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HomeMy WebLinkAboutSubsoils ReportHuddleston-Berry Engineering & Testing, LLC 2789 Riverside Parkway Grand Junction, Colorado 81501 Phone: 970-255-8005 Info@huddlestonberry.com November 27,2024 Project#O I 303-0 1 06 Clayton Homes 671 23 Road Grand Junction, Colorado 81505 Attention: Mr. Tent Bubar Subject:Geotechnical Investigation 314 Coryell Ridge Glenwood Springs, Colorado Dear Mr. Bubar, This letter presents the results of a geotechnical investigation conducted by Huddleston-Berry Engineering & Testing, LLC (HBET) for 314 Coryell Ridge in Glenwood Springs, Colorado. The site location is shown on Figure 1 - Site Location Map. The proposed construction is anticipated to consist of a new single-family residence. The scope of our investigation included evaluating the subsurface conditions at the site to aid in developing foundation recommendations for the proposed construction. Site Conditions At the time of the investigation, the site was occupied by an existing residence and miscellaneous piles of debris. The topography at the site consisted of slight to moderate slopes down to the north. Vegetation primarily consisted of grasses and weeds. The site was bordered to the west and east by residential properties, and to the north and south by Coryell Ridge Road. Subsurface nvestisation The subsurface investigation included four test pits at the site as shown on Figure 2 - Site Plan. The test pits were excavated to depths of between 5.5 and 7.0 feet below the existing ground surface. Typed test pit logs are included in Appendix A. As indicated on the logs, the subsurface conditions encountered at the site were slightly variable. Test Pits TP-|, TP-2, and TP-3, conducted in the north and northeast portions of the site, encountered 1.0 foot of topsoil above brown, moist, stiff lean clay with sand and gravel soils that extended to depths of between 2.0 and 4.0 feet below the existing ground surface. The clay soils were underlain by tan, moist, dense gravels, cobbles, and boulders in a silty sand matrix to the bottoms of the excavations. Groundwater was not encountered in TP-l, TP-2, or TP-3 at the time of the investigation. Test Pit TP-4, conducted in the northeast portion of the site, encountered 1.0 foot of topsoil above tan to brown, moist, stiff lean clay with sand and gravel soils that extended to the bottom of the excavation. Groundwater was not encountered in TP-4 atthe time of the investigation. N \ (n .\) $ \.\ d 314 Coryell Ridge #01303-0106 12t04/24 Laboratorv Testins Laboratory testing was conducted on samples of the native soils collected from the test pits. The testing included grain-size analysis, Atterberg limits determination, natural moisture content determination, and maximum dry density and optimum moisture oontent (Proctor) determination. The laboratory testing rcsults are inclutlcd in Appentlix B. The laboratory testing results indicate that the native clay soils are slightly plastic. In general, based upon the Atterberg limits and our experience with similar soils in the vicinity of the subject site, the native clay soils are anticipated to be slightly collapsible. The sand matrix present in the gravel, cobble, and boulder soils were indicated to be non-plastic. In general, based upon the Afferberg limits of the sand matrix and the presence of large particles, the native gravel, cobble, and boulder soils are anticipated to be fairly stable under loading. Foundation Rccommcndations Based upon the results of the subsurface investigation and nature of the proposed construction, shallow foundations are generally recommended. Spread footings and monolithic (turndown) structural slab foundations are both appropriate alternatives. However, as discussed previously, the native clay soils are anticipated to be slightly collapsible. Therefore, in order to provide a uniform bearing stratum and reduce the risk of excessive differential movementso it is recommended that the foundations be constructed above structural fill extending to the dense gravel, cobble, and boulder soils. However, a minimum of l2-inches of structural fill is recommended. The native c soils, exclusive of topsoil, are suitable for reuse as struetural fill; provided partielcs in excess of 3-inches in diameter are removed. Imported structural fill should consist of a granular, non-expansive, nogfugAgj&igg material with greater than 107o passing the #200 sieve and Liquid Limit of less than 30. However, all proposed imported structural fill materials should be approved by HBET. For spread footing foundations, the footing areas may be trenched. Howevero for monolithic slab foundations, the structural fill should extend across the entire building padarea to a depth of 24- inches below the tumdown edges. Structural fill should extend laterally beyond the edges of the foundations a distance equal to the thickness of structural fill for both foundation types. Prior to placement of structural fill, it is recommended that the bottom of the foundation excavation in the dense gravel, cobble, and boulder soils be moisture conditioned and proofrolled to HBET's satisfaction. Structural fill should be moisture conditioned, placed in maximum 8- inch loose lifts, and compacted to a minimum of 95o/o of the standard Proctor maximum dry density for fine grained soils and 909/a of the modified Proctor maximum dry densitv for coa-rse grained soils, within + 2o/o of the optimum moisture content as determined in accordance with ASTM