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Home My WebLink AboutSubsoils Report for Foundation DesignI (tA f;,ffilfi'ffifflEHni'*'i *"' An Employcc Owncd Compony 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com www.kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado SUBSOIL STT'DY FOR FOTINDATION DESIGN PROPOSED LOG HOUSE 6534 COTJNTY ROAD 331 GARFIELD COUNTY, COLORADO PROJECT NO.24-7-223 JUNE 5,2024 PREPARED FOR: MIKE KITE 6534 COTJNTY ROAD 331 srLT, coLoRADO 81652 mike.kite2@aol.com $s rllf Pntstr TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY....... PROPOSED CONSTRUCTION SITE CONDITIONS FIELD EXPLORATION SUBSURFACE CONDITIONS FOUNDATION BEARING CONDITIONS.. DESIGN RECOMMENDATIONS..................... FOUNDATIONS......... FOUNDATION AND RETAINING WALLS FLOOR SLABS TINDERDRAIN SYSTEM SIiRFACE DR ATNAGE ......... LIMITATIONS FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4 and 5 - SWELL-CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS I -1- 1 I l$r ,r\.rr rf',\ wi 1 a -3- -J- -4- -J- -6- -6- 1 i '4; lF'fr' t'1 r,ilr. : *df # t O!..* lub rtlt- r 'l;r*r,q{t, llr "jJlart, 5 rC' d'i4 x4r,$ ,[ ff Kumar & Associates, lnc. o Project No. 24-7-223 PURPOSE AND SCOPE OF STUDY This report presents the results ofa subsurface study for a proposed log house to be located at 6534 County Road 331, Garfield County, Colorado. The project site is shown on Figure 1. The purpose of the study was to develop recommendations for foundation design. The study was conducted in accordance with our agreement for geotechnical engineering services to Mike Kite, dated April 2,2024. A field exploration program consisting of exploratory borings was conducted to obtain information on subsurface conditions. Samples of the subsoils and bedrock obtained during the field exploration were tested in the laboratory to determine 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 At the time of our study, design plans for the residence had not been developed. The building is proposed in the area roughly between the exploratory boring locations shown on Figure 1. We assume excavation for the building will have a maximum cut depth up to about 6 feet below the existing ground surface. For the purpose of our analysis, foundation loadings for the structure were assumed to be relatively light to moderate and typical of the proposed type of construction. If building location, grading or loading information are significantly different than described, we should be notified to re-evaluate the recommendations presented in this report. SITE CONDITIONS The subject site was developed with a metal shop and two small storage outbuildings at the time of our study. The ground surface is sloping down to the south at grades estimated at between 5 and 10 percent. Vegetation consists ofjuniper, sagebrush, grass and weeds. There was evidence of minor grading for the existing development. Sandstone bedrock was visible on the ground surface approximately 50 feet north of the proposed building area. FIELD EXPLORATION The field exploration for the project was conducted on April 9, 2024. Two exploratory borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. The borings were advanced with a 4-inch diameter continuous flight auger powered by a truck- mounted CME-458 drill rig and logged by a representative of Kumar & Associates, Inc. Kumar & Associates, lnc. @ Project No. 24-7-223 .| Samples of the subsoils and bedrock were taken with a 2-inch LD. spoon sampler. The sampler was 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-1586. 'l'he 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 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. Below aboutYz foot of organic topsoil, the subsoils consist of stiff to hard, sandy clay with rock fragments. At depths of about 5 feet in Boring I and 8 feet in Boring 2 claystone bedrock was encountered. A layer of sandstone was encountered in Boring 2 from about 4 to 8 feet deep between the clay and claystone. The clay soil and claystone bedrock can possess an expansion potential when wetted. Laboratory testing performed on samples obtained during the field exploration included natural moishtre content and density and grain size analyses. Swell-consolidation testing was performed on relatively undisturbed drive samples of the clay subsoils and claystone bedrock. The sandstone was too hard for undisturbed sample testing. The swell-consolidation test results, presented on Figures 4 and 5, indicate low compressibility under relatively light surcharge loading and a nil to moderate expansion potential when wetted under a constant light surcharge. 