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Home My WebLink AboutSubsoil Study for Foundation Design 03.26.19tcrttu": t{lffi&ls¡oe&s,hc. Gestechnical and Malerials Engineers aftl tnvironmenlal scbnt¡sb An Ernployea Otmed Cornpony 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com www.kumarusa.com Offìce Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit Coun$, Colorado RECEIVED OcT 2 2 2019 GARFIELD COUNTY COMMUNITY DEVELOPMENT SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED SHOP BUILDING 252 COUNTY ROAD 167 GARFIELD COUNTY, COT,ORADO PROJECT NO. 19-7-171 MARCH 26,2019 PREPARED FOR: CATTLE CREEKMILL}VORK ATTN: TODD MCCAlIIN 252 COUNTY ROAD 167 GLENWOOD SPRTNGS, COLORADO 81601 Todd úùtC attleCreekMillwork. com TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION SITE CONDITIONS SUBSIDENCE POTENTIAL FIELD EXPLORATION SUBSURFACE CONDITIONS FOTINDATION BEARING CONDITIONS DESIGN RECOMMENDATIONS FOUNDATIONS FOUNDATION AND RETAINING WALLS FLOOR SLABS LINDERDRAIN SYSTEM. SITE GRADING,................ SURFACE DRAINAGE............... LIMITATIONS FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4 - GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS 1 1 1 2- J. J -2- -1- Kumar & Associales, lnc.Project No. 19-7-'171 I /. PT'RPOSE AIÍD SCOPE OF STUDY This report presents the results of a subsoil study for a proposed shop building to be located at 252 Cornty Road 167, Garfield County, Colorado. The project site is shown on Figure 1. The purpose of the study was to develop recommendations for the foundation design. The study was conducted in accordance with our proposal for geotechnical engineering services to Cattle Creek Millwork dated March ll,20l9. 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 shop will be a 7,200 square foot, single-story structure. The structure will be a steel frame and metal skin with a slab-on-grade floor. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 5 feet. We assume relatively light to moderate 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 project site is currently developed with a wood frame building to the north and a metal building to the east of the proposed shop building. The area of the proposed shop is cunently a gravel surfaces parking/stotage arca. The ground surface is relatively flat and gently sloping across the site then slopes down at about 2honzantal to I vertical grade along the western and Kumar & Associates, lnc.Project No. 1S-7-171 -2- southem edges of the property. The steep slopes could be covered with push-out fill and are vegetated with mostly sparse grass and weeds. The area around the site is developed with light industrial, commercial and residential buildings. Coryell Road is west of the site and Coryell Ridge Road is south of the site. SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the site. These rocks are a seguence of gypsiferous shale, fine-grained sandstone and siltstone with some massive beds of gypsum and limestone. There is a possibility that massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the property. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can produce areas oflocalized subsidence. Sinkholes were not observed in the immediate area of the subject site. No evidence of cavities was encountered in the subsurface materials; however, the exploratory borings were relatively shallow, for foundation design only. Based on our present knowledge of the subsurface conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of future ground subsidence on the site throughout the service life of the proposed structure, in our opinion, is low; however, the owner should be made aware of the potential for sinkhole development. If further investigation of possible cavities in the bedrock below the site is desired, we should be contacted. FIELD EXPLORATION The field exploration for the project was conducted on Ma¡ch 20,2019. 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, lnc. Samples of the subsoils were taken with a l%inch LD. 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 ponetration tost 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 Kumar & Associates, lnc.Project No. 19.7-171 -J- 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 consistofabout Yztolt/zfeetofsilty, clayey, sandygravel fill overlyingnatural slightly silty, sandy gravel with cobbles and possible boulders. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and possible boulders and practical auger refusal was encountered at 12 feet in Boring 2. Laboratory testing performed on samples obtained from the borings included natural moisture content and gradation analyses. Results of gradation analyses performed on small diameter drive samples (minus llzinch fraction) of the coarse granular subsoils are shown on Figure 4. