the project includes construction of infrastructure for the replacement of the Runway 18 Medium Intensity Approach Lighting System with Runway

Alignment Indicator Lights (MALSR) on Runway 18 at HUM. This also includes the installation of concrete foundations for an equipment shelter and lights at various locations in the proximity to the runway, and an HDD utility crossing in the vicinity of Terrebonne Bayou. In addition, pavements will be constructed for access roads and maintenance areas.

Based on provided plan and profile information, existing grades along the lighting alignment range from approximately El. +5 to +9 ft, except in the vicinity of Terrebonne Bayou where a bottom elevation of approximately El. -5 ft is indicated. As shown on a conceptual grading and drainage plan provided by Jacobs, grade will be raised between approximately 6 and 8 feet at the MALSR equipment shelter location. The shelter structure is planned to be supported on a slab on grade foundation. Jacobs provided Fugro with the proposed boring locations and requested Fugro perform a geotechnical investigation to support the project.

1.2 Scope of Work

The purposes of our geotechnical study were to 1) explore and evaluate the subsurface soil and groundwater conditions at the proposed exploration locations, and 2) provide geotechnical recommendations to assist Jacobs in the design and construction of foundations for the proposed structures.

We accomplished these purposes by:

Drilling a total of five (5) soil borings. One (1) soil boring to a depth of 60-ft below existing site grade, three (3) soil borings to a depth of 40-ft, and one (1) soil boring to a depth of 12-

ft. Boring locations and depths were provided by Jacobs.

Performing one (1) concrete coring within the existing blast pad at a location provided by

Jacobs.

Performing field and laboratory tests on selected soil samples to assess pertinent geotechnical engineering soil properties.

Analyzing field and laboratory test results to develop engineering recommendations for this project.

Preparing this report, summarizing our findings and recommendations.

Environmental assessment, compliance with state and federal regulatory requirements, assessment of potential migration, and/or environmental analyses, including those associated with biological agents, were beyond the scope of this study. We were neither asked nor authorized to evaluate the environmental conditions at the site. A geologic fault study was also beyond the scope of this project.

1.3 Applicability of Report

The explorations and analyses for this study and the conclusions and recommendations presented in this report were selected or developed based on our understanding of the project, as described above and in later sections of this report. If pertinent details of the project have changed or otherwise differ from our descriptions, we request notification and authorization to review the changes and modify our conclusions and recommendations if needed.

We have prepared this report exclusively for Jacobs to use as a guide for the design’s geotechnical aspects and construction of proposed structures. We have conducted this study using the standard level of care and diligence normally practiced by recognized engineering firms performing similar services under similar circumstances at the same time and locality. We intend for this report, including all illustrations and appendices, to be used in its entirety. Fugro makes no claim or representation concerning any activity or condition falling outside the specified purposes to which this report is directed. The observations, conclusions, and recommendations presented in this report may not apply to locations not explored by our borings or areas outside the project boundaries. This report should be made available for information only and not as a warranty of subsurface conditions.

1.4 Variations in Subsurface Conditions

Our interpretations of soil and depth-to-water conditions, as described in this report, are based on data obtained from our sample borings, laboratory tests, and our experience. Although we have allowed for minor variations in the subsurface conditions, our recommendations may not be appropriate for subsurface conditions other than those reported herein. It is possible that some undisclosed variations in soil or groundwater conditions might occur outside the boring locations, especially the extent and depth of any surficial conditions and possible fill materials.

We recommend careful observations during construction to verify our interpretations. Should variations from our interpretations be found, we recommend that we be notified and authorized to evaluate what, if any, revisions should be made to our recommendations.

2. Field Exploration

This section includes information relating to our field exploration activities for this project. We have included a general discussion on drilling methods, sampling methods, depth-to-water observations, and borehole completion.

2.1 General

Five (5) soil borings (designated as B-1 through B-5) and one (1) pavement core (designated as

P-1) were performed for the project. The pavement core was retained by FAA personnel. The boring target locations and depths were provided by Jacobs. The soil boring and core locations were located and staked in the field by FAA and Jacobs onsite personnel using a handheld GPS.

The borings were drilled on March 8 and March 9, 2024, with an ATV-mounted drilling rig using a combination of dry-auger and wet-rotary drilling techniques. The as-drilled boring locations are presented on the Exploration Plan on Plate 2. The boring logs for this study are presented on

Plates 3 through 7 with a key identifying the terms and symbols used on Plates 8a and 8b. The coordinates for the explorations and approximated (from Google Earth) ground surface elevation at exploration locations are indicated on the logs.

