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Home My WebLink AboutSubsoil Study for Foundation Design 02.12.2024l{3n Kuma & A*soclabs, lnc.@ Geotechnical and Materials Engineers and Environmental Scientists An Employsc OrvnGd Compony 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com www.kumarusa.com Oflfice Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE 5970 COUNTY ROAD 109 GARFIELD COUNTY, COLORADO PROJECT NO.23-7-705 FEBRUARY 12,2024 PREPARED FOR: TODD CHRISTMAN 5970 COUNTY ROAD 109 CARBONDALE, COLORADO 81623 todd@ unionpropertvcapital.com ',{\t $ R. N TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION SITE CONDITIONS -J- J a-J- -J- -4- -4- SUBSIDENCE POTENTIAL. FOI.INDATIONS .... FLOOR SLABS......: FIELD EXPLORATION SUBSURFACE CONDITIONS ...... DESIGN RECOMMENDATIONS ...... - 5 - 6- UNDERDRAIN SYSTEM.............. ..., 6 . SURFACE DRAINAGE ,,..7 . LIMITATIONS 7- FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - GRADATION TEST RESULTS TABLE 1 _ SUMMARY OF LABORATORY TEST RESULTS Kumar & Associates, lnc, @ Project No. 23-7-705 -3- PURPOSE AND SCOPE OF STUDY This report presents the results ofa subsoil study for a proposed residence to be located at 5970 County Road 109, Garfield County, 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 proposal for geotechnical engineering services to Todd Christman dated December 15, 2023. 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 reporl 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 an attached --- a below grade mechanical room. Ground floors will either be slab-on -grade or over craw the residence and slab in the garage and ADU. Gradi ng for the structure is assumed to be relatively minor with cut depths between about Z'to 10 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 desuibed above, we should be notified to re-evaluate the recommendations contained in this report. SITE CONDITIONS The lot was occupied with an existing residence which will be razed and the new residence constructed in its place. Vegetation consists of grass with trees and landscaping. The ground surface through most of the proposed building footprint has a gentle to moderate slope down toward the Crystal River which borders the lot on the northeast side. The ground surface wis covered in2to 3 inches of patchy snow. SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian Age Eagle Valley Evaporite underlies most of the lower Roaring Fork valley, including the subject site. These rocks are a sequence of gypsiferious shale, fine- Kumar & Associates, lnc. @ Project No. 23-7-705 -4- grained sandstone/siltstone, and limestone with some massive beds of gypsum. 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 of localized subsidence. During previous work in the arca, several broad subsidence areas and sinkholes have been observed. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the lower Roaring Fork River valley. No evidence of subsidence or sinkholes was observed on the property or 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 at the site throughout the service life of the structure, in our opinion is low, however the owner should be 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 January 23,2024. Three exploratory borings were drilled at the locations shown on Figure 1 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 and Associates. Samples of the subsoils were taken with a l3A rnch 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. In Boring l, below about 6 inches of topsoil, the subsoils consist of dense sandy gravel and cobbles with probable boulders (river alluvium) down to the explored depth of 3% feet. In Boring 2, below about 6 inches of topsoil, and in Boring 3, below about 6 inches of road base gravel and 6 inches of topsoil. The subsoils consist of about lYzto 2 feet of medium dense sandy gravel and Kumar &Associates, lnc, @ Project No, 23.7.705 -5- clay underlain by dense silty sandy gravel and cobbles with probable boulders (river alluvium) down to the maximum explored depths of 3 and 4 feet, respectively. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and boulders and drilling refusal was encountered in all three borings in the deposit. 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 I%-inch fraction) of the coarse granular subsoils are shown on Figure 3. 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. DESIGN RECOMMENDATIONS FOLINDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we recommend the buildings be founded with spread footings bearing on the natural granular soils. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural granular soils should be designed for an allowable bearing pressure of 3,000 psf. Based on experience, we expect settlement of footings designed;d'ffited as discussed in this section will be about I inch or less. 2) The footings should have a minimum width of_Ejnches for continuous walls and 2.feet-fot 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 3_6 inches below exterior grade is typically used in this atea. 4) Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least l0 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 45 pcf for the onsite sand and gravel soil as backfill. Kumar & Associates, lnc. @ Project No. 23-7-705 -6- All topsoil, clay soil, existing fill and any loose or disturbed soils should be removed and the footing bearing level extended down to the relatively dense natural granular soils. The exposed soils in footing area should then be moistened and compacted. 