PRELIMINARY GEOTECHNICAL INVESTIGATION UCCS ACADEMIC OFFICE BUILDING COLORADO SPRINGS, COLORADO

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1 PRELIMINARY GEOTECHNICAL INVESTIGATION UCCS COLORADO SPRINGS COLORADO Prepared for: UNIVERSITY OF COLORADO AT COLORADO SPRINGS Facilities Services 1420 Austin Bluffs Parkway Colorado Springs Colorado Attention: Mr. Gary Reynolds CTL T Project No. CS October Mark Dabling Blvd Colorado Springs Colorado Telephone: Fax:

2 TABLE OF CONTENTS SCOPE... 1 SUMMARY... 1 SITE CONDITIONS... 2 PROPOSED DEVELOPMENT... 3 SITE GEOLOGY... 3 FIELD INVESTIGATION... 3 SUBSURFACE CONDITIONS... 4 Existing Fill... 4 Natural Clay and Sand... 5 Bedrock... 5 Groundwater... 5 Seismicity... 6 SITE GRADING AND UTILITIES... 6 CONSTRUCTION CONSIDERATIONS... 7 Foundations... 8 Floor Systems and Slabs-on-Grade... 8 Subsurface Drainage... 9 Pavements... 9 CONCRETE... 9 SURFACE DRAINAGE...10 CONSTRUCTION OBSERVATIONS...10 GEOTECHNICAL RISK...10 LIMITATIONS...11 FIG. 1 LOCATION OF EXPLORATORY BORINGS FIG. 2 SUMMARY LOGS OF EXPLORATORY BORINGS APPENDIX A SWELL CONSOLIDATION TEST RESULTS TABLE A-1 SUMMARY OF LABORATORY TESTING UNIVERSITY OF COLORADO AT COLORADO SPRINGS

3 SCOPE This report presents the results of our Preliminary Geotechnical Investigation for the proposed Academic Office Building to be constructed on the campus of the University of Colorado at Colorado Springs. This report includes a description of subsurface and groundwater conditions found in our borings and our opinions regarding the potential influence of these conditions on site development and building construction. The report also includes preliminary geotechnical design and construction criteria for installation of buried utilities and site grading concepts for building foundations floor slabs and pavement sections and our opinions with respect to the influence of subsurface conditions on site development. We believe this study was completed in general conformance with our proposal (CS ) dated September No preliminary documents or construction plans were available for the proposed building at the time of this report. Our understanding of the project is based on the owner s verbal description of the proposed construction. The report was prepared based on conditions interpreted from conditions found in our exploratory borings results of laboratory tests engineering analysis and our experience. As the project documents become more definitive we should review the plans to formulate design and construction recommendations. Evaluation of the site for the possible presence of potentially hazardous materials (Environmental Site Assessment) is beyond the scope of this investigation. The following section summarizes our evaluation. A more complete description of the conditions found our interpretations and our recommendations are included in the report. SUMMARY 1. Subsurface conditions encountered in our exploratory borings drilled within the vicinity of the planned building consisted of a layer of existing fill underlain by natural sand and clay soils. Claystone bedrock with occasional layers of sandstone was encountered in both borings underlying the natural soils. Samples of the natural clay and claystone exhibited low to moderate measured swell values when wetted. UNIVERSITY OF COLORADO AT COLORADO SPRINGS 1

