No preview available
HomeMy WebLinkAboutSubsoil Studyl(fllå'ffi[ffi#rnl,liå*"'5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email : kaglenwood@kumarusa.com www.kumarusa.comAn Employcc Orncd Compony Office Locations:, Denver (HQ), Parker, Colorado Sp.ings, Fort Collins, Glenwood Springs, and Summit County, Colorado RECEIVED JUI [r I 2ii?2 GARFIELD COI.,!NTY COMMUNITY DEVELOPMENT SUBSOIL,STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE 129 \ry,EST HOME AVENUE ". SILT, COLORADO 'r '-ì .ia ',:P.ROJECT NO. 2l-7 -7 99 ¡' DECEMBE,IK-27,2021 PREPARED FOR: CINDY RENOVA 156 NATIYE SPRINGS DRIVE RIFLE, COLORADO 81650 renova c@yahoo.com TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY .... PROPOSED CONSTRUCTION SITE CONDITIONS FIELD EXPLORATION SUBSURFACE CONDITIONS .... DESIGN RECOMMENDATIONS FOUNDATIONS FLOOR SLABS. UNDERDRAIN SYSTEM ...... SURFACE DRAINAGE LIMITATIONS FIGURE I - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 _ LEGEND AND NOTES FIGURES 4 AND 5 - SÏIiELL.CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS ...,,-2 - I 1 1 a a ..-2 - -?- 4- 4- -5- Kumar & Associates, lnc. o Projec{ No. 2l-7-799 PTIRPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located at 129 West Home Avenue, Silt, Colorado. The project site is shown on Figure l. The purpose of the study was to develop recommendations for the foundation design. The study was conducted in accordance with our agreement for geotechnical engineering services to Cindy Renova dated October 5,2021. A field exploration program consisting of exploratory borings was conducted to obtain information on the subsurface conditions. Samples of the subsoils obtained during the field exploration were tested in the laboratory to detetmine their classification, compressibility or swell and other engineering characteristics. The results of the field exploration and laboratory testing were analyzedto develop recommendations for foundation types, depths and allowable pressures for the proposed building foundation. This report summarizes the data obtained during this study and presents our conclusions, design recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION Development plans for the lot were not available at the time of our study. We understand that the construction consists of a single-story, single-family residence. Ground floors will be structural over crawlspace for the living area and slab-on-grade for the garage (if constructed). Grading for the structure is assumed to be relatively minor with cut depths between about2 to 4 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. If building loadings, location or grading plans change significantly from those described above, we should be notified to re-evaluate the recommendations contained in this report. SITE CONDITIONS The subject site was generally vacant at the time of our field exploration and was being used as a storage yard for various materials and equipment. The ground surface slopes gently down to the south and was partly covered with driveway gravel. Vegetation consists of sparse weeds with bushes and trees mostly along the perimeter of the lot. An earthen ditch follows the east side of the property and was flowing at the time of our field exploration. Kumar & Associates, lnc. o Project No. 21-7-799 a FIELD EXPLORATION The field exploration for the project was conducted on October 14,2021. Two exploratory borings were drilled at the locations shown on Figure I to evaluate the subsurface conditions. The borings were advanced with 4-inch diameter continuous flight augers powered by a truck- mounted CME-458 drill rig. The borings were logged by a representative of Kumar & Associates. Samples of the subsoils were taken with a 2-inch I.D. spoon sampler. The sampler was driven into the subsoils at various depths with blows from a 140 pound hammer falling 30 inches. This test is similar to the standard penetration test described by ASTM Method D-1586. The penetration resistance values are an indication of the relative density or consistency of the subsoils. Depths at which the samples were taken and the penetration resistance values are shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils encountered, below about one foot of driveway fìll, consist of stiff/medium dense, sandy silt and silty sand with clayey zones down to the maximum drilled depth of 26 feet. Laboratory testing performed on samples obtained from the borings included natural moisture content and density and finer than sand grain size gradation analyses. Results of swell- consolidation testing performed on relatively undisturbed