Geotechnical Engineering Report

Transcription

1 Geotechnical Engineering Report Science & Health Careers Center Oakton Community College Des Plaines, Illinois October 4, 11 Terracon Project No Prepared for: Oakton Community College Des Plaines, Illinois Prepared by: Terracon Consultants, Inc. Naperville, Illinois Responsive Resourceful Reliable

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3 TABLE OF CONTENTS Page EXECUTIVE SUMMARY... i 1.0 INTRODUCTION PROJECT INFORMATION Project Description Site Location and Description Typical Profile Water Level Observations RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION Geotechnical Considerations Earthwork Site Preparation Engineered Fill Material Requirements Fill Placement and Compaction Requirements Earthwork Construction Considerations Grading and Drainage Drilled Shaft Foundations Drilled Shaft Foundation Design Recommendations Drilled Shaft Foundation Construction Considerations Floor Slab Floor Slab Design Recommendations Floor Slab Construction Considerations Below Grade Walls Lateral Earth Pressures Subsurface Drainage Pavements Pavement Design Recommendations Pavement Construction Considerations Seismic Site Class... APPENDIX A FIELD EXPLORATION Exhibit A-1 Field Exploration Description Exhibit A-2 Boring Location Plan Exhibits A-3 to A-21 Boring Logs Exhibits A-22 & A-23 ReMi Seismic Testing Results APPENDIX B LABORATORY TESTING Exhibit B-1 Laboratory Testing Exhibits B-2 Chemical Test Results APPENDIX C SUPPORTING DOCUMENTS Exhibit C-1 General Notes Exhibit C-2 Unified Soil Classification Responsive Resourceful Reliable

4 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No EXECUTIVE SUMMARY The following items represent a brief summary of the findings of our subsurface exploration and our geotechnical recommendations for the proposed Science & Health Careers Center planned at Oakton Community College in Des Plaines, Illinois. This summary should be reviewed in conjunction with the complete report. Based on the subsurface conditions encountered in the borings, the anticipated structural loads (600 to 1,000 kip column loads), and the preliminary building plans provided to us at the time this report was prepared, it is Terracon s opinion that the proposed 3-story building should be supported on drilled shaft foundations. Geotechnical recommendations for design and construction of drilled shaft foundations are provided in this report. Existing fill materials (comprised primarily of lean clay with variable amounts of sand and gravel) were encountered to depths of about 2½ to 6 feet below existing surface grades at most of the boring locations. Based on conditions encountered in the borings, it appears that some compactive effort was applied to portions of the fill; however, no documentation regarding placement and compaction of the fill was provided for our review. If the existing fill will be left in place below slabs, pavements or other features, additional observation and testing of the existing fill should be performed to reduce the risk of adverse slab/pavement performance. The soils encountered in the upper few feet at the boring locations generally consisted of lean clays with traces of sand and gravel (both fill and native soils). The moisture content of these soils was relatively high (ranging from about to 31 percent) at many of the boring locations. Subgrades comprised of clay soils with relatively high moisture contents often become unstable when they are disturbed and/or subjected to construction traffic. Therefore, some undercutting or stabilization of the subgrade will likely be required to facilitate compaction of new engineered fill or to provide a stable subgrade for grade supported floor slabs and pavements. A -year flood elevation of feet and a 0-year flood elevation of 636. feet were indicated on the preliminary plans provided to us. The ground surface elevation at the building area borings generally ranged from about 632 to 634 feet. Therefore, even though the depth to water was variable at the boring locations, and water was not encountered at some boring locations, it is likely that water will be encountered in excavations at this site. The contractor should anticipate this and plan for the appropriate dewatering needed to control seepage and facilitate construction. Responsive Resourceful Reliable i

5 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No Close monitoring of the construction operations discussed herein will be critical in achieving the design subgrade support. We therefore recommend that Terracon be retained to provide observation/testing during this portion of the work. This summary should be used in conjunction with the entire report for design purposes. It should be recognized that details were not included or fully developed in this section, and the report must be read in its entirety for a comprehensive understanding of the items contained herein. The section titled GENERAL COMMENTS should be read for an understanding of the report limitations. Responsive Resourceful Reliable ii

