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Home My WebLink AboutSubsoil Studyl(trtmffm:F'*" :: ,nn €lnpfioryoc tna'rod Correcny -5020 {ìounly lì.oad 154 Glcrrrvo<¡d Springs. CO Bló01 ¡rhone: (970) 945-7988 lax: (970) 945-8454 ernail : kaglenwoo<if¿r)ku¡narusa.corn ut!ll¡,.k u Dg¡9s4,-ceul O{lice Locations ilenve¡ { HQ), Parkrr Colorado Springs, Forl Collins, Gle¡woocl Springs, and Sumniit Couut¡,, Colo¡ad<l SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT SD-7, ASPEN GLEN SUNDANCE TRAIL AI\D BALD EAGLE WAY GARFIELD COUNTY, COLORADO PROJECT NO. 19-7-285 JUNE t4o20t9 PREPARED F'OR: WIIITNEY WARI) P.O. BOX 870 EDWARDS, COLORADO 81632 (woward@me.com) TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY..... PROPOSED CONSTRUCTION ........ SITE CONDITIONS...... SUBSIDENCE POTENTIAL. ............ FIELD EXPLORATION .................... SUBSURFACE CONDITIONS ......... - 1 - I I _) _ ..... - 3 - ,...,- 4. -7 - ..,''......'.,'.',. 7 - FOL'NDATION BEARING CONDITIONS -3- DESIGN RECOMMENDATIONS FOI.INDATIONS .,........-4- FOUNDATION AND RETAINING WALLS ....................5 - FLOOR SLABS.... TINDERDRAIN SYSTEM ......... - 6. SURFACE DRAINAGE........ LIMITATIONS FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 . LOGS OF EXPLORATORY BORINGS FICURE 3 - LEGEND AND NOTES FIGURE 4 - SWELL-CONSOLIDATION TEST RESULTS FIGURE 5 - GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS Kumar & Associates, lnc. o Project No. 19-7-285 PURPOSE AND SCOPE OF STUDY This report presents the results ofa subsoil sfudy for a proposed residence to be located on Lot SD-7, Aspen Glen, Sundance Trail and Bald Eagle Way, Garfield County, Colorado. The project site is shown on Figure 1. The purpose of the sludy was to develop recommendations for the foundation design. The sfudy was conducted in accordance with our proposal for geotechnical engineering services to Whitney Ward dated lll4ay 2,2A19. A field exploration progËm 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 werc 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 recornmendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION Plans for the proposed residence were not available at the tirne of our sfudy. The proposed construction is assumed to be a 2-story structure with attacheð garage. Ground fioors are assumed to be structural over crawlspace or slab-on-grade. Grading for the structu¡e is assumed to be relatively minor with cut depths between about 3 to 5 feet. We assume relatively light foundation loadings, typical of the proposed tlpe of construction. When building location, grading and loading infomation have been developed, we should be notified to re-evaluate the recommendations presented in this report. SITE CONDITIONS The subject site was vacant at the time of our field exploration. The ground swface is relatively flat with grades of less than 5o/o. Elevation difference across the building area is estimated at Kumar & Associates, lnc. 'Project No. 19-7-285 -2- around I to 2 feet. Vegetation consists of grass and weeds. There is an artificial pond on the southeast boundary of the lot. To our knowledge, the pond is constructed with an impervious liner to prevent leakage. SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen 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 gypsua deposits associated with the Eagle Valley Evaporite underlie po*ions of the lot. Dissolution of the g)?sum under certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. During previous work in the area, several sinkholes were observed scattered tlloughout Aspen Glen, mainly east of the Roaring Fork River. A small sinkhole was mapped about 200 fbet no(heast of Lot SD-7. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the middle tc¡ lower Roaring Fork River valley. Sinkholes were not observed in the irnmediate area of the subject lot. No evidence of cavities was etlcounte¡ed in the subsurface materials; however, the exploratory borings were relativeiy 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 SD-7 throughout the service life ofthe proposed residence, in our opinion, is low; however, the owner should be made aware of the potential fcrr sinkhole clevelopment. If further investigation of possible cavities in the bedrock below the site is desired, we should tle contacted. F'IELD EXPLORATION The field exploration for the project was conducted on May 8,2019. 