2.2 Soil Sampling Methods

Soil samples from soil borings were generally taken continuously from the existing grade to a depth of about 16 feet and at 5-ft intervals thereafter to the boring completion depths. Borings were logged in general accordance with the Standard Practice for Description and Identification of

Soils (Visual-Manual Procedures) (ASTM D2488).

Our field procedure for cohesive soil sampling was conducted in general accordance with the

Standard Practice for Thin-Walled Tube Sampling of Soils for Geotechnical Purposes (ASTM

D1587). Undisturbed samples of cohesive soils were generally obtained by hydraulically pushing a 3-inch-diameter, thin-walled tube a distance of about 24 inches. The samples were extruded in the field and visually classified by one of our geotechnical personnel. Field estimates of the undrained shear strength of the recovered samples were obtained by using a hand penetrometer and/or torvane. Portions of each recovered soil sample were placed into appropriate containers for transportation to our laboratory.

Our field procedure for sampling cohesionless and select cohesive soils was conducted in general accordance with the Standard Test Method for Standard Penetration Test and Split-Barrel

Sampling of Soils (ASTM D1586). A description of the SPT tests is presented on Plate 8b. An automatic hammer was used to obtain the hammer blows for each SPT sample. Our geotechnical personnel recorded the hammer blows for each sampling interval. The SPT N-value, described on

Plate 8b, is recorded on the boring logs and is uncorrected. The soil samples obtained from the split barrel sampler were visually classified and packaged for transportation to our laboratory.

2.3 Short-Term Depth-to-Water Observations

Each boring was initially drilled using dry-auger techniques to determine depth-to-water levels at the project site. Once water was encountered, drilling was temporarily stopped, and water level readings were obtained. Drilling then continued to the boring completion depth using the wet-rotary method. The interpreted depth-to-water conditions are discussed further in Section

4.3 of this report and are noted on the boring logs (Plates 3 through 7).

2.4 Borehole Completion

The soil borings performed for this study were backfilled upon completion with cement-bentonite grout from the bottom up. When grout returned to the surface, the excavations were topped off by pouring grout from the surface.

3. Laboratory Testing

The laboratory testing program for this study was directed primarily toward evaluating the classification properties, undrained shear strength, and compressibility characteristics of the foundation soils. Our laboratory tests were performed in general accordance with the appropriate standards as shown in Table 3.1.

Table 3.1: Summary of Tests Performed and Methods

Test Type Test Destination

Moisture Content ASTM D2216

Atterberg Limits ASTM D4318

Percent Finer than a No. 200 Sieve ASTM D1140

Sieve Analysis ASTM D6913

UU-Triaxial Compression ASTM D2850

One-Dimensional Incremental Consolidation ASTM D2435 pH ASTM D4972

Electrical Resistivity ASTM G-57

Sulfate Content ASTM D516

Chloride Content ASTM D512

3.1 Classification Tests

The classification tests included tests for natural moisture content, liquid and plastic limits

(collectively termed Atterberg Limits), sieve analysis, and percent finer than a No. 200 sieve.

These tests aid in classifying the soils and are used to correlate the results of other tests performed on samples taken from different borings and/or different depths. The results of the classification tests are presented on the boring logs on Plates 3 through 7, in Appendix A, Summary of Test Results, and in Appendix B, Grain Size Curves.

3.2 Undrained Shear Strength Tests

We measured the undrained shear strength of select undisturbed samples of cohesive soils by performing unconsolidated undrained triaxial compression tests. Natural moisture contents and dry unit weights were determined as routine parts of the compression tests. The results of the laboratory shear strength tests, along with the field estimates of shear strengths, are presented on the boring logs on Plates 3 through 7, and in Appendix A, Summary of Test Results.

3.3 One-Dimensional Incremental Consolidation Test

We measured the compressibility characteristics of the foundation soils by performing one (1) one-dimensional incremental consolidation test. Natural moisture contents and dry unit weights were routinely determined for the test samples. Consolidation test results and plots of effective vertical stress versus void ratio, are presented in Appendix C, Consolidation Test Curve.

3.4 Corrosion Tests

Three (3) corrosion series tests were performed for this project. Corrosion series tests included pH, resistivity, chlorides, and sulfates. Corrosion testing was performed in Fugro’s Houston, Texas laboratory. The results of the laboratory corrosion tests are discussed in Section 10 and are presented in the Appendix D, Corrosion Test Results.

