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Home My WebLink AboutSubsoils ReportlGrtHÏ,ffil[',i#fÉ:in'1'Êü**' An Employcc Owncd Compony 5020 County Road 154 Glenwood Springs, CO 8l 601 phone: (970) 945-7988 fax: (970) 945-8454 email : kaglenwood@kumarusa.com wwwkumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 256, TRONBRTDGE RIVER VISTA GARFIELD COUNTY, COLORADO PROJECT NO.21-7-480 JUNE 29,2021 PREPARED FOR: SCIB, LLC --'--ATTN: LUKE GOSDA 0115 BOOMERANG ROAD, SUrTE 52018 ASPEN, COLORADO 81611 TABLE OF CONTENTS PURPOSE AND SCOPE OI. S'I'UDY .. BACKGROUND INFORMATION PROPOSED CONSTRUCTION SITE CONDITIONS.. SUBSIDENCE POTENTIAL... FIELD EXPLORATION... SUBSURFACE CONDITIONS FOUNDATION BEARING CONDITIONS .. DESIGN RECOMMENDATIONS .................... FOUNDATIONS FOUNDATION AND RETAINING V/ALLS NONSTRUCTURAL FLOOR SLABS UNDERDRAIN SYSTEM ............. SITE GRADING SURFACE DRAINAGE LIMITATIONS FIGURE 1 - LOCATION OF EXPLORATORY BORING FIGURE 2 - LOG OF EXPLORATORY BORTNG FIGURE 3 - GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS I-z-- a-z-- 2- a--l- J 4 4 5 6 6 6 1 -8- 1 1 1 Kumar & Associates, lnc, o Project No, 21.7.480 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot256,Ironbridge, River Vista, 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 agreement for geotechnical engineering services to SCIB, LLC dated lll4ay 25,2021. A field exploration program consisting of an exploratory boring 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 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. BACKGROUND INFORMATION The proposed residence is located in the existing Ironbridge development. Hepworth-Pawlak Geotechnical, Inc. (now Kumar & Associates) previously conducted subsurface exploration and geotechnical evaluation for the development of Villas North and Villas South parcels, Job No. 105 115-6, report dated September 14,2005, and performed observation and testing services during the infrastructure construction, Job No. 106 0367, between April 2006 and April 2007. The information provided in these previous reports has been considered in the current study of Lot256. PROPOSED CONSTRUCTION At the time of our study, design plans for the residence had not been developed. The residence will likely be a one or two-story, wood-frame structure with structural slab foundation and no basement or crawlspace. Grading for the structure is assumed to be relatively minor with cut depths between about 2 to 3 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. Kumar & Associates, lnc. @ Project No. 2'l-7-480 -2- SITE CONDITIONS Lot256 is bordered on the east by River Vista, and on the west by the Ironbridge Golf Course. The lot was vacant at the time of our field exploration. Vegetation consists of grass and weeds with some sage brush. The lot slopes gently down to the west through most of the building envelope then steeply down in the western part about 5 feet to the adjacent golf course. River Vista is on a fill bench made for residence construction that was placed during the subdivision development in 2006 to 2007 . SUBSIDENCE POTENTIAL Eagle Valley Evaporite underlies the project area which is known to be associated with sinkholes and localized ground subsidence in the Roaring Fork Valley. A sinkhole opened in the cart storage parking lot located east of the Pro Shop and north of the Villas South parcel in January 2005. Irregular surface features were not observed in the Villas South parcel that could indicate an unusual risk of future ground subsidence. Localized variable depths of debris fan soils which could indicate ground subsidence were generally not encountered by the previous September 14, 2005 geotechnical study in the Villas South parcel. The subsurface exploration performed in the area of the proposed residence on Lot 256 did not encounter voids. In our opinion, the risk of future ground subsidence on Lot 256 throughout the service life of the proposed residence is low and similar to other areas of the Roaring Fork Valley where there have not been indications of ground subsidence, however, the owner should be made aware of the potential for sinkhole development. If ftirther 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 June 1l,202L One exploratory boring was drilled at the location shown on Figure 1 to evaluate the subsurface conditions. The boring was advanced with 4-inch diameter continuous flight augers powered by a truck-mountecl CME- 458 drill rig. The boring was logged by a representative of Kumar & Associates, Inc. Samples of the subsoils were taken with l% inch and 2-inch LD. spoon samplers. The samplers were 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 lvhich the samplcs wcrc takcn and thc pcnctration