The URL can be used to link to this page

Home My WebLink AboutSubsoil Studyl.* iiçl[ffir:ffi1'"nËü** An Emdoycc Oryncd Compony 5020 CountyRoad 154 Glenwood Springs, CO 81601 phone: (910)945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com wwwkumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado SUBSOIL STT]DY FOR FOUNDATION DESIGN PROPOSED RESIDENCE 11707 corINTY ROAD 245 (BITFORD ROAD) GARFTELD COUNTY, COLORADO PROJECT NO.20-7-547 ocToBER 30, 2020 PREPARED FOR: TODD AND KATIE HUi\DERTMARK C/O DAYBREAK CONSTRUCTION ATTN: DANA YERIAI\ P.O. BOX 587 GLENWOOD SPRTNGS, COLORADO 81602 davbreakconst@hotmail.com TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION SITE CONDITIONS. FIELD EXPLORATION. SUBSURFACE CONDITIONS DE SIGN REC OMMENDATIONS FOUNDATIONS FOUNDATION AND RETAINING WALLS FLOOR SLABS... UNDERDRAIN SYSTEM ............. SITE GRADING....... SURFACE DRAINAGE LIMITATIONS. FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4 and 5 - GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS 1 ...-2 - J J 4 5 5 6 6 .....- 1 - I 1 -7 - Kumar & Associates, lnc.6 Project No.20-7-547 PURPOSE AND SCOPE OF STT]DY This report presents the results of a subsoil study for a proposed residence to be located at 11707 County Road 245 (Buford Road), in Garfield County west of New Castle, Colorado. The project site is shown on Figure 1. The purpose of the study was to develop reconìmendations for foundation design. The study was conducted in accordance with our proposal for geotechnical engineering services to Todd and Katie Hundertmark dated September 23,2020. 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 anaþed 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 borings were located in an existing excavation cut atthe expected building area. The proposed residence is assumed to be a two story wood frame structure over a walkout basement, and the ground floor will be slab-on-grade. Grading for the structure is assumed to be siguificant with cut depths between about 2 to l0 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. If the building location, grading and loading information change, we should be notified to re- evaluate the recommendations presented in this report. SITE CONDITIONS County Road 245 (Buford Road) runs along the north east edge of the parcel. The lot is mostly natural and drops with a very steep from Buford Road for approximately 15 yards, then continues in a moderately sloping manner down to the south west. There is a short, graveled drive and an existing storage building near the entrance to the site, and an unimproved track that runs to the immediate south west of the building site. The building site is approximately 50 yards Kumar & Associates, lnc. @ Project No. 20-7-547 I-L- down a steep to moderately steep slope from, and south west of, Buford Road and has an existing cut excavated into the slope. The cut ranges from approximately 8 feet deep on the northwest corner to 6 feet deep on the northeast comer to ground level at the southwest and southeast corners. Inside the excavation is a large wood scrap and slash pile, and to the excavation's southwest is a boulder and spoil pile. Below the excavation and spoil pile is a moderately to strongly sloping meadow. Vegetation within the building envelope consists of grass and weeds. Sand, gtavel, and small cobbles were observed on the ground surface. There are juniper trees and brush upslope of the excavation toward Buford Road. FIELD EXPLORATION The field exploration for the project was conducted on September 28,2020. Two exploratory borings were drilled at the locations shown on Figures I to evaluate the subsurface conditions. The borings were advanced with a 4-inch diameter continuous flight auger powered by a truck- mounted CME 458 drill rig. The borings were logged by a representative of Kumar & Associates, Inc. Samples of the subsoils were taken with I% 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-l586. 