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HomeMy WebLinkAboutSubsoil Study for Foundation Design 12.13.18RECEIVED JUL t 2 znrs H.PVKUMAR GARFTELD couNTv ^. 5020 countyRoad 154 co' MU Nrry orur ror"r'nl Glenwood springs'.co 81 60 1;ttr Phone: (970) 945-7988 Emair : hpksre'.,i,äofÍlJrToruJåT Geotechnicaf Engineering I Engineering Geology Materials Testing I Environmental Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado December l3,20l8 Jep Bracey and Julie Ferrero 4406 Autumn Mist Court Katy, Texas77450 leo smail.cofir Project No. l8-7-709 Subject: Subsoil Study for Preliminary Foundation Design, Proposed Residence, Lot 23, Filing 9, Elk Springs, Kingbird Court, Garfield County, Colorado Dear Jep and Julie: As requested, H-P/Kumar performed a subsoil study for preliminary design of foundations at the subject site. The study was conducted in accordance with our agreement for professional services to you dated November 27,2018. The data obtained and our recontmendations based on the general proposed construction and subsurface conditions encountered are presented in this rqnrt. Proposed Construction: Development plan for the proposed residence were not available at the time of our study. We understand the residence will be located within the upper, northern part of building envelope shown on Figure 1. We assume the structure will be one or two stories with a structural floor over crawlspace or slab-on-grade. Cut depths are assumed to range between about 3 to ó feet. Foundation loadings for this type of construction are assumed to be relatively light and tlpical of the proposed tlpe of construction. When building location, grading and foundation loadings have been developed, we should be notified to re-evaluate the recommendations presented in this report. Site Conditions: The site is currently vacant and located on the downhill side of a broad ridge hending from west to east. The site slopes from around 10 to 15 percent, generally down to the southeast. Vegetation at the site consists of native gfass, sage brush and juniper and pinon trees. About Yzfootof snow covered the lot at the time of our study. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating three exploratory pits at the approximate locations shown on Figure l. The logs of the pits are -2- presented on Figure 2. The subsoils encountered, below about Yzfootoftopsoil and I to lY'feet of sandy silt and clay, consist of basalt cobbles and boulders in a calcareous sandy silt matrix. Results of swell-consolidation testing performed on relatively undisturbed sample of the silty clay, presented on Figures 3 and 4, indicate low initial compressibility under existing low moisture conditions and light loading and a low collapse (settlement under constant load) or low swell potential when wetted. No free water was observed in the pits at the time of excavation and the soils were slightly moist. Preliminary Í'oundation Recommendations:- Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, we recommend spread footings placed on the undisturbed natural, basalt rock soils designed for an allowable soil bearing pressure of 2,000 psf for support of the proposed residence. The upper clay soils have variable compression/expansion potential after wetting and should be removed from below footing areas. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. The topsoil, clay soils and loose disturbed soils encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural basalt rock soils. Voids created from boulder removal at footing grade should be backfilled with concrete or a structural material such as road base compacted to at least 98 percent of standard Proctor density at a rnoisture content near optimum. Extedor footings should be provided with adequate cover above their bearing elevations for frost protection. Placement of footings at least 36 inches below the exterior grade is typically used in this area. 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 be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 50 pcf for the on-site soil as backfill excluding organics and rock larger than 6 inches. Floor Slabs: The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded slab-on-grade construction. The clay soils should be evaluated for expansion potential at the time of construction and may need to be removed and replaced with structural fill. To reduce the effects of some differential movemento floor slabs should be separated from all bearing walls and columns with expansion joints which allow unrestrained vertical movernent. Floor slab control joints should be used to reduce damage due to shrinkage cracking. The requirements for joint H-PVKUMAR Project No. 18-7-709 -3- 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 below grade slabs to facilit¿te drainage. This material should consist of minus 2-inch aggregate with less than 50% passing 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 soils devoid of vegetation, topsoil and oversized rock. Underdrain System: Although free water was not encountered during our exploration, 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 runoffcan create a perched condition. 