6 GEOTECHNICAL ENGINEERING REPORT SCIENCE & HEALTH CAREERS CENTER OAKTON COMMUNITY COLLEGE DES PLAINES, ILLINOIS Terracon Project No October 4, INTRODUCTION Terracon Consultants, Inc. (Terracon) has completed a subsurface exploration for the proposed Science & Health Careers Center planned at the Oakton Community College campus in Des Plaines, Illinois. Twenty () borings were performed at the site to depths ranging from approximately to 0 feet below the existing ground surface. Boring logs and a Boring Location Plan are included in Appendix A. Borings 1 through 12 were located within the proposed new Science & Health Careers Center building area. Borings 13 through were located near the existing Oakton Community College building, and were requested to provide preliminary information for a potential future addition to that building (not addressed in this report). Borings through were performed in the north part of Parking Lot D (not currently planned for additional development), and Borings 1 and were performed in the peninsula on the west side of Oakton Lake (where grades may be lowered to balance the floodplain area and account for the grade increases in the new development). This report describes the subsurface conditions encountered at the boring locations, presents the test data, and provides geotechnical engineering recommendations regarding the following items: site preparation and earthwork design and construction of drilled shaft foundations floor slab subgrade preparation lateral earth pressures pavement subgrade preparation recommended minimum pavement sections seismic site class 2.0 PROJECT INFORMATION Project information was provided by Legat Architects and is summarized below. Responsive Resourceful Reliable 1

7 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No Project Description ITEM Site layout Structure Maximum loads Maximum allowable settlement Pavements Grading DESCRIPTION See Appendix A, Exhibit A-2 Boring Location Plan The proposed building will be a three-story structure located in the southern part of the existing Parking Lot D. The building footprint is larger in the upper floors due to overhangs. The plan areas of the first, second and third floors will be about 24,000, 2,000, and 36,000 square feet, respectively. Current grade within most of the building area is at about 633 feet (USGS datum), and the 0-year flood elevation is approximately 636. feet. Therefore, the first floor elevation is planned to be at about elevation 640. feet. In the west part of the building, fill will be placed above current grade to develop a subgrade for a slab-on-grade. In the east part of the building, the first floor slab will be a structural slab supported on the building s foundation system, and the portions of the columns extending below the first floor level will be screened by a curtain wall that extends to existing ground level. A wall with unbalanced backfill is planned at the junction between the structural slab and slab-on-grade areas of the building. According to the project structural engineer (Harley Ellis Devereaux), column loads are expected to range from approximately 600 to 00 kips. Maximum allowable settlements for the building were not provided. The following values were assumed: Columns: 1 inch Walls: ¾ inch over 40 feet A new parking lot is planned south of the new building, and some of the existing pavements in Parking Lot D may be reconstructed. Fills of up to 7 feet are expected to develop the floor slab subgrade in the west part of the building. Cuts/fills of 2 feet or less are expected in the remainder of the development area. Responsive Resourceful Reliable 2

8 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No Site Location and Description ITEM Location Current Site Improvements Existing topography DESCRIPTION Oakton Community College campus, 00 East Golf Road, Des Plaines, Illinois Existing pavements are present within the north part of the proposed new building area. The south part of the proposed new building area is currently a lawn area. Based on the site topographic plan prepared by Manhard Consulting, surface elevations within the proposed new building area currently range from about 632 to 634 feet. 3.0 SUBSURFACE CONDITIONS 3.1 Typical Profile Subsurface conditions at each boring location are described on the individual boring logs in Appendix A. The stratification boundaries shown on the boring logs represent the approximate depths where changes in material types occur. In-situ, transitions between material types can be more gradual. Based on the results of the borings, subsurface conditions on the project site can be generalized as follows: Description Approximate Depth to Bottom of Stratum Material Encountered Consistency/Density Surface to inches Topsoil / topsoil fill N/A Surface 2 2 Stratum 1 3 to inches 2½ to 6 feet 2 to 4 inches of asphalt over 6 to 12 inches of crushed stone aggregate Fill: lean clay with variable amounts of sand Stratum 2 3 to feet Lean clay, trace sand and gravel Medium stiff to stiff Stratum 3 40 to 0 feet Lean clay, trace sand and gravel; with occasional seams/layers of silty clay, silt and sand 1. Surface 1 was encountered in Borings 1 through and through. 2. Surface 2 was encountered in Borings 7 through and Stratum 1 was encountered in Borings 1 trough, 11, 13,, and through. N/A N/A Stiff to very stiff Responsive Resourceful Reliable 3

9 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No Water Level Observations The borings were observed during and after the completion of drilling for the presence and level of water. The water level observations are summarized in the following table. Observed Water Depth (ft) 1 Boring Number While Drilling After Drilling 1 None 61 13½ None 3 3 6½ ½ 11 None 12 ½ None None ½ None Below existing grade Water was not encountered in the remaining borings at the time of our exploration. However, the absence of water at a boring location does not necessarily mean that the boring terminated above the subsurface water level. Trapped water could occur within existing fill materials, and perched water could occur above lower permeability soil layers and within seams/layers of silt or sand. Due to the relatively low permeability of the cohesive soils encountered in the borings, longer term observations in cased holes or piezometers, sealed from the influence of surface water, would be required for a better evaluation of the groundwater conditions on this site. A -year flood elevation of feet and a 0-year flood elevation of 636. feet were indicated on the preliminary plans provided to us. The ground surface elevation at the building area borings generally ranged from about 632 to 634 feet. Therefore, even though the depth to water was variable in the borings, and water was not encountered at some boring locations, it is likely that water will be encountered in excavations at this site. Water levels may fluctuate due to seasonal variations in the amount of rainfall, runoff, and other factors not evident at the time the borings were performed. Trapped or perched water could occur above lower permeability soil layers. Water level fluctuations and perched water should be considered when developing design and construction plans and specifications for the project. Responsive Resourceful Reliable 4