4 2. At the time of drilling groundwater was not encountered in either of the exploratory borings. When water levels were checked again two days after the completion of drilling operations water was measured in one of the borings at a depth of 21.5 feet below the existing ground surface. Groundwater conditions may affect the installation of drilled pier foundations. 3. We believe grading and utility installation can be accomplished using conventional heavy-duty equipment. 4. We expect the soils encountered at the anticipated lowest floor elevation of the proposed construction will consist of grading fill natural sands and clays and possibly sandstone and claystone bedrock if a basement level is included. To reduce the risk of excessive total and differential movements of potentially heavily-loaded foundation walls underlain by a widely varying combination of non-expansive soil and expansive soil and bedrock materials we anticipate drilled piers bottomed in the underlying bedrock will be an appropriate foundation alternative. 5. New moisture conditioned and densely compacted grading fill and the onsite natural soils likely provide good support characteristics for lightly loaded slab-on-grade floors. Slabs bearing on or near expansive claystone may experience movement and associated damage. Where claystone bedrock is present near the finished floor level which may occur in a basement area subexcavation of the claystone and replacement with moisture conditioned fill will likely be an appropriate method to mitigate the effects of the expansive materials and should allow for the installation of a slab-on-grade floor. If some floor movement cannot be tolerated a structurally supported floor should be provided. The risk of poor slab performance cannot be fully evaluated until plans and floor elevations are defined. 6. For planning purposes pavement thicknesses for full-depth asphalt sections for parking lots and access driveways in the range of 4 to 6 inches are anticipated. Concrete pavement 6 inches thick is expected at the trash dumpster site. 7. Surface drainage should be designed for rapid runoff of water away from the proposed building. Conservative irrigation practices should be followed to avoid excessive wetting. Water should not be allowed to pond adjacent to the structure or over exterior slabs or pavements. SITE CONDITIONS The site of the proposed Academic Office Building is situated between Regent Circle and Austin Bluffs Parkway at the location of the existing CITI Building on the camps of the University of Colorado at Colorado Springs. The CITI Building is a one- UNIVERSITY OF COLORADO AT COLORADO SPRINGS 2

5 story wood-frame structure with brick veneer and wood siding exterior wall treatments. A basement level that walls out at the southwest corner of the structure is present beneath the building. The ground surface at the site slopes downward to the south and southwest near Regent Circle and then flattens out to the north of Austin Bluffs Parkway in the area of existing building. Vegetation on the site consists of irrigated sod deciduous trees and pine trees. An existing paved automobile parking lot is situated to the west of the proposed building location. PROPOSED DEVELOPMENT We understand the proposed Academic Office Building is in the preliminary conceptual planning stage. Preliminary concepts indicate the building will be a three or four-story structure and may include a basement level. The building is to provide space for academic offices. Foundation loads are expected to be moderate to high. Paved access driveways and additional automobile parking area are anticipated as part of the overall development. SITE GEOLOGY Published geologic mapping ( Geologic Map of the Pikeview Quadrangle El Paso County Colorado Jon P. Thorson Christopher J. Carroll and Mathew L. Morgan Colorado Geological Survey 2001) indicates the site is underlain locally by alluvial deposits (Qfo). The upper member of the Laramie Formation (Klu) comprises the underlying bedrock found beneath the near-surface soils. Conditions encountered in our borings generally confirm the mapping although our borings suggest some man-made fill has been placed to adjust site grades. FIELD INVESTIGATION Our field investigation included drilling two exploratory borings at the general location of the proposed building footprint. The borings were advanced to depths of 25 and 35 feet using 4-inch diameter continuous-flight auger and a truck-mounted drill rig. Drilling was observed by our field representative who logged the conditions found in the borings and obtained samples. Graphical logs of the conditions encountered in the UNIVERSITY OF COLORADO AT COLORADO SPRINGS 3

