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HomeMy WebLinkAboutSubsoil Study for Foundation Design 04.22.2021lGnU***gggfl;ü*" An Enploy;a Olrncd Compoq¡ 5020 Cormty Road 154 Gle¡rwood Springs, C0 81601 phone (970) 945-7988 fax (970) 945-M54 emait kaglenwood@kunrarum,com wwv¡.kurna¡usa.com Office l,ocalions: Denver (HQ), Parksr, Colorado Spingss FtrÎ Colling Glenr*'ond Springg and Summit ComS, Colmado April22,202l Alius Design Group Attn: Michael Edinger 108 Diamond A Ranch Road Carbondale, Colorado 81623 michael@'aliusdc'com project No. 21-7-26g Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot E-54, Aspen Glen Subdivision,4TSDiamond A Ranch Road, Garfield County, Colorado Dear Michael: 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 Alius Design Group dated March 15,2021. 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 residence were not available at the time of our study. The proposed residence is assumed to be a one- or two-story residence with attached garage located in the area of the pits shown on Figure l. Ground floors are assumed to be a combination of structural over crawlspace and 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 reporl. Site Conditions: The subject site was vacant at the time of our field exploration. A pond is located north of the subject site. Minor overlot grading as part of the original subdivision development may have placed a small amount of fill to level the lot. The ground surface is relatively flat in the building area with a slope dov¿n to the pond at a grade of around 10 percent. Subsidence Potential: Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen Subdivision. These rocks are a sequence of grpsiferous shale, fine-grained sandstone and siltstone with some massive beds of rypsum and limestone. There is a possibility .| that massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the lot. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. During previous work in the area, several sinkholes were observed scattered throughout the Aspen Glen Subdivision. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the lower Roaring Fork River Valley Sinkholes were not observed in the immediate area of the subject lot. The nearest mapped sinkholes are 600 feet west and 700 feet northeast of this lot. No evidence of cavities was encountered in the subsurface materials; however, the exploratory pits were relatively shallow, fbr fbundation design only. Based on ouT present knowledge of the site, it cannot be said for certain that sinkholes will not develop. In our opinion, the risk of ground subsidence atLotB-54 is low and similar to other lots in the area but the owner should be aware of the potential for sinkhole development. Subsurfncc Conditions: The subsurface conditions at the site were evaluated by exoavating two exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are presented on Figure 2. The subsoils encountered, below aboutYz to 1 foot of topsoil, consist of dense, very sandy gravel with cobbles to the maximum explored depth of 5Yz feet. Results of a gradation analysis performed on a sample of clayey gravel (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 to moist. Foundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, we recommend spread footings placecl on the unclistt¡rbecl natural granular soil clesignecl 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 disturbed soils and topsoil encourtered at the foundation bearing level within the excavation should be removed and the footing bearing level extended dor¡¡n to the undisturbed natural soils. Exterior footings should be ---.---:l-l ---l¿l- -l----^¿- ^-----. -1-^--- t1--:--l-^^-:--- ^l^--^L^--^ 1^-r-^^t.--^¿^^i^- rìl^^^-^-¿ ^fpruvrugu wrtrr aucquatg çuvEl ¿ruuvg uttill uti4rlllg tirgvilltuilS rur rrust PrutEurrurr. r-rd.u('ilrçrr] ur 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 unsupportecl length of at least 10 feet. Foundatjon walls acting a"s retaining structures should be designed to resist a lateral earth pressure based on an cquivalcnt fluid unit weight of at least 50 pcf for the on-site soil as backfill. Kumar & Åssociates, lnc. o Project No. 21-7-26ß -J tr'loor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly to moderately 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% 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 least95Yo 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. We recommend vapor retarders conform to at least the minimum requirements of ASTM 81745 Class C material. Certain floor types are more sensitive to water vapor transmission than others. For floor slabs bearing on angular gravel or where flooring system sensitive to water vapor transmission are utilized, we recommend a vapor barrier be utilized conforming to the minimum requirements of ASTM 81745 Class A material. The vapor retarder should be