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Home My WebLink AboutSubsoil Study for Foundation Design 12.10.24I(tAfl3ffififfifffiili.*i*'" An Emdoycc Owncd Compony 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email : kaglenwood@kumarusa.cem www.kumarusa.com Office l-ocations: Durver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado SUBSOIL STT]DY F'OR FOUNDATION DESIGN PROPOSED SHOP/GARAGE AF{D ADU 6533 COUNTY ROAD 214 GARFTELD COUNTY, COLORADO PROJECT NO.24-7-587 DECEMBERI0,2024 PREPARED FOR: JORDA}I ARCHITECTURE ATTN: BRAD JORDAI\ P.O. BOX 1031 GLEIYWOOD SPRINGS, COLORADO 81602 bradi ordanarchitect@ smail.com N \....$) .\ $ TABLE OF'CONTENTS PURPOSE AND SCOPE OF STI]DY PROPOSED CONSTRUCTION ..... SITE CONDITIONS... FMLD EXPLORATION SUBSURFACE CONDITIONS ...... FOUNDATION BEARING CONDITIONS DESIGN RECOMMENDATIONS ..................... FOUNDATIONS FOUNDATION AND RETAINING WALLS FLOOR SLABS UNDERDRAIN SYSTEM .............. SURFACE DRAINAGE LIMITATIONS FIGURE 1 - LOCATION OF DGLORATORY BORINGS FIGTIRE 2. LOGS OF EX?LORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4 and,5 - SWELL-CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS I 1 I 1 aL- .| Fl -2- a-J- -4- 5 5 5 Kumar & Associates, lnc. @ Project No. 24-7-587 PTJRPOSE AND SCOPE OF STUDY This report presents the results ofa subsoil study for a proposed shop/garage and accessory dwelling unit (ADU; to be located at 6533 County Road 214, Garfield County, Colorado. The project site is shown on Figure 1. The pu{pose of the study was to develop recommendations for the foundation design. The sfudy was conducted in accordance with our agreement for geotechnical engineering services to Jordan Architecture dated October 7,2024. 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 deterrrine 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 sfudy and presents our conclusions, design recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION The proposedbarn/garuge and ADU will be a two-story wood-frame structure with the garage and barn space on the ground floor and the ADU on the upper floor. Ground floor could be structural over crawlspace or slab-on-grade. Grading for the structure is assumed to be relatively minor with cut depths between about 2to 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 property was developed with a single-story residence and two outbuildings at the time of our field exploration- The ground surface was gently stoprng down to the south. There was evidence of minor cut and fiIl grading for the existing development. Vegetation consists of grass and weeds. FIELD EXPLORATION The field exploration for the project was conducted on November 27,2024. 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 kuck- mounted CME-45B drill rig. The borings were logged by a representative of Kumar & Associates,Inc. Kumar & Associates, Inc. @ ProJect No.2'l-7-587 -2- Samples of the subsoils were taken with l%-inch and 2-nchl.D. spoon samplers. The samplers were driven into the subsurface materials 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 density or consistency of the subsoils and hardness of the bedrock. Depths at which the samples were taken and the penetration resistance values are shovm 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 subsurface materials encountered below about Yzto I foot of fill mainly consist of medium dense, silty sand with scattered gravel to approximately 19 feet deep where hard sandstone bedrock was encountered to the maximum explored depth of 20 feet. A layer of stiff, sandy silt was encountered in Boring I from lz to 3 feet deep. 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, presented on Figures 4 and 5, indicate typically low to moderate compressibility under loading and low to moderate collapse potential when wetted. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at the time of drilling ond thc subsoils were slightly moist. FOUNDATION BEARING CONDITIONS The upper sand and silt soils encountered in the borings possess low bearing capacity and typically moderate compressibility potential under loading. The underlying sandstone bedrock possesses relatively high bearing capacity and typically low settlement potential. The proposed gatagelbam and ADU can be founded with spread footings bearing on the natural sand and silt soils with a risk of foundation settlement mainly if the bearing soils bccomc wcttcd. A lower settlement risk option would be to extend the bearing level down to the underlying sandstonc bedrock with a deep foundation system such as helical piers or micro-piles. provided below are recommendations for a spread footing foundation system. If reeommendations for a deen foundation system are desired we should be contacted to provide them. DESIGN RECOMMENDATIONS FOUNDATIONS 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 Kumar & Associates, lnc. @ Project No.24-7-587 a-J- natural soils with a risk of settlement if the bearing soils become wetted and precautions should be taken to keep the bearing soils dry. The design and construction criteria presented below should be observed for a spread footing foundation system. l) Footings placed on the soils should be designed for an allowable soil bearing 1,500 Based on experience, we expect initial settlement of constructed as discussed in this section 3) will be about I inch or less. Additional, post-construction settlement could occur if the bearing soils become wetted. The magnitude of additional settlement would depend on the depth and extent of additional wetting but could be on the order of I to lrA inches. The footings should have a minimum width of 20 inches for continuous walls and 2 feet for isolated pads. 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 Ltea. 2) 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 (if any) should also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining Walls" section of this rePort. 5) All existing fill, 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 ofthe geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FOUNDATION 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 55 pcf for backfill consisting of the on-site soils. Cantilevered retaining structures which are separate from the building and can be expected to deflect sufficiently to mobilize the futl 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 backfrll consisting of the on-site soils. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, traffrc, construction materials and equipment. Kumar & Associates, lnc. @ Project No.24-7-587 -4- 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 strucfure. An underdrain should be provided to prevent hydrostatic preisure buildup behind walls. Backfill should be placed in uniform lifts ond compactcd to at least 90% of the maxinrum standard Proctor density at a moisture content near optimum. Backfill placed in pavement and walkway areas should be compacted to at least 95%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 causc cxcessive lateral pressure on the wall. Some settlement of deep foundation wall backfill should be expected, cvcn if the material is placed conectly, and could rcsult in distress to facilities constructed on the backfill. 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 350 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 least 95Yo of the maximum standard Proctor density at a moisfure 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 ollow unrcstrained vertical movement. Floor slab control joints should be used to reduce damage due to shrinkagc 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 relatively well graded sand and gravel such as road base should be placed beneath slabs-on-grade for support. This material should consist of minus 2-nchaggregate with at least 50% retained on the No. 4 sieve and less than l2o/o passing the No. 200 sieve. A1l filImaterials for support of floor slabs should be compacted to at least 95Yo of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on-site granular soils dcvoid of vegetation, topsoil and oversized ruck. Kumar & Associates, lnc. o Project No. 2+7-587 5 UNDERDRAIN SYSTEM It is our understanding the proposed finished floor elevation at the lowest level is at or above the surrounding grade. Therefore, a foundation drain system is not required. It has been our experience in the areathatlocal 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 and wall drain system. A shallow crawlspace and. garage floor areas should not need to be protected with an underdrain with proper foundation wall bacldrll and surface grading. If the finished floor elevation of the proposed structure is revised to have a floor level below the surrounding grade, we should be contacted to provide recoflrmendations for an underdrain system. A11 earth retaining structures should be properly drained. SIIRFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at all times after the building has been completed: 1) Inundation ofthe foundation excavations andunderslab areas should be avoided dwing construction. 