6 borings the results of field penetration resistance tests and laboratory test data are presented in Fig. 2. Swell-consolidation test results are presented in Appendix A. Laboratory test data are summarized in Table A-1. Soil and bedrock samples obtained during this study were returned to our laboratory and visually classified. Laboratory testing was then assigned to representative samples. Testing included moisture content and dry density swell-consolidation sieve analysis and water-soluble sulfate content tests. To evaluate potential heave the swell test samples were wetted under applied pressures that approximated the overburden pressure (the weight of overlying soil). SUBSURFACE CONDITIONS Subsurface conditions encountered in our exploratory borings consisted of a layer of existing fill underlain by natural sand and clay soils. Claystone bedrock with occasional layers of sandstone was encountered in both borings underlying the natural soils. The pertinent engineering characteristics of the soils and bedrock encountered are discussed in the following paragraphs. Existing Fill A layer of existing fill about 3 to 7 feet thick was encountered at the ground surface in both borings. The fill consisted of clayey sand and sandy clay. The fill was dense (sand) or very stiff (clay) based on the results of field penetration resistance testing and our observations during drilling operations. The fill was apparently placed when the CITI Building was constructed or possibly when Regent Circle was extended. We are not aware of specific documentation regarding the placement and compaction of the fill material such as the results of field density testing and so the fill is of suspect quality. If free from deleterious substances we anticipate the fill can probably be excavated moisture conditioned and densely compacted as new fill within the planned development. If documentation of fill placement and testing is available we should review the information to determine if the fill is suitable for the proposed construction. UNIVERSITY OF COLORADO AT COLORADO SPRINGS 4

7 Natural Clay and Sand About 10 feet of natural sandy to very sandy clay was encountered beneath the existing fill in boring TH-1. The clay was stiff to very stiff based on the results of field penetration resistance tests. Two samples of the clay tested in our laboratory exhibited low measured swell values of 0.1 and 0.2 percent when wetted under estimated overburden pressure. About 16 feet of natural clayey or silty sand was found underlying the fill layer in boring TH-2. The sand was medium dense to dense based on the results of field penetration resistance tests. Two samples of the sand tested in our laboratory contained 14 and 15 percent clay and silt-size particles (passing the No. 200 sieve). Our experience indicates the sands are typically non-expansive when wetted. Bedrock Sandy claystone bedrock and slightly silty sandstone were found in the borings drilled at the site beneath the natural soils at depths of 13 and 23 feet below the existing ground surface. Claystone appeared to be the predominant bedrock material. Field penetration resistance test results indicated the bedrock was medium hard to very hard. Two samples of the sandy claystone tested in our laboratory exhibited measured swell values of 0.1 and 1.2 percent when wetted which is indicative of slightly to moderately expansive material. A sample of the sandstone contained 8 percent silt and clay-sized particles (passing the No. 200 sieve). The sandstone is typically non-expansive or exhibits low measured swell values when wetted. Groundwater At the time of drilling groundwater was not encountered in either of the exploratory borings. When water levels were checked again two days after the completion of drilling operations water was measured in one of the borings at a depth of 21.5 feet below the existing ground surface. Our experience indicates groundwater can occur in different forms below this site. Water can be found in the fissures within the bedrock. Perched groundwater tables can also form at the interface between the UNIVERSITY OF COLORADO AT COLORADO SPRINGS 5

8 overlying granular materials and underlying bedrock. The occurrence of groundwater the volume and elevation will fluctuate in response to seasonal precipitation variations surface drainage and landscaping irrigation. Groundwater conditions may affect the installation of drilled pier foundations. Seismicity This area like most of central Colorado is subject to a degree of seismic activity. We believe the soils and bedrock on the site classify as Site Class C (dense soil and soft rock) according to the 2009 International Building Code (2009 IBC). A geophysical study is required to evaluate the shear wave velocity (V100) profile at the site to potentially allow for an upgrade to Site Class B. Our firm can provide a site-specific geophysical seismic study using the ReMi micro-tremor surface method if desired. SITE GRADING AND UTILITIES No grading plans were available for our review during the preparation of this study. Based on the existing site topography and our understanding of the planned construction we estimate maximum cuts and fills of 5 to 10 feet will be necessary to achieve the desired building pad elevation and grades within the associated parking areas and access driveways. Permanent cut and fill slopes should be no steeper than 3:1 (horizontal to vertical). Our office should be contacted to review the site grading plans once they are prepared. All remnants of the existing CITI Building including foundation elements floor slabs below-grade walls exterior concrete flatwork the superstructure and buried utilities will need to be removed from the site before grading of the property can begin. Prior to grading fill placement existing fill and vegetation should also be removed from the site. The existing fill should be excavated to expose the underlying natural soils. Organic topsoil can be stockpiled and placed in landscaped areas. Fill materials within the building footprint should consist of the on-site sand and clay soils and silty to clayey sandstone (if encountered). If free from deleterious substances we anticipate the existing fill can probably be incorporated into the new site grading fills. The grading fill should be moisture conditioned to within 2 percent of optimum moisture content and compacted in UNIVERSITY OF COLORADO AT COLORADO SPRINGS 6

