Attachment 12 - MAHG 23-00002 Question 1A Geotechnical Report.pdf

Keesler Air Force Base

Proposed New Tower Foundations (2)

Report of Subsurface Investigation and Data Transmittal

Prepared for:

VECTRUS SYSTEMS CORPORATION

SESI Project No: M22‐430 July 28, 2022

MOBILE ꞏ MONTGOMERY ꞏ SUMMERDALE ꞏ DESTIN ꞏ PANAMA CITY ꞏ TALLAHASSEE ꞏ BATON ROUGE ꞏ MANDEVILLE ꞏ NEW ORLEANS

5460 Rangeline Road

Mobile, AL 36619

Tel: (251) 344-7711

Fax: (251) 443-9000 www.soearth.com

Geotechnical, Environmental & Construction Materials Testing

M o b i l e O f f i c e

VECTRUS SYSTEMS

Keesler AFB BOS

508 L Street Bldg 4705

Kessler AFB, MS, 39534

ATTENTION: Mr. Eric Nelson

REFERENCE: Report of Subsurface Investigation and Data Transmittal

Proposed New Tower Foundations (2)

Keesler AFB, MS

SESI Project No: M22‐232

Dear Mr. Nelson:

Southern Earth Sciences, Inc. (SESI) has completed the subsurface investigation and engineering evaluation for the referenced project. This data transmittal outlines our understanding of the project, includes data obtained during the investigation and presents estimated allowable passive earth pressure calculations for each proposed tower location to assist with foundation design.

We appreciate this opportunity to be of service. Please do not hesitate to contact us if you have any questions.

Sincerely, SOUTHERN EARTH SCIENCES, INC.

Caleb Davis, E.I. Matt Coaker, P.E.

Project Manager Vice President

Registered, Mississippi 20350

CD/mc

Attachments

VECTRUS SYSTEMS CORPORATION

Subsurface Investigation and Data Transmittal

Keesler Air Force Base Tower Foundations

SESI Project Number: M22‐430

July 28, 2022 i

1.0 Project Information ............................................................................................................................................. - 1 -

2.0 Field Investigation ......................................................................................................................... ‐ 1 ‐

3.0 Generalized Subsurface Conditions .............................................................................................. ‐ 1 ‐

4.0 Groundwater ................................................................................................................................. ‐ 2 ‐

5.0 Preliminary Foundation Considerations ....................................................................................... ‐ 2 ‐

7.0 Estimated Passive Earth Pressures ............................................................................................... ‐ 3 ‐

8.0 Drilled SHAFT Foundation Installation Considerations ................................................................. ‐ 3 ‐

9.0 General Comments and Limitations ............................................................................................. ‐ 4 ‐

APPENDIX 1

Test Location Plans

APPENDIX 2

CPT Sounding Logs

APPENDIX 3

Allowable Passive Pressure vs. Depth Graphs

Keesler Air Force Base Tower Foundations

SESI Project Number: M22‐430

July 28, 2022

- 1 -

1.0 PROJECT INFORMATION

Based on our understanding of the provided information, the project will consist of the construction of new communication towers at two (2) different locations within Keesler Air Force Base. The information presented within this submittal is intended to assist the foundation designer in determining the appropriate foundation size and embedment depth necessary to support the proposed towers. No foundation plans, loading information or additional project details were available at this time.

2.0 FIELD INVESTIGATION

A total of two (2) Cone Penetration Test (CPT) sounding was performed at accessible locations near the proposed tower locations. A Test Location Plans showing the approximate sounding locations can be seen in Appendix 1.

The CPT soundings were performed in accordance with ASTM Specification D‐5778 using a 20‐ton

Hogentogler Electronic CPT rig. The CPT soundings were advanced to depths approximately 100 to 110 feet below the existing ground surface. CPT Log sheets graphically showing the cone tip resistance, friction, equivalent N‐value and interpreted soil type at each sounding location is attached in Appendix 2.

Soil classifications were interpreted from methods recommended by Robertson and Campanella.

