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Home My WebLink AboutSubsoil Study for Foundation Design 01.30.18H.PVKUMAR Geotechnical Engineering I Engineering Geology Materials Testing I Environmental 5020 County Road 154 Glenwood Springs, C0 81601 Phone: (970) 945-7988 Fax (970) 945-8454 Email: hpkglenwood@kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 24, BLOCK 4 BATTLEMENT CREEK VILLAGE 88 BOULDER RIDGE DRIVE GARFIELD COUNTY, COLORADO PRO.IECT NO. 17-7-869 .IANUARY 30,2018 PREPARED F'OR: ANDREW TERRAZAS C/O RUSSELL CARTWRIGHT 18 VALLEY VIEW PLACE PARACHUTE, COLORADO 81625 @ î{lR 0 6 2018 BY: R TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY. PROPOSED CONSTRUCTION .. SITE CONDITIONS . FIELD EXPLORATION SUBSURFACE CONDITIONS FOUNDATION BEARING CONDITIONS DESIGN RECOMMENDATIONS FOUNDATIONS FLOOR SLABS UNDERDRAIN SYSTEM ..... SURFACE DRAINAGE ........ LIMITATIONS FIGURE 1 - LOCATION OF EXPLORATORY BORING FIGURE 2 -LOG OF EXPLORATORY BORING FIGURES 3 &. 4 - SWELL-CONSOLIDATION TEST RESULTS TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS 1 1 I n -2- -3 - a a .',.'.......- 4.\ -5 -6- H-P=KUMAR Project No. 17-7-869 PURPOSE AND SCOPE OF STUDY This report ptesents the results of a subsoil study for a proposed resiclence to be located on Lot 24, Block 4, Battlement Creek Village, 88 Boulder Ridge Drive, Garfield County, Colorado. The project site is shown on Figure 1. The pulpose of the study was to develop recommendations for the foundation design. The study was conducted in accoldance with our agreement for geotechnical engineering services to Andrew Terrazas c/o Russell Cartwright dated December 13, 2017. An exploratory boring was drilled to obtain information on the subsurface conditions. Samples of the subsoils obtained cil.rring the field exploration were tested in the laboratory to determine their classification, cornpressibility or swell ancl other engineering characteristics. The results of the fielcl exploration ancl laboratory testing were analyzed ta develop recommendations for foundation types, depths ancl allor.vable pressures for the proposed building foundation. This repoft summarizes the clata 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 proposed residence will be a one story wood-frame structure with an attached lVz story garage. Ground floors rvill be structural over crawlspace with slab-on-grade in the garage. Grading for the structure is assumed to be relatively minor r,vith cut depths betr,veen about 2 to 4 feet. 'We assLlme relatively light foundation loadings, typical of the proposed type of construction. If building loadings, location or grading plans change significantly frorn those described above, we should be notified to re-evaluate the recommendations contained in this report. SITE CONDITIONS The site was vacant at the time of field exploration. The lot is bounded by Boulder Ridge Drive on the north and nearby developed lots on the other sides. The terrain is moderately sloping on H-PÈKUMAR ., the south half becoming strongly sloping on the north half of the lot down to the north. Elevation difference across the assumed building area is estimated at about 2 or 3 feet. Vegetation consisted of sagebrush, grass and r.veeds. Residences in thc vicinity were one to two stories. FIELD EXPLORATION The field exploration for the project was conducted on December 20,2017 . One exploratory boring was clrilled at the location shown on Figure 1 to evaluate the general subsurface conditions. The boling was advanced with 4 inch diameter continuous flight aLlgers por.vered by a truck-mottnted CME-458 drill rig. The boling was logged by a representative of H-P/Kumar. Samples of the sttbsoils were taken with 1% inch and 2 inch LD. spoon samplers. The samplers r,vere driven into the subsoils at varions depths with blows from a 140 pound hammer falling 30 inches. This test is similar to the standard penetration test described by ASTM Methocl 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 