Loading...
HomeMy WebLinkAboutHORSETOOTH EAST BUSINESS PARK PUD, FILING TWO - PRELIMINARY - 43-94A - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTf &43 6-p • - --------- j3-5 a PAD B I BORING LOCATION DIAGRAM PROPOSED HORSETOOTH EAST DEVELOPMENT FORT COLLINS, COLORADO NOVEMBER 1994, NOT TO SCALE CT No: 1942079 Earth Engineering Consultants Earth Engineering Consultants, Inc. Propose Horsetooth East Development November 18, 1994 Page 8 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 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 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 W.W. Reynolds Company 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. Earth Engineering Consultants, Inc. Propose Horsetooth East Development November 18, 1994 Page 7 Positive drainage should be developed across the pavements and away from the pavement edges to avoid wetting of the pavement subgrades. Water allowed to pond on or adjacent to the pavements can result in saturation of pavement subgrades and premature failure of the pavement section. UNDERGROUND STORAGE TANKS Ground water was encountered at a depth of approximately 9 feet in the boring performed 'I closest to where the convenient store/service station will be constructed. If underground storage Il tanks will extend below or near that depth, consideration should be given to the effects of I buoyancy on the underground storage tank. Also, the potential for instability of the bottom of the excavation and sides of the trench near the ground water table should be considered when Iinstalling the underground storage tank. Concerning corrosion of the buried tanks, conditions consisting of interbedded zones of clay and sand may create corrosive conditions of the subgrade materials. Care should be taken to properly bed the tanks. Additional testing may be warranted if steel tanks will be used. OTHER CONSIDERATIONS Care should be taken in completing site excavations to develop stable side slopes. Based on the materials encountered in the test borings, we estimate side slopes for short-term excavations would be relatively stable with slopes no steeper than 2 horizontal to 1 vertical. Deeper excavations or long term slopes should be evaluated on an individual basis. The near surface site soils contained varying amounts of silt, sand and clay. A portion of those soils may become unstable and exhibit strength loss when wetted. High silt content materials may also show high erosion potential. Earth Engineering Consultants, Inc. Propose Horsetooth East Development November 18, 1994 Page 6 Positive drainage should be developed away from all structures to avoid wetting the floor slab subgrades or bearing materials. Wetting of the bearing materials can result in softening of the support soils and settlement of the structures. PAVEMENTS Based on previous work we have completed in this area, we anticipate the "R" value of the site soils would be on the order of 8. Based on anticipated traffic volumes consisting predominately of automobiles and light trucks in the light duty areas and moderate amounts of heavy trucks in the heavy duty areas, our recommended pavement sections for this development are provided below in Table 1. Those recommend pavement sections are based on evaluation of the site materials using the 1986 American Association of State Highway and Transportation Officials (AASHTO) design procedures. An equivalent daily load axle rating of 8 was assumed for the heavy duty traffic areas and EDLA of 3 was assumed for the light duty areas. Alternative pavement sections could be considered and we would be pleased to evaluate alternatives at your request. Recommended Pavement Sections Light Duty Heavy Duty Composite Section HBP 3" 3" Aggregate Base 4" 8" Asphaltic concrete for use in the pavements should consist of hot bituminous pavement materials compatible with the City of Fort Collins criteria for SC1 or SC2 blends. Aggregate base should be compatible with Colorado Department of Transportation requirements for Class 5 or Class 6 base. Earth Engineering Consultants, Inc. Propose Horsetooth East Development November 18, 1994 Page 5 from the foundation excavations prior to placement of reinforcing steel and foundation concrete. We estimate the long term settlement of footing foundations designed and constructed as outlined above would be small, less than 1/2-inch. FLOOR SLAB AND PAVEMENT SUBGRADES All existing vegetation and/or topsoil should be removed from beneath floor slabs and pavements. After stripping and completing all cuts and prior to placement of any fill, floor slabs or 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 materials 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. A portion of the near surface site soils have high silt contents and occasional zones of silty sand materials were encountered. It may be necessary to develop and maintain lower moisture contents in those materials to avoid developing unstable subgrades. Fill materials required to develop the floor slab or pavement subgrades should consist of approved, low volume change materials, 