10 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION 4.1 Geotechnical Considerations Based on the subsurface conditions encountered in the borings, the anticipated structural loads, and the preliminary building plans provided to us at the time this report was prepared, it is Terracon s opinion that the proposed 3-story building should be supported on drilled shaft foundations. Recommendations for design and construction of drilled shaft foundations bearing in stiff to very stiff native clay soils are provided in Section 4.3 of this report. Existing fill materials (comprised primarily of lean clay with variable amounts of sand and gravel) were encountered to depths of about 2½ to 6 feet below existing surface grades at most of the boring locations. Based on conditions encountered in the borings, it appears that some compactive effort was applied to portions of the fill; however, no documentation regarding placement and compaction of the fill was provided for our review. Since deep foundations (drilled shafts) are recommended for support of the building s structural loads, the presence of existing fill materials to the depths encountered is not expected to affect the foundation design. The following considerations are provided regarding the impact of the existing fill on new grade supported building floor slabs and pavements. If portions of the existing fill will be left in place, the existing fill should be thoroughly observed and tested before the fill is used to support new slabs and pavements. The existing pavements in Parking Lot D have been supported on the fill, and these pavements have reportedly performed in a satisfactory manner for the owner. However, it should be noted that undocumented fill may contain soft or loose soils or other unsuitable materials; these conditions may not be disclosed by the widely spaced, small-diameter borings. If these conditions are present and are not discovered and corrected during construction, larger than normal settlement resulting in cracking or other damage could occur in slabs, pavements, utility lines and any other elements supported on or above the existing fill. These risks can be reduced by thorough observation and testing during construction, but they cannot be eliminated without complete removal and replacement of the fill. To reduce the risk of adverse performance and provide more uniform support for slabs and pavements, any fill materials that will be left in place below new slab and pavements should be observed and tested. Where unsuitable conditions are observed, the materials should improved by scarification/compaction or be removed and replaced with engineered fill that is placed and compacted as recommended in this report. The soils encountered in the upper few feet at the boring locations generally consisted of lean clays with traces of sand and gravel (both fill and native soils). The moisture content of these soils was relatively high (ranging from about to 31 percent) at many of the boring locations. Subgrades comprised of clay soils with relatively high moisture contents often become unstable when they are disturbed and/or subjected to construction traffic. Therefore, some undercutting or Responsive Resourceful Reliable

11 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No stabilization of the subgrade will likely be required to facilitate compaction of new engineered fill or to provide a stable subgrade for floor slabs or pavements. A -year flood elevation of feet and a 0-year flood elevation of 636. feet were indicated on the preliminary plans provided to us. The ground surface elevation at the building area borings generally ranged from about 632 to 634 feet. Therefore, even though the depth to water was variable at the boring locations, and water was not encountered at some boring locations, it is likely that water will be encountered in excavations at this site. The contractor should anticipate this and plan for the appropriate dewatering needed to control seepage and facilitate construction. Our recommendations for earthwork, design and construction of drilled shaft foundations, lateral earth pressures for below grade walls, subgrade preparation for grade supported floor slabs, and pavements for the facility are presented in the following sections. 4.2 Earthwork Recommendations for site preparation, excavation, subgrade preparation and placement of engineered fill for the project are provided below Site Preparation Pavements, curbs, sidewalks and other existing improvements that are currently present within proposed construction areas should be removed. Existing utilities that would interfere with the proposed new construction should be removed or relocated. Excavations created by demolition/removal of existing improvements should be observed and evaluated prior to placement of new fill. The demolition contractor should be aware of project requirements for backfilling so that removal of recently placed fill materials and replacement of under controlled conditions is not necessary when building construction commences. Organic soils, root systems, and other unsuitable materials should also be stripped from proposed construction areas during site preparation. The drill crew noted a relatively thick topsoil layer (up to inches thick) at some of the boring locations. However, since samples of this layer were not obtained and organic content tests were not performed, additional exploration (such as shallow test pits) may be advisable so the earthwork contractor can evaluate the required stripping depth. Organic soils removed during site preparation could be utilized as fill for landscaped areas, but these materials should not be used as fill beneath the proposed building or pavement areas. The soils exposed following removal of existing improvements should be observed and tested prior to placing new engineered fill and/or construction of new slabs and pavements. The exposed soils should be proofrolled using a loaded tandem-axle dump truck with a gross weight of at least 2 tons, or similarly loaded equipment. Areas that display excessive deflection Responsive Resourceful Reliable 6