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. FOIJNDATION BEARING CONDITIONS The clay soils and claystone bedrock encountered at the site are expansive. Shallow foundations placed on the expansive soils similar to those encountered at this site can experience movement causing structural distress if the clay or claystone is subjected to changes in moisture content. A drilled pier foundation can be used to penetrate the expansive materials to place the bottom of the piers in a zone of relatively stable moisture condition and make it possible to load the piers sufficientiy to resist upiift movements. Using a picr foundation, cach column is supported on a ^:--l^ l-:ll^l -:^- ^-l rL^ L--illi-^^ ---^11- ^-^ f^----l-l l- 1---,--- ---,-,--,L-t t, : -fsilrBrtr utllrnLl PrEr arru urs uurruurB wdils ars ruullugu uil Braug ugaills supputtgu uy a sctle$ ul piers. Loads applied to the piers are transmitted to the bedrock partially through peripheral shear stresses and partially through end bearing pressure. In addition to their ability to reduce differential movements caused by expansive materials, straight-shaft piers have the advantage of providing relatively high supporting capacity and should experierue a relativuly slrall auruult u.l movement. Spread footings placed on sandstone bedrock encountered at Boring 2 may be feasible for foundation support. The feasibility could be evaluated before excavation down to bedrock such as with exploratory pits. Kumar & Associates, lnc. @ Project No. 24-7-223 a-J- DESIGN R-ECOMMENDATIONS FOTINDATIONS Based on the expansive clay and claystone data obtained during the field and laboratory studies, we recommend straight-shaft piers drilled into the claystone bedrock be used to support the proposed structure. The design and construction criteria presented below should be observed for a straight-shaft pier foundation system: 1) The piers should be designed for an allowable end bearing pressure of 30,000 psf and an allowable skin friction value of 3,000 psf for that portion of the pier in bedrock. 2) Piers should also be designed for a minimum dead load pressure of 15,000 psf based on pier end area only. If the minimum dead load requirement cannot be achieved, the pier length should be extended beyond the minimum penetration to make up the dead load deficit. This can be accomplished by assuming one-half the allowable skin friction value given above acts in the direction to resist uplift. 3) Uplift on the piers from structural loading can be resisted by utilizing 75o/o of the allowable skin friction value plus an allowance for the weight of the pier. 4) Piers should penetrate at least 5 pier diameters into the bedrock. A minimum penetration of 10 feet into the bedrock and a minimum pier length of 20 feet are recommended. 5) Piers should be designed to resist lateral loads assuming a modulus of horizontal subgrade reaction of 50 tcf in the clay soils and a modulus of horizontal subgrade reaction of 200 tcf in the bedrock. The modulus values given are for a long, 1-foot-wide pier and must be corrected for pier size. 6) Piers should be reinforced their fuIl length with one #5 reinforcing rod for each 14 inches of pier perimeter (minimum of 3) to resist tension created by the swelling materials. 7) A 4-inch void form should be provided beneath grade beams to prevent the swelling soil and rock from exerting uplift forces on the grade beams and to concentrate pier loadings. A void form should also be provided beneath pier caps. 8) Concrete utilized in the piers should be a fluid mix with sufficient slump so that concrete will fill the void between the reinforcing steel and the pier hole. We recommend a slump in the range of 7 to 9 inches. The pier holes should be concreted the same day they are drilled' crete. The9) Pier holes should be properly cleaned prior to the placement of con drilling contractor should mobilize equipment of sufficient size to effectively drill through possible coarse soils and cemented bedrock zones. 10) Although free water was not encountered in the borings drilled at the site, some seepage in the pier holes may be encountered during drilling. Dewatering Kumar & Associates, lnc. o Project No. 24-7-223 -4- equipment may be required to reduce water infiltration into the pier holes. If water cannot be removed prior to placement of concrete, the tremie method should be used after the hole has been cleaned of spoil. In no casc should concrete free fall into more than 3 inches of water. l1) Care should be taken to prevent the forming of mushroom-shaped tops of the piers which can increase uplift force on the piers from swelling soils. 12) A representative ofthe geotechnical engineer should observe pier drilling operations on a full-time basis. FOTINDATION 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 65 pcf for backfill consisting of the on-site soils and 50 pcf tbr backfill consisting of imported granular materials. Cantilevered retaining structures 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 55 pcf for backfill consisting of the on-site soils and 45 pcf for backfill consisting of imported granular materials. 