rcsistancc values are slrown ou the Log of Exploratory Boring, Figure 2. The samples were returned to our laboratory tor review by the project engineer and testing. Kumar & Associates, lnc. o Project No. 21.7.480 -3- SUBSURFACE CONDITIONS A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. Below about a 6-inch root zone, the subsoils consist of very stiff to dense, gravelly sandy silt fill down to a depth of about 15 feet. This was underlain by medium dense, slightly gravelly sand and silt alluvial fan deposits down to about 20 feet where medium dense, silty sand and gravel alluvial fan deposits were encountered down to about 3l/z feet. This was underlain by dense, slightly silty sandy river gravel and cobble alluvium to the drilled depth of 41 feet. Drilling in the coarse granular soils with auger equipment was difficult due to the cobbles and possible boulders. Laboratory testing performed on samples obtained from the boring included natural moisture content and density, and gradation analyses. Results of gradation analyses performed on a sample of the more granular soils (minus I%-inch fraction) are presented on Figure 3. The laboratory testing is summarized in Table 1. No free water was encountered in the boring at the time of drilling and the subsoils were slightly moist to moist. FOUNDATION BEARING CONDITIONS The upper 15 feet of soils encountered in the boring consist of fill placed mainly in 2006 as part of the subdivision development. The field penetration tests and laboratory tests performed for the current study, and review of the field density tests performed during the fill construction indicate the structural fill was placed and compacted to the project specified minimum 95% of standard Proctor density. Alluvial fan soils which tend to collapse (settle under constant load) when wetted were encountered below the fill. The amount of settlement will depend on the thickness of the compressible soils due to potential collapse when wetted, and compression of the wetted soils following construction. Relatively deep structural fill as encountered will also have some potential for long-term settlement but should be significantly less than the alluvial fan deposits. Proper grading, drainage and compaction as presented below in the Surface Drainage section will help to keep the subsoils dry and reduce the settlement risks. A heavily reinforced structural slab or post-tensioned slab foundation designed for significant differential settlements is recommended for the building support. As an alternative, a deep foundation that extends down into the underlying dense, river gravel alluvium could be used to reduce the building settlement risk. Kumar & Associates, lnc, o Project No, 21-7.480 -4- DESIGN RECOMMENDATIONS FOUNDATIONS Consiclering the subsurface conclitions encountered in the exploratory boring and the nature of the proposed constmction, we recommend the building be founded with a heavily reinforced structural slab or post-tensioned slab foundation bearing on at least 15 feet of the existing compacted structural fill. If a deep foundation system is considered for building support, we should be contacted for additional recommendations. The design and construction criteria presented below should be observed for a heavily reinforced structural slab or post-tensioned slab f'oundation system. 1) A heavily reinforced structural slab or post-tensioned slab placed on compacted structural f,rll should be designed for an allowable bearing pressure o{ I,SOO prf ._. The post-tensioned slab placed on structural fill should be designed for a wetted distance of 10 feet or at least half of the slab width, whichever is greater. Foundation settlement is estimated to be about I to I% inches based on the long- term compressibility of the frll. Additional settlement of about I to 2 inches is estimated if the underlying debris fan soils were to become wet. Settlement from the deep wetting would tend to be uniform across the building area and the settlement potential of the fiIl section should control the design. 2) The thickened sections of the slab for support of concentrated loads should have a minimum width of 20 inches. 3) The perimeter turn-down section of the slab 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. If a frost- protected foundation is used, the perimeter turn-down section should have at least 18 inches ofsoil cover. 4) The foundation should be constructed in a "box-like" configuration rather than with irregular extensions which can settle differentially to the main building area. The foundatiou walls, where pruvidetl, shoultl be heavily reinfurued top und bottom to span local anomalies such as by assuming an unsupported length of at least 14 fcct. Foundation walls acting as retaining structures, if any, should also be designed to resist latcral carth prcssurcs as discusscd in thc "Foundation and Retaining Walls" section of this report. 