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HomeMy WebLinkAboutSubsoil Study for Foundation Design 01.24.2025Kumar& Associates, Inc.° 1(+Aand Geotechnical and Materials Engineers 5020 County Road 154 Environmental Scientists Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com An Employee Owned Company www.kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado January 24, 2025 Alius Design Group Attn: Michael Edinger 108 Diamond A Ranch Road Carbondale, Colorado 81623 micliael@aliusde.com Project No. 25-7-124 Subject: Subsoil Study for Foundation Design, Proposed Residence, County Road 100 North of Rim Ledge Road, South of 5655 County Road 100, Garfield County, Colorado Dear Mr. Edinger: As requested by Smith Mountain Builders, Kumar & Associates, Inc. performed a subsoil study for design of foundations at the subject site. The study was conducted in accordance with our agreement for geotechnical engineering services to you dated January 16, 2025. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Proposed Construction: The proposed residence will be one to two stories over a crawlspace or basement level located west of County Road 100, north of Rimledge Road, on the site in the area of the pits shown on Figure 1. Ground floor will be structural over crawlspace or slab -on - grade. Cut depths are expected to range between about 2 to 7 feet. Foundation loadings for this type of construction are assumed to be relatively light and typical of the proposed type of construction. If building conditions or foundation loadings are significantly different from those described above, we should be notified to re-evaluate the recommendations presented in this report. Site Conditions: The site was vacant and vegetated with grass and sparse weeds. About 6 inches of snow covered the site. The site is relatively flat with a gentle slope down to the southeast. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are presented on Figure 2. The subsoils encountered consist of about 1 foot of topsoil overlying medium stiff to stiff, sandy silty clay. Results of swell -consolidation testing performed on relatively undisturbed samples of sandy silty clay, presented on Figures 3 and 4, indicate low compressibility under existing moisture conditions and light loading and a low collapse potential -2- when wetted. The samples were moderately compressible under increased loading after wetting. The laboratory test results are summarized on Table 1. No free water was observed in the pits at the time of our observation and the soils were moist. Foundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, we recommend spread footings placed on the undisturbed natural soil designed for an_allowable soil bearing pressure of 1,500 psf for support of the proposed residence. The soils tend to compress after wetting and there could be some post -construction foundation settlement. Footings should be a minimum width of 18 inches for continuous walls and 2 feet for columns. The topsoil and loose disturbed soils encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural soils. Exterior footings should be provided with adequate cover above their bearing elevations for frost protection. Placement of footings at least 36 inches below the exterior grade is typically used in this area. Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 12 feet. Foundation walls acting as retaining structures should be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 55 pcf for the on -site soil as backfill. Floor Slabs: The natural on -site soils, exclusive of topsoil, are suitable to support lightly loaded slab -on -grade construction. To reduce the effects of some differential movement, floor slabs should be separated from all bearing walls and columns with expansion joints which allow unrestrained vertical movement. Floor slab control joints should be used to reduce damage due to shrinkage cracking. The requirements for joint spacing and slab reinforcement should be established by the designer based on experience and the intended slab use. A minimum 4-inch layer of free -draining gravel should be placed beneath basement level slabs to facilitate drainage. This material should consist of minus 2-inch aggregate with less than 50% passing the No. 4 sieve and less than 2% passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95% of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on -site soils devoid of vegetation, topsoil and oversized rock. Underdrain System: Although free water was not encountered during our exploration, it has been our experience in the area and where there are clay soils that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched condition. We recommend below -grade construction, such as retaining walls, crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. Project No. 25-7-124 Kumar & Associates, Inc. -3- The drains should consist of drainpipe placed in the bottom of the wall backfill surrounded above the invert level with free -draining granular material. The drain should be placed at each level of excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum 1% to a suitable gravity outlet. Free -draining granular material used in the underdrain system should contain less than 2% passing the No. 200 sieve, less than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least I Meet deep. An impervious membrane such as 20 mil PVC should be placed beneath the drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils. Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) Inundation of the foundation excavations and underslab areas should be avoided during construction. 2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95% of the maximum standard Proctor density in pavement and slab areas and to at least 90% of the maximum standard Proctor density in landscape areas. Free -draining wall backfill should be covered with filter fabric and capped with about 2 feet of the on -site, finer graded soils to reduce surface water infiltration. 3) The ground surface surrounding the exterior of the building should be sloped to drain away from the foundation in all directions. We recommend a minimum slope of 12 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in pavement and walkway areas. A swale may be needed uphill to direct surface runoff around the residence. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy irrigation should be located at least 5 feet from the building. Consideration should be given to the use of xeriscape to limit potential wetting of soils below the foundation caused by irrigation. Limitations: This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this time. We make no warranty either express or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory pits excavated at the locations indicated on Figure 1 and to the depths shown on Figure 2, the proposed type of construction, and our experience in the area. Our services do not include determining the presence, prevention or possibility of mold or other biological contaminants (MOBC) developing in the future. If the client is concerned about MOBC, then a professional in this special field of practice should be consulted. Our findings include interpolation and extrapolation of the subsurface conditions identified at the exploratory pits and variations in the subsurface conditions may not become evident until Project No. 25-7-124 Kumar & Associates, Inc. 41 -4- excavation is performed. If conditions encountered during construction appear different from those described in this report, we should be notified at once so re-evaluation of the recommendations may be made. This report has been prepared for the exclusive use by our client for design purposes. We are not responsible for technical interpretations by others of our information. As the project evolves, we should provide continued consultation and field services during construction to review and . monitor the implementation of our recommendations, and to verify that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the recommendations presented herein. We recommend on -site observation of excavations and foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer. If you have any questions or if we may be of further assistance, please let us know. Respectfully Submitted, Kumar & Associates, jnG .�,n Riw�,.. ft Daniel E. Hardin, P J: 1 �7 i Rev. by: SLP DEH/ kac attachments Figure 1 — Location of Exploratory Pits Figure 2 — Logs of Exploratory Pits Figures 3 and 4— Swell -Consolidation Test Results Table 1 — Summary of Laboratory Test Results Kumar & Associates, Inc. 0 Project No. 25-7-124 U r � 150 0 150 300 APPROXIMATE SCALE -FEET 25-7-124 Kumar & Associates l LOCATION OF EXPLORATORY PITS Fig. 1 PIT 1 PIT 2 0 0 Sl WC=12.1 DD=108 WC=11.7 �- w DD=97 —:w w I 5 5 _ CL CL WC=18.5 0 DD=104 z J — 10 10 -- LEGEND TOPSOIL. HAND DRIVE SAMPLE. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON JANUARY 16, 2025. 2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3 THE ELEVATIONS AR E EXPLORATORY PITS TO DEPTH.WERE NOT MEASURED AND THE LOGS OF THE EXPLORATO 4. THE EXPLORATORY PIT LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. PITS WERE BACKFILLED SUBSEQUENT TO SAMPLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216); DO = DRY DENSITY (pcf) (ASTM D 2216). �ry 25-7-124 Kumar & Associates LOGS OF EXPLORATORY PITS F19. 2 l(+AIU.iltt2l & ASsociateS, InC.° Geoinhnisal and Malerials Eng and &MranmunW Se+enti ineers TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 25.7-124 SA6IPLE LOCATION NATURAL NATURAL GRADATION ATTERBERG LIMITS UNCONFINED MOISTURE DRY GRAVEL SAND PERCENT PASSING NO. PLASTIC LIQUID LIMIT COMPRESSIVE STRENGTH SOIL TYPE PIT DEPTH CONTENT DENSITY l%) (%) 200 SIEVE INDEX Ik % % % 1 2 12.1 108 Sandy Silty Clay Sandy Silty Clay 6 18.5 104 80 Sandy Silty Clay 2 3 11.7 97