12 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No (pumping) or rutting during proofroll operations should be improved by scarification/compaction or by removal and replacement with engineered fill Engineered Fill Material Requirements Engineered fill should meet the following material property requirements: Fill Type 1 USCS Classification Acceptable Location for Placement 4 Cohesive 2, -ML Below/adjacent to slabs and pavements Granular GW, GP, GM, GC SW, SP, SM, SC Below/adjacent to slabs and pavements Unsuitable CH, MH, OL, OH, PT Non-structural locations 1. Engineered fill should consist of approved materials that are free of organic matter and debris. Cohesive fill materials should have liquid limit less than 4 and a plasticity index less than ; cohesive soils that do not meet these criteria should be considered unsuitable. Frozen material should not be used, and fill should not be placed on a frozen subgrade. A sample of each material type should be submitted to the geotechnical engineer for evaluation prior to use on this site. 2. Based on visual and tactile examination of recovered soil samples and the results of the laboratory tests, most of the on-site lean clay soils (native and fill) would meet the criteria for engineered fill. However, any organic materials, rock fragments larger than 3 inches, and other unsuitable materials should be removed prior to use of the existing fill materials in new fill sections. 3. A large portion of the on-site lean clay soils had moisture contents of percent or greater. Significant drying (if weather conditions are favorable) and/or incorporation of a chemical modifier (such as lime or Class C fly ash) will be required to reduce the moisture contents of wet soils so they can be properly compacted in new fill sections. In our experience, modified Proctor optimum moisture contents in the range of 11 to percent would be expected for these types of soils. 4. Since deep foundations (drilled shafts) are recommended, recommendations for materials to be placed below/adjacent to foundations are not provided. However, any backfill for below grade walls or adjacent to grade beams should meet the material and compaction requirements recommended in this section and Section Fill Placement and Compaction Requirements Fill Lift Thickness Item Minimum Compaction Requirement 1, 2 Below Slabs-on-grade, Upper 12 inches of Areas to be Paved Description inches or less in loose thickness when heavy, selfpropelled compaction equipment is used. 4 to 6 inches in loose thickness when hand-guided equipment (i.e., a jumping jack or plate compactor) is used. % of the material s modified Proctor maximum dry density (ASTM D 7). This level of compaction should extend beyond the edges of footings at least inches for every foot of fill placed below the foundation base elevation. Responsive Resourceful Reliable 7

13 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No Item Minimum Compaction Requirement 1, 2 Below 12 Inches in Areas to be Paved, Landscaped Areas Description 0% of the material s maximum modified Proctor dry density (ASTM D 7) Moisture Content of Cohesive Soil 4-2% to +3% of modified Proctor optimum (ASTM D 7) Moisture Content of Granular Material 3 Workable moisture levels 1. We recommend that each lift of fill be tested for moisture content and compaction prior to the placement of additional fill or concrete. If the results of the in-place density tests indicate the specified moisture or compaction limits have not been met, the area represented by the test should be reworked and retested as required until the specified moisture and compaction requirements are achieved. 2. If granular material is a coarse sand or gravel, is of a uniform size, or has a low fines content, compaction comparison to relative density (ASTM D 423/424) may be more appropriate. 3. The gradation of a granular material affects its stability and the moisture content required for proper compaction. Moisture levels should be maintained to achieve compaction without bulking during placement or pumping when proofrolled. 4. Significant drying of the on-site clay soils will be required to reach the moisture content range recommended for compaction Earthwork Construction Considerations The geotechnical engineer should be retained during the construction phase of the project to observe earthwork and to perform necessary tests and observations during demolition/removal of existing improvements, subgrade preparation, proofrolling, placement and compaction of compacted engineered fills, backfilling of excavations, and just prior to construction of grade supported building floor slabs. Clay soils with high moisture contents (greater than percent) were encountered within the upper several feet of the soil profile at most of the boring locations. These soils will be sensitive to disturbance from construction activities, particularly if further wetted by surface water or seepage. Therefore, it is anticipated that some areas of the site will become unstable during proofrolling and construction operations. The amount of stabilization required would be highly dependent upon weather conditions during construction and drainage measures implemented during mass grading and construction. Some means of subgrade stabilization will likely be required to facilitate construction. In general (weather permitting), scarifying, drying and recompacting the exposed subgrades is expected to be the most economical means of improving these soils prior to placing new fill. However, this option is typically less effective where soft/wet soils are thicker than about one foot, and this method is also dependent on weather conditions. Alternatives for subgrade stabilization could include undercutting unsuitable (wet, low strength, and/or disturbed) soils followed by the addition Responsive Resourceful Reliable