5) The root zone and any loose or disturbed soils should be removed. Additional structural fill placed below the slab should be compacted to at least 98% of the Kumar & Associates, lnc. @ Project No. 21-7-480 -5- 6)A maximum standard Proctor density within 2 percentage points of the optimum moisture content. ve of the geotechnical engineer the compaction of the fill materials and observe all excavations to concrete to evaluate bearing conditions. FOLINDATION 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 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 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 at least 40 pcf for backf,rll 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. Backf,rll should be placed in uniform lifts and compacted to at least 90Yo of the maximum standard Proctor density at a moisture content near optimum. Backfill placed in pavement and walkway 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. 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 0.35. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 350 pcf. The coeff,rcient of friction and passive pressure values recommended above assume ultimate soil Kumar & Associates, lnc, @ Project No. 21-7-480 -6- strength, Suitahle thctors of saf'ety should be included in the design to limit the strain rvhich will occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against the sides of the footings to resist lateral loacls shouhlbe c:ompar:tecl to at lcast 95% of the maximum standard Proctor density at a moisture content near optimum. NONSTRUCTURAL FLOOR SLABS Compacted structural fill can be used to support lightly loaded slab-on-grade construction separate from the building foundation. The fill soils can be compressible when wetted and can result in some post-construction settlement. To reduce the effects of some differential movement, nonstructural floor slabs should be separated from buildings to allow unrestrained vertical movement. l'loor 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, such as road base, should be placed beneath slabs as subgrade support. This material should consist of minus 2-inch aggregate with at least 50% retained on the No. 4 sieve and less than l2o/o passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95Yo of maximum standard Proctor density at a moisture content near optimum. Required fiIl can consist of the on- site predominantly granular soils devoid of vegetation, topsoil and oversized rock. UNDERDRAIN SYSTEM It is our understanding the finished floor elevation at the lowest level is at or above the surrounding grade. Therefore, a foundation drain system is not required. Tt has heen our experience in the area that local pcrched 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, be protected from wetting and hydrostatic pressure buildup by an underdrain and wall drain systern. If the finished floor elevation of the proposed structure has a floor level below the surrounding grade, we should be contacted to provide recommendations for an underdrain system. All earth rctaining structurcs should bc propcrly draincd. SITE GRADING Extensive grading was performed as part of the existing Villas South development. Additional placement and compaction of the debris fan soils could be needed to elevate the site to design Kumar & Associates, lnc, @ Project No, 21.7.480 -1- grades and reduce the risk of excessive differential settlements and building distress. In addition, the water and sewer pipe joints should be mechanically restrained to reduce the risk ofjoint separation in the event of excessive differential settlement. Additional structural fill placed below foundation bearing level should be compacted to at least 98% of the maximum standard Proctor density within 2o/o of optimum moisture content. Prior to fill placement, the subgrade should be carefully prepared by removing any vegetation and organic soils and compacting to at leastg5o/o of the maximum standard Proctor density atnear optimum moisture content. The fill should be benched into slopes that exceed 20%o grade. Permanent unretained cut and fill slopes should be graded at2horizontal to I 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 Precautions to prevent wetting of the bearing soils, such as proper backfill construction, positive backfill slopes, restricting landscape irrigation and use of roof gutters, need to be taken to help limit settlement and building distress. The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) Inundation of the building structural slab foundation excavations 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 nonstructural 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 5 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in paved areas. Graded swales should have a minimum slope of 3%. 