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Home My WebLink AboutSubsoils Report for Foundation DesignI $A [m'n$.ffio"m;'iE;,,,," An Emoloycc Orncd Comoony 5020tCorrrnty Road 154 Glenwood Spnirngs, CO 8n601 phone:: (9?0) 945-7988 faN::(9fl0) 945-8454 email : kaglenwood@lkumarusa.colll www.kumarusa.com Office Ir-ocafions; Denven (HQ)l Farke4 Coliorado'Springs, Fort Coltrins, G.lenwood Springs, and Surnrnii Cbun{g Colonrdb, SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT IIT,IRONBRIDGE 241 SILVER MOUNTAIN DRIVE GARFTELD COUNTY, COLORADO PROJECT NO.24-7-681 JANUARY 7,2025 PREPARED FOR: RED DEER REALTY ATTN: LEO CARMICHAEL 0766 RIVER BEND WAY GLENWOOD SPRTNGS, COLORADO 81601 0eocarmichaelS258@email.com ) { $ l.t -$ s N t TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION SITE CONDITIONS SUBSIDENCE POTENTIAL ........... FIELD EXPLORATION SUBSURFACE CONDITIONS FOI-INDATION BEARING CONDITIONS DESIGN RECOMMENDATIONS ... FOUNDATIONS FLOOR SLABS UNDERDRAIN SYSTEM SURFACB DRAINAGE............... FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS TABLE 1 _ SUMMARY OF LABORATORY TEST RESULTS 1 I 1 I FOUNDATION AND RETAINING WALLS ................- 4 - -2- .-2 - J .......- 3 - -?- ........- 4 - ........- 5 - 5- ....- 6 - l{rm&lmci@hc.o Ptoldllo.2+7flr PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot llT,Ironbridge, 241 Silver Mountain Drive, 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 Red Deer Realty dated December 2,2024. Hepworth-Pawlak Geotechnical (now Kumar & Associates) previously conducted a preliminary subsoil study for Lots 108 to I l8 and presented the findings in a report dated December 6, 2002, Job No. 101 196-1. 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 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 Building plans for the residence were in progress at the time of our study. In general, the proposed building will be in the middle part of the lot as shown on Figure 1 and be a I or 2 story structure possibly above a walkout lower level. Ground floor could be slab-on-grade or structural above crawlspace. Grading for the structure is assumed to be relatively minor with cut depths between about2 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 the field exploration and the ground surface appeared mostly natural, with come construction debris scattered on the surface of the lot. The ground surface has a moderate slope down to the southeast with about 6 feet of elevation difference across the building envelope. Vegetation consisted of sagebrush, grass and weeds in the building area. The lot surface was covered with about 6 inches of snow at the time of our visit. SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Ironbridge Subdivision. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some Kumar & Associates, lnc. @ Project No, 24-7-68;'l 2- 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 oertaln condltlons con cause slnkholes to develop and can produce areas of localized sutrsidence. During prcvi'nrs studies frrr Ilotttrrillge and other developnrents, hrnatl subsidence areas and sinkholes have been observed including sinkholes in the central to northern parts of lronbridge. 'l'hese sinkholes appeared similar to others associated with the Eagle Valley Evaporite in areas of the lower Roaring Fork River valley. Sinkholes were not observed in the immediate area of the subject lot or in the southern part of Ironbridge. 