The URL can be used to link to this page

Home My WebLink AboutSubsoil StudylGrtiiffiifl'åi'ffËHf i':,iå*'" 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. cortt Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Sumrnil Counry, Colorado ItLÜË-lVF":' - ", r. f\!l r{liti ll / r\;' 8$,i5'it-þB"t'?'"''il¿'i SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 2T9, rRONBRrDGE BLUE HERON VISTA GARFIELD COUNTY, COLORADO PROJECT NO. 21-7-591 AUGUST 9,2021 PREPARED FOR: SCIB, LLC ATTN: LUKE GOSDA 0115 BOMMERANG ROAD, SUITE 52018 ASPEN, COLORADO 81611 TABLE OF CONTEN'I'S PURPOSE AND SCOPE OF STUDY BACKGROLIND INFORMA TION 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 BORING FIGURE 3 - SWELL-CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS ..-2- a 1 1 1 1 ..-3- ..-3- aJ J 5 6 6 6 7 .-7 - Kumar & Associates, lnc. @ Project No. 21.7.591 PURPOSE AND SCOPE OF STUDY This report presents the results ofa subsoil study for a proposed residence to be located on Lot2l9,Ironbridge, Blue Heron Vista, 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 study was conducted in accordance with our agreement for geotechnical engineering services to SCIB, LLC dated July 9, 2021. An exploratory boring was drilled 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, compressibility or swell 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. 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 1 15-6, 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 Lot279. 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 and fill depths up to 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 frorn those described above, we should be notified to re-evaluate the recommendations contained in this report. Kumar & Associates, lnc. o Project No. 21-7-591 I-L- SITE CONDITIONS The subjcct site was vacant at the time of our field exploration. The lot is located in the north part of the Villas North Parcel. The natural terrain prior to development in 2006 sloped down to the east at about 5o/o grade. The subdivision area was elevated by filling on the order of 10 feet above the original ground surface to create a relatively flat and gently sloping building site off Blue Heron Vista. Vcgctation consists of sparsc grass and weeds with scattered sage bnlsh. SUBSIDENCE POTENTIAL Eagle Valley Evaporite underlies the project area which is known to be associated with sinkholes and localized ground subsidence in the lower Roaring Fork River valley. A sinkhole opened in the cart storage parking lot located east of the Pro Shop and west of the Villas North parcel in January 2005. Irregular surface features were not observed in the Villas North parcel that could indicate an unusualrìsk of future grouncl subsiclence. Variable depths of the clebris fan soils were locally encountered by the previous September 14,2005 geotechnical study which indicates there could have been localized subsidence of the river gravel deposits. The current subsurface exploration pertbrmed in the area ot'the proposed residence on Lot 279 did not encounter voids. ln our opinion, the risk of future ground subsidence on Lot 279 tkroughout the service life of the proposed residence is low and similar to other areas of the lower Roaring Fork River valley where there have not been indications of ground subsidence. FIELD EXPLORATION The field exploration for the project was conducted on July 14, 2021 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-mounted CME- 458 drill rig. The boring was logged by a representative of Kumar & Associates, Inc. Samples of the subsoils were taken with 1%-inch and 2-inch I.D. 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 which the samples were taken and the penetration resistance values are shown on the Log of Explorafory Boring, Figure 2. The samples were returnecl to our laboratory fbr review by the project engineer and testing. Kumar & Associates, lnc. @ Project No.21.7.591 J SUBSURFACE CONDITIONS A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The subsoils consist of about 9 feet of compacted fill soils overlying medium dense, silty to very silty gravelly sand (alluvial fan deposit) to a depth of 16 feet where dense, silty sandy gravel with cobbles (river gravel deposit) was encountered down to the maximum explored depth of 21 feet. Laboratory testing performed on samples obtained from the boring included natural moisture content and density and finer than sand grain size gradation analyses. Results of swell- consolidation testing performed on a relatively undisturbed drive sample of the alluvial fan soil, presented on Figure 3, indicate low to moderate compressibility under conditions of loading and wetting. The laboratory testing is summarizedin Table 1. No free water was encountered in the boring at the time of drilling and the subsoils were typically slightly moist. FOUNDATION BEARING CONDITIONS The upper 9 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 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%o 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 weffed, and the future 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 typically less than the alluvial fan deposit. Proper grading, drainage and compaction as presented 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 deposit could be used to reduce the building settlement risk. DESIGN RECOMMENDATIONS FOL]-NDATIONS Considering the subsurface conditions encountered in the exploratory boring and the nature of the proposed construction, we recommend the building be founded with a heavily reinforced Kumar & Associates, lnc, o Project No. 21-7-591 4 structural slab or post-tensioncd slab t'oundation bcaring on 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 foundation system. 1) A heavily rcinforccd structural slab or post-tcnsioned slab placed on compactecl structural fill should be designed for an allowable bearing pressure of 1,500 psf. 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. Settlement of foundation is estimated to be about I to l% inches based on the long-term compressibility of the fill. Additional settlement of about 1 inch 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 fill section should control the design. 2) The thickened sections of the slab for support of concentrated loads should have a minimuln width of 20 inches. 3) The perimeter tum-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 foundation walls, where provided, should be heavily reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 14 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) 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 maximum standard Proctor density within 2 percentage points of the optimum moisture content. 