9 thin lifts to at least 95 percent of maximum standard Proctor dry density (ASTM D 698). Sandstone if placed as grading fill should be mechanically broken down into particles of less than 2 inches in diameter. Expansive claystone bedrock (if encountered) should be placed as fill outside of the planned building footprint as much as possible or be removed from the site. The placement and compaction of the grading fill should be observed and tested by a representative of our office during construction. Our borings suggest the on-site soils and bedrock (if encountered) can be excavated using conventional heavy-duty equipment. The grading fill and natural soils will likely cave into unsupported near-vertical utility trench excavations. Based on the Occupational Safety and Health Administration (OSHA) criteria governing excavations the grading fills and natural soils will probably classify as Type C soils. The bedrock will probably classify as Type B soil. Temporary excavations in Type B and Type C materials require a maximum slope inclination of 1:1 and 1.5:1 (horizontal to vertical) respectively unless the excavation is shored or braced. Should groundwater seepage occur flatter slopes may be necessary. The contractor s competent person should evaluate the soils at the time of excavation and determine appropriate safety measures. We recommend utility trench backfill be placed in thin loose lifts moisture conditioned to within 2 percent of optimum moisture content and compacted to at least 95 percent of maximum standard Proctor dry density (ASTM D 698). Personnel from our firm should periodically observe utility trench backfill placement and test the density of the backfill materials during construction. CONSTRUCTION CONSIDERATIONS Our preliminary opinions regarding foundations floor systems subsurface drainage and pavements are presented below for the anticipated construction. Once plans for the office building become more defined our office should be contacted to provide specific design criteria and construction recommendations. UNIVERSITY OF COLORADO AT COLORADO SPRINGS 7

10 Foundations Based on data from our exploratory borings subsurface conditions across the site will likely consist of grading fills and natural sand and clay soils underlain by claystone and sandstone bedrock. To reduce the risk of excessive total and differential movements of potentially heavily-loaded foundation walls underlain by a widely varying combination of non-expansive and expansive soil and bedrock materials we anticipate drilled piers bottomed in the underlying bedrock will be an appropriate foundation alternative for the proposed office building. For planning purposes we anticipate a maximum allowable end pressure of to psf and an allowable skin friction of 2500 to 3500 psf for the portion of pier in comparatively unweathered bedrock will be appropriate for preliminary pier sizing. We anticipate a minimum deadload pressure of to psf will be appropriate for initial design. The presence of potentially caving sands and groundwater at the site may require the use of temporary casing to install some of the drilled piers. Our office should provide site-specific foundation recommendations and design criteria for the planned structure after site grading plans have been prepared and the building location and floor elevations have been established. Floor Systems and Slabs-on-Grade We expect a conventional slab-on-grade floor is considered to be an attractive floor system alternative for at-grade portions of the proposed building. We judge the risk of poor slab performance will likely be low where new sandy to clayey moisture conditioned and densely compacted grading fill natural sand and/or sandstone are present at or near floor slab elevations. Should claystone bedrock be encountered at or near floor slab elevations such as in a basement level subexcavation of the claystone and replacement with moisture conditioned granular fill will likely be an appropriate method to mitigate the effects of the expansive materials and should allow for the installation of a slab-on-grade floor. If some floor movement cannot be tolerated a structurally supported floor should be provided. The risks associated with poor slab-ongrade performance cannot be evaluated fully until the plans become better defined and floor slab elevations are established. UNIVERSITY OF COLORADO AT COLORADO SPRINGS 8