Correlations between Cone Resistance values and Standard Penetration Testing "N" values were performed according to the methods developed by Robertson, Campanella and Wightman. The soil types and stratigraphy shown on the CPT Log sheets is based upon material parameters measured and evaluated as the cone is advanced.

3.0 GENERALIZED SUBSURFACE CONDITIONS

The subsurface descriptions below are generalized to highlight the major subsurface stratigraphy encountered across the site. CPT Sounding Logs attached in Appendix 2 present specific information at individual sounding location including soil description, stratification, ground water level, and soil strength.

This information is representative of conditions encountered at the sounding locations. Variations may occur and should be expected between sounding locations. The stratification represents the approximate boundary between subsurface materials as the actual transition may be gradual.

Subsurface conditions vary considerably between the two tower locations. At test location CPT‐1, soils consist of medium dense to very dense sand to a depth of approximately 20 feet below the ground surface followed by soft to medium stiff silty and clayey soils to a depth of approximately 40 feet. Soils encountered below a depth of 40 feet consist of medium dense to very dense sand to termination of the sounding at approximately 100 feet beneath the existing ground surface.

Keesler Air Force Base Tower Foundations

SESI Project Number: M22‐430

- 2 -

At test location CPT‐2, soils within the upper 7 feet consist of medium dense to very dense sand underlain by soft to medium stiff silty and clayey soils with intermediate thin lenses of medium dense silty sand to a depth of 45 feet. Soils below 45 feet consist of medium dense to very dense sand and silty sand to a depth of approximately 60 feet underlain by medium stiff to stiff sandy silt and loose clayey sand to a depth of approximately 95 feet. Soils below a depth of 96 feet consist of medium dense silty sand and sand to termination of the sounding at approximately 110 feet below the existing ground surface.

4.0 GROUNDWATER

The CPT sounding holes collapsed upon rod removal at approximately 6 feet below existing grade at location CPT‐1 and at approximately 4.5 feet at location CPT‐2. A hole collapse often occurs at or slightly above the groundwater or saturated soil level but can also occur due to the presence of loose soils without the presence of groundwater. At location CPT‐1, using back calculation of hydrostatic pressures measured in the sands between about 70 feet below existing grade, the static groundwater was calculated to be approximately 8.5 feet below the existing ground surface, which is within the expected depth range of groundwater in the area based on our experience with other projects on Keesler Air Force Base.

Fluctuation in the level of the groundwater table will occur due to variances in rainfall, drainage, types of soil present and other factors not evident at the time measurements were made. Shallower perched groundwater conditions may develop after periods of rainfall. All reference to depth was made with respect to the existing ground surface encountered at the time of our investigation. Groundwater levels should be verified prior to construction.

5.0 PRELIMINARY FOUNDATION CONSIDERATIONS

Our evaluation of subsurface conditions and possible foundation alternatives for this project has been based on our experience with similar communication tower projects and subsurface data obtained during the investigation. In evaluating the CPT soundings, we have used empirical correlations previously established between correlated standard penetration resistances, measured cone tip and side resistance values, soil index properties and foundation stability. Soil parameters used in the evaluation were derived from the CPT sounding data using the interpretation software RAPID CPT® by Dataforensics.

Based on our experience with similar tower structures, vertical and lateral loadings as well as overturning moment forces will be significant. Shallow foundations will likely not be feasible due to the soft, compressible soils encountered beginning at depths ranging from approximately 10 to 20 feet and extending to approximately 45 feet below the existing ground surface. Although loading information is not known at this time, we anticipate that stresses from a shallow foundation system would significantly stress soft soils below 10 feet, resulting in several inches of settlement and a marginal Factor of Safety against bearing capacity failure. Shallow foundations are, in our opinion, not considered a viable

Keesler Air Force Base Tower Foundations

SESI Project Number: M22‐430

July 28, 2022

- 3 -alternative for these tower foundations. A deep foundation system would mitigate settlement and the potential of bearing capacity failure by transferring structural loads through the soft, compressible soils to deeper, more competent sand bearing strata encountered below approximately 45 feet. Estimated

Passive Earth Pressures are discussed in the following sections for the foundation designers use in preliminary foundation sizing. Recommendations for design and construction of driven or augercast pile foundations can be provided upon request once additional project information is developed.