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 90Yo of the maximum standard Proctor density at a moisture content slightly above optimum. Backfill placed in pavement areas should be compacted to at least 95Yo 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. We recommend imnnrfed orenrrler snilc f^r hqnlrfillino fnrrnrlofinn rrrollc onr{ rofainina ofnrnfrrrao___'f "_--- vtqrrJ eus rvtslrrruS \tlr uvlurvrt because their use results in lower lateral earth pressures and the backfill will help improve the subsurface drainage. Subsurface drainage recommendations are discussed in more detail in the "Underdrain System" section of this report. Imported granular wall backfill should contain less than25oh passing the No. 200 sieve and have a maximum size of 6 inches. Granular materials should be placed to within 2 feet of the ground surface and extend to at least 3 feet outside the wall and to an envelope defined as a line sloped up from the base of the wall at an angle of at Kumar & Associates, lnc. @ Project No. 24-7-223 5 least 30 degrees from vertical. At least the upper 2 feet of the wall backfill should be a relatively impervious on-site soil or a pavement structure should be provided to reduce surface water infiltration into the backfill. Shallow spread footings may be used for support of retaining walls separate from the residence, provided some differential movement and distress can be tolerated. Footings should be sized for a maximum allowable bearing pressure of 2,000 psf for bearing on the clay soil and 4,000 psf for bearing on the bedrock. The lateral resistance of 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 0.35. Passive pressure 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 moisture content near optimum. FLOOR SLABS Floor slabs present a problem where expansive materials are present near floor slab elevation because sufficient dead load cannot be imposed on them to resist the uplift pressure generated when the materials are wetted and expand. We recommend that structural floors with crawlspace below be used for all floors in the building that will be sensitive to upward movement. Slab-on-grade construction could be used in the garage area provided the risk of distress is understood by the owner and mitigation measures are taken to limit potential movement and distress. We recommend placing at least 3 feet of CDOT Class 6 base course as structural fill below floor slabs to help mitigate slab movement due to expansive soils. To reduce the effects of some differential movement, nonstructural floor slabs should be separated from all bearing walls, columns and partition walls with expansion joints which allow unrestrained vertical movement. Interior non-bearing partitions resting on floor slabs should be provided with a slip joint at the bottom of the wall so that, if the slab moves, the movement cannot be transmitted to the upper structure. This detail is also important for wallboards, stairways and door frames. Slip joints which allow at least llrinches of vertical movement are recommended. Floor slab control joints should be used to reduce damage due to shrinkage cracking. Joint spacing and slab reinforcement should be established by the designer based on experience and the intended slab use. Required fill placed beneath slab areas should consist of imported granular material, excluding topsoil and oversized rocks. The suitability of structural fill materials should be evaluated by the geotechnical engineer prior to placement. The filI should be spread in thin horizontal lifts, Kumar & Associates, lnc. o Project No.2#7-223 -6- adjusted to at or above optimum moisfure content, and compacted to 95% of the maximum standard Proctor density. All vegetation, topsoil and loose or disturbed soil should be removed prior to filIplacement. The above recommendations will not prevent slab heave if tho expansive soils underlying slabs- on-grade become wet. However, the recommendations will reduce the effects if slab heave occtus. All plumbing lines should be pressure tested before backfilling to help reduce the potential for wetting. UNDERDRAIN SYSTEM Although groundwater was not encountered during our exploration, it has been our experience in the area and where clay soils are present and bedrock is shallow, that local perched groundwater may develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched condition. Therefore, we recommend below-grade construction, such as crawlspace and basement areas, be protected from wetting by an underdrain system. The drain should also act to prevent buildup of hydrostatic pressures behind foundation walls. The underdrain system should consist of rigid perforated PVC drainpipe surrounded by free- draining granular material placed at the bottom of the wall backfill. The drain lines should be placed at each level of excavation and at least I foot below lowest adjacent finish grade, and sloped at a minimum%o/o grade to a suitable gravity outlet. Free-draining granular material used in the drain system should consist of minus 2-inch aggregate with less than 50o/o passing the No. 4 sieve and less than2%o passing the No. 200 sieve. The drain gravel should be at least 2 feet deep and covered with filter fabric. An impervious membrane such as 20 or 30 mil PVC (pond liner type material) should be placed beneath the drain gravel in a trough shape and attached to the foundation wall with mastic to contain the drain water. This is very important where void form is used since it can act as a conduit for water to enter the crawlspace and under slab areas. SURFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at all times after the residence has been complctcd: 1) Excessive wetting or drying of the foundation excavations and underslab areas should be avoided during eonstruction. Drying eould increase the expansion potential of the clay soils and claystonc. 