4) Roof downspouts and drains should discharge at least 5 feet beyond the foundation and preferably into a subsurface solid drainpipe. 5) Landscaping which requires regular heavy irrigation should be located at least 10 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. 21-7-480 -8- LIMITATIONS This study has been conducted in accordancc with generally accepted geotechnical engineering principles and practices in this area at this time. V/e make no warranty either express or implied. Thc conclusions ancl recommendations submitted in this report are based upon the data obtained from the exploratory boring drilled at the location 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 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 boring 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. Vy'e 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 verifr 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. David A. Noteboom, Staff Engineer Revierved by: Steven L. Pawlak, P DN/kac rn 1 15222 lal Kumar & ¡{ssociates, lnc. e Project No. 21-7-480 E : I I LOT 255. I PROPERTY LINE I o ,BORING 1',i oLÔT 256 I(¡ @oo () "sc)o srn I .+ I J r' t\ \ \ û Qo s, o s, d LOT 251 s_ d 10 20 APPROXIMATE SCALE-FEET Fig. 1Kumar & Associates LOCATION OF EXPLORATORY BORING21 -7 -480 BORING 1 EL. 5980' LEGEND _0 R00T ZONE; SANDY T0 VERY SANDY, GRAVELLY Sll.T, FILL, FIRM, SLIGHTLY MOIST, BROWN. i ! 32/ 12 WC=6.1 DD=1'1 I -200=57 FILL: SANDY TO VERY SANDY SILT WITH GRAVEL, VERY STIFF TO DTNSE, SLIGHTLY MOIST, GRAYISH TAN TO BROWN. -5 41/6,50/4 SAND AND SILT (SM_lYlL); SLIGHTLY GRAVELLY, MEDIUM DENSE/STIFF, SLIGHTLY Mo|ST, BRoWN. ALLUVTAL FAN DEPoSTT 30/12 WC=6.5 DD=1 '1 2 -200=41 GRAVEL AND SAND (CM-SM); SILTY, WITH SILTY LAYERS, MEDIUM DENSE, SLIGHTLY MOIST, BROWN, ALLUVIAL FAN DEPOSITS. GRAVEL (GP_GM); SANDY TO VERY SANDY, SLIGHTLY SILTY, COBBLES AND POSSIBLE BOULDERS, DENSE, MOIST, LIGHT BROWN AND GRAY MIX. ROUNDID ROCKS, RIVER ALLUVIUM.35/ 12 ! I DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE. _ 15 DRTVE SAMPLE, 1 3/8-rNCH r.D. SpLrT Sp00N STANDARD PENETRATION TEST.13/12 WC=5.8 DD=1 10 -200=42 11 712DR|VE SAMPLE BL0W C0UNT. INDICATES THAT 31 BLOWS 0F"'I '. A 14o-POUND HAMMER FALLING 50 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. F- t¡J t¡JtL ITt-(L t¡lo 20 38/6,50/6 NOTES THE EXPLORATORY BORING WAS DRILLED ON JUNE 11, 2021 WITH A 4-INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2 THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED APPROXIMATELY BY PACING FROM FEATURTS SHOWN ON THE SITE PLAN PROVIDED. 44/ 12 WC=4.6 +4=26 -200=26 1 THE ELEVATION OF THE TXPLORATORY BORING WAS OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THT SITE PLAN PROVIDED. 4 THE EXPLORATORY BORING LOCATION AND ELEVATION SHOULD BE CONSIDERED ACCURAÏE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED._ .10 34/ 12 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOG REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. zÃ 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT THE TIME OF DRILLING. 7. LABORATORY TEST RESULÏS: WC = WATER CoNTENT (%) (ASTM D 2216); DD = DRY DENSITY (pcf) (ASTM D 2216); +4 = PERCENTAGE RETAINED ON NO.4 SIEVE (ASTM D 6913); -200 = PERCENTAGT PASSING N0. 200 SIEVE (ASTM D 1140). 50 /3 21 -7 - 480 Kumar & Associates LOG OF EXPLORATORY BORING Fig. 2 E ö 100 90 ao 60 50 10 30 20 t0 o 0 t0 20 30 40 50 60 80 90 foo - .005 .300 75 76.2 127 200 DIAMETER OF IN MI RS CLAY TO SILT COBBLES GRAVEL 26 % SAND LIQUID LIMIT SAMPLE 0F: Silly crovelly Sond 48% PLASTICITY INDEX SILT AND CLAY 26 % FROM:Boringl@25' Th6s6 lesl rosulls opply only lo lh6sompl€s whlch w6re lssl€d. Tholosling r€porl shqll nol bo reproduc6d,excepl ln full, wilhoul lhe wrltlenqpprovol of Kumqr & Associqles, lnc, Sl6v6 qnolysls lostlng ls psrform6d lnoccordonce wlth ASTM D69'13, ASTM D7928, ASIM Cl56 ondlor ASTM Dtt40. HYDROMETER ANALYSIS 7 HRS SIEVE ANALYSIS SfÂNDARO SERIES CLEAR SQUARE l I l I l I I I I I I l I ¡ l I I SAND GRAVEL FIN E MEDIUM COARSE FIN E COARSE 21 -7 -480 Kumar & Associates GRADATION TEST RESULTS Fig. 3 lC,.iffii:ffiffi1'rÊ;;*''TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.21-7-480Sand and Silt with GravelSilty Gravelly SandGravelly Sandy Silt (Fill)Very Silty Gravelly SandSOIL TYPEillUNCONFINEDCOMPRESSIVESTRENGTH("/"1PLASTICINDEXATTERBERG LIMITS(%lLIQUID LIMIT571442264826t%lSANDPERCENTPASSING NO.200 stEVEGRAVEL(%')NATURALDRYDENSITY16.119tt21106.55.84.6i1/z5125NATURALMOISTURECONTENTDEPTHSAMPLEBORING2y,1