Log of Exploratory Boring, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS A graphic log of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils consist of about Yz feet of topsoil overlying very stiff, sandy silt to a depth of abor-rt 8 feet where underlain by hard, sandy silty clay. At a depth of about 13 feet, dense, clayey silty sandy basalt gravels with cobbles with boulders were encoltntered down to the drilled depth of 23Vzfeet. Drilling in the dense coarse granular soils with auger equipment was difficult due to the cobbles and possible boulders and drilling refusal was encollntered in the deposit. The upper sandy silt soils appear to be wind-blown loess and the underlying soils are alluvial/debris fan deposits. H.P*KUMAR Project No. 17-7-869 a-J- Laboratory testing performed on samples obtained from the borings included natural moisture content, dry density, and finer than sand size gradation analyses. Results of swell-consolidation testing performed on relatively undisturbed clrive samples of the silt and clay soils are presented on Figures 3 ancl4. The silty sample (Figure 3) shows lorv to moderate compressibility under conditions of loading and wetting i,vith a moderate hydro-compressive potential. The clay sample (Figure 4) shows low compressibility under a constant light surcharge with moderate expansion ttpon wetting, and moderate compressibility when loaded after wetting. The laboratory testing is summarized in Table l. No free water was encountered in the boring at the time of drilling and the subsoils were slightly moist Þ.OUNDATION BEARING CONDITIONS The sandy silt soils encountered at shallow cut clepth tend to compress when they become r,vettecl ttnder load. Lightly loaded spread footings bearing on the upper soils can be used for foundation sttpport of the residence with risk of settlement and building distress, primarily if the bearing soils become wetted. Sources of wetting inclucle excessive irrigation near the foundation, poor surface drainage adjacent to foundation rvalls and utility line leaks. Precautions should be taken to prevent wetting of the bearing soils. Cut depth for the foundation shoulcl be lirnited to 3 feet due to the underlying expansive clay soils. A deep foundation system, such as helical piers or micro-piles, extencling dorvn into the dense granular soils could be used to provide a low risk of building settlement and distress. Below are recommendations for a spreacl footing foundation bearing on natnral subsoils. If recommendations for a deep foundation system are desired, r,ve shonld be contacted. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory boring and the nature of the proposed construction, we recommend the building be for-rnded ',vith spread footings bearing on the natural fine-grained soils with some risk of movement. H.PIKUMAR Project No. 17-7-869 -4- The design and construction criteria presented belor.v shoulcl be observed for a spread footing foundation systenr. 1) Footings placed on the undisturbed natural granular soils should bc dcsigned fbr an allolvable bearing presslìre of 1,500 psf. Based on experience, rve expect settlement of footings designed and constrncted as discussed in this section will be about I inch or less. Additional settlement on the order of 1 inch could if the bearing soils become wetted. 2) The footings shoulcl have a minimum'uvidth of 20 inches for continuous walls and 2 feet for isolated pads. 3) Exterior footings and footings beneath unheated areas should be provided rvith adequate soil cover above their bearing elevation for frost protection. Placement of foundations at least 36 inches belolv extelior grade is typically uscd in this afea. 4) Continuons foundation walls shoulcl be reinforced top and bottom to span local anomalies such as by assuming an LlnsLrpported length of at least 14 feet. Foundation walls acting as retaining stntctures shoulcl also be clesigned to resist a lateral earth pressLlre corresponding to an equivalent fluid unit r,veight of at least 50 pcf. 5) Any existing fill, all topsoil and any loose or distulbed soils should be removed and the footing bearing level extencled down to the undisturbed natural soils. The exposed soils in footing area should then be moistened and compacted. 