14 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No of crushed stone aggregate (typically on the order of 12 to inches) to improve subgrade stability, or the incorporation of a chemical additive such as lime, Class C fly ash or portland cement. The need for stabilization and most appropriate type of stabilization will be dependent upon soil, groundwater and weather conditions, the construction schedule and methods of construction that will be used. As noted above, the -year and 0-year flood elevations are reportedly above current surface grades within the proposed building area. Therefore, it is likely that water will be encountered in excavations at this site. Seepage should be expected in excavations for this project, and the contractor is responsible for employing appropriate dewatering methods to control seepage and facilitate construction. In our experience, dewatering of excavations in clay soils can typically be accomplished using sump pits and pumps. If excessive seepage from sand seams/layers is encountered, a more extensive dewatering system (such as multiple sump pits/pumps or well points) could be required. Care should be taken to avoid disturbance of prepared subgrades. Unstable subgrade conditions could develop during general construction operations, particularly if the soils are wetted and/or subjected to repetitive construction traffic. New fill compacted above optimum moisture content or that accumulates water during construction can also become disturbed under construction equipment. Construction traffic over the completed subgrade should be avoided to the extent practical. If the subgrade becomes saturated, desiccated, or disturbed, the affected materials should either be scarified and compacted or be removed and replaced. Subgrades should be observed and tested prior to construction of slabs and pavements. As a minimum, excavations should be performed in accordance with OSHA 2 CFR, Part 126, Subpart P, Excavations and its appendices, and in accordance with any applicable local, state, and federal safety regulations. The contractor should be aware that slope height, slope inclination, and excavation depth should in no instance exceed those specified by these safety regulations. Flatter slopes than those dictated by these regulations may be required depending upon the soil conditions encountered and other external factors. These regulations are strictly enforced and if they are not followed, the owner, contractor, and/or earthwork and utility subcontractor could be liable and subject to substantial penalties. Under no circumstances should the information provided in this report be interpreted to mean that Terracon is responsible for construction site safety or the contractor s activities. Construction site safety is the sole responsibility of the contractor who shall also be solely responsible for the means, methods, and sequencing of the construction operations Grading and Drainage During construction, grades should be developed to direct surface water flow away from or around the site. Exposed subgrades should be sloped to provide positive drainage so that saturation of subgrades is avoided. Surface water should not be permitted to accumulate on the site. Responsive Resourceful Reliable

15 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No Final grades should slope away from the building to promote rapid surface drainage. Accumulation of water adjacent to the building could contribute to significant moisture increases in the subgrade soils and subsequent softening/settlement. Roof drains should discharge into a storm sewer or several feet away from the building. 4.3 Drilled Shaft Foundations Based on the anticipated column loads (600 to 1,000 kips) and the subsurface conditions encountered at the boring locations, we recommend that the proposed new building be supported on drilled shaft foundations (also referred to as caissons or drilled piers ). Since bedrock or hard clay soils were not encountered within the maximum 0-foot depth explored by the borings, the drilled shafts will derive their capacity from a combination of side friction and end bearing in the stiff to very stiff native clay soils encountered in the borings. Belled shafts could be used to increase the end bearing area; the diameter of the bell should not exceed 3 times the diameter of the shaft. Design recommendations and construction considerations for drilled shaft foundations are provided in the following sections Drilled Shaft Foundation Design Recommendations Design parameters for drilled shafts are provided in the following table. Elevation (feet) Above to 630 Soil Description Frost Zone (0 to 3½ ft) Fill / medium stiff to stiff native clay DESIGN DATA SUMMARY Allowable End Bearing Pressure (psf) 1 Allowable Side Friction 1, 3, 4 (psf) Allowable Passive Pressure (psf) Ignore 27 2, to 62 to 60 Stiff to very stiff native clay; with occasional silt seams/layers sand seams Stiff to very stiff native clay; with occasional silt seams/layers sand seams Ignore 0,000, ,000 Responsive Resourceful Reliable

