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HomeMy WebLinkAboutHORSETOOTH EAST BUSINESS PARK PUD SECOND - Filed SER-SUBSURFACE EXPLORATION REPORT -t.. .., i.„ _...,,,.....,,,..„...„....„,, , . ii s x.........„.„.„,•,.... ..,,, ‘ r.,. ...... ,..„....,,„.....,..._.. .,,,, :- I 7.,.,....;...li 2.„„,,•.,,,,,,............,,,,,....7..____ . 1„,..„.7,.•,.... ..,. .,...-. 7.::::,..7.,--.141R 4 , w::. SUBSURFA(.;Le EXr111()N REPriu) r LITTLE BIC; HORN 1)i.:le'ELOPMENT HORSE-1'00'1'1-i ICASI' BliSINESS PARK IN 11-,'()It'l' C01...INS, (7.(-)L.,()R, A 1)0 F.'E(' 1)1;?).(..).1/i„,(."/' NO. 1.1.)8 24)2 2 II67. 1.,,,..4,TaflirAiJitt.'T[-•:,:-',„,..t fill- , . r,..i., , •--...,...._ . .,. - v , , . , , . 1,.d:•,.P.., 1i41,,,,f:.,.,,-;i!....;,zo.*IF',....--;,, .... . . ,, 4.; I it I it 7.,.... Ni 11 p . .t 4,-..,r-,..,isi,c-_-_At‘'-'11-1 Et4._itiNz_c_r:-.-L.: I C014SUUrat-57_;, itIC.I I E EC IEARTH ENGINEERING CONSULTANTS, INc. March 21 1998 W.W. Reynolds 1613 Prospect Parkway Fort Collins, Colorado 80525 I Attn Ms. Libby Glass Re: Subsurface Exploration Report Little Big Horn Development Horsetooth East Business Park111FortCollins, Colorado EEC Project No. 1982022 Ms. Glass: Enclosed, herewith, are the results of the geotechnical subsurface exploration completed by Earth Engineering Consultants, Inc. for the referenced project. In summary, the subsurface materials encountered at the site consisted of a variable blend of soft to stiff cohesive soils and loose to medium dense essentially granular soils overlying highly weathered claystone bedrock at depths of approximately 24 to 25 feet. Groundwater was encountered at a depth of approximately 15 feet at the time of our field exploration. 111 Based on the anticipated loads from the three-story portion of the structure and on the subsurface conditions encountered, we recommend the new building be supported on "deep" foundations extending to bear in the highly weathered to weathered claystone bedrock. Recommendations arc provided in the enclosed report for support of the building on drilled caisson foundations although alternative foundations including auger cast piling or driven piling could be considered. The near4 surface soils show relative ly low plasticity and low potential for volume change with variation in moisture content. Those soils could be used for direct support of floor slabs and pavements for the proposed improvements. CENTRE FOR ADVANCED TECHNOLOGY 2301 RESEARCH BOULEVARD, SUITE I 04 FORT COLLINS, COLORADO 80526 970) 224-1 522 (FAx) 224-4564 Earth Engineering Consultants, Inc. EEC Project No. 1982022 March 21, 1998 Page 2 Geotechnical recommendations concerning design and construction of foundations and support of floor slabs and pavements are provided in the text of the attached report. We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report, or if we can be of further service to you in any way,wa , please do not hesitate to contact us. Very truly yours; Earth En.i ing Consultants, Inc. 4"1"44;* 4?' 1 k: 23957 KA , Lester L. Li E. Principal Engineer 111 LLL/dmf I I I I I I SUBSURFACE EXPLORATION REPORT LITTLE BIG HORN DEVELOPMENT HORSETOOTH EAST BUSINESS PARK FORT COLLINS, COLORAI)O EEC PROJECT NO. 1982022 I I I SUBSURFACE EXPLORATION REPORT LITTLE BIG HORN DEVELOPMENT HORSETOOTH EAST BUSINESS PARK FORT COLLINS, COLORADOI- EEC PROJECT NO. 1982022 March 21, 1998 INTRODUCTION The subsurface exploration for the proposed Little Big 1-Iorn office building to be constructed on Parcel G of the Horsetooth East Business Park in Fort Collins, Colorado, has been completed. Seven soil borings extending to depths-of approximately 25 to 40 feet below present site grades were advanced in the proposed building area to develop information on existing subsurface conditions. Individual boring logs and a diagram indicating the approximate boring locations are included with this report. We understand the Little Big Horn flex space building will include single-story and three-story areas and will be constructed as slab-on-grade. Foundation loads for that structure are estimated to be light to moderate with maximum column loads on the order of 200 to 300 kips and maximum continuous wall loads on the order of 6 kips per lineal foot. Floor loads will be light, less than 100 psf. We expect traffic on the site drive and parking areas will be limited to low volumes of automobiles and light trucks. A delivery drive on the west side of the building may include a larger volume of truck traffic. borings,The purpose of this report is to descrtbc, the subsurface conditions encountered in the her g , analyze and evaluate the test data and provide geotechnical recommendations concerning design and construction of the foundations and support of floor slabs and pavements. EXPLORATION AND TESTING PROCEDURES The boring locations were established in the field by Earth Engineering Consultants, Inc. (EEC) personnel by pacing and estimating angles from identifiable site features. Those approximate II 11 Earth Engineering