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Home My WebLink AboutSubsoil Study for Foundation Design 10.11.2018H-PVKUMAR Geotechnlcal Engíneering I Engineedng Geology Materials Testing I Environmental 5020 County Road 154 Glenwood Springs, CO 91601 Phone: (970) 94S-798S Fax: (970) 945-8454 Email: hpkglenwood@kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado October l1,2AL8 Red House Architecture Attn: Bruce Barth 815 Blake Street Glenwood Springs, Colorado 81601 bruce @ l edhousearchitecture.com Project No.18-7-554 Subject: Subsoil Study for Foundation Design, Proposed Zonakis Residence, Lot 1, Block 8, Los Amigos Ranch, TBD Elk Springs Drive, Garfield County, Colorado Gentlemen: As requested, H-PÆ(umar performed a subsoil study for design of foundations at the subject site The study was conducted in accordance with our proposal for geotechnical engineering services to Red House Architects dated September 4, 2018. The data obtained and our recommendations based on the proposed constructibn and subsurface conditions encorintered are presented in this report. Proposed Construction: The proposed residence will be 2 stories with walkout basement level located on the site as shown on Figure 1. Ground floor could be structural over crawlspace or slab-on-grade. Cut depths are expected to range between about 3 to 10 feet. Foundation loadings for this type of construction are assumed to be relatively light and typical of the proposed type of consfruction. If building conditions or foundation loadings are significantly different from those described above, we should be notified to re-evaluate the recommendations presented in this report. Site Conditions: The subject site was vacant at the time of our field exploration. The ground surf'ace is sloping down to the south at a grade of around 1O to 157c. Elevation difference across the building area is about l0 feet and across the lot is about 30 feet. Vegetation consists ofgrass, weeds, sagebrush, and pinyon pines. L Subsurface conditions: The subsurface cônditions at the site were evaluated by excavating ttuce explula{.ory pits ât the approximate locations shown on Figure 1. The logs of the pits are presented on Figure 2. The subsoils encountered, below about 1 to 2 feet of topsoil, mainly consist of very stiff, calcareous sandy silt and clay. Basalt rock soil in a calcareous sand siit matrix was encountered at 7 feet inPit 2. Results of swell-consolidation testing performed on a relatively undisturbed sample of sandy silt and clay, presented on Figure 3, indicate low compressibility under existing moisture conditions and light loading and a low collapse potential when wetted' No free water was observed in the pits at the time of excavation and the soils were slightly moist. Foundation Recommendations: considering the subsoii conditions encountered in the exploratory pits and the nature of the proposed construction, spread footings placed on the undisturbed nalural soil designed for an allowable soil bealing pressure of 1,500 psfcan be used for support of ths proposcd resi,Jeuce with a risk of movement. 'l'he soils tend to compress after wetting and there could be post-construction foundation settlement of around vzto lvzinches depending on the depth and extent of wetting. Footings should be a minimum width of 20 inches for continuous walls and 2 feet fur columns. The topsoil and loose disturbed soils encountered at the fuundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural soils. The exposed soils should then be moistened to near optimum and compacted. Exterior 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 sho'ld be heavily 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 ¡esist a lateral earth pressure based on an equivalent ftuid unit weight of at least 55 pcf for the on-site soil as backfili. Floor Slabs: The natural on-site soils, exclusive of topsoil can be used to support lightly loaded slab-on-grade construction with a risk of movement if the bearing soils are 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 rinrestrained vertical movcment. Floor slab control joints shoilld be used to reduce damage due to shrinkage cracking. The requirements for H-PtKUMAR Project No. 18-7-SS4 -3- 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 less than SOVa passing the No. 4 sieve and less lhan TVo passing the No. 200 sieve All fill materials for support of floo¡ slabs should be compacted to at least95Vo of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on- site soils devoid ofvegetation, topsoil and oversized rock. Underdrain System: Although free water was not encountered during our exploration, it has been our experience in the area and where there are clay soils that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground durìng spring runoff can create a perched condition. We recommend below-grade construction, such as retaining walls, crawlspace 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 lVo ta a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than ZVo passingthe No. 200 sieve, less than 507o passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least lYz feet 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. Surface Drainage: Proper surface grading and drainage will be critical to keeping the bearing soils dry and limiting potential building movements. The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: i) Inundation ofthe foundation excavations and underslab areas should be avoided during construction. H.PVKUMAR Project No. 18-7-554 -4- ?) Extcrior backfill shuultl tre adjusted to near optimum moisture and compacted to at least 957o af the maximum standard Proctor density in pavement and slab areas and to at least 90vo of the maximum standard P¡octor density in landscape areas. Free-draining wall backfill should be covered with filter fabric and capped with about 2 feet of the on-site, finer graded soils to reduce surface water infiltration. 3) The ground surface surrounding the exterior ofthe building should be sloped to drain away from the foundation in all directions. We ¡ecommend 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 pavement and walkway areas. A swale will be needed uphill to direct surface runoff around the residence. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscapi0g which requires regular heavy irigation should be located at least !0 feet from the building. Consideration should be given to the use of xeriscape to Iimit potential wetting of soils below the foundation caused by irrigatit-rn. Limitations: This study has becn conducted in accortlance with generally accepted geotechnical engineering principles and practices in this area a[ Lhis time. We make no warranty either express or implied' The conclusions and recommendations submitted in this report are basctl upon the data obtained from the exploratorypits excavated at the locations indicated on Figure 1 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 ar the exploratory pits and vadations 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 H.PùKUMAR Project No. 18-7-554 -5- should provide continued consultation and field services during construction to review and monitor the implementation of our recommendations, and to verify that the recommendations have been appropriately interprete.d. Significant clesign changes may require additional analysis or modifications to the recommendations presented herein. We rccommend on-site observation ofexcavations and foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer. If you have any questions or if we may be of further assistance, please let us know. Respectfully Submitted, H-P+KUMAR James H. Parsons, E.I. Reviewed by: Steven L. Paw JHP/kac attachments Figure 1 Exploratory Pits Figure 2 - Logs of Exploratory Pits Figure 3 - Swell-Consolidation Test Results Table 1 - Summary of Laboratory Test Results â r s?22 olpl¡ Project No. 18-7-554 d J --=w \ -*K- '\qi #ffi lÐ 79a ,E rù&1rtr PRt HO 67s5* J-- ffi Pt'l 2 -..-\ \----67g0 # ,¡ n\\9h +679 PIT 1 PIT 3 t @ lress, +6790.9 .o ..-. 80-8'-.. w rN LO EVÊ VËL = St'f NOT TO SCALE 1 8-7-554 H-PryKUMAR LOCATION OF EXPLORATORY PITS Fig. 1 ù € s9 PIT I EL. 6786.s' Fll 2 EL. 6779'PIT 3 EL. 6788.s' t-U LJb- I :Ê FGUo o 5 0 10 5 F l¡J LJt! Irts(L l¡l lf I WC=9.2 ÐÐ=78 -200= 69 WC=9.8 -t DD=96 10 LEGEND TOPSOIL; SANDY SILT AND CLAY W|TH ROOTS, BROWN. :t_LL.¡flD cl4y-(|4L CLli :Afqy,vrRy slFF, sLtGHrLy MorsT, LtcHT sRowN, sLtGHTLy r0HEAVILY CALCAREOUS, SLIGHTLY POROUS. BASALT cRAVEL AND cCI.BB!E.?...(9!); cALcAREous sANDy stLT M,ATRtx, MEÐtuM DENSE,SLIOHTLY MOIST, GRAY AND WHITE. HAND DRIVEN 2-INCH DIAMETER LINER SAMPLE. DISTURBED BULK SAMPLE. PRACTICAL DIGGING RIFUSAL. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON SEPTEMBER 26,2018, 2. IHE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROMFEAÏURES SHOWN ON THE SITE PLAN PROVIDED. 5. THE ELTVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTTRPOLATION BETWEENCONTOURS ON THE SITE PLAN PROVIDED, 4. THE EXPLORATORY PIT LOCATIONS AND SLEVAIIONS SHOULD BE CONSIDERED ACCURATT ONLYTO THE DECREE IMPLIED BY THE MEIHOD USID. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT IHEAPPROXIMATE EOUNDARIES BETWEEN MATERIAL TYPES AND THÊ TRANSITIONS MAY BI GRADUAL. 6. CROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF DRILLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTTNT (%) (ASTM Ù 2216); DD = DRY DENSIIY (pct) (asru Ð 2216); -200 = PERCENTAGE PASSTNG NO, 200 STEVE (A5TM D r r 40). I WC=1 1.8 -200=59 I F t, I 1 8-7-554 H-PryKUMAR LOGS OF EXPLORATORY PITS Fig. 2 SAMPLE OF: Sondy Sili ond Cloy FROMTPiI 3@7' WC = 9.8 %, DÐ = 96 pcf J -.tU3 I 7() F Õ = tz (J rl ADOITiONAL COMPRESSION UNDTR CONSTÅNT PRESSURE DUI TO WETTING -j-l- \ \) I I ¡ I !-13a0. _1 2 -A l-0 ÀPPLIED RE - KsF t0 1 8-7-554 H.PryKUMAR SWELL-CONSOLIDATION TEST RISULTS Fig. 3 H.P*KUMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProject No. 1 8-7-SS4SOILTYPESandy Silt and ClaySandy Silt and ClaySandy Silr and CIayUNCONFINEDCOMPRESSIVESTRENGTHPERCENTPASSINGNO. 200SIEVELIQUIDLIMITPLASTICINDEX6959NATURALDRYDENSITYGRAVELSAND%t(%\7896NATURALMOISTURECONTENT(o/"19.2I 1.89.8DEPTH(ftìsvz6Vz-77PITI2-t