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HomeMy WebLinkAboutHOME STATE BANK - Filed GR-GEOTECHNICAL REPORT/SOILS REPORT -GEOTECHNICAL EXPLORATION REPORT HOME STATE BANK SOUTH SHIELDS STREET AND RAINTREE DRIVI FORT COLLINS, COLORADO PROJECT NO. 1052013 111 4• 01 EEC 111 EARTH ENGINEERING CONSULTANTS, INC. FYI. A.....A.., Pxsr R :1 R(eU+ llifspianki-- aH. slY`iv.4; EEC 4 EARTH ENGINEERING Ili CONSULTANTS, INC. III February 18, 2005 Home State Bank 1111 Attn: Mr. Steve Fobes 303 East Mountain Avenue Fort Collins, CO 80524 1111 Re: Geotechnical Exploration Report Home State Bank S. Shields and Raintree Drive 1111 Fort Collins, Colorado Project No. 1052013 IIMr. Fobes: IllEnclosed, herewith, are the results of the geotechnical subsurface exploration requested for the proposed Home State Bank at the northwest corner of South Shields Street and IIRaintree Drive in Fort Collins. In summary, the subsurface soils encountered in the test borings consisted of low to moderate plasticity lean clay with increasing amounts of sand IIwith depth. Groundwater was not encountered in the completed site borings. Based on the soils observed at the test boring locations, it is our opinion the proposed 111 lightly loaded sturcture could be supported on conventional footing foundations bearing on a zone of the site cohesive soils reconditioned to reduce swell potential. Construction IIof a basement for the structure may reduce or eliminate the over excavation requirement below the footings and floors. Although the reconditioning of subgrades below Illpavements could be limited, some movement of the pavements should be expected. Geotechnical recommendations concerning design and construction of footing U foundations and support of floor slabs and pavements are presented in the text of the attached report. II II ll4396 GREENFIELD DRIVE WINDSOR, COLORADO 80550 970) 224-1522 FAX (970) 663-0282 Earth Engineering Consultants,Inc. Project No.1052013 National Inspection Services February 18,2005 Page 2 We appreciate the opportunity to be of service to you on this project. If you have any questions concerning the enclosed report, or if we can be of further service to you in any other way,please do not hesitate to contact us. Very truly yours, Earth Engineering Consultants,Inc. National Inspection Services ii,.. ; _...,,,,,,.., 7 1' 23957 . x-zt- i builficv- • (Ajc*-ri-e'li r, Lester L. Litton, P.E. William J. Warren Principal Engineer President II II II U p I U U I II m GEOTECHNICAL EXPLORATION REPORT HOME STATE BANK SOUTH SHIELDS AND RAINTREE DRIVE FORT COLLINS, COLORADO PROJECT NO. 1052013 February 18, 2005 111 INTRODUCTION The geotechnical subsurface exploration for the proposed Home State Bank to be constructed west of South Shield Street and north of Raintree Drive in Fort Collins, Colorado, has been completed. To develop subsurface information in the area of the proposed improvements, five (5) soil borings to depths of approximately 10 to 15 feet below present site grades. Individual boring logs and a diagram indicating the approximate boring locations are included with this report. 11 We understand this project will involve the construction of a new bank building with drive-up services and associated paved drive and parking areas. The new building is expected to be single story and may contain a full basement. Foundation loads for the structure are expected to be light. A detached drive-up banking area is expected to be north of the building with drive and parking utilizing much of the rest of the site. It is expected the site pavements will be used by low to moderate volumes of automobiles and light trucks. 111 An existing single family residence will be razed prior to construction of the new building. The existing structure includes a full basement and a number of trees and shrubs on the site that will require removal. Small grade changes will be needed to develop final 11 grades on the site for the new construction. I The purpose of this report is to describe the subsurface conditions encountered in the borings, analyze and evaluate the test data and provide geotechnical recommendations concerning design and construction of foundations and support of floor slabs and pavements. I U Earth Engineering Consultants,Inc. EEC Project No. 1052013 National Inspection Services February 18,2005 Page 2 EXPLORATION AND TESTING PROCEDURES I The boring locations were established in the field by representatives of Earth Engineering Consultants, Inc. by pacing and estimating angles from identifiable site features. The approximate boring 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 field measurements. Photographs of the site taken at the time of drilling are included with this report. The borings were performed using a truck-mounted, CME-45 drill rig equipped with a hydraulic head employed in drilling and sampling operations. The boreholes were advanced using 4-inch nominal diameter