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Home My WebLink AboutSubsoil StudyKtfimiflmmifü-* An ËmploVac Owtcd ComPonY 5020 CountY Road 154 Glenwood Springs, CO 8ló01 Phone: (970) 945'7988 , fax: (970) 945'8454 email: kaglenwood@kumarusa.com ytwli.kulqaruÉe.cS!û Office Locations: Denver ft{Q), Par*er, Colorado Springs, Fort Collins, Glenwood Springs, and Summit Counry, Colorado March 5,2021 Gruenefeldt Construction Attn: Dan Gruenefeldt P.O. Box 1920 Basalt, Colorado 81621 danØsruenefeldt.com Project No.2l-7-205 Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot FW-l, Fairways atAspen Clen Sub¿¡vision, TBD Golden Bear Drive, Garfield County, Colorado Dear Dan: As requested, Kumar & Associates, Inc. performed a subsoil study for design ofrfoundations at the subject site. The study was conducted in accordance with our agreement for:geotechnical engineering services to you dated February 12,2021. 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 will be one story over a crawlspace with an att¿ched garage locate.d on the site as shown on Figure t. The garage floor will be slab-on'grade. Cut depths are expected to range between about 2to 3 feet. Foundation loadings for this type of construction are assumed to be relatively light and fypical of the proposed type ôf construction. If building conditions or foundation loadings are signifìcantly different from those described above, we should be notifîed to re-evaluate the recommendations presented in this report. Site Conditions: The site was vacant and covered with about 4 inches of snow at the time of our site visit on February 17,2021. The site was relatively flat and vegetated with grass and weeds in the building area. There were aspen and fir trees in the front (north) corners of the lot. There was a low berm along the property line on the east side ofthe lot. The adjoining lots to the east and west of the lot were developed with 2-story residences. There is an existing pond located south of the lot. Subsidence Potential: The lot is underlain by Pennsylvania Age Eagle Valley Evaporite bedrock. The evaporite contains gypsum deposits. 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 (Chen-Northem, Inc. 1991 and 1993) several broad depression areas and smaller size sinkholes were observed in the Aspen Glen development, mainly to the east ofthe Roaring Fork River. Sinkholes were not observed in the immediate area of the subject lot. The nearest mapped sinkhole is about 400 feet north of this lot. The exploratory pits were relatively shallow, for foundation design only. Based on our present knowledge of the site, it a cannot be said for certain that sinkholes will not develop. In our opinion, the risk of ground subsidence at Lot FIV-I is low and similar to other lots in the area but the owner should be aware of the potential for sinkhole development. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits at the approximate locations shown on Figure l. The logs of the pits are presented on Figure 2. The subsoils encountered, below about t/z foot of topsoil, consist of medium stiffto stiff, sandy silty clay with widely scattered cobbles down to the pit depths of 5 to 6 feet. Results of swell-consolidation testing performed on relatively undisturbed samples of the sandy silty clay, presented on Figures 3 and 4, indicate low compressibility undçr existing moisture conditions and light loading and a minor expansion potential or low collapse potential when wetted. Results of a percent finer than sand size gradation analysis showed the sillclay content of the soils to be 84 percent. 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 encountergd in the exploratory pits and the nature of the proposed construction, ws recommend spread footings placed on the undisturbed natural soil designed for an allowable soil beari ry3g|1$. support of the proposed residence. The soils tend to compress after wetting and there-could be post-construction foundation settlement of around I inch or more:depending mainly on the depth and extent of wetting. Footings shoutd be a minimum width of20 inches for continuous walls and 2 feet for columns. Loose and disturbed soils encounteredrat the foundationbearingl,ffiationshouldberemovedandthefootingbearingIevel 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 heavily reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least ï2 îeet. Foundation walls acting as retaining structures should be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 50 pcf for the on-site soil as backfïll. tr'toor Stabs: 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 forjoint spacing and slab reinforcement should be established by the designer based on experience and the intended slab use. A minimum 4-inch layer of road base gravel should be placed beneath the garage slab to provide support. This material should consist of minus Z-inch aggregate with less than 50% passing the No. 4 sieve and less than lTo/a passing the No. 200 sieve. Kumar & Associatet, lnc, o ProJect No. 21-7-205 -J- All fill materials for support of floor slabs should be compacted to at least9ío/o of maximum standard Proctor densþ at a moisture content near optimum. Required fill can consist of the on- site clay soils devoid of vegetation, topsoil and oversized rock. Underdrain System: The proposed shallow crawlspace should not require an trnderdrain system provided that good surface drainage is maintained around the residence. lf an underdrain is installed, 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 lVoto a suitable gravity outlet such as a drywell. Free-draining granular material used in the underdrain system should contain less than 2o/o 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 l%feetdeep. An impervious membrane such as 20 mil PVC should be placed beneath the drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting ofthe bearing soils. Surface Drainage: The following drainage precautions should be observed during consffuction 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 90% of the maximum standard Proctor density in landscape areas. Free-draining wall backfïll should be capped with about 2 feet ofthe on-siteo finer graded soils to reduce surface water infiltration. 3) The ground surface surounding the exterior of the building should be sloped to drain away from the foundation in all directions. lffe recommend a minimum slope of 12 inches in the first l0 feet in unpaved areas and a minimum slope of 2Yrinches in the first l0 feet in pavement and walkway areås. 4) Roof downspouts and drains should discharge well beyond the lirnits of all backfill. 5) Landscaping which requires regular heavy inigation should be located at least 5 fe€t from the building. Consideration should be given to the use of xeriscape to limit potential wetting of soils below the foundation caused by irtigation. 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 Kumar & AsEociates, lnc. o Prcj,ec{ l{o. 21-7-245 4 the area. Our services do not include determining the presence, preve,ntion or possibility of mold or other biological contaminants {MOBC) developing in the future. Ifthe client is concerned about MOBC, then a professional in this special field of practice should be consulted. tur findings include interpolation and extrapolation of the subsurface conditions iderrtified at the exploratory pits and variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountercd during conskuction appear different from those described in this report, we should be notified at oncæ so re-evaluation of The recommendations may be made. This report has been pre,pared for the exciusive use by our client for design purposes. lü/e are not responsible for technic¿l.interpretations by others of our information. As the pro¡ect evolves, we should provide continued eonsultation and field services during construction to review and monitor the irnplementation of or¡r recommendations, and to veriry that the recommendations have been appropriately interpreted. Significant design changes may require additional anaiysis ormodifications to the recommendations presented herein. We recommend on-eite observation of excavations and foundation bearing strata and testing of structural fill by a represørtative of the geotechnical engineer. If you have any questions or if we may be of fi.¡rther assistance, please let us know. Respecttully Submiued, Kumar & Asso*i*tes, Daniel E. Rev. by: SLP DEH/kac attachments Figure 1 * Loeation of Exploratory Pits Figure 2 - Logs of Exploratory Pits Figrres 3 and 4 - Swell-Consolidation Test Results Table I - Summary of Laboratory Test Results cc:Rakowski-Millard - Al Rakowski (çly¡_¿I]dçsËå$.eat) RßFERßNCES Chen-Northern, fnc., 199'1., Prelíminary Geotechnícal Engíneeríng Sudy, Proposed Áspen GIen Development, Garfield County, Calorado, prepared for Aspen GIen Cornpany, dated December 20,1991, Job No. 4112 92. Chen-Norflrerno lnc, 1993, Geotechníeøl Engineeríng Sudyþr Prelimínary Plant Design, Aspen Glen Development, Garfield County, Colorado, prepared for Aspen Glerr Company, dated May 28, 1993, Job No. 4 11292. Kumar t,ås*oriËtê$, lnc. il'Projeet Na, 214"2øâ {(.{ì,11/ ,,iai)t':,A"Il\l-L¡Jt¡¡l¡Ib¡J()ahl¡,t--xo&o-ô-1r)o(\IIc\¡oo(ú'ıornooð$Eãvv1bo-É.oæ.oo-><T¿JtLozol-()oJct¡lÀ åI É PIT 1 PIT 2 0 0 F.t¡Jt¡lt! I Jt-fLf¡lÉl wc I 0.0 IVC= 18.3 DD=91 -200=84 þ t¿JUl¡ Itt--o- lJJo DD=86 5 WC=15.1 DD= I 02 5 10 10 LEOEND TOPSOIL; ORCANIC SANDY SILTY CLAY, FIRM' MOIST' DARK BROWN. CLAY (CL); SILTY, SANDY, WIDELY SCATTERED COBBLES, MEDIUM STÍFF TO'STIFF, SLIGHTLY MOIST TO MOIST, BROWN. F HAND DRIVE SAMPLE. NOTË9 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON FEBRUARY 17, 2021. r THE LOCATIONS OF THE EXPLORATORY PITS WERE PROVIDED BY THE CLIENT. 3. THE ELEVATIONS CIF THE EXPLORATORY PITS WERE NOT MEASURED AND THE'LOGS OF THE EXPLORATORY PITS ARE PLOTTED TO DEPTH. 1. THE EXPLORATORY PIT LOCATIONS SHOULO BE CONSIDERED ACCURATE ONLY TO THE OEGREE 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 THg PITS AT TI{E TIME OF EXCAVATION. 7. LABORATORY TEST RESULTS: wc = WATER CONTENT (X) (ASTM D 2216); DD = DRY DENSITY (PCT) (ISTU D 2216); -2OO= PERCENTAGE PÀSSING NO. 2OO SIEVE (ASTM D 1140)' 21 -7 -205 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2 SAMPLE OF: Sondy Sllty Cloy FROM:PltlOS' WC = 10.0 %, DD = 86 pcf h ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 2 0x j-z l¡¡.U' t-1 z.ot- ô =-oov,z.o(J_g -10 -12 -11 -1ô - KSF 21-7-205 Kumar & Associates SWELL-CONSOLIDATION TEST RESULT Fig. 3 ã E ht SAMPLE OFr Sondy Sllty Cloy FROM:Pit2O5' WC = l5.l tl, DD = 102 pcf 0N j-1 l¡l-v, t-2 z.o l- ô o,nz,oC)_4 .t 21 -7-205 Kumar & Associates SWELL-CONSOLIDATION TEST RESULT Fis. 4 Kr-rf mfimm;fü*"TABLE,ISUMIIIARY OF LABORATORY TEST RESULTSNo.2lSOLTYPËSandy Silry ClaySandy Silty ClaySandy Silty CIayur{coilFlt{EDcowRËssfvESIRENGTHLilfTSPLISTGlt¡DÐ(UQUIDUMTPERCEIITPASSåG l¡O.æ0 sFr¡r84SAND(%)GRAVEL{Ìô}869I102ilATURAIDRYDEt¡SffYloûll10"018.3IJINATURATMOISTUREcoNTEt{rftl.ocATroilDEPTHtñtJJ5SATPI"EBORIIIGI2