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Home My WebLink AboutSubsoil Study for Foundation Design 10.04.2023l(tn ffimr&bd#"hc.6 Geotechnical and ltlaterials Engineers 5'02:0'Comty Road [54 andEnvironmental Scientists Glenwood lSprimgs, CIO 8['60{ phone: (970) 945-7988 fax: (970) 945-8!t54 'enmil : il<agflenwood@;kiu,rnanusa.'oorn An Employcc Owttccl Compoty www.kumarusa.com ,Office [,ocations: Denver r(f{Q), trarkor, i0otorado Spnings, Fort Collins, Glenwood Sprrings, anil Sumnit Oounty, tColorarilo SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT H17, FTLTNG 7, ASPEN GLEN 15 HORSESHOE LANE GARFTELD COUNTY, COLORADO PROJECT NO. 23-7-522 ocToBER 4,2023 PREPARED FOR: JOHN AND MARLISSA WESTERFIELD 211 CENTRAL PARK WEST APT 3E NEW YORK, NEW YORI( 10024 iwestv59@email.com marlissaw228 1@email.com TABLE OF'CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION SITE CONDITIONS.. SUBSIDENCE POTENTIAL IIIELD EXPLORATION SUBSURFACE CONDITIONS _') _ a a -) .- I - I 1 -6- FOLINDATION BEARING CONDITIONS DESIGN RECOMMENDATIONS I.OUNDA'I'TONS FOUNDATION AND RETAINING WALLS FLOOR SLABS LTNDERDRAIN SYSTEM SURFACE DRAINAGE................ LIMITATIONS FIGURE 1 - LOCATION OF EXPLORATORY BORTNGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4 and 5 - SWELL-CONSOLIDATION TEST RESULTS TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS _1_ lfumrrt Acsoctiles, lnc. o nrcicdilo.z$t-Uz PURPOSE AND SCOPE OF'STUDY This report presents the results ofa subsoil study for a proposed residence to be located on LotHl7, Aspen Glen, 15 Horseshoe Trail, 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 proposal for geotechnical engineering services to John and Marlissa Westerfield dated August 25,2023. 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, design recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION The residence will be located on the lot shown on Figure 1. The design for the residence was conceptual at the time of this study, and for purposes of analysis it is assumed the building will be a one-or two- story wood frame structure with an attached garage. Ground floors are assumed to be structural over crawlspace or slab-on-grade in the living areas and slab-on-grade in the attached garage. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 5 feet. We assume relatively light foundation loadings, typical of the assumed 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 the field exploration and the ground surface appeared to have been lightly graded for development. The terrain was nearly flat, with a gentle slope down to the northeast. Elevation difference across the building envelope is about 3 feet. Vegetation consisted of sparse grasses and weeds. The golf course is adjacent to the south west side of the lot. SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen development. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and Kurnar E AssociatEs, lnc. @ Project f{o.23;7-622 "| 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 lot. 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, several sinkholes were observed scattered throughout the development, mostly east of the Roaring Fork River. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in other areas of the Roaring Fork River Valley. 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 H17 throughout the service life of the proposed residence, in our opinion, is low and similar to other nearby platted lots; 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 September 13,2023. 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-45B drill rig. The borings were logged by a representative of Kumar & Associates. Sarnples of the subsoils were taken with l% inoh and 2 inch I.D. spoon samplers. The samplers were driven into the subsoils at various depths with blows fi'om 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 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 encountered, below about/z foot oftopsoil, consisted ofabout 9/zfeet ofhard to stiff; sandy silty clay underlain by relatively dense, silty sandy gravel and cobbles with probable small boulders that extended down to the maximum explored depth of 12 feet. Drilling in the dense coarse granular soils with auger equipment was difficult due to the cobbles and boulders and drilling refusal was encountered in both borings in the deposit. lfti'mar& AscsciaSes, llnc. o lProject No.23-7-522 -3- Laboratory testing performed on samples obtained from the borings included natural moisture content and density and percent finer than sand size gradation analyses. Results of swell- consolidation testing performed on relatively undisturbed drive samples of the silty clay soils, presented on Figures 4 and 5, indicate low compressibility under conditions of light loading and existing moisture conditions, and low to moderate compressibility under conditions of loading and wetting. The laboratory testing is summarized in Table L No groundwater was encountered in the borings at the time of drilling and the subsoils were slightly moist. FOUNDATION BEARING CONDITIONS The silty clay soils possess low bearing capacity and tend to settle when wetted. The underlying dense coarse granular soils possess moderate bearing capacity and relatively low settlement potential. At assumed excavation depths, the subgrade soils are expected to consist of the silty clay. Spread footing bearing on these soils should be feasible for foundation support with some risk of movement. The risk of movement is primarily if the bearing soils were to become wetted, and precautions should be taken to prevent wetting. Based on our experience in the area, the silty clay soils typically do not possess an expansive potential and the potential for expansion can be neglected in the foundation design but should further be evaluated at the time of construction. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we believe the building can be founded with spread footings bearing on the natural soils with some risk of movement. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural soils should be designed for an allowable bearing pressure otlJ-QQ-pSL Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about I inch or less. There could be some additional movement if the bearing soils if the bearing soils were to become wetted. The magnitude of the additional movement would depend on the bearing conditions and depth and extent of the wetting, but may be on the order of %to 1 inch. 2) The footings should have a minimum width of 18 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 Kurnar& Assooiates, |nc. o Proiect No.23-7-522 -4- 4) of foundations at least 36 inches below exterior grade is typically used in this atea. Continuous foundation walls should be heavily reinforced top and bottom to span local anomalies and better withstand the effects of some differential movement such as by assuming an unsupported length of at least 12 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. All existing fill, topsoil and any loose disturbed soils should be removed and the footing bearing level extended down to the firm natural soils, and the subgrade should then be moistened and compacted. A representative ofthe geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FOLINDATION AND RETAINING WALLS Foundation walls and retaining structures which are laterally supported and can be expected to undergo only a slight amount of det-lection should be designed tbr 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 clay soils. Cantilevered retaining structures which are separate from the residence and can be expected to deflect sufficiently to mobilize the full active eafth 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 soils. The backfill should not contain topsoil or oversized (plus 6-inch) rocks. 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 90%o of the maximum standard Proctor density at a moisture content slightly above optimum. Backfill placed in pavement and walkway areas should be compacted to at least 95Vo 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. Use of a select granular material such as base course and increasing compaction to at least 98%o standard proctor density could be done to reduce the backfill settlement. s) 6) f(umar& Acrociiles, Nnc. @ Fmjedtlo.2T7.5in 5 The lateralresistance 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 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 placed against the sides of the footings to resist lateral loads can consist of the on-site soils and should be 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. There could be some slab movement if the sandy clay subgrade were to become wetted. 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 sand and gravel, such as road base, should be placed immediately beneath slabs-on-grade for support. This material should consist of minus 2-inch aggregate with at least 50% retained on the No. 4 sieve and less than 12o/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 fill can consist of imported coarse granular material, such as CDOT Class 5 or 6 aggregate base course. UNDERDRAIN SYSTEM Although groundwater was not encountered during our exploration, it has been our experience in the area and where clay soils are present that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can also create a perched condition. We recommend below-grade construction, such as deep crawlspaces, retaining walls, and basement areas be protected from wetting and hydrostatic pressure buildup by an underdrain system. An underdrain around shallow crawlspace areas (less than 4 feet deep) may not be needed with adequate compaction of foundation backfill and positive surface slope away from foundation walls. If installed, the drains should consist of 4 inch diameter PVC drainpipe placed in the bottom of the wall backfill surrounded above the invert level with free-draining granular material. The Kumar& Associates, lnc. @ Project No.23-7-522 -6- drain should be placed at each level of excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum %Yo to a suitable gravity outleto a sump and pump system or to a properly constructed drywell. Free-draining granular material used in the underdrain system should contain less than 2Vo pass\ng 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 l%feet deep and be covered by filter fabric such as Mirati 140N. SURFACE DRAINAGE Positive surface drainage is a very important aspect of the project to prevent weffing of the bearing soils. The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: l) Inundation ofthe foundation excavations and underslab areas should be avoided during construction. 