continuous flight augers and samples of the 111 subsurface materials encountered were obtained using split-barrel and California barrel sampling techniques in general accordance with ASTM Specification D-1586 and by pushing thin-walled "Shelby" tube samplers in general accordance with ASTM Specification D-1587. In the split-barrel and California barrel sampling procedures, standard sampling spoons are driven into the ground by means of a 140-pound hammer falling a distance of 30 inches. The number of blows required to advance the 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. In the California barrel and Shelby" tube sampling procedures, relatively undisturbed samples of the subsurface soils are obtained in the field. All samples obtained in the field were sealed and returned to the laboratory for further examination, classification and testing. Field resistivity tests were completed at one location on the site. That testing was completed using a Neilson Model 400 resistivity meter with 4-pin Werner electrode configuration at variable spacing. Results of the field resistivity test are provided with this report. Laboratory moisture content tests were completed on each of the recovered samples. The unconfined strength of appropriate samples was estimated using a calibrated hand penetrometer. Washed sieve analysis and Atterberg limits tests were performed on 111 I U Earth Engineering Consultants,Inc. EEC Project No. 1052013 National Inspection Services February 18,2005 Page 3 selected samples to evaluate the quantity and plasticity of the fines in the subgrade materials. Swell/consolidation tests were completed on selected samples to evaluate the soil's tendency to change volume with variation in moisture content. Results of the field boring and laboratory testing are indicated on the attached boring logs and summary Usheets. As 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 System, based on the soil's texture and plasticity. The estimated group symbol for the Unified Soil Classification System is shown on the boring logs and a brief description of that classification system is included with this report. 111 SITE AND SUBSURFACE CONDITIONS The proposed development includes approximately 1 acre of land located northwest of the intersection of Raintree Drive and South Shield Street in Fort Collins, Colorado. The development property has an existing one-story residence located near the southeast property corner with a detached garage, shed and well house located west of the residence. Several trees were observed in the vicinity of the residence. Surface drainage across the site is generally to the northwest with the maximum difference in ground surface elevation across the site estimated to be less than 5 feet. An EEC field engineer was on site during drilling to evaluate the subsurface conditions encountered and direct the drilling activities. Classification of the soils encountered was based on visual and 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 laboratory testing and engineering evaluation. Based on the results of the field borings and laboratory testing, subsurface conditions can be generalized as follows. Approximately 3 to 6 inches of topsoil and vegetation was encountered at the surface at the boring locations. The topsoil and vegetation was underlain by brown lean clay with I Earth Engineering Consultants,Inc. EEC Project No. 1052013 National Inspection Services February 18,2005 Page 4 varying amounts of silt and sand. The lean clay was stiff to very stiff in consistency and showed moderate swell potential at current moisture and density conditions. The lean clay increased in sand content with depth and included scattered zones of sandy/gravelly soils. Borings B-2, B-4 and B-5 were terminated at a depth of approximately 10 to 15 feet below ground surface in the site lean clay. The lean clay encountered in borings B-1 and B-3, transitioned into clayey sand, or sand and gravel at depths of approximately 7 to 8 feet below ground surface. Those borings were terminated at a depth of approximately 15 feet below ground surface in the granular/essentially granular soils. The stratification boundaries shown on the boring logs represent the approximate locations of changes in soil types"; in-situ, the transition of materials may be gradual and indistinct. GROUNDWATER OBSERVATIONS Observations were made while drilling and after completion of boring to detect the presence and level of free water. At that time, free water was not encountered in any of the drilling locations. Perched and/or trapped water maybe encountered in more permeable zones in thePp subgrade soils at times throughout the year. Trapped water is commonly encountered in more permeable, granular soil zones. Fluctuations in groundwater levels and in the location and amount of perched water may occur over time depending on variations in hydrologic conditions, irrigation activities, and other