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 117 throughout the service life of the proposed residence, in our opinion, is low; 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. F'IELD EXPLORATION The field exploration for the pro.lect was conducted on December 71,2024. Three 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. Samples of the subsoils were taken with a l/"inch I.D. spoon sampler. The sampler was 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 thdpenetration resistance values are shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to our laboratory for revicw by thc projcct cnginccr and tcsting. SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils consist about %foot of topsoil overlying very dense, silty to slightly silty sandy gravel and cobbles with boulders. Drilling in the coarse granular soils with auger equipment was difficult due to the cobbles and boulders and drilling refusal was encountered in all 3 borings in the deposit. Laboratory testing performed on samples obtained from the borings consisted of natural moisture content and finer-than-sand-size gradation analyses. Kumar & Associates, lnc. @ Froirect No.2+7"681 -3- No free water was encountered in the borings at the time of drilling and the subsoils were slightly moist. FOUNDATION BEARING CONDITIONS The natural gravel and cobble soils encountered below the topsoil are suitable for support of spread footing foundations with moderate bearing capacity and relatively low settlement potential. All topsoil and clay soils (if any) should be removed from beneath the proposed building arca. Attypical foundation depths for the general proposed type of construction, we expect the excavation will be down into the gravel and cobble soils. Groundwater level is generally known to be well below the assumed depth of excavation' DESIGN RECOMMENDATIONS FOLTNDATIONS Considering the subsurface conditions encountered in the exploratory borings, our experience in the area, and the nature of the proposed construction, we recommend the building be founded with spread footings bearing on the natural granular soils. The design and construction criteria presented below should be observed for a spread footing foundation system. l) Footings placed on the undisturbed natural granular soils should be designed for an allowable bearing pressure of}Q!. ps! 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 l6 inches for continuous walls and 2 feetfor 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 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 ofthis report. 5) The topsoil, any fine-grained soil, and loose or disturbed soils should be removed and the footing bearing level extended down to the relatively dense natural granular soils. The exposed soils in footing area should then be moistened and compacted. 6) A representative ofthe geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. Kumar & Associates, lnc. @ ProjGct No, 2+7-iSN 4 FOUNDATION AND RETAININC 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 Lhe basis of an equivalenl. fluitJ unit weighl" uf at lcast 45 puf ft-rr bar"kfill cousisting 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 35 pcf for backfill consisting of the on-site granular soils. Backfill should not contain organics or rock larger than about 5 inches. 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% of the maximum standard Proctor density at a moisture content near optimum. Backfill placed in pavement and walkway areas should be compacted to at least95Yo 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. 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 0.50. 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 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 iootings to resist iaieral ioads shouid be a granuiar materiai compacted to at least 959lu of thc maximum standard Proctor dcnsity at a moisturc contcnt ncar optimum. FLOOR SLABS The natural on-site granular soils, exclusive of topsoil, are suitable to support lightly loaded slab- on-grade construction. 