Consultants, Inc. EEC Project No. 1982022 111 March 21, 1998 Page 2 ilboring locations are indicated on the attached boring location diagram. The locations of the borings should be considered accurate only to the degree implied by the methods used to make the IIfield measurements. The field borings were performed using a truck mounted, CME 55 drill rig equipped with a hydraulic head eibployed in drilling and sampling operations. The borings were advanced using 4-inch nominal diameter continuous flight augers and samples of the subsurface materials encountered were obtained using split-barrel and California barrel sampling techniques in general accordance with ASTM Specification D-1586. In that sampling procedure, standard sampling111spoonsareadvancedintothesubgradeusinga140-pound hammer falling a distance of 30 inches. The number of blows required to advance the standard samplers is recorded and is used to estimate the in-situ relative density of cohesionless soils and, to a lesser degree of accuracy, the consistency of cohesive soils and hardness of weathered bedrock. In the California barrel sampling procedure, Irelatively undisturbed samples of the subgrade materials are obtained in removable brass liners. All samples obtained in the field were sealed and returned to the laboratory for further examination, classification and testing. Moisture content tests were completed on each of the recovered samples. The unconfined strength of appropriate samples was estimated using a calibrated handpenetrometer. Washed sieve analysisbY and Atterberg limits tests were used to evaluate the percentage and plasticity of the subgradeImaterials. Swell/consolidation tests were completed to evaluate the subgrade materials' tendency to change volume with variation in moisture content. Results of the outlined tests are indicated on the attached boring logs and summary sheets. IAs a part of the testing program, all samples were examined in the laboratory by an engineer and classified in accordance with the attached General Notes and the Unified Soil Classification 111 System, based on the soil's texture and plasticity. The estimated group symbol for the Unified Soil Classification System is indicated on the boring logs and a brief description of that II classification system is included with this report. 4, N 111 Earth Engineering Consultants, Inc. EEC Project No. 1982022 March 21, 1998 IIPage 3 NSITE AND SUBSURFACE CONDITIONS The Little Big Horn building will be constructed on the east side of Automation Way between Big Horn Drive and Horsetooth Road in Fort Collins, Colorado. The development site is relatively ; level and covered with sparse vegetation and grasses at the time of our field exploration. Evidence k of prior building'construction was not observed at the site by EEC site personnel. itAn EEC geologist was on site during drilling to evaluate the subsurface conditions encountered and direct the drilling activities. Field logs prepared by EEC site personnel were based on visual rtand tactual observation of disturbed samples and auger cuttings. The final boring logs included with this report may contain modifications to the field logs based on results of the laboratory ritesting and engineering evaluation. Based on results of the field borings and laboratory testing, subsurface conditions can be generalized as follows. Approximately three to four inches of vegetation and/or topsoil was encountered at the surface at the boring locations. The topsoil/vegetation was underlain by lean clay with varying amounts of silt and sand. The lean clay soils showed low plasticity with low potential for volume change with variation in moisture content. Those soils were generally soft to stiff although occasional zones of very stiff material were observed. The cohesive site soils extended to depths of approximately 17 to 18 feet in borings B-1, B-2, B-4 and B-5 and to depths of approximately 24 feet at boringIIIlocationsB-3 and B-6. In borings B-1 B-2, B-4 and B-5, the cohesive site soils were underlain b essentiallygranulargY materials consisting of fine to coarse sand with varying amounts of silt and clay. The essentially granular soils were colored olive brown and were typically medium dense. Those soils extended to depths of approximately 24 to 25 feet. Claystone bedrock was encountered beneath depths of approximately 24 to 25 feet at the boring klocations. The claystone bedrock was highly weathered and soft near the surface; however, became less weathered and moderately hard with depth. The claystone was moderately plastic and i III' Earth Engineering Consultants, Inc. EEC Project No. 1982022 g B N March 21, 1998 Page 4 would be subject to volume change with variation in the soil's moisture content. The claystonekil bedrock extended to the bottom of the borings at depths of approximately 30 to 40 feet. IR The stratification boundaries indicated on the boring logs represent the approximate locations of changes in soil and rock types; in-situ, the transition of materials may be gradual and indistinct. EWATER LEVEL OBSERVATIONS 4 Observations were made while drilling and after completion of the borings to detect the presence and depth to the hydrostatic groundwater table. At two of the boring locations, field piezometers were installed in the open boreholes prior to backfilling to allow for longer term observations ofI; groundwater levels. 