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HomeMy WebLinkAboutSAGE CREEK - PDP - 25-98B - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTEarth Engineering Consultants, Inc. EEC Project No. 1992020 March 16, 1999 Page 10 Pavements It is our understanding that both the on -site and off -site pavements are to be designed to City of Fort Collins requirements. Final pavement section designs will be based on the estimated 18-kip daily single load axle (EDLA) and the Hveem 'R' value as determined for the subgrade materials. According to City of Fort Collins Street Standards, the 'R' value sample used for the laboratory testing cannot be collected prior to the installation of all "in -street" underground utilities. After the 'R' value is determined and provided to the City Engineering Department, Engineering Department personnel will supply the EDLA for the on and off -site streets. At that time, pavement section recommendations -can be provided. For cost estimation purposes, the City has provided approximate pavement sections on Table 2, Section 2.03.04 of the Design and Construction Criteria, Standards and Specifications for Streets, Sidewalks, Alleys and Other Public Ways. Those estimated sections are as follows. For residential local streets, 3.5 inches of hot bituminous pavement (HBP) on 6 inches of aggregate base; for residential collector streets, 5 inches of HBP on 10 inches of aggregate base; for minor arterials (such as Larimer County Road 36), 6 inches of HBP on 12 inches of aggregate base can be expected. These pavement sections are approximate and final designs will be provided after completion of the additional exploration and analysis. We anticipate that additional testing will be required in order to complete those final pavement designs. 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 Earth Engineering Consultants, Inc. EEC Project No. 1992020 March 16, 1999 Page 9 of the height of the wall. Using the active stress analysis, we recommend the below grade walls be designed an equivalent fluid pressure of 35 pounds per cubic. That equivalent fluid pressure does not include a factor of safety nor an allowance for hydrostatic loads. Surcharge loads or point loads placed in the wall backfill would also add to the lateral pressures on the below grade walls. Pavement Subgrades All existing vegetation and/or topsoil should be removed from pavement areas. After stripping and completing all cuts and prior to placement of any fill or pavements, we recommend the exposed 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 the standard Proctor procedure. The moisture content of the scarified soils should be adjusted to be within the range of -1 to +3 % of standard Proctor optimum moisture. High silt content soils were occasionally encountered in the test boring performed at this site. These higher silt content soils should be adjusted to a drier moisture so that instability of the materials will not occur during construction. Fill materials required to develop the pavement subgrades should consist of approved, low -volume change materials, free from organic matter and debris. The near surface site soils could be used for fill in these areas. We recommend those fill soils 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. After completion of the pavement subgrades, care should be taken to prevent disturbance of those materials prior to placement of the overlying pavements. The higher silt content site soils could be easily disturbed by construction activities if these soils are allowed to become wetted. Soils which are disturbed by construction activities should be reworked in -place or, if necessary, removed and replaced prior to placement of overlying fill or pavements. Earth Engineering Consultants, Inc. EEC Project No. 1992020 March 16, 1999 Page 8 Below Grade Areas Care should be taken in establishing the subgrade elevations for the basement areas to maintain suitable separation between seasonal high groundwater and the base of the basement excavations. Field piezometers have been installed to allow for longer term monitoring of the groundwater levels. We have found that high seasonal groundwater is commonly encountered during late summer with the lowest water level observations observed in later winter. We recommend a perimeter drain system be installed around all below grade areas to reduce the potential for development of hydrostatic loads on below grade walls and/or infiltration of surface water into below grade areas. In general, a perimeter drain system would consist of perforated metal or plastic pipe placed around the exterior perimeter of the structure and sloped to drain to a sump or free outfall where reverse flow cannot occur into the system. The perimeter drain should be surrounded by an appropriate granular filter soil and either the filter soil or the drain line should be encased in a filter fabric to reduce the potential for an influx of fines into the system. Backfill placed above the exterior perimeter drain should consist of approved, low -volume change materials which are free from organic matter and debris. The on -site granular and low plasticity cohesive soils could be used as fill in these areas. The top 2 feet of the backfill should be an essentially cohesive material to reduce the potential for an influx of water into the below grade drain system. We recommend those fill soils be placed in loose lifts not to exceed 9 inches thick, adjusted in moisture content and compacted to at least 90% of the material's standard Proctor maximum dry density. The moisture content of the backfill soils should be adjusted to be within the range