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HomeMy WebLinkAboutSubsoils Report for Foundation DesignBLKE-06-A6-f56 umr-olar-/ezi GEOTECH NICAL INVESTIGATION REPORT Single-Fa mily Residence Lot 1 County Road 311 Silt, Colorado Geo Quest Project No.: 24-156 June t9,2024 Prepared for: Patrick Gilson 110b county road 121 Carbondale CO 81623 Prepared by: Geo Quest, LLC PO Box 1372 Rifle, CO 81650 Phone: 970-318-6784 $ N s.. .s G GEo Glugsr {970) 318-6784 PO Box 1372 Rifte, CO 81650 geoqufftco@pm.me GEOTECHNICAL INVESTIGATION REPORT Single-Family Residence Lot 1 County Road 311 Silt, Colorado Geo Quest Project No.:24-156 June L9,2024 Prepared by: Kevin E. Dye, P.E. Principal 6lts/24 57r59 GEo Gluzsr {970} 918-6784 PO Box 1372 Rifle,CO 81650 geoquestco@pm.me 1.0 PURPOSE AND SCOPE OF STUDY. 2.0 PROPOSED CONSTRUCTION TABLE OF CONTENTS 6.4 DRAINAGE CoNSIDERATIONS 7.0 EARTHWORK RECOMMENDATIONS 7.1- SITE GRUBBING AND STRIPPING .... 7.2 BUTLDTNG Pao PRepaRnnoN ................ 7.3 FILL MATERIAL 7.4 CoMPAcrroru RreurReuENTS.... 1. t 3 4 4 4 5 6 6 7 7 8 9 9 9 9 9 3.0 stTE coNDtTtoNs 4.0 SUBSURFACE INVESTIGATION 5.0 SUBSURFACE CONDITIONS 6.0 RECOMMENDATIONS TABLE OF CONTENTS (Continued) List of Figures FrcuRe L - PRoJEcTAND AppRoxrMnrs Bonrrue LocATtoN Mnp ........... FIeune 2 -VIEW LooKING NoRTH Teglr 2 - BoRtNG DEprHs, GRoutrtowRrrn Drprus Rruo Aue rn RrrusRt-.. 2 3 List of Tables .6 il Proposed Single-Family Residence Silt, Colorado Geo Quest No. 24-L56 1.0 PURPOSE AND SCOPE OF STUDY This report presents the results of our geotechnical investigation for improvements to a property south of Silt, Colorado with the following legal description: Parcel: 240112400262, Section: 12, Township:7, Range: 92,Lot:L Our scope of services included a subsurface investigation, laboratory testing, geotechnical engineering analyses, and preparation of this report. The purposes of this investigation were to evaluate the subsurface conditions at the site and to develop geotechnical recommendations to guide design and construction of the proposed single-family residence and OWTS. An OWTS soil evaluation will be delivered as a companion document to this report. Our scope of services included the following: r Drill 5 borings to evaluate the subsurface conditions at the proposed building site. o Laboratory testing of the soils encountered during the field exploration to evaluate pertinent engineering properties of the soil, o Foundation design recommendations, including allowable bearing pressure, approximate depth to bearing stratum, and estimated movement. r Floor slab design considerations and floor slab subgrade preparation recommendations. o Earthwork, including recommendations for fill placement and compaction, suitability of the site soil for reuse as engineered fill, and subgrade preparation. 2.0 PROPOSED CONSTRUCTION The project will consist of constructing a new single-family residence. The location of the project site is presented in Figure 1, Project Locdtion Mop.The project will include the construction of a one story, lightly loaded residential structure with a basement, OWTS, pole barn and associated infrastructure. A conceptual structure location map was used at the time of the investigation to select boring locations. A site grading plan was not available when this report was prepared. lt was assumed that grade changes of less than 4 feet will be required to develop the final site grades. I Proposed Single-Family Residence Silt, Colorado Geo Quest No. 24-15b l.\PflRfiXlN4t\Tt. pitoiEe:l sll"F P tJ) o __9 E 4 oo CR 311 Proposed OWTS Area Proposed Home Site Proposed Pole Barn Site $rHddd+i'r-'r::T,.: . Lr L i 660fl r Figure 1- Project and Approximate Boring Location Map 2 Proposed Single-Family Residence Silt, Colorado Geo Quest No. 24-156 3.0 slTE coNDtTtoNs The proposed home, pole barn and OWTS locations are presented in Figure 1. The site is bordered on the east and south by CR 311, East Divide Creek along the west and a private property to the north. The home and OWTS locations are situated in or near trees, bushes and boulders strewn across the ground surface. The terrain in this area generally slopes northwest and there is a gulley between the home and OWTS locations. The pole barn location is near the southwest corner of the property in a small pasture or field that is generally flat, grassy and lies at a lower elevation than the other improvements. Figure 2 presents a view of Boring B-1 being drilled near the proposed southeast corner of the home site. Figure 2 - View looking north 3 Proposed Single-Family Residence Silt, Colorado Geo Quest No. 24-156 4.0 SUBSURFACE INVESTIGATION 4.1 Field Exploration Five boring were drilled on May 25,2024 to depths of 