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HomeMy WebLinkAboutSoils Report 05.10.2017H-PKUMAR Geotechnical Engineering Engineering Geology Materials Testing l Environmental 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax: (970) 945-8454 Email: hpkglenwoad@kumanisa.com Office Locations: Parker, Glenwood Springs, and Silverthorne, Colorado SUBSURFACE STUDY FOR FOUNDATION DESIGN PROPOSED RANCH HOUSE BIG MOUNTAIN RANCH COUNTY ROAD 252, NORTH OF RIFLE GARFIELD COUNTY, COLORADO PROJECT NO. 17-7-263 MAY 10, 2017 PREPARED FOR: EGGERS ARCHITECTURE, INC. ATTN: DON EGGERS P. O. BOX 798 KREMMLING, COLORADO 80459 domeggers@eggersarchitecture.com TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - I - SITE CONDITIONS - 2 - FIELD EXPLORATION - 2 - SUBSURFACE CONDITIONS - 2 - FOUNDATION BEARING CONDITIONS - 3 - DESIGN RECOMMENDATIONS - 4 - FOUNDATIONS - 4 - FLOOR SLABS - 5 UNDERDRAIN SYSTEM - 6 - SURFACE DRAINAGE _ 7 - LIMITATIONS - 7 - FIGURE 1 - LOCATION OF EXPLORATORY BORING AND PITS FIGURE 2 - LOGS OF EXPLORATORY BORING AND PITS FIGURE 3 - LEGEND AND NOTES FIGURES 4 through 9- SWELL -CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS H -P. KUMAR Project No. 17-7-263 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsurface study for the proposed ranch house residence to be located at Big Mountain Ranch, near County Road 252, north of Rifle, Garfield County, Colorado. The project site is shown on Figure I. The purpose of the study was to develop recommendations for foundation design. The study was conducted in general accordance with our agreement for geotechnical engineering services to Eggers Architecture, Inc., dated March 28, 2017. A field exploration program consisting of an exploratory boring and pits was conducted to obtain information on subsurface conditions. Samples of the subsoils and bedrock obtained during the field exploration 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 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 residence will be a single story, log structure located on the property as shown an Figure 1. The building floor will be structurally supported over crawlspace in the living arca and slab -on - grade in the attached garage. We assume excavation for the building will have cut depths of about 3 to 4 feet below the existing ground surface. For the purpose of our analysis, foundation loadings for the structure were assumed to be relatively Tight and typical of the proposed type of construction. The residence will have 3 bedrooms and have an on-site wastewater treatment system (OWTS) located to the northwest. If building loadings, location or grading plans are significantly different from those described above, we should be notified to re-evaluate the recommendations contained in this report. H-P%KUMAR Project No. 17-7-263 -�- SITE CONDITIONS The proposed building site is vacant and the ground surface appears mostly natural. The vegetation had been removed in the building area at the time of our field exploration and about the upper 1 foot of ground was disturbed. The terrain is relatively flat and strongly sloping down to the northwest at grades estimated at about 3 to 5%. Vegetation outside the cleared building site consisted of moderately thick oak brush with an understory of grass and weeds. There were scattered cobbles and boulders up to about 2 feet in diameter on the ground surface in areas. FIELD EXPLORATION The field exploration for the project was conducted on April 6 and 21, 2017. Initially two backhoe pits (Pits 1 and 2) were excavated at the building site to evaluate the shallow subsoil conditions. Due to expansive soil and weathered claystone encountered in the pits, an exploratory boring (Boring 1) was subsequently drilled to better evaluate the subsurface conditions. The pit and boring locations are shown an Figure 1. The pits were excavated with a backhoe provided by the ranch. The boring was advanced with 4 inch diameter continuous flight auger powered by a truck -mounted CME 45B drill rig. The pits and boring were logged by a representative of H-P/Kumar. Samples of the subsoils and bedrock in the boring were taken with a 2 inch I.D. spoon sampler. The sampler was driven into the subsoils and bedrock 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-1586. The