'We recommend below-grade construction, such as retaining walls, crawlspace and baseme,lrt 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 lo/o to a suitable gravity outlet. 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 lYz feet deep. Surface Drainage: 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 95o/o 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. Free-draining wall backfill should be capped with about 2 feet of the on-site, finer graded soils to reduce surface water infiltration. H-P*KUMAR Project No. 18-7-709 4 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 12 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in the first l0 feet in pavement and walkway areasi. A swale will be needed uphill to direct surface runoffaround the residence. Roof downspouts and drains should discharge well beyond the limits of all backfill. Landscaping which requires regular heavy irrigation should be located at least 10 feet from the building. Consideration should be given to the use of xeriscape to limit potential wetting of soils below the foundation caused by inigation. 4) Limitations: This study has been conducted in accordance with generally accepted geotechnical engineering princþles 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 pits excavated at the locations indicated on Figure I and to the depths shown on Figure 2,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 pits 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 at once so 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 veriff that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the recommendations presented herein. 'We recommend on-site observation s) H.PVKUMAR Project No. 1B-7-70S 5 of excavations and foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer. If you have any questions or if we maybe of further assistance, please let us know. Respectfully Submitted, H-P*KU]V¡IAR Steven L. Pawlak, P.E. Reviewed by: Daniel E. Hardin, P. E. SLP/kac attachments Figure 1 - Location of Exploratory Pits Figure 2 - Logs of Exploratory Pits Figures 3 and 4 - Swell-Consolidation Test Results Table 1 - Summary of Laboratory Test Results cc:DM Neuman Construction Company- Jason Neuman (jmn@dmneuman'com) H-Prtçg¡y¡q¡¡Project No. 18-7-709 il ti tl,ã ¡i r .Ìl ü:; iil ";4 ir i.iì fl 1 c* .t I' KINGBIRD COURT !- a-; t¡ñ.** t¡ åq L , +"â rì I !+ tf l 1 f. I t j4 f.(t t -tr "*' : t-! Iò i 30 o -lö APPROXIMATE SCALT-T TT I :ft'-.{* f .'t tlr\ ê S¡r rf.+¡#¡* I tFr f*.,, PIT 2 I IF f l. Ê ff F*.-p f !I *r.t I 5ì ?{rav '*... f ¡.t {CDt tË t #,t t\û !r*¡l¡ i;: ,rÇ 18-7 -709 H-PryKUMAR LOCATION OF EXPLORATORY PITS Fig. 1 , I I t : É PIT 1tL. 1 00' Ptl 2 EL. 99 PIT 5 EL. 90 o 0 Ft¡J t¡J LL IIFo- L¡JÕ WC= 1 0.1 DD=78 WC= l 1.0 DD= 1 06 t"-l¡J IJ lÀ I-t-fLl¡lô-t -J 5 5 LEGEND TOPSOIL; ORGANIC SANDY SILT AND CLAY, DARK BROWN, FROZEN CLAY AND SILT BROWN, MOÐERA (CL-ML); SANDY, BASALT ROCKS, VERY STIFF, SLIGHTLY MOIST, WHITE TO TELY CALCAREOUS, BLOCKY AT PIT 3. BASALT COBBLES AND BOULDERS (GM): CALCAREOUS SANDY SILT MATRIX, MEDIUM DÊNSE TO DENSE, SLIGHTTY MOIST, GRAY AND WHITE. SUBANGULAR ROCK. Fl t HAND DRIVEN z''-DIAMETER LINER SAMPLE. DISTURBED BULK SAMPLE. PRACTICAL DIGOING REFUSAL. NOTES 1, THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON DECEMBER 4,2018 2, THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY TAPING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE MEASURED BY HAND LEVEL AND REFER TO PIT 1 AS ELEVATION 1OO" ASSUMED. 4. THE EXPLORATORY PIT 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 PIT LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF DI6GING. PITS WERE BACKFILLED SUBSEQUENT TO SAMPLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216)I DD = DRy DENSTTY (pcr) (ASTU D 2216). o .b/ . /.= 18-7 -709 H-PryKUMAR LOGS OF EXPLORAÏORY PITS Fig. 2 3 Ð. SAMPLE OF: Colcoreous Sondy Sllt ond Cloy FROM:Pit2s^1' WC = 10.1 %, DD = 78 pcf lhc ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 2 ñ JJ ¡¡J3tn I zot- ofotnz.o() 0 -2 -4 -6 -8 -10 *12 18-7-709 H-PryKUMAR SWELL-CONSOLIDATION TESÏ RESULTS Fis. 5 t I 4 ! ¿ì ı 3 SAMPLE OF: Sondy Cloy, Blocky FROM: Pit 3 @ 1.5' WC = 11.A %, DD = 106 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING lnc- 2 x JJ l¡J =v, I z.otr o =otnzo() 0 -1 -2 -3 -4 1.0 t0 18-7 -709 H-PryKUMAR SWELL-CONSOLIDATION TEST RESULTS Fig. 4 H-P*KUMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProject No. 1&'7-709SOILTYPECalcareous Sandy Silt andClaySandy Clay, BlockyUNCONF¡I{EDcoitPREsstvESTRENGTH{osfìATÎERBERG UiiIlSPLASTICINDEX(o/olLIQUIDLIMIT(o/olPERCENTPASSINGNO.200SIEVESAND$lGRAVELv;lNATURALDRYDENSITY(pc'f)78106NATURALMO|sTURECOIITENT(o/"1I0.I11.0SAIIPLE LOCATIONDEPTHtft)1It/2PIT23