4. General Site Conditions

This section contains interpreted site and subsurface conditions based on our field exploration and laboratory testing programs. This section also includes a discussion and interpretation of the depth-to-water conditions encountered at the site during our field exploration.

4.1 Site Description

The project site/alignment is located at the existing Houma-Terrebonne Airport, beginning near the northern end of Runway 18 and generally extending northward past the intersection of

Aviation Road and East Main Street, across Bayou Terrebonne, and terminating at East Park

Avenue. Jacobs provided Fugro with the pavement core and boring locations. Pavement core P-1 was located within the existing blast pad near the northern terminus of Runway 18. Boring B-1 was located in the grass field northeast of the existing Runway 18 and directly east of the existing approach lighting structures. Borings B-2, B-3, and B-4 were located in the grassy area within the alignment of the existing approach lighting structures extending from Runway 18 north across Bayou Terrebonne. Boring B-5 was located along the southern side of East Park

Avenue and approximately 250 feet southeast of the intersection between East Park Avenue and

Lafayette Woods Boulevard. Overhead powerlines were located within the vicinity of Boring B-5.

A Vicinity Map provided on Plate 1, depicts the site’s general location in reference to East Main

Street and East Park Avenue. The site was generally flat and covered with minor vegetation at the time of our field exploration. Existing access roads are gravel-surfaced. The Exploration Plan, provided on Plate 2 shows the approximate locations of the borings, however Fugro did not survey the boring locations.

4.2 Subsurface Conditions

A generalized subsurface profile across the site is presented on Plate 9. Based on the review of laboratory test results, the following is a general description of the soils encountered in the borings along with their Unified Soil Classification System (USCS) designation.

Boring B-1 generally consisted of alternating layers of lean and fat clay (CL, CH) and silt (ML) from the existing ground surface to a depth of 18.5 ft, followed by a layer of silty sand (SM) to a depth of 43.5 ft, underlain by a layer of fat clay (CH) to the completion depth of the boring.

Boring B-3 disclosed a layer of lean clay (CL) from the existing ground surface to a depth of 18.5 ft, followed by relatively thin layers of silty sand (SM), poorly graded sand with silt (SP-SM), and clayey sand (SC) to a depth of 38.5 ft, underlain by a layer of fat clay (CH) to the completion depth of the boring. Borings B-1 and B-3 were drilled to depths of 60 ft and 40 ft, respectively.

The strength tests and N-values conducted on cohesive materials generally indicated a soft to stiff consistency. The N-values in the cohesionless layer indicated a loose to dense consistency.

Borings B-2 and B-4 generally consisted of alternating layers of lean and fat clays (CL, CH) from the existing ground surface to the completion depth of the boring. Boring B-5 disclosed a lean clay (CL) fill layer from the existing ground surface to a depth of 2 ft, followed by a layer of native lean clay (CL) to a depth of 3 ft, underlain by a layer of silt (ML) to the completion depth of the boring. Notable details included approximately 4 ft of organic clay (OH) encountered in B-2 at 14 ft below existing grade and 5 ft of wood encountered in B-4 at 23.5 ft below existing grade.

Borings B-2 and B-4 were drilled to a depth of 40 ft and Boring B-5 was drilled to a depth of 12

ft. The strength tests and N-values conducted on cohesive materials generally indicated a very soft to very stiff consistency.

Detailed information relating to the subsurface conditions encountered at the site is presented on the boring logs on Plates 3 through 7. A key identifying the terms and symbols used on the boring logs is presented on Plates 8a and 8b.

4.3 Depth-to-Water Conditions

To estimate the depth-to-water at the project site, soil borings for this study were initially drilled using dry auger drilling techniques. A summary of the groundwater measurements is presented in Table 4.1.

Table 4.1: Summary of Groundwater Measurements

Boring ID Depth to Initial Groundwater (ft) Depth of Groundwater After 15-minute waiting period (ft)

B-1 10.0 3.9

B-2 10.0 5.0

B-3 8.0 3.9

B-4 10.0 3.0

B-5 N/E N/E

N/E = Groundwater was not encountered.

It should be noted that short-term water levels recorded in the open boreholes should not be considered to represent a long-term condition. It is possible that the water levels in the open boreholes may not have had enough time to completely stabilize. More accurate determinations of groundwater levels are usually made from long-term standpipe piezometer readings;

however, the water level is likely to be influenced by the adjacent bayou.

