Geotechnical_Report.pdf

May 26, 2010 L - 74,782S

REPORT OF SOILS EXPLORATION

SECURITY FORCES BUILDING ADDITION

ILLINOIS AIR NATIONAL GUARD

SPRINGFIELD, ILLINOIS

PREPARED FOR

THE BENHAM COMPANIES, LLC

622 EMERSON ROAD, SUITE 600

ST. LOUIS, MISSOURI 63141-6728

PREPARED BY

TESTING SERVICE CORPORATION

1701 WEST MARKET STREET

BLOOMINGTON, ILLINOIS 61701

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May 26, 2010 L - 74,782S

REPORT OF SOILS EXPLORATION

SECURITY FORCES BUILDING ADDITION

ILLINOIS AIR NATIONAL GUARD

SPRINGFIELD, ILLINOIS

INTRODUCTION

This report presents results of our site exploration which was performed to determine subsurface soil and groundwater conditions at the site of the addition to the Security Forces Building at the Illinois Air National Guard in Springfield, Illinois. The geotechnical services were performed at the request of Mr. Richard Gabler of The Benham Companies, LLC (Benham) in accordance with the scope of services contained in TSC Proposal No. 44,313, dated January 15, 2010. Results of field and laboratory work and recommendations based upon that work are included in the following sections of this report.

SITE/PROJECT DESCRIPTION

The site of the existing Illinois Air National Guard (IANG) facility is located in the northeastern portion of the Capital Airport in Springfield, Illinois. The Security Forces Building is located in the southwestern portion of the facility. The project will include the demolition of the existing apparatus bay which is in the central portion of the building. This section has floor space of approximately 4,980 square feet with a 17' high roof. The adjacent structures on both sides of the apparatus bay are two-stories with masonry walls, precast concrete and a structural steel frame. This building is supported on a drilled pier foundation system bearing at a depth of approximately 25 feet below grade.

The new construction will consist of a high-bay building with a partial second floor. The structural system will include a steel frame and masonry exterior walls. The slab-on-grade of the new construction will match that of the sections of the building that are to remain.

Security Forces Building Addition Illinois Air National Guard Springfield, Illinois L - 74,782S May 26, 2009

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FIELD EXPLORATION

Two (2) soil test borings were completed on the project site. These borings were located on the north and south sides of the apparatus bay and were extended to a depth of approximately 35 feet below the existing ground surface. The boring locations are shown on the Boring Location Plan included in the Appendix of this report.

The borings were drilled and sampled according to currently recommended American Society for Testing and Materials (ASTM) specifications. Outlines of these procedures are included in the Appendix. Soil sampling was performed at 2-1/2 foot intervals to a depth of 15 feet and at 5 foot intervals thereafter to the termination depth of each boring. Most samples were obtained in conjunction with the Standard Penetration Test, for which the driving resistance of a 2 inch diameter split-spoon sampler provides an indication of the relative density of granular materials and consistency of cohesive soils. Selected samples of the cohesive soil deposits were obtained by thin walled tube methods. Water level readings were taken during and following completion of the drilling operations.

LABORATORY TESTING

Soil samples were examined in the laboratory to verify field descriptions and to determine classifications in accordance with the Unified Classification System. Laboratory testing included moisture content determinations on all cohesive soil types. Measurements of unconfined compressive strengths on natural cohesive soil samples were made. A calibrated penetrometer was also utilized to provide estimates of the unconfined compressive strength. Selected samples were also tested to determine dry unit weight values.

All phases of the laboratory testing program were conducted in general accordance with applicable ASTM standards. The results of these tests are shown on the Boring Logs included in the Appendix.

Springfield, Illinois L - 74,782S May 26, 2009

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SUBSURFACE CONDITIONS

Both borings were drilled though the existing concrete pavement adjacent to the building. The concrete at these locations is approximately 8 to 10 inches thick and is underlain by a sand and gravel base extending to a depth of approximately 2 to 2-1/2 feet. What appears to be fill soils placed during the construction of the existing building were noted below the sand and gravel. The fill consists predominately of silty clay. The fill is loose in relative density with N values of 5 to 6 blows per foot. Corresponding moisture content values are generally near 30 percent. These deposits were sampled to depths of approximately 8 to 11 feet.

The underlying undisturbed native soils directly below the fill at Boring 4, drilled on the north side of the building, consist of low strength silty clay and clayey silt. These soils also contain some organic matter and have moisture content values near 30 percent and extend to a depth of approximately 13-1/2 feet.