4.5 to L2.5 feet with a Giddings #25 truck mounted drill rig and 4-inch solid stem auger. Boring L (B-L) and B-2 were located at the proposed house location, Boring B-3 and B-4 were at the pole barn location and Boring B-5 was within the proposed OWTS area. The proposed house, barn and OWTS locations were marked with stakes at the time of our field investigation. The approximate boring locations are presented on Figure i.. Samples of the subsurface materials were obtained from the borings at select depths by driving either a standard split-spoon or modified california barrel sampler. Bulk samples of the soil were also recovered from auger cuttings as the borings were advanced. The samples were transported to our laboratory where they were examined by the geotechnical engineer and a program of laboratory testing was conducted. Penetration resistance measurements were made by driving the samplers into the subsurface materials with a 140-pound hammer falling 30 inches. The number of blows required to drive the sampler 12 inches, after an initial penetration of 6 inches for the standard sampler, constitutes the penetration value. The penetration value can be correlated to the relative density of granular soil and the consistency of cohesive soil. Water levels were recorded in each boring at completion of the drilling operations if encountered. The borings were backfilled with the auger cuttings. 4.2 Laboratory Testing The recovered soil samples were classified by the geotechnical engineer in accordance with the Unified Soil Classification System (USCS). Laboratory tests were then performed on select samples to evaluate the pertinent engineering properties of the soil. The laboratory testing was conducted in general accordance with the American Society for Testing and Materials (ASTM) test procedures. The following laboratory tests were performed for this evaluation: 4 Proposed Single-Family Residence Silt, Colorado Geo Quest No, 24-156 r Water Content o Liquid and Plastic Limits e Grain Size Particle Analysis . Swell/collapse Table 1 presents a summary of the laboratory testing performed on select samples that were collected with the standard spit spoon or modified California samplers, Table 1- laborato Summa 5.0 SUBSURFACE CONDITIONS The borings generally encountered up to 12 inches of topsoil over clayey sand to the bottom of borings. Each boring had auger refusal (AR) on cobbles or boulders except boring B-3. Boring B-2 reached AR at 2.5 feet and was attempted again 4 feet to the east where AR was reached again at 4.5 feet. Random boulders of up to 3 feet in diameter or possibly larger should be anticipated during construction. Borings B-3 and B-4 were much closer to the elevation of the nearby creek than the other borings and had increasing moisture below about 5 feet. Groundwater was encountered at a depth of L0 feet in boring B-4. Variations in the groundwater level may occur seasonally. The magnitude of the variation will be largely dependent upon the amount of spring snowmelt, duration and intensity of precipitation, irrigation practices, site grading changes, and the surface and subsurface drainage characteristics of the surrounding 5 Classificatr'on Boring lD Sample Depth {ftt Moisture Content l%l Particle Size Analyses (% Gravel, Sand, Fines) Atterberg Limits rL Pr Swell/Collapse Loaded with 1000 psf uscs B-1 3 7.1, OG 70s 30F 24LL, 10 Pt sc B-2 4 0.00 sc B-3 4 10 13.2 to 22.8 OG 63to65S 35to37F 30 LL, 1,4 to 17 Pl sc B-4 4 1,1.6 OG 62S 38F 28 LL, 14 Pt SC area Proposed Single-Family Residence Silt, Colorado Geo Quest No. 24-L56 Table 2 -Groundwater and r Refusal 5.0 RECOMMENDATIONS 5.1 Foundations The proposed single-family residence and basement can be supported by spread footings bearing in the clayey sand. The foundation excavation should anticipate intermittent cobbles and/or boulders up to 3 feet in diameter or larger. Large diameter material that is removed from the foundation bearing zone will leave voids that should be backfilled with the clayey sand and properly moisture conditioned and compacted as described in Section 7. It is possible that a dense sand, gravel and cobble layer may be encountered near the bottom of the residence excavation due to the presence of the nearby creek and alluvial river gravels. lf the dense river gravel layer is encountered during foundation excavation Geo Quest recommends placing a 1-2-inch-thick layer of the onsite clayey sand as a leveling course over the rough and uneven excavation surface of cobbly material. This will reduce possible point loads on the shallow foundation footing and create a workable, flat surface for foundation construction. The fill should be placed with proper moisture and