4.4 Seismic Site Classification

In accordance with the 2021 International Building Code (IBC) and ASCE 7-16, the design of structures must consider dynamic forces resulting from seismic events. These forces are dependent upon the magnitude of the earthquake event as well as the properties of the soils that underlie the site. As part of the procedure to evaluate seismic forces, the code requires the evaluation of the Seismic Site Class, which categorizes the site based upon the characteristics of the subsurface profile within the upper 100-ft of the ground surface. The borings for the project extended to a maximum depth of 60 feet, therefore we extrapolated soil conditions from the maximum depth of the borings to the depth required for site classification purposes. The site classification for seismic design was based on correlations with the shear strength values and standard penetration test (SPT) blow counts obtained from the soil borings. Site specific dynamic soil properties were not obtained as part of our study. We recommend a Site Classification ‘E’ be applied for this project.

5. Site Preparation

This section presents our recommendations associated with site drainage, subgrade preparation, site grading, the results of our area settlement analysis due to the proposed site grade raise at the MALSR equipment shelter location, and settlement monitoring.

5.1 Site Drainage

Establishing proper drainage and removing ponded water, where present at the time of construction, will be a key aspect of site preparation. Prior to construction, an adequate drainage plan should be provided to reduce the potential to saturate the subgrade soils. Most subgrade problems are attributable, at least in part, to poor site drainage. We recommend that an effective

“site drainage plan” be devised by others prior to commencement of construction to provide positive drainage away from the planned limits of construction and off the site, both during and after construction. The drainage plan should consist of sloping the subgrade in conjunction with the use of lateral ditches and drainage inlets to transmit water away from the features associated with this project and offsite, as necessary.

5.2 Subgrade Preparation

Subgrade preparation should consist of stripping and discarding existing pavements and crushed stone, vegetation/organic materials, topsoil, debris, weak or soft soils, fill soils and any deleterious materials to expose competent, stiff natural, stiff cohesive soils capable of supporting construction traffic and subsequent backfill activities. Based on our borings, a minimum stripping depth of between 6 and 8 inches is recommended; however, this depth should be revised as necessary at the start of site grading as surficial soils are exposed. If present, trees and their entire “root-ball” systems should also be completely removed from any structure and pavement locations. Any existing utilities and other underground obstructions should be identified and relocated as necessary to facilitate construction activities.

Stripped subgrades in structure and paving areas should then be moisture conditioned as necessary to achieve a moisture content between 1 and 4 percent wet of optimum. The moisture content at the time of construction should be monitored. If the moisture content is dry of optimum, the upper 8 inches of soil should be scarified, followed by moisture conditioning and recompaction in accordance with Section 12.3 of this report.

The Geotechnical Engineer-of-Record, or their qualified representative, should observe the exposed subgrade during site preparation. Where possible, onsite observation should include proof rolling the exposed subgrade with a heavy (20 ton), rubber-tired vehicle (e.g., fully loaded dump truck) to evaluate the condition of the subgrade. Areas of the subgrade that are observed to be soft, wet, weak, or contain deleterious materials should be over-excavated to expose competent, cohesive soils and replaced using structural sand fill, structural clay fill, lime-stabilized clay fill, or flowable fill. Material and placement requirements for structural sand fill, structural clay fill, lime-stabilized clay fill, and flowable fill are provided in Section 12.3 of this report. In confined areas where proofrolling is not feasible (such as small foundation excavations), visual observation and probing should be conducted to verify the competency of the foundation soils. The Geotechnical Engineer-of-Record, or their qualified representative, should observe proofrolling and/or probing operations to detect weak soils. If the subgrade is deemed to be competent via a properly performed proofrolling or probing operation, then backfill operations may commence.

5.3 Site Grading

Per Jacobs, grade will be raised between approximately 6 and 8 feet at the planned MALSR equipment shelter location. Elsewhere, fill depths on the project are expected to not exceed approximately 2 feet. At the shelter location, we recommend that structural sand fill (Section

12.3.1) be placed in compacted lifts to the proposed finish grade. Fill slopes be inclined no steeper than 4H:1V (horizontal:vertical).

We anticipate that a 6-month settlement waiting period following completion of grade raise will be incorporated into the construction schedule. Temporary surcharge loads and/or ground improvement (e.g., wick drains) are not required to accelerate settlements unless the estimated post-construction settlements presented in Section 5.4 are not acceptable for the proposed structure.