penetration resistance values are an indication of the relative density or consistency of the subsoils and bedrock. Samples from the pits were obtained with relatively undisturbed, hand driven 2 -inch diameter liners. Depths at which the samples were taken and the penetration resistance values arc shown an the Logs of Exploratory Boring and Pits, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils encountered, below 1% to 3 feet of organic topsoil, consisted of nil to 31/2 feet of stiff, H-P%KUMAR Project No. 17-7-263 -3 - sandy clay underlain by nil to 2 feet of very stiff/medium dense, sandy clay and gravel with scattered cobbles. Below depths of 5 to 7 feet, medium hard to hard weathered claystone was encountered underlain in the boring at a depth of 131/2 feet by less weathered and very hard claystone bedrock that extended down to the boring depth of 26 feet. Laboratory testing performed on samples obtained during the field exploration included natural moisture content and density, and swell -consolidation testing. The results of the swell - consolidation testing, provided on Figures 4 through 9, indicate the clay and claystone materials typically have low compressibility under relatively Tight surcharge loading and a low to relatively high swell potential when wetted under a constant 1,000 psf surcharge. Swell pressures up to about 5,000 to 7,000 psf were typically measured on the weathered claystone samples and about 15,000 psf on a sample of the claystone bedrock. One sample (Boring 1 at 10 feet) of the weathered claystone showed a low hydro -compression potential and moderately high compressibility when loaded after wetting. The sample was likely partly disturbed from the sampling process. The laboratory testing is summarized in Table 1. No free water was encountered in the boring or pits at the time of drilling or excavation and the subsoils and bedrock were generally moist. FOUNDATION BEARING CONDITIONS The subsoils and bedrock encountered at the site are expansive. Shallow foundations placed on the expansive materials similar to those encountered al this site can experience movement causing structural distress if the clay/claystone is subjected to changes in moisture content. A drilled pier foundation can be used to penetrate the expansive materials to place the bottom of the piers in a zone of relatively stable moisture conditions and make it possible to load the piers sufficiently to resist uplift movements, and is recommended for foundation support of the residence. In addition to their ability to reduce differential movements caused by expansive materials, straight -shaft piers have the advantage of providing relatively high supporting capacity. The piers can be constructed relatively quickly and should experience a relatively small amount of movement. H-P€KUMAR Project No. 17-7-263 A 4 -inch void form should be provided beneath grade beams -4 - DESIGN RECOMMENDATIONS FOUNDATIONS The design and construction criteria presented below should be observed for a straight -shaft drilled pier foundation system: I) The piers should be designed for an allowable end bearing pressure of 25,000 psf and an allowable skin friction value of 2,500 psf for that portion of the pier in bedrock. 2) Piers should also be designed for a minimum dead load pressure of 10,000 psf If the minimum dead load requirement cannot be based on pier end area only. achieved, the pier length should be extended beyond the minimum penetration to make up the dead load deficit. This can be accomplished by assuming one-half the allowable skin friction value given above acts in the direction to resist uplift. 3) Uplift on the piers from structural loading can be resisted by utilizing 75% of the allowable skin friction value plus an allowance for the weight of the pier. 4) The piers should be at least 12 inches in diameter and should penetrate at least three pier diameters into the bedrock. A minimum penetration of 10 feet into the bedrock and a minimum pier length of 20 feet arc also recommended. The 20 feet minimum depth is measured from the ground surface near the top of pier or adjacent excavation depth, whichever is greater. 