16 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No The allowable end bearing capacity includes a factor of safety of 3, and the allowable side friction and passive pressure values include a factor of safety of The drilled shaft should extend below elevation 60 feet to achieve this allowable end bearing capacity. 3. For belled shafts (if used), side friction resistance should be neglected along the belled portion of the shaft and for a distance of one bell diameter above the top of the bell. 4. Side friction values provided in the table are for compressive loads. In designing to resist uplift loads, the allowable side friction values provided for compressive loading could be used along with the effective weight of the drilled shaft. For belled shafts, the effective unit weight of the soil above the bell within a cylinder defined by the bell perimeter can also be used for uplift resistance. Buoyant concrete and soil weights should be used below the water table. For shafts subjected to uplift loads, the drilled shaft reinforcing steel should extend through the length were side friction is considered, and reinforcing steel should extend into the bell if the bell uplift resistance is considered. The following table provides estimated post-construction settlements of drilled shaft foundations that are designed and constructed as recommended in this report. Elastic compression of the drilled shafts should be added to these values. DESCRIPTION Estimated maximum total settlement Estimated maximum differential settlement VALUE ¾ inch ½ inch Pier caps or grade beams along the building s perimeter areas should extend at least 3½ feet below the lowest adjacent final grade for frost protection. Drilled shafts should be spaced at least 3 shaft diameters apart (center-to-center) or 3 bell diameters if belled shafts are used. If this spacing cannot be maintained, stresses from adjacent shafts could overlap in the bearing soils, resulting in larger settlements. Individual shafts could be designed to resist lateral loads using the allowable passive soil pressures provided in the above table. The allowable passive pressures would apply to the projected diameter of the shaft and require some movement to mobilize resistance. Lateral resistance within the frost depth (3½ feet below final grade) should be ignored. Group action for lateral resistance of drilled shafts should be taken into account when center to center spacing is less than diameters in the direction of loading. Design parameters for allowable passive resistance in the direction of the load should be reduced in accordance with the following table. Responsive Resourceful Reliable 11

17 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No Passive Resistance Reduction Factors Shaft Spacing (Shaft Diameters) Reduction Factor D 1.0 6D 0.7 4D 0.4 3D 0.2 Lateral loads perpendicular to a row of shafts with center to center spacing of 3 diameters or less would cause the foundations to react essentially as a vertical wall. For this case, an allowable passive pressure equivalent to that exerted by fluids weighing 0 and 70 pcf above and below groundwater, respectively, should be used for the projected shaft diameters. With spacing of greater than 3 diameters, the values provided above for individual shafts may be used. As an alternative to using the allowable passive pressure parameters, lateral loading on the drilled shafts could be analyzed using the LPILE computer program. LPILE analyzes shaft deflection as a function of the design loads, shaft design and construction, and subsurface conditions. Soil parameters for LPILE analysis of the drilled shafts are provided in the following table. LPILE Soil Parameters Elevation (feet) Above 630 LPILE Material Type 1 Layer Description Effective Unit Weight 2 (pcf) Internal Angle of Friction (degrees) Undrained Shear Strength (psf) Static Soil Modulus Parameter, k (pci) Strain ε 0 3 Frost Depth to Clay 60-1, to 62 2 Clay 6-2, to 60 2 Clay 70-3,000 1, LPILE material types: 2 = stiff clay with free water, 3 = stiff clay without free water 2. Maximum water level assumed at elevation 630 feet Drilled Shaft Foundation Construction Considerations Drilled shafts for this project should have a minimum diameter of 30 inches. The bottom of each drilled shaft excavation should be cleaned of loose material before placing reinforcing steel and concrete. If water is present in a drilled shaft excavation and cannot be removed by conventional means (such as pumping), concrete should be placed using a tremie or concrete pump. Concrete should be placed as soon as possible after the foundation excavation is Responsive Resourceful Reliable 12

18 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No completed. Closely spaced shafts should have a staggered construction schedule that allows for the concrete to set before an adjacent shaft is drilled. Water was observed shallower than the expected drilled shaft depths at several of the boring locations; therefore, the contractor should expect that temporary casing will be required for excavation and construction of the drilled shafts. Temporary casing must also be used if personnel need to enter the shafts to clean and/or observe the bearing surface. Care should be taken when removing temporary casing during concrete placement. During casing removal, the concrete level should be maintained a sufficient distance above the bottom of the casing to counteract hydrostatic and earth pressure on the annular spacing outside of the casing. Placement of loose soil backfill around the casing should not be permitted around the casing prior to removal of the casing. Drilled shaft concrete should be designed with a slump of approximately to 7 inches to help facilitate removal of temporary casing and reduce the possibility of concrete arching. Water that accumulates in drilled shaft excavations should be removed prior to concrete placement, or a tremie method should be used for placement of the concrete. 4.4 Floor Slab The following recommendations for grade supported floor slabs would apply to the west part of the building. We understand the east part of the building will have a structural slab that will be supported on the building s foundation system Floor Slab Design Recommendations Floor slab support ITEM Granular leveling course 2 Modulus of subgrade reaction DESCRIPTION Native soils, tested and evaluated existing fill, or new engineered fill materials that have been prepared in accordance with section 4.2 and tested/approved by the geotechnical engineer 6 inches of well-graded granular material 0 pci for a soil subgrade prepared as recommended in this report Note: a value of 0 pci can be used at the top of the compacted granular leveling course 1. Floor slabs should be structurally independent of building footings and walls supported on the footings to reduce the potential for floor slab cracking caused by differential movements between the slab and foundation. 2. The floor slab should be placed on a leveling course comprised of well-graded granular material (e.g., IDOT CA-6 aggregate) compacted to at least % of the material s modified Proctor maximum dry density (ASTM D 7) Responsive Resourceful Reliable 13