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 Kumar & Associates, lnc. @ Project ltlb, 2&7-6E1 5 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 2-inch aggregate with at least 50% retained on the No. 4 sieve and less thanZVo passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95o/o of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on-site gravel soils devoid of vegetation, topsoil, and oversized rock. LTNDERDRATN SYSTEM Although free water 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 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 l%oto a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than 2Yo passingthe 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 lVz feet deep. SURFACE DRAINAGE 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 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 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 covered with filter fabric and capped with about 2 feet of the on-site finer grained 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 inigation should be located at least 5 feet from foundation walls. Kumar & Associates, lnc. @ Project No. 2+'t-681 -6- IJNf,ITI\TIONS This fltudy h8 bm mductsd in amorrdre wift generally accepedgmt€fuicat cogiming principles md pnaoim in fris aca d tre time of ftis study. We nnnke no ururmty cifrer cx1rcss u impliod- The mclusiw md rmendations submiiffid in tris rqfrt ae bassd rym fts dda *trinsf ftm tre €xplmdry buingp drilld at the llocdftns indicdod on Figwc l, fre pn4mod type of m*ucilim snd orr experience in tdlrc uca- Our snioes do dinclndeaaumininsfrefrcsenoe" pvrrdimorpossibility ofmldcrotrabiologicfll omtminmb (ildOBC) dttt/clqli4g in lho fuurc. Iffte client is mmod Sod hdOBC, {hen a professimal in frris rysial field ofpactioe should be comhd- Ou findings inclode infierpoldim md mapolmim offrc subwrfrce omditions idediffisil * the @ormy bnings md vuidims in fte mbwfroc mditisrs may dbecome evidertrudil excavdim is perftrnod- If mditims enooffierul dudng mffirction apper diffired ftam ltffi kibed in ftis ryort, w'e Smld be oolifid m ftd ro-cnaluation of the rmddions may be made. This rqort hm becn prqmod fm ihe exrlrnft/e rm by our client fu dc*im p** V[e ue not rcrydle for tofrical iderllrddims by otrtrs of our infsmration As lhclrojod crroilvcs, we SmK pmvidc smlinuod milffiion ild fidd services duriry Wuuion to rwiew md mmih fre irylmion of m rmenddi<ms" and to veri& tdhqt me rmmddim hanebunErytryrideilyideryEfisd- Sigtrifrcmtdesign changesmaXrrcqufuea&titionat maltfsis or dificdims to fte rmaddim prcsmtod herein. We rmcnd cn*ib obecrndim of excandims md fmddfun bcming s{re md King of strutual ffi by a n4resc'rtatirac of tregpotofuical enginffi- ReepoctfttrySiffio4 Kumar & Associates, fnc. David A. Not6oom, 91a1ff renginecr Rwiwerlb5n Stcr/€nLPawlak, DAlSlkac I lvD Kumar & Associates, lnc. @ Proiect No. 24-7-581 e \&/ Qq- '-1:*" i 1 1 1 I I I i I ! I I i ! i L I l I ,q S{/ ,r--I I ! I BORING 1 I t, I 1 ! I j I L I .), .*,*.**""./ *s:,T"iHlii{ii i 'Lre ?4il1i ] ,b cl.I( I \ 1 \ ) I /6, 1 II I \ j I ) \ I 1 i I \ j iI/ BORING lt o I/ \o I I l, l lj I I I I i 1 I I I I I I i 241 SILVER IINTAIN DRIVF I 1 0 1 APPROXIMATE SCALE-FEET 24-7 -681 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1 BORING 1 BORING 2 BORING 3 'ry F ry o FLI LJ t! I-F.Llrlo s0/1 WC=2.0 -2UU=34 F LJtJu- I-F TL Lrlo 5 5 LEGEND TOPSOIL; ORGANIC SILTY SAND WITH SCATTERED GRAVEL & COBBLES, FIRM, MOIST, BROWN GRAVEL (0V); COSBLES AND BOULDERS, SANDY, SILTY, DENSE, SLIGHTLY MOIST, BROWN, ROUNDED ROCK. i DRTVE SAMPLE, 1 5/8-|NCH t.D. SpLtT SPOoN STANDARD PENETRATTON TEST .^ u ' DRIVE SAMPLE BLOW COUNT. INDICATES THAT 30 BLOWS OF A 1 4O-POUND HAMMER-"/ ' FALLTNG J0 TNCHES WERE REQU|RED To DRtvE THE SAMPLER I tNcHES. i PRACTICAL AUGER REFUSAL. WHERE SHOWN ABOVE BOTTOM OF BORING, INDICATES THAT MULTIPLE ATTEMPTS WHERE MADE TO ADVANCE THE HOLE. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON DECEMBER 1 1 , 2024 WITH A 4-INCH-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. 5. 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 EONTENT (%) (ASTM D2216)I -2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM Dl140) 24-7-681 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 K+rf H,'*lflffifffi*Hfi** TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No.24-7-681 UNCONFINED COMPRESSIVE STRENGTH SOIL TYPE Silty Sand and Gravel ATTERBERG LIMITS PLASTIC INDEX Pl"l 34 LIQUID LIMTT t%) PERCENT PASSING NO. 200 slEvE GRADATION SAND Plt GRAVEL (o/.1 NATURAL DRY DENSITY (ocfl 2 2.0 NATURAL MOISTURE CONTENT lolol SAMPLE LOCATION DEPTH {ftt BORING 2