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Home My WebLink AboutSubsoil Study for Foundation Design 06.05.17H-PVKUMAR Gootochnlcal Englncrdng I Englnordn¡ Geology MEtad¡lB Tosüng I Envlronmrnlal 5020 County Road 154 Glenwood Springs, C0 81601 Phone: (970) 94S7988 Fax (970) 945-8454 Email: hpkglenwood@kumarusa,com Office Locations: Parker, Glenwood Sprlngs, and Silverthome, Colorado SI.]BSOIL STUDY FOR FOUNDATION DESIGN PROPOSED BARN BIG MOUNTAIN RANCH couNTY ROAD 252, NORTH Or RrFLE GARFTELD COUNTY, COLONADO PROJECT NO. 17-7-263 JUNE 5,2017 PREPANED FOR¡ EGGERS ARCHITECTURE, INC. ATTN: DON EGGERS P. O. BOX 798 KRßMMLING, COLORADO 80459 don,eesers @ e g gprsarchitecture.com TABLE OT CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION srrE coNDmIoNs -2- FIELD EXPLORATION 2- 4- 6- SUBSURFACE CONDITIONS ...-) - - a- t FOUNDATION BEARINC CONDITIONS ....... DES TGN RECOMMENDATIONS FOUNDATIONS FLOOR SLABS..... UNDERDRAIN SYSTEM LIMITATIONS... FIGURE I . LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 . LECEND AND NOTES FIGURES 4 through 6- SWELL-CONSOLIDATION TEST RESULTS TABLE I- SUMMARY OF LABORATORY TEST RESULTS -,(- -?- _\_ I I H.PÈKUMAR Projecl No, 17-7-263 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed barn to be located at Big Mountain Ranch, near County Road 252, north of Rifle, Garfield County, Colorado. The project site is shown on Figure l. The purpose of the study was to develop recommendations for the foundation design. The study was supplemental to our agreement for geotechnical engineering services to Eggers Architecture, Inc., dated March 28,2017. \üe previously performed a subsurface study for foundation design of the proposed ranch house at the site and submitted our findings in a report dated May lA,2Ol7, Project No. l7-7-263. A field exploration program consisting of exploratory borings was conducted to obtain information on the subsurfuce conditions. Samples of the subsoils obtained during the field explorafion were tested in the laboratory to determine their classification, compressibility or swell 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 obtnined during this study and presents our conclusions, design recommendalions and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION The proposed barn will be ä two story structure located on the property as shown on Figure l. Ground floor will be slab.on-grade at an elevation slightly above the existing ground surface. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 4 feet. Wc assume relatively light foundation loadings, typical of the propo.sed type of construction. If building loadings, location or grading plans change significantly from those described above, we should be notified to re-evaluate the recornmenclations contained in this report. H.P+KUIVIAR Project No. 17-7-263 -7 - SITE CONDITIONS The proposed building site is vncunt and the ground surface flppe¿¡rs mostly natural. The terrain is relatively flat with a gentle slope down to the west- Vegetation consists of grass and weeds with nearby scattered oak brush stands. There are scûttered cobbles and boulders on the ground surface in nearby areas. About 6 inches of snow covered the site at the time of our field exploration. FIELD EXPLORATION The field exploration for the project was conducted on April 21, 2017. Two exploratory borings were drilled at the locations shown on Figure I to evaluate the subsurface conditions. The borings were udvanced with 4 inch diametcr continuous flight augers powered by a truck- rnounted CME-458 drill rig. The borings were logged by a representative of H-P/Kumar. Samples of the subsoils were taken with a 2 inch I.D. spoon strnpler. The sampler was driven into the subsoils at variou.s depths with blows from a 140 pound hammer falling 30 inchcs. This test is similar to the standard penetration test described by ASTM Method D-15E6. The penetration resistance values are an indication of the relative density or consistency of the subsoils, Depths at which the samples werc taken and the penetrâtion resistance values are shown on the Logs o[Exploratory Borings, Figure 2. The