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Home My WebLink AboutSubsoil Study for Foundation Design 06.16.21rcn *i'rilfi#:1'fdfr ii$' * " An Employcc Owncd Compony 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email : kaglenwood@kunrarusa.collr rvww. kunr aru sa.conl Ollice Locations: Denver (l-tQ). Parker. Colorado Springs. Fort Collins. Glenrvood Slrrings. and Sunrmit Countl'. Colorado June 16,2021 DTDT, Inc. Attn: Ken Garrett 3900 S. Wadsworth Blvd., Suite 465 Lakewood, Colorado 80235 dtdtinc@yahoo.com Job No. 21-7-420 Subject:Subsoil Study for Foundation Design, Proposed Residence, Lot33, Filing 9, Elk Springs, 0052 Grosbeak Place, Garfield County, Colorado Dear Ken: As requested, Kumar and 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 DTDT, Inc. dated May 6, 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 design had not been determined at the time of our study. In general, it is assumed to be a two story, wood frame structure over crawlspace or basement with slab-on-grade floor and with an attached slab-on-grade garage. Cut depths could range between about 3 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 site is vacant and vegetated with juniper and pinyon trees, with grasses and sage. The lot is bordered on the northwest by Grosbeak Place. The lot is on a natural hilltop and slopes moderately down to the south. The ground surface is natural with basalt cobbles and boulders visible on the surface. 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. In Pit 1 , below about 1 foot of topsoil, the subsoils consist of about IYz feet of very stiff sandy silty clay overlying medium dense to hard basalt gravel and cobbles aeSs 'N excavated depth of 4% feet. In Pit 2, below about I foot of topsoil, the subsoils consist of about 1 foot of very stiff sandy silty clay overlying a hard pale-tan calcareous sand and silt with scattered basalt rocks that continues down to the excavated depth of 4 feet. In Pit 3, below about -2- l%feet of topsoil, medium dense to hard basalt gravel and cobbles with possible boulders in a calcareous pale-tan and gray silt matrix was encountered down to the excavated depth of 5 feet. Digging was difhcult due to the highly calcareous matrix and basalt rocks and practical digging refusal was encountered in all three pits. Results of swell-consolidation testing performed on a relatively undisturbed sample of clay soils, presented on Figure 3, indicate low compressibility under existing moisture conditions and light loading and a minor expansion potential when wetted. Results of a gradation analysis performed on a sample of calcareous sand and silt soils (minus 3-inch fraction) obtained from the site are presented on Figure 4. 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, highly calcareous sand and silt or basalt rock soil below the clay soils designed for an allowable soil bearing pressure o{-2;990+gfq support of the proposed residence. The sand and silt 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. The topsoil, clay soils, and any 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. Utility trenches and deep cut areas may require rock excavating techniques such as chipping and blasting. Voids creatcd from boulder removal should be backfilled with road base compacted to at least 95% of standard Proctor density at a moisture content near optimum or with concrete. We should observe the completed foundation excavation for bearing conditions. Exterior footings should be provided with adequate soil cover above their bcaring elevations for frost protection. Placement of footings at leasl{inghes lelow the exterior grade is typically used in this area. Continuous foundation walls should be heavily reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 12 feet. Foundation walls aefino as refainino qfrrrcfrrras shnrrld he dccioned fn racict q lqierql eqrth nrcccrrre hqcerl ^n qn*--"'D equivalent fluid unit weight of at least 50 pcf for the on-site soil or imported gravel as backfill, excluding organics 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 efl-ects 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 than50o/o passing the No. 4 sieve and less than 72Yo passing the No. 200 sieve. If a basement is constructed, the gravel layer should be relatively free draining with less thart2Yo passing the No. 200 seive. Kumar & Associates, lne . o Projeet No. 21-7-420 -3 - All fill materials for support of floor slabs should be compacted to at least 95Yo of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on-site soils devoid of vegetation, topsoil, clay, and oversized rock or a suitahle imported sand and gravel such as '/+-inch road base. Underdrain System: Although free water was not encountered during our exploration, 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 areas, and basements, 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 I foot below lowest adjacent finish grade and sloped at a minimum lYoto a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than 2%o passingthe No. 200 sieve, less than 50%o passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least lYzfeet deep. Surface Drainage: The fbllowing 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 95Yo 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 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 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. 