5) Piers should be designed to resist lateral loads assuming a modulus of horizontal subgrade reaction of 50 tcf in the clay soils and a modulus of horizontal subgrade reaction of 200 tcf in the bedrock. The modulus values given arc fora Iong, 1 - foot -wide pier and must be corrected for pier size. 6) 7) Piers should be reinforced their full length with at least one #5 reinforcing rod for each 14 inches of pier perimeter to resist tension created by the swelling materials. to prevent the swelling soil and bedrock from exerting uplift forces on the grade beams and to concentrate pier loadings. A void form should also be provided beneath pier caps. H -P KUMAR Project No. 17-7-263 -5- 8) Concrete utilized in the piers should be a fluid mix with sufficient slump so that concrete will fill the void between the reinforcing steel and the pier hole. We recommend a slump in the range of 6 to 8 inches. 9) Pier holes should be properly cleaned prior to the placement of concrete. The drilling contractor should mobilize equipment of sufficient size to effectively drill through cobbles and possible cemented bedrock zones. Concrete should be placed the same day the pier hole drilling is completed. 10) Although free water was not encountered in the boring at the site, some seepage in the pier holes may be encountered during drilling. If water cannot be removed prior to placement of concrete, the tremie method should be used after the hole has been cleaned of spoil. In no case should concrete free fall into more than 3 inches of water. 11) Care should be taken to prevent the forming of mushroom -shaped tops of the piers which can increase uplift force on the piers from swelling soils. 12) A representative of the geotechnical engineer should observe pier drilling operations on a full-time basis. FLOOR SLABS Floor slabs present a problem where expansive materials are present near floor slab elevation because sufficient dead Toad cannot be imposed on them to resist the uplift pressure generated when the materials arc wetted and expand. We recommend that structural floors with crawlspace below be used for all floors in the building that will be sensitive to upward movement. Slab -on -grade construction may be used (such as in the garage area) provided the risk of distress is understood by the owner. We recommend placing at least 3 feet of imported road base as structural fill below floor slabs in order to mitigate slab movement due to expansive soils. To reduce the effects of some differential movement, nonstructural floor slabs should be separated from all bearing walls, columns and partition walls with expansion joints which allow unrestrained vertical movement. Interior non-bearing partition walls resting on the floor slab should be provided with a slip joint at the bottom of the wall so that, if the slab moves, the movement cannot be transmitted to the upper structure, This detail is also important for H-PkKUMAR Project No. 17-7-263 -6 - wallboards, stairways and door frames. Slip joints which allow at least 2 inches of vertical movement are recommended. Floor slab control joints should be used to reduce damage due to shrinkage cracking. Joint spacing and slab reinforcement should be established by the designer based on experience and the intended slab use. Required fill placed beneath slabs should consist of a suitable imported granular material such as CDOT Class 2, 5 or 6 road base. The fill should be spread in thin horizontal lifts, adjusted to at or above optimum moisture content, and compacted to at least 95% of the maximum standard Proctor density. Prior to the structural fill placement, all topsoil and loose disturbed soil should be removed and the subgrade moistened to slightly above optimum and compacted. The above recommendations will not prevent slab heave if the expansive soils underlying the structural fill becomes wet, however, the recommendations will reduce the effects if slab heave occurs. All plumbing lines should be pressure tested before backfilling to help reduce the potential for welting. UNDERDRAIN SYSTEM Although groundwater was not encountered during our exploration, it has been our experience in mountainous areas and where clay soils are present and bedrock is shallow, that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can also create a perched condition. Therefore, we recommend below -grade