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HomeMy WebLinkAboutSoils Report 08.13.2019GEOLOGIC REVIEW AND SOILS ENGINEERING 886 MESA DRIVE RIFLE, CO Prepared For: Pinnacle Homes Prepared By: r i h :bfrrri.:•.�'l.;�r.'r4•.; :•i r4Y: tv.• r.: r% Y.4>Yrrr . • CAPSTONE ENTERPRISES WEST, LLC GEOTECHNICAL AND MINING ENGINEERING TESTING AND INSPECTION SERVICES 618 PARTEE DRIVE GRAND JUNCTION, CO 81504 PHONE (970) 250-3331 August 13, 2019 Job No. 4439 CA PST0NE ENTERPRISES W ES T, LLC GEOTECHNICAL AND MINING ENGINEERING TESTING AND INSPECTION SERVICES 618 PARTEE DRIVE GRAND JUNCTION, CO 81504 PHONE (970) 250-3331 August 13, 2019 JOB # 4439 Attn: Bill Grace Pinnacle Homes 2755 North Ave #105 Grand Junction, CO 81501 Subject: Geologic Review and Soils Engineering Report 886 Mesa Drive Rifle, CO 81650 At your request, Capstone Enterprises West, LLC directed and mapped the three test pits excavated at 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. A percolation test for a septic system design was also performed. The results of which are cover in a separate report. The following maps show the location of the parcel and the approximate location of the excavations. CAPSTONE ENTERPRISES WEST, LLC 2 JOB NUMBER 4439 .—Site Location h . . t� • ,* fps L , a Ili "44 V4 `it 11111.41.14 f 1 t. r^ TP -1 i r 4 .. . itt 4h •- TP -2 l,r,nIwt . P +r .4 CAPSTONE ENTERPRISES WEST, LLC 3 JOB NUMBER 4439 SITE DESCRIPTION The property has been virtually undisturbed grazing land until the development of the subdivision. Geologically, the bedrock in the area is the Shire Member of the Wasatch Formation (Tws). This particular site has been the site of erosional and depositional environments. The bedrock was eroded at some time in the past then blanketed with layers of silt, sand and gravel. • Qlo - Wind deposited silt • Qto- Water deposited terrace sediments • Qsw- Landslide deposited sediments SUBSURFACE INVESTIGATIONS The geologic logs of the test pits are presented on the following page. No water was encountered in the test pits nor was the evidence of a season high water table. CAPSTONE ENTERPRISES WEST, LLC 4 JOB NUMBER 4439 TP -1 VIII K 10 1oroli 0000.0 0400 10044 $1+: TEST PIT GEOLOGY TP -2 Topsoil- Silt w/ Roots Reddish Tan Silt Firm Dry Clayey Silt PI = 13 Dry Density = 117.1 pcf Moisture = 11.5% 10 10 Topsoil- w/ Roots Reddish -Tan Silt Brown Silty Clay PI = 10 Dry Density = 100.4 pcf Moisture = 7.6% 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. The specimen compacts or "consolidates". After the initial load stabilizes, the specimen is saturated, and the specimen will either swell or consolidate further. The results for the native materials are presented on the following pages. The relative compactions are calculated from a Standard Proctor Test presented later in this report. CAPSTONE ENTERPRISES WEST, LLC 5 JOB NUMBER 4439 TP -1 at 2 ft PERCENT STRAIN 0.00% -1.00% -2.00% -3.00% -4.00% -5.00% -6.00% -7.00% -8.00% -9.00% -10.00% CONSOLIDATION TEST REPORT 00 V /ATE 2AD DED 1 00 Job No.4439 Mesa View APPLIED PRESSURE - psf 00 Job Number Job No.4439 Mesa View Sample Source TP -1 at 2 ft Sample Description Silt Natural Dry Density 117.1 pcf 106% Relative Compaction Natural Moisture Content 11.5% -3.2% From Optimum Saturated Moisture Content 15.4% This sample was very well consolidated and exhibited 0.6% swell, if 6 feet of this material were to swell 0.6% that would result in vertical displacement of less than 1/2 inch. Proper moisture conditioning of the foundation subgrade will reduce this risk even further. CAPSTONE ENTERPRISES WEST, LLC 6 JOB NUMBER 4439 PERCENT STRAIN TP -2 at 4 ft 0.00% 1 -1.00% -2.00% -3.00% -4.00% -5.00% -6.00% -7.00% -8.00% -9.00% -10.00% CONSOLIDATION TEST REPORT 00 1 OC)0 0 WAT :RAD DED \\ Job No.4439 Mesa View APPLIED PRESSURE - psf 00 Job Number Job No.4439 Mesa View Sample Source TP -2 at 4 ft Sample Description Silt Natural Dry Density 100.4 pcf 91% Relative Compaction Natural Moisture Content 7.6% -7.1% From Optimum Saturated Moisture Content 21.9% This sample has relatively good compaction. However, it will require moisture conditioning and recompaction to produce a suitable foundation subgrade. 