5.4 Settlement Due to Site Grade Raise

Raising grade at the proposed equipment shelter location will incur significant settlements within the underlying foundation soils. Settlements will occur over time, both during and following fill placement, and will vary across the grade raise area. In general, settlements due to grade raise will include settlement within the fill under its own weight and settlement of subgrade soils due to the weight of the fill. Settlement analysis from the self-weight of the structural sand fill was not performed as these immediate settlements are considered negligible compared to primary consolidation settlements. This subsection presents soil design parameters used in the settlement analyses, the settlement analysis method, and computed settlements with estimated time-rate of settlement.

5.4.1 Soil Compressibility Parameters

Soil compressibility parameters used in the settlement analyses are presented in Table 5.1. We relied on laboratory data in conjunction with established correlations from the local geotechnical literature for similar soils to assign compressibility parameters.

Table 5.1: Design Parameters for Area Settlement Analyses – MALSR Equipment Shelter

Top

Depth

[ft]

Bottom

Elevation

[ft]

Soil

Description

Total Unit

Weight γt

[pcf]

Es

[ksf](1) Cc

(2) Cr

(3) e0

(4) P’c

[ksf] (5)

0 4 Fat Clay (CH) 115 - 0.30 0.03 0.95

6.7 to

3.5

4 19 Lean Clay and

Silt (CL, ML) 118 - 0.23 0.05 0.87

3.5 to

2.1

19 43 Silty Sand (SM) 120 400 - - - -

43 60 Fat Clay (CH) 100 - 0.68 0.14 1.59

3.1 to

4.9

Notes:

1 = 1D Modulus (Constrained modulus)

2 = Compression Index

3 = Re-compression Index

4 = Initial void Ratio

5 = Preconsolidation Pressure

5.4.2 Computed Consolidation Settlement and Time Rate of Settlement

Long-term consolidation settlements will occur over a period of several years as the cohesive soils consolidate. In general, the consolidation process begins with the application of load on the soil resulting in the generation of excess pore water pressures. The excess pore water pressures gradually dissipate due to the expulsion of water from the soil voids accompanied by a concurrent increase in the effective stress of soils. As the excess pore water dissipates, the load is transferred to soil particles compressing the soils and resulting in settlement. The rate of settlement is a function of soil characteristics such as compressibility, permeability, and the distance of the drainage path for the excess pore water to travel.

We calculated the settlements of the foundation soils due to the weight of the fill using the computer program Settle 3 developed by Rocscience. This program first computes net stress changes at selected locations and depths beneath loaded areas using Boussinesq’s theory of stress distribution. Then, the software calculates consolidation settlements of clay by computing net stress changes at selected locations and depths beneath the loaded areas. The program uses soil compressibility parameters to evaluate the change in thickness of individual layers and computes the overall movement at the selected locations. Immediate settlements were calculated within cohesionless soil layers, and primary consolidation settlements were calculated within cohesive layers.

Our settlement model incorporates the assumptions listed below.

An embankment load with approximate top plan dimensions of 45 feet by 45 feet and

4H:1V side slopes

Structural sand fill unit weight of 120 pounds per cubic foot (pcf);

Incremental placement of up to 8 feet of sand over a period of 30 days; and

Settlement was evaluated to the maximum explored depth of 60 feet below existing site grades. Loading stresses below this depth are considered minor and therefore, settlement below this depth is considered negligible.

Table 5.2 below provides estimated settlement of the subsurface soils over a period of 3 years upon completion of grade raise due to the weight of structural sand fill for the anticipated fill height.

Table 5.2: Estimated Settlement Due to Site Grade Raise

Area

Total Settlement at Ground Surface, inches

1 Month after

COG(1)

6 Months after COG

1 Year after

COG

3 Years after

COG

MALSR Shelter 2.4 3.5 3.7 3.9

(1) COG = Completion of Grade Raise

5.4.3 Variations in Settlement Analysis

We performed detailed settlement analyses using our interpreted design parameters based on the soil conditions encountered during this study and the anticipated loading from fill placement. Actual compressibility characteristics of natural soils may vary and differ from what we assumed in our analyses leading to variation in our settlement estimates. The actual post-construction settlements will vary depending on several factors such as construction period, variability of permeability and compressibility of natural soils, and the actual amount of fill placed to achieve design grade. As such, differential settlements should be expected within the project site because of variable consolidation characteristics of the soils.