Somewhat higher strength silty clay deposits were sampled below depths of 11 to 13-1/2 feet. These soils have unconfined compressive strength values typically between 1.5 and 2.0 tons per square foot (tsf).

Corresponding moisture content values are between 20 and 25 percent. These soils were sampled to depths of approximately 22 to 23 feet.

Hard sandy clay was encountered below these soils at both locations. These high strength deposits have unconfined compressive strength values as high a 7.0 tsf and moisture content values that are generally near 10 percent. These soils were sampled to the termination depth of 35 feet.

Free water was encountered while drilling at depths ranging from approximately 11 to 13 feet. Upon completion and removal of the augers, the free water level was on the order of 10 feet.

Springfield, Illinois L - 74,782S May 26, 2009

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RECOMMENDATIONS

Foundation Recommendations

The near surface soils at both boring locations include layers of soft silty clay and loose clayey silt with moisture content values as high as 30 percent extending to depths of 11 to 13-1/2 feet. In view of these conditions, we recommend that the foundations extend through these soft and loose soils to minimize the potential for excessive settlement. Due to the required depths of the excavations that will be required to provide support below these soils, construction of drilled pier or caisson foundations is recommended. We recommend a bearing depth of approximately 25 feet which corresponds to an elevation of approximately 75 based upon an assumed elevation of 100 for the top of the existing floor slab. Drilled piers or caissons bearing in the hard sandy clay soils found at or below this depth may be design using a net allowable bearing pressure of 15,000 pounds per square foot (psf).

We understand that the foundations may also be subject to uplift forces associated with wind loads. Due to the low strengths of the near surface soils, we recommend that adhesion between the drilled piers or caissons and these deposits be neglected above an elevation of approximately 86. Below this elevation and extending to an elevation of 77, we recommend an adhesion value of 500 psf. Below this elevation, an adhesion value of 1,000 psf is recommended.

In view of the overlying soft and loose soils, it is recommended that temporary steel casing be used to support the walls of the drilled piers or caisson shafts. This will minimize the inflow of water during belling and cleaning operations. We anticipate that temporary casing may be required to an elevation of 77.

Pumps may also be required to remove water that does seep into the shaft to allow placement of concrete under dry conditions.

Springfield, Illinois L - 74,782S May 26, 2009

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Care should be exercised in the installation of the casing to make sure that it is sealed into a clay layer that will maintain a water-tight seal when the soil is removed from inside the through the entire depth of the overlying fill. The last few feet of clay drilling and the removal of a portion of the clay from inside the casing should be delayed until concrete is on the job. When the drilling operations and inspections are complete, concrete should be placed inside the casing immediately. During simultaneous concrete placing and casing removal operations, sufficient concrete should be maintained inside the casing to offset the hydrostatic head of the groundwater outside the casing and prevent the intrusion of soil and groundwater in the pier concrete.

Seismic Considerations

We have also reviewed information regarding the site seismic classification considering the soil profile encountered in the borings on the project site and deeper borings that have been drilled to a depth of 100 feet on nearby projects. The average undrained shear strength of the soils in the upper 100 feet is estimated to be in excess of 2,000 psf. Based upon the criteria contained in Table 1613.5.2 of the 2006 International Building Code and this average shear strength, we recommend Site Class C.

Groundwater Control

As previously noted, some groundwater seepage was noted from the high moisture content clay and silt deposits in the upper regions of the site. Based upon these conditions, some groundwater seepage into shallow grade beam or pier cap excavations is expected. We anticipate that conventional sump and pump arrangements should be capable of removing this groundwater.

Springfield, Illinois L - 74,782S May 26, 2009

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Site Subgrade Preparation

We anticipate that the existing concrete slab-on-grade in the apparatus bay will be demolished to allow for the new construction. After slab is removed and prior to placement of new fill or concrete slabs, the subgrade should be proof-rolled in order to detect the presence of unsuitable soil types. The proof-roll should be performed using a loaded dump truck or other approved piece of heavy rubber-tired construction equipment. All soft or unstable materials defined by proof-rolling should either be reworked and recompacted or, if that does not improve subgrade stability, removed and replaced. The near surface silty clay soils have relatively low strengths and high moisture contents. Therefore, subgrade instability is expected in most areas, particularly during periods of wet weather.

Clay soils can typically be stabilized by reducing the moisture content and recompacting. For obvious reasons this will work best in hot, dry and windy weather, which may or may not be the case at the time construction is completed. Based upon an estimated optimum moisture content near 15 percent for the on site soils, reductions in the moisture of 10 percentage points or more may be required.

