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HomeMy WebLinkAboutSoils Report 06.21.2020GEOLOGIC REVIEW AND SOILS ENGINEERING REPORT TRACT 37 ANTLERS ORCHARD DEVELOPMENT SILT, COLORADO Prepared For: J Caliber Construction 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 martin@capstonewest.com June 21, 2020 Job No. 4546 CAPSTONEy° ENTERPRISES (NEST, LLC GEOTECHNICAL AND MINING ENGINEERING TESTING AND INSPECTION SERVICES 618 PARTEE DRIVE GRAND JUNCTION, CO 81504 PHONE (970) 250-3331 martin ©capstonewest. com JOB #4546 June 21, 2020 Attention: J Caliber Construction Rifle, CO Subject: Foundation Recommendations TRACT 37 ANTLERS ORCHARD DEVELOPMENT SILT, COLORADO Per your request, Capstone Enterprises West, LLC (Capstone) performed a geotechnical investigation on the foundation materials the property off of Harvey Gap Road. The purpose of the work was to determine the nature of the material on site and to make recommendation for the foundation. SITE LOCATION The site is in the southwest quarter of section 36 Township 5 South Range 92 West. The following map show the general location. SITE DESCRIPTION The property is a 10 acre parcel that was undisturbed grazing land before the development of the subdivision. The central topographic feature of this lot is a mild ridge that runs diagonally across the property from the southwest corner to the northeast corner. The ground slopes off to the northwest, the south west and the southeast at approximately 5 to 10%. Capstone Enterprises West, LLC 2 Job 4546 tft MM IN Mzw f 151 wiW 111 BMW .11 —w Site Location Rifle 5 . 14, M1W Silt t GEOLOGIC DESCRIPTION Bedrock in the area has been mapped as the Sandstone Unit of the Wasatch Formation (Twss). The USGS surface geology map is presented on the following page with the approximate property line. Capstone Enterprises West, LLC 3 Job 4546 LIST Of NAP DISIS AIfISiCNLiLL DE409rs IMMIX LINTS ALLUVIAL D609ID ETA 1 n.aw....».ww..vw.—.M q Y'rr'.ir•P+IY-y r. -W. Ali Nola. ..E.rW.rrN11.1sl f4 1 D....rOma.111•,,.d. La J DSrr.rr rl�Rr .�1 ALLUVIAL AND COLLUVIAL DIi09TS CA 1 14 r�.rla•MWirIWYlr airlLlry 1 �.J Aflrrrr♦r11Y/1LiIYr apart C1 ^.YEY--I1Wi-.- EVLLt W. WOWS 1 r Dm..rwWH.r.rY11.1 _a . � IYYIr�rILEI�KrIr-y n H1 f Ilmlorlfl Warr AtiW C.kb ._r..1.1.111 NY.a/ewir lam As 1 — Il..rr�«.�d.ylW4ro.� Tws �i'bp' SUBSURFACE INVESTIGATIONS Capstone directed the excavation of 6 test pits at the site the locations were surveyed in using a handheld GPS. The coordinates were loaded into Google Earth. The property line was downloaded from the Garfield County GIS website. The following image shows the test pit locations and the approximate property line. The actual property line will need to be surveyed in, to establish the property line setbacks prior to construction. The geologic logs are presented on the following page, them then the Google Earth image. Capstone Enterprises West, LLC 4 Job 4546 4 10 TP -1 TP -4 Silty Clay Alluvium Formational Sandstone Silty Clay Alluvium 10 TP -2 T P-5 Firm Silty Clay Silty Clay Alluvium PI=8 Formational Sandstone Silty Clay Alluvium Debris Flow Firm Silt Firm Brown Clay TP -3 T P-6 Capstone Enterprises West, LLC 5 Job 4546 Silty Clay Alluvium Formational Mudstone PI = 12 Silty Clay Alluvium Firm Silt I •� .-war -Z tam ^+ ir • + e! * +w' •4r . . ir s'.7. r 4 • , i *j t � o rA�! M VitiV I' TMP ?is�?t, i 14 + ••r�~lk • .ii,'Rig; 11%. rNi. `4• t 1 . i' . _ • 1) !_1,-'-'1-1 ,04 lb* Pri70/117 t• • it'. *.s.• 3 .. • L LABORATORY TESTING 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. However, the formational bedrock could not be tested in this manner. 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 6 Job 4546 Plasticity Index (PI) 0-15 Inherent Swelling Capacity Low 10-35 20-55 Medium High 35+ (After Seed et al. 1962) Very High The results presented below indicate there is a low potential for swelling for the silty clay material. While the mudstone sample hada slightly high capacity to swell. Material Source Depth Liquid Limit Plastic Limit Plasticity Index Swell Potential Alluvium TP -2 1-2 ft 29 21 8 Low Mudstone Fines TP -3 4-6 ft 32 20 12 Low -Moderate The Atterberg Limits Tests indicate the alluvial material is suitable for structural fill, if the material is not too coarse. Samples of the Wasatch sandstone and mudstone bedrock were also tested to determine how they would react to excessive water. The following photos are the before and after photos for the formation sandstone and formational mudstone being inundated with water. After soaking overnight, there was virtually no deterioration of the rock only a crack opening up and dust being washed off the rock. The mudstone samples deteriorated in a matter of minutes. To test the swell potential of the mudstone a remolded sample was prepared and a SweII/Consolidation test was run on the sample. The results follow the photos. Capstone Enterprises West, LLC 7 Job 4546 Capstone Enterprises West, LLC 8 Job 4546 Capstone Enterprises West, LLC 9 Job 4546 TP -3 at 4-6' ft PERCENT STRAIN 2.00%- 1.00% 0.00% -1-00% -2.00% -3.00% CONSOLIDATION TEST REPORT 1Q0 )DED WATERA 11000 10000 -4.00% • -5.00% Job No.4546 TRACT 37 Job Number Sample Source Sample Description Natural Dry Density Natural Moisture Content Saturated Moisture Content