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HomeMy WebLinkAboutSubsoil StudyI (+rt *itilfl'ff*'fÉtrf ¡"nÊ' å' *"' 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.kumaLusa.com Office Locations: Denver (HQ), Palker, Colorado Springs, Fort Collins, Clenwood Springs, and Surnmit County, Cololado July 11,2022 Edgar Cuc 1853 County Road 109 Glenwood Springs, Colorado 81601 valenzcuc@,gmail.com Project No. 22-7-350 Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 60, Filing 7, Elk Springs, 38 Aster Drive, Garfield County, Colorado Dear Edgar: 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 };4ay 9,2022. 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-story residence over a walkout basement level with an attached ganage located in the building envelope shown on Figure 1. Ground floors will be slab-on-grade. Cut depths are assumed to range between about 2 to 8 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 gently sloping down to the southwest and southeast. Basalt cobbles and boulders were visible at the surface. Vegetation consists of grass, weeds and sage brush. 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 I foot of topsoil, consist of up to lzfoot ofstiff, sandy clay overlying dense, basalt cobbles and boulders in a calcareous sandy silt matrix. Refusal to backhoe digging was encountered in all three pits at depths of IYz to 3 feet. Results of a gradation analysis performed on a sample of highly calcareous silty sandy gravel matrix (minus 3-inch fraction) obtained from the Pit 1 on 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 to moist. 1 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 fine-grained soils tend to compress after wetting and there could be some post-construction foundation settlement. Footings should be a minimum width of 16 inches for continuous walls and2 feet for columns. Topsoil, sandy clay 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 silty sandy basalt rock 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 alateral earth pressure based on an equivalent fluid unit weight of at least 50 pcf for the on-site soil as backfill, excluding topsoil and rock larger than 6 inches. 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%o passing the No. 4 sieve and less than 2o/o passing the No. 200 sieve. All flrll 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 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 clay soils are present, 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 prolectecl from wetting and hydrostatic pressure buildup by an underdrain system. Kumar & Associates, lnc. o Project No. 22-7-350 -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 lo/oto a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than 2o/o passingthe 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 llz feet deep. 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 95o/o 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 recornmend 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 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 held 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 notrfiecl at onoe so re-evaluatron oI the recommendations may be made. Kumar & Associates, lnc. o Project No, 22-7-350 -4- 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 aná monitor the implementation of our recofirmendations, 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 Respectfully Submitted, Kumar & Associates, In ''- l Daniel E. Hardin, Reviewed by: ft*/- Steven L. Pawlak, P.E. DEH/kac attachments Figure 1 - Location of Exploratory Pits Figure 2 -Logs of Exploratory Pits Figure 3 - Gradation Test Results Kumar & Associates, lnc.Project No. 22-7-350 July 12, 2O22 - 08t32oñv\Pro¡.cb\2022\22-7-J50 subloil srldy, Propo..¿l-0{oò./\l!T¡-o{ß rr(¡tñ(----)="t\Fr (¡>ou)-Fl_ù3_12.c)r¡l.o{(Doo)oIt-trnox--{rn(./)C)f-rftI-¡rrlrft--{l'.JN)I!IO.l(¡o^c3o)-AoØØoa.It)oØt-oc)-.{Oz.oTlrïl><Tt-oÐ--{On-u=U''TlI i J PIT 1 Pt'l 2 PIT 5 0 0 t--t! UJ LL I-t- o_ L¡Jo I +4=54 -2OO=1 4 F UJ t¡JtL I-t- o_t!o 5 Ã LEGEND TOPSOIL; ORGANIC SILT AND CLAY, SANDY, FIRM, SLIGHTLY MOIST, DARK BROWN. BASALT COBBLES AND BOULDERS (GM-GP); IN A SANDY SILTY CLAY MATRIX, DENSE, SLIGHTLY MOIST, LIGHT BROWN, CALCAREOUS. cLAY (CL), StLTY, SANDY, STIFF, SLIGHTLY MOIST, BROWN. F t HAND DRIVE SAMPLE DISTURBED BULK SAMPLE I PRACTICAL AUGER REFUSAL. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A CATsOs MINI-EXCAVATOR ON MAY 12, 2022. 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. 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: +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422); _ZQO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1 1 4O). 22-7 -350 Kumar & Associates LOGS OF EXPLORATORY PIÏS lig. 2 L E I ñ t00 90 a0 70 50 50 10 30 20 fo o 0 lo 20 50 10 50 60 70 ao 90 to0 2- 6 .125 DIAMETER OF PARTICLES IN MILLIMETERS CLAY TO SILT COBBLES GRAVEL 54 % SAND 32 LIQUID LIMIT SAMPLE OF: Silly Sondy Grovel Molrix Soils PLASTICITY INDEX SILT AND CLAY 14 % FROM:Pit1e^2'-3' Thoso r€sl resulls opply only to lho sompl€s whlch wero lasl6d. Th€ lesllng rsport sholl not bs rqproducad, oxcepl ln full, wlthout lhê wrlllenqpprovol of Kumor & Assoclolos, lnc. Siovo onolvsis l.slÌno is oerformed ln occordoncå wlth ASíJ Ddgl3, ÀsTM 07928, ASTM C136 ond/or ASTM Dl1,10. SIEVE ANALYSISHYDROMETER ANALYSIS TIME READINGS 24 HRS 7 HRS U.S. STANDARD SERIES CLEAR SQUARE OPENINGS \/A, a/Ln 1 1/t, / / l l I I I I I I' SAND GRAVEL FINE MEDTUM lCOanSe FINE COARSE 22-7 -350 Kumar & Associates GRADATION TEST RESULTS Fig. 3