construction, such as crawlspace and basement areas, be protected from wetting by an undcrdrain system. The drain should also act to prevent buildup of hydrostatic pressures behind foundation walls. The undcrdrain system should consist of a drainpipe surrounded by free -draining granular material placed at the bottom of the wall backfill. The drain lines should be placed at each level of excavation and at least 1 foot below lowest adjacent finish grade, and sloped at a minimum 1% grade to a suitable gravity outlet. Free -draining granular material used in the drain system should consist of minus 2 inch aggregate with Tess than 50% passing the No. 4 sieve and less than 2% passing the No. 200 sieve. The drain gravel should be at lease 11 feet deep and covered by filter fabric such as Mirafi 140N. H-PkKUMAR Project No. 17.7-263 -7 - Void forth below the foundation can act as a conduit for water flow. An impervious liner such as 20 or 30 mil PVC should be placed below the drain gravel in a trough shape and attached to the foundation wall above the void form with mastic to keep drain water from flowing beneath the wall and to other areas of the building. SURFACE DRAINAGE Positive surface drainage is a very important aspect of the project to prevent wetting of the bearing materials below the residence. The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) Excessive wetting or drying of the foundation excavations and underslab areas should be avoided during construction. Drying could increase the expansion potential of the clay and claystone materials. 2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95% of the maximum standard Proctor density in pavement areas and to at least 90% of the maximum standard Proctor density in landscape areas. 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 10 feet in paved areas. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy irrigation, such as lawn, and sprinkler heads should be located at least 10 feet from foundation walls. LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this arca at this time. We make no warranty either express or implied. The conclusions and recommendations submitted in this report arc based upon the data obtained from the exploratory boring drilled and exploratory pits excavated 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 H -P KUMAR Project No. 17-7-265 -8 - contaminants (MOBC) developing in the futureIf 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 boring and pits and variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountered during construction appear to be 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 verify that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications of the recommendations presented herein. We recommend on-site observation of excavations and foundation bearing strata, observation of pier drilling, and testing of structural fill by a representative of the geotechnical engineer. Sincerely, H -P k• KU David A. Young, P.E. Reviewed by: Steven L. Pawlak, P.E. DAY/kac cc Giard Homes — Roger Giard (roaer.giard@giardhomes.com) KRM Consultants — Tim Hennum (tim@krmconsultants.com) H-PkKUMAR Project No. 17-7.263 EXISTING - STORAGE BUILDING 100 0 100 200 APPROXIMATE SCALE -FEET 17-7-263 H-P4----KUMAR RANCH HOUSE SITE BIG MOUNTAIN RANCH LOCATION OF EXPLORATORY BORING AND PITS Fig. 1 — 0 — 5 — 10 — 20 1- — 25 — 30 BORING 1 14/12 WC=12.7 DO=108 27/12 50/5 WC=12.5 00=117 50/5 WC=17.9 D0=95 50/4 WC=10.5 DD=124 49/12 WC=10.0 00=127 50/3 PIT 1 PIT 2 00=112 WC=19.3 00=105 / /WC=19.1 00=105 0 ---- 5 10- 15- 20 5- 20 -- 25- 30 5- 30 -- 17-7-263 H-PtiKUMAR LOGS OF EXPLORATORY BORING AND PITS Fig. 2 LEGEND —7 1 L 7-0 • ••••• —7 TOPSOIL; HIGHLY ORGANIC SILTY CLAY WITH SCATTERED COBBLES, FIRM. MOIST, DARK BROWN. CLAY (CL); SANDY, STIFF, MOIST. REDDISH BROWN, MEDIUM PLASTICITY. CLAY AND GRAVEL (CL—GC); SANDY, SCATTERED COBBLES, VERY STIFF/MEDIUM DENSE, MOIST, MIXED BROWN, LOW TO MEDIUM PLASTIC TY. WEATHERED CLAYSTONE; MEDIUM HARD TO HARD, MOIST, LIGHT BROWN, MEDIUM PLASTICITY. ICLAYSTONE BEDROCK; VERY HARD, MOIST, LIGHT BROWN, MEDIUM PLASTICITY. hRELATIVELY UNDISTURBED DRIVE SAMPLE; 2—INCH I.D. CALIFORNIA LINER SAMPLE. 1 HAND DRIVEN LINER SAMPLE. 