2) Exteriorbackfrll should be adjusted to near optimum moisture and compacted to at least 95%6 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 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 10 feet in paved areas. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy irrigation should be located at least l0 feet from foundation walls. LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area atthis 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 services do not include determining the presence, prevention or possibility of mold or other biological contaminants (MOBC) developing Kumar & Associates, lnc. @ Project No.2'l-7-587 -6- in the future. If the client is concerned about MOBC, then a professional in this special fiel<l 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 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 should provide continued consultation and field services during construction to review and monitor thc implcmcntation of our reconulcntlalions, and to veri$r 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 of excavations and foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer. Respectfu lly Submitted, Kumar & Associateg lnc. }r'rt tFT. ?aanaa.- James H. Parsons, P.E. Reviewed by: Steven L. JHP/kac (n 5222 Kumar & Associates, lnc. @ Prnioet iln 9d-?-EA7. l 'rY. E it I E:.41:JC 51 uR c I! 3 :iaa,!i c'oa,4ry'r EoAo 2/-4 ,ry \ryitness Corner N 1/16(s 89'2,1'15" "! 82'i I 16PL5276i3 6533 Pnan tll. 3 60 APPROXIMATE SCALE_FEET I 6l: ;,C:tS -i;il'lsL:l?j /o,:i.I :'-r.-tl- -c1:n s{o?rr-:r CO!'. r' Wo ter ter |i/e/l Yy'o ter Refer to D€toil Poge 2 of 2 5r;co l&oili,:i BORING T o r\t.\l)t l I -::ricist;5 BORING 1 ,}l ilt, IT the sltlrs-ii t: aF62!1 S*r:51:-::2 ffi.OaJcl.;:5 &Ir-- # d .+ i 63it!ty f Sign 24-7-587 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1 BORING 1 EL. 5654' BORING 2 EL. 5632' 0 0 17/12 WC=5.5 -2OO=79 8/12 tNC=12.7 DD= 1 03 5 15/12 1 4/12 WC=7.8 DD=97 5 l- trJ LrJ l! I-F(L L.Jo 10 2s/12 WC=4.2 -2OO=24 18/12 10 Ftrl LrJ aL I-F(L IJr:i 15 20/12 WC=7.7 DD= 1 O5 15 20 50/6 50/1 2A 24-7-587 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 e E E LEGEND n FILL: SILT AND SAND, SCATTERED GRAVEL, FIRM, MOIST, BROWN. SILT (ML); SANDY, VERY sTlFF, SLIGHTLY MolST, LIGHT BROWN SAND (SM); SILTY, SCATTERED GRAVEL, MEDIUM DENSE, SLIGHTLY MOIST, LIGHT BROWN. ffil L!i.:ii+l liii+:idl E:t-it'...l| SANDSTONE; HARD, SLIGHTLY MOIST, LIGHT BROWN. F i DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE. DRIVE SAMPLE, 1 3/B-INCH l.D. SPLIr SPOON STANDARD PENETRATION TEST .1"6 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 17 BLOWS OF A 140-POUND HAMMER "/ '' FALLTNG 50 tNcHES WERE REeUIRED To DRtvE THE SAMPLER 12 lNcHES. NOTES 1 THE EXPLORATORY BORINGS WERE DRILLED ON NOVEMBER 27,2024 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. 3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED. 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. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING 7. LABORATORY TEST RESULTS:wc = wATER CONTENT (%) (ASTM 02216); DD = DRY DENSITY (pct) (asru D22t6): -200= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM Dl140). Fig. 3Kumar & Associates LEGEND AND NOTES24-7-587 t $ I SAMPLE OF: Sllty Sond FROM: Boring 1 O 14' WC = 7.7 %, DD = tOS pcf i I I ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 1 l I I i I I I ! l h d i I I I I I l L I I I I I I i l I i i 2 0 j-z lll =a t-4 z.IF o3-oo anz.o()_g -10 APPUEO 24-7-587 Kumar & Associates SWELL.CONSOLIDATION TEST RESULTS Fig. 4 E SAMPLE OF: Silty Sond FROM: Boring 2 tO 2' WC = 12.7 %, DD = 103 pcf i ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETT]NG hrihK I i : i I J 1 0 )q j-1 L.l =a t-2 zIF !-soazotJ-4 -5 -6 t001 24-7-587 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 5 I(+'T Xumar & Associates, lnc.@ Geotechnical ard Materials Engineers and Environmerrtal Scientists TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No.24.7-587 SOIL TYPE Sandy Silt Silty Sand Silty Sand Silty Sand Silty Sand UNCONFINED COMPRESSIVE STRENGTH (osfl ATTERBERG LIMITS PLASTIC INDEX lolol LIQUID LIMIT t%l PERCENT PASSING NO, 200 stEvE 79 24 NATURAL DRY DENSIW GRAVEL SAND (%)(/"1 5.5 103 103 97 I NATURAL MOISTURE CONTENT M) 4.2 7.7 t2.7 7.8 SAMPLE LOCATION DEPTH tftl 2 9 1 4 2 4 BORING 1 2