drive samples of the sand and silt soils, presented on Figures 4 and 5, indicate low compressibility under existing moisture conditions and light loading and aminor collapse potential when wetted under constant light surcharge. The laboratory testing is summarized in Table l. Free water was encountered at a depth of about 22 feet in Boring 1 at the time of drilling. The upper soils were slightly moist to moist with depth. DESIGN RECOMMENDATIONS FOLINDATIONS The upper sand and silt soils generally have low bearing capacity and possess a low settlement potential mainly when wetted. Precautions should be taken to keep the bearing soils dry during and after construction. The subgrade soils should be funher evaluated at the time of excavation for bearing conditions. Kumar & Associates, lnc. @ Project No. 2l-7-799 -and,the infcndcdsl¿b-use. A lui¡lqluqa-i¡lcLþySrpf-tgl-atiyçly wqll gIq{Le-{qqnd qnq -3- Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, the building can be founded with spread footings bearing on the upper natural soils with a risk of movement mainly if the bearing soils are wetted. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural soils should be designed for an allowable bearing pressure of 1,500 psf. Based on experience, we expect movement of footings designed and constructed as discussed in this section will be about 1 inch or less. There could be additional post-construction settlement if the bearing soils become wetted. The magnitude of the additional settlement would depend on the depth and extent of wetting but could be up to about I inch. Z) The footings should have a minimum width of l8 inches for continuous walls and 2 feet for isolated Pads. 3) Exterior footings and footings beneath unheated areas should be provided with adequate soil cover above their bearing elevation for frost protection. Placement of foundations at least 36 inches below exterior grade is typically used in this area. 4) Continuous foundation walls should be heavily reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 14 feet. Foundation walls acting as retaining structures should also be designed to resist a lateral earth pressure corresponding to an equivalent fluid unit weight of at least 50 Pcf. 5) Topsoil and any loose disturbed soils should be removed and the footing bearing level extended down to the firm natural soils. The exposed soils in footing area should then be moistened and compacted. 6) A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FLOOR SLABS The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade construction. There could be some slab movement if the subgrade soils are wetted. 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 Kumar & Associate¡, lnc. o Projec't No. 21-7-799 -4- such as cDor class 6 road base, should be placed beneath slabs for subgrade support' This material should consist of minus z-inch aggregatewith at least 50oá retained on the No' 4 sieve and less fhan l2o/opassing the No' 200 sieve' All fill materials for support of floor slabs should be compacted to at leastg5o/o of maximum standard proctor density at a moisture content above optimum. Required fill can consist of the on-site soils devoid of vegetation, topsoil and debris' LTNDERDRAIN SYSTEM It is our understanding the proposed ground floor elevation is near the surrounding grade and that the crawlspace is relatively shallow, around 3 feet' Therefore' a foundation drain system is not recommended. If a basement level is considered, we recommend an underdrain be provided to protect the lower level from wetting and hydrostatic pressure buildup' If the finished floor elevation of the proposed residence is revised to have a floor level below the surrounding grade, we should be contacted to provide recommendations for an underdrain system. All earth retaining structures (site walls) should be properly drained' SURFACE DRAINAGE Providingpropersurfacegradinganddrainagewillbecriticaltolimitingthesubsurfacewetting below the foundation and the risk of building movement and distress. The foilowing 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. Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95Yo of themaximum standard Proctor density in pavement and slab areas and to at least 90% of the maximum standard Proctor density in landscape areas' 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 10 feet in unpaved areas and a minimum slope of 3 inches in the first l0 feet in paved areas' Roofdownspoutsanddrainsshoulddischargewellbeyondthelimitsofall backfill. 