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Home My WebLink AboutD13-0015 Subsoil Study.pdf I u rill-f;ntl,il.: (ILIItCchilic.1 Got - } `I oFtec IS HEPWORTH-PAWLAK GEOTECHNICAL SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 2, BLOCK 5, VAIL VILLAGE 8TH FILING 1027 PTARMIGAN ROAD VAIL, COLORADO JOB NO. 113 222A JULY 26, 2013 PREPARED FOR: TRIUMPH DEVELOPMENT ATTN: TRAVIS COGGINS 12 VAIL ROAD, SUITE 200 VAIL, COLORADO 81657 travis(atrium hdev.com Parker 303-841-7119 • Colorado Sprin-s 719-633-5562 • Silverthorne 970-468-1989 TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY........................ _ I _ .................................... PROPOSED CONSTRUCTION................................................................................. - 1 - SITECONDITIONS................................................................................................... - 2 - GEOLOGIC CONDITIONS....................................................................................... - 2 - FIELD EXPLORATION........................ SUBSURFACE CONDITIONS.............................................. - 3 - FOUNDATION BEARING CONDITIONS ............................................................... - 3 - DESIGN RECOMMENDATIONS......................................... - 4 - FOUNDATIONS.................................................................................................... - 4 - FOUNDATION AND RETAINING WALLS........................................ - FLOORSLABS................................................................. - 6 - UNDERDRAINSYSTEM...................................................................................... - SITEGRADING .................................................................................................... - 7 - SURFACEDRAINAGE......................................................................................... - 7 - LIMITATIONS .......................................................................................................... 8 FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4 AND S- SWELL-CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 2, Block 5, Vail Village 8h Filing, 1027 Ptarmigan Road, Vail, Colorado. The' project site is shown on Figure 1. The purpose of the study was to develop recommendations for the foundation design. The study was conducted in accordance with our proposal for geotechnical engineering services to Triumph Development, dated June 12, 2013. A field exploration program consisting of exploratory borings was conducted to obtain information on the subsurface conditions. Samples of the subsoils 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 existing residence on the lot will be razed for construction of the new residence. The proposed residence will be a 2-story structure above a walkout lower level located as shown on Figure 1 with a sub-basement below the uphill, garage area about 17 feet deep. A swimming pool will be located outside of the building at the walkout level. Ground floors will be slab-on-grade. Grading for the structure is assumed to be fairly extensive with cut depths between about 10 to 18 feet. We assume relatively light to moderate foundation loadings, typical of the proposed type of construction. If building loadings, location or grading plans change significantly from those described above, we should be notified to re-evaluate the recommendations contained in this report. Job No. 113 222A GeCPt�Ch - 2 - SITE CONDITIONS The lot is.occupied with a 2-story residence possibly above crawlspace or basement and slab-on-grade floor in the garage. The ground surface is moderately sloping down to the northwest with about 10 feet of elevation difference across the building footprint. Vegetation consists of lawn, bushes and mature evergreen trees. The Vail Golf Course adjoins the north side of the lot. Gore Creek is located about 500 feet north of the lot. GEOLOGIC CONDITIONS The lot is located on alluvial deposits formed from coalescing fans of drainages that flow out of the south valley side. The official Town of Vail geologic hazard maps adopted in 2000 show Lot 2 to be outside of potential debris flow, snow avalanche and rockfall. Based on our review of the site, we concur that the lot is outside of the mapped hazards. FIELD EXPLORATION The field exploration for the project was conducted on June 26, 2013. Two exploratory borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. The borings were advanced with 4 inch diameter continuous flight augers powered by a truck-mounted CME-4513 drill rig. The borings were logged by a representative of Hepworth-Pawlak Geotechnical, Inc. Samples of the subsoils were taken with a 2 inch I.D. spoon sampler. The sampler was driven into the subsoils 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. Depths at which the samples were taken and the penetration resistance values are shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. Job No. 113 222A G(�OFtech - 3 - SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils consist of about 5 feet of loose silty sand with gravel and cobble fill overlying medium dense, silty to clayey sand with gravel and scattered cobbles. A sandy clayey silt layer within the sand soils was encountered at 14 feet in Boring 2, and silty sandy gravel and cobbles with possible boulders was encountered below the sand soils at a depth of 18 feet in Boring 2. Laboratory testing performed on samples obtained from the borings included natural moisture content and density and finer than sand size gradation analyses. Results of swell-consolidation testing performed on drive samples of the fill and natural granular soils, shown on Figures 4 and 5 indicate the fill soils are highly compressible and the natural sand soils have low to moