238715 GEOTECH REPORT R1.pdf

MMMEEETTT

Midwest Engineering and Testing, Inc.

geotechnical - environmental - materials engineers 1701 West Market Street

Bloomington, IL 61701 309-821-0430

FAX 309-821-1242

www.metgeotech.com

February 11, 2022

Lt. Col. Robert Mitchell Illinois Air National Guard Abraham Lincoln Capital Airport Springfield, Illinois 62707

Re: Subsurface Exploration and Foundation Recommendations

Proposed Communications Tower Illinois Air National Guard Springfield, Illinois MET Project No. B23001

Dear Mr. Mitchell:

In accordance with your request, Midwest Engineering and Testing, Inc. (MET) has completed a geotechnical exploration and evaluation of the subsurface conditions for the above-referenced project. Our geotechnical report in .pdf format, which includes our findings and recommendations regarding design and construction of the foundation system, is being submitted via e-mail. Hard copies of the report can also be provided, if so desired.

MET appreciates the opportunity to be of service during this phase of the project. If there are any questions or comments you may have regarding the content of this report, or if we may be of any further service, please contact us at your convenience.

Sincerely, Midwest Engineering and Testing, Inc.

Douglas P. Ramsey, P.E.

Principal Engineer

Daniel E. Tappendorf, P.E.

President

SUBSURFACE EXPLORATION

AND

FOUNDATION RECOMMENDATIONS

Abraham Lincoln Capital Airport Springfield, Illinois

Prepared For

February 11, 2022

MET File No. B23001

TABLE OF CONTENTS Page

INTRODUCTION…………………………………………………………………………………. 1

General Scope Authorization

SITE AND PROJECT DESCRIPTION…………………………………………………………. 1

SEISMIC CONSIDERATIONS…………………………………………………………….……. 2

FIELD EXPLORATION……………………………………………………………………….…. 1

Scope Drilling and Sampling Procedures Field Tests and Measurements Standard Penetration Tests Water Level Measurements Ground Surface Elevations

LABORATORY TESTING………………………………………………..…………….…..…

General Laboratory Tests and Measurements Visual Classification Moisture Content Tests Hand Penetrometer Tests Unconfined Compression Test Dry Density Determination

DESCRIPTION OF SUBSURFACE CONDITIONS……………………………….….….…… 4

General Soil Conditions Groundwater Observations

FOUNDATION DISCUSSION AND RECOMMENDATIONS.……………………………

Foundation Design Spread Footings Spread Footings With Ground Improvement Caissons/Drilled Piers General Foundation Considerations

CONSTRUCTION CONSIDERATIONS………………………………………………….…

Groundwater Control Excavations

GENERAL COMMENTS……………………………………………………….………..….….. 8

APPENDIX

Boring Location Plan Soil Boring Logs General Notes

Subsurface Exploration and Foundation Recommendations

Illinois Air National Guard Springfield, Illinois

INTRODUCTION

General

This report presents the results of a geotechnical exploration completed for the proposed communications tower planned at the Illinois Air National Guard (IANG) facility in Springfield, Illinois. The purpose of this study was to document the subsurface conditions encountered and to establish related parameters for use by the design engineers and architects. Included herein are the results of the subsurface exploration, field and laboratory soil test data, and recommendations regarding design and construction of the foundation system.

Scope

The scope of services included a reconnaissance of the site, subsurface exploration, field and laboratory testing of the soil samples collected, and engineering analysis and evaluation of the data.

Authorization

Authorization to provide these services was in the form of a Proposal Agreement No.

21-160, dated October 20, 2021, between the Illinois Air National Guard and Ramsey Geotechnical Engineering, LLC (RGE). Subsequent to approval of this agreement, the RGE Bloomington, Illinois office merged with Midwest Engineering and Testing (MET) and this exploration was completed by MET in February of 2022.

SITE AND PROJECT DESCRIPTION

The existing Illinois Air National Guard facility is located on the northeastern portion of the Abraham Lincoln Capital Airport in Springfield, Illinois. The new communications tower is planned in a grass covered area on the northeastern portion of the facility.

SEISMIC CONSIDERATIONS

Based upon the soil strength and density information through a depth of 100 feet in the area of the project site, it is our opinion that Site Class D as defined in Table 1613.5.2 of the International Building Code (IBC) – 2015 be utilized for design. The project site is located at approximate latitude 39.5095°N and longitude 89.6649°W. At this location, the 0.2 second period (SS) and 1.0 second period (S1) spectral acceleration values, as determined from the USGS U.S. Seismic Design Maps Web Application, are 0.253g and 0.119g, respectively.

Illinois Air National Guard Springfield, Illinois

FIELD EXPLORATION

Scope

The subsurface exploration consisted of drilling one (1) soil test boring at the location of the tower as staked at the site by the IANG. This boring was drilled to a depth of 35 feet below the existing ground surface. The boring location is shown on the Boring Location Plan, prepared and provided by the IANG, a copy of which is included in the Appendix.

The following sections provide a description of field drilling and testing procedures utilized.

Drilling and Sampling Procedures

The soil boring was performed with a truck-mounted drilling rig equipped with a rotary head. Conventional, continuous-flight, hollow-stem augers were used to advance the hole with representative samples obtained employing split-barrel sampling techniques in general accordance with ASTM Procedure D-1586. A sampling interval of 2.5 feet was used through a depth of 15 ft., with 5 ft. intervals thereafter.

Field Tests and Measurements

Standard Penetration Tests: During the sampling procedure, Standard Penetration Tests (SPTs) were performed at regular intervals through the depth of the boring. The SPT value ("N" or blow counts) is defined as the number of blows required to advance a 2-inch O.D., split-barrel sampler a distance of one foot by a 140-pound hammer falling 30-inches. These values provide a useful preliminary indication of the consistency or relative density of most soil deposits and are included on the Soil Boring Log included in the Appendix.

Water Level Measurements: Water level observations were made during the soil boring operations. Groundwater information is noted on the Soil Boring Log.

Ground Surface Elevations: The ground surface elevation at the boring location was interpolated from available aerial photographs of the site. The elevation information is provided on the Soil Boring Log.

Illinois Air National Guard Springfield, Illinois

LABORATORY TESTING

Additional significant characteristics of the foundation materials were determined in the laboratory to provide data on which to classify and quantitatively assess the engineering properties of the soil samples obtained. The types of soils encountered were identified and logged on the boring record. The results of the field and laboratory tests are presented on the Soil Boring Log.

Laboratory Tests and Measurements

Visual Classification: A soils engineer visually classified all samples in accordance with the Unified Soil Classification System (ASTM D-2488) terminology. An explanation of the symbols used in this system is included in the Appendix to this report.

Moisture Content Tests: The natural moisture content of all samples was determined by ASTM method D-2216 and is recorded on the Soil Boring Log as a percentage of the dry weight of the soil.

Hand Penetrometer Tests: Cohesive specimens extracted from the split-barrel sampler were tested in the laboratory with a calibrated soil penetrometer. This device provides an approximation of the unconfined compressive strength of the soils, and is useful, along with other soil parameters, in evaluating the soil strength characteristics. The results are denoted with an asterisk on the Soil Boring Log beneath the column labeled "QU".

Unconfined Compression Tests: The undrained shear strength of the cohesive soils was determined from unconfined compression tests on specimens obtained from the split-barrel samplers. Soil strength values of samples obtained by the SPT method must also be considered, recognizing that this sampling method provides a representative, but somewhat disturbed sample. The results are listed on the Soil Boring Log beneath the column labeled "QU".

Dry Density Determination: The dry density was determined on the cohesive soils where intact samples were available. The results are listed on the Soil Boring Log beneath the column labeled "ϫDRY".

The laboratory testing was performed in general accordance with the respective ASTM Methods, as applicable. The results are included on the Soil Boring Log. Unless notified to the contrary, all samples will be disposed of after one (1) month.

Illinois Air National Guard Springfield, Illinois

DESCRIPTION OF SUBSURFACE CONDITIONS

The types of foundation materials encountered at the test boring locations are described on the Soil Boring Log. The lines delineating the changes in strata on the logs represent an approximate boundary between the various soil classifications. It must be recognized that the soil descriptions are considered representative for the specific test-hole location, but that variation may occur between the sampling intervals and boring locations. A summary of the major soil profile components is described in the following paragraph. A more detailed description and supporting data for each boring location can be found on the individual Soil Boring Log.

Soil Conditions

Surface deposits of dark brown clayey topsoil, slightly less than one foot in thickness, were noted at the boring location.

The materials directly below the topsoil and extending to a depth of 3 feet consist of clayey silt. This non-cohesive deposit is loose in relative density with an N value of 8 blows per foot. The corresponding moisture content value is approximately 23 percent.

Deposits of silty clay were noted below a depth of 3 feet, extending to the termination depth. To a depth of approximately 17 feet, these cohesive soils are typically very soft to soft in relative consistency. The unconfined compressive strength values are typically between 0.25 and 0.5 tons per square foot (tsf) in this depth range with corresponding moisture content values generally between 20 and 35 percent.

A slightly higher strength silty clay layer was noted between depths of approximately 17 and 27 feet. These soils have unconfined compressive strength values in the range of

0.75 to 1.0 tsf with moisture content values between 20 and 25 percent.

Somewhat higher strength silty clay glacial till deposits were encountered at a depth of approximately 27 feet, extending to the termination depth. These soils have unconfined compressive strength values that are in excess of 4.5 tsf. Moisture content values in these deposits are below 10 percent.

Groundwater Observations

Free water was noted in the bore hole while drilling at a depth of approximately 33 feet.

Upon completion and removal of the augers, the water level was at a depth of approximately 30 feet.

Illinois Air National Guard Springfield, Illinois

It must be recognized that groundwater levels fluctuate with time due to variations in seasonal precipitation, lateral drainage conditions, and soil permeability characteristics.

FOUNDATION DISCUSSION AND RECOMMENDATIONS

Foundation Design

In evaluating the subsurface conditions in combination with the magnitude of the expected foundation loads, we have considered conventional shallow spread footing foundations and a deep foundation system consisting of drilled piers/caissons for support of the structure. Design and construction recommendations for these foundation types follow.

Spread Footings

The near surface deposits consist of relatively low strength silty clay. Based upon the relative strength of these soils, a maximum net allowable bearing pressure of 500 pounds per square foot (psf) would be recommended for foundations bearing above a depth of 17 feet below the existing ground surface. Based upon the expected foundation loads and this extremely low allowable bearing pressure, this foundation type is not considered practical.

Spread Footings With Ground Improvement

Ground improvement consisting of Rammed Aggregate Piers (RAP) or Vibro Stone Columns (VSC) could be considered to potentially allow for construction of spread footings at conventional bearing depths. We anticipate that they would have to extend to a depth on the order of 30 feet to reinforce the upper loose/soft deposit. It has been our experience that an allowable bearing pressure of 4,000 to 5,000 psf can be achieved with this type of ground improvement method. The feasibility of this system along with depths, spacing and allowable bearing pressures should be confirmed with a firm the designs these ground improvement elements.

Illinois Air National Guard Springfield, Illinois

Caissons/Drilled Piers

A caisson or drilled pier foundation system has also been considered for support of the structure. This foundation type is typically most practical when there is a relatively high strength soil deposit overlying soft or loose near surface soils. As previously noted, the glacial till silty clay deposits found at and below a depth of approximately 27 feet have notably higher strengths than the overlying soils. A net allowable bearing pressure of 10,000 psf is recommended for design of drilled piers or caissons extending into the glacial till at a depth of approximately 30 feet.

Final design of the drilled pier/caisson foundation system will likely also require an analysis of the adhesion (skin friction) and lateral response of the shafts.

Recommended adhesion values and soil modulus values (k) to be used in the computer program LPILE to complete this analysis are provided in the following table.

Depth (ft.) Soil Type Adhesion (psf) k (pci) Soil Strain E50

Above 17 Soft Clay 100 30 0.02

From 17 to 27 Stiff Clay 400 300 0.007

Below 27 Hard Clay 1,200 2,000 0.004

General Foundation Considerations

The recommended bearing pressures and foundation capacities are based upon a factor of safety of 3 for normal operating conditions. For transient loading conditions resulting from wind or seismic events, the factor of safety may be reduced to 2.25.

In general, the performance of the foundation systems on this site is dependent on the various factors, which have been discussed. Potential load responsive settlements should remain within tolerable limits (estimated to be less than 1.0 inch) if the suggested design and construction criteria are followed. It is recommended that the preparation and installation of the foundations be monitored and tested by a representative of the soils engineer.

Illinois Air National Guard Springfield, Illinois

CONSTRUCTION CONSIDERATIONS

Groundwater Control

Based on the boring information, it is not anticipated that significant groundwater seepage will be experienced in possible shallow foundation excavations. Should any seepage be encountered, filtered sump pumps or other dewatering devices should be made available to control the water and maintain reasonably dry conditions.

Because the foundation materials are subject to deterioration when exposed to free moisture, every effort should be made to keep the soils dry, during and after construction. Site runoff and discharge water from roof drains should be diverted away from the foundation and directed towards on-site retention areas, natural drainage ways or municipal sewer systems. Such measures reduce the potential for the softening and possible erosion of the foundation subgrade soils.

In view of the notably lower strength silty clay soils above the recommended bearing depth for drilled piers/caissons, temporary steel casing will likely be required to support the walls of the shafts if this foundation type is constructed. This will also minimize the inflow of water during belling and cleaning operations. Casing extending to a depth of 30 feet may be required. Pumps may also be required to remove water that does seep into the shaft to allow for placement of concrete under dry conditions.

Excavations

All excavations should be performed in accordance with the requirements detailed in the OSHA Excavation Regulations and Procedures, Section 1926 Subpart P. Based upon the soil boring data, Type A, B and C soils were all encountered through a depth of 15 feet.

The maximum allowable slopes for these soil types are shown in the following table.

Soil Type Maximum Allowable Slopes for Excavations Less than 20 ft. deep Horizontal : Vertical (H:V)

A ¾ : 1 B 1: 1 C 1½:1

All excavations should be monitored by a Competent Person, as defined by the OSHA standard, and appropriate shoring or sloping techniques used to prevent cave-ins.

Illinois Air National Guard Springfield, Illinois

GENERAL COMMENTS

This geotechnical exploration and foundation analysis has been conducted to aid in the evaluation of the foundation conditions for the proposed communications tower planned at the IANG facility in Springfield, Illinois. The recommendations presented herein are based on the available soil information obtained and the design information provided.

Any changes in the soil conditions encountered during construction, or in the building design or location, should be brought to the attention of the soils engineer to determine if modifications in the recommendations are required. The final design plans and specifications should also be reviewed by the soils engineer to determine that the recommendations presented herein have been interpreted and implemented as intended. It is recommended that the earthwork and foundation operations be monitored by the soils engineer, to test and evaluate the bearing capacities, and the selection, placement, and compaction of controlled fills.

This geotechnical study has been conducted in a manner consistent with that level of care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions. The findings, recommendations, and opinions contained herein have been promulgated in accordance with generally accepted practice in the fields of foundation engineering, soils mechanics, and engineering geology. No other representations, expressed or implied, and no warranty or guarantee is included or intended in this report.

APPENDIX

Untitled Map Write a description for your map.

Legend

Air National Guard 183rd Wing

4000 ft

N

N Image Landsat / Copernicus

Image Landsat / Copernicus

Image Landsat / Copernicus

1260818291N Oval

1260818291N Line

1260818291N Text Box Boring Location for Comm Tower

0.75*

0.25*

0.25*

0.45 0.5*

0.33 0.25*

1.03 1.0*

0.74 0.75*

4.5+*

4.5+*

Dark brown clayey TOPSOIL (OL) Loose brown-dark brown clayey SILT, trace sand (ML)

Medium stiff dark brown very silty CLAY, trace sand (CL)

Very soft to soft dark brown-gray very silty CLAY, trace sand (CL)

Very soft gray very silty CLAY, trace sand

(CL)

Stiff to medium stiff gray silty CLAY, trace sand (CL)

Hard gray very silty CLAY, little sand and gravel (CL)

End of Boring at 35.0'

* Approximate unconfined compressive strength based on measurements with a calibrated pocket penetrometer.

0.8

3.0

6.0

13.0

17.0

27.0

579.2

577.0

574.0

567.0

563.0

553.0

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

88.7

97.7

100.5

105.7

50/5"

23.1

23.3

33.9

35.0

30.2

26.9

25.1

21.4

8.2

8.4

CME 45

2-1-22 2-1-22

Communications Tower, Illinois Air National Guard, Springfield, IL

33.0 '

B-1 B23001

580.0

Illinois Air National Guard, Abraham Lincoln Capital Airport, Springfield, IL 62707

30.0 '545.0 approximate boundaries between soil types;

DATE STARTED

AT END OF BORING

DATE COMPLETED

SAMPLE

WC DRY DEPTHN

in-situ, the transition may be gradual.

