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Home My WebLink AboutSubsoil Studyl(+rt*i'pilfi',i:"riÉffn'""e;;'*^ An Employcc Owned Compcny 5020 County Road 154 Glenwood Springs, CO 8ló01 phone: (970) 945-7988 fax: (970) 945-8454 email : kaglenwood@kumarusa.com www.kumarusa.com Office Locationsl Denver (HQ), Pæker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado SUBSOIL STUDY F'OR FOT]NDATION DESIGN PROPOSED RESIDENCE LOT 6, MITCHELL CREEK, F'ILTNG I CREEKSIDE COT]RT GLENWOOD SPRTNGS, COLORADO PROJECT NO.20-7-470 ocToBER 2,2020 PREPARED FOR: JEAN SMITH 173 MEL REY ROAD GLENWOOD SPRTNGS, COLORADO 81601 ieanandrandv@smail.com TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY..... PROPOSED CONSTRUCTION SITE CONDITIONS...... FIELD EXPLORATION SUBSURFACE CONDITIONS ... FOUNDATION BEARING CONDITIONS DESIGN RECOMMENDATIONS FOUNDATIONS FOUNDATION AND RETAINING WALLS FLOOR SLABS UNDERDRAIN SYSTEM LIMITATIONS FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4 and 5 - CRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS 1 1 1 -2^ 1 J- ..- 3 - ..- 3 - ..-4- ..- 5 - ..- 5 - -7 - Kumar & Aseociatès, lnc. @ Project No. 20-l-470 PT]RPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 6, Mitchell Creek, Filing 1, Creekside Court, Glenwood Springs, 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 engineerirtg services to Jean Smith dated August 18, 2020. 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 determine their classification and other engineering characteristics. The results of the field exploration and laboratory testing were analyzed to 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 The proposed residence will be a one and two-story structure with a partial basement. Ground floors will be partly structural above crawlspace and slab-on-grade in the basement and garage areas. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to I feet below the existing ground surface. 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 COIIDITIONS The lot was vacant of structures at the time of our field exploration. The ground surface slopes moderately down to the south with around 6 feet of elevation difference in the building envelope. An active, earthen irrigation ditch flows to the east through the southern part of the lot as shown Kumar & Associates, lnc. @ Project No. 20-7-470 a'L' on Figurc l. Vcgctation mainly consists of grass and wecds with brush outsidc of thc building envelope. FTELD EXPLORATION The field exploration for the project was conducted on August 24,2020. Three exploratory borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. The borings were advanced with 4-insh diameter continuous flight augers powered by a truck- mounted CME-458 drill rig. The borings were logged by a representative of Kumar & Associates, Inc. Samples ofthe subsoils were taken with l%inch and 2-inch I.D. spoon samplers. The samplers were clriven 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-l586. The penetration resistance values are an indication of the relative densþ 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. SUBSURX'ACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils, below aboutt/zfoot of root zone topsoil, consist of about 2 to 8 feet of silty, slightly clayey sand with gravel overlying sahd, silt and clay to depths of about 16 to 18 feet underlain by dense, silty sand and gravel to the boring depths of2l to 26 feet. Laboratory testing performed on samples obtained from the borings included natural moisture content and density and gradation analyses. The samples were,generally too rocky to perform swell-consolidation testing. Results of gradation analyses performed on small diameter drive samples (minus l%-inchtiaction) of the coarse granular subsoils are shown on Figures 4 and 5 The laboratory testing is summarized in Table 1. No free water was encountered in the borings at the time of drilling or when checked 2 days later and the subsoils were slightly moist to moist with depth. Kumar & Assoclates, lnc, @ Project No, 20-7-470 -3- F'OUi\DATION BEARING COFIDITIONS The upper alluvial soils encountered to depth of 16 to l8 feet are relatively low density and judged to be compressible