of -1 to +3% of standard Proctor optimum moisture. Backfill soils which will support pavements, steps, patios, sidewalks or similar improvements should be compacted to at least 95% of standard Proctor maximum dry density. Basement walls will be subject to lateral earth pressures. Below grade walls for residential structures are commonly designed using active lateral stress distribution analysis. The active lateral stress analysis includes an assumption of slight wall rotation, typically assumed to be 0.5 % Earth Engineering Consultants, Inc. EEC Project No. 1992020 March 16, 1999 Page 7 No unusual problems are anticipated in completing the excavations required for construction of the footing foundations. Care should be taken during construction to avoid disturbing the foundation bearing materials. Any 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 construction of the footing foundations. We estimate the long-term settlement of footing foundations designed and constructed as outlined above would be less than 1 inch. Floor Slab Subgrades We recommend all existing vegetation/topsoil be removed from beneath the floor slab areas. After stripping and completing all cuts and prior to placement of any floor slabs or fill, the exposed subgrades should be scarified, adjusted in moisture content and recompacted. In areas with higher plasticity materials or if the subgrades become dry and desiccated prior to floor slab construction, it may be necessary to increase the moisture in a thicker zone of material to reduce the potential for post -construction movement. Fill soils required to develop the floor slab subgrades should consist of approved, low -volume change materials which are free from organic matter and debris. A majority of the near surface soils could be used for fill beneath floor slabs. Normally, low -volume change materials would have a liquid limit of 40 or less and plasticity index of 18 or less. Those materials should contain a minimum of 15 % fines, material passing a #200 sieve. Care should be taken after development of the floor slab subgrades to prevent disturbance of the in -place materials. Care will also be needed to maintain the moisture levels in the subgrades prior to floor slab construction. Materials which are loosened or disturbed by construction activities or materials which become wet and softened or dry and desiccated should be reworked prior to placement of the overlying floor slabs. oil Earth Engineering Consultants, Inc. EEC Project No. 1992020 March 16, 1999 Page 6 Care should taken after preparation of the subgrades to avoid disturbing the in -place materials. Positive drainage should be developed away from the structures and across and away from the pavement edges to avoid wetting of subgrade materials. Subgrade materials allowed to become wetted subsequent to construction of the residences and/or pavements can result in unacceptable performance of those improvements. Footing Foundations Based on materials observed at the boring locations, it is our opinion the proposed single-family residences could be supported on conventional footing foundations bearing on the natural site soils or newly placed and compacted fill developed as outlined above. We recommend those footing foundations extend through any existing vegetation and/or topsoil and bearing in the natural, soft to stiff lean clay soils or newly placed and compacted fill. For design of footing foundations bearing in the natural site soils or newly placed and compacted 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 include full dead and live loads. Occasional soft zones were observed in the natural site soils. Care should be taken during foundation construction to evaluate the anticipated bearing materials. If unacceptable materials are observed at that time, overexcavation and backfill procedures may be necessary to develop acceptable foundation bearing. Those conditions can best be evaluated in the field during construction. Exterior foundations and foundations in unheated areas should be located at least 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 24 inches. Trenched foundations or grade beam foundations could be used in the near surface cohesive materials. If used, we recommend trenched foundations have a minimum width of 12 inches and formed continuous foundations have a minimum width of 8 inches. Earth Engineering Consultants, Inc. EEC Project No. 1992020 March 16, 1999 Page 5 had not yet begun when observations were completed in March of 1999. The depths to water at each of the boring locations are indicated on the boring logs. Perched and/or trapped water may be encountered in more permeable zones in the subgrade soils at times throughout the year. Perched water is commonly encountered in soils immediately overlying less permeable bedrock materials. Fluctuations in ground water levels and in the location and amount of perched water may occur over time depending on variations in hydrologic conditions, irrigation activities on surrounding properties, and other conditions not apparent at the time of this report. Groundwater level may also be impacted by water levels in the canals adjacent to and crossing the site. ANALYSIS AND RECOMMENDATIONS Site Preparation All existing vegetation and/or topsoil should be removed from beneath fill, roadway or building subgrade areas. After stripping and completing all cuts and prior to placement of any fill, floor slabs or pavements, we recommend the exposed 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 materials should be adjusted to be within the range of -1 % to +3% of standard Proctor optimum moisture at the time of compaction. Scarification and recompaction of subgrade soils in basement areas of the residential units would not be required. Fill soils required to develop the building areas or pavement subgrades should consist of approved, low -volume change materials which are free from organic matter and debris. The near surface lean clay soils could be used as fill in these areas. 