6) A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evalnate bearing conclitions. F'LOOR SLABS The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade construction with a risk of settlement if the bearing soils become wetted. To reduce the effects of some differential movement, flool slabs should be separated from all bearing walls and columns with expansion joints r,vhich 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 H-PtKUMAR Project No. 17-7-869 -5- the intended slab use. A minimum 4 inch layer of sand ancl gravel road base should be placed beneath slabs for suppolt and to facilitate drainage. This material should consis{. of minus Z inch aggregate r,vith at least 5oa/o retained oh thc No. 4 sicvc and less than I27c pass\ng the No. 200 sieve. All fill materials for support of floor slabs should be cornpacted to at least 95Vo of maximum standard Proctor density at a moisture content ncar optimum. Required fill can consist of the on- site soils devoid of vegetation, topsoil and oversizecl rocks. UNDERDRAIN SYSTEM If the gror-rnd-level finished floor elevation of the residence is at or above the surrounding gracle, a foundation drain system is not rec¡,rirecl. It h¿rs been oul experience in the area that local perched grouudwater can develop cluring times of heavy precipitation or seasonal runoff. Frozen gronnd ch-rring spring runoff can create a perched condition. An underdrain system is not recommended around the planned shallow cralvlspace ¿rrea to help limit the potential for wetting below the shallow footings. We recommend belor,v-gracle construction, such as letaining walls, be protectecl from rvetting and hydrostatic pressltre buildup by ern unclerdrain system. The drains should consist of clrainpipe placed in the bottom of the wall backfill snrrouncled above the invert level with free-clraining granular material. The drain should be placed at least I foot below lowest adjacent finish grade and sloped at a minimum l%o to a sllitable gravity outlet. Free-draining grannlar material used in the underdrain system should contain less than TVo passing the No. 200 sieve, less than 507o passing the No. 4 sieve ancl have a maximum size of 2 inches. The drain gravel backfill should be at least lVz feet deep. SURFACE DRAINAGE Providing proper grading and drainage around the buildings will be critical to limiting snbsurface wetting and adequate performance of the structure. The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: H-PVKUMAR Projeci No. 17-7-869 -6- 1)Inundation ofthe foundation excavations and underslab areas should be avoided during construction. Exterior backfill should be adjusted to near optirnum moisturc and compacted to a{. least 95Vo <sl the maximum standard Proctor density in pavement and slab areas and to at least 90Vo of the maximum standard Proctor density in landscape areas. The ground sttrface 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 10 feet in paved aroas. Roof downspottts and drains should discharge well beyond the limits of all backfill. Landscaping which requires regular heavy irrigation should be locatcd at least 10 feet frorrt founda{.ion walls. Consideration should be given to use of xeriscape to reduce the potential for wetting of soils below the building cansed by irrigation. 