under conditions of loading and wetting. Spread footings placed on the natural soils can be used for the foundation support with a risk of settlement and distress mainly if the bearing soils are wetted. A low settlement risk alternative would be to support the building on a deep foundation such as pile or piers that extend down into the underlying, relatively dense granular soils encountered below depth ofabout 16 to 18 feet. Ifa deep foundation is desired, we should be contacted for additional analysis and recommendations. DESIGN RECOMMENDATIONS FOI.INDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we recommend the building be founded with spread footings bearing on the natural, predominantly granular soils. The design and construction criteria presented below should be observed for a spread footing foundation system. l) Footings placed on the undisturbed natural granular soils should be designed for an allowable bearing pressure of 1,500 psf. Based on experience, we expect initial settlement of footings designed and constructed as discussed in this section will be about I inch or less. Additional post-construction settlements of around % to 1 inch could occur depending on the depth and extent of wetting. 2) The footings should have aminimum width of 18 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 âfêfl¡ 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 12 feet. Foundation walls acting as retaining structures should also be designed to resist Kumar & Aseociates, lnc. o Project No. 20-7-470 -4- lateral earth pressures as discussed in thc "Foundation and Retaining Walls" section of this report. The topsoil, any existing fill and loose or disturbed soils should be removed and the footing bearing level extended down to the natural, predominantly granular soils. The exposed soils in footing area should then be moistened and compacted. A representative ofthe geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FOLINDATION AND RETAINING WALLS Foundation walls and retaining structures which are laterally supported and can be expected to undergo only a slight amount of deflection should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 50 pcf for backfill consisting of the on-site soils. Cantilevered retaining structurei which are separate from the residence and can be expected to deflect sufficiently to mobilize the full active earth pressure condition should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 45 pcf for backfill consisting of the on-site soils. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The pressures recommended above assume drained conditions behind the walls and a horizontal backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain should be provided to prevent hydrostatic pressure buildup behind walls. Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum standard Proctor density at near optimum moisture content. Backfill placed in pavement and walkway areas should be compacted to at least95%o of the maximum standard Proctor density. Care should be taken not to overcompact the backfill or use large equipment near the wall, since this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall backfill should be expected, even if the material is placed correctly, and could result in distress to facilities constructed on the backfill. Backfill should not contain organics, debris or rock larger than about 6 inches. s) 6) Kumar & A¡¡ociates, lnc, @ Project No, 20-7.470 -5- The lateral resistance of foundation or retaining wall footings will be a combination of the sliding resistance of the footing on the foundation materials and passive earth pressure against the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated based on a coefficient of friction of 0.40. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 375 pcf. The coefficient of friction and passive pressure values recommended above assume ultimate soil strength. Suitable factors of safety should be included in the design to limit the strain which will occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against the sides of the footings to resist lateral loads should be compacted to at least95o/o of the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS 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 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 Z-inch aggregate with at least 50o/o retained on the No. 4 sieve and less thanT%o passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least95%o of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on- site granular soils devoid of vegetation, topsoil and oversized rock. LINDERDRAIN 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 and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. Shallow crawlspace and Kumar & Associates, lnc. @ Projec{ No. 20-7-470 -6- gùrege ereûs should not be provided with a pel'irìeter foundation drain to help keep the bearing soils dry. 'l'he drains should consist of drainpipe placed in the bottom of the wall backfill sumounded above thc invcrt lcvcl with frec-draining granular material. The drains should be placed at each level of excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum 170 to a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than 2%o passingthe No. 200 siove, less than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least lYzfeet deep. 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 of the bearing soils. SURFACE DRAINAGE Proper surface grading and drainage will be important to prevent wetting of the bearing soils and limit potential building settlement and distress. The following drainage precautions shoulcl be observed during construction and maintained at all times after the residence has been completed: 1) lnundation 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. 3) The ground surface surrounding the exterior of the building should be sloped to drain away lïom the fbundation 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 10 feet in paved areas. Free-draining wall backfill should be covered with filter fabric and capped with about 2 feet of the on-site soils to reduce surface water infiltration. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy irrigation should he located at least 5 feet from foundation walls. Consideration should be given to use of xeriscape to reduce the potential for wetting of soils below the building caused by irrigation Kumar & Associates, lnc. @ Project No. 20-7-470 7- 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 borings drilled at the locations indicated on Figure 1, the proposed type of construction and our experience in the area. Our seruices do not include determining the presence, prevention or possibility of mold or 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 borings 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 repofi, 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 should provide continued consultation and field services during construction to review and monitor the implernentation of our recommendations, and to veri$i 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 ofexcavations and foundation bearing strata and testing ofstructural frll by a representative of the geotechnical engineer. Respectfully Submitted, . K¡.rnaa¡" & Asso*:i:lÉes, Steven L. Pawlak, P Reviewed by: i\l ¡..I ì,- ...,- --, , -l{ t! {-¡ '.,'ì-t,,_. \ * Daniel E. Hardin, P.E. SLP/kac 1 5222{, Kumar & Âsscciates, lnc. 'Projeet hlc. 20-7"d.7CI !-LJLJt!Il¿lJ()(nl¡Jl-ioÉ.fLfLoc\¡I:]¡!.¡,Od__Jt.1 l:t'---:¡9r .¡-- i,:l i-r st,5ûr "08'57"f 9ó 53Nior'û8 57"\^/ I 10.Û0',jäi'i i-.r¡l::''.i l-i-i:,t.JtiiilI-;l1_-,_j.|:ot)+IIi!,t¡!IIk< -.1.e'l :.Q:'--) a.< r:<i:--.x _q!,€):)c\1:,ãijIi':):),rio--coal()c4;()cocoUiTlliI_\ _-IIctze,o@n!I-c'r)(>-oUncÐU)¡1uoÕI:1: .'.ta-,=..1'i ç¡''Jfîi)-:1-.+lú)):-.ca .rt-1".'j ':'t:)=iìlû¡r)c'zÉ,o;:rlD @-Jqc{@t\lf,ltJl¡lã13==lìä(Jl >(,zlÉurl fØol ør<IIII,Iíl r; Íilìì.fDa.-: a rIIL --*It ,,ç1'ì ,r'.U_:i'--.LI ;O N:,í.!: c¡I,4, -:., e,o,-t'.- ,-' ElTI.:r h-.--+""+--\¡:-., l'-': ¡ ii:a;r !.:oN{IÌ\Ioc{aosoo(tt|t,oöL(5Ef\¿(n(,z.