conditions not apparent at the time of this report. We have typically noted lowest groundwater levels in late winter and shallowest groundwater levels in mid to late summer. p I Earth Engineering Consultants,Inc. EEC Project No. 1052013 National Inspection Services February 18,2005 Page 5 ANALYSIS AND RECOMMENDATIONS Site Preparation An existing residence and associated improvements were observed in the south/eastern portion of the site at the time of our exploration. The residence appears to contain a full basement. Within the proposed building or pavement areas, all existing site improvements should be completely removed. In addition, the existing trees and and shrubs along with root structures and desiccated soils should be completely removed. Care will be needed to see that any disturbed and/or soft or loose zones of in-place material associated with the existing site improvements are also removed. 111 The near surface lean clay soils were dry and dense at the time of our exploration and showed moderate swell potential at current moisture and density conditions. If the 111 building is to be non-basement, the lean clay soil should be removed to at least 3 feet below foundation bearings and/or floor slab subgrade and the over excavation areas backfilled with moisture conditioned fill soils. The over excavation should extend at least 2 feet laterally in all directions beyond the edges of the foundations. Use of the over excavation beneath the building will reduce the potential for post construction movement, with the moderately expansive lean clay soils but that potential would not be eliminated. If a basement will be constructed for the new building, it may be possible to significantly reduce or possibly eliminate the overexcavation zone. With somewhat variable site conditions, the in place soils should be closely evaluated at the time of construction to establish the swell potential of expected bearing or subgrade soils. U Fill soils required to redevelop foundation and/or floor slab subgrades should consist of approved, low-volume change materials which are free from organic matter and debris. The site lean clay or clayey sand could be used for fill beneath the proposed site improvements. Alternatively, imported soils could also be used as fill in these areas. Typically, soils with a liquid limit less than 40 and a plasticity index less than 18 could be used as low-volume-change fill. The fill should have a minimum of 15% fines (material U Earth Engineering Consultants,Inc. EEC Project No. 1052013 National Inspection Services February 18,2005 Page 6 passing the #200 size sieve)to help reduce the potential for water to pond in the subgrade soils. Those fill soils should be placed in loose 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 density. The moisture content of the fill soils should be adjusted to be within the range of±2%of standard Proctor optimum moisture at the time of compaction. Foundations For site subgrades prepared as outlined above, it is our opinion the proposed lightly loaded structure could be supported on conventional footing foundations. We recommend those foundations bear on natural, low swell potential sandy lean clay in basement areas Nor suitable structural fill placed and compacted as outlined above in non basement areas. For design of the footing foundations bearing in natural, essentially cohesive soils or suitable structural fill, we recommend using a net allowable total load soil bearing pressure not to exceed 1,500 psf. The net bearing pressure refers to the pressure at foundation bearing level in excess of the minimum surrounding overburden pressure. Total load should be based on full dead and live loads. We recommend the bearing materials be closely observed and tested at the time of construction to see that the footing foundations are not placed on or immediately above unsuitable materials. If expansive soils are encountered at foundation bearing level, overexcavation/backfill procedures may be needed to develop suitable foundation bearing. The presence of expansive materials and the extent of overexcavation required can be best addressed in the field at the time of excavation. Exterior foundations and foundations in unheated areas should be located a minimum of 30 inches below adjacent exterior grade to provide frost protection. We recommend Iformed continuous footings have a minimum width of 12 inches and isolated column foundations have a minimum width of 24 inches. Trenched foundations or grade beam foundations could be used in the near surface cohesive soils. If used, we recommend trenched foundations have a minimum width of 12 inches and formed grade beam foundations have a minimum width of 8 inches. I I Earth Engineering Consultants,Inc. EEC Project No. 1052013 National Inspection Services February 18,2005 Page 7 1 Care should be taken during construction to avoid disturbing the foundation bearing materials. Foundation