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HomeMy WebLinkAboutSubsoils Report for Foundation 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 email: kaglenwood@kumarusa.com www.kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado October 10, 2025 Aspen Valley Land Trust Attn: Brian Hightower 320 Main Street, Suite 204 Carbondale, Colorado 81623 brian@avlt.org Project No. 25-7- 204 Subject: Subsoil Study for Foundation Design, Proposed Ranch Development, Phase 1, 1837 County Road 100 (Catherine Store Road), Aspen Valley Land Trust, Garfield County, Colorado Gentlemen: As requested, 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 Aspen Valley Land Trust dated July 29, 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 ranch development, Phase 1, will consist of various buildings including a multi-purpose building, pole barn, ranch shop, ag buildings, and community kitchen located on the site as shown on Figure 1. Ground floors will be slab-on-grade. Cut depths are expected to be up to about 3 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: There are existing cabins and ranch buildings at the site. Topography is valley bottom gently sloping terrain down to the north. Vegetation consists of native grass, weeds, and hay fields. An irrigation ditch borders the project site to the north. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating 7 exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are presented on Figure 2. The subsoils encountered, below about ½ to 2 feet of topsoil or granular Aspen Valley Land Trust Project No. 25-7-204 October 10, 2025 Page 2 Kumar & Associates, Inc.® fill, consist of dense sandy silty gravel and cobbles and small boulders down to the maximum depth explored of 4 feet. Results of a gradation analysis performed on a sample of gravel (minus 5-inch fraction) obtained from the site are presented on Figure 4. Free water was observed in the pits at depths of 2 to 3 feet at the time of excavation and the soils were moist to wet. Foundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, we recommend spread footings or mat slabs placed on the undisturbed natural granular soil designed for an allowable soil bearing pressure of 3,000 psf or subgrade modulus of 250 tcf for support of the proposed ranch development buildings. Footings (or thickened slab sections) should be a minimum width of 18 inches for continuous walls and 2 feet for columns. The topsoil, existing fill 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 granular 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 10 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 45 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, non-structural 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 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 gravel soils devoid of vegetation, topsoil and oversized rock. We recommend vapor retarders conform to at least the minimum requirements of ASTM E1745 Aspen Valley Land Trust Project No. 25-7-204 October 10, 2025 Page 3 Kumar & Associates, Inc.® Class C material. Certain floor types are more sensitive to water vapor transmission than others. For floor slabs bearing on angular gravel or where flooring system sensitive to water vapor transmission are utilized, we recommend a vapor barrier be utilized conforming to the minimum requirements of ASTM E1745 Class A material. The vapor retarder should be installed in accordance with the manufacturers’ recommendations and ASTM E1643. Underdrain System: It is our understanding the proposed finished floor elevation at the lowest level is at or above the surrounding grade. Therefore, a foundation drain system is not required. It has been our experience in mountainous areas 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 and wall drain system. A shallow crawlspace should not need to be protected with an underdrain with proper foundation wall backfill and surface grading. If the finished floor elevation of the proposed structure is revised to have a floor level below the surrounding grade, we should be contacted to provide recommendations for an underdrain system. All earth retaining structures should be properly drained. Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the structures have 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. 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 6 inches in the first 10 feet in unpaved areas and a minimum slope of 2 inches in the first 10 feet in pavement and walkway areas. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 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 Kumar & Associates Kumar & Associates Kumar & Associates Kumar & Associates