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HomeMy WebLinkAboutHOMESTEAD PUD SECOND - Filed SER-SUBSURFACE EXPLORATION REPORT - (4)JUN 0 1 2004 E E C May 26, 2004 Splittgerber Professional Builders P.O. Box 271307 Fort Collins, Colorado 80527-1307 Attn: Mr. Rick Splittgerber Re: Subgrade Development Homestead Heights (Cornerstone and Hearthstone Drives) Fort Collins, Colorado EEC Project No. 1034086P Mr. Splittgerber: As you know, in April of this year, Earth Engineering Consultants, Inc personnel completed a pavement design for Cornerstone and Hearthstone Drives. We understand Cornerstone and Hearthstone Drives were in-service roadways under Larimer County jurisdiction; however, have recently been adopted to fall within the City of Fort Collins Urban Growth Area. The purpose of this letter is to summarize the concerns of City of Fort Collins construction inspection personnel concerning the roadway subgrades and the history of our discussions concerning construction of the roadways. We understand Cornerstone and Hearthstone Drives were paved county roadways in service for approximately 6 years. We understand that the roadways as constructed performed well during that period. In the fall of 2003, the existing asphalt pavement was removed to allow for installation of water services and a sanitary sewer utility. We understand the pavement section that was in place at the time of removal consisted of approximately 3 inches of asphaltic concrete overlying 6 inches of aggregate base course. In early May 2004, at the time of subgrade preparation for repaving of the referenced roadways, areas of dark grey clay were observed to be coming to the surface through the reconditioning process. The dark grey clay was blended with .the roadway surface aggregates to develop a stable paving platform. At that time, Earth Engineering Consultants, Inc. was contacted by City of Fort Collins inspection personnel who suggested the dark grey clay and aggregate base blend materials were unacceptable as roadway subgrade due to "organic content" and would need to be removed and replaced. CENTRE FOR ADVANCED TECHNOLOGY 2301 RESEARCH BOULEVARD, SUITE I 04 FORT COLLINS, COLORADO 80526 970) 224-1522 (FAx) 224-4564 Earth Engineering Consultants,Inc. EEC Project No. 1034086P May 26,2004 Page 2 On May 10, 2004, EEC personnel observed the reconditioned roadway subgrades and a test pit completed within Cornerstone Drive. Dark grey clay was observed in the test pit at a depth of approximately 18 inches below subgrade elevation. Two samples of the dark grey clay were returned to our lab for further examination, classification and testing. The dark grey clay showed low swell potential at current moisture and density conditions. Results of the completed swell tests are provided on the attached summary sheets. Based on the materials observed, it is our opinion, the grey clay contained a minimal amount of organic matter and could be allowed to remain in place for construction of the roadway. On May 13, 2004, EEC personnel met with City of Fort Collins personnel on site to determine what the City of Fort Collins would require to allow the project to continue. At that time Earth Engineering Consultants suggested that fly ash stabilization could be used to provide a stable working platform and develop a higher quality roadway. That option was rejected by City of Fort Collins construction inspection personnel. It was determined at that time that additional test pits would be excavated within the roadway areas to establish the depth of overexcavation/replacement mandated by City of Fort Collins. On May 14, 2004, EEC personnel met with City of Fort Collins and Gerrard Excavating personnel to observe test pit excavation. Based on the materials observed in the completed test pits, City of Fort Collins personnel recommended a 2-foot overexcavation/replacement operation be completed to develop the roadway subgrades. At that time it was discussed that the residential lots in the area could be robbed of lean clay soils for use in redeveloping roadway subgrade. Upon further discussions with the project developer, it was decided that a higher level of confidence in developing a stable roadway subgrade would result by using an essentially granular overexcavation backfill. We understand a class 7 structural fill from the Lafarge Kyger Pit is proposed for use as backfill. The results of several completed gradation tests on that material were faxed to City of Fort Collins for further review. At this time the City of Fort Collins has approved the Kyger Pit class 7 structural backfill for use as roadway subgrade overexcavation backfill. Earth Engineering Consultants,Inc. EEC Project No. 1034086P May 26,2004 Page 3 We understand that a proofroll will be required on the developed subgrades prior to construction of the overlying pavement section. At this time we understand the roadway pavement sections will be constructed as approved without pursuing any reduction in the pavement section thicknesses based on increased support from the structural fill subgrade. We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this letter, 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 En ineering Consultants, Inc. c7,1\00 REGIST Reviewed by: o.• JON 6 0AM/dl 44, Wolf von Carl witz, P.E. Leste : itton, P.E. Project Engineer Principal Engineer cc: Jim Ringenberg—Dwyer, Ringenberg & Funk Bill Nicholl— Gerrard Excavating Rick Richter—City of Fort Collins