bearing materials which are loosened or disturbed by the construction activities or materials which become dry and desiccated or wet and softened should be removed and replaced or reworked in place prior to placement of the overlying foundations. We estimate the long-term settlement of footing foundations designed and constructed as outlined above would be less than 1 inch. Floor Slab and Pavement Subgrades All existing vegetation and/or topsoil should be removed from floor slab and pavement areas. In addition, any existing site improvements should be removed along with associated fill and back fills. If a basement is not constructed, over excavation/backfill procedures will be needed below the floor slab. After stripping and removing all improvements and existing trees/shrub, 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±2% of standard Proctor optimum moisture at the time of compaction. Scarification and compaction should not be completed in the basement area of the structure 111 Fill materials required to develop floor slab or pavement subgrades should consist of approved, low-volume change materials which are free from organic matter and debris. The site lean clay and clayey sand could be used as fill in these areas. Those fill materials should be placed in loose lifts not to exceed 9 inches thick, adjusted in moisture content as recommended for the scarified soils and compacted to at lest 95% of the material's standard Proctor maximum dry density. Care should be taken after preparation of the subgrades to avoid disturbing the prepared materials. Subgrade materials which are loosened or disturbed by the construction I Earth Engineering Consultants,Inc. EEC Project No. 1052013 National Inspection Services February 18,2005 Page 8 activities or materials which become dry and desiccated or wet and softened should be removed and replaced or reworked in place prior to placement of the overlying floor slabs or pavements. Below Grade Areas We recommend a perimeter drain system be installed around all below grade areas to reduce the potential for seepage of infiltration water into below grade areas and/or development of hydrostatic loads on the below grade walls. In general, a perimeter drain 01 system should consist of perforated metal or plastic pipe placed at approximate foundation bearing level around'the exterior perimeter of the structures. The perimeter drain line should be sloped to gravity drain to a sump area or free outfall where water can be removed without reverse flow occurring in the system. The perimeter drain line should be surrounded by a minimum of 6 inches of appropriately sized granular filter soil and either the filter soil or drain line should be surrounded by an appropriate filter fabric to reduce the potential for infiltration of fines into the system. I Backfill placed above the perimeter drain line 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 I change fill. Based on materials observed at the boring locations and results of laboratory testing, it is our opinion the site soils could be used as low-volume change fill adjacent to the structure. We recommend those fill materials be placed in loose lifts not to exceed 9 inches thick, 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 fill soils should be adjusted to be within the range of ±2% of standard Proctor optimum moisture at the time of compaction. For design of below grade walls where appropriate steps have been taken to eliminate hydrostatic loads, we recommend using an equivalent fluid pressure of 35 pounds per cubic foot. The recommended design equivalent fluid pressure is based on an active Earth Engineering Consultants,Inc. EEC Project No. 1052013 National Inspection Services February 18,2005 Page 9 stress distribution case where slight rotation is expected in the below grade walls. The rotation expected to develop an active stress distribution case results in deflection on the wall of approximately 0.5% times the height of the wall. That deflection may result in stress cracks on the interior of the basement walls, particularly near the center of spans between corners or other restrained points. The recommended equivalent fluid pressure does not include an allowance for hydrostatic loads nor does it include a factor of safety. Surcharge loads placed adjacent to below grade walls or point loads placed in the wall backfill may add to the lateral pressures of below grade walls. Site Pavements Pavement subgrades should be developed as outlined above. After preparation of the pavement subgrades, care should be exercised to prevent disturbance of those materials prior to placement of the overlying pavements. The near surface lean clay would be subject to instability at elevated moisture contents. If construction occurs during wet periods of the year, the site lean clay would be subject to strength loss with a tendency to "pump" with excessive moisture infiltration. Depending