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HomeMy WebLinkAboutSubsoil Studyrcrf iåffi å'triffffiirfi'; o' *" An Emplayca Owned Gompany 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fa.r: (970) 945-8454 ernail : kaglenwood(@kumarusa.com wwwkumatusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collhs, Glenwood Springs, and Summit Corurty, Colorado Ãpri|8,2021 Robby Sille 11236 Tayport Loop New Port Richey, Florida 34654 rs i I le@.tampab ay.rr. com Project No. 21-7-166 Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot28, Filing 9, Elk Springs, 81 Kingbird Drive, Garfield County, Colorado Dear Robby: 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 January 31,2021. 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 for the preparation of this report. The proposed residence is assumed to be a two-story wood-frame structure with attached garage located on the site in the area of the pits shown on Figure 1 . Ground floors will likely be a combination of structural over crawlspace and slab-on-gracle. Cut depths are expected to range between about 2 to 5 feel. 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 building envelope corners were marked and approximately 6 inches of snow was present. The ground surface is gently sloping down to the south. Vegetation consists of grass and weeds in the building area with sagebrush and juniper trees on the east and west sides of the building area. -2- Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating three exploratory pits at the approximate locations shown on Figure I . The logs of the pits are presented on Figure 2. The subsoils encountered, below about Vzto I foot of topsoil, consist of up to 5/z feet of very stiff, sandy silty clay underlain by dense, basalt gravel and cobbles in a highly calcareous cemented sandy silt rratrix down to the maximum excavated depth of 6%feet. Results of swell-consolidation testing performed on relatively undisturbed samples of the clay soils, presented on Figures 4 and 5, indicate low compressibility under existing low moisture conditions and light loading and a low expansion potential or moderate collapse potential when wetted under constant light surcharge. Results of a gradation analysis performed on a sample of silty gravel (minus 3-inch fiaction) obtained from the site are presented on Figure 6. No free water was observed in the pits at the time of excavation and the soils were slightly rnoist. Foundation Bearing Conditions: The upper clay soils encountered in the pits possess a low bearing capacity and low expansion or settlement potential when wetted. The underlying basalt gravel and cobble soils possess a moderate bearing capacity and typically low settlement potential when wetted. We recommend topsoil and shallow clay soils be removed and spread footings be placed entirely on the underlying granular soils. 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, basalt rock soils designed for an allowable soil bearing pressure of 2,500 psf for support of the proposed residence. The topsoil and clay soils have variable expansion/compression potential and should be removed from below building areas. We should observe the cornpleted building excavation for bearing conditions prior to forming footings. Our experience in this area indicates that the basalt rock soil can be excavated a few feet with a heavy-duty trackhoe but rock excavation techniques could also be needed such as for deeper cuts and trenches. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. Topsoil, clay and loose disturbed soils encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended ciown to the undisturbed natural basalt rock soils. Voids created from boulder removal at footing grade should be backfilled with concrete or a structural material such as road base compacte d to at least 98 percent of standard Proctor density at a moisture content near optimum. Exterior footings shoLrld be provided with adequate cover above their bearing elevations for frost protection. Placement of footings at least 36 inches below the exterior gracle is typically usecl in Kumar & Associates, lnc. @ Project No. 21-7-166 J this area. Continuous foundation walls should be reinforced top and bottorn to span local anomalies such as by assuming an Lìnsupported length of at least 72 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 larger than 6 inches or imported granular material such as road base. Floor Slabs: The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded slab-on-grade construction with a risk of rnovement if placed on the upper clay soils. The subgrade should be evaluated for slab support and possible need for structural fill such as road base at the tirne of excavation. 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 movernent. Floor slab controljoints 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 50Yo passing the No. 4 sieve and less than 2Yo passing the No. 200 sieve. All filImaterials for support of floor slabs should be compacted to at least95Yo of maxtmum 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 ol imported road base. Underdrain System: Although free water was not encountered during our exploration, it has been our experience in the arcathat local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoffcan create a perched condition. We recommend below-grade construction, such as retaining walls, crawlspace and basement areas (if any), 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 7o/oto a suitable gravity outlet. Free-draining granular material used in the underdrain system should Kumar & Associates, lnc. @ Project No. 21-7-166 -4- contain less than 2Yo 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 7%feetdeep Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) 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 backfrll (if any) 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 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. 