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. CAPSTONE ENTERPRISES WEST, LLC 7 JOB NUMBER 4439 Plasticity Index (PI) Inherent Swelling Capacity 0-15 10-35 Low Medium 20-55 35+ High Very High (After Seed et al. 1962) The results presented below indicate there is a low potential for swelling for the silty clay material. While the shale samples have a slightly high capacity to swell. This was confirmed in the swell consolidation tests. Material Source Depth Silty Clay TP -1 Silty Clay TP -2 2-3 ft Liquid Limit 32 Plastic Limit Plasticity Index Swell Potential 19 1-3 ft 28 13 Low to Moderate 18 10 Low to Moderate The Atterberg Limits Tests indicate the silt soils is marginally suitable for foundation structural fill. The in place dry densities of the material tested in the Swell/Consolidation Tests and a grab sample ranged from 100.4 to 117.1 pounds per cubic foot. These are relative compactions of only 91 % and 106%. DESIGN CONSIDERATIONS As mentioned earlier, Wasatch Formation is the bedrock unit in this area. The alluvial and colluvial sediments overlaying the Wasatch suitable for structural fill when properly compacted. The lower density material demonstrated collapse when saturated, while the well compacted sample from TP -1 exhibited slight swelling when saturated. It is important to make the foundation subgrade as uniform as possible to prevent differential movement. CAPSTONE ENTERPRISES WEST, LLC 8 JOB NUMBER 4439 DESIGN RECOMMENDATIONS HOME FOUNDATION We recommend this residence be constructed on a conventional stemwall and footer foundation system resting on a compacted mat of native soil. The mat should be a minimum of 2 thick; one foot of soil removed and replaced after the subgrade has been moisture conditioned and compacted. A maximum bearing load of 1,500 psf should not be exceeded. A lateral earth pressure of 45 psf per linear foot should be designed for. The following sketch shows the general requirements for the foundation pad. Landscape Backfill +92% Compaction at or above Opt MC Native Backfill +95% Compaction +/-2% Opt MC Base of Footer Subgrade Moisture Conditioned and Compacted +95% Compaction Near Opt MC EXCAVATION The topsoil should be removed and stockpiled for landscaping. The footprint of the foundation should be excavated 2 feet below the bottom of the planned foundation elevation. The excavation should extend laterally 2 feet from the footprint of the foundation. HOME SUBGRADE PREPARATION If moisture conditioning is required, the subgrade should be scarified a depth of 8 to 10 inches and thoroughly moisture conditioned to near optimum. Any soft spots noticed during compaction should be removed or reconditioned. CAPSTONE ENTERPRISES WEST, LLC 9 JOB NUMBER 4439 BACKFILL Any imported structural fill should consist of non -expansive, granular material with a PI of less than 10. The material should be moisture conditioned and placed in 4-6 inch lifts depending on the size of equipment used. The structured fill should be compacted to at least 95 percent of the maximum standard Proctor density at a 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 silty sand 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 -1/4" crusher fines, unless the concrete forms can be set immediately after compaction testing. SLAB CONSTRUCTION Slab -on -grade construction may be used if the same subgrade preparation as described earlier is used: • 1 -foot excavation below foundation • Moisture condition bottom of excavation (preferably overnight) • Compact subgrade and backfill to greater than 95% of Standard Proctor at +/- 2% of optimum moisture • Cap silty fill with -1/4" crusher fines if needed 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 II modified) should be used in all concrete exposed to the on-site soils. CAPSTONE ENTERPRISES WEST, LLC 10 JOB NUMBER 4439 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 drainage away from structures and exterior slabs must be maintained at all times. Landscaped 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 92% 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. LIMITATIONS The analysis and recommendations submitted in this report are based in part upon the data obtained from the excavations, field observations and laboratory testing. 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. CAPSTONE ENTERPRISES WEST, LLC 11 JOB NUMBER 4439 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 Tong -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 12 JOB NUMBER 4439