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Home My WebLink AboutSubsoil Study for Foundation Design 06.27.18H.PVKUMAR Geotqclnleal Engineering I Engineedng Geology Materials Testing | Ënvironmental 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax (970) 945-8454 Email: hpkglenwood@kumarusa.com Ofüce Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado SUBSOIL STT]DY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT S-14,IilLING 8, ASPEN GLEN SADDLEBACK ROAD GARFIELD COUNTY, COLORADO PROJECT NO. 18-7-411 JUNE 27,2018 REVISED JTJLY 18,2018 PREPARED FOR: RM CONSTRUCTION ATTN: BLAKE PILAND 5O3O COUNTY ROAD 154 GLENWOOD SPRTNGS, COLORADO 81601 @ TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY............ PROPOSED CONSTRUCTION SITE CONDTTIONS SUBSIDENCE POTENTTAL FIELD EXPLORATION SUBSURFACE CONDITIONS FOUNDATION BEARING CONDITIONS ......... DES IGN RECOMMENDATIONS FOIJNDATIONS FOUNDATION AND RETAINING V/ALLS FLOOR SLABS UNDERDRAIN SYSTEM SURFACE DRAINAGE LIMITATIONS FIGURE 1 . LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4 - SWELL-CONSOLIDATION TEST RESULTS FIGURE 5 . GRADATION TEST RESULTS TABLE I- SUMMARY OF LABORATORY TEST RËSULTS I ,,,,.,,'.,- 2 1 2- 3- 3- H.PèKUMAR Project No. 18-7-411 PURPOSA, AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot S-14, Filing 8, Aspen Glen, Saddleback Drive, Garfîeld 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 proposal for geotechnical engineering services to RM Construction dated June 13, 2018. 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, 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, dcsign recommendations and other geuf.echnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION The proposed residence will be a two story structure over crawlspace. Garage floor will be slab- on-grade. Grading for the structure is assumed to be relatively minor with cut depths between about 4 to 6 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. SITE CONDITIONS The lot was vacant at the time of field exploration. The terrain is relatively flat with a slight slope down to the north. The ground surface is natural with minimal grading from road construction. There is a berm with Iandscaped trees along the north side of the lot. Vegetation H.P!KUMAR Project No. '18-7-41 1 -2- consists of grass and weeds and the trees planted on the berm. Nearby buildings include one and two story single family residences. STJBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the subject site and the nearby areas of the Aspen Glen Development. 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 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 area, sinkholes have been observed scattered throughout the Roaring Fork River valley. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in other areas of the Roaring Fork River valley. The nearest mapped sinkhole is located aboutVq mile south east of this lot. Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities was 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 on Lot S-14 throughout the service life of the proposed residence, in our opinion, is low and similar to other lots in Aspen Glen; however, 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 for the project was conducted on June 18, 2018. Two exploratory borings were drilled at the locations shown on Figure I to evaluate the subsurface conditions. The borings were advanced with 4 inch diameter continuous flight augers powered by a truck- mounted CME458 drill rig. The borings were logged by a representative of H-P/Kumar. 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 3û H.PÈKUÍVIAR Project No. 18-7-411 a-J- 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. The subsoils below about I foot of topsoil consist of lÙVz to 12 feet of stiff, sandy clay to clayey sand overlying slightly clayey sandy gravel and sand with cobbles at depths of llVzto 13 feet down to the maximum depth explored, 17 feet. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and drilling refusal was encountered in the deposit. Laboratory testing performed on samples obtained from the borings included natural moisture content and gradation analyses. Results of swell-consolidation testing performed on relatively undisturbed drive samples, presented on Figure 4, indicate low to moderate compressibility under conditions of loading and a nil to low expansion potential when wetted under a constant light surcharge. Results of gradation analyses performed on a small diameter drive sample (minus lYzinch fraction) of the coarse granular subsoils are shown on Figure 5. The laboratory testing is summarized in Table L No free water was encountered in the borings at the time of drilling FOUNDATION BAARING CONDITIONS The upper sandy clay soils appear to possess an expansion potential when wetted which could result in movement of footings bearing on the soils if they become wetted. Surface runoff, landscape irrigation, and utility leakage are possible sources of water which could cause wetting. A lower risk alternative would be to place the foundation entirely on the underlying relatively dense river gravels or remove and replace a certain depth of