2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95Yo 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 l0 feet in unpaved areas and a minimum slope of 3 inches in the first l0 feet in paved areas. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy irrigation, such as sod, and lawn sprinkler heads should be located at least 5 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 and 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 locations 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 borings and variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountered lfumar& Acsociates, lnc. @ Frqiec{ to.23-7622 -7- during oonstudion ryerditraut ftmltosedcscribod fu1ftisrqnnt, rve shouldbenotifiod so that ro.eirafudftm of fte rooommaddions may be made- Thisrqodhasbeenpnryaredfor&€exclusiveusebyomcliertfudcsign1nrrp6€s- Weuenot rcepm$ible for tochnical int€ryrctdions by ofrem of our infomatim- lls fu project cnolveg we shorildprovide ontinrrcd msultaim d fictd seivioes dudag@ffiucfion to rwie;w md mmitor ft€ irylementation of our rmmaddionq and to veri& that the rmendations hane b€en rypopiarcly intspr€ficd- Significd dcign ^ha'rg€s mny rcquirc additional malysis mmodifications to fte remrrrmcdations pmted huein We rsmend on*ite obserndion ofexcavations andfomddionbeuing ffisqt testingofstructural fillby arqresentdiveof fte gsotefuical €ngirc. RepoctfirllySubmifioc Kumar & Associates" Inc. Itavid ANoteboom, Statr Rarienrodby: Dmiel E Hdditr" DElllkac Cc: Kl\Designworks-(wayl and @ka-desi enworks. com) Kumar & Associates, lnc. o Project No. 23-7'522 lBM ELEV,=6051,46' to tt 7.5'Utility, Drolnage & l.rlgotlon Eosem€nt -eZe Iot F/B Edge of Asphalt 11.5'Droinoge. Accass I 20.0'Bulldlng Env€lopo -. s 89's8'JJ" E- 4.77, w 0roinage Eot€ment 20.0' Bfilding Enwlopo v w Vo ov 'o) t::-z- w w w v v f,o/ f/6 :a 7.5'ut{lty, & lr.igotlon Drainog€ Eca€m6nt q9 fdge ol Fqirwoy w v v I 0 40 APPROXIMATE SCALE-FEET 23-7 -522 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1 BORING 1 EL. 8,056' BORING 2 EL. 8,054.5' 0 0 3s/12 21/1? WC=7.8 DD=99 5 e/12 WC= 1 2.5 DD=102 43/12 WC=7.8 DD=1 1 4 -200=83 E F trJt! L! I-F o_ TJo F lrJL! LL I-FL UJo 10 52/ 12 54/12 10 20 /o 15 15 23-7 -522 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 t o- I I LEGEND TOPSOIL, SANDY SILTY CLAY WITH ROOTS AND ORGANICS, FIRM, DRY TO SLIGHTLY MOIST, MEDIUM BROWN, CLAY (CL) SILTY, SANDY, HARD TO ST|FF, SLtcHTLy MO|ST, MEDTUM BROWN, SLTGHT TO TRACE CALCAREOUS, OCCASIONAL SLIGHT POROSITY. W GRAVEL (GM) WrrH CoBBLES AND PROBABLE SLIGHTLY MOIST, GRAY. BOULDERS, SANDY, SILTY, VERY DENSE, DRIVE SAMPLE, 2_INCH I.D. CALIFORNIA LINER SAMPLE. i DR|VE SAMPLE, 1 3/8-rNCH r.D. SpLtT SPOON STANDARD pENETRATTON TEST lql1? DRIVE SAMPLE BLOW COUNT. |NDICATES THAT 39 BLOWS OF A 14o-POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. f enlcrrcll AUGER REFUSAL. NOTES 1 THE EXPLORATORY BORINGS WERE DRILLED ON SEPTEMBER 13,2023 WITH A 4-INCII-DIAMETER CONTINUOUS-FLIGHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED. 4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D2216); DD = DRY DENSITY (PCt) (ISTV D2216); -2OO = PERCENTAGE PASSING NO. 200 SIEVE (ASTM Dl140). 23-7 -522 Kumar & Associates LEGEND AND NOTES Fig. 3 I SAMPLE OF: Sondy Silty Clcy FROM:Boringl@4' WC = 12.5 %, DD = 1O2 pcf ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING I ft6!€ t€at r..ult8 opply only lo the somplss t€ded. fte t .tinq rcpod 3holl not b. reproduccd, .xc6pt in full, wibout thc *dR€n opprovol ol Kumor ond ksociotc!, lnc. S*ell Consolidotlon tolting podormd in occordoncs with Sil D-4546. I 1.0 - KSF 10 100 1 J J IJ =(n 0 -1 -2zo F a Ioazoo -3 -4 23-7 -522 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4 I E q q 9 SAMPLE OF: Sondy Silly Cloy FROM:Boring2@2' wc = 7,9 %, DD = 99 pcf ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING I \ l l I I ) ftcs t d rc3ulta apply only to th6 rmploe t6€t€d. fte taating 6pod rholl not b. roproduc.d, €rc€pt in rull, wibout thc wfrftn opprovol d(omor ond &:ociotc!, lnc. Sf,lll bmolidotion t Eting p.dom.d in tc@rdonc. $th ffi D-4546- 2 _JJ trJ =v1 I zotr o Joazoo 0 2 4 b 8 1.0 aPPL|ED PRESSURE IKSF 10 r00 23-7 -522 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 5 KrnffififfiF;** := TABLE 1 SUMMARY OF LABOMTORY TEST RESULTS No.23-7-522 ATTFRBF IG I IMITSGRADATION GRAVEL f/"1 SAND Pkl PERCENT PASSING NO. 200 stEVE LIQUID TIMIT t0kl to/ol PLASTIC INDEX aosfl UNCONFINED COMPRESSIVE STRENGTH SOIL TYPEBORING ftt DEPTH to/"\ NATURAL MOISTURE CONTENT (Dcn NATURAL DRY DENSITY Sandy Silty ClayI412.5 102 Sandy Silty Clay7.8 9922 83 Sandy Silty Clay47.8 114