æ.octÉ.ot--É.oJo-><l¡Jl&oz.c)tr(JoJl'tf! t I E I BOR¡NG 1 EL. 5784' BORING 2 EL. 5779.5' BORING 5 EL. 5780.8' 0 0 s/12 20/12 WC=6.6 DD=1 1 7 -2OQ=44 22/12 29/12 5 17/12 WC=4.8 DD=118 -2OO=26 1s/ 12 5 17/12 10 5/12 WC=12.5 DD=1 1 f -2OQ=64 10 1e/12 15/12 t-t¡J l¿lLr I:ct-.L L¡Jô 15 12/ 12 e/12 34/12 15 t- l,¡l bJb IIFfL LJÕ 20 203s/12 41 /12 43/12 25 41 /12 25 50 30 WC=3.4 DD=1 18 +4=1 6 -200=44 WC=7.0 DD=1 1 2 *4=12 -200=51 \NC=2,4 +4=40 -2OO=18 20-7-470 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 t ¡ E I LEGEND N n t?'::v u TOPSOIL; SILTY CLAYEY SAND WITH ORGANICS, R00T ZONE. SAND MIXËD (sM-sc); BROWN, SILTY, SLIGHT CLAY, GRAVELLY, LOOSE TO MEDIUM DENSE, SLIGHTLY MOIST, SUBANGULAR ROCK. SAND, SILT AND CLAY (SC-CL); GRAVELLY, SCATTERED COBBLES, LOOSE TO MEDIUM DENSE, BROWN. SAND AND GRAVEL (SM-GM); SILTY, POSSIBLE COBBLES, DENSE, MO|ST, LIGHT BROWN. F i DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE DRTVE SAMPLE, 1 5/8-|NCH t.D. SPLll SPOON STANDARD PENETRATION TEST ozrc DRIVE SAMPLE BLOW COUNT. INDICATES THAT 9 BLOWS OF A 140-POUND HAMMER"/.. FALLING 30 INCHES WERE REQUIRED To DRIVE TIIE SAMPLER 12 INCHES. -> DEPTH AT WHICH BORING CAVED WHEN CHECKED ON AUGUST 26,2020, NOTES THE EXPLORATORY BORINGS WERE DRILLED ON AUGUST 24, 2O2O 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 MEASURED BY HAND LEVEL AND RËFER TO THE BENCHMARK ON FIG. 1. 4, THE EXPLORATORY BORING 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 BORING LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATËR WAS NOT ËNCOUNTERTD IN THE BORINGS AT TI{E TIME OF DRILLING OR WHEN CHECKED 2 DAYS LATER. 7. LABORATORY TEST RESULTS: wc = WATER CONTENT (%) (ASTM D2216); DD = DRY DENSITY (pcf) (ASTM D2216);+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913); *2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM 01140). 20-7-470 Kumar & Assoclates LEGEND AND NOTES Flg. 3 Ê ü É Ë to0 90 æ 70 ao 50 Æ EO 20 lo o o to 20 to 4 Ð 80 70 t0 ¡0 I þ E CLAY TO SILT COBBLES GRAVEL 12 N SAND 37 '4 LIQUID LIMIT PLASTICIÏY INDEX SAMPLE OF: Vcry Sondy Slll ond Cloy wllh Grovcl SILT AND CLAY 51 '( FROM: Borlng 'l O 7.5' & 10' (Comblnod) 2 g r00 90 to ,o to 50 ít) JO 20 lo o to 20 50 ß 50 GO 70 æ so t00 e = E Ë DIAMETER OF 2,OIN MILLIMETERS CLAY TO SILT COBBLES CRAVEL 40 % SAND UQUID LIMIT SÀMPLE OF: Sllly Sond ond Grovel 12% PLÀSTICIW INDEX SILT AND CLAY 18 % FROM: Borlng 1 O 20' ¡! 25' (Comblned) fh.!. l.rl rrlullr oÞply only lo lh. lqmpl.¡ vhloh w.ro l.d!d. Th!l.'llng nport rholl nol b. roproducrd, cxcrÞl ln lull, wllhoul lh. vrltlrñ opprcvol of Kumar t A$oolott!, lno. Sbva qnqly¡lr t tllng lr p.rlomrd lnqcoodqno! Tlth ASfl, Dô0,l5, ASTil D7928. ASIM Cf56 cndlor ASIM Dll4O. I.IYDROMEÍER ANALYSIS SIEVE AXALYSIS CLUR SQUAFE OPETITOS ttt af^. I t/r.r!t{atz,t HiS 7 HRSu utl l¡ lltr lrt¡t iEADtNoS dôltN tevt{ dltr Ì l l I I 1 i lrI i¡¡t¡ SAND GRAVEL MEDIUM COARSE FINE COARSEFINE HYDROMETER ANALYSIS SIEVE ANALYSIS IIYT RruN63 14 HRS 7 Hñ5 u.s. s ND iD sERtEs CBR SOUARE OPEflING a/^. ltl. t 1tt / /I /I ì i I . -"1- Ì.---'f- I 't-. I ¡¡t¡ I SAND GRAVEL FINE MEDTUM ICOARSE FINE COARSE 20-7-474 Kumar & Associates GRADATION TEST RESULTS Fi9. 4 t HYDROMETER ANALYSIS SIEVE ANALYSIS ltrt nËaDlHog g,t HRS 7 HRs u.3. sf No n0 $ills cttai touatt ilt¡t¡o! ttt tfl. I ttrr I I I I l L j I l I I SAND GRAVEL I ! ui_,-1_.2 lza FINE MEDIUM FINE COARSE ä Þ Ë r0o t0 l0 70 a0 50 ,ro 30 20 rÒ 0 0 to 20 to & 50 to ta to ¡o foo ¡ E E t,t a CLAY TO SILT COBBLES GRAVEL 16 N SAND 10 '1 LIQUID LIMIT PI.ASTICITY INDEX SAMPLE. OFr Vðry Sllty Cloy.y Sond wlth Grov.l SILT AND CLAY 14 % FR0M: Borlng 5 O 5' ¡r 10' (Combln¡d) th!r! l ¡l rcrulh opply only lo lh. roóÞlâa whlôh 9ah lðltâd. fh¿l[llng ruÞorl rholl nol br nprcducrd,rro.pl ln lull, wlthoul lhc wrlll.n opÞrcvol ol Kumor ¿l Aræolold, lno, Slrva onolyrlr l[flng b pcrloñ.d lñ occordoñc. rllh AsfM 06915. ASfl¡ 07928, ASTY C136 ond/or ASIM D1l,lo. 20-7-470 Kumar & Associates GRADATION TEST RESULTS Fig. 5 l(+rtiiffi fiffifffiir'iiå'*"TABLE 1SUMMARY OF LABORATORYTEST RESULTSNo.20-7470BORII{GJ2I10520 &,25combined7Yz &. l0combined5ffttDEPII{SATPLE LOCATION5&10combined2.47.06.6(%liIATURALlilolStURECONTENT3.412.s4.8118111118rt2TT7NATURALDRYDENSÍTY(7.)GRAVEL("/,1SAND1640I2404237446426I85144PERCEiITPASSING NO.200 $arEÍohlLIQUID LIMTTt%rPLASTICINDEXATTERBERG LIMITSfosflUNCONFINEDCOMPRESSruESTRENGTHVery Siþ Clayey Sandwith GravelSandy Silt and Clay withGravelSilty Clayey Sand withGravelSiþ Sand and GravelVery Sandy Silt and Claywith GravelVery Silty Clayey Sandwith Gravel (Fill)SOIL TYPE