7.0 ESTIMATED PASSIVE EARTH PRESSURES

Data obtained from the CPT soundings has been used to estimate allowable passive earth pressures to the full depth of the soundings. These pressures have been developed to assist with foundation design of the proposed communication tower structures. Soil parameters used to estimate the allowable passive earth pressures have been derived from CPT sounding data using the interpretation software RAPID CPT® by Dataforensics, as well as correlation of measured cone tip and side resistance values with accepted geotechnical references and our general knowledge of similar soil conditions. A Factor of Safety of 3.0 has been applied to these calculated passive earth pressure values. Allowable Passive Earth Pressure vs. Depth graphs are attached in Appendix 3.

The user should exercise sound engineering judgment and be thoroughly familiar with earth pressure theory, structural the capabilities and limitations of CPT information before using this data for design purposes. While the CPT sounding is representative of subsurface conditions at its respective location and for the respective vertical reach, local variations characteristic of the subsurface materials of the region are anticipated and may be encountered.

8.0 DRILLED SHAFT FOUNDATION INSTALLATION CONSIDERATIONS

Drilled shaft foundation excavation and installation at this site will be difficult as a result of the presence of relatively shallow groundwater, granular soils below the groundwater level and very soft, silt and clay soils between depths of approximately 10 and 45 feet below ground surface. The use of permanent or temporary casing and the wet/slurry method of construction will likely be necessary. If drilled shafts are selected for use on these projects, all aspects of drilled shaft construction, including quality control, should be conducted in accordance with Section 803.03 of the current edition of the MDOT Standard

Specifications for Road and Bridge Construction and the Federal Highway Administration (FHWA)

Publication No. FHWA‐IF‐99‐025 titled Drilled Shafts: Construction Procedures and Design Methods.

Inspection of shaft construction should be made by experienced personnel to verify that the shafts are installed as designed.

Keesler Air Force Base Tower Foundations

- 4 -

9.0 GENERAL COMMENTS AND LIMITATIONS

While the CPT soundings are representative of subsurface conditions at their respective locations and for their respective vertical reaches, local variations characteristic of the subsurface materials of the region are anticipated and may be encountered. The delineation between soil types shown on the logs is approximate and the description represents our interpretation of subsurface conditions at the designated test locations and on the particular date explored.

This report has been prepared in order to aid in the evaluation of this project and to assist the engineers in the project planning and structural design. At the time of writing, changes were still being considered to foundations, site grading, and other aspects of the project that could have a significant impact on the applicability or relevance of the recommendations provided in this report. SESI should be consulted as the design process continues to ensure that the recommendations provided in this report are still applicable, and that they are being properly interpreted.

This report is intended for use with regard to the specific project discussed herein as we understand it at this time, and any substantial changes in the project, loads, locations, or assumed grades should be brought to our attention so that we may determine how such changes may affect our conclusions and recommendations. We would appreciate the opportunity to review the plans and specifications for construction to ensure that our conclusions and recommendations are interpreted correctly.

Professional judgments on design alternatives and criteria are presented in this report. These are based partly on our evaluations of technical information gathered, partly on our understanding of the characteristics of the project being planned, and partly on our general experience with subsurface conditions in the area. We do not guarantee performance of the project in any respect, only that our engineering work and judgments rendered meet the standard of care of our profession.

This report is exclusively for the use and benefit of the addressee(s) identified on the first page of this report and is not for the use or benefit of, nor may it be relied upon by any other person or entity. The contents of this report may not be quoted in whole or in part or distributed to any person or entity other than the addressee(s) hereof without, in each case, advanced written consent.