samples were returned to our laboratory for rcview by the project engineer and testing. SUBSURFACE CONDITIONS Graphic logs of thc subsurface conditions encountered irt the site are shown on Figure 2. The subsoils encountered, below 2 feet of organic topsoil, consisted of medium dense, clayey to very clayey sand that was typically gravelly, contained scattered cobbles and probable boulder.s, and extended down to the maximum depth drilled of 3l feet, Drilling in the granular soils with auger equipment was occasionally difficult due to the cobbles and probable boulders. H-PIKUMAR Projecl No. 17.7-263 3 Laboratory tcsting performcd on srmples obtained from the borings included natural moisture content and density, and percent finer than sand size gradation analyses. Results of swell- consolidation testing performed on relatively undisturbed drive.samples, presented on Figure 4 through 6, generally indicate moderate compressibility under conditions of light loading and wetting with a low hydro-compression potential. One sample (Boring I arTV{) showed low compressibility and a low swell potential when wetted under a constant light surcharge. The more compressible samples were probably partly disturbed due to the rock content. The laboratory testing is summarized in Table l. No free water was encountered in the borings at the time of drilling and the subsoils were moist to slightly moist with depth. FOUNDATION BEARING CONDITIONS The clayey to very clayey sand soils generally possess moderate bearing capacity and relatively low settlement potential. Lightly lolded spread footings bearing on these soils should be feasible for foundation support of the building with some risk of settlement. The risk of settlement is primarily if the bearing soils were to become wetted and precautions should be taken to prevent wett¡ng. Tlre low swell potential encountered in one of the samples is believed to be an anomaly and can probably be neglected in the foundation design but should be further evaluated at the time of excâvation. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurfuce 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 with some risk of movement. Once foundation plans and loading information are available, we should review our recommendations and perform settlement analy.ses ns needed. H.PIKUMAR Projecl No. 17-7-263 -4- The design and construction criteria presented below shoulel bc obscrvcd for a spreacl footing foundation system. l) Footings placed on th€ undisturbed naturûl granulur soils should be dcsigned for an allowable bearing pressure of 2,000 psf. Based on experience, we expect initial settlement of footings designed and constructed as discussed in this section will be up to about I inch depending on the foundation loadings. There could be .some additional settlement if the bearing soils were to become wetted. The magnitude of the additional settlement would depend on the depth and extenr of the wetting but mry be on the order of !/z to I inch. 2) The footings should have a minimum width of l8 inches for continuous walls and 2 fect for i.solated 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 42 inches below exterior grade is recommended for this area of Garfield County. 4) Continuous foundation walls should be well reinforced top and bottom ro span local anomalies and better withstand the effects of some differential movement such as by assuming an unsupported length of at least l2 feet. Foundation walls acting a.s retaining structures should also be designed to resist a lateral earth presriure corresponding to an equivalent fluid unit weight of at least 55 pcf. 5) The topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the frrm natural granular soils. Expansive .soils may need to be sub-excavated below design bearing level and replaced with granular structurul lill compacted to at least 987o of standard Proctor den.sity at near oPtimum moisture content. The exposed soils in footing area should then be moislened as needed and compacted. 