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at the time of drilling and the subsoils were slightly moist to moist. FOUNDATION BEARING CONDITIONS At assumed excavation depths, we expect the subgrade will consist of natural gravel soils. The natural gravel soils at the site possess moderate bearing capacity, relatively low settlement potential, and are considered competent bearing materials for the support of shallow foundations and slabs-on-grade provided the gravels remain undisturbed during construction. The existing fill is not considered suitable for the support of shallow foundations and slabs-on-grade, in its current condition, potential compressibility and uncertain density. There is also potential for the fill depth to increase along the top of the steep slope which should be further evaluated at the time of construction. DESIGN RECOMMENDATIONS FOLINDATIONS 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 granular soils. Kumar & Associates, lnc.Project No. 19-7-171 -4- 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 3,500 psf. Based on experience, \rye expect settlement of footings designed and constructed as discussed in this section will be about I inch orless. 2) The footings should have a minimum 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 area. 4) Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 10 feet. Foundation walls acting as retaining structures (if any) should also be designed to resist lateral earth pressures as discussed in thc "Foundation and Retaining Walls" section of this report. 5) All existing fill, topsoil and any loose or disturbed soils should be removed and the fboting bearing level extended down to the relatively dense natural granular soils. The footings should set back from the steep slope face aminimum horizontal distance of 8 feet. This could require the west perimeter footing to be deepened below the minimum frost depth. Thc cxposcd 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 (if any) which are laterally supported and can be expected to undergo only a slight amount of dcflection 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 granular soils. Cantilevsrcd rctaining structures which are separate from the structure and can be expected to deflect sufficiently to mobilize the full active earth pressure Kumar & Associates, lnc.Project No, 19.7-171 -5- condition should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 35 pcf for backfill consisting of the on-site granular soils. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, traffrc, 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 95o/o of the maximum standard Proctor density at a moisture content near optimum. 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 backfiil 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. 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 0.50. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 300 pcf. The coefficient of füction and passive pressure values recommended above assume ultimate soil strength. Suitable factors of safety should be included in the design to lirnit 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 a granular material compacted to at least 95o/o of the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS The natural on-site soils, exclusive of existing fill, are suitable to support lightly to moderately loaded slab-on-grade construction. The existing fill can support the slab-on-grade after it has been excavated and replaced, then compacted to 95o/o of the standard Proctor. To reduce the Kumar & Associates, lnc.Projecl No, 1g-7-171 -6- 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 relatively well graded sand and gravel should be placed beneath interior slabs for support. This material should consist of minus 2-inch aggregate with at least 50% retained on the No. 4 sieve and less than l2o/opassing the No. 200 sieve. All fill materials fcrr support of floor slabs should be compacted to at leastgSYo of maximum standard Proctor density at a moisture content ncar optimum. Required fill can consist of the on- site granular soils devoid of vegetation, topsoil and oversized rock. 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 bscn 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 and wall drain system. If the finished floor elevation of the proposed structure is revised to have a floor level below the surrounding glade, we should be contacted to provide recommendations for an underdrain system. All earth retaining structures should be properly drained. SITE GRADING The risk of construction-induced slope instability at the site appears low provided the building is located above the steep slope as planned and cut and fill depths are limited. We assume cut depths tbr tbundation construction will not exceed 5 feet. Fills should be limited to about 5 feet and not extend onto the steep downslope along the west and south sides of the building. Embankment fills should be compacted to at leastglo/o of the maximum standard Proctor clensity Kumar & Associates, lnc,Projec{ No. 19-7-171 -7 - near optimum moisture content. Prior to fill placement, the subgrade should be carefully prepared by removing all vegetation and topsoil and compacting to at least95o/o of the maximum standard Proctor density. The filI should be benched into slopes that exceed 20% grade. Permanent unretained cut and fill slopes should be graded at2hoizontal to 1 vertical or flatter and protected against erosion by revegetation or other means. This office should review site grading plans for the project prior to construction. SURFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at all times after the structure 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 95%o of the maximum standard Proctor density in pavement and slab areas and to at least 90o/o 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 6 inches in the first 10 feet in unpaved areas and a minimum slope of 2Yz inches in the first l0 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 5 feet from foundation walls. LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this arcaat 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 exploratoryborings drilled excavated at the locations indicated on Figure l, 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 Kumar & Associates, lnc.Project No. 19-7-171 -8- (MOBC) developing in the fi¡ture. If the client is concernecl about MOBC, then a professional in this special field of pracfice 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 pu{poses. 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 implementation of our recomrnendations, and to verify 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. Respectfully Submitted, Kumar & Associates, Inc. Shane J. Robat, P.E. Project Manager Reviewed by: Steven L. Pawlak, SJR/kac f $ä3r I Kumar & Assocíates, lnc.Project No. 19-7-171 Ë: w :v l 2ÉË'BoRtNc i\ {- {:nr: to \1 -ì \ \ 1, t \\\ i\\\ \ ( ø {t I ,\\\\i I I I I 1," ,|: 1,. ì \t I I I ì \ I\\I \\\\it Ih\ì\\11 \ \\\\1\\\\\\\\\\)\\t\t\\t\\\\ \\\I \I\11T!Tì ,} \ ) \\\\ [1 \t\r\\\\1t\r\liiTl\\\lt\\\ t!ir1ïÌTri,ril\ \vÌ Irjl\r,l tillntr\\\ I ä ',\ \ø t 20 APPROXIMATE SCALE-FEET \ f,¡ 19-7-171 Kumar & Associates LOCATION OT TXPLORATORY BORINGS Fig. 1 t ã ùI I WC=2.7 +4=50 -200=1 1 BORING 1 EL. 5976.5'BORING 2 EL. 5975' 0 0 35/12 46/12 5 73/ 10 46/12 5 t-l¡l l¡JLL I-FfL l¿,Õ 10 48/t2 50/6 10 -F-(L t¡lo 15 32/12 15 20 20 WC= f .6 +4=57 -200= 1 0 19-7-171 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 I Í ' LEGEND- m W FA i FILL GRAVEL, SILTY, SANDY, CLAYEY, BROWN, MEDIUM DENSE, MOIST. ÇRAVEL (Gry-GM); SANDY, SL¡G|{TLY SILTY, WITH COBBLES ANÐ BoULDERS, BRowN, DENSE TO VERY DENSE, SLIGI{TLY MOIST. DRTVE SAMPLE, 1 318-tNCH t.D. SPLIT SPOON. STANDARD pENETRATTON TEST .1Ã,712 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 35 BL0WS 0F A 140-POUND HAMMER--l'- FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. I enacrrcnL AUcER DRTLLTNG REFUsAL. NOTES THE EXPLORATORY BOR'NGS WERE DRILLED ON MARCH 20, 20'19 WIÎH 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 DR¡LLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216);+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D A22); -2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1140). 19-7 -171 Kumar & Associates LTGEND AND NOTES Fig. 3 e HYDROTII'ER ANALYSIS--- --riüÊTãorxæ 14 ltffi 7 HFS5 llx t5 ¡tN 30!lx tgvrx ¡ltx I I I I / I I ¡ I I ¡ ¡ I I It / I ---1 I I I I I I I I I _*1- - -1-- I I I {r-2 SAND GRAVEL FINE MEDIUM FINE COARSE SIEVE ANALYSIS u,3. 2 ø Ê Eñ too 90 80 7Q ¡o 30 € s0 20 to o o to 20 lo ao s 30 70 & t0 = Ë E Ë OF IN CLAY TO SILT COBBLES GRAVEL 50 X SAND 59 X LIQUID LIMIT pLASTICtTy tNDEx SAMPLE 0F: Sllghtly Sllly Sondy Grovel SILT AND Ct¡Y 11 X FROM: Eorfng I e 2.5' ond 5'(Comblned) 3 Þ B F tæ e0 ao 7ö ao s & 50 20 to HYDROMEIER ANALYSIS 5t x0^n0 sERc¡SOUATE I ¡/ I I I 1 I I I I I ¡ I I I /I I I I /I I Il'--I i ,*.,1---l I ¡ t SAND F'NE MEDIUM COARSE FINE o to 20 30 4 $ 80 70 co e0 ã E E Ë SIEVE ANAIYSIS to0 DIAMETER OF INM CI-AY TO SILT GRAVEL COARSE COBBLES GRAVEL 57 % SAND 53 UQUIO LIMIT SAMPLE OF: Sllghtly Stlly Sondy Grovet % PI¡STICITY INDEX SILÏ AND CI¡Y IO X FROI{: 8orh9 2 O 2,5' ond 5' (0omblned) lh.¡. lalt Erult¡ opÞly only lo lhcromplo! whlôh w.E l.drd, lh.Llllñt rporl lhsll nol b. hþþduc.d,dccpt ln lull. rlthoul th. writla¡oppruydl ol l(uñor & A!¡dlot.r, tñc,Sl.v. oñolyrlr l.lllno t. Þ.rtom.d lñoccordonco wltò ^Sftl D¿22, ASil Cl¡6sndlor ASll¡ 0ll¡ll¡. 19-7-17 1 Kumar & Associates GRADATION TEST RESULTS Fig. 4 l(+rl.u.w, ¡¡fs.Geotechnical and Materials Engineersand Environmental Scientistskumarusa.comTABLE 1SUMMARY OF LABORATOHV TEST RESULTSNo.19-7-171SOIL TYPESlightly Silty Sandy GravelSlightly Silty Sandy Gravel{psf}UNCONFINEDCOMPRESSIVESIRENGTHPLASTICINDEXg.lHàLrourD t_MnPERCEÀIÎPASSING NO.200 srEvEII3910335057NATURALDRYDENSTfYl'/òSANDVrlGRAVELNATURALùIOISTURECONTENTBORlNGLOCATIONDEPTH2.71.62Yz and 5combined2Yz and 5combined12