5) LandscaPing which requires regular heavy inigation should be located at least l0 feet from foundation walls'Consideration should be given to use of xeriscape 2) 3) 4) to reduce the the building caused-by ir+igation' Kumar & Associates, lnc' o Project No.21'7'799 Project No. 21'7'799 Kumar & Associates, lnc' @ -5- LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering princþles and practices in this arca atthis time. we make no waranty either express or implied' The concrusions and recommendations submitted in this report are based upon the data obtained from the exploratory borings drilled at the locations indicated on Figure 1, 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 professionar in this special field of practice shourd be consulted. our findings incrude interpolation and extraporation of the subsurface conditions identified at the exploratory borings and variations in the subswface 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 so that 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 shouldprovidecontinuedconsultationandfieldservicesduringconstructiontoreviewand monitortheimplementationofourrecommendations,andtoverirythattherecommendations have been appropriately interpreted. significant design changes may require additional analysis ormodificationstotherecommendationspresentedherein.Werecommendon-siteobservation of excavations and foundation bearing strata and testing of structural fi[ by a rçresentative of the geotechnical e'ngineer' RespectfullY Submitted, Kumar & Associates, Inc' Steven L. Paw SLP/kac 18222 oII aHOME AVE HIGHWAY 6 z, it 5 I Ø{ ,NTËRSTATT I*70 z{i 1- VICINITY MAP NOT TO SCALE :.. r SIT€ Wì wfr, '4: ..*:,rrÊ*Þt. -ã-- HOME AVE **',å ;a '-1- ì.¡é.'i* "':' ".if i. 'r *,*-. ._... *-'t ¡ \rÉ.|¡.!-- { i¡ffi,nÌ .-'*t :S,o*' ì*, '.''i I'': 'ìi i'. l .l ,Èi- L- t.' frìL .-l**! I *ry +È Ì-1 -. OBorlng 1 ï * : .è, ãrl rr.sh. .F,r" ;- .-.,& 1 29 WEST HOME AVENUE 2 40 APPROXIMATE SCALE_FEET Fig. 1LOCATION OF TXPLORATORY BORINGSKumar & Associates21 -7 -799 I BORING 1 BORING 2 0 0 12/ 12 WC=6.7 DD=101 8/ 12 WC=10.2 DD= 1 07 -2OO=46 5 5 e/12 WC= 10.4 DD=99 -2OO=62 e/12 WC=15.6 DD=1 06 10 10 1s/12 WC=9.4 DD= 1 06 1e/'t2 ¡-t¡lt¡l LL I :Ef-(L t¡Jô 15 l-l¡lldtL ITt--o-t¡lo 15 8/ 12 7/12 20 20 6/12 WÇ=28.4 DD=95 -200=90 4/ 12 .-->- 25 25 4/ 12 30 30 Fig. 2LOGS OF EXPLORATORY BORINGSKumar & Associates21 -7 -799Ë 9 LEGEND F|LL; SAND AND SILT, VERY STIFF, MIXED BROWN, COVERED WITH ROAD BASE GRAVEL. SILT AND SAND SLIGHTLY MOIST (ML-SM); STRATIFIED, SLIGHTLY CLAYEY ZONES, STIFF/MEDIUM_ DENSE, io uo¡sr wtTH DEPTH AND wET AT cRoUNDwATER LEVEL, LIcHT BRowN. DRIVE SAMPLE, 2_INCH I.D. CALIFORNIA LINER SAMPLE ^ 2.. DRIVE SAMPLE BLOW COUNT. INDICATES THAT 9 BLOWS OF A 14o-POUND HAMMER "/ '' FALLTNG Jo TNcHES wERE REoUIRED To DRIvE THE SAMPLER 12 lNcHES. -=- DEPTH TO WATER LEVEL ENCOUNTERED AT THE TIME OF DRILLING. .--> DEPTH AT WHICH BORING CAVED. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON OCTOBER 14.2021 WITH A 4_INCH DIAMETER CONTINUOUS-FLIGHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 5. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE NOT MEASURED AND THE LOGS OF THE EXPLORATORY BORINGS ARE PLOTTED TO DEPTH. 4. THE EXPLORATORY BORING LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER LEVELS SHOWN ON THE LOGS WERE MEASURED AT THE TIME AND UNDER CONDITIONS INDICATED. FLUCTUATIONS IN THE WATER LEVEL MAY OCCUR WITH TIME. 7. LABORATORY TEST RESULTS: wc = WATER CONTENT (%) (ASTM D2216); DD = DRY DENSITY (PCt) (NSTV D2216)I -ZOQ= PERCENTAGE PASSING NO. 200 SIEVE (ASTM 01140). Fig. 3LEGEND AND NOÏTSKumar & Associates21 -7 -799 ¡ - lz:2Epñ-7-799 SühollZ,99-04 locoNSoLrDATroN - SWELL (%)IàI(¡I(¡IÀJIoIo=i9o<il<-ttt-o, tÞ |tli9 oi.N,ãÞ9o@ill n'qãqá9!t+IIz.>99f¡ c,t¡Ð=Fs9ðã.?€i8rr! -r <)xå"ÐgiDz\I!.çPr¿11(o5lJ){mt-t-Ic)oz.UIof(f,-{oz.-{fî(^-{nmtltr-tU,N)I\¡I\¡rc)(ox30¡9ooØoo.oocn toSubro¡lCoNSoLTDATTON - SWELL (%)o¡\)I(^TTtrmooooãäiil=P@Flsrr90o, j'3ñ(oa'lr:og@e:qåot,Or='ttgCoNSoLTDATTON - SWELL (%)zo€?frl |rl--{ <-.: mzzc,{c-uoz.ol..tI(¡IàN)I!I\¡(o(.oxc30)eo(r,@oa.o)ooU'€frlt-rIc)oz.U1Ot-(:l-{oz.-{fÎtJ1-J7rrlU)ct--{LltTt(o(,IÉääil 5P.otDfrlL9 oi' alNdogo@ó'lloËð"åor q:!gt\zo€?m frt-l<-'mzz.c,Jc!ozI\T Ilfumr & Assoclabs, lnc.@Geotechnical and Materials Engineersand EnvÌronmental ScientistsTABLE ISUMMARY OF LABORATORY TEST RESULTSNo.21-7-799SOIL TYPESand and SiltVery Sandy SiltSand and SiltSlightly Sandy Clayey SiltVery Silty Clayey SandSand and SiltlosflUNCONFINEDCOMPRESSIVESTRENGTH(ololPI-ASTtCINDEXATTERBELIQUID LIMITlolJ629046PERCENTPASSING NO,200 slEvESAND(f/")(%)GRAVEL1019910695r07106NATURATDRYDENSTTYlocfì6.710.49.428.4r0.215.65NATURALMOISTURECONTENTDEPTH2y,50I202%sAiBORIN(I2