6) A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditlons. FLOOR SLABS The natural on-site soils, exclusive of topsoil, should be suitable to support lightly loaded slab- on-grade construction. There is some risk of slab movement if the subgrade were to become H.PIKUMAR Project No. 17-7-263 5- wetted as discussed above. A depth (typically l¡,4 feet) of non-expansive granular material, such as road base, could be provided below the slab to reduce the risk of movement. The road base can consist of CDOT Class 5 or 6 material. We should further evaluatE the subgrade condition and need for sub-excavâtion and replacement with imported road base at the time of Iconstruction. ì 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 controljoints should be nsed 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 6 inch layer of well graded sand and gravel road base should be placed immediately beneath floor "slabs at grade" for support and to facilitate drainage. This material should consist of minus 2 inch aggregate with at least 5OTo retained on the No. 4 sieve and less than lTqo passing the No. 200 sieve. Nl nll materials for support of floor slabs should be compacted to at least 957o of rnaximum standard Proctor density at a moisture content near optimum. Required lTll can consist of the on- site granular soils devoid of vegetation, topsoil and oversized (plus 6 inch) rocks, or a suitable granular material such as road base can be imported. UNDERÞRAIN SYSTEM It is our understanding the finished floor elevation at the lowest level is at or above Lhe surrounding grade. Therefore, a foundation drain systenì is not required. It has been our experience in mountainous are¿¡s that local perched groundwater can develop during tirnes of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can also creüte a perched condition. We recommend below-grade construction, such as retaining walls, crawlspace and basement areas, be protected from welting and hydrostutic pressure buildup by an underdrain and wall drain system. If the finished floor elevation of the proposed structure has a floor lcvel below the surrounding grade, we should be contacted to provide recomrnend¡tions for an underdrain system. All earth retaining stn¡ctures should be properly drained. H.PtKUMAR Project No, 17-7-263 -6- SURFACE DRATNAGE Positive surface drainage is a very important aspect of the project to prevent wetting of thc foundation bearing and floor slab subgrade soils. The following drainage precautions should be observed during construction and maintained at all times sfter the building has been completed: I ) Inundation of the foundation excavations and underslab areas should be avoided during construction. 2) Exterior backfill should be adjusted to neâr optimum moisture and compacted to at least 95?o of the maximum standard Proctor density in pavemenr and slab areas and to at least 9OVo oî the maximum standard Proctor density in landscape areâs. 3) The ground surface sumoundirtg the exterior of the building should be sloped to drain away from the foundation in all directions. We recommend a minimum slope of l2 inches in the first l0 feet in unpaved areas and a minimum slope of 3 inches in the first l0 feet in paved âreas. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which require.s regular heavy irrigation should be located ar least l0 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. TIMITATIONS This study has been conducted in accordance with generally uccepted geotechnical engineering principles and practices in this arefl ût this time. Vfe make no warrânty either express or impliecl. The conclusions and recommendations submitted in this report are based upon the dara obtained from the exploratory borings drilled at the locations indicated on Figure l, 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 (MCIBC) developing in the future. lf 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 nol. become evident until excavation is performed. If conditions encountered H.P*KUMAR Projecl No. 17-7"263 -7- during construction ilppear different from those described in this repot't, rve should be notified so that re-evalufltion of the recommendâtions 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 