19 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No Joints should be constructed at regular intervals as recommended by the American Concrete Institute (ACI) to help control the location of cracking. It should be understood that differential settlement between the floor slabs and foundations could occur. If moisture vapor transmission through the concrete slab is a concern, a vapor barrier should be used. The need for, and placement of, the vapor barrier should be determined by the architect or slab designer based on the proposed floor covering treatment, building function, concrete properties, placement techniques, and construction schedule. For further guidance concerning the use of a vapor barrier system, refer to Sections 302 and 360 of the American Concrete Institute (ACI) Manual of Concrete Practice Floor Slab Construction Considerations On most project sites, the site grading is generally accomplished early in the construction phase. However, as construction proceeds, the subgrade may be disturbed by utility excavations, construction traffic, desiccation, rainfall, etc. As a result, corrective action may be required prior to placement of the granular leveling course and concrete. The condition of the floor slab subgrades immediately prior to placement of the granular leveling course and construction of the slabs. Particular attention should be paid to high traffic areas that were rutted and disturbed earlier and to areas where backfilled trenches are located. Areas where unsuitable conditions are located should be repaired by scarification/compaction or by removing the affected material and replacing it with engineered fill. 4. Below Grade Walls 4..1 Lateral Earth Pressures Walls with unbalanced backfill levels (e.g., below grade building walls and/or cast-in-place concrete cantilever retaining walls) should be designed for earth pressures at least equal to those indicated in the following table. Earth pressures will be influenced by structural design of the walls, conditions of wall restraint, methods of construction and/or compaction and the strength of the materials being restrained. The active condition assumes some wall movement and is commonly used for free-standing concrete cantilever retaining walls. The "at-rest" condition assumes no wall movement and is used for design of building walls, dock walls, and other walls that are fixed and cannot rotate. The recommended design lateral earth pressures do not include a factor of safety and do not provide for possible hydrostatic pressure on the walls. Responsive Resourceful Reliable

20 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No Lateral Earth Pressure Parameters Pressure Conditions Coefficient For Backfill Type Equivalent Fluid Unit Weight (pcf) Surcharge Pressure, P 1 (psf) Earth Pressure, P 2 (psf) Active (K a ) Granular Cohesive (0.33)S (0.42)S (40)H (0)H At-Rest (K o ) Granular - 0. Cohesive (0.)S (0.)S (60)H (70)H Passive (K p ) Granular 3.0 Cohesive Conditions applicable to the above recommendations include: For active earth pressure, wall must rotate about base, with top lateral movements of about H to H, where H is wall height For passive earth pressure to develop, wall must move horizontally to mobilize resistance. Uniform surcharge, where S is surcharge pressure In-situ soil backfill weight a maximum of 1 pcf Horizontal backfill and surface in front of the wall, compacted to between and 0 percent of standard Proctor maximum dry density No loading from compaction equipment or other construction equipment No loading from nearby foundations No dynamic loading Ignore passive pressure in frost zone Backfill placed against structures should consist of granular or cohesive engineered fill. For the granular values to be valid, the granular fill must extend out from the base of the wall at an Responsive Resourceful Reliable

21 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No angle of at least 4 degrees from vertical for the active and at-rest cases and at an angle of at least 60 degrees from vertical for the passive case. To calculate the resistance to sliding, a value of 0.4 should be used as the ultimate coefficient of friction between the concrete and the underlying clay soil Subsurface Drainage Drains should be constructed at the base of below grade walls/retaining walls to reduce the risk of hydrostatic loading. The drain pipe should be located with its invert at the bottom of the wall and should be surrounded with free-draining granular material graded to prevent the intrusion of fines. A minimum 2-foot wide layer of free-draining granular material should be placed adjacent to the wall. For exterior locations, the granular material should extend from the drainage pipes to within about 2 feet of final grade and be capped with a cohesive fill material that is placed and compacted as recommended in Section 4.2 of this report. At interior locations, the granular material should extend up to the floor slab subgrade elevation. As an alternative to filter graded gravel, free-draining 1-inch nominal size gravel could be used for the drains if the entire system, including the gravel, is encapsulated with an appropriate geotextile filter fabric. The drainage networks (pipes) for subdrains should be sloped to provide positive gravity drainage to sumps equipped for automated pumping or to a down gradient storm sewer or other suitable outlet that will allow gravity drainage. Redundant pumps with battery backup power could be considered to reduce the risk of hydrostatic pressure and seepage in the event of pump and/or power failure. Periodic maintenance of drainage systems is necessary so that they do not become plugged and inoperative. A prefabricated drainage structure placed against below grade walls may also be used as an alternative to free-draining granular fill above the pipe. A prefabricated drainage structure consists of a plastic drainage core or mesh that is covered with filter fabric to prevent soil intrusion. The drainage structure is fastened to the wall after the wall has been waterproofed. 4.6 Pavements Pavement Design Recommendations Pavement thickness design is dependent upon: the anticipated traffic conditions, subgrade and paving material characteristics, and climate conditions at the project site. Specific information regarding anticipated vehicle types, axle loads and traffic volumes was not provided. In developing our recommendations, we have considered that traffic will consist primarily of automobile traffic and a limited number of delivery trucks and trash collection trucks. The Parking Areas pavement section is for automobile traffic only. The Drives pavement section considers automobile traffic and a maximum of five delivery trucks/trash collection trucks Responsive Resourceful Reliable

