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Home My WebLink AboutSubsoil Study for Foundation Design 04.19.2018H,PTI(UMAR 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax (970) 945-8454 Errrail: lr¡-rkgl*lrwor:¡rl @ kr¡ rìlatltsâ.cotrì Geotechnical Engineering I Engineering Geology Materials Testing I Environmental Office Locations; Parker, Glenwood Springs, and Silverthorne, Colorado RFGE yÈD $^ÏLo"t^yrtuuriluilrûD1r:fri#.ïfSUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 1, TELLER SPRINGS COUNTY ROAD 109 GARFIELD COUNTY, COLORADO PROJECT NO. 18-7-187 APRIL I9,2OI8 PREPARED FOR: RIDGE RUNNER CONSTRUCTION ATTN: BRENT LOUGH 1655 COUNTY ROAD 109 GLENWOOD SPRINGS, CO 81601 TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION FIGURE 1 - LOCATION OF EXPLORATORY BORING FIGURE 2 -LOG OF EXPLORATORY BORING FIGURES 3 TO 5 - SV/ELL-CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS 1 1 SITE CONDITIONS SUBSIDENCE POTENTIAL .. FIELD EXPLORATION SUBSURFACE CONDITIONS DESIGN RECOMMENDATIONS ........... FOUNDATIONS ;................. FOUNDATION AND RETAININC \MALLS NONSTRLTCTLTRAL FLOOR SLAB S UNDERDRAIN SYSTEM........... SURFACE DRAINAGE ............... LIMITATIONS.... n a a-L- -3 - FOUNDATION BEARING CONDITIONS ............- 3 - 4- 4- 5- 6- 7- 7- .-8- H-P* KUMAR Project No. r8-7-r87 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 1, Teller Springs Subdivision, County Road 109, 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 Ridge Runner Construction dated March 5,2018. 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, comprcssibility or swell and other engineering characteristics. The results of the field exploration and laboratory testing were analyzedto develop recommenclations fclr foundation types, depths and allowable pressures for the proposed building foundation. This report summarizes the ilata obtainecl cluring this stucly and presents our conclusionso 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 story, wood frame structure over a walkout basement with, possibly, an attached garage. Ground floor is proposed to consist of a structural slab-on-grade. Grading for the structure is assumed to involve cut depths between about 4 to IO 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 reconìmendations contained in this report H-P + KUMAR Project No. r8-7-r87 -2- SITE CONDITIONS The lot was vacant at the time of the field exploration. The terrain was strongly sloping down to the northeast with grades of 14 to 18 percent. Vegetation consisted of sage brush and scattered juniper trees with an understory of sparse grass and weeds. There was no snow cover at the time of our study. SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the 'l'eller Springs Subdivision. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some massive beds of gypsum and limestone. There is a possibility that massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions of f.he lot. Dissolution of the gypsurll under certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. 'l'he subsurface exploration performed in the area of the proposed residence on Lot I did not encounter voids. In our opinion, the risk of future ground subsidence on Lot 1 throughout the service life of the proposed residence is low and similar to other areas of the Roaring Fork River valley where there have not been indications of ground subsidence, but the owner should be made aware of the potential for sinkhole development. If further investigation of possible cavities in the bedrock below the site is desired, we should be contacted. FIELD EXPLORATION The field exploration was conducted on March 16,2018. 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 H-P/Kumar. 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 inchcs. This tcst is similar to thc standard pcnctration tcst dcscribed H-PÈ KUMAR Project No. :.8-7-:.87 ^-J- 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 Exploratory Boring, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The subsoils, below a thin root zone, consist of about 90 feet of medium dense to dense, slightly silty to very silty sand and gravel with cobbles down to the maximum drilled depth of 90 feet. The gravel and cobbles were angular to subangular and consisted of siltstone fragments. The subsoils appeared to be more dense below about '15 feet. Laboratory testing performed on samples obtainecl from the boring inchrclecl natural moisture content and density and finer than sand size gradation analyses. Results of swell-consolidation testing performed on relatively undisturbed drive samples of the silty sand matrix soils, presented on Figures 3 to 5, indicate low compressibility under light loading and a low collapse potential (settlement under constant load) when wetted. The samples were moderately to highly compressible under increased loading after wetting. The laboratory testing is summarized in Table 1. Free water was not encountered in the boring at the time of drilling. The subsoils were slightly moist. FOUNDATION BEARING CONDITIONS The subsoils below the site have a low settlement potential