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HomeMy WebLinkAboutSoils Report 07.08.2017GEOLOGIC REVIEW AND SOILS ENGINEERING LOT 23 RAPIDS VIEW LANE NEW CASTLE, COLORADO Prepared For: Chronos Builders Grand Junction, Colorado Prepared By: CAPSTONE ENTERPRISES WEST, LLC GEOTECHNICAL AND MINING ENGINEERING TESTING AND INSPECTION SERVICES 618 PARTEE DRIVE GRAND JUNCTION, CO 81504 PHONE (970) 250-3331 capstonewest@juno.com July 8, 2017 Job No. 4100-2 CAPSTONE ENTERPRISES WEST, LLC GEOTECHNICAL AND MINING ENGINEERING TESTING AND INSPECTION SERVICES 618 PARTEE WIVE GRAND JUNCTION, C0.81504 PHONE (970) 250-3331 FAX (970) 241-9721 July 8, 2017 JOB # 4100-2 Attn: Chronos Builders 637 25 Road Grand Junction, CO 81505 Subject: Geologic Review and Soils Engineering Report Lot 23 Rapids View Lane New Castle, CO At your request, Capstone Enterprises West, LLC directed the excavation of two test pits dug on the aforementioned property. The purpose of our work was to determine if the soils are suitable for support of the proposed foundation for the structure. Or, if necessary, to provide recommendations to prepare a proper soil sub grade for support of the proposed structure. Additionally one of the holes was used as the profile hole for an Onsite Waste -water Treatment System (OWTS) The following maps show the location of the parcel and the approximate location of the excavations. The test results and the OWTS design are contained in a separate report. The following maps show the lot and test pit locations. CAPSTONE ENTERPRISES WEST, LLC JOB NUMBER 4100-2 Rifle Silt New Castle 0, Site Location e f .•HH+lVP STP -2 • TP -•1. 2.0114,1,07 SITE DESCRIPTION Geologically, the bedrock in the area is the Molina Member of the Wasatch Formation. This unit is made up of sandstone and mudstone. At this site the bedrock has been capped with alluvial sediments from the Colorado River that CAPSTONE ENTERPRISES WEST, LLC 3 JOB NUMBER 41.00-2 borders the subdivision to the north. The following image taken from the Garfield County GIS website shows that this lot is outside- of the flood plain. ' SUBSURFACE INVESTIGATIONS The geologic logs of the test pits are presented on the following page. The sediments overlaying the bedrock change gradation from gravel with boulders to sandy silty day. The contacts betw-een the ,different soil types are quite distinct. Ground water was encountered in TP -1 at 7.1 feet below the surface. There was no evidence of a seasonal water table above this elevation. It should be noted that runoff at the time was q tte high and the- river was near seasonal high. TP -1 Topsoil- Silty Clap Abundant Roots Reddish Brown Silty Clay wi Gravel PI = 10 Sandy Gravel e, Cobbles Pl=rip Sandy Gravel w/ Boulders Moist Water Table 6/22/17 10 CAPSTONE ENTERPRISES WEST, LLC 4 JOB NUMBER 4100-2 TP -2 Topsoil- Silty Clay Abundant Roots Reddish Brown Silty Clay e: Gravel Sandy Gravel Cobbles LABORATORY TESTING AND RESULTS The suitability for foundation material is generally determined by two tests: the Swell/Consolidation test and the Atterberg Limits test. The Swell/Consolidation test consists of placing an undisturbed sample of material in a device that applies a load to the soil. TIie specimen compacts or "consolidates". After the initial- toad stabilizes, the specimen is saturated and the specimen will either swell or consolidate further. The distribution of gravel in the silty clay made it impossible to collect at intact specimen for Swell/Consolidation testing. The Atterberg Limits Test gives an indication of the mechanical properties of fine grained materials. The first part of the test is to determine the Plastic Limit of the material. Then the Liquid Limit is determined. The difference between the Liquid Limit and the Plastic Limit is defined as the Plasticity Index. Swell potential based on the plasticity limit (PI) is shown on the following page. Plasticity Index (PI) Inherent Swelling Capacity 0-15 Low 10-35 Medium 20-55 High 35-F Very 1-1 igh (After Seed et al. 1962) The results presented below indicate there is a low potential for swelling for both the silty material and the fines in the gravel. Material Source Depth I Liquid Plastic Plasticity Percent j Limit Limit Index Passing 200 mesh Red Brn. Silty Clay TP -2 1-3 ft 28 18 10 52.7 % Sandy Gravel TP -1 2.5- NP NP 1.8 % 4.5ft CAPSTONE ENTERPRISES WEST, LLC 5 JOB NUMBER 4100-2 Based on the gradations and Atterberg Limits TP -1 1' to 2' was classified as CL - ML (Silty Clay or Clayey Silt). The gravel is classified as a well graded gravel GW. The Atterberg Limits Tests indicate the silty soil is suitable for foundation structural fill. . The strength of soils and aggregates is a function of their density. The denser a given material is, the stronger it is. The maximum dry density of a material is determined by running an ASTM D-698,, Moisture -Density Relation Test. This is commonly called the Standard Proctor Test. Samples with different moisture contents are compacted with equal forces and a curve of the moisture density relationship is established. The result of the Standard Proctor for a composite sample of the gravely, silty clay is presented on the following page. CAPSTONE ENTERPRISES WEST, LLC 6 JOB NUMBER 4100-2 Chronos Builders MOISTURE -DENSITY RELATION IASTM D-698) Rapids View Job 4100 Composite Gravely Silty Clay 125.0 123.0 119.0 120.4 pcf @ 11.8% MOISTURE 117.0 115.0 / 5% 7/0 9/0 1 % 1 3% 1 5% MOISTURE CONTENT% CAPSTONE ENTERPRISES WEST, LLC 7 JOB NUMBER 4100-2 DESIGN CONSIDERATIONS As mentioned earlier, the Molina Member of the Wasatch Formation is the bedrock unit in this area. Any swelling potential in the mudstones would have been stabilized years ago from the Colorado River's inundation of the gravels blanketing the bedrock. The altuvial- sediments are suitable for structural fig when properly compacted. DESIGN RECOMMENDATIONS FOUNDATIONS We recommend this structure be constructed on a