22 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No per day. If heavier vehicle types or higher traffic volumes are expected, Terracon should be notified and these recommendations should be reviewed. Recommended minimum pavement sections for parking areas and drives are provided in the following table. Pavement Area Parking Areas Drives Trash Container Pad 1 Minimum Pavement Section 3 ACC Crushed Stone Aggregate 2 4 ACC Crushed Stone Aggregate 2 7 PCC 4 Crushed Stone Aggregate 1. Portland cement concrete pavements are recommended for areas subject to repeated truck traffic, truck turning areas, and trash container pads. The trash container pad should be large enough to support the container and the tipping axle of the trash collection vehicle. 2. IDOT CA-6 or an approved alternate gradation. Pavements and subgrades will be subject to freeze-thaw cycles and seasonal fluctuations in moisture content. The pavement sections provided in the table above were developed based on local soil and climate conditions. Asphalt, concrete and aggregate base course materials for pavements should conform to the applicable Illinois DOT "Standard Specifications of Road and Bridge Construction. Concrete pavement should be air-entrained and have a minimum compressive strength of 4,000 psi after 2 days of laboratory curing (ASTM C 31). Construction traffic on the pavements was not considered in developing the estimated minimum pavement thicknesses. If the pavements will be subject to construction equipment/vehicles, the pavement sections should be revised to consider the additional loading. The pavement sections provided above assume that the subgrade soils will not experience significant increases in moisture content. Paved areas should be sloped to provide rapid drainage of surface water and to drain water away from the pavement edges. Water should not be allowed to accumulate on or adjacent to the pavement, since this could saturate and soften the subgrade soils and subsequently accelerate pavement deterioration. Periodic maintenance of the pavements will be required. Cracks should be sealed, and areas exhibiting distress should be repaired promptly to help prevent further deterioration. Even with periodic maintenance, some movement and related cracking may still occur and repairs may be required. Responsive Resourceful Reliable

23 Geotechnical Engineering Report Science & Health Careers Center Des Plaines, Illinois October 4, 11 Terracon Project No Pavement Construction Considerations Pavement subgrades should be prepared in accordance with the recommendations presented in Sections 4.1 and 4.2 of this report. Grading and paving is commonly performed by separate contractors and there is often a time lapse between the end of grading operations and the commencement of paving. Subgrades prepared early in the construction process may become disturbed by construction traffic. Non-uniform subgrades often result in poor pavement performance and local failures relatively soon after pavements are constructed. Depending on the paving equipment used by the contractor, measures may be required to improve subgrade strength to greater depths for support of heavily loaded concrete/asphalt trucks. Before paving, pavement subgrades should be proofrolled with a loaded tandem-axle dump truck (minimum gross weight of 2 tons) or other approved rubber-tired equipment providing an equivalent subgrade loading. Proofrolling of the subgrade should help locate soft, yielding, or otherwise unsuitable soil at or just below the exposed subgrade level. Unsuitable areas observed at this time should be improved by scarification and compaction or be removed and replaced with engineered fill. 4.7 Seismic Site Class Code Site Class 0 International Building Code (IBC) 1 D 1. In general accordance with Table of the IBC. 2. The 0 IBC requires a site soil profile determination extending a depth of 0 feet. The geophysical testing extended to a depth of 0 feet. The maximum depth explored in the borings was approximately 0 feet, with the borings terminating in stiff to very stiff clay soils. The site class was evaluated using the shear wave velocities estimated from the geophysical testing and conditions encountered in the borings. Please refer to Appendix A, Exhibit A-1 for a description of the geophysical testing used to evaluate the IBC seismic site class. The geophysical test results are presented in Appendix A, Exhibits A- and A GENERAL COMMENTS Terracon should be retained to review the final design plans and specifications so comments can be made regarding interpretation and implementation of our geotechnical recommendations in the design and specifications. Terracon also should be retained to provide observation and testing services during grading, excavation, foundation construction and other earth-related construction phases of the project. Responsive Resourceful Reliable