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 material's standard Proctor maximum dry density. 1* M Earth Engineering Consultants, Inc. EEC Project No. 1992020 March 16, 1999 Page 4 In borings B-1, B-2, B-4, B-5, B-6, B-7, and B-10, the overburden soils were underlain by highly weathered claystone bedrock. The claystone was colored gray, tan and rust and was moderately hard. The bedrock contained varying layers with greater or lesser percentages of clay and silt sized materials. The highly weathered bedrock extended to the bottom of the borings at depths of approximately 15 feet. - The stratification boundaries indicated on the boring logs represent the approximate location of changes in soil and rock types; in -situ, the transition of materials may be gradual and indistinct. GROUND WATER OBSERVATIONS Observations were made while drilling and after completion of the borings to detect the presence and level of free water. Piezometers were installed at two of the boring locations in July of 1998. Groundwater observations were completed in those piezometers on August 12, 1998. Those piezometers were subsequently destroyed by grass mowing activities along Larimer County Road 36. Piezometers were installed in borings B-7 through B-10 in March of 1999 to allow for longer term water level measurements. Groundwater measurements were completed in those piezometers on March 12, 1999. In July of 1998, free water was observed at depths ranging from approximately 8 to 12 feet in the southern and western portions of the site when measured while drilling. Free water was not encountered in the borings located in the northeastern portion of the site. In August of 1998, groundwater levels in the B-1 and B-2 piezometers were 5.5 feet and 8 feet below present ground surface, respectively. In March of 1999, free water was observed at depth ranging from 8 feet to 12 feet in borings B-8, B-9, and B-10. No free water was observed in B-7, in the southeastern portion of the site. On March 12, 1999 groundwater depths measured in the B-7 through B-10 piezometers ranged from 8 to 13 feet below present site grades. The piezometer installed in boring B-10 is at a lower elevation near the irrigation canal in the northwestern portion of the site and exhibited the shallowest groundwater reading. It should be noted that the higher groundwater levels that were observed in August of 1998 were seen during irrigation season while irrigation Earth Engineering Consultants, Inc. EEC Project No. 1992020 March 16, 1999 Page 3 observation of disturbed samples and auger cuttings. Coring and/or petrographic analysis may reveal other rock types. SITE AND SUBSURFACE CONDITIONS The development parcel is located north of Larimer County Road 36 and west of Larimer County Road 9 in Larimer County, Colorado. The project site is presently undeveloped farm ground. Surface drainage at the site is generally towards the north and east with a maximum difference of ground surface elevation across the site on the order of 10 to 20 feet. The majority of the parcel is relatively level, however the site slopes down toward the irrigation canal along the northern boundary. Evidence of prior building construction was not observed at the project site by EEC field personnel. J, An EEC field engineer was on -site during drilling to direct the drilling activities and evaluate the subsurface materials encountered. Field descriptions of the materials encountered were based on visual and tactual observation of disturbed samples and auger cuttings. The boring logs included with this report may contain modifications to the field logs based on results of laboratory testing and engineering evaluation. Based on results of field and laboratory evaluation, subsurface conditions can be generalized as follows. Approximately 3 to 6 inches of vegetation and/or topsoil were encountered at the surface of the boring locations. The topsoil and/or vegetation was underlain by brown/reddish brown to reddish tan lean clay which contained varying amounts of silt, sand, and gravel. The cohesive soils were soft to stiff and exhibited low to moderate plasticity. The overburden soils typically extended to depths of approximately 9 to 15 feet. In borings B-3 and B-9, the cohesive materials were underlain by dense brown to reddish brown granular materials which extended to the bottom of the boring in B-3 (15.5 feet below present ground surface) and to a depth of 12 feet in B-9. In boring B-9, the granular materials were underlain by interbedded lean clay and sand. Those materials extended to the bottom of the boring to a depth of 15.5 feet below present ground surface. f Earth Engineering Consultants, Inc. EEC Project No. 1992020 March 16, 1999 Page 2 EXPLORATION AND TESTING PROCEDURES The boring locations were selected and established in the field by Earth Engineering Consultants, Inc. (EEC) personnel. The field locations were established by estimating angles and distances from identifiable site references. The locations of the borings should be considered accurate only to the degree implied by the methods used to make the field measurements. The borings were performed using a truck mounted CME 45 drill rig and a truck -mounted Diedrich D-50 drilling rig equipped with a hydraulic head employed in drilling and sampling operations. The boreholes were advanced using 4-inch nominal diameter continuous flight augers. Samples of the subsurface materials encountered were obtained using split -barrel and California barrel sampling procedures in general accordance with ASTM Specification D-1586. 