11; At the time of drilling, groundwater was observed at depths of approximately 14 to 19 feet below present ground surface. Water level measurements in the field piezometers completed IIapproximately 24 hours after drilling indicated water levels on the order of 14 to 17 feet. Based on those water level observations and on the moisture contents of the subgrade materials, it is our opinion the hydrostatic groundwater table was approximately 14 to 17 feet below present ground surface at the time the borin gs were performed. I' Fluctuations in groundwater levels can occur over time with variations in hydrologic conditions I and other conditions not apparent at the time of this report. Zones of perched and/or trappedIwatercanalsobeencounteredinmorepermeablezonesinsubgradesoilsattimesnesthroughoutthe year. The location and amount of perched/trapped water can also vary over time depending onIvariationsinhydrologicconditionsandotherconditionsnotapparentatthetimeofthisreport. ft I 1 P Earth Engineering Consultants, Inc:EEC Project No. 1982022 March 21, 1998 Page 5 ANALYSIS AND RECOMMENDATIONS Foundations Considering the relatively low strength of the subgrade soils and relatively high loads imposed from the three- ',- story portion of the structure, we recommend the Little Big Horn building be supported on deep foundations extending to bear in the moderately hard, weathered shale bedrock. Recommendations are provided in this report for drilled caissons piers)drilled for foundation support. Alterative types of foundations which could be considered would include auger cast pile and several types of driven piling. We would be pleased to provide further recommendations regarding these alternative deep foundations at your request. Drilled caisson foundations should be extended to bear in moderately hard, highly weathered shale. The surface of the shale bedrock was encountered at depths on the order of/4 feet below site grades at the time of our subsurface exploration. We recomme nd the drilled caisson 111 foundations penetrate the shale bedrock by a minimum length of 8 feet. For design of drilled caisson foundations extending at least 8 feet,into the weathered claystone bedrock, we recommend using a total load end bearing pressure of 20,000 psf. is Additional pier capacity could be developed by extending the drilled shafts deeper into the highly weathered to weathered bedrock and taking advantage of frictional resistance between the concrete shaft and surrounding bedrock. An allowable skin friction value of 2.000 pounds per square foot could be used for that portion of the shaft extending to depths greater than 8 feet below the surface of the bedrock. Based on the groundwater conditions observed at the time of our exploration. we anticipate it will during necessary to use temporary casing to prevent an influx of soil and water into the open boreholes r construction. When placing concrete in the temporary casings, care should be taken to maintain sufficient head of concrete to avoid displacement of the plastic concreterete by the surrounding soil and water pressures. We recommend a concrete slump between 5 and 8 inches 1111 Earth Engineering Consultants, Inc.EEC Project No. 1982022 March 21, 1998 111 Page 6 be used to prevent bridging across the temporary casing and to insure continuous contact with the reinforcing steel. Care should be taken at the time of construction to thoroughly clean the bearing surface of the bedrock. If drilling equipment used is not capable of maintaining a clean surface, we recommend a minimum shaft diameter of 30 inches be used to allow for hand cleaning. We estimate the long-term settlement of drilled pier foundations designed and constructed as outlined above would be less than 1/2 inch. i . Floor Slab and Pavement Subgrades All existing vegetation and/or topsoil should be removed from beneath the floor slab and pavement areas. After stripping and completing all cuts and prior to placement of any fill, floor slabs or MR pavements, we recommend the in-place soils be scarified to a minimum depth of 9 inches, adjusted in moisture content and compacted to at least 95% of the material's maximum dry density as determined in accordance with ASTM Specification D-698, the standard Proctor procedure. The moisture content of the scarified soils should be adjusted to be within the range of ±2% of standard Proctor optimum moisture at the time of compaction. is Fill soils required to develop the floor or pavement subgrades should consist of approved, low- volume change materials which are free from organic matter and debris. Normally, soils with a liquid limit of 40 or less and