when wetted (collapse). However, the depth of these soils combined with potential wetting could result in excessive settlements, possibly on the order of 6 to 12 inches. The amount of settlement will depend on the extent of wetting and potential compression of the soils after wetting. Sources of wetting includc irrigation, surface water runoff and utility line leaks. A H-P+ KUMAR Project No. r8-7-r87 -4- heavily reinforced structural slab foundation designed for significant differential settlements is recommended for the building support. DESIGN RECOMMENDATIONS FOUNDATIONS 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 structural slab foundation bearing on at least 6 feet of compacted structural fill. Adjoining portions of the house that are not on the structural slab, such as an attached garage, should be constructed to be structurally separate from the main house. The design and construction criteria presented below should be observed for a structural slab foundation system. 1) A heavily reinforced structural slab placed on about 6 feet ofstructural fill should be designed for an allowable bearing pressure of 1,500 psf or subgrade modulus of 125 tcf. The slab should be designed to be able to span 10 feet. Based on experience, we expect initial settlement of the slab foundation designed and constructed as discussed in this section will be about 1 inch or less. Additional settlement could occur if the bearing soils were to become wetted. The magnitude of the additional settlement would depend on the depth and extent of wetting but may be on the order of several inches. 2) The thickened sections ofthe slab for support ofconcentrated 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 the 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 of soil cover. H-P + KUMAR Project No. r8-7-r87 -5- 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 should also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining 'Walls" section of this report. The organic root zone and any loose or disturbed soils should be removed. Structural fill placed below the slab bearing level should be compacted to at least 98Vo of the maximum standard Proctor density at a moisture content near optimum. The on-site soils can be used as structural fill. A representative of the geotechnical engineer should evaluate the compaction of fill materials and observe all footing excavations prior to concrete placement to evaluate bearing conditions. FOUNDATION 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 at least 50 pcf for backfill consisting of the on-site soils. Cantilevered retaining structures which are separate from the building 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, 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 imposecl on a founclation wall or s) 6) H-PI KUMAR Project No. r8-7-r87 -6- retaining structure. An underdrain should be provided to prevent hydrostatic pressure buildup behind walls. Backfill shoulcl be placed in uniform lifts and compacted to at least 907o of the maxtmum standard Proctor dcnsity at a moisture content near optimum. Backfill placed in pavement and walkway areas should be compacted to at least 957o of the maximum standard Proctor density. Care should be taken not to overcompact the backfill or uss 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 300 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 ofpassive resistance. Fill placed against the sides ofthe footings to resist lateral loads should be compacted to at least 957o 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 main building foundation. To reduce the effects of some differential movement, slabs-on-grade should be separated from the building 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 H-P + KUMAR Project No. r8-7-r87 -1- established by the designer based on experience and the intended slab use. A minimum 4-inch layer ofwell-graded sand and gravel, such as road base, should be placed beneath slabs for support. This material should consist of minus Z-inch aggregate with at least 507o rctained on the No. 4 sieve and less than l27o passing the No. 200 sicvc. All fill materials for support of floor slabs should be compacted to at least 957o of maximum standard Proctor density at a moisture content near optimum. Required fill can consist ofthe on-site soils devoid ofvegetation, topsoil and oversized rock. UNDERDRAIN SYSTEM Although free water was not encountered during our exploration, 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 runoffcan also create a perched condition. We recommend below-grade construction, such as basements, crawlspaces or retaining walls, be protected from wetting and hydrostatic pressure buildup by an underdrain 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 1 foot below lowest adjacent finish grade and sloped at a minimum l7o to a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than 2Vo passing the No. 200 sieve, less than 507o passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least IVz feet deep. An impervious membrane such as 20 mll PVC should be placed beneath the drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils. SURFACE DRAINAGE Precautions to prevent wetting of the bearing soils, such as proper backfill construction, positive backfill slopes, restricting landscape inigation and use of roof guttors need to be H-P* KUMAR Project No. :.8-7-r.87 -8- taken to 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 ofthe foundation excavations and underslab areas should bc avoided during construction. 