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HomeMy WebLinkAboutHARMONY TECHNOLOGY PARK SECOND HARMONY ROAD AND CAMBRIDGE AVENUE - Filed SEPD-SURFACE EXPLORATION/PAVEMENT DESIGN REPORT -GEOTECHNICAL SUBSURFACE EXPLORATION REPORT CAMBRIDGE AVENUE CONSTRUCTION/ HARMONY ROAD IMPROVEMENTS FORT COLLINS, COLORADO EEC PROJECT NO. 1042058 7, EE S EARTH ENGINEERING CONSULTANTS, INC. I l Ll I 4 A EC August 30, 2004 F E ' A EARTH ENGINEERING CONSULTANTS, INc. Imago Enterprises, Inc. 140 Palmer Drive Fort Collins, Colorado 80525 Attn: Mr. Les Kaplan Re: Geotechnical Subsurface Exploration Cambridge Avenue Construction/Harmony Road Improvements Fort Collins, Colorado EEC Project No. 1042058 Mr. Kaplan: Enclosed, herewith, are results bf the geotechnical subsurface exploration completed by Earth Engineering Consultants, Inc. (EEC) personnel for the referenced project. In summary, the subsurface soils encountered in borings completed in both the turn lane areas on Harmony Road and along the Cambridge Avenue alignment south of Harmony Road consisted of lean clays with varying amounts of silt and sand. Those soils were slightly to moderately plastic with laboratory measured swell potential ranging from low to moderate. Higher swell potential was observed in very dry near surface soils with lower swell potential in deeper, moister soils. Results of field borings and laboratory tests on the subgrade soils are provided with this report. Also included with this report is a mix design for stabilization of the subgrade soils using Class C fly ash. Final pavement design will be completed after receiving traffic load information from City of Fort Collins Engineering Department. 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 other way, please do not hesitate to contact us. cc: Mike Brake - J.R. Engineering Rick Richter - City of Fort Collins Engineering Department (4) CENTRE FOR ADVANCED TECHNOLOGY 2301 RESEARCH BOULEVARD, SUITE 104 FORT COLLINS, COLORADO 80526 970) 224-1522 FAX (970) 224-4564 GEOTECHNICAL SUBSURFACE EXPLORATION CAMBRIDGE AVENUE CONSTRUCTION/ HARMONY ROAD IMPROVEMENTS FORT COLLINS, COLORADO EEC PROJECT NO. 1042058 August 30, 2004 INTRODUCTION The subsurface exploration for the proposed construction of Cambridge Avenue south of Harmony Road and new turn lanes at the Harmony Road/Cambridge Avenue intersection has been completed. Six (6) soil borings were completed to depths of approximately 10 feet in proposed acceleration/deceleration and turn lanes along Harmony Road. Six (6) additional sets of borings were completed along the Cambridge Avenue alignment extending south of Harmony Road to approximately Rock Creek Drive. At each of the test locations, one (1) boring to a depth of approximately 5 feet was completed above an in -place sanitary sewer line and one (1) other boring was completed to a depth of approximately 10 feet outside of the area of the sewer line excavation. Individual boring logs and diagrams indicating approximate boring locations are provided with this report. We understand this project will involve the construction of Cambridge Avenue from Harmony Road extending south to approximately Rock Creek Drive. In addition, a left- hand turn lane will be constructed for west bound Harmony Road at the Cambridge Avenue intersection and deceleration/acceleration lanes will be constructed on east- bound Harmony Road at the intersection. A sanitary sewer line was installed along the Cambridge Avenue alignment in July of 2001. It is our understanding, cuts and fills less than 1 foot from present grade will be required to develop subgrades for Cambridge Avenue. Small cuts are also expected for developing the subgrades for the acceleration/deceleration and turn lanes on Harmony Road. The purpose of this report is to describe the subsurface conditions encountered in the test borings, analysis and evaluate the test data and provide recommendations for subgrade preparation for the new pavements. Pavement section design will be completed after traffic information is provided by City of Fort Collins Engineering Department. Earth Engineering Consultants, Inc. EEC Project No. 1042058 August 30, 2004 Page 2 EXPLORATION AND TESTING PROCEDURES The test borings were performed with a 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 subsurface materials encountered were obtained using split -barrel and California barrel sampling procedures in general accordance with ASTM Specification D-1586. Additional thin walled tube Shelby tube) samples were obtained 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,Tequired 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 materials. Additional bulk samples were obtained from the auger cuttings. All samples obtained in the field were sealed and returned to the laboratory for further examination, classification and testing. Moisture content tests were completed in each of the recovered samples. Atterberg limits and washed sieve analysis tests