4) Roof downspouts and drains should discharge well beyond the lirnits of all backfi11. 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 arca at this time. We make no warranty either express or irnplied. 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 1 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 fìeld 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 Kumar & Associates, lnc. @ Project No. 21-7-166 -5- 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 implementation of our recommendations, and to verifu that the recommendations have been appropriately.interpreted. Significant design changes may require additional anaþsis or modifications to the recommendations presented herein. We recomrnend 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 & James H. P Reviewed by: ffi*,/, Steven L. Pawlak, P.E. JHP/kac attachments Figure 1 - Location of Exploratory Pits Figure 2 - Logs of Exploratory Pits Figure 3 - Legend and Notes Figures 4 and 5 * Swe1l-Consolidation Test Results Figure 6 - Gradation Test Results Table 1 * Summary of Laboratory Test Results I 58663 Kumar & Associates, lnc. @ Project Nc, 21"7.166 ¡ ¡ LOr 27 rR4N q LOr 20 LOT 29 t0 UflLl7Y LOT T9 o W 50 0 50 100 APPROXIMATE SCALE-FEET '09"8 l1' Hc KMAR E DUMASS 008 / / 14, / 42 sq. ft 2.620 dc.+* 21 -7 -1 66 Kumar & Associates LOCATION OF TXPLORATORY PITS Fîg. ê PIT 1 EL. 1 01' P EL. lT2 110 PIT 3 EL. I 04' 110 'l 10 F TJL! l-L Iz.o t-- ld-Jl¡l 105 WC=9.6 DD=83 105 Ft¡Jtilt! Iz tr UJJ L¡J WC=8.8 DD=95_rn-Ao '100 100 -. +4=44-l -zoo=13 95 95 WC=8.4 DD=1 1 1 21 -7 -1 66 Kumar & Associates LOGS OF EXPLORATORY PITS Fig, 2 E YI I "r ? LEGEND TOPSOIL; SILT AND CLAY, SANDY, ORGANIC, FIRM' MOIST, DARK BROWN CLAY (CL); SANDY, SILTY, SLIGHTLY cALcAREoUS AND PoRoUS AT s FEET DEEP, VERY STIFF, SLIGHTLY MOIST, BROWN. GRAVEL (OV-UH); HtGHLy CALCAREOUS SANDY SILT MATRIX, BASALT COBBLES, HARD/DENSE, SLIGHTLY MOIST, PALE TAN. HAND DRIVEN 2-INCH DIAMETER LINER SAMPLE. t DISTURBED BULK SAMPLE. I PRACTICAL DIGGING REFUSAL. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A RUBBER TRACK EXCAVATOR ON MARCH'IO, 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 MEASURED BY HAND LEVEL AND REFER TO THE SOUTHEAST BUILDING ENVELOPE CORNER AS 1OO, ASSUMED ELEVATION, 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 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 EXCAVAT¡ON. PITS WERE BACKFILLED SUBSEQUENT TO SAMPLING. 7, LABORATORY TEST RESULTS: Wc = WATER CONTENT (%) (ASTM D 2216); DD = DRY DENSITY (PCt) (NSTV D 2216)i +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (¡STU O ¿ZZ); _2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1 1 4O). Fig.3LEGEND AND NOTTS21 -7 -1 66 Kumar & Associates I SAMPLE OFr Cloy FROM:Pit2e-3' WC = 8.4 "/o, DD = 111 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING l- \ \ Ih$ô t63t þ8ulb oÞply ônt to b. lompl.s tôsbd. fto tè3ting r.port ¡holl ¡ot bo rápmducod. sxcðpt ln full, wilhout thô *ñtton opprovol of(uhor ond Àsoclotô!. lnc. S*êll ]omolldotlôn t$llng p€formad ln lccodonce with Aslil D-454ô. ñ JJt! =U1 I z() tr Õ:lo(n z.oo 2 1 0 1 2 1,0 APPLIED PRESSURE - KSF 10 100 21 -7 -1 66 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig. 4 I I E I I SAMPLE OF: Silty Sondy Cloy FROM:Pit2s^5' WC = 9.6 %, DD = 83 pcf I ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING \ \ \ i Thâs6 t6st rêBulib opply ont to thô rdmplê! têstcd. ftê têsting rêpôd ,holf not bo roprcducôd, 6xc6pt lñ full, wnhout thô wrllt.n opprovol ôt(umor ond AsBôclotê!, ¡ñc. S*álì coñâolidotiôn tælhg pôlormåd ln occordoncé wÍth AW D-454ô. 2 0 JJt! =U) I zotr Õ:io U)zoO -2 -4 b -B 1 0 -12 -14 1,0 APPLIED PRESSURE - KSF 10 100 SWILL_CONSOLIDATION TEST RESULTS Fig.521 -7 -1 66 Kumar & Associates E 3: HYDROMEfER ANALYSIS SIEVE ANALYSIS U.S. SIANDARD SÉRIES CLEAR SQUARE OPENINOS a/^' a/^" 1 1/t" TIMÊ RüDINGS 24 HRS 7 HRS lUtN¡ulN t: -l-all-l---¡'l'" 6 too 90 80 70 80 50 40 30 20 t0 0 o 10 20 30 { 50 60 70 80 90 too ¡ e 152 DIAMETER OF PARTICLES IN MILLIMETERS CLAY TO SILT COBBLES GRAVEL 44 % SAND 43 % LIQUID LIMIT - PLASTICITY INDEX SAMPLE OF: Colcoreous Sllly Grovel ond Sdnd SILT AND CLAY 13 % FROM:Plt1q-2'-3' Th.s. Ì.sl rårulls opply ôhly lô lhê somples whlch wsro lóslód. Th6 l6sllng r6porl sholl nol br raproducåd, ôxcopl ln lull, wllhoul ihô wrlllôn oÞprovdl of Kumor & Àssoololos' lnc. slwô onolysls l.sllhg ls prrformod ln occorddncô wlth ASTM 06913, ASTM 07928, ASTM c136 dnd/or AsfM 01140. SAND GRAVEL FINE MEÞrUM lCOAnSr F¡N E COARSE 21 -7 -166 Kumar & Associates GRADATION TEST RESULTS Fis. 6 l(+rl*itïf;'åifå'Ëtrr1þ;*"'TABLE 1SUMMARY OF LABORATORY TEST RESULTSSOIL TYPESandy Ciayfa1J43958.869441J52z-J12aJA11183LIQUID LIMITClaySiity Sandy ClayGRADATION8.49.6SAMPLE LOCATIONDEPTHPITCalcareous Silty Graveland SandUNCONFINEDCOMPRESSIVESTRENGTHPLASTICINDEXPERCENTPASSING NO.200 SIEVENATURALDRYDENSITYNATURALMOISTURECONTENTSAND(%\GRAVEL(%)No.21'7.166