silty sandy clay soils with compacted structural fill. The subgrade should be observed for bearing conditions and further evaluated for heave potential at the time of construction. H.PryKUIVIAR Project No. 18-7-411 -4- DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we recommend the building be founded with spread footings bearing on at least 3 feet of compacted structural fill or on the natural gravel subsoils. The design and construction criteria presented below should be observed for a spread footing foundation system. l) Footings placed on at least 3 feet of structural fill over the clay soils should be designed for an allowable bearing pressure of 2,000 psf. Based on experience, we expect initial settlement of footings designed and constructed as discussed in this section will be about I inch or less. There is a heave potential for the soils if the clay soils were to become wetted. The movement would be differential and could be about Vz ta L inch for a wetted depth on the order of l0 feet below footing bearing level. Use of a full depth basement would reduce the heave potential with less depth of clay soils below the foundation bearing level. 2) The footings should have a minimum width of 16 inches for continuous walls and 2 feet for 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 36 inches below exterior grade is typically used in this area. 4) Continuous foundation walls should be 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. 5) All existing fill, topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the natural soils. The clay soils should be rernt¡ve<l ft¡r 3 feet below footing grade and the design bearing level re* H.P!KUMAR Project No. 18-7-411 -5- 6) established with compacted stntctural fill to reduce heave potential. The fill should be a well graded granular material such as 3/c inchroad base (CDOT Class 6) and compacted to at least 98Vo of standard proctor density at a moisture content near optimum. The fill should extend laterally beyond the footing a distance at least equal to one-half the depth of fill below the footing. Structural fill placed to reduce the heave risk should be at least 3 feet deep below the footings. A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FOI]NDATION 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 55 pcf for backfill consisting of the on-site fine-grained 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 45 pcf for backfill consisting of the on-site fine-grained 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. Backfill should be placed in uniform lifts and compacted to at least gAVo of the maximum standard Proctor density at a moisture content near optimum. Backfill 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 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 H.PÈKUMAR Project No. 18-7-41'l -6- fac.ilities constructed on the backfill. Backfill should not contain organics, clebris or rock larger than about 6 inches. 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 0.45 for gravel fill bearing soils. Passive pressure of compacted backfill 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 placêd against the sides ofthe footings to resist lateral loads should be a nonexpansive material compacted to at least 95Vo of. the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade construction. The clay soils possess a heave potential when wetted which could result in slab movement and distress if the bearing soils become wetted. The risk of slab movement can be reduced by removing the clay soils and placing at least 2 feet of compacted structural fill, such as road base, below the slab. 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 free-draining gravel should be placed beneath basement level slabs to facilitate drainage. This material should consist of minus 2inch aggregate with at least 507o retained on the No. 4 sieve and less than 2Vo passing the No. 200 sieve. H.PIKUfVIAR Projecl No. 18-7-411 -7 - All fill materials for support of floor slabs shourld be compacted to at least 95a/o uî nuxirnurn standard Proctor density at a moisture content near optimum. Required fill can consist of imported 3/q" road base devoid of vegetation, topsoil and oversized rock. UNDERDRAIN SYSTEM Although free water was not encountered during our exploration, it has been our experience in this area that 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, crawlspace and basement areas, 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 I foot below lowest adjacent finish grade and sloped at a minimum l7o to a suitable gravity outlet or sump and pump. Free-draining granular material used in the underdrain system should contain less than TVo 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 172 feet deep. An impervious membrane, such as 20 mil PVC, should be placed beneath the drain gravel in a trough shape ancl attached to the foundation wall with mastic to prevent wetting of the bearing soils. SURFACE DRAINAGE Proper surface drainage will be critical to limit potential for wetting below the building. 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 be avoided during construction. 