In areas where unstable subgrade conditions are encountered, removal and replacement with select granular fill can also be used for stabilization. This is generally required in areas of low strength silt deposits. Typically, placement of 12 to 24 inches of coarse aggregate is required. The coarse aggregate may consist of crushed stone or gravel between about 1/4 to 3 inches in size and containing no fines.

IDOT gradations CA-1, CA-5 and CA-7 meet these criteria. The aggregate should be placed in maximum 18 inch lifts and compacted to a dense and stable A geotextile fabric cloth can also be used as a separation layer between the soft soils and aggregate to provide additional stability.

New fill otherwise should consist of approved granular materials or inorganic silty clays of medium to high plasticity. It is recommended that compaction for building pad and pavement areas be to a minimum of 95 percent of maximum dry density as determined by the Modified Proctor Test (ASTM D 1557). The fill should be placed in approximate 9-inch lifts loose measure, with each lift compacted to the specified density prior to placement of additional fill.

Springfield, Illinois L - 74,782S May 26, 2009

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CLOSURE

It is recommended that full time site observations and testing be provided by Testing Service Corporation personnel during foundation construction to document that soils capable of achieving the recommended bearing capacity have been encountered at the planned bearing elevation. In addition, monitoring of building materials and fill placement and compaction should be completed to document compliance with the recommended procedures and specifications.

The analysis and recommendations submitted in this report are based upon the data obtained from the two

(2) soil borings performed at the locations indicated on the Boring Location Plan. This report does not reflect any variations which may occur between these borings, the nature and extent of which may not become evident until during the course of construction. If variations are then identified, the recommendations contained in this report should be reevaluated after performing on-site observations.

Douglas P. Ramsey Registered Professional Engineer Illinois No. 062-040905

Michael V. Machalinski, P.E.

Vice President

Concrete Pavement Loose brown clayey SAND and GRAVEL

(SC/GC)

FILL - Dark brown silty CLAY, trace sand, very moist to moist (CL)

Tough brown-gray silty CLAY, trace sand, moist (CL-CH)

Hard brown sandy CLAY, some gravel, moist (CL) Hard gray sandy CLAY, some gravel, moist

(CL)

End of Boring at 35.0'

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

0.8

2.5

11.0

23.0

25.0

99.2

97.5

89.0

77.0

75.0

SS

SS

SS

ST

SS

ST

SS

SS

SS

SS

97.1

104.3

4.1

28.9

28.6

26.6

25.0

22.4

22.1

10.9

8.8

9.3

0.5*

0.5*

0.75*

1.76 1.75*

1.52 1.5*

1.93 1.75*

4.5+*

4.5+*

4.5+*

5-18-10 5-18-10

Security Forces Building Addition, Illinois Air National Guard, Springfield, I

13.0 '

B-3 L-74,782

100.0

The Benham Companies, LLC, 622 Emerson Rd., Ste. 600, St. Louis, MO 63141

Caved @ 5.0'65.0 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

Concrete Pavement Loose brown clayey SAND and GRAVEL

(SC/GC)

FILL - Brown-dark brown silty CLAY, trace sand, moist (CL) FILL - Brown fine to medium SAND, damp

(SP)

Possible Fill - Soft dark brown-gray silty CLAY, trace sand, very moist (CH)

Stiff dark brown silty CLAY, trace sand, very moist (CH)

Loose dark brown clayey SILT, trace organics and roots, very moist (OH)

Tough brown-gray silty CLAY, trace sand, moist (CH)

Hard brown sandy CLAY, some gravel, moist (CL)

Hard gray sandy CLAY, some gravel, moist

(CL)

End of Boring at 35.0'

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

A

B

0.8

2.0 3.0

5.0

8.0

11.0

13.5

22.0

28.0

99.1

97.9 96.9

94.9

91.9

88.9

86.4

77.9

71.9

SS

ST

SS

SS

ST

SS

ST

SS

SS

SS

102.8

91.9

88.4

97.2

104.9

6.9 20.9

5.9

30.5

29.0

30.5

25.9

22.2

10.5

10.2

10.4

1.0*

0.5*

0.75*

1.39 1.5*

1.90 1.75*

7.20 4.5+*

6.20 4.5+*

4.5+*

5-18-10 5-18-10

Security Forces Building Addition, Illinois Air National Guard, Springfield, I

11.0 '

B-4 L-74,782

99.9

The Benham Companies, LLC, 622 Emerson Rd., Ste. 600, St. Louis, MO 63141

10.0 '64.9 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