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HomeMy WebLinkAboutPROSPECT COMMONS (FORMERLY GREENS) PUD - FINAL - 15-95A - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTEarth Engineering Consultants, Inc. Prospect Greens May 12, 1995 Page 7 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 REMAX 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 Y 14 A 2 b Z�'°�� FW y ° av r C B, U¢ SU Xd Q W yy r. ♦ Iy _o � �s z W (i —.Z �a .> n O u fi , .. aQ � L_—L4 G I M1 ♦ Wa a $ p� N a a-3 a ca .. I Lia. �� 5 ZOO N a. Q 6p!ppt9��1 I .,tlRS✓3n ,0 '�r ma �i TEST BORING LOCATION DIAGRAM PROSPECT GREENS P.U.D. FORT COLLINS, COLORADO PROJECT No: 1952030 Earth En; 1 Earth Engineering Consultants, Inc. Prospect Greens May 12, 1995 Page 6 considered to reduce the potential for instability at the time of construction. We would be pleased to provide additional recommendations concerning stabilization of the subgrades, if needed at that time. Stabilization of these subgrades could be typically be used to reduce the pavement section if the stabilization is appropriately designed. - After preparation of the floor slab or pavement subgrades, care should be taken to avoid disturbing the in -place materials. Materials which are loosened or disturbed by the construction activities should be reworked in place or removed and replaced prior to placement of the floor slabs or pavements. Positive drainage should be developed across the pavements and away from pavement edges to avoid wetting of the pavement subgrades. Subgrades which become wetted subsequent to construction could result in premature failure of the pavement subgrades. PAVEMENTS °' Information concerning the remolded strength of the pavement subgrade soils was not available at the time of this report. Recommandations concerning the pavement section will be fowarded when that information becomes available. 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 Earth Engineering Consultants, Inc. Prospect Greens May 12, 1995 Page 5 Care will be needed during construction to avoid disturbing the foundation bearing soils. A portion of the subgrade soils contain relatively high percentages of silt and would be subject to instability and strength loss when wetted. Particular care will be necessary to avoid disturbing these materials. Bearing soils which become loosened or disturbed by construction activities or soils which become dry and desicated or wet and softened should be removed and replaced prior to placement of footing foundations or the footing foundations should be extended to bear beneath the unacceptable materials. We estimate the long-term settlement of the footing foundations designed and constructed as recommend above would be less than 3/4 inch. FLOOR SLAB AND PAVEMENT SUBGRADES All existing vegetation and/or topsoil should be removed from beneath the floor slabs and pavements. After stripping and completing all cuts and prior to placement of any fill, floor slabs or pavements, we recommend the exposed subgrades 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 percent of standard Proctor optimum moisture. A drier moisture may be required for the high silt content soils to reduce the potential for instability. Any fill material required to develop the floor slab or pavement subgrades should consist of approved, low volume change materials which are free from organic matter and debris. The near surface cohesive and essentially granular soils meet the general criteria for low volume change fill. Those materials should be place in loose lifts not to exceed 9-inches thick, adjusted in moisture content as recommended for the scarified soils and compacted to at least 95 % of the materials' standard Proctor maximum dry density. A portion of the near surface site soils contain relatively high silt contents and may exhibit instability and strength loss when wetted. Stabilization of the pavement subgrades could be Earth Engineering Consultants, Inc. Prospect Greens May 12, 1995 Page 4 Depth to ground water can vary 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 at times throughout the year in more permeable zones interbedded with the cohesive soils. Perched water is commonly encountered in soils overlying less permeable highly weathered bedrock. The location and amount of perched water can also vary over time depending on variations in hydrologic conditions and other conditions not apparent at the time of this report. ANALYSIS AND RECOMMENDATIONS FOUNDATIONS Based on the materials observed at the test boring locations, it is our opinion the proposed the lightly loaded structures could be supported on conventional footing foundations. We recommend those foundations extend through all existing vegetation and/or topsoil and bear in the natural, stiff to very stiff lean clay with varying amounts of sand or in the medium dense granular materials with varying amounts of silt and/or clay. For design of footing foundations bearing on the natural, stiff to vary stiff cohesive soils or medium dense granular materials, we recommend using a net allowable total load soil bearing pressure not exceed 2500 psf. The net bearing pressure refers the pressure at foundation bearing level in excess of the minimum surrounding overburden pressure. Total load implies full dead and live loads. The footings should be designed for a minimum dead load of 500 psf to reduce the potential for movement with moisture fluctuations in the subsurface soils. 