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 granular 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 well graded sand and gravel (such as road base) should be placed beneath interion slabs-on-grade for subgrade support. This material should consist of minus 2-inch aggregate with at least 50% retained on the No. 4 sieve and less than l2%o passing the No. 200 sieve. A minimum 4-inch layer of free draining gravel should be placed beneath the below grade mechanical room floor slab to facilitate drainage. This material should consist of minus 2-inch aggregate with at least 50Yo rctained on the No. 4 sieve and less than 2%o passing the No. 200 sieve. All fill materials for supporl of floor slabs should be compacted to at least 95o/o of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on-site granular soils or suitable imported granular fil1 devoid of vegetation, topsoil and oversized rock. L]NDERDRAIN SYSTEM 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 runoffcan create a perched condition. We recommend below-grade construction, such as retaining walls, crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain and wall drain system. The drains should consist of drainpipe placed in the bottom of the wall backfill surrounded above the invert level with free-draining granular material. The drain should be placed at each level of excavation and at least I foot below lowest adjacent finish grade and sloped at a minimum l%o to a suitable gravity outlet or drywell. Free-draining granular material used in the underdrain s) 6) Kumar & Associates, lnc, @ Project No. 23-7-705 -7 - system should contain less than 2o/o passingthe No. 200 sieve, less than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least l% feet deep. SURFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: l) Inundation of the 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 95o/o 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 6 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 finer graded soils to reduce surface water infiltration. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 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 i, 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 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 Kumar & Associates, lnc. o Project No. 23.7.705 -8- should provide continued consultation and field services during construction to review and monitor the implonentation of our recommendations, and to veriry 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, Kumsr & Asss!€iates, In*" David A. Noteboom, StaffEngineer Reviewed by: Steven L. Pawlak, SLP/kac Cc: Hinge Architects &es{@Jsp&ardqEts,q{s " e**il Kssst*& Acseeffi& Fne" a Fro,ssi Sls. t97-ffi N 15 0 APPROXIMATE SCALE_FEET 109 *TO COUNTY ROAD 12.20' \-- x-7 -7A5 Kumar & Associates LOCATION OF TXPLORATORY BORINGS Fig. 1 F I s F F I BORING 1 EL. 6,1 02' BORING 2 EL. 6,1 04' BORINO 3 EL. 6,1 00' 0 tr5 0 F LrJtdt! IrFo- Lrlo F Lrl LrJ LL I-F(L tdo 33/12 WC=5.6 *4=31 -2OO=23 26/6,1s/o 21/12 WC=11.1 *4=17 -2OO=34 25/2, 1o/o LEGEND NNt-v GRAVEL DRIVEWAY FILL; DENSE, MOIST/FROZEN, MIXED GRAY AND BROWN TOPSOTL; ORGANTC SANDY S|LT, SLIGHTLY CLAYEY WrrH SCATTERED GRAVEL, F|RM/FROZEN, MOIST, DARK BROWN. GRAVEL AND COBBLE (GM) SANDY, S|LTY, PROBABLE BOULDERS, DENSE, SLtcHTLy MO|ST, MIXED GRAY AND BROWN WITH RED. GRAVEL AND CLAY (Gc-cL); SANDY, SILTY, MEDIUM DENSE, MOIST, DARK BROWN MlX. DR|VE SAMP:E, 1 S/9-|NCH r.D. SPL|T SPOON STANDARD PENETRATTON TEST. 33/ 12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 33 BLOWS OF A 1 4O-POUND HAMMER FALTING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. PRACTICAL AUGER REFUSAL. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON JANUARY 23, 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 RESULTSI WC = WATER CONTENT (%) (ASTM D2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913); -200= PERCENTAGE PASSING No.200 SIEVE (ASIM 01140). i t 23-7 -7 05 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 6 I t00 90 EO 70 ao 50 40 30 20 10 o HYDROMETER ANALYSIS IIME REAOINGS HRS 7 HRS SIEVE ANALYSIS .1. -i -.-f .t -.-"j* -i i,,,i,:,,i,,,,:.':: ,:j:r.,::i:.;j-;:,f;l,t;,1--t,i,L.';',.t'itt.-;,i;,,,tt,t,i '-,j,'.,i'j,..,t,i o to 20 30 40 50 60 70 ao so 100 =b .300 r .500 .125 PARTICLES 1.18 2.O ILLIMETERS 152 DIAMETER OF INM CLAY TO SILT COBBLES GRAVEL 31 % SAND 16 % LIQUID LIMIT - PLASTICITY INDEX SAMPLE OF: Sllly Grovelly Sond SILT AND CLAY 23% FROM:Boringl@2' 2 & too 90 80 70 50 40 30 ao t0 0 to 20 30 40 50 60 70 80 90 ?b & .123 ARTICLES IN 2,O D OF CLAY TO SILT COBBLES GRAVEL 17 % SAND LIQUID LIMIT SAMPLE OF: GroYelly Cloy€y Sond 49% PLASTICITY INDEX SILT AND CLAY 34 % only lo lh6 FROM:BoringS@2'sompl6s which Iho losllng roport shqll nol bo r€producod, oxcopt ln full, wlthoul the wrlll€n opprovol of Kumor & Assoclol€s, lnc, Sleve onolysls t.sllng ls p.rformsd ln qccordonc€ wlth ASTM 06313, ASTM 07928, ASTM Cl36 ond,/or ASTM Dl140. SAND GRAVEL FINE MEDTUM lcornse FIN E COARSE HYDROMETER ANALYSIS HRS 7 HRS SIEVE ANALYSIS OPENINCS { iiiil i:lll - --t, ti,r,,tt ,i.t. ,t;,.j ,',,-i it,r tt-'i,,,--..,,1.,',t .,,,J ,, '''''\ SAND GRAVEL FI NE MEDTUM lcoansE FINE COARSE 23*7 -705 Kumar & Associates GRADATION TEST RISULTS Fig.3 ICA*iffift*trfffi$f i*"' *7 TABLE 1 SUMMARY OF LABORATORY TEST RESULTS No.23-7-705 SAMPT LOCATION noN AT LIMITS BORING tffl OEPTH r0l.1 NATURAL MOISTURE CONTENT NATURAL DRY DENSITY 16cll GRAVEL (:/"1 SAND Pl PERCENT PASSING NO, 200 stEVE to/"\ LIQUID LIMIT tr/^\ PLASTIC INDEX (osf) UNCONFINED COMPRESSIVE STRENGTH SOIL TYPE I 2 5.6 3l 46 Silty Gravelly Sand 3 2 1l.t 17 49 34 Gravelly Clayey Sand