compaction to reach 95% maximum dry density of a standard Proctor as discussed in Section 7. A maximum allowable bearing pressure of 2,500 pounds per square foot (psf) may be used for the clayey sand'Theallowablebearingpressure,ppfiFffiadplusdesignliveloadconditions'Thedesign bearing pressure can be increased by one-third or as allowed by local code, when considering transient loads, such as wind or seismic. Resistance to lateral loads will be provided by the passive earth pressure acting against the vertical face of footings and the frictional resistance acting along the base of the footings. An ultimate passive earth pressure resistance of 350 pounds per square foot per foot (psf/ft) is recommended for design. A 6 Boring lD Total Depth (ftt Auger Refusal Depth to Groundwater (ft1 B-1 12.5 Yes None B-2 4.5 Yes None B-3 1L.5 No None B-4 10.0 Yes 10 B-5 5.0 No None Proposed Single-Family Residence Silt, Colorado Geo Quest No. 24-156 coefficient of sliding resistance of 0.45 is recommended for design. The lateral load resistance should incorporate a factor of safety of at least 1.5. The bottom of the shallow foundation footings should bear a minimum of 36 inches below the final site grade for frost considerations. Strip footings should have a minimum width of L5 inches and isolated column pad foundations should have a minimum dimension of 24 inches. We estimate that the total post-construction movement of foundations supported as recommended herein will be on the order of 1 inch or less. We estimate that the differential movement between comparably sized and loaded foundations could be half the total foundation movement. Additional foundation movement can occur if water from any source infiltrates the foundation subgrade. Therefore, proper drainage should be provided in the final design and during construction. 6.1.1 pore Barn Foundation ( n ol- i-, ;i;[ r*Ml fut/nl{, Pole barn piers should extend , tfi,rnrr of 3 feet below the ground surface. The piers should be at least 8 inches in diameter and could be concrete piers or wooden posts set in holes and filled with concrete. Piers may be designed for an allowable end bearing capacity of 2,500 psf. lf wooden poles set in concrete is selected, we recommend the posts be suspended off the bottom of the boring 6 inches. The top of the concrete should be domed to prevent water from ponding on the surface and promoting decay of the wood posts. 6.2 Floor Slab The floor slab subgrade should be prepared in accordance with the recommendations presented in Section 7: Earthwork Recommendations section of this report. Additional floor slab design and construction recommendations are as follows: ' Positive separations and/or isolation joints should be provided between slabs and all foundations, columns, or utility lines to allow independent movement. . Controljoints should be provided in slabs to control the location and extent of cracking. ' lnterior trench backfill placed beneath slabs should be compacted in accordance with recommended specifications outlined herein. . Barriers to reduce the potential for vapor rise through the slab are recommended. . Floor slabs should not be constructed on frozen subgrade. 7 Proposed Single-Family Residence Silt, Colorado Geo Quest No.24-156 Other design and construction considerations, as outlined in Section 302.1 R of the "ACl Design Manual", are recommended. 5.4 Drainage Considerations Properly functioning foundations and slabs on grade require appropriately constructed and maintained site drainage conditions. Therefore, it is extremely important that positive drainage be provided during construction and maintained throughout the life of the structures. lt is also important that proper planning and control of landscape and irrigation be performed. The building should be provided with downspout extensions to direct water away from the structures. Roof downspouts should discharge onto sloped surfaces that are well beyond the limits of all backfill. The ground surface around the structures should be sloped to drain away from the building area in all directions. We recommend a slope with L2 inches of drop in the first 10 feet for all unpaved surfaces. lnfiltration of water into utility or foundation excavations must be prevented during construction. Backfill against footings, exterior walls, and in utility and sprinkler line trenches should be well compacted and free of all construction debris to reduce the potential for moisture infiltration. Planters or other surface features that could retain water adjacent to the structures should be avoided. lf planters and/or landscaping are adjacent to or near the structures, we recommend the following: . Grades should slope away from the