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 CME-458 drill rig. The borings were logged by a representative of Kumar & Associates. Kumar & Associates, lne.Project No. 19-7-285 -3- 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 slrown on the Logs of Exploratory Borings, Figure 2. The samples were retumed 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 consist of about 6 inches of topsoil overlying relatively dense, silty sand and gravel with cobbles in Boring 1 and very stif{ sandy silt and clay in Boring 2. Relatively dense, silty sand ancl gravel with cobbles was encoulltered in Boring 2 at a depth of 6 feet. The sand and glavel continued down to the maximum drilled depth of 11 feet in both trorings. Drilling in the dense, coarse granular soils was difficult due to cobbles and possible boulders resulting in near practical auger drilling refusal. Laboratory testing performed on samples obtained from the borings included natural moisture content and density and gradation analyses. Results of a sweil-consolidation test performed on a relatively undisturbed drive sample of the clay and silt soils, presented on Figure 4, indicate low compressibility under conditions of light loading and low moisture content with a low hydro- compression potential under a 1,000 psf loading. Results of gradation analyses performed on small diameter drive samples (minus I%-inch fraction) of the coarse granular subsoils are shown on Figure 5. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at the tirne of ddlling and the subsoils were slightly moist. F'OUNDATION BEARING CONDITIONS The natural sandy clay and silt soils within about the upper 6 feet of Boring2 are low density and highly compressible rnainly when wetted. The underlying sand and gravel soils possess moderate bearing capacity and typically low settlement potential. At assumed excavation depths Kumar & Associates, lnc.':Froject No. 19-7-285 -4- we expect fhe subgrade will expose sandy clay and silt, and silty sand and gravel. Excavations of less than 6 feet in depth rnay need to be deepened to expose the less compressible gravel soils The sub-excavated depth can be backfilled with structural fill. Spread footings should be feasible for foundation support of the residence with a risk of differential movement due to variable bearing conditions. DESIGN RECOMMENDATIONS FOTINDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we recorrmend the building be founded with spread footings bearing on the natural granular soils or compacted structural fill. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural granular soils or compacted structural fill should be designed for an aliowable bearing pressure of 2,500 pq[. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about I inch or less. 2) The footings should have a minimum width of 16 inches for continuous walls and 2 feet fbr isolated pads. 3) Exterior footings and footings beneath unheated areas should be provided with adequale soil cover above their bearing elevation for frost protection. Placement of foundations at least 36 inches below exterior grade is typically used in this 'àrea. 4) Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 12 feet. Foundation walls acting as retaining structures should aiso be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining Walls" section of this report. 5) The low-density clay and silt soils, topsoil and any loose disturbed soils should be removed and the footing bearing levcl extended down to the relatively dense natural granular soils. The exposed soiis in footing area should then be moistened Kumar & Associates, lnc. :Project No. 19-7-285 5 and compacted. Structural fill placed below footing areas should be a relatively well graded granular soil compacted to at least9So/o of standard Proctor density at near optimum moisture content and extend at least one-half the filI depth below the footing laterally beyond the edges of the footing. A representative ofthe geotechnical engineer should 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 granular 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 granular soils. Backfill should not contain organics or rock larger than about 6 inches. All foundation and retaining skuctures 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 95Yo of the maximum standard Proctor density at a moisture coßtent near optimum. Backfill placed in pavernent and walkway areas should be compacted to at least9ío/o of the maximum standard Proctor density. Ca¡e 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. Sorne 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 6) Kumar & Associates, lnc.'i Project No. 19-7-285 -6- the side of the footing. Resistance tr: sliding at the bottoms of the footings can be calculated based on a coefficient of friction of 0.50. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 400 pcf. The coefficient of friction and passive pressure values recommended above asstxne ultimate soil strength. Suitable factors of safety should be included in the design to linit the strain which will occur at the ultimate strenglh, particularly in the case of passive resistance. Fill placed against the sides of the footings to resist laterai loads should be a granular material compacted to at least 95o/o af the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS The natural on-site soils, exclusive of topsoil, are suitable to supporl lightly loaded slab-on-grade construcfion. To reduce the effects of some differential movement, floor slabs should be separated from all bearing walls and columns with expansion joints which allow unrestrairied vertical moverlent. Floor slab control joints should be used to reduce damage due 1o 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 gnvel should be placed beneath basement level slabs to facilitate drainage. This material should consist of minus 2 inch âggregate with at least 50% retained on the No. 4 sieve and less than2o/o passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95% of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on- site granular soils devoid ofvegetation, topsoil and oversized rock. UNDERDRAIN SYSTEM Althougþ &ee wafer was not encountered during our exploration, it has been our experience in the area that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring 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 shouid tre placed at each level of excavation and at least 1 ftrot below lowest adjacent finish grade and sloped at a minimurn 1olo to Kumar & Associates, lnc. ì'Projecl No. 19-7-285 -7 - a suitable gravity outlet or drywell. Free-draining granular material used in the underdrain system should contain less than 2% passing the No. 200 sieve, less than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least lk feet deep. SURFACE DRAINAGE The following drainage precautions should be observed during construction and rnaintained at all times after the residence has been completed: l) Inundation ofthe foundation excavations and underslab areas should be avoided during construction. 2) Exlerior backfill should be adjusted to near opfimum moisture and compacted to at least 95o/a of the maximum standard Proctor density in pavement and slab areas and to at least 90% of the maximum standard Proctor density in landscape areas. 3) The ground surface surrounding the exterior of the building should be sloped to drain away from the foundation in all directions. We recommend a minimum slope of 6 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in the first l0 feet in paved areas. Free-draining wall backfill should be covered with filter fabric and capped wi¡h about 2 feet of the on-site finer graded soils to reduce surface water infiltration. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy irrigation should be located at least 5 feet ffom foundation walls, LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this time. We make no warranty either express or implied. The conclusions and reconmendations submitted in this reporl are based upon the data obtained from the exploratory borings driiled at the locations indicated on Figure 1, the proposed type of construction and our experience in the area. Our services do not inciude detennining the presence, prevention or possibility of mold or other biological contaminants (MOBC) developing in the future. lf the client is concemed about MOBC, then a professional in this special field of Kumar & Associates, lnc.:Project No. 19"7-285 -8 practice should be consulted. Our findings include interpolation and extrapolation of the subsurface conditions identified at fhe 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. Significant desigrr 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, Kunrar .