2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 957o of the maximum standard Proctor density in pavoment and slab areas and to at least 907o 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 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. Graded swales should have a minimum slope of 37o. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy inigation 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 imigation. LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at the time of this study. '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 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 fielcl of practice should be H-P* KUMAR Project No. r8-7-r87 -9 - 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 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 verify that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the recommendations presented herein. 'We recommend on-site observation of excavations and foundation bearing strata and testing of structural fill by a representative ofthe geotechnical engineer. Respectfully Submitted, H-PE KUMAR Daniel DEH/kac cci Michael Manchester @ manchester-architects. com Dale Kaup dale@kaupengineering.com H-P + KUMAR Project No. r8-7-r87 BORING 1 È L6 ÈÈdı ) I s0 100 APPROXIMATE SCALE-FEET 18-7 -187 H-PryKUMAR LOCATION OF EXPLORAÏORY BORINGS Fig.1 d9 1l- ñ ¡ II Þ 4 3 3.g ; I BORING 1 EL. 1 038' 0 (10)LEGEND1s/12 WC=1.7 DD= 1 05 -2OO=37 SAND AND GRAVEL (CV-SV): SLTGHTIY SILTY T0 VERY SILTY, SCATTERED COBBLIS, MEDIUM DENSE TO DENSE, SLIGHTLY MOIST, LIGHÏ BROWN. ANGULAR AND SUBANGULAR ROCK FRAGMENTS. DRIVE SAMPLE, 2-INCH I.D, CALIFORNIA LINER SAMPLE.10 54/12 WC= 1 .2 DD=1 1 25/12 WC=1.7 DD= 1 20 -2OO=26 þ I DR|VE SAMPLE, 1 3/8-|NCH t.D. SPL|T SP00N STANDARD PENETRATION TEST. 1ı /11 DRIVE SAMPLE BL0W C0UNT. INDICATES THAT 19 BL0WStJl t1 oF A 140-pouND HAMMER FALLTNG 30 tNcHES lvtRE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. 20 36/ 12 WC=2.3 -200=39 NOTES 30 50/ 12 \NC=2.2 DD= 1 20 -2OO=40 THE EXPTORATORY BORING WAS DRILLED ON MARCH 16, 2018 WITH A 4-INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2. THE EXPLORATORY BORING WAS LOCATED BY THE CLIENT. 40 47/12 WC=2.5 DD=113 -200=35 3. THE ELEVATION OF THE EXPLORATORY BORING WAS OBTAINED BY INTERPOLATION BETWIEN CONTOURS ON THE SITE PLAN PROVIDED. F t¡J L¡.j LL IT t-- o_ LrJÕ 4. THE EXPLORATORY BORING LOCATION AND ELEVATION SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 50 5. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT THE TIME OF DRILLING. 7, LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216); DD = DRY DENSITY (PCf) (ASTM D 2216); -200 = PERCENTAGE PASSING N0. 200 SIEVE (ASTM D fi40). 60 70 50/6 WC=3.4 DD= 1 25 -ZOQ=41 80 90 18-7 -187 H-PryKUMAR LOG OF EXPLORATORY BORING Fis. 2 9 4 I SAMPLE 0F: Silty Sond wilh Grovel FROM:Boringl@5' WC = 1.7 %, DD = 105 pcf -2OQ = 37 % ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING ( \ (\ fresê test r.sults qpply only to th€ Êomplos t€st€d. ft€ t6sting repod sholl not be råproduc€d,6xcópt iñ full, without th€ writkn opprovol of Kumor ond A3sociot€s, lnc. Swell Consolidot¡on t€sting pldormsd iñ occo.doncd w¡th AÍM D-4546. 1 0 ñ JJul =tn I zotr o =o U1z.o(J -1 -2 -3 -4 -5 -6 -7 1.0 D PRESSURE _ KSF 10 100 18-7 -187 H-PryKUMAR SWELL_CONSOLIDATION TEST RESULTS Fig.3 SAMPLE OF: Silty Sond wilh Grovel FROM: Boring 1 @ 15' WC = 1.7 %, DD = 120 pcf -200 -- 26 % I ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING \ I I 1 0 àq JJlrt =U1 I zo =olotnzoo -1 -2 -3 -4 E -6 -7 -8 1.0 D PRESSURE - KSF 10 100 18-7 -187 H-PVKUMAR SWELL-CONSOLIDATION TEST RESULTS Fig. 4 I -ãì|JlÀ t ! 4 I SAMPLE OF: Very Silty Sond wilh Grovel FROM:Boringl@30' WC = 2.2 %, DD = 120 pcf -2OO = 40 % ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING ) (\ ( I fhæê t€st r€sulls opply oniy to th6 6ompl€s tsstsd. th6 tcating rapod sholl ñot b€ r€produced, sxcspt in full. without th€ w.itten opprovol of Kùñor ond Associotes, lnc. Swell Consolidotìon t.sting pefofmed ¡n occordoñcê wìth ASIM D-4546. 1 ñ JJ L¡J =U1 I zo F o =o tt1zo() 0 -1 -2 -3 -4 -5 -6 ED PRESSURE - KSF 10 100 18-7 -187 H.PryKUMAR SWTLL-CONSOLIDATION TIST RESULTS Fig. 5 H.PTI(UMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProject No. 18-7-187SOILTYPE2.3Silty Sand with GravelSlightly Sitty Sandy Gravel2.5Silty Sand with GravelVery Silty Sand1.5Very Silty Sand withGravelSilty Sand with GravelVery Silty Sand withGravelCOLLAPSE(%lATTERBERG LIMITSPLASTICINDEX(%lLIQUIDLIMIT(%lPERCENTPASSINGNO.200SIEVE3711263940354tGRADATIONSAND%lGRAVEL%lNATURALDRYDENSITYlocfl105t20t20113r25NATURALMOISTURECONTENT(%l1.7r.2172.32.22.53.4SAMPLE LOCATIONDEPTH(ft15101520304076BORING1