2) Exterior backfill shor¡ld be adjusted to near optimum moisture and compacted to at least 957o of the maximum standard Proctor density in pavement and slab areas and to at least 90Vo of the maximttm standard Proctor density in landscape areas. H.P*KUMAR Project No. 18-7-411 -8- 4) The ground surface surrounding the extorior of the building should be slrrpect to clrain away from the foundation in all directions. Wc rccommcnd a miuimuur 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. Free-draining wall backfill should be capped with about 2 feet of the on-site soils to reduce surface water infiltration. Roof downspouts and drains should discharge well beyond the limits of all backfill. Landscaping which requires regular heavy irigation should be located at least l0 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. LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles amd 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 Iocations 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 futu¡e. If the client is concerned about MOBC, then a professional in this special ñeld 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 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. Signifîcant design changes may require additional analysis or mr.¡difications to the recommendations prcscnted herein. We recourmend on-site observation 1) 5) H-PÈKUIVIAR Projecl No. 18-7-411 -9- of exoavations and foundation bearing strata and tcsting of structural fill by a representative of the geotechnical engineer. Respectfully Submitted, H-P*KUMAR James H. Parsons, E.I. Reviewed by: Daniel E. Hardin, P JHP/kac ( Project No. 18-7-411 üt, --T--1--* râ E 1 "T -\ I f. L- .-.û *l Y i---+l'.+:ljr--t vra¡ .!+.' ,. ASPEN GLEN 'ï.;.:ì3:¡j- '\ EL BORING I \ ,, . ... ,,, ... À 1--*-- *"i:.-*-r_ ,___:__|. LOT S-r4.FILING 8-\ rta ar1oï BORING 2 '.\ .\ r SADDLEEACK OR'VE ROAD ELEVATION ASSUHED t00', 15 APPROXIMATI SCALE-FEET 18-7 -41 1 H.PryKUMAR LOCATION OF EXPLORATORY BORINGS Fig. 1 BORING 1 EL. gg.5'BORING 2 EL. 9g' .0 0 12/ 12 WC=6.3 DD= I 07 11/12 WC=7.1 DD=1 O5 -5 512/ 12 WC=6.8 0D=1 13 s/12 WC=1 1.8 DD=1 I 1 -200=45Ft¡JLILL IT¡-o- tr.lÕ 0 14/12 WC=7.8 DD= l 09 -2OO=49 lo |-l¡l ¡¿.4 ¡,! IIt-fL l¡Jô 7 /12 WC=15.3 DD=1 1 3 - 15 1554/ 12 WC=1.'l +4=52 -200=1 0 5a/6 -20 20 18-7 - 41 1 H-PryKUMAR LOGS OF EXPLORATORY BORINGS Fig. 2 TOPSOIL, CLAYEY SAND WITH SCATTERED GRAVEL, MOIST, BROWN. cLAy (cL): SL|GHTLY SANDY, MEDTUM ST|FF, SLtcHTLy MOTST TO MO|ST, BROWN. G!A_V!L _AND SAND (cc-sc): CLAYEY wtTH CoBBLES, MEÐtuM DENSE To DENSE, sLtcHTLyMOIST, GRAY. RELATIVELY UNDISTURBED ÐRIVE SAMPLE; 2-INCH I.D. CALIFORNIA LINER SAMPLE. DRIVE SAMPLE; STANDARD PENETRATION TEST (SPT), 1 3/8 INCH I.D. SPLIT SPOON SAMPLE, ASTM D_I586. 14/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT t4 BLOWS OF A 140-POUN0 HAMMER'',.- FALLING 50 INCHES WERE REOUIRED TO DRIVE THE CALIFORNIA OR SPT SAMPLER 12 INCHES. I pRrcrclL AucER REFUSAL. I NOTES.I. ÏHE EXPLORATORY EORINGS WERE DRILLED ON JUNE 18,2018 WITH A 4_INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY TAPING FROM TEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXFLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFERTO THE BENCHMARK ON FIG. 1. 4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES SETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT IHE APPROXIMATE SCIUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOÏ ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216)I DD = DRY DENSITY (PCf) (ASTM D 2216);+4 = PERCENTAGE RETAINED oN No. 4 SIEVE (ASTM D a22); -2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1 1 4O). F I 1 8-7-41 1 H-PVKUMAR LTGTND AND NOTTS Fig. 3 SÀMPLE OFr Sondy Cloy FROM:Boringl@5' WC=6.8%,ùù=tfspcf N JJ Llt3ul I zo F- c¡ J()azo() 2 0 -t -2 APPLITD t0 à( J) l¡J =UI I z(f F ô J() vtzo(J 0 -1 2 -3 .l PRESSURI -l0 EXPANSION UNDER CONSTANT PRESSURE UPON WETTING SAMPLE OF: Sondy Cloy FROM: Boring2€ 2.5' tNC = 7.1 %. tÐ = tOS pcf of r¡th ldd. lùç NO MOVEMENT UPON WETTING 18-7 -41 1 H-PVKUMAR SWTLL_CONSOLIDATION TTST RISULTS Fig. 4 HX5 HYDROUSÍËR ANALYSIS SIEVE AMLYSIS 3tÁrs3 ,lqq i I .....t. I 1 I I I I { SANt)GRAVEL FINE MEDIUM COARSE FINE coaRsÊ roo 0g ao to to 50 40 ¡o 20 to o r Hts ,!s. {ll! I i i lour!!a!n rTrt I i T II o to 20 EO ¡to 50 co 70 to 90 r00 I I Ë t ! Ë H I '.oo2 l I.oi¡,æt BIAMETÊR OF IN CLAY TO SILT COgÊLES GnAVEL 32 X 5AND ¡8 X SILT ANO CLÂY IO X SAMPLË OF: Sllghtly Cloycy Sondy Grovcl FROII:BorlngtglS' Th.ta lrrl rorultt optlt only lo lhô¡omÞl[ rhlch $rc larhd. th.l.rllng raÞort rholl ¡ot b. ngrodua.d,lrccpl ln tull. rllhout lh. Trill.n spprcvol ol K!ñqr & Aroclot!¡, l¡c,Sl0. onoltll¡ l.¡tlng lr ptrlom.d ln ôêcordoncr rlth ASïl¡ D¡122. ASIH Ct36añd/or ASII¡ Oll.l0. 18-7 -41 1 H-PVKUMAR GRADAÏION TTST RESULTS Fis. 5 H.P*KUMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProject No. l8-7-411SOILTYPESandy ClaySandy ClayVery Glayey SandSlightly Clayey SandyGravelSandy ClayVery Clayey SandSandy ClayUNCONFINEDcofitPREsstvESTRENGTHlosfìPLASTICINDEXlo/olLIQUIDLIMIT(o/"1PERCENTPASSINGNO.200SIEVE491045NATURALDRYDÊNSITYGRAVELSAND(v'l(vol38526.31071131091051,11113NATURALMOISTURECONTENT(%l6.87.81.17.111.813.3SAMPLE LOCATIONDEPTH(frtzYz51015zYz510BORING12