5.5 Consolidation Settlement Monitoring

Settlement monitoring can be used to compare predicted and actual settlements and may be used to estimate future volumes of fill needed to achieve the final site grade. We recommend that the results of the settlement-monitoring program be reviewed by the Geotechnical Engineer during the construction phase. Based on our time rate of settlement estimates, we recommend monitoring settlements for at least 6 months after completion of grade raise.

Settlement plates can be used to monitor near-surface settlements. Please note that settlement plates must be installed prior to placement of fill to provide meaningful data. As such, the instrumentation must be modified to accommodate the grade increase as it occurs and must also be protected from construction equipment during fill placement. Monitoring of the instrumentation and subsequent evaluation must be performed by the Geotechnical Engineer. At least two (2) settlement plates, at opposing corners of the filled area, should be installed to monitor the progression of settlement as the site grade is raised.

6. Soil Parameters for Engineering Design

The project consists of infrastructure for the replacement of the Runway 18 Medium Intensity

Approach Lighting System with Runway Alignment Indicator Lights (MALSR) on Runway 18 at

HUM and equipment shelters and lights at various locations in the proximity to the runway. This section summarizes design soil parameters used in the engineering analyses and presents soil parameters for use by others in the design of the HDD utility crossing below Bayou Terrebonne.

6.1 Design Soil Properties - General

Soil parameter profiles were prepared based on the results of the field and laboratory test programs. Due to the variable soil conditions across the site, two separate soil profiles were developed for this study and are shown in Tables 6.1 and 6.2.

Table 6.1: Design Soil Parameters (based on Borings B-1 and B-3)

Depth Soil Type Unit Weight

(pcf) Cohesion (psf) Friction Angle (degrees)

0 to 5 Lean to Fat

Clay (CL,CH) 115 700 -

5 to 18 Lean Clay

(CL)

115 500 -

18 to 33 Silty Sand

(SM, SP-SM)

120 - 28

33 to 38

Silty to

Clayey Sand

(SM, SC)

120 - 30

38 to 43 Fat Clay (CH) 100 500 -

43 to 60 Fat Clay (CH) 100 700 -

Table 6.2: Design Soil Parameters (based on Borings B-2, B-4, and B-5)

Depth Soil Type Unit Weight

(pcf) Cohesion (psf) Friction Angle (degrees)

0 to 5

Lean to

Fat Clay, Silt (CL, CH, ML)

115 700 -

5 to 10

Lean to

Fat Clay, Silt (CL, CH, ML)

115 500 -

10 to 20

Lean to

Fat Clay, Organic

Clay (CL, CH, OH)

90 500 -

20 to 40

Lean to

Fat Clay

(CL, CH)

100 500 -

6.2 Design Soil Properties – HDD Utility Crossing

Soil parameters presented in Tables 6.3 and 6.4 may be used by others for engineering evaluation of the HDD utility crossing.

Table 6.3: Design Soil Parameters for HDD Utility Crossing (based on Boring B-3)

Depth Soil Type Unit Weight

(pcf)

Cohesion at

Top of Layer

(psf)

Cohesion at

Bottom of Layer

(psf)

Friction

Angle

(degrees)

Estimated Shear

Modulus (ksf)

0 to 5 Lean Clay

(CL)

115 700 700 - 140-720

5 to 18 Lean Clay

(CL)

115 500 500 - 50-280

18 to 33

Silty Sand

(SM, SP-

SM)

120 - - 28 570-1,000

33 to 38 Clayey

Sand (SC) 120 - - 30 1,000-1,500

38 to 40 Fat Clay

(CH)

100 500 500 - 50-280

Note:

Soil parameters interpreted based on results of geotechnical laboratory testing and correlations with strength parameters. Range of estimated shear modulus values based on empirical relationships presented in FHWA GEC

No. 5, Evaluation of Soil and Rock Properties. Shear wave velocity measurements should be performed for more accurate determinations of shear modulus, as needed.