5) Landscaping which requires regular heavy inigation 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 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 assumed type of construction, and our experience in the area. Our services do not include determining the presence, prevention or possibility of mold or Kumar & Associates, lnc. @ Project No. 2'l-7-420 -4- other biological contaminants (MOBC) developing in the future. If the client is concemed 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 perfbrmed. If conditions encountered during construction appear different from those described in this report, we should be notitied 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 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 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, Inc. David A. Noteboom, Staff Engineer Reviewed by: Steven L. Paw attachments Fi gure Figure 3 - Pits Pits Test Results Figure 4 - Gradation Test Results Table I - Summary of Laboratory Test Results a $2n Kumar & Associates, lnc, @ Project No. 21-7-420 € a 9 lp.N .(, L z *o B\H Bl8 \{ol PIT 2 z ILr ++ + 585'l8'3 7\v / \ toxtS' UNUTY EASEHENT N86'J6,4JT-liz.iz't- .E FIH Erslg tE; PIT 1 LOT 33 oo52 I 02,557 sg. ft. 2.J54 oc.+- N8g'*!5'5111/ I t5.4J'o PIT 3 ,z2nY!> T3, COMMON AR& 8 LOT J4 6f LOT J2 s N Ns t 165.00 LOT JI 0 030 APPROXIMATE SCALE-FEET LOCATION OF EXPLORATORY PITS Fig. 121-7 -420 Kumar & Associates I I l * PIT 1 PIT 2 PIT 3 0 0 Ftrl Lrl LL IIF(L Ldo WC=10.7 DD= 1 02 FL]l!tL I-F o_ LJo1+4=49 200='l 6 q LEGEND ToPSolL; ORGANIc SANDY SILTY CLAY, FIRM, MOIST, BR0WN CLAY (CL); SANDY, SILTY, VERY STIFF, SLIGHTLY MOIST, BROWN BASALT GRAVEL AND SILT (GM_ML); CALCAREOUS MATRIX, COBBLES, POSSIBLE BOULDERS, MEDIUM DENSE/HARD, SLIGHTLY MOIST, PALEITAN AND GRAY. HIGHLY CALCAREOUS SAND AND SILT (SM-ML); SCATTCRED BASALT ROCKS, HARD, SLIGHTLY MOTST, PALEITAN. F t HAND DRIVEN 2-INCH DIAMETER LINER SAMPLE DISTURBED BULK SAMPLE t PRACTICAL DIGGING REFUSAL. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON MAY 11,2021 2. THE LOCAT|ONS OF THE EXPLORATORY P|TS WERE MEASURED APPROXIMATELY BY PAE|NG 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 SAMPLINC. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216); DD = DRY DENSITY (PCt) (NSTV D 2216);+4 = PERCENTAGE RETAINED oN No. 4 SIEVE (asrU O +zz); -2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 11AO); 21 -7 -420 Kumar & Associates LOGS OF EXPLORATORY PITS Fi1. 2 SAMPLE OF; Sondy Silty Cloy FROM: Pit 1 @ 1.5' WC = 1O.7 %, DD = 1OZ pcf The lh EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 1 ;q JJ Lil =UI I zotr o =o anz.oc) 0 -1 -2 -5 1.0 APPLIED PRESSURE - KSF r00 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig.320-7 -420 I € J .: : P ..i HYDROMETER ANALYSIS SIEVE ANALYSIS 'I OO 90 8o 70 6o 50 /i0 30 20 to TIME READINOS HRS 7 HRS MIN 15 MIN sOMIN 19MIN ]MIN I MIN floo *50 ir,ao l3o f16 irlo #8 3/8: 3/1" t t/?"516"0 10 -30 10 ,to = -50 '70 ao o1 - I I lll I I l-l l lllll I l l I lllll.00t ,oo2 .oo5 .o09 .ol9 .037 .o75 .150 .300 .600 l.ta I lrtltlttt .tt. t,t.t2-36 4.75 9.5 t9 38.t 2.O LLIMETERS .125 s2 DIAMETER OF PARTICLES IN MI CLAY TO SILT COBBLES GRAVEL 49 % SAND 55 % LIQUID LIMIT - PLASTICITY INDEX SAMPLE OF: Highly Colcoreous Sond ond Sili SILT AND CLAY 16 % FROM: Pit 2 @ 3' lo 4' Thcsc lesl resulls opply only io lhe sqmplss whlch wer. l€sl6d, The l.s{lng r€porl shqll nol b6 r.produc.d, exccpl ln full, wllhoul ihe wrlil€n opprovol of Kumor & Associoles, lnc. Sicve onolysis losting is parform.d ln occorddncc wlth ASTM D6913, ASTM D7928, ASTM C136 ond,/or ASTM Dr1,+0. SAND GRAVEL FINE MEDIUM COARSE FINE COARSE 21 -7 -420 Kumar & Associates GRADATION TEST RTSULTS Fis.4 rcn & Associates, lnc.@ and Materials Engineers Environmental Scientists TABLE 1 SUMMARY OF LABORATORY TEST RESULTS No.2l-7-420 SOIL TYPE Sandy Silty Clay Highly Calcareous Sand and Silt (psfl UNCONFINED COMPRESSIVE STRENGTH PLASTIC INDEX (%l ATTERBERG LIMITS (%l LIQUID LIMIT PERCENT PASSING NO. 200 stEVE 61 SAND tf/"| 35 GRADATION tf/"| GMVEL 49 (ocfl NATURAL DRY DENSITY 102t0.7 (%l NATURAL MOISTURE CONTENTH (ft) DEP'] t,1 J-, SAMPLE LOCATIOi PIT 1 2