D698 and D1557, respectively. Structural fill should be extended to within 0.l-feet of the bottom of the foundation. No more than O.i-feet of gravel should be placed below the footings or turndown edge as a ieveiing course. Huddleston-Bgrry DnBln..rinA & T.rrin!, l-l-C 2Z:U008 ALL PROJECTS\o1303 - Clayton Homes\o1303-0106 3 l4 Coryell tudge\200 - Geo\o1303-0106 LRl20424.doc 314 Coryell tudge #01303-0106 12104124 For structural fill consisting of the native soils or imported granular materials, and foundation building pad preparation as recommended, a maximum allowable bearing capacity gl2,500 psf may be used. In addition, a modulus of subgrade reaction of 150 pci may be used for structural fill consisting of the native soils and a modulus of 200 pci may be used for suitable imported structural fill. Foundations subject to frost should be at least 36 inches below the finished grade. Water soluble sulfates are common to the soils in Western Colorado. Therefore, at a minimum, cement adequate for Sulfate Exposure Class Sl is recommended for construction at this site. Any stemwalls or retaining walls should be designed to resist lateral earth pressures. For backfill consisting of the native soils or imported granular, non-free draining, non-expansive material, we .e.o--"nd that the walls be designed for an equivalent active fluid unit weight of 45 pcf in areas where no surcharge loads are present. An at-rest equivalent fluid unit weight of 65 pcf is recommended for braced walls. Lateral earth pressures should be increased as necessary to reflect any surcharge loading behind the walls. Native gravel, cobble, and boulder soils in excess of 3-inches in diameter should not be used as backfill. Non-structural Floor Slab and Exterior Flatwork Recommendations In order to limit the potential for excessive differential movements of slabs-on-grade it is recommended that non-structural floating floor slabs be constructed above a minimum of 18- inches of structural fill with subgrade preparation and fill placement in accordance with the Foundation Recommendations section of this report. It is recommended that exterior flatwork be constructed above a minimum of 12-inches of structural fill. Drainase Recommendations Gradins andl dlrainsge are critical to the lons-term performance of the structure. Grading around the structurJshould be designed to carry precipitation and runoff away from the structure. It is recommended that the finished ground surface drop at least twelve inches within the first ten feet away from the structure. It is also recommended that landscaping within five feet of the structure include primarily desert plants with low water requirements. In addition, it is recommended that automatic irrigation, including drip lines, within ten feet of foundations be minimized. HBET recommends that surface downspout extensions be used which discharge a minimum of 15 feet from the structure or beyond the backfill zone, whichever is greater. However, if subsurface downspout drains are utilized, they should be carefully constructed of solid-wall PVC and should daylight a minimum of 15 feet from the structure. In addition, an impermeable membrane is recommended below subsurface downspout drains. Dry wells should not be used' General Notes The recommendations included above are based upon the results of the subsurface investigation and on our local experience. These conclusions and recommendations are valid only for the proposed construction. Huddlcston-Berry E ginc.ring& T.srin8, LLC aJz:v008 ALL PROJECTS\01303 - Clayton Homes\ol303-0106 314 coryell Ridgevoo - Go\01303-0106 LRl20424 doc 314 Coryell Ridge #01303-0106 t2/04/24 Huddlcston-Berry Engin.critr! & T.rtin8. l-t-C As discussed previously, the subsurface conditions encountered at the site were slightly variable. However, the precise nature and extent of subsurface variability may not become evident until construction. As a rcsult, it is recommended that HBET provide construction materials testing and engineering oversight during the entire construction process. In addition, the homeowner and auy subcotrtractors working on the project should be provided a copy of this report and informed of the issues associated with the presence of moisture sensitive subgrade materials at this site. It is important to note th.st- the recommendations herein sre intended to reduce the rish of structural movement and/or damage, to vorving degrees, associated with volume change of the native soils. However, HBET cannot nredict long-term changes in subsurface moisture conditions and/or the precise magnitude or ertent of volume change in the native soils. lhhere significant increases in subsurface moisture occur due to ooor grading, imoroper stormwater management, utilitt line failare, excess itigation, or other cause. either during construction or the result of actions of the propeftv owner. several inches of movement are possible. I! addltlon, anv failure to comnlv with the recommendations in this renort relesses Huddleston- Berrv Eneineerine & Testine. LLC of anv liabilitv with resard to the structure nerformance. We are pleased to be of service to your project. Please contact us if you have any questions or comments regarding the contents of this report. Respectfully Submitted : Huddleston-Berry Engineering and Testing, LLC Michael A. Berry, P.E. Vice President of Engineering 4Z:U008 ALL PROJECTS\01303 - Claylon Homes\01303-01 06 3 14 Coryell Ridge\200 - cs\01303-0l06 LRl2O424.doc FIGURES APPENDIX A Typed Test Pit Logs