14/12 NOTES DRIVE SAMPLE BLOW COUNT. INDICATES THAT 14 BLOWS OF A 140—POUND HAMMER FALLING 3D INCHES WERE REQUIRED TO DRIVE THE CAL+FORNIA SAMPLER 12 INCHES. 1. THE EXPLORATORY PITS WERE EXCAVATED ON APRIL 6, 2017 WITH A BACKHOE. THE EXPLORATORY BORINGS WERE DRILLED ON APRIL 21, 2017 WITH A 4—INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BORING AND PITS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES ON THE SITE PLAN. 3. THE ELEVATIONS OF THE EXPLORATORY BORING AND PITS WERE NOT MEASURED AND THE LOGS OF THE EXPLORATORY BORINGS AND PITS ARE PLOTTED TO DEPTH. 4. THE EXPLORATORY BORING AND PIT LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING AND PIT LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING OR PITS AT THE TIME OF DRILLING OR EXCAVATION, FLUCTUATIONS IN THE WATER LEVEL MAY OCCUR WITH TIME. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (X) (ASTM D 2216); DD = DRY DENSITY (pef) (ASTM D 2216). 17-7-263 H-P-WUMAR LEGEND AND NOTES Fig. 3 CONSOLIDATION - SWELL O — 2 —3 — 4 —5 — 6 —7 -8 SAMPLE OF: Woolhered Claysione FROM: Boring 1 0 10' WC = 17.9 %, DD = 95 pci MN Mr ~Ai 1Ny N14 Y V. wen** 1M1/1. 11. INY.I n'wt 4144 nM M fteryluneL ..sM i. Manor ol/ M -111M, moi. 7w1 N menrimmia rill 0-044 ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING t.o APPLIED PRESSURE - KSr 10 100 17-7-263 H-P%KUMAR SWELL -CONSOLIDATION TEST RESULTS Fig. 4 CONSOLIDATION - SWELL 6 5 4 3 2 1 0 —1 —2 SAMPLE OF: Cloyslane FROM: Boring 1 0 15' WC = 10.5%, OD = 124 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 1,1.1. MN mots •P. r .► M V* .Mph. M.1.1. h. MTI'1 nport dad NIA 111. rwsn4~1, IMMO 01 ML ..44 IN ..1M..A.�.1 K 111.01.1r 4114 Y.p1., ML 7.1 rewprrp M1 AnY 0.d.�1 1.0 APPLIED PRESSURE KSr 10 100 17-7-263 H-PtiKUMAR SWELL -CONSOLIDATION TEST RESULTS Fig. 5 8 7 6 5 4 CONSOLIDATION 3 2 1 0 —1 —2 3 SAMPLE OF: Claysfoncs FROM: Oaring 1 0 201 WC = 10.0 X. DD = 127 pci EXPANSION UNDER CONSTANT PRESSURE UPON WETTING inn Int r.. * q/. 1 Qn =mole, s._. A y.lty i *Id .M N rwwlewM. �...� ti A4..M.ut w .wt.. wow' r kw. awl Af.wl..n. Y.u. 1.1 muni spe WYE ...I M ..rrr...ti A!Th w 1.0 APPLIED PRESSURE - KSr 10 100 17-7-263 H -P KUMAR SWELL --CONSOLIDATION TEST RESULTS Fig. 6 a -a f SAMPLE OF: Sandy Clay FROM: PH 1 0 3.5' WC = 17.9 %, DD = 107 pct -1 J W 1 CONSOLIDATION -3 2 1 0 -1 -2 3 — EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 1.0 APPLIED PRESSURE - 4451• f0 100 SAMPLE OF: Pit 1 0 6' FROM: Weathered ClaysIone WC = 15.6 %, D0 = 108 pcf 4P... Wit .will. .�/� ..y I. r. r.u... �.a.t. L. 1.M:... .V M.4__ pv...k M ...1/10.4...1/10.4. M with, N/fd at ■__ — 4.WMr, 4Y. 1..11 mewls.* rM A$IY 0-4344 EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 1.0 APPLIED PRESSURE - KSr 10 100 17-7-263 H-P-t4KUMAR SWELL -CONSOLIDATION TEST RESULTS Fig. 7 1 1 1 1 .>Z x • CONSOLIDATION - SWELL CONSOLIDATION - SWELL 2 1 0 — 1 —2 — 3 1 — 1 — 2 —3 — 4 SAMPLE OF: Weathered Clayslone FROM: P11 1 0 8' WC = 13.2 X, DO = 312 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 1.0 APPLIED PRESSURE - NSF 10 107 SAMPLE OF: Sandy Clay with Gravel j FROM: Pil 2 0 4' j WC = 19.3 '/., DO = 105 pcf them VIIYOLIM4y le One ,.t . w mkore..,r.p M nn .w mol .rwr W M..eYl.. I. 1.4 e. w1.i , !rlr' d M w..lbt. i, ISYY o-454611.. NO MOVEMENT UPON WETTING 1.0 APPLIED PRESSURE - KM" 10 100 17-7-263 H-P�KUMAR SWELL -CONSOLIDATION TEST RESULTS Fig. 8 3 .. 2 CONSOLIDATION - SWELL 1 0 SAMPLE OF: Weathered Cloystone FROM: Pit 2 0 9' WC = 19.1 X. DO = 105 pcf I.S. I..t n.Ps ways, la To ...re. M..(. I14 u.I.y twirl MIM Y. nw..r•...mpl In I L .OFt h ..0.. SOWN* / .I.n.1 wt ti1dsn. R SWI Cslrp0n I in - +ILII D-Ii1& EXPANSION UNDER CONSTANT PRESSURE UPON WETTING i.0 APPLIED PRESSURE — KSf 10 I00 17-7-263 H -P KUMAR SWELL -CONSOLIDATION TEST RESULTS Fig. 9 Project No. 17-7- 263 w a J N cs U >, 'a VI IWeathered Claystone 11 IWeathered Claystone 11 C.1 =_ 0 ;, 0 CJ 0 >, 0 Sandy Clay Weathered Claystone Weathered Claystone 11 Sandy Clay with Gravel Weathered Claystone UNCONFINED COMPRESSIVE STRENGTH (PSF) r ATTERBERG LIMITS PLASTIC INDEX (Y�) /may 5 V 4 .7.1 -t PERCENT PASSING NO. 200 SIEVE GRADATION ._. a z GRAVEL (%) NATURAL DRY DENSITY tpc, I C n 'n nl — N — O co .-- .— O O NATURAL MOISTURE CONTENT J%) r-, f i 4n N c, r• in O o O t• t0 V'i c.1 r•j rn c4 c4 LOCATION DEPTH (R) C in O �n SAMPLE BORING — el