structures. r Planters should slope away from the structures and should not pond water. Drains should be installed in enclosed planters to facilitate flow out of the planters. . Watering within 10 feet of the structure should be kept to a minimum. lrrigation systems should be situated on the far side of any planting and away from the buildings to reduce the potential for infiltration beneath the structure from possible leaks. . A minimum horizontal distance of 36 inches should be maintained between the building foundations and shallow-rooted plants. ln a like manner, for deeper-rooted plants, a minimum of 72 inches should be maintained between the building foundations and the plants. lt's advisable that deeper-rooted plants have a low water requirement. r Trees should be planted no closer than a distance equal to one-half their mature height or fifteen feet, whichever is greater, from the buildings. These recommendations will help reduce the potential for soil movement and the resulting distress but will not eliminate this potential. 8 Proposed Single-Family Residence Silt, Colorado Geo Quest No. 24-156 7.0 EARTHWORK RECOMMENDATIONS Site preparation and earthwork operations should be performed in accordance with applicable codes, safety regulations, and other local, state, or federal guidelines. Foundation excavations should be observed by Geo Quest before reinforcing steel, forms or concrete are placed. The evaluation of earthwork should include observation and testing of engineered fills, subgrade preparation, foundation bearing soils, and other geotechnical conditions exposed during the construction of the project. 7.1 Site Grubbing and Stripping Topsoil, existing vegetation, tree root balls, fill soils and other deleterious materials should be removed from the proposed building area. All exposed surfaces should be free of mounds and depressions, which could prevent uniform compaction. 7.2 Building Pad Preparation The building area should be excavated, as required, to the planned bottom of footing or slab. The base of footing and slab excavations should be scarified to a minimum depth of 8 inches, moisture conditioned and compacted in accordance with Section 7.4. lf weak, saturated or unsuitable soil is encountered during the foundation excavation it should be removed, dried and placed according to Section 7.4 or imported granular fill should be used in its place. Any voids that are encountered or created by the removal of soil, cobbles or boulders should be replaced with imported granular fill or the onsite clayey sand and properly placed and compacted as described in section 7.4. 7.3 Fill Material The onsite soil may be used as backfill on the site with proper moisture modification and compaction. lmported structuralfillshould consistof granularsoilwith no more than 35 percent passingthe No.200 sieve, a maximum liquid limit of 40 percent and a maximum plasticity index of 15. 7.4 Compaction Requirements Fill should be placed in horizontal lift thicknesses that are suitable for the compaction equipment being used but in no case should exceed 8 inches by loose measure. Scarified and recompacted subgrades in the 9 Proposed Single-Family Residence Silt, Colorado Geo Quest No. 24-L56 building area should be moisture conditioned to a water content between plus or minus 2 percentage points of the optimum water content, and recompacted to at least 95 percent of the standard Proctor (ASTM D698) maximum dry density. lmported structural fill should be compacted to at least 95 percent of the modified Proctor (ASTM DL557) maximum dry density at a water content that is plus or minus 2 percentage points of the optimum water content. Geo Quest should be contacted for compaction testing of fill during construction. 8.0 LIMITATIONS The recommendations in this report are based on our field observations, laboratory testing, and our present understanding of the proposed construction. lt is possible that subsurface conditions can vary beyond the limits explored. lf the conditions found during construction differ from those described in this report, please notify Geo Quest immediately so that we can review our report considering those conditions and provide supplemental recommendations as necessary. We should also review this report if the scope of the proposed construction, including the proposed loads or structure locations change from that described in this report. This report is prepared solely for the Owner and project design team. This report was prepared in substantial accordance with the generally accepted standards of practice for geotechnical engineering as they exist in the site area at the time of our investigation. No warranty is expressed or implied. 10