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. Based on our observations of the near surface site soils, it is our opinion those materials could be used as low volume change fill beneath the floor slab and pavements. We recommend those fill soils be placed in loose lifts not to exceed 9-inches thick, adjusted in moisture content as recommended for the scarified materials and compacted to at least 95 % of the materials standard Proctor maximum dry density. Care should be taken after preparation of the subgrades to avoid disturbing the in -place materials. Subgrade soils which are disturbed by the construction activities should be removed I and replaced or reworked in place prior to construction of floor slabs or pavements. G, I I; Earth Engineering Consultants, Inc. n Propose Horsetooth East Development I� November 18, 1994 Page 4 Fluctuations in ground water levels can occur over time depending on variations in hydrologic conditions and other conditions not apparent at the time of this report. In addition, zones of perched and/or trapped water may be encountered in more permeable zones in the subgrade materials at times throughout the year. Long term monitoring in site piezometers which are �II sealed from the influence of surface of surface would be required to more accurately evaluate ground water conditions and fluctuations. ANALYSIS AND RECOMMENDATIONS FOUNDATIONS Based on the materials observed at the boring locations, it is our opinion the proposed lightly loaded buildings could be supported on conventional footing foundations. We recommend those footing foundations extend through all existing vegetation and/or topsoil and bear in the natural, stiff to very stiff lean clay or medium dense granular materials. For design of footing foundations bearing in the natural, stiff to very stiff cohesive soils or medium dense granular soils, 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. 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 formed continuous footings have a minimum width of 16-inches and isolated column foundations have a minimum width of 30-inches. Trenched foundations (grade beam foundations) should not be used in the near surface variable soils. No unusual problems are anticipated in completing excavations required for construction of the footing foundations. Care will be necessary to see that the foundation bearing materials are not disturbed during construction. Soils which are loosened or disturbed by the construction activities or materials which become dry and desiccated or wet and softened should be removed Earth Engineering Consultants, Inc. Propose Horsetooth East Development November 18, 1994 Page 3 An EEC technician was on -site during drilling to direct the drilling activities and evaluate the materials encountered in the test borings. The EEC field technician maintained a log of the ID materials encountered based on field observations of disturbed samples and auger cuttings. Final boring logs included with this report may contain modifications to the field logs based on the results of laboratory testing and engineering evaluation. Based on results of the field borings, subsurface conditions can be generalized as follows. Approximately 4 to 6 inches of vegetation and/or topsoil was encountered at the ground surface at the boring locations. The topsoil/vegetation was underlain by lean clay with varying amounts of silt and sand. The cohesive soils were stiff to very stiff. Interspersed in the cohesive soils were zones of silty sand and fine to medium sand with varying amounts of silt and clay. The granular soils were medium dense and were generally colored varying shades of brown. The variable overburden soils extended to the bottorn of all borings except borings B-5 and B-9. At those locations, the overburden soils extended to depths of approximately 22 feet. Below that depth the subsurface materials consisted of tan siltstone/sandstone bedrock. The siltstone/sandstone was highly weathered and poorly cemented. The bedrock extended to the bottom of those borings at a depth of approximately 25 feet. The stratification boundaries shown 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. GROUND WATER CONDITIONS Observations were made while drilling and after completion of borings to detect the location of site ground water. Free water was observed at depths of approximately 9 to 14 feet in the site borings at the time of drilling. Two-inch nominal diameter field slotted PVC piezometers were installed at three of the boring locations to allow for longer term monitoring of ground water levels. Approximately 3 days after completion of the field borings, ground water levels were observed at depths ranging from approximately 9 to 14 feet at those boring location. Based on the ground water level observed, it is our opinion the depth to the hydrostatic ground water table was on the order of 9 to 14 feet at the time the borings were performed. Earth Engineering Consultants, Inc. Propose Horsetooth East Development November 18, 1994 Page 2 The field borings were performed using a truck -mounted, rotary type 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 