2) 3) 4) LIMITATIONS This stucly 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 obtainecl from the exploratory boring drilled at the location inclicated on Figure l, the proposed type of construction and our experience in the area. Onr services do not inclucle determining the presence, prevention or possibility of niold or other biological contaminanis (MOBC) developing in the fttture. If the client is concerned about MOBC, then a professional in this special field of practice should be consulted. Our fîndings include extrapolation of the subsurface conditions identified at the exploratory boring and variations in the subsurface conditions may not become evident ttntil 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. s) H-P!KUMAR Project No. 17-7-869 -7 - 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 infonnation. As thc project evolves, lve should provide continued consultation and field services during construction to review and monitor tlte intplerttetttatiort of our recommenclations, and to verify that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the recommendations presented herein. We lecommend on-site observation of excavations and foundation bearing strata and testing of structnral fill by a representative of the geotechnical engineer. Respectfully Submitted, H-P+ KU rvrAF¡ t/øl,{r Shane M. Mello, Staff Engineer Reviewecl by David A. Yor-rng, P. SMM/kac H-PÈKUMAR Project No. 17-7-869 f, 3 \É 4 êt t Ç t) ,? u Tl \ _-,J, i l.alÉ¡'-' \ I i r'' t":, ìr, i'i' ¿a\.;. \ til 1\,j {- I 1 I LOT 2488 BOULDER RIDGE DRIVE o BORING 1 i-,I '*. ¡ I ê. \ (i ¡"#r LOT 25 6i- l,- lf t\ t 1 rl s *'! + dtI çl¡togt Þ-Ê' 7 LOT 26 fr\ oÊ 50 4oo 0 APPROXIMATE SCALE_FEET 17 -7 -869 H-PryKUMAR LOCATION OF IXPLORATORY BORING Fig.1 P ¡ &e 3 BORING 1 LEGEND 0 TOPSO|L; ORGANlC SANDY SILT, FIRM, SLIcHTLY MOlST, BROWN. 21 /12 WC=5.0 DD-96 srLT (ML); SANDY, VtRy STIFF, SL|GHTLY MO|ST, LtcHT BROWN. 5 15/ 12 lr/a.-? o DD= 1 02 -200=9 1 CLAY (CL); SILTY, SANDY, CALCAREOUS, HARD, SLIGHTLY MOIST, PALE BROWN, POSSIBLE SHALE BLOCK. BASALT GRAVTL (CV-CC); WITH COBBLTS AND BOULDERS, SANDY, SILTY, CLAYTY, DENSE, SLIGHTLY MOIST, MIXED BROWN. 10 60/ 12 WC=7.6 DD=115 ! i DRIVI SAMPLT, 2_INCH I.D. CALIFORNIA LINTR SAMPLE. Ft!t¡l L¡- I:ft'- Â_ L¡Jo DR|VE SAMPLE, 1 3/8-INCH t.D. SpLtT Sp00N STANDARD PENETRATION TIST. 15 54/ 12 71 ¡12DR|YE SAMPLT BL0W C0UNT. INDICATES THAT 21 BLOWS 0F-./'-A 14o-POUND HAMMTR FALLING 30 INCHES WERE RTQUIRTD TO DRIVE THE SAMPLTR 12 INCHTS, f enaclcaL AUGER REFUSAL. 20 38/6,50/ 1 NOTES 1 THE TXPLORATORY BORING WAS DRILLID ON DTCEMBTR 20, 2017 WITH A 4-INCH DIAMETIR CONTINUOUS FLIGHT POWER AUGTR. 2. THT LOCATION OF THE TXPLORATORY BORING WAS MIASURTD APPROXIMATELY BY PACING TROM FEATURTS SHOWN ON THE SITE PLAN PROVIDEO. 25 3. ÏHE ELEVATION OF THE EXPLORATORY BORING WAS NOT MEASURIO AND THE LOG OF THE EXPLORATORY BORING IS PLOTTID TO DEPTH. 4. THE EXPLORATORY BORING LOCATION SHOULD BE CONSIDERED ACCURATT ONLY TO THE DIGREE IMPLIED 8Y THE METHOD USED. 5. THE LINTS BETWEEN MATER¡ALS SHOWN ON THE EXPLORATORY BORING LOG REPRISENT THE APPROXI¡/ATE BOUNDARIIS BETWEEN MATERIAL TYPTS AND THT TRANSITIONS MAY BE GRADUAL. 6. GROUNDWAÏER WAS NOT ENCOUNTERTD IN THT BORING AT THE TIMT OF DRILLING, FLUCTUATIONS IN THT GROUNDWATIR LEVTL MAY OCCUR WITH TIMI. 7. LABORATORY TEST RESULTS: WC = WATER CONTTNT (%) (ASTM D 2216); DD = DRY DENSTTY (pcf) (lSiU O ZZ1O); -2OO = PTRCTNTAGE PASSING NO. 2OO SIEVE (ASTM D 1 1 4O), 17 -7 -869 H-PryKUMAR LOG OF TXPLORATORY BORING Fig. 2 2 SAMPLE OF: Sondy Silt FROM:Boringl@2.5' WC = 5.0 %, ÐD = 96 pcf ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING I I I I I I in InD-ß€. 0 JJt¡l =ln I zo F ô JoØzo() -1 -2 3 -4 -5 -6 -7 1,0 APPLIED - KSE 10 17 -7 -869 H.PryKUMAR SWELL_CONSOLIDATION TEST RTSULTS Fig. 3 2 I SAMPLE OF: Sondy Silty Cloy FR0M: Boring 1 @ 10' WC = 7.6 %, DÐ = 115 pcf l I_î ! EXPANSION UNDER CONSTANT PRESSURE UPON WETTING I I I l ln D-66. 5 2 JJ l.¡J =U) I zo 1- ô Jo tJ1zo() 1 0 -1 -2 -3 1.0 APPLIED t0 100 17 -7 -869 H-PryKUMAR SWELL_CONSOLIDATION TEST RESULTS Fig. 4 H.P*KUMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProjectNo.lT-7-869 "SAMPLE LOCANATURALMOISTURECONTENTNATURALDRYDENSITYGRADATTERBERGUNCONFINEDCOMPRESSIVESTRENGTHGRAVEL%lSANDPERCENTPASSINGNO.200SIEVELIQUIDLIMITPLASTICINDEXSOILTYPEBORINGDEPTHl%)1zvz5.096Sandy Silt53.9r029ISandy Silt101.6115Sandy Siity Clay