plasticity index of 18 or less could be used as low volume change fill. Soils similar to the near surface silty/sandy lean clay could be used as low volume change fill. We recommend those materials he placed in loosed lifts not to exceed 9 inches thick, adjusted in moisture content and compacted to at least 95% of the material's standard Proctor maximum dry OFdensity. The top 12 inches of the pavement subgrades immediately beneath the pavements should be compacted to at least 98% of standard Proctor maximum dry density. N I D" ii Earth Engineering Consultants, Inc. EEC Project No. 1982022 IIMarch 21, 1998 Page 7 IIAfter preparation of the subgrades, care should be taken to avoid disturbing the in-place materials. Materials which are loosened or disturbed by the construction activities or materials which become wet and softened or dry and desiccated should be removed and replaced or reworked in place prior to placement of overlying floor slabs or pavements. I = Pavements III We anticipate the main drive and parking area for the new building will be used predominately by automobiles and light trucks. A delivery area for use by heavier vehicles is located on the westasideofthebuilding. Recommendations are provided below for alternative pavement s • rsections based on previous experience with similar traffic and subgrade conditions. a TABLE I - RECOMMENDED PAVEMENT SECTIONS LIGHT DUTY HEAVY DUTY CompositeaSurface As halt (CCX) 3,,halt or'4" Aggregate Base (5 or 6) 6"12"a Full Dep th Asphalt Surface Asphalt (C or CX) 2 1/2" 3"a. Base Asphalt (G) 3 5 Portland Cement Concrete PCC Pavement 4 1/2" 6" a l' , Asphaltic concrete for use in surface course materials for the pavement areas should be consistent with City of Fort Collins criteria for Grading C or CX materials. The asphaltic concrete base should be compatible with City of Fort Collins criteria for grading G. Aggregate base should be 11 consistent with Colorado Department of Transportation requirements for Class 5 or Class 6 l aggregate base materials. Portland cement concrete, if used, should have a minimum compressive i 1 f ili EI EEC Project No. 1982022 Earth Engineering Consultants, Inc. March 21, 1998 ill Page 8 iistrength of 3,500 psi at 28 days and should be air entrained. The recommended pavement section is based on a non-reinforced Portland cement concrete section.6 iiiAlternative pavement sections could be considered and we would be pleased to provide additional. alternative pavement recommendations, at your request. If construction occurs during wet periods of the year, it maybe necessary to stabilize the subgrades to establish a suitable base for placementofthepavementsection. That stabilized portion could be used as part of the pavement section and, therefore, would reduce the aggregate and/or asphalt surfacing requirements outlined above. it Other Considerations Positive drainage should be developed across the pavements and away from the pavement edgesI. 1,to avoid wetting of the subgrades. Subgrade materials allowed to become wetted subsequent toLconstructioncanresultinprematurefailureofthepavementsection.I' IPositive drainage should be developed away from the new building to av oid wetting the bearings 9 materials or floor slab subgrades. Subgrades allowed to become wetted subsequent to construction can result in unacceptable performance of the structure. It GENERAL COMMENTS The analysis and preliminary recommendations presented in this report are based upon the data obtained from the soil borings performed at the indicated locations and from any other information discussed in this report. This report does not reflect any variations which may occur between borings or across the site. The nature and extent of such variations may not become evident until r.. construction. If variations appear evident, it will be necessary to re-evaluate the recommendationsit,,b. of this report. It is recommended that the geotechnical engineer be retained to review the plans and specifications so that comments can be made regarding the interpretation and implementation of our geotechnical II— mi t. -' L. Earth Engineering Consultants, Inc. ill EEC Project No. 1982022 March 21, 1998 Page 9 recommendations in the design and specifications. It is further recommended that the geotechnical si engineer be retained for testing and observations during earthwork and foundation con_ struction phases to help determine that the design requirements are fulfilled. This report has been prepared for the exclusive use of W.W. Reynolds for specific application to the Jro'eetP discusged and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranty, express or implied, is made. In the event that any changes are in the nature, design or location of the project as outlined in this reportplanned, the conclusions and recommendations contained in this report shall not be considered valid unless theiichangesarereviewedandtheconclusionsofthisreportmodifiedorverifiedinwritingbythe geotechnical engineer. 1111 1111 0 10 ill uI I 4, 11111,