Division lines between deposits represent

WATER TABLE

GROUND SURFACE

END OF BORING

WHILE DRILLING

JOB

24 HOURS

ELEV. SOIL DESCRIPTIONS

NO. TYPE

D I S T A N C E

B E L O W

S U R F A C E

I N

F E E T

L E N G T H

R E C O V E R Y

DRILL RIG NO.

PROJECT

CLIENT

BORING

ELEVATIONS

Qu

GENERAL NOTES

SAMPLE IDENTIFICATION

Visual soil classifications are made in general accordance with the Unified Soil Classification System on the basis of textural and particle size categorization, and various soil behavior characteristics.

Visual classifications should be substantiated by appropriate laboratory testing when a more exact soil identification is required to satisfy specific project applications criteria.

PARTICLE SIZE +

Boulders: 8 inches

Coarse Sand: 2 mm to 4 mm

Silt: 0.005 mm to 0.074 mm

Cobbles: 3 to 8 inches Medium Sand: 0.42 mm to 2 mm Clay: - 0.005 mm Gravel: 5 mm to 3 inches

Fine Sand: 0.074 to 0.42 mm

DRILLING & SAMPLING SYMBOLS

SS: Split-spoon, 2” O.D. by 1 3/8” I.D.

ST: Shelby Tube, 2” O.D. or 3” O.D., as noted in test RB: Roller Bit AU: Auger Sample WS: Wash Sample DB: Diamond Bit BS: Bag Sample CB: Carbide Bit HA: Hand Auger

SOIL PROPERTY SYMBOLS

N: Standard penetration count, indicating number of blows of a 140 lb. Hammer with a 30-inch drop, required to advance a split-spoon sampler one (1) foot.

Qu: Unconfined compressive strength, tons per square foot (tsf).

Qp: Calibrated hand penetrometer resistance, tsf.

MC: Moisture Content, % LL: Liquid Limit PL: Plastic Limit PI: Plasticity Index Dd: Dry density, pounds per cubic foot (pcf).

PID Photoionization Detector (Hnu meter) volatile vapor level, ppm

SOIL RELATIVE DENSITY AND CONSISTENCY CLASSIFICATION

NON-COHESIVE SOILS COHESIVE SOILS

Classifier N-Value Range Classifier Qu Range (tsf) N-Value Range very loose 0 – 3 very soft 0 – 0.25 0 – 2 loose 3 – 7 soft 0.25 – 0.5 2 – 5 medium dense 7 – 15 medium stiff 0.5 – 1.0 5 – 10 dense 15 – 38 stiff 1.0 – 2.0 10 – 14 very dense 38 + very stiff hard

2.0 – 4.0

4.0 +

14 – 32 32 +

GROUNDWATER

Approximate Groundwater level at time noted on soil boring log, measured in open bore hole unless otherwise noted. Groundwater levels often vary with time, and are affected by soil permeability characteristics, weather conditions, and lateral drainage conditions.

UNIFIED SOIL CLASSIFICATION

MAJOR DIVISIONS

SYMBOL

TYPICAL DESCRIPTION

GW

Well-graded gravels and gravel-sand mixtures

Clean

Gravels

GP

Poorly-graded gravels and gravel-sand mixtures

GM

Silty gravels and gravel-sand-silt mixtures

Gravel and

Gravelly Soils

Gravels with Fines GC

Clayey gravels and gravel-sand-clay mixtures

SW

Well-graded sands and gravelly sands

Clean Sands

SP

Poorly-graded sands and gravelly sands

SM

Silty sands and sand-silt mixtures

COARSE

GRAINED

SOILS

Sand and Sandy Soils

Sands with Fines SC

Clayey sands and sand-clay mixtures

ML

Inorganic silts or clayey silts of slight plasticity

CL

Inorganic clays of low to medium plasticity

Silts and Clays of Low Plasticity

OL

Organic silts and organic silty clays of low plasticity

MH

Inorganic silts of high plasticity

CH

Inorganic clays of medium to high plasticity

FINE

GRAINED

SOILS

Silts and Clays of High Plasticity

OH

Organic clays of medium to high plasticity

Highly Organic Soils

PT

Peat, humus and swamp soils with high organic contents

Note: Dual symbols are used to indicate borderline classifications.