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 CONDTTIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils consist of a thin topsoil "root zone" layer overlying 4 to 5% feet of loose to medium dense clayey, silty, sand, underlain by 10 to l2r/z feet of medium dense sandy, silty gravel, underlain by medium dense to loose, wet, clayey, silty, gravel and sand down to the final sampling depth of 31 feet. Laboratory testing performed on samples obtained from the borings included natural moisture content, density, and gradation analyses. Results of gradation analyses performed on small Kumar & Associates, lnc. @ Project N0.20-7-547 -J- diameter drive samples (minus l%-inch fraction) of the sand subsoils from both borings are shown on Figure 4 and5. The laboratory testing is summarizedinTable 1. Free water was encountered in Boring I at 18 feet, I inches deep and in Boring 2 at I8 feet deep at the time of drilling and, the upper subsoils were slightly moist to moist. DE STGN RECOMMEIIDATIONS 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 the natural granular soils. 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 should be designed for an allowable bearing pressure of 1,500 psf. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. 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 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 feeL Foundation walls acting as retaining structures should be designed in accordance with the recommendations in the "Foundations 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 relatively dense natural granular soils. The exposed soils in footing area should then be moistened and compacted. Kumar & Associates, lnc. o Project No. 20-7-547 -4- If water seepage is encountered, the footing areas should be dewatered before concrete placement. A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FOUNDATION AND RETAINING V/ALLS 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 residence and can be expected to deflect sufficiently to mobilize the fuIl 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 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 content near optimum. Backfill in pavement and walkway areas should be compacted to at least 95o/o of the maximum standard Proctor density. Care should be taken not to over-compact 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. Backfill should not contain organics, debris, or rock larger than about 6 inches. We recommend free-draining granular soils for backfilling foundation walls and retaining structures because their use results in lower lateral earth pressures and the backfill can be incorporated into the underdrain system. 6) Kumar & Associates, lnc. @ Project No.20-7-547 -5- 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. 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, particularþ in the case of passive resistance. Fill placed against the sides of the footings to resist lateral loads should be a granular material compacted to at least 95%o 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. 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 2-inchaggregate with at least 50% retained on the No. 4 sieve and less than 2Yopassing 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 granular soils devoid of vegetation, topsoil and oversized rock. LTNDERDRAIN SYSTEM Free water was encountered during our exploration, and it has been our experience in mountainous areas 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 Kumar & Associates, lnc. @ Project No. 20-7-547 -6- 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 1 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 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 lYzfeet deep. An impervious membrane such as 20 mil 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. SITE GRADING The risk of construction-induced slope instability at the site appears low provided the building is located above the steep slope as planned and cut and fill depths are limited. 