installed in accordance with the manufacturers' recommendations and ASTM 81643. Underdrain System: Although free water was not encountered during our exploration, it has been our experience in the area 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 (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 1o/oto a suitable gravity outlet, drywell or sump and pump. Free-draining granular material used in the underdrain system should contain less than 2Yopassingthe No. 200 sieve, less than 50% passing the No. 4 sieve and have a maximum stze of 2 inches. The drain gravel backfill should be at least lVz feet deep. Kumar & Âssochtes, Inc. 3 Project No. 21-7-2ú -4- 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 shouldbe avoided during construction. 2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95% of the maximum stanclarclProctor clensity 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 capped with about 2feet of the on-site, ftner 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 l0 feet in pavement ancl walkway areas. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. Limitations: This study has been oonducted in aocordance with generally accepted geoteclurical 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 indicatcd on Figurc I and to the depths shown on Figure 2, the proposed type of construction, and our experience in the area. Or¡r services clo not include determining the presence, prevention or possibility of mold or other biological contaminants (MOBC) cleveloping in the future Tf the client is çoncemed 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 a¡e not responsible for technical interpretations by others of our information. As the project evolves, we should provide continued consultation and freld services during oonstruotion to review and monitor the implementation of our recommendations, and to verify that the recommendations have been appropriately interpreted. Signifrcant design changes may require additional analysis Ksmar & Ässocíates, lnc. o Projec.t No. 21-7-2ú -5- or modifications to the recommendations presented herein. We recommend on-site observation of excavations and foundation bearing strata and testing of structural fiIl 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, Kr:msr & ilssoci*tes, Inc" Ð"-r1t?þ. 1@ Jarnes H. Parsons, P.E. ' Reviewed by: Daniel E. JHP/kac attachments of Exploratory Píts Figure 2 - Logs of Exploratory Pits Figure 3 - Gradation Test Results Table 1 - Summary of Laboratory Test Results t. Kumar & Aesocíates, lnc, .''ProjectNo. 21',7-288 ! l.¡læ "; f ROW ,:i L'cHtAvt 23 ST ^r|{932 LE * ASHTON R &,SU I /l 3003060 APPROXIMATE SCALE_FEET 478 DIAMOND A RANCH ROAD LOT E-54 21 -7 -268 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1 ç ai I PIT 1 EL. 100.0' PIT 2 EL. 99 0 0 t- L¡J UJl! I-FfL l¿Jô 5 -, +4=57 -l -zoo=s 5 t- L¡J L¡JtL I-FrL¡¡lo l0 '10 D TOPSOIL; CLAY, SANDY, SCATTERED GRAVEL, ORGANICS, FIRM, MOIST, BROWN. GRAVEL (GM); SANDY WITH COBBLES, SCATTERED BOULDERS, DENSE, MOIST TO SLIGHTLY MOIST WITH DEPTH, BROWN TO GRAY WITH DEPTH. lll, I DISTURBED BULK SAMPLE REFUSAL TO BACKHOE DIGGING NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A RUBBER TRACKED EXCAVATOR ON APRIL 2, 2021. 2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY TAPING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 5. THE ELEVATIONS OF THE EXPLORATORY PITS WERE MEASURED BY HAND LEVEL AND REFER TO THE GROUND SURFACE AT PIT 1 AS 1OO FEET ASSUMED BENCHMARK. 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 ÀPPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE ÏRANSITIONS 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 (ASIM D 422); -2OO= PERCENTAGE PASSING N0. 200 SIEVE (ASTM D 1140). Kumar & Associates LOGS OF EXPLORATORY PITS rî9. 221-7-268 a HìC,ROMETER Al¡ALY3|3 TIVE REÐIN6 14 HRg 7 HRg ¡ıvtN / / I/ I i i ì 1 ì I I l I I l i/ /t 1 l I ,ì ûÍ B 100 90 80 70 60 50 40 30 20 lo o fo 20 30 40 60 30 70 ao 00 t00 É É H .@2 .t 50 .so i -125 IN MILLIMETERS CLAY IO SILT COBBLES GRAVEL 57 % SAND LIQUIO LIMIT SAMPLE OF: Very Sondy Grovel 4091 SILT AND CLAY 3 % PLASTICITY INOEX FROM; Boring 1 O 4.5' to 5.5' Th.e! lcal rrsults opply only lo lh. somplcs whlch wcrc lcslcd. th¡ l!3llng rcporl sholl nol bê r.produc.d, excepl ln full, wllhoul lhe wrlllen opprovdl ol Kumor & Ai¡ociol¡r, lnc.sl.vr Enolyeh l.lllng i! p6rlormed ln occordqnc! wlth ASTM 05913, AsTy Ð7928, ASTM C136 qnd/qr ASIM Dl14o. SAND GRAVEL FINE COARSEFINEMEDIUMCOARSE Fig. 321 -7-268 Kumar & Associates GRADATION TEST RTSULTS I (+rI $ffi¡[*-#fffif*$Ë;n''**tu:TABLE ISUMMARY OF LABORATORY TEST RESULTSNo.21-7-268SOIL TYPEVery Sandy Gravel(ps0UNCONFINEDCOMPRESSIVESTRENGTHPLASTICINDEX(o/o)ATTERBERG LIMITS(o/olLIQUID LIMITPERCENTPASSING NO.200 stEvEJ(/"1SAND40GRADÀTION(:/"1GRAVEL57(ocûNATURALDRYDENSITYlo/olNATURAL¡IOISTURECONTENTfft)DEPTH4%to 5%ISAMPLE LOCATIONPIT