2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95% of thc maximum standard Proctor density in pavement and slab areas and to at least 90Yo of the maximum standard Proctor density in landscape areas. Free-draining wall backfill should be covered with filter fabric and capped with about 2 feet of the on-site finer-graded soils to reduce surface water infiltration. 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 Kumar & Associates, lnc. @ Project No. 24-7-223 -7 - 4) 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. Roof downspouts and drains should discharge well beyond the limits of all backfill. Landscaping which requires regular heavy irrigation, such as sod, and lawn sprinkler heads should be located at least 10 feet from foundation walls. s) LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this areaat 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 &illed 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 (MOBC) developing in the future. If the client is concerned 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 to be different from those described in this report, we should be notified at once so 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 implementation of our recommendations, and to veriff that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications of 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. Sincerely, Kumar & Associates, lnc. James H. Parsons, P.E. Reviewed by: s'h*/.Q*tL Steven L. Pawlak, P.E JHPlkac tL / ft 58669 Kumar & Associates, lnc. @ Project No.24-7-223 .r b 'rqt}a P V,,I ?, t- . t.ry B ir -,IF ."*!. tv 2$' ri si{g , .tL Y tt"- *&$+F {*E,- oa 'Tr i i"r ,,]i --4-lrl{ l+>'-. \i> .. -la' tt: - /.ltr o.-U t#:s ; iO o oE Fz loO { rO lr)(o t kt \" -.'l7 .(/:, ,,r'- &;n 6,i..F *',,'1t )' lJ J () (n oF Foz. FO NN I It- I$N ao .qooao od L(5 E)Y U1Oz. Eo@ E.oF EoJLX lfJ 14o z.IF (JoJ O) l! E I t BORING 1 BORING 2 0 0 13/12 WC=7.1 DD=l02 -2OO=40 37/12 WC=7.5 DD=1 1 9 t-tdtd LL I-F(L Lrlo 5 41/12 WC= 1 5.0 DD=1 1 0 35/3,15/o 5 FtJtilL! I-F(L TJo 10 50/5 WC=8.5 DD=12Q eo/12 WC= 1 0.0 DD=122 l0 24-7-223 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 LEGEND TOPSOIL; ORGANIC SANDY SILT WITH ROOTS, FIRM, SLIGHTLY MOIST, LIGHT BROWN TO MEDIUM BROWN. CLAY (CL); SANDY TO VERY CLAYEY SAND, WITH SCATTERED BEDROCK FRAGMENTS, VERY STIFF TO HARD, SLIGHTLY MOIST TO MOIST, BROWN. SANDSTONE BEDROCK, VERY HARD, SLIGHTLY MOIST, LIGHT GRAY. CLAYSTONE BEDROCK, VERY HARD, SLIGHTLY MOIST, RED-BROWN. DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE. 1 q 71 2 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 1 3 BLOWS OF A 1 40-POUND HAMMER.-,'- FALLING 30 INCHES WERE REQUIRED To DRIVE THE SAMPLER 12 INCHES. NOTES 1 THE EXPLORATORY BORINGS WERE DRILLED ON APRIL 9, 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 NOT MEASURED AND THE LOGS OF TIIE 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 WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D2216); DD = DRY DENSITY (PCt) (ASTU D2216)I _2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM Dl140). 24-7-223 Kumar & Associates LEGEND AND NOTES Fig. 3 E I SAMPLE OF: Sondy Cloy FROM:Boringl@4' WC = 15,0 %, DD = 110 pcf ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE OUE TO WETTING JJ lrJ =tt1 I z.o F o =otnzoc) ;s JJ lrJ =a I z.o F o =oazoo 1 0 -1 -2 -5 -4 5 4 3 2 1 0 -'l -2 SAMPLE OF: Cloystone Bedrock FROM:Boringl@9' WC = 8.5 %, DD = 120 pcf ln EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 24-7 -223 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4 SAMPLE OF: Sondy Cloy FROM:Boring2@2' WC = 7.3 %, DD = 119 pcf Xurur dnd bsoclotaa. lnc. Srall Cdrollddtlon tctlng prfomrd ln @cordonc. wlth ASTV 0-+54€. lo EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 5 4 5 ;s J^ )Z lrJ =a ll z (J tr 3ooaz.oo_1 -2 -3 -4 t.0 APPLIED PRESSURE - KSF 10 24-7 -223 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 5 E a =I I l(tA Kumal & Associates, lnc.' Geotechnical and Materials Engineers and Environmental Scientists TABLE 1 SUMMARY OF LABORATORY TEST RESULTS SOIL TYPE Very Clayey Sand Sandy Clay Claystone Bedrock Sandy Clay Claystone Bedrock losfl UNCONFINED COMPRESSIVE STRENGTH lVol PLASTIC INDEX ATTERBERG LIMITS LIQUID LIMIT lo/.1 PERCENT PASSING NO. 2O() SIEVE 40 SAND vt GRADATION (%) GRAVEL 102 lI0 t20 119 r22 (ocfl NATURAL DRY DENS]IY lohl NATURAL MOISTURE CONTENT I7 15.0 8.3 t.J 10.0 2 4 9 2 9 {ft1 DEPTH SAMPLE LOCATION BORING I 2 No.24'7-223