Keesler Air Force Base Tower Foundations

APPENDIX 1

Test Location Plans

KEESLER AIR FORCE BASE

TOWER FOUNDATIONS

BILOXI, MS

VICINITY MAP

SESI JOB #: M22-430

PROJECT

AREA

PROJECT

AREA

MEADOWS DR

LAR

C

H

ER

BLVD

S

N

EW

BILOXI, MS

TEST LOCATION PLAN

SESI JOB #: M22-430

S

N

EW

CPT-1

CPT SOUNDING

NOT TO SCALE

H ST

2N

D S

T

G ST

BILOXI, MS

TEST LOCATION PLAN

SESI JOB #: M22-430

S

N

EW

CPT-2

CPT SOUNDING

NOT TO SCALE

CMSGT ETCHBERGER W

AY

HANGAR RD

PHANTO

M S

T

Keesler Air Force Base Tower Foundations

APPENDIX 2

CPT Sounding Logs

Southern Earth Sciences Operator: Danny Hines

Sounding: CPT-1

Cone Used: DDG1349

GPS Data: N30.41039 W88.91489 Groundwater: Collapsed and dry at 5.8-ft.

CPT Date/Time: 6/17/2022 11:22:50 AM

Location: Keesler AFB Comm. Towers

Job Number: M22-430

Maximum Depth = 100.07 feet Depth Increment = 0.164 feet

Asphalt Surface

*Soil behavior type and SPT based on data from UBC-1983

Tip Resistance

Qc TSF

Depth (ft)

Local Friction

Fs TSF

Pore Pressure

Pw PSI 90-10

Friction Ratio

Fs/Qc (%)

Soil Behavior Type*

Zone: UBC-1983

1 sensitive fine grained 2 organic material 3 clay

4 silty clay to clay 5 clayey silt to silty clay 6 sandy silt to clayey silt

7 silty sand to sandy silt 8 sand to silty sand 9 sand

10 gravelly sand to sand 11 very stiff fine grained (*) 12 sand to clayey sand (*)

SPT N*

60% Hammer

Southern Earth Sciences Operator: Danny Hines

Sounding: CPT-2

Cone Used: DDG1349

GPS Data: N30.40345 W88.91906 Groundwater: Collapsed and dry at 4.5-ft.

CPT Date/Time: 6/17/2022 10:03:01 AM

Location: Keesler AFB Comm. Towers

Job Number: M22-430

Maximum Depth = 110.07 feet Depth Increment = 0.164 feet

Grassed surface.

*Soil behavior type and SPT based on data from UBC-1983

Tip Resistance

Qc TSF

Depth (ft)

Local Friction

Fs TSF

Pore Pressure

Pw PSI 180-20

Friction Ratio

Fs/Qc (%)

Soil Behavior Type*

Zone: UBC-1983

1 sensitive fine grained 2 organic material 3 clay

4 silty clay to clay 5 clayey silt to silty clay 6 sandy silt to clayey silt

7 silty sand to sandy silt 8 sand to silty sand 9 sand

10 gravelly sand to sand 11 very stiff fine grained (*) 12 sand to clayey sand (*)

SPT N*

60% Hammer

Keesler Air Force Base Tower Foundations

APPENDIX 3

Allowable Passive Pressure vs. Depth Graphs

4620 , 20

2452 , 20

2928 , 30

3528 , 30

3844 , 36

4492 , 36

5186 , 42

7085 , 42

8243 , 50

14918 , 87

13272 , 87

15358 , 100

0.0

20.0

40.0

60.0

80.0

100.0

120.0

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000

D

EP

TH

FT

PASSIVE EARTH PRESSURE (KSF)

Passive Pressure

Keesler AFB Commumication Towers Foundations

Ultimate Passive Earth Pressure vs. Depth

SESI Project M22‐430 Location CPT‐1

1211 , 7

1003 , 7

1194 , 11

1579 , 11 1859 , 13

1299 , 13

1489 , 17

2190 , 17

1842 , 18 1937 , 20

2758 , 20

3371 , 24

2467 , 24

3467 , 45

6808 , 45

9575 , 61

9189 , 61 9609 , 69

8409 , 69

9146 , 83

10346 , 83

11030 , 96

12388 , 96

14546 , 110

0.0

20.0

40.0

60.0

80.0

100.0

120.0

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000

D

EP

TH

FT

PASSIVE EARTH PRESSURE (KSF)

Passive Pressure

Keesler AFB Commumication Towers Foundations

Ultimate Passive Earth Pressure vs. Depth

SESI Project M22‐430 Location CPT‐2