conventional stemwall and footer or slab on grade foundation system resting on a compacted fill mat. The mat should be 2 feet thick and the subgrade should be compacted before constructing the mat. A maximum bearing load of 2,000 psf should not be exceeded. EXCAVATION The topsoil should be removed and stockpiled for landscaping. The footprint of the foundation should be excavated approximately 2 feet below the surface to the top of the sandy gravel The excavation should extend laterally 3 feet from the footprint of the foundation. SUBGRADE PREPARATION Once the over -excavation has been completed, the subgrade should be moisture conditioned and compacted. Any soft spots noticed during compaction should be removed or reconditioned. Ideally the moisture conditioning should allow the water to soak in overnight. BACKFILL All structural fill should consist of non -expansive, granular material with a PI of less than 10. The native soils meet these requirements. The material should be moisture conditioned and placed in 6 inch lifts. The structured fill should be compacted to at least 95 percent of the maximum standard Proctor density at a CAPSTONE ENTERPRISES WEST, LLC 8 JOB NUMBER 4100-2 moisture content (±)2% of optimum. We recommend that Capstone staff be contracted to perform field moisture density testing to confirm compaction is being obtained. Tests should be performed after the 1 foot of fill is compacted and at the final grade. The relatively fine texture of the native clayey silt is prone to break up under traffic; therefore,, Capstone recommends that once the silt is compacted it be capped with a more traffic resistant material such as -3/8" crusher fines, if the forms cannot be placed within a day or two of pad completion. SLAB CONSTRUCTION Slab -on -grade construction may be used if the same subgrade preparation as described earlier is used: • 2 foot excavation below foundation • Moisture condition bottom of excavation (preferably overnight) • Compact subgrade and backfill to greater than 95% of Standard Proctor at +1- 2% of optimum moisture • Cap silty fill with -3/8" crusher fines Slabs should be provided with control joints to reduce damage due to shrinkage cracking. It is recommended control joints be spaced at 15 feet on centers or Tess. WATER SOLUBLE SULFATES Gypsum crystals were observed in the sediments. This indicates a sulfate content of in excess of 2000 ppm. This concentration of water soluble sulfates represents a severe degree of sulfate attack on concrete exposed to these materials. Based on this observation,, sulfate resistant cement -(Type 11 modified) should be used in all concrete exposed to the on-site soils. SURFACE DRAINAGE AND LANDSCAPING The success of shallow foundations and slab -on -grade systems is contingent upon keeping the subgrade soils at more or less constant moisture content, and by not allowing surface drainage a path to the subsurface. Positive' surface drainageaway from structures and exterior slabs must be maintained at all times. Landscaped CAPSTONE ENTERPRISES WEST, LLC 9 JOB NUMBER 4100-2 areas should be designed and built such that irrigation and other surface water will be collected and carried away from foundation elements. The final grade of the foundations backfill and any overlying concrete slabs or sidewalks should have a positive slope away from.foundation walls on all sides. We recommend a minimum slope of 12 inches in the first 10 feet; however, the slope can be decreased to 4 inches in 10 feet if the ground surface adjacent to foundations is covered with concrete slabs or sidewalks. Backfill material should consist of non -expansive, non -free draining granular material. Backfill material should be placed near optimum moisture content and compacted to at least 90% of maximum standard Proctor density in landscaped areas and to at least 95% maximum standard Proctor density beneath structural areas (sidewalks, patios, driveways, etc.). All roof downspouts and faucets should discharge well beyond the limits of all backfill. Irrigation within ten (10) feet of foundations and driveway slabs should be carefully controlled and minimized. The collapsing soils are very sensitive to moisture changes. Thus, control of watering and downspouts next to foundation members is essential. CAPSTONE ENTERPRISES WEST, LLC 10 JOB NUMBER 4100-2 LIMITATIONS The analysis and recommendations submitted in this report are based in part upon the data obtained from the excavations and field observations. The nature and extent of variation may not become evident until construction. If variations then appear, it will be necessary to reevaluate the recommendations in this report. It is recommended that the geotechnical engineer be provided the opportunity for general review of the final design and specifications in order that earthwork and foundation recommendations may be properly interpreted and implemented in the design and specifications. It is also recommended that the geotechnical engineer, or a qualified geo-technician under his supervision, be retained to provide continuous engineering services during construction of the foundation, excavations, and earthwork phases of the work. This is to observe compliance with the design concepts, specifications, or recommendations and to modify these recommendations in the event that subsurface conditions differ from those anticipated. This report, does not constitute a warranty either expressed or implied, as no one can predict the long -tern changes in subsurface moisture conditions resulting from improper grading, excessive irrigation by the home owner or neighbors or other causes during and after construction. If you have any questions, or if we may be of further assistance, please do not hesitate to contact us. Respectfully Submitted: CAPSTONE ENTERPRISES WEST, LLC Martin W. Chenoweth, PE Registered Professional Engineer MWC CAPSTONE ENTERPRISES WEST, LLC 11 JOB NUMBER 4100-2