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 variable overburdened soils. Earth Engineering Consultants, Inc. Prospect Greens May 12, 1995 Page 3 Approximately 4 to 8 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 materials observed were slightly plastic and exhibited swell pressures of approximately 500 to 600 psi. The cohesive swells were interbedded with zones of sandy silt and silty sand with varying amounts of clay. ' The granular materials generally became more prevalent with depth and were courser and cleaner with depth. The granular materials were generally medium dense while the cohesive soils were stiff to very stiff. The borings were terminated at depths of approximately 6 to 14 feet in granular soils except for boring B-6. At that location, the overburden soils extended to depth of approximately 8 feet and were underlain by highly weathered sandstone bedrock. The sandstone bedrock was colored brown and was poorly cemented. The bedrock extended to the bottom of that boring at a depth of approximately 12 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. Classification of the bedrock was based on visual and tactual observation of disturbed samples and arger cuttings. Coring.and/or petrographic analysis may reveal other rock types. WATER LEVEL OBSERVATIONS Observations were made while drilling and after completion of the borings to detect the presence and depth to free water. In addition, in borings B-4 and B-6 (performed in the lower areas of the site), field slotted PVC piezometers were installed in the open bore holes prior to backfilling. The piezometer installations allow for longer term monitoring of ground water levels at those locations. At the time of drilling, the depth to free water ranged from approximately 10 to 14 feet. Free water was not observed in the shallower pavements borings nor in boring B-1 at the north end of the site. Approximately four days after drilling, free water was observed at depths of approximately 6 to 8 feet in the two borings on the south end of the site where piezometers had been installed. Earth Engineering Consultants, Inc. Prospect Greens May 12, 1995 Page 2 The 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 in the borings were obtained using split -barrel sampling procedures in general accordance with ASTM Specifications 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 soils and hardness of weathered bedrock. All samples obtained in the field were sealed and returned to the laboratory for further examination, classification and testing. SITE AND SUBSURFACE CONDITIONS The proposed Prospect Greens P.U.D. will be located south of East Prospect Road and east of ' Stover Street in Fort Collins. The development parcel encompasses approximately 2-1/2 acres. Surface drainage on the site is towards the south, towards Spring Creek. The project site is ' currently horse pasture with ground covering of sparse vegetation. Evidence of prior building construction was not observed at the site by EEC field personnel. An EEC field geologist was on site during drilling to observed the materials encountered in the test borings and direct the drilling activities. Logs of the materials encountered were developed by EEC field personnel based on visual and tactual observation of the disturbed samples and auger cuttings. Final boring logs included with this report may contain modifications to those 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. E SUBSURFACE EXPLORATION REPORT PROPOSED PROSPECT GREENS P.U.D. EAST PROSPECT ROAD NEAR STOVER STREET FORT COLLINS, COLORADO EEC PROJECT NO. 1952030 INTRODUCTION The subsurface exploration for the proposed Prospect Greens P.U.D. in Fort Collins, Colorado, has been completed. Four (4) soil borings extending to depths of approximately 12 to 15 feet below present site grades were advanced in the proposed building areas to develop information ton existing subsurface conditions relative to support lightly loaded foundations and floor slabs. Two other borings were advanced in proposed drive areas to develop information with regard to support of pavements. Individual boring logs and a diagram indicating the approximate boring locations are included with this report. We understand the Prospect Greens P.U.D. will be constructed south of East Prospect Road and East of Stover Street in Fort Collins. The development will involve the construction of 17 patio homes on an approximate 2-1/2 acre parcel. It is expected those residences will be single story wood frame structures with light foundation and floor slab loads. Foundation loads are expected to be less than 2.5 kips per lineal foot for continuous wall loads and 30 kips for individual column. Floor loads are estimated to be less than 100 psf. It is anticipated the proposed structures will be non -basement. A paved entry street and underground utilities will be installed as a part of this project. 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 borings locations were selected by Earth Engineering Consultants, Inc. (EEC) personnel and establish in the field by pacing and estimating angles from the references indicated on the attached boring location diagram. The approximate boring locations should be considered accurate only to the degree implied by the methods used to make the field measurements. i ' May 12, 1995 ' REMAX First Associates, Inc. 3665 JFK Parkway Fort Collins, Colorado 80525 Attn: Mr. Ron Young ' RE: Subsurface Exploration Report Proposed Prospect Greens P.U.D. East Prospect Road near Stover Street Fort Collins, Colorado EEC Project No. 1952030 Mr. Young: I D) EARTH ENGINEERING CONSULTANTS, INC. Enclosed, herewith, are the results of the subsurface exploration performed by Earth Engineering Consultants, Inc. (EEC) for the referenced project. In summary, the soils observed in the test borings performed at this site consisted of interbedded strata of lean clay with varying amounts of silt and sand and predominately granular soils containing varying amounts of silt and clay. The cohesive soils were slightly plastic and exhibited small potential for volume change with variation in moisture content. It is our opinion the near surface natural soils could be used for direct support of footing foundations for the lightly loaded structures. Some slight movement should be expected for pavements and slabs -on -grade supported directly on the cohesive site materials. In the lower portions of the site, free water was observed at a depth at approximately 6 to 8-feet four days after completion of the borings. Geotechnical recommendations concerning design and construction of foundations and support floor slabs and pavements are presented 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 the enclosed report, or if we can be of further service to you in any other way, please don't hesitate to contact us. Very truly yours, Earth Fjwjmring Consultants, Inc. CI Lester L. lion, P.E. Principal Engineer cc: (4) Gary Odehnal, Parsons and Associates Principal Engineer Centre For Advanced Technology 2301 Research Boulevard, Suite 104 Fort Collins, CO 80526 (970) 224-1522 FAX 224-4564 (a SUBSURFACE EXPLORATION REPORT PROPOSED PROSPECT GREENS P.U.D. EAST PROSPECT ROAD NEAR STOVER STREET FORT COLLINS, COLORADO EEC PROJECT NO. 1952030 I P) EARTH ENGINEERING CONSULTANTS, INC.