'We assume the cut depths for the basement level will not exceed one level, about 10 feet. Fills should be limited to about 8 to 10 feet deep, especially at the uphill side of the residence where the slope steepens. Embankment fills should be compacted to at least 95Yo of the maximum standard Proctor density near optimum moisfure content. Prior to fill placement, the subgrade should be carefully prepared by removing all vegetation and topsoil and compacting to at least 95o/o of the maximum standard Proctor density. The fill should be benched into the portions of the hillside exceeding 20o/o grade. Permanent unretained cut and fill slopes should be graded at2honzontal to 1 vertical or flatter and protected against erosion by revegetation or other means. The risk of slope instability will be increased if seepage is encountered in cuts and flatter slopes may be necessÍry. If seepage is encountered in permanent cuts, an investigation should be conducted to determine if the seepage will adversely affect the cut stability. This office should review site grading plans for the project prior to construction. SURFACE DRAINAGE The following drainage precautions should be observed during construction, and maintained at all times after the construction has been completed: Kumar & Associates, lnc. @ Project No.20-7-547 -7 1)Inundation of the foundation excavations and underslab areas should be avoided during construction. Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95o/o of the maximum standard Proctor density in pavement and slab areas and to at least 90Yo of the maximum standard Proctor density in landscaps areas. 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 l0 feet in paved areas. Free-draining wall backfill should be covered with filter fabric and 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 irrigation 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. 2) 3) s) LIMTTATIONS 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 during construction appear different from those described in this report, we should be notified so that re-evaluation of the recommendations may be made. 4) Kumar & Associates, lnc. @ Project No. 20-7-547 -8- 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 recoürmendations, and to verifo that the recoûtmendations 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 filI by a representative of the geotechnical engineer. Respectfully Submitted, Kumar & Associ¡tes, Inc. David Noteboom, Staff Engineer Reviewed by: Daniel E. Hardin, DNlkac Kumar & Associates, lnc. @ Proiect No. 20-7-547 BORING 2 o ):444ft,.tørr,Vil o BORING 1 BOTTOM LEVEL OF EXISTING BUILDING EXCAVATION NOT TO SCALE 20-7 -547 Kumar & Associates LOCATION OF TXPLORATORY BORINGS Fig.1 ¡ I WC= 1 2.3 +4=58 -2AA=21 BORING 1 BORING 2 0 0 10/ 12 5 16/ 12 WC=8.2 DD=1 1 6 -2OO=42 58/ 12 WC=8.1 DD= 1 06 -200=59 10 12/ 12 WC= 10.6 DD=115 *'4=28 -200=35 1015/ 12 WC=7.9 DD= 1 35 +4=43 -ZQO=27 '15 15 F-t¡J bJlÀ I :EFo-tJo 17 /12 21/12 F L¡J Lrl LL I-t-fLt¡lô o 20 20 15/ 12 16/ t2 25 25 2e/ 12 4/12 30 50 1s/ 12 6l 12 55 55 20-7 -547 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 ì 3 € ¡ N TOPSOIu SILTY SAND, ROOT ZONE SAND (SM); SILTY, GRAVELLY TO VERY GRAVELLY, MEDIUM DENSE, SLIGHTLY MOIST' RED BROWN MIX W GRAVEL BROWN (GM); GRAVEL, SANDY TO VERY SANDY, SILTY, MEDIUM DENE, SLIGHTLY MOIST, RED, MIX. SAND (SC-SM) S|LTY, CLAYEY, WITH RAVEL, MEDIUM DENSE, WET, RED, BROWN MlX. DRIVE SAMPLE, 2_INCH I.D. CALIFORNIA LINER SAMPLE. i DRTVE SAMPLE, 1 s/1-INCH l.D. SPLIT SPOON STANDARD PENETRATION TEST. .