verify 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 of excavations and foundation bearing striltâ and testing of structural frll by a representative of the geotechnical engineer. Respectfully Submitted, H-P\ David A. Young, P.E. Reviewed by: teven L. Pawlak, P.E. DAY/kac cc: KRM Consultants - Tim llennunr (tim@krmconsultants.com) rÌ !.:f ó }I.PìKUMAR PtojectNo, 17-7-263 \ Edge of Vegetation (typicol) Elcctric¡l Transformcrs tÀfÀ Lin Vegetation Itypicall SCALE: 1" = 50' of 17-7-263 H-PÈKUMAR(iætKtnr{sl Ë¡qtHr10 | !.noneañ¡1o üôôlogy l"J¿ìeri¿lf Tqrtrm | [4vlrmmrl¡l LOCATION OF EXPLORATORY BOHINGS Figure 1 s rt BORING 1 EL.100' BORING Ët. 96 2 0 0 16/ t2 52/ t2 WC= 15.5 QS=l1'l 24/ t2 WC=7.8 0D=1 1 I -200=35 51/12 $50/1 5 64/ 12 WC=8.5 DD=l I 4 r0 2S/t2 46/ 12 WC=11.5 DD= 1 07 to 15 ?3/12 WC=7.4 DD=l t? 25/12 ls t-t¡¡r¡J ITt-o-t¡¡o t-t¡ l¡Jlù I Lt-o- l¡Jú¡ 20 5O/ 4 20 25 4A/ 12 WC=6.4 0D= 1 29 -20O=59 25 $0 52/ t2 50 55 17 -7 -263 H-PryKUMAR LOGS OF EXPLORATORY BORINGS BARN SITT Fis. 2 g à å !t LEGEND N TOPSOIL; HIGHLY ORGÂNIC SILTY CLAY WITH SCATTER€O COSBLES, FIRM, MOIST, OARK 8ROWN, SANO (5C); CTAYEY TO VERY CLAYEY, TYPICALLY GRAVÊLLY, SCATTERED COEBLES, PROBABLE BOULÐERS, MEDIUM DENSE, MOIST TO SLIGHTLY MOIST WITH DEPTH, BROWN. LOW TO I,IEOIUM PLÂSTIC FINES. þ RELATIVELY UNDISTURBEO DRIVE SAMPLE¡ 2-INCH I.D. CALIFORNIA LINÉR SAMPLE. 167¡2 DRIVE SAMFLE BLOW COUNT, INDICATES IHAT 16 BL0W5 OF A 140-POUN0 HAMMER'-,'- T,ALLING 50 INCHES WERE REQUIREO TO ORIVE THE CALIFORNIA SAMPLER I2 INCHES. NOTES 1 THE EXPLARATORY BORINGS WERE DRILLED ON APRIL 21,2017 WITH A 4-INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2. THE LOCATIONS OF TIIT EXPLORATORY EORINGS WERE MEÀsURED APFROXIMATELY 8Y PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIOED. 5. THE ELEVATIONS OF THE EXPLORATORY BORINGS WEÊE APPBOXIMATEO 8Y HÀND LEVEL ANO REFER T0 GROUND SURFACE AT gORlNc t = lO0', ASSUMED ELEVAT|ON. 4. lHE EXPLORATORY BORING LOCATIONS ANO ELEVATIONS SHOULO SË CONSIDERED ACCURAT€ ONIY ÌO THE OEGREE'IMPLIED BY THE MEIHOT} USED. 5. THE LINES BETWEEN MATEßIALs SHOWN ON THE EXPLORÀTORY EORING LOGS REPREsENT THE APPROXIMATE BOUNT}ARIES BETWEEN MATTR¡AL TYFÉs AND THE TÊAN5ITIONS MAY BE GRÀOUAI. 6. GROUNOWATER WAS NOf ENCOUNTEREO IN THE BORINGS AT THE TIME OF ORILLING. 7. IABORATORY TEST RESULTS: WC = WATER CONTENÍ (%) (ASTM O 2216)¡D0 c DRy DENS|Ty (pcf) (lStU O 2216)i _2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1140). t7 -7 -263 H.PryKUMAR LEGEND AND NOTES Flg. 3 : e I t Ã0 j-l l¡J¡ 3ñ l-2 zIt- c¡ otn oct -4 t00 SAMPLE OFr Very Cloycy Sond FROM:8orlnglC7.5' WC = 8.¡ ll, DD = !14 pcf i I t { I -_-_-,t...--, ^ I I-i I I .t EXPATSION UNDER CONSTANT PRESSURE UPON WETTING 1 'i 1 I ¡ ¡ i I l I I 1 ..1. llti l1 17-7-263 H-PTKUIVIAR SWELL-CONSOLIDATION TTST RESULT5 Flg. 4 ã SAMPLÉ OF: Cloyey Sond wllh Grovel FROM:BorlnglOtS' WC = 7.4 ?6, D0 = ll7 pcl I i i' i-: ' ì ì' I I I 1't I j I i I I I I I ! I I I i '. Ì I I I I I l I l I AODITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING I 0 N JJ l¡J3tn I z9t- a oqzo C, -l -5 -4 -6 -7 -8 t0 17 -7-263 H-PryKUMAR SWILL-CONsOLIDATION TEST RESULTS Fí9. 5 ¡ i SAMPLE OF: Vory Cloyey Sond wllh Grovel FROM:Borlng2Ol0' WC = ll.5 ,¿, [tD = 107 pcf I .1. I I I I I ¡ I -t I i i I i I i I i I I I I I I I I j i I I : ; ì i I I L i I l I II i I I ¡ I I i I I : I ! , 1 I I I I 1 I I I i l l L I i ADDITIONAL COMPRESSION UNDER CONSTANT PñT5SURE DUE TO WETTING I I 1 j : ¡.,''.*'.1 I i ¡ j I,ï I t I I II t f I l I .l I i i l I I I I I 0 x l]J =ln I 0 o Joø o() -1 -2 _? -4 -5 -6 -7 17 -7 -263 H-PryKUMAR SWELL-CONSOLIDATION TEST RESULTS Fis. 6 H-P\KUMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProject No-17-7-261Barn SiteSOILTYPEVery Clapy SandClayey Sand with GravelClayey Sand with GravelVery Clayey Sand withGravelClayey Sand with GravelVery Clayey Sand withGravelUNCONFIt¡EDcouPREssrvESTRENGTHIPSF}ATTERBERGUMMSPl¡sncINDËXt%lLNt,lDuutrP/alPERCEHTPASSINGtto.200SIEVE3933GRADATIONSAilDt%tGRAVELllolNATURALDRYOENSITYfi¡êfll14lt7129Iilil8tÐ7NAruRALüorsTuRËCOI{TEI'lT10/.18.37.76.4r5.3?-8r t.5_ôcÂlrt)NDEPTH{ñ}7rht5?q2V+5t0SAT¡PLEBORINGI7