Table 6.4: Design Soil Parameters for HDD Utility Crossing (based on Borings B-4 and B-5)

Depth Soil Type Unit Weight

(pcf)

Cohesion at

Top of Layer

(psf)

Cohesion at

Bottom of Layer

(psf)

Friction

Angle

(degrees)

Estimated Shear

Modulus (ksf)

0 to 5

Fill &

Native:

Lean to

Fat Clay

(CL, CH)

115 700 700 - 140-720

5 to 10

Silt &

Lean Clay

(ML, CL)

115 500 500 - 50-280

10 to 20

Silt &

Lean Clay

(ML, CL)

90 500 500 - 50-280

20 to 40

Fat Clay

(CH),

Wood

100 500 500 - 50-280

Note:

Soil parameters interpreted based on results of geotechnical laboratory testing and correlations with strength parameters. Range of estimated shear modulus values based on empirical relationships presented in FHWA GEC

No. 5, Evaluation of Soil and Rock Properties. Shear wave velocity measurements should be performed for more accurate determinations of shear modulus, as needed.

7. Shallow Foundations

We understand that the lightly loaded equipment and structures may be supported on shallow foundations and/or shallow slabs-on-grade assuming the equipment and structures can accommodate the anticipated settlement presented herein. From a geotechnical perspective, the performance of a shallow foundation system should provide an adequate factor of safety against shear failure of the foundation soils and reduce the potential for excessive settlements due to stressing of the underlying foundation soils. As such, shallow foundations should be designed such that their applied bearing pressures do not exceed the allowable bearing pressure of the underlying soils. In addition, settlement resulting from the applied pressures (both total and differential) should be considered.

7.1 Foundation Depth

Shallow spread and strip footings should bear on competent in-situ soils at a depth of at least 2-ft below the lowest adjacent finished grade and at least 1-ft into undisturbed, natural in-situ soils

(Footings should not be placed on fill). Frost depth is not a concern at this site with regard to foundation embedment. To mitigate differential settlement, foundations for any particular structure should bear on similar materials and not a combination of different materials, such as fill and native soils. If weak, soft, or otherwise unsuitable soils are encountered at the proposed foundation depths, these soils should be over-excavated and replaced with flowable fill. Based on groundwater levels at the time of our field investigation, foundation excavations greater than

2 feet in depth may encounter groundwater.

7.2 Allowable Bearing Pressure

The allowable bearing pressure for shallow foundations is a function of, among other items, the depth of the foundation, the strength of the foundation soils, the shape of the foundation, and the recommended factor of safety. We are providing allowable bearing pressures for shallow spread and strip footings, under the various loading conditions in the table on the following page. These allowable bearing pressures do not consider the potential settlement associated with the applied pressures. Our settlement estimates for various foundation sizes corresponding to different applied pressures are presented later in this section.

Table 7.1: Allowable Bearing Capacity Recommendations

Allowable Bearing Pressure Recommendations

Foundation Type * Foundation

Embedment†

Loading Conditions#

Sustained

(F.S‡= 3)

Total

(F.S. = 2)

Transient

(F.S. = 1.5)

Square Spread Footings 2 ft 1,000 psf 1,500 psf 2,000 psf

Rectangular Spread Footings and Strip Footings 2 ft 850 psf 1,250 psf 1,650 psf

Notes

* = The allowable bearing pressures presented are applicable for square and rectangular spread footings (widths and lengths between about 5 ft and 15 ft) and strip footings (widths of at least 1.5 ft).

† = Spread and strip footings should bear on natural, firm to stiff cohesive soils a minimum of 2 ft below final grade and should have an embedment of at least 1 ft below into natural, undisturbed soils. See Section 7.1.

‡ = F.S. refers to factor of safety.

# = Refer to report text for additional information relating to loading conditions.

Sustained loading conditions as described in this report refer to the combination of properly factored dead and, in some cases, a portion of the sustained live loads. Total loading conditions as described in this report refers to the combination of properly factored dead and live loads.

Transient loading conditions refer to the combination of properly factored dead, live, and infrequent transient (i.e., wind and seismic) loads.

With respect to failure of the foundation soils, the allowable bearing capacities in the previous table include a factor of safety of at least 3 for sustained loading, 2 for total loading, and 1.5 for transient loading. Foundations should be proportioned so that the maximum contact pressure under various load combinations does not exceed the allowable bearing capacity given previously. Net bearing pressure and gross bearing pressure are defined on Plate 10 of this report. To calculate values of We, Ws, Wf from Plate 10, we recommend using buoyant unit weights of 60 pcf for soil and 90 pcf for reinforced concrete.