on the time of year when construction occurs, it may be necessary to stabilize the subgrades to allow for the placement of the overlying pavement section. Stabilization 111 of the subgrade would develop higher strength subgrade which could be used as part of the pavement section thereby reducing the thickness of overlying aggregate base course and/or asphalt surfacing. Additional recommendations concerning subgrade stabilization can be provided, if desired. We expect traffic on the site pavements will generally consist of low to moderate volumes of automobiles and light trucks. We anticipate the subgrades in those areas will consist of lean clay. Alternative composite and concrete pavement sections are provided below in Table 1 for both light and heavy-duty pavement areas. Those pavement sections are based on assumed traffic volumes. "Light duty"pavements would include those areas with low to moderate traffic volumes consisting of automobiles and light trucks. "Heavy duty"pavement areas would include higher volume areas such as entrance drives or areas where heavier trash or delivery trucks would be expected. I Earth Engineering Consultants,Inc. EEC Project No. 1052013 National Inspection Services February 18,2005 Page 10 I TABLE 1 —PAVEMENT SECTION RECOMMENDATIONS Light Duty Heavy Duty IAlternative A—Composite Section Surface Asphalt(Grading S or SX) 31/2" 5,, Aggregate Base (Class 5 or 6) 6" 8 111 Alternative B — Composite on Fly Ash Stabilized Subgrade Surface Asphalt(Grading S or SX) 3" 4" Base Asphalt(Grading SG) 4" 4" Fly Ash Stabilized Subgrade 12"12" Alternative C—Portland Cement Concrete Pavement 5" 6" I Asphalt surfacing should consist of grading S (3/4 inch minus) or grading SX (1/2 inch minus) hot bituminous pavement consistent with Colorado Department of Transportation CDOT) requirements. Aggregate base should be consistent with CDOT requirements for Class 5 or Class 6 aggregate base. In dumpster or truck loading and unloading areas, asphalt pavement sections subject to increased loads and truck turning movements would likely show poor performance. Similarly, drive thru areas may show poor performance with an asphalt surface. We recommend concrete pavement sections be considered in these areas. Portland cement concrete, if used, should have a minimum 28-day design compressive strength of 3,500 psi and should be air entrained. The recommended Portland Cement Concrete pavement section is based on non-reinforced concrete although woven wire or fiber mesh should be considered for control of shrinkage cracks. I Earth Engineering Consultants,Inc. EEC Project No. 1052013 National Inspection Services February 18,2005 Page 11 The recommended pavement sections are minimums and, as such, periodic maintenance should be expected. Areas expected to carry heavier trucks or higher volumes of trucks may require thicker pavement sections. Alternative pavement sections could also be considered and we would be pleased to review any alternatives at your request. Other Considerations Soil resistivity was measured in the range of approximately 6000 to 7500 ohm-cm in the field testing. Those results indicate a slightly aggressive environment for corrosion of buried ferrous metals. The results of the resistivity tests are attached. Positive drainage should be developed across and away from the site pavements and away from the structures to avoid ponding of water adjacent to those improvements. Site landscaping should be designed to avoid ponding of water adjacent to site improvements. Roof drains should be designed to discharge at least 5 feet away from the buildings and away from the pavement areas. Water allowed to pond on or adjacent to the pavements and site structures can result in unsatisfactory performance of those improvements over time. 11111 GENERAL COMMENTS The analysis and 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 further exploration or construction. If variations appear evident, it will be necessary to re-evaluate the recommendations 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 recommendations in the design and specifications. It is further recommended that the geotechnical engineer be retained for testing and N Earth Engineering Consultants,Inc. EEC Project No. 1052013 National Inspection Services I February 18,2005 Page 12 observations during earthwork and foundation construction phases to help determine that the design requirements are fulfilled. This report has been prepared for the exclusive use of Home State Bank for specific application to the project discussed 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 in the nature, design or location of the project as outlined in this report are planned, the conclusions and recommendations contained in this report shall not be considered valid unless the changes are reviewed and the conclusions of this report modified or verified in writing by the geotechnical engineer. N N p I I I t I