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Home My WebLink AboutSubsoil StudyI(t t iåp;lf;#iffß:l;niiyi'*" REGËIVED þ,{AY ! I ?û22 GARFIELD COUNTY COMMUNITY DEVELOPMENÏ An Ëmployee Owned Çampar¡y 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email : kaglenwood@kumarusa.com rvwwkumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado June24,202l Matthew and Kim Gillen 5906 l4th Sheet North Arlington, Virginia 22205 gillenmk(a)gmail.com Project No. 21-7-450 Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot2, Filing 8, Elk Springs,2I3l Elk Springs Drive, Garfield County, Colorado Dear Matthew and Kim: 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 May 14,202I. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Proposed Construction: Plans for the proposed residence were not available at the time of our study. The proposed residence is assumed to be a one- or two- story wood frame structure possibly over a lower walkout level with attached gara;ge located in the area of the exploratory pits shown on Figure 1. Ground floors could be structural over crawlspace or slab-on-grade. Cut depths are expected to range between about2 to 6 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 subject site was vacant at the time of our field exploration. The ground surface is sloping down to the south at a grade of about 8 percent. Vegetation consists ofjuniper trees with an understory of grass and sagebrush. Basalt cobbles and boulders are scattered on the surface and a small basalt cliff is downhill/south of the building area. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating three 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 Yzfoot of topsoil, consist of dense 2 basalt gravel, cobbles and boulders in a calcareous sandy silt matrix. Results of a gradation analysis performed on a sample of the calcareous sandy silt and gravel matrix (minus 3-inch fraction) obtained from the site are presented on Figure 3. No free water was observed in the pits at the time of excavation and the soils were slightly 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 bearing pressure of 2,000 psf for support of the proposed residence. The matrix soils tend to compress after wetting under load and there could be some post-construction foundation settlement. Footings should be a minimum width of l6 inches for continuous walls artd2 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 alateral earth pressure based on an equivalent fluid unit weight of at least 50 pcf for the on-site soil as backfill excluding organics and rock fragments larger than 6 inches. Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade construction. Slab subgrade can be re-established with suitable onsite soils or imported 3/o-inchroad base sand and gravel. 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 relatively well graded sand and gravel such as road base should be placed beneath slabs for support" This material should consist of minus 2-inch aggregate with less than 50% passing the No. 4 sieve and less than l2o/o passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95o/o of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on- site soils or imported granular soils devoid of vegetation, topsoil and oversized rock. Kumar & Associates, lnc. @ Project No. 2'l-7-450 a-J- Underdrain System: Although free water was not encountered during our exploration, it has been our experience in the areathat 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. 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 lYo to a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than 2o/, 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 llzfeet deep. 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 andunderslab areas shouldbe avoided during construction. 2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95o/o of the maximum standard Proctor density in pavement and slab areas and to at least 90o/o of the maximum standard Proctor density in landscape areas. Free-draining wall backfill should be covered with filter fabric and capped with about2 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 l0 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in pavement and walkway areas. A swale should be provided uphill to direct surface runoffaround 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. 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 Kumar & Associates, lnc. @ Project No. 21-7-450 -4- upon the data obtained from the exploratory pits excavated at the locations indicated on Figure I and to the depths shown on Figure 2,theproposed 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 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 implernentation of our recommendations, and to veriff 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 filI by a representative of the geotechnical engineer. If you have any questions or if we may be of further assistance, please let us know Respectfu lly Submitted, K.zexrcsx & .&ss**ia*es, James H. Parsons, P Reviewed by: *.*,/. Steven L. Pawlak, P.E. JHPlkac attachments Figure 1 - Location of Exploratory Pits Figure 2 - Logs of Exploratory Pits Figure 3 * Gradation Test Results {,wmar &, êxsaæçàatee " lmc. ø Pr*jeet frNo. 21-7"45* E t I '<í>.2,. "¿- ',, : í¡ ::' l ç .' ai:: -; $ $ a\ { ii a í''). \i ..:b APPROXIMATE SCALE-FEET 21 -7 -450 Kumar & Associates LOCATION OI EXPLORATORY PITS 1Fig. PIT 1 EL. 6882' PIT 2 EL. 6880' PIT 3 EL. 6874.5' 0 0 F-IJ t¡.jtL ITt- o_tdô I WC= 1 3.3I +4=7o -2Q0=6 F L¡lt¡ltL I-FfLt¡lo Ã 5 TOPSOIL; SILT, SANDY, GRAVELLY, BOULDERS, FIRM, SLIGHTLY MOIST, BROWN BASALT GRAVEL (GM); COBBLES, BOULDERS UP TO 48 INCHES, HIGHLY CALCAREOUS, SANDY SILT MATRIX, DENSE, SLIGHTLY MOIST, PALE-TAN. t DISTURBED BULK SAMPLE. I PRACTICAL DIGGING REFUSAL. NOTES 1 . THE EXPLORATORY PITS WERE EXCAVATED WITH A MINI EXCAVATOR ON MAY 26, 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 OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED. 4. THE EXPLORATORY PIT LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENÏ 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 D2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ISTU O ¿ZZ); -2OO= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1 1 40). 21 -7 -450 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2 e g I HYDROMETËR ANÀLYSIS SIEVE ANALYSIS TIME READINGS 24 HRS 7 HRS l,' U.S. STANDÂRD SERIES !1 CLEAR SOUARE OPENINGS alRd\/a-11/.ô l ......i' :t/-,.,i i. ii. iiiil ¡i;:i 100 90 ao 70 60 50 IO 30 20 to o o to 20 30 10 50 60 70 ao 90 - too 76,2 200.125 DIAMETER OF PARTICLES IN MILLIMETERS CLAY TO SILT COBBLES GRAVEL 70 % SAND 24 % LIQUID LIMIT - PLASTICITY INDEX SAMPLE OF: Colcoreous Sondy Sill ond Grovel Molrix SILT AND CLAY 6 % FROM: Pit 2 @ 2' lo 3' Thoso losl rosulls opply only lo lh€ somplqs whlch wer€ l€sled. Th€ l€sllng roporl sholl nol bo roproducod, oxcopl lñ tull, wllhoul lh€ wr¡ll€n opprovol of (uñqr & Assoc¡olos, lno. Slev. oñolysls losllñg 13 porform€d ln occordoncê wlth ASIM D6913, ASIM D7928, ASÍM C136 ond/or ASTM Dl140. SANO GRAVEL FINE MEDTUM lCOanSe FINE COARSE 21 -7-450 Kumar & Associates GRADATION TEST RESULTS Fis. 3