6) A representative of the geotechnical engineer should evaluate the compaction of the fill materials and observe all footing excavations prior to concrete placement to evaluate bearing conditions. Kumar & Associates, lnc. @ Project No.2'1.7.591 5 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 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 backfill 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. The pressures recotnmended 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 90o/o 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 backf,rll 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 325 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 ultirnate 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 95o/o of the maximum standard Proctor density at a moisture content near optimum. Kumar & Associates, lnc. o Project No. 21-7-591 -6- NONSTRI ICTTIRAL FLOOR SLABS Compacted structural fill can be used to support lightly loadecl slab-on-grade construction scparatc from the building foundat.ion. The fill soils can be compressible wllcn wcttcd and carr 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. 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, 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%o retained on the No. 4 sieve and less than l2Yo 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 fill can consist of the on-site 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. It has been our experience in the areathat 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, be protected from wetting and hydrostatic pressure buildup by an underdrain and wall drain system. 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 retaining structures should be properly drained. SITE GRADING Extensive grading was perf'ormed as part of the existing Villas North development. Âdditional placetneut and compaction of strucl"ural fill soils could be needed to elevate the site to design gracles ancl reduce the risk of excessive differential settlements and building distress. In addition, the water ancl 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 Kumar & Associates, lnc. @ Project No. 21.7.591 -7 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 least95o/o of the maximum st¿indard Proctor density atnear optimum moisture content. The fill should be benched into slopes that exceed 20o/o grade (if any). Permanent unretained cut and filI 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 95%o of the maximum standard Proctor density in pavement and nonstructural slab areas and to at least 90Yo 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 inigation. LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this time. V/e make no warranty either express or implied. The conclusions and recommendations submitted in this report are based upon the data obtained Kumar & Associates, lnc. @ Project No, 21-7-591 -8- from the exploratory boring drilled at thc location indicated on Figure l, the proposed type of construction and our experience in the area. Our services do not include determining the prescnce, prcvcntion or possibility of mold or other biologioal contaminants (MOBC) developing in the fi¡ture. 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 stlhsr¡rface conditions iclentified at the exploratory boring and variations in the subsurface conditions may not become evident'until excavation is performed. If conditions encountercd during construction appear diflerent 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 the implementation of our recommendations, 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 cxcavations and foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer. Respectfully Submitted, Kumar & Associates, Inc. /ø4tr*. PuactTa,- James H. Parsons, P.E. Reviewed by: Steven L. Pawlak, JHP/kac Kumar & Associates, lnc. (Project No. 21.7-591 E I LOT 280 o,, ----o LOT 2'78 10 0 10 20 APPROXIMATE SCALE_FEET BORING 1 LOT o 2'7 9 $n 21 -7 -591 Kumar & Associates LOCATION OF EXPLORATORY BORING Fig. 1 ,r ñ Ë e 6 E e BORING 1 E1.5960'LEGEND 0 FILL: SAND AND SILÏ, GRAVEILY, MEDIUM DENSE TO DENSE, SLIGHTLY MOIST TO MOIST, MIXED BROWN. 27 /12 SAND (SM); SILTY T0 VERY S|LTY, GRAVELLY, SLTGHTLY CLAYEY, MEDIUM DENSE, SLIGHTLY MOIST, GRAY_BROWN. tr s1 /12 WC= 1 2.0 DD=1 21 -200=60 GRAVEL (cU); SUrv, SANDY, COBBLES, POSSIBLE BOULDERS, DENSE, SLIGHTLY MOIST, LIGHT BROWN. ROUNDED ROCK. 46/ 12 DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE. 10 16/ 12 WC=6.5 -200=38 I DRIVE SAMPLE, 1 3/8-rNCH r.D. SPL|T SP00N STANDARD PENETRATION TEST.f- L¡l LI LL IIFo- L¡Jô nor'n DRIVE SAMPLE BLOW COUNT. INDICATES THAT 18 BLOWS 0Ftat tL A 14o-pouND HAMMER FALLTNG Jo TNCHES WERE REQUTRED TO DRIVE ÏHE SAMPLER 12 INCHES, 15 7/6,50/4 WC= 1 3.1 DD='1 1 4 NOTES THE EXPLORATORY BORING WAS DRILLID ON JULY 14, 2021 WITH A 4-INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2 THT LOCATION OF THE EXPLORATORY BORING WAS MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 20 50/6 THE ELEVATION OF THE EXPLORATORY BORING WAS OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED, 25 4, THE EXPLORATORY BORING LOCATION AND ELTVATION SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5, THE LINES BETWEEN MATERIALS SHOWN ON THE IXPLORATORY BORING LOG RTPRESENT THE APPROXIMATT BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6 GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT THE TIME OF DRILLING. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216); DD = DRY DENSITY (pcf) (ASTM D 2216); -2OO = PTRCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1140). 7 21 -7 -591 Kumar & Associates LOG OF EXPLORATORY BORING Fis. 2 ¡ E 1 I SAMPLE 0F: Silt ond Sond FROM: Boring 1 @ 15' WC = 13.1 %, DD = 114 pcf innot be reproduced, full, w¡thout the vdfr€n opprovol of ond ksoc¡otes, lnc. Sw€ll in ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 1 às -)J L¡l =tt1 I z.o F o Jo U)zoO 0 -1 -2 -3 -4 1.0 APPLIED PRESSURE - KSF 10 100 21 -7 -591 Kumar & Associates SWTLL_CONSOLIDATION TEST RISULTS Fig. 3 rcltåffih:#rffin'""3;,**TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.21-7-591SOIL TYPESandy Silt with GravelSilty Sand with GravelSilt and SandlosflUNCONFINEDCOMPRESSIVESTRENGTHPLASTICINDEXfol"1ATTERBERG LIM]TSt%lLIOUID LIMITPERCENTPASSING NO.200 stEvE6038SAND(%)GRADATION%tGRAVELlocflNATURALDRYDENSITY12Itt4(o/"1NATURALMOISTURECONTENT12.06.5IaJ1tfoDEPTH51051SAMPLE LOCATIONBORING1