were completed on selected samples to evaluate the percentage and plasticity of fines in the subgrades. Swell/consolidation tests were performed on representative samples to evaluate the soil's tendency to change volume with variation with moisture content. Results of the outlined tests are indicated on the attached boring logs. The Hveem stabilometer R-value was determined for a representative portion of a composite sample obtained from the borings along Cambridge Avenue. In addition, portions of the composite sample were blended with 11, 13 and 15% Class C fly ash and tested for moisture/density relationship and compressive strength of the compacted samples. The percent fly ash was based on dry unit weights. Test results of the density and compressive strength testing are indicated on the attached summary sheets. Earth Engineering Consultants, Inc. EEC Project No. 1042058 August 30, 2004 Page 3 As a part of the testing program, all samples were examined in a 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 indicated on the boring logs and a brief description of that classification system is included with this report. SITE AND SUBSURFACE CONDITIONS The portion of Cambridge Avenue to be constructed is approximately t/Z mile east of Ziegler Road and extends south from Harmony Road in southeast Fort Collins. A sewer line was installed along the Cambridge Road alignment in July of 2001. At that time, borrow materials from the nearby Brookfield project were used to backfill the sewer line as the in -situ materials were extremely wet from flood irrigation on adjacent property. The field density test results completed at the time of that backfill placement met the project compaction requirement of at least 95% of standard Proctor maximum dry density. The Cambridge Road alignment is presently undeveloped excluding the in -place utilities. Harmony Road (Colorado State Highway 68) is a four -lane major arterial with asphalt surfacing and paved shoulders. Borrow ditches are located to the north and south of that roadway. Based on field borings and laboratory testing, subsurface conditions can be generalized as follows. Sparse vegetation and/or topsoil were encountered at the surface at the boring locations along Cambridge Avenue. Four to six inches of asphaltic concrete underlain by 6 to 8 inches of aggregate base course was observed in the turn lanes along the south of the existing Harmony Road. For the center left-hand turn lane, approximately 6 inches of vegetation and/or topsoil was encountered at ground surface. The subgrade soils observed in the test borings generally consisted of lean clay with varying amounts of silt and sand although occasional clayey sand or silty sand zones were observed. The natural soils contained occasional calcareous zones and the fill soils Itcontained occasional gravelly zones. The in -situ soils were generally stiff to very stiff and were slightly to moderately plastic. The swell potential for the in -place soils ranged It Earth Engineering Consultants, Inc. EEC Project No. 1042058 August 30, 2004 Page 4 from low to moderate with higher swell potential observed in very dry and hard near surface soils. At moderate moisture content, the in -place soil showed low swells. The cohesive soils generally extended to the bottom of the borings at depths ranging from approximately 5 to 10 feet below present site grades. The stratification boundaries indicated on the boring logs represent the approximate location of changes in soil types; in -situ, the transition of materials may be gradual and indistinct. In addition, the soil borings show conditions at the test borings locations; variations in subsurface conditions can occur relatively short distances from the boring locations. GROUNDWATER CONDITIONS - Observations were made while drilling after completion of the borings to detect the presence and location of groundwater. At the time of drilling, no freewater was observed in the test borings. When the sewer line was installed along Cambridge Avenue in July of 2002, significant soft and wet subgrade swells were observed, presumably as a result of flood irrigating on adjacent properties. Development of the properties adjacent to the roadway will eliminate the flood irrigation; however, we understand detention areas are planned immediately west of Cambridge Avenue which will likely result in elevated moisture contents within the subgrades. Fluctuations in groundwater levels can occur over time depending on variations in hydrologic conditions and other conditions not apparent at the time of this report. Perched and/or trapped water can be encountered in more permeable zones innerbedded with any subgrade soils. I _ Earth Engineering Consultants, Inc. EEC Project No. 1042058 August 30, 2004 Page 5 ANALYSIS AND RECOMMENDATIONS Harmony Road Turn Lanes/Accelleration/Decelleration Lanes Harmony Road is a 4-lane asphalt surfaced state highway with asphalt paved shoulders. The subgrade