subsurface materials encountered were obtained using split -barrel sampling procedures in general accordance with ASTM Specification D-1586. In the split -barrel sampling procedure, a standard 2-inch O.D. split -barrel sampling spoon is 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 split -barrel sampler 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 materials and hardness of weathered bedrock. All samples obtained in the field were sealed and returned to the laboratory for further examination, classification and testing. Moisture content tests were performed on each of the recovered samples. In addition, Atterberg limits and washed sieve analysis tests were performed on selected samples. One remolded swell/consolidation test was also completed on a near surface sample. 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 materials' 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. Classification of the bedrock was based on visual "and tactical observation of disturbed samples and auger cuttings. Coring and/or petrographic analysis may reveal other rock types. SITE AND SUBSURFACE CONDITIONS The proposed development site is located south of Horsetooth Road and east of Timberline Road in Fort Collins, Colorado. Site drainage is generally to the south with a maximum difference Iin ground surface elevations across the site on the order of 5 to 7 feet. The site is presently an open field with ground cover consisting of weeds and grasses. Evidence of prior building construction was not observed at the site by EEC field personnel. SUBSURFACE EXPLORATION REPORT PROPOSED HORSETOOTH EAST DEVELOPMENT FORT COLLINS, COLORADO EEC PROJECT NO. 1942079 INTRODUCTION The subsurface exploration for the proposed Horsetooth East Development to be located south of Horsetooth Road and west of Timberline Road in Fort Collins, Colorado, has been completed. Ten (10) exploration borings extending to depths ranging from approximately 15 to 25 feet below present site grades were advanced to develop information on existing subsurface conditions in the proposed development area. Individual boring logs and a diagram indicating the approximate boring locations are included with this report. We understand the Horsetooth East Development is presently planned to include six (6) commercial development sites and a convenient store/service station. It is expected the site structures will be single story, slab -on -grade (non basement) buildings. Foundation loads for the site structures are estimated to be light with continuous wall loads less than 3 kips per lineal foot and column load less 30 kips. Floor,loads are expected to be less than 100 psf. Paved drive and parking areas will be constructed in conjunction with the site buildings. It is expected those site pavements will be used predominately by automobiles and light trucks, although a portion of the pavements may experience heavier truck loading. Small grade changes, involving cuts and fill less than 2 feet, are expected to develop the site grades for this property. 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. EXPLORATION AND TESTING PROCEDURES The boring locations were selected and established in the field by representatives of Earth Engineering Consultants, Inc. (EEC). The. field locations were established by pacing and estimating angles from the references 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. November 18, 1994 W.W. Reynolds Company 1600 Specht Point Road Fort Collins, Colorado 80525 Attn: Ms. Libby Glass RE: Subsurface Exploration Report D Proposed Horsetooth East Development Fort Collins, Colorado EEC Project No. 1942079 Ms. Glass: I DI EARTH ENGINEERIN( CONSULTANTS, INC. Enclosed, herewith, are the results of the subsurface exploration you requested for the proposed Horsetooth East Development to be located south and east of the intersection of Horsetooth and Timberline Roads in Fort Collins, Colorado. In summary, the subsurface soils encountered in the test borings completed at this site consisted of low plasticity cohesive soils with interbedded zones of silty sands. Those soils were underlain at depth by highly weathered sandstone/siltstone bedrock. Based on the materials encountered at the test boring locations, it is our opinion the proposed lightly loaded site buildings could be supported on conventional footing foundations. The near surface low plasticity cohesive materials could also be used for direct support of floor slabs and pavements. Geotechnical recommendations concerning design and construction of the foundations and support of floor slabs and pavements are presented in the text of attached report. We appreciated the opportunity to be of service to you on this project, if you have any questions D 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. Reviewed by: P.E. Principal Engineer cc: Eldon Ward, Cityscape Principal I 2600 Canton Ct, Suite A Fort Collins, CO 80525 (303) 224-1522 FAX 224-4564 SUBSURFACE EXPLORATION REPORT PROPOSED HORSETOOTH EAST DEVELOPMENT FORT COLLINS, COLORADO EEC PROJECT NO. 1942079 EARTH ENGINEERING CONSULTANTS, INC.