^ I.ı DRIVE SAMPLE BLOW COUNT. ¡NDICATES THAT 1O BLOWS OF A 14o-POUND HAMMERtv/ t¿ FALLINc SO TNCHES WERE REQUTRED TO DRIVE THE SAMPLER 12 INCHES. ! oTpTH To WATER LEVEL AND NUMBER OF DAYS AFTER DRILLING MEASUREMENT WAS MADE ---> DEPTH AT WHICH BORING CAVED. NOTES I. THE EXPLORATORY BORINGS WERE DRILLED ON SEPTEMBER 28, ZO2O 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 ARE AT THE SAME ELEVATION. 4. THE EXPLORATORY BORING LOCATIONS 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 LEVELS SHOWN ON THE LOGS WERE MEASURED AT THE TIME AND UNDER CONDITIONS INDICATED. FLUCTUATIONS IN THE WATER LEVEL MAY OCCUR WITH TIME. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D2216); DD = DRY DENSITY (pct) (ASTU Ð2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM 06913); -2OQ= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM 01140). 20-7 -547 Kumar & Associates LTGTND AND NOTES Fig. 3 3 e .i'; É{.,à "áiì Ëi âd ı r00 90 80 70 60 50 40 50 20 10 o to 20 30 40 50 60 70 ao 90 - 100 Lt8 200 .425 152 DIAMETER OF IN RS CLAY TO SILT COBBLES CRAVEL 28 %SAND 39 %SILT AND CLÄY 33 % SAMPLE OF: Silty Sond ond Grovel FROM:BoringI€9' = too 90 a0 70 60 50 40 JO 20 10 o o to 20 30 40 50 60 70 ao 90 to0 = .oo2 .o05 150 .500 î9 54.1 7e.2 I DIAMETER SIN CLAY TO SILT COBBLES GRAVEL 3A %SAND 41 %SILT AND CLAY 21 % SAMPLE OF: Silly Sond ond Grovel FROM: BorÌng 1 @20'&25' The!6 lssl r€sulls qpply only lo lhê somplos whlch we¡e lesled. lhe legllng r€port shqll nol be rgproduc€d, excapl ln full, wlthoul lho wrlll6n opprovol of Kumor & Assocìolos, lnc. slgvo onqlys¡s lsslíng ls p6rform6d in occordonce wlth ASÍM D6915, ASTM 07928, ASTM c136 qnd/or ASTM D'|140. SIEVE ANALYSISHYDROMETER ANALYSIS CLEAR SOUARE OPENINGS a/u, at^r 1 t/r. u.s. SÍÀNDARD SÉR|ES ¡Âô 4¡ô ¡1ô ¡16 ¡iO f8 TIME REAOINGS t1HRS21 BRS 7 iii I ! I I I I ì/ I I I i I I i j I tltt GRAVELSAND MEDIUM ICOARSE FIN E COARSEFINE SIEVE ANALYSISHYDROMETER ANALYSIS CLEAR SOUÀRE OPENIXGS ./^6 a/1. 1 1lr" U.S. SÎANDARD SERIES ¡50 ¡¡o ¡30 t16 ato ¿87 HRS TIME REAOI{GS 6ôUtN iqMlN 4MlN ì¡llfÌ I I i I 1 I i tll, i t,- lilltt t!lr ¡i i I ,lr tl rrrril GRAVELSAND COARSEFI NE MEDIUM COARSE FINE 20-7 -547 Kumar & Associates GRADATION TTST RESULTS Fig. 4 3 I q Iı H r00 90 ao 70 60 50 40 30 20 to o o 10 20 30 ,+(, 50 60 70 ao 90 too z- .o57 .o75 ,'t50 DIAMETER OF IN CLAY TO SILT COBBLES GRAVEL 43 %SAND 30 %SILT AND CLAY 27 % SAMPLE OF: Sqndy Silty Grovel FROM:Boring2AlO' Thes€ lrsl rosulls opply only lo lh€ sqmplæ whlch w€.o loslsd. The l€sl¡ng rsporl sholl nol bo reproduced, excepl ln full, wllhoul lhe wrltlen opprovo¡ of Kumor & Assoclotes, lnc. Slcv. onolysls losllng ls psrformod in occordqnco wllh ASn 06915, ASTM D7928, ASTM C136 ond/or ASTU Dll,fo. SIÊVE ANALYSISHYDROMËTER ANALYSIS CLEAR SQUARE OPENIHGS att t . ttr TIMÉ READINGS 2,1 HRS 7 HRS ta ¡5d ¡& ¡lô ato ta¡im ¡r6:'t-titI rt r -,1----r-L ,--,,- -l I + . -D- GRAVELSAND FINE MEDIUM COARSE FINE COARSE 20-7 -547 Kumar & Associates GRADATION TTST RESULTS Fig. 5 l(+rtKumr & Associates, lnc. @Geotechnical and Materials Engineersand Environmental ScientistsTABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.20-7-547Gravelly Silty Sand11642Silty Sand and GravelSilty Sand and GravelSandy SiltSandy Silty GravelSOIL TYPELIQUID LIMITUNCONFINEDCOMPRESSIVESTRENGTHPLASTICINDEXJJ2l5927PERCENTPASSING NO.2(l(l SIEVE30(%)SAND394l283843GRADATIONt%)GRAVEL113106135locflNATURALDRYDENSITY8.17.9lo/"1NATURALMOISTURECONTENT8.210.6t2.350IffrlDEPTH4920&2512SAMPLE LOCATIONBORING