11 Subsurface Drainage At the time of our investigation we were not aware whether or not the proposed construction will include habitable below-grade areas such as a basement level. For planning purposes foundation drain installation should be anticipated around all belowgrade construction within the project site with the potential exception of non-habitable areas that can be constructed as water-tight structures such as elevator pits. Pavements Pavement subgrade soils across the site will likely consist of new sandy to clayey grading fills and natural silty to clayey sands and sandy to very sandy clay. We anticipate the grading fills and natural sands will generally provide good subgrade support characteristics for pavement systems. The natural clay will provide comparatively poor pavement support qualities. Where granular subgrade soils are encountered pavement thicknesses for full-depth asphalt concrete sections for parking lots and access driveways in the range of 4 to 6 inches are likely. Pavement thicknesses for full-depth asphalt concrete sections in areas where clay is the predominant subgrade material will likely be on the order of 1 to 2 inches thicker. We recommend a concrete pavement be provided at the trash dumpster site. The concrete pavement should be at least 6 inches thick and large enough to support the entire length of the trash truck and dumpster during the emptying process. When possible during grading sands should be placed in the upper 2 feet of the subgrade in pavement areas to reduce the required asphalt concrete thickness. Final pavement section recommendations can be provided once site development and grading plans are prepared. CONCRETE Concrete in contact with soils can be subject to sulfate attack. We measured the soluble sulfate concentration in one sample from this site at less than 0.1 percent. Sulfate concentrations less than 0.1 percent indicate Class 0 exposure to sulfate attack for concrete in contact with the subsoils according to ACI 201.2R-01 as published in the 2008 American Concrete Institute (ACI) Manual of Concrete Practice. For this level of sulfate concentration the ACI indicates Type I/II cement can be used for concrete in UNIVERSITY OF COLORADO AT COLORADO SPRINGS 9

12 contact with the subsoils. In our experience superficial damage may occur to the exposed surfaces of highly permeable concrete even though sulfate levels are relatively low. To control this risk and to resist freeze-thaw deterioration the water-to-cementitious material ratio should not exceed 0.50 for concrete in contact with soils that are likely to stay moist due to surface drainage or high water tables. Concrete subjected to freezethaw cycles should be air entrained. SURFACE DRAINAGE The performance of this project will be influenced by surface drainage. When developing an overall drainage plan consideration should be given to drainage around the proposed building and away from paved areas. Drainage should be planned such that surface runoff is directed away from foundations and is not allowed to pond adjacent to the building or over pavements. We recommend slopes of at least 6 inches in the first 10 feet for the area surrounding the building where possible. Roof downspouts and other water collection systems should discharge well beyond the limits of all backfill around the structure. Proper control of surface runoff is also important to prevent the erosion of surface soils. Sheet flow should not be directed over unprotected slopes. Water should not be allowed to pond at the crest of slopes. Permanent slopes should be seeded or mulched to reduce erosion. Special attention should be paid to compact soils behind the curb and gutter sections adjacent to streets and in utility trenches. CONSTRUCTION OBSERVATIONS We recommend that CTL Thompson Inc. provide observation and testing services during construction to allow us the opportunity to verify whether soil conditions are consistent with those found during our investigation. If others perform these observations they must accept responsibility to judge whether the recommendations in this report remain appropriate. GEOTECHNICAL RISK The concept of risk is an important aspect with any geotechnical evaluation primarily because the methods used to develop geotechnical recommendations do not UNIVERSITY OF COLORADO AT COLORADO SPRINGS 10