APPLIED PRESSURE - psf Job No.4546 TRACT 37 TP -3 at 4-6' it Remolded Mudstone 118.8 pcf 9.7% 17.2% The remolded mudstone sample did swell, exerting a swell pressure of 2,800 psf with a volume change of 1.7%. DESIGN CONSIDERATIONS While the bedrock is mapped as the Sandstone Unit of the Wasatch Formation the building site may encounter the same mudstone excavated in TP -3. If mudstone is encountered the thickness should be determined. If it can be removed and the foundation built on sandstone the problem can be eliminated. If the mudstone is too thick to remove entirely from the foundation footprint, a buffer of granular non -free -draining structural fill Capstone Enterprises West, LLC 10 Job 4546 can protect the mudstone from getting wet and distribute the swell pressure to minimize the effects on the foundation. The alluvial and colluvial sediments overlaying the bedrock are suitable for structural fill when properly compacted. The alluvial material at the site is low plasticity (Pi's of 7 to 9) this indicates that it is suitable for structural fill provided the any cobble sized rock (3" or greater) are not included in the fill. If this cannot be avoided, the foundation pad should be capped with a layer of fine aggregate. DESIGN RECOMMENDATIONS We recommend this residence be constructed on a stemwall footer foundation. Depending on the soils/rock encountered in the foundation excavation the foundation pad will have different requirements as follows: Foundation Material Over excavation I Pad Width ' Thickness 1 Sandstone 1 ft. r 3 in. Mudstone 3 ft. , 24 in. Maximum Bearing Pressure Dead Load 4,000 psf N/A 4,000 psf 1 800 psf The following sketches show the different foundation requirements base on the subgrade materials. Landscape Backfill +92% Compaction at or above Opt MC 1.0 Min. Imported Backfill 3" Minimum Leveling Coarse Formational Sandstone Capstone Enterprises West, LLC 11 Job 4546 Landscape Backfill +92% Compaction at or above Opt MC - 3.0 Min. 2.0' Minimum Compacted Structural Fill (+95% Compaction) Granular Non-Free-Draing Formational Mudstone BACKFILLING One of the best methods to protect a foundation and flatwork from changes in moisture content is the backfill around the perimeter with a low permeability fill (clayey) and compacting it at 92 % of the maximum dry density of the material at above optimum moisture content. The final contours must slope away from the foundation and flatwork at slope greater than 10 inches in the first 10 feet. Runoff should be directed into a drainage channel that transports the water to designed discharge point for the lot. DRAINAGE AND IRRIGATION Care must be taken to prevent stormwater from getting near the foundation. At this site an interceptor swale should be built uphill from the residence to divert water away from the structure. The success of any foundation and concrete flatwork is contingent upon keeping the sub grade soils at more or less constant moisture content, and by not allowing surface drainage a path to the subsurface. Positive surface drainage away from the structures 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 foundation's backfill and any overlying concrete slabs or sidewalks should have a positive slope away from the foundation walls on all sides. We recommend a minimum slope of 10" in the first ten feet; however, the slope can be decreased to 3" in ten feet if the ground surface adjacent to the foundation is covered with concrete slabs sidewalks or pavement. • Utility trenches may allow water to travel some distance and reach the foundation pad if left on checked. The water, sewer and dry utility trenches to the residence must be Capstone Enterprises West, LLC 12 Job 4546 backfilled with a low -permeability (clayey) material to prevent water movement toward the residence. • As much as practical, we recommend, landscaping vegetation that is common to semi- arid climates, with low moisture requirements. A "drip" system of watering could be utilized to keep water usage low. Dry -type landscaping is encouraged. • Areas close to foundation elements, where snow will drift and accumulate, should be protected from standing water during periods of snowmelt. • Landscaped areas should be placed away from the foundation elements, and be designed to drain surface runoff away from the foundation elements. • The structure should have a rain gutter system that directs water away from the foundation elements. • Water from downspouts should be directed away from the foundation in a well compacted ditch to minimize infiltration. An impermeable liner should be used if the backfill is permeable. • The builder and homeowner must always be careful not to route drainage onto a neighboring lot. LIMITATIONS The analysis and recommendations submitted in this report are based test excavations and laboratory testing performed by Capstone. 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. Any changes from these recommendations must be approved by the engineer in writing. Unapproved changes become the sole responsibility of that individual or company performing that Capstone Enterprises West, LLC 13 Job 4546 work and assume all liability for the changes and their results. 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 14 Job 4546