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 and hardness of weathered bedrock. In the California barrel sampling procedure, relatively undisturbed samples 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 performed on each of the recovered samples. In addition, selected samples were tested for fine content and plasticity by washed sieve analysis and Atterberg limits tests. Swell/consolidation tests were completed on selected samples 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. 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 sample'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. Classification of the bedrock was based on visual and tactual SUBSURFACE EXPLORATION REPORT RUFF PROPERTY I! LARIMER COUNTY, COLORADO EEC PROJECT NO. 1992020 I. I March 16, 1999 INTRODUCTION The subsurface exploration for the proposed residential development to be constructed on the Ruff I! property located in the Slh of the SE'/a of Section 5, Township 6 North, Range 68 West of the 6th P.M. in Larimer County, Colorado, has been completed. Ten (10) soil borings extending to I' depths of approximately 15 feet below present site grades were advanced in the proposed J development area to obtain information on existing subsurface conditions. Six of those borings ' were completed in July of 1998 (EEC Project No. 1982074) and the other four were completed in March of 1999. An additional three (3) borings extended to depths of approximately 3 feet were advanced in the pavement of Larimer County Road 36 to evaluate the existing pavement sections and subgrade materials. Individual boring logs and a diagram indicating the approximate boring locations are included with this report. The proposed development will include. approximately 80 acres of mixed density residential Idevelopment. Paved streets and utilities will be developed as part of this project. It is anticipated the structures to be constructed will be one or two-story, wood frame, single-family residences with full basements. Foundation loads for the proposed structures are expected to be light with continuous wall loads less than 2.5 kips per lineal foot and column loads less than 30 kips. Floor Iloads are expected to be less than 100 psf. It is expected the site roadways will be used by low volumes of light vehicles (automobiles and light trucks). Small grade changes are expected to develop final site grades. IThe 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 Iand construction of foundations and support of floor slabs and pavements. Earth Engineering Consultants, Inc EEC Project No. 1992020 March 16, 1999 Page 2 footing foundation bearing in the near surface cohesive materials. Because occasional zones of softer/looser materials were observed in the test borings, care will be required to see that footing foundations are supported on suitable strength soils. Highly expansive soils were not encountered in the test borings; however, the zones of moderate plasticity cohesive materials will necessitate care �I in developing floor subgrades to maintain a low potential for post -construction movement. Geotechnical recommendations concerning design and construction of foundations and support of '! floor slabs and pavements are presented in the text of the attached report. 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. t� Very truly yours, Earth Engineering Consultants, Inc. Michael .Coley, E.I.T. MJC/LLL/dmf EEC:` EARTH ENGINEERING CONSULTANTS, INC. ' March 16, 1999 James Company 2919 Valmont Road, Suite 204 ' Boulder, Colorado 80301 Attn: Mr. Jim Postle ' Re: Subsurface Exploration Report ' Ruff Property (S'/2 SE'/4 Section 5, T6N, R68W) Larimer County, Colorado EEC Project No. 1992020 Mr. Postle: I Enclosed, herewith, are the results of the subsurface exploration completed by Earth Engineering Consultants, Inc. personnel for the referenced project. This report is update to our report of August 1 12, 1998 for the S'/z SE'/4 Section 5, T6N, R68W (EEC Project No. 1982074). Site access was limited due to agricultural activities in the summer of 1998; EEC personnel were unable to complete an exploration of the entire site at that time. In March of 1999, four borings were advanced on the ' property and three borings completed in the pavement of Larimer County Road 36 to complete field work for the proposed development. The enclosed report provides recommendations for the property ' development based on the borings completed to date. In summary, the subsurface materials encountered in the test borings consisted of low to moderate plasticity cohesive soils with occasional medium to coarse grained granular soil zones. Highly weathered claystone bedrock was encountered beneath the overburden soils at depths of approximately 9 to greater than 15 feet below present site grades. Groundwater was encountered at depths of 8 to 12 feet below present site grades. Based on the materials we observed at the boring locations, it is our opinion lightly loaded residential structures could be supported on conventional CENTRE FOR ADVANCED TECHNOLOGY 2301 RESEARCH BOULEVARD; SUITE 104 FORT COLLINS, COLORADO 80526 (970) 224-1522 (FAx) 224-4564 No Text Earth Engineering Consultants, Inc. EEC Project No. 1992020 March 16, 1999 Page 11 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 the James 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.