7.3 Resistance to Uplift Loads

The uplift capacity of a shallow foundation formed in an open excavation will be limited to the weight of the foundation and any soil directly above the foundation. For design purposes, the ultimate uplift resistance may be based on buoyant unit weights for soil and concrete of 60 pcf and 90 pcf, respectively. We recommend that the calculated ultimate uplift capacity be reduced by a factor of safety of 1.2 to compute the allowable uplift resistance.

7.4 Resistance to Lateral Loads

Horizontal loads acting on a shallow foundation formed in an open excavation will be resisted by passive earth pressure acting on one side of the foundation and by adhesion at the base.

However, we recommend neglecting passive pressure unless area paving, consisting of at least 4 to 6 inches of concrete or hot-mix asphaltic concrete extending out at least 5 feet from the edge of the foundation is provided on all sides. For design purposes, the resistance due to adhesion and passive soil pressure can be assumed to develop simultaneously.

We should be contacted for additional discussions on passive pressure if pavements, as discussed above will be utilized. For concrete foundations poured in good contact with undisturbed, natural firm to stiff cohesive soils as previously discussed, the allowable base adhesion may be taken as 175 psf. For the soil conditions encountered at this site at the recommended depth, we feel this allowable value will provide a factor of safety of at least 2 with respect to the ultimate lateral resistance.

7.5 Resistance to Overturning Moments

The contact pressure distribution of shallow foundations subject to overturning moments will be trapezoidal. The design of the foundation should be such that 1) full contact and positive pressure is maintained below the foundation base and 2) the maximum contact pressure does not exceed the allowable bearing capacity recommendations previously presented for the foundation soils.

7.6 Estimated Settlement

A detailed settlement analysis was beyond the scope of this study. However, based on our experience, we estimate the settlement due to soil compressibility from structural loads of properly designed and constructed shallow spread footings less than about 10-ft by 10-ft with a sustained net pressure less than 1,000 psf to be less than about 1-inch if founded on competent natural soils. Estimated settlement is reduced to ½-inch or less for a sustained net pressure value of approximately 500 psf.

In addition to the settlement induced by structure loads, if footings are placed in or immediately adjacent to areas where the site grade has been recently raised, additional settlement can be expected due to consolidation of the underlying soils from placement of the fill. The amount of this additional settlement will depend on the amount of grade raise at the footing location.

All things equal, differential settlements between individual foundations should be expected and may be on the order of one-half of the total settlement. However, differential settlements between foundations may be greater if there are variances in subsurface conditions, loading conditions, and construction procedures. If shallow foundations are selected for use on the project, we would be pleased to perform a detailed settlement analysis to evaluate differential movements on a case-by-case basis.

7.7 Slabs-on-Grade

We understand that selected structures may be supported on a slab-on-grade foundation with turned-down edges. The reinforcement design in the slab-on-grade will be dependent on the anticipated slab loading. For lightly to moderately loaded slabs conventional reinforcement will likely be suitable, whereas for heavily loaded slabs additional reinforcement, up to a structural slab, may be required. We recommend limiting the applied pressure beneath slabs-on-grade to

500 psf. Applied pressures greater than 500 psf will likely require the use of supplemental foundations such as spread footings. The following subsections provide recommendations for the design and construction of a slab-on-grade foundation.

7.7.1 Subgrade Preparation

To reduce the potential for foundation distress, the subgrade below the slab-on-grade foundation should be properly prepared including stripping all significant organic and other deleterious materials. The moisture content at the time of construction should be monitored. If the moisture content is dry of optimum, moisture conditioning may be required.

Before grade is raised, the exposed subgrade should be proofrolled and observed for areas that appear to be soft, wet, weak, or containing deleterious materials. In confined areas where proofrolling is not feasible (such as small foundation excavations), probing should be conducted to verify the competency of the foundation soils. The Geotechnical Engineer-of-Record, or their qualified representative, should observe proofrolling and probing operations to detect weak soils.

Weak, wet, and otherwise deleterious soils should be removed and replaced with properly compacted structural clay fill. The removal and replacement activities should extend laterally at least 3 feet beyond the edge of the slab footprint. If the subgrade is deemed to be competent via a properly performed proofrolling or probing operation, then backfill operations may commence. The exposed subgrade should then be brought to design grade using properly placed and compacted structural clay fill. The objective is to create a uniform, low permeability, relatively homogeneous foundation base of low plasticity structural clay fill for the slab-on-grade. All slabs-on-grade should be underlain by a minimum of 12 inches of structural clay fill to provide uniform support across the slab area.