* .,{isçeialer- lnç" James H. Parsons, E.I. Reviewed by: Steven L. Pawlak, JHP/kac cs: Sam ass. colTl { *}?åt (,I'q Kumar & Associates, lnc.',Project No. 19-7-285 7 \ x! :,": .,,¿ ti \¿t ;1. \ ç.,i l.t \ :'_:; \ SD:7 2t,9*9 SQ. FT. EoRtNgt ( ,,\ Iq"â APPROXIMATE SCALE-FTTT 19-7 -285 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1 BORING 1 EL. 100' BORING 2 EL. 100' 0 0 2116,50/2 WC=7.0 +4=38 -2OA=23 24/12 q 10/1 J0/A 3A/12 WC=8.6 DD=94 Fl¡l LJL I-Fo-Uô L Ir l--.fL TJô '' 0 10 2516,5A l3 41 /12 WC=1.9 *4=41 -200=1 6 l5 15 19-7-285 Kumar & Associates LOGS OF EXPLORATORY BORINGS rig. 2 E è LEGEND TOPSOIL SAND WITH GRAVÊI, SILTY, SCATTERED COBBLES, SLIGHTLY MOIST, SROWN. CLAY AND SILT (CL*MI); SANDY, SLICHTLY CATCAREOUS, VERY STIFF, SLIGHTLY MOIST, RED. GRAVEL AND SAND (CM-SM): StLTy, COBELES, ÐEN5E, POSS|BLE BOULDERS, SLtcHTLy MO|ST TO MO|ST, ROUNDED ROCK, GRAY/BROWN. DRIVE SAMPLI, 2-INCH I.D. CÂLIFORNIÁ LINER SAMPLE. DRIVE SAMPLE, 1 3/8-INCH LD. SpLtT SPOON STANDARD PENETRATTON TESÏ. 7a¡12 DRIYE SAMPLE ELOW COUNT. INDICATES'lll{T 21 ELOWS OF A Í4O-POUND HAMMER-','- FALLING 30 INCHES WERE REQUIREO TO DRIVE THF SAMPIER t2 INCHES. NOTES THE EXPLORATORY BORINGS WERE DRITLËÐ ON MAY 8,2OI9 WITH A 4-INCH-DIAMTTER CONTINUOUS-FLICHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MËASURED APPROXIMATELY BY PÀCING FROM FEAÏURES SHOWN ON THE SITE PLAN PROVIDEÞ, 3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEÀSURSO 8Y HÂND LEVEL ÂND REFER TO BORING 1 ELEVATION 100,, ASSUMED. 4.THE EXPLORÂTORY BORING LOCATIONS AND ELEVATIONS SHOULD SE CONSIDERED ACCURATT OÑLY TO THE D€OREE IMPLIED BY fHE METHOD USED. 5. THE LINES BETWEEN lvlÁTER¡ALS SHOWN ON THt EXPLORATORY BORING LOGS RgPREsEl,¡T THt APPROXIMATE BOUNDÂRITS STTWEEN MATERIAL TYPES AND IHE TRANSITIONS MÂY BE GRAÐUAL. 6, GROUNDWATER WAS NOT ENCOUNTEREO IN THg BORINGS AT THE TIME OF DRILLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%).(ASTM Ð2216)I DD = DRY DENSIIY (PCf) (ASTM 02216);+4 = PÊRCENTAGE RETAINED ON NO. 4 SIEVE (ÀsTM 069f3); -200= PERCENIAGE PASSING NO. 200 SIEVE (ASTM 01140). nu) ffit'. r-{ l:ó1 rJ l- l_l i 19-7-285 Kumar & Associates LTGTND AND NOTTS Fig. 3 E SAMPLE OF: Sondy Cloy ond Silt FROM:Borlng2OS' WC = 8.6 ?6, DD = 94 pcf ri ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUT TO WETTING 2 0x j-2 l¡J =vl t_4 oË !-sonzou-6 -10 -12 1 9-7-285 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fis. 4 å E !oo ao to 70 a0 !o & !o 20 10 o HYDROMSTTI ANALYSIS srEvg ANALYS|S ilvg RusK sr ¡D nD sEt¡gt cB¡ 90uÆE oP[xtx$ !/ir rr^. I r/t- i 1 / I I I t I I 1 i /¡ 1 ,.,),., I 1 I ... .-1. I ¡ /.1'- I' I l ì I I I I l- ¡ I ORAVEL I I-' -l' I SAND 't FINE MEDIUM FINE COARSE lo 20 s & 50 æ ,o æ ¡o !oo B þ ÞI Ë ..t CLÁY TO SILT COSBLÊS GRAVEL 38 X SAND LIOUID LIMI¡ SAIJPLE 0F: Sllt Grovel o.d Sond 39X PIASTTCITY r'¡OÉX SILT ANO CLAY 2T X FROM; Borlng I O2.5' ã ÞB F 'N ¡o to 70 s go 40 lo 20 ro o HYDRO}¡ËTER ANALYSIS SIIVE ÀXALYSIS lXt nudxG cu^R sou^nt oPt¡r|cs a/^, tltt t 1/.. t I'--1' i 1 ¡ ! t-'¡ i Ir --- -l i j t I I l I I GRAVT! 1 t r- t 1 t I SAND FINE MEDIUM FINE coARsg 10 ¡o ¡o 10 !o so 70 to ¡o roo I H Ë OIAMgTf,R CLAY TO SIII cosaLEs GR^VIL 4t x sÁND LIQUID LIMIT SATJPLE OF; Sllly G.ovel qnd Sond 43 X SILT AND CLAY PLASTICITY II'¡DTX FROM:Borlng2el0' 16X lh.tr l.rl t.sull! opply o¡lt to lha aqmp¡es whlch raÞ h¡lad. Thi l.slfng nporl Eholl nol b. r.p¡oducôd,c¡c.pl ln lull, wllhoul lh. wlllcn opprcvol ol Xumor & A¡toc¡olcs. lnc. Sl.v. ôñôly!l! l.rt¡ng h Þ.rloñ.d ln ôc€ord.n.. wllh ÄSlM D8915. ASfl¡ 07928, ASÍl¡ Ct36 o¡dlo¡ AS'M 0ll,l0. Fig. 5GRADATION TTST RTSULTS19-7 *285 Kumar & Associates It..irllit,:'i.ãairiiì.r*l ¡.i:i :tiâr¡ì :nit i.tii1ìt'*i;,; lt'ì¡ ¡i:ììïiiîirilùriiìi iìiìiiiiìi.risäi.iirr:tisiå,ñl'ìiTABLE 1SUMMARY OF LABORATORY TEST RESULTS19.7.285SOIL TYPESilty Gravel and SandSandy Clay and SiltSilty Gravel and Sand(psflut¡cot¡Ftt{ÊDcoHPRESSTVESIREI{GTHL[[IrSl:lolPLASTICINDÐ(AIIMILIQUID LIilfTpERCÊt{TPASSING NO.200 stEvE236143SANO(%)3938I4GRADATIONGRAVEL("/.)(ocfl1{ATURALORYDENSTY94lolo\NATURALIJIOISTURECONÍÊNT7,08.61.910ffrtDEPÍH)t/"152BORIN6