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HomeMy WebLinkAboutSubsoil Study for Foundation Design 05.25.2021t (;l;A ilJþifi'trtrffinriiÍü *' " An Employcc Owncd Compony 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email : kaglenwood@kumarusa.com www.kumarusa,com Of;ñce Locations: Denver (FtQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado iN4ay 25,2021 Gruenefeldt Construction Attn:Dan Gruenefeldt P.O. Box 1910 Basalt, Colorado 81621 dan@ gruenefeldtconstruction.com RECEIVED AUü íJ i: ?ü2} GARF¡ELD COUNTY COMMUNITY DEVELOPMENT Project No. 2l-7-379 Subject:Subsoil Study for Foundation Design, Proposed Residence, LotBZ, Aspen Equestrian Estates, 2 Equestrian Way, Garfield County, Colorado Dear Dan: 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 you dated April 27,2021. 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 a one to two story wood frame structure located on the site in the area of the pits shown on Figure 1. Ground floor will be slab- on-grade. Cut depths are expected to range between about 2 to 4 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 at the time of our subsoil study. The building area is vegetated with grass and weeds with a large spruce tree in the southeast part of the building area. Smaller spruce trees are located to the west of the building area and cottonwood trees are located south and east of the building area. There appears to have been minor overlot grading,probably at the time of subdivision development. The site is relatively flat with a slight slope down to the south. Blue Creek is located to the south of the lot. An existing on-story wood frame house is located on Lot 83, to the west of this lot. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating three exploratory pits at the approximate locations shown on Figure l. The logs of the pits are presented on Figure 2. The subsoils encountered, below about l to l% feet of topsoil, sandy clay -2- fill or sandy clay consist of medium dense, slightly silty sand and gravel with cobbles down to the pit depths of 3 to 4 feet. No free \ryater was observed in the pits at the time of excavation and the soils were slightly moist to moist. Subsidence Potential: The site is underlain by PennsylvaniaAge Eagle Valley Evaporite bedrock. The evaporite contains gypsum deposits. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. Sinkholes were not observed in the immediate area of the subject lot. The pits dug at the site were shallow, for foundation design only. Based on our present knowledge of the site, it cannot be said for certain that sinkholes will not develop. In our opinion, the risk of ground subsidence at Lot B2 is low and similar to other lots in the area but the owner should be aware of the potential for sinkhole development. 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 gravel soil below the clay and fill soils designed for an allowable soil bearing pressure of 2,500 psf for support of the proposed residence. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. Loose and disturbed soils and existing fill encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural gravel soils. We should observe the completed foundation excavation for bearing conditions. 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 l0 feet. Foundation walls actingas retaining structures (if any) should be designed to resist alateral earth pressure based on an equivalent fluid unit weight of at least 50 pcf for the on-site soil as backfïll. Floor Slabs: The natural on-site gravel 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 forjoint spacing and slab reinforcement should be established by the designer based on experience and the intended slab use. A minimum 4 inch layer offree-draining gravel should be placed beneath slabs-on-grade to act as a break for Kumar & Associates, lnc. o Project No. 21-7-379 -J- capillary moisture rise and facilítate drainage. This material should consist of minus 2-inch aggregate with less than 50% passing the No. 4 sieve and less than2%o passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95%ó 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. Underdrain System: An underdrain system is not needed for the proposed slab-on-grade ground floor construction. Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: l) Inundation ofthe 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%o of the maximum standard Proctor density in pavement and slab areas and to at least 90/o 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 3 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 data obtained from the exploratory pits excavated at the locations indicated on Figure I 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 possibilþ 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 identifred at the exploratory pits and variations in the subsurface conditions may not become evident until 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. Kumar & Aseociates, lnc. o Project No. 21-7-379 4 This report has been prepared for the exclusive use by our client for design pu{poses. 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 verifu 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 Respectfrrlly Submitted, Kumar & Associates, Inc. Daniel Rev. by: SLP DEHlkac attachments Figure 1 - Location of Exploratory Pits Figure 2 - Logs of Exploratory Pits ü/s(, ( Kumar & Aeeo€iatcs, lne, ¿'Projeet No. 21'7-379 PIT 1 Pt't 2 PIT 5 0 0 t-l¡l t¡J l! IIF-ùt¡lo Fl¡J LrJl! ITFo- t¡Jo 5 5 LEGEND TOPSOIL: ORGANIC SANDY SILTY CLAY, FIRM, SLIGHTLY MOIST, DARK BROWN. FILL: SANDY CLAY WITH GRAVEL, MEDIUM STIFF, SLIGHTLY MOIST, DARK BROWN. SAND AND CLAY (SC-CL): SILTY, MOIST, MEDIUM STIFF, BROWN. SAND AND GRAVEL (GM-cP): wlTH COBBLES, SLIGHTLY SILTY, MEDIUM DENSE, MOIST, BROWN NOTES I. THE EXPLORATORY PITS WERE EXCAVATED WITH A CAT 305 MlNl EXCAVATOR ON ¡tlAY 14,2021. 2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE NOT MEASURED AND THE LOGS OF THE EXPLORATORY PITS ARE PLOTTED TO DEPTH. 1. 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. 21 -7 -379 Kumar & Associates LOGS OF EXPLORATORY PIÏS lis. 2 Ê I d EQUESTRIAN WAY 0 APPROXIMATE SCALE-FEET tl PIT I E] PTT 2 LOT B_2 F'fT t 21 -7 -379 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1