13 comprise an exact science. We never have complete knowledge of subsurface conditions. Our analysis must be tempered with engineering judgment and experience. Therefore the recommendations presented in any geotechnical evaluation should not be considered risk-free. Our preliminary recommendations represent our judgment of those measures that are necessary to increase the chances that the structure will perform satisfactorily. It is critical that all recommendations in this report are followed during design and construction. LIMITATIONS Plans for the proposed building were in the preliminary schematic phase at the time of this report. The recommendations presented should be considered to be preliminary. Once the plans become better defined our firm should be contacted to formulate geotechnical design criteria and construction recommendations. Our borings were located to obtain a reasonably accurate indication of subsurface foundation conditions. The borings are representative of conditions encountered at the exact boring location only. Variations in subsurface conditions not indicated by the borings are possible. We recommend a representative of our office observe the completed foundation excavation. Representatives of our firm should be present during construction to perform construction observation and materials testing services. We believe this investigation was conducted with that level of skill and care normally used by geotechnical engineers practicing in this area at this time. No warranty express or implied is made. If we can be of further service in discussing the contents of this report or in the analysis of the influence of the subsoil conditions on design of the structure from a geotechnical engineering point-of-view please call. UNIVERSITY OF COLORADO AT COLORADO SPRINGS 11

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17 APPENDIX A SWELL CONSOLIDATION TEST RESULTS TABLE A-1 SUMMARY OF LABORATORY TESTING UNIVERSITY OF COLORADO AT COLORADO SPRINGS

18 3 2 EXPANSION UNDER CONSTANT PRESSURE DUE TO WETTING 1 COMPRESSION % EXPANSION APPLIED PRESSURE - KSF CLAY VERY SANDY (CL) DRY UNIT WEIGHT= 111 PCF TH-1 AT 4 FEET MOISTURE CONTENT= 14.6 % 3 2 EXPANSION UNDER CONSTANT PRESSURE DUE TO WETTING 1 COMPRESSION % EXPANSION APPLIED PRESSURE - KSF CLAY VERY SANDY (CL) DRY UNIT WEIGHT= 103 PCF TH-1 AT 9 FEET MOISTURE CONTENT= 22.9 % UNIVERSITY OF COLORADO AT COLORADO SPRINGS S:\CS \CS \115\2. REPORTS\CS _SWELL.XLS Swell Consolidation Test Results FIG. A-1

19 3 2 EXPANSION UNDER CONSTANT PRESSURE DUE TO WETTING 1 COMPRESSION % EXPANSION APPLIED PRESSURE - KSF CLAYSTONE SANDY DRY UNIT WEIGHT= 109 PCF TH-1 AT 19 FEET MOISTURE CONTENT= 19.2 % 3 2 EXPANSION UNDER CONSTANT PRESSURE DUE TO WETTING 1 COMPRESSION % EXPANSION APPLIED PRESSURE - KSF CLAYSTONE SANDY DRY UNIT WEIGHT= 108 PCF TH-2 AT 24 FEET MOISTURE CONTENT= 18.9 % UNIVERSITY OF COLORADO AT COLORADO SPRINGS S:\CS \CS \115\2. REPORTS\CS _SWELL.XLS Swell Consolidation Test Results FIG. A-2

20 TABLE A-1 SUMMARY OF LABORATORY TESTING ATTERBERG LIMITS SWELL TEST RESULTS* PASSING WATER MOISTURE DRY LIQUID PLASTICITY APPLIED SWELL NO. 200 SOLUBLE DEPTH CONTENT DENSITY LIMIT INDEX SWELL PRESSURE PRESSURE SIEVE SULFATES BORING (FEET) (%) (PCF) (%) (%) (%) (PSF) (PSF) (%) (%) DESCRIPTION TH CLAY VERY SANDY (CL) TH CLAY VERY SANDY (CL) TH SANDSTONE SLIGHTLY SILTY TH CLAYSTONE SANDY TH FILL SAND CLAYEY TH <0.1 SAND CLAYEY (SC) TH SAND SILTY (SM) TH CLAYSTONE SANDY * SWELL MEASURED WITH ESTIMATED IN-SITU OVERBURDEN PRESSURE. NEGATIVE VALUE INDICATES COMPRESSION. Page 1 of 1