soils observed in the test borings at this location consist of moderate plasticity lean clays with low to moderate swell potential. State highway construction would typically involve removal of subgrade soils and placement of minimum of 2 feet of aggregate subbase with a minimum R-value of 40. Although higher swell potential was observed in near surface materials, we expect that removal of that depth of soil from beneath the new roadways will also remove the higher swell materials from that location. In general, we believe the acceleration/deceleration lanes and turn lanes could be constructed supported on the placed zone of R40 material. Thickness design for the roadways in this area would be based on an R-value of 40. Traffic load information provided by the City of Fort Collins will be used to design the overlying pavement section. Cambridge Avenue The subgrade materials along Cambridge Avenue also consists of low to moderate plasticity lean clay with varying amounts of silt and sand. The subgrade soils generally showed low swell potential although a swell of 31/s% was recorded with a 150 psf surcharge load on a relatively dry near surface sample. A 10-feet deep storm drain is still to be placed in the street right-of-way. Placement of the backfill for the drain will increase the moisture in the near surface soils. However, care will be needed to maintain moisture in the subgrades or adjust that moisture at the time of construction of the pavement. With the lean clay subgrade soils and expected detention adjacent to Cambridge Avenue and flood irrigation continuing to occur on the properties adjacent, we recommend the Cambridge Avenue subgrades be fly ash stabilized to provide increased stability of those M Earth Engineering Consultants, Inc. EEC Project No. 1042058 August 30, 2004 Page 6 subgrades during construction. Additional recommendations concerning fly ash stabilization of the subgrades are provided with this report. All existing vegetation and/or topsoil should be removed from the Cambridge Avenue subgrades. After stripping and completing all cuts and prior to placement of any fill, we recommend the in -place 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 f2% of standard Proctor optimum moisture at the time of compaction. Fill soils required to develop the pavement subgrades should consist of approved, low - volume change materials that are free from organic matter and debris. The site lean clay soils could be used for fill in the Cambridge Avenue subgrades. 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 soil's standard Proctor maximum dry density. After developing the approximate subgrade elevations, we recommend the pavement subgrades be stabilized through the addition of 13% Class C fly ash, based on dry unit weights. Fly ash stabilization of the subgrades should be completed from back -of -curb to back -of -curb and should include a 12-inch stabilization depth. After blending the subgrade soils with the Class C fly ash, the resulting subgrade will be 1 to 1'/2 inches higher than the preblended elevation. These blended soils should be adjusted in moisture content and compacted to at least 95% of the material's standard Proctor maximum dry density. The moisture content of the soils should be adjusted to be within the range of -3 to +1 of standard Proctor optimum moisture content at the time of compaction. The maximum strength of the fly ash stabilized subgrade soils is attained through compaction slightly dry of standard Proctor optimum moisture content for maximum dry density. In addition, compaction and finish grading should be completed on the fly ash stabilized subgrade within 2 hours from the introduction of the fly ash of the initial blending of the Earth Engineering Consultants, Inc. EEC Project No. 1042058 August 30, 2004 Page 7 fly ash and subgrade soils. A suggested specification for subgrade stabilization utilizing Class C fly ash is included with this report. Pavement Sections Pavement section design is based on subgrade conditions and anticipated traffic volume. A Hveem stabilometer R-value of 6 was determined for the sandy clay subgrade soils. That R-value would be used for design of the pavements along Cambridge Avenue. Assuming 2 feet of R40 material is placed in the turn lane areas along Harmony Road, an R-value of 40 would be utilized for the pavement design in this area. Subgrade soils stabilized with Class C fly ash will provide subgrade support for Cambridge Avenue and credit obtained for an increased strength of the subgrade. Pavement sections for this project would be provided after estimated traffic volumes are supplied by the City of Fort Collins Engineering Department. 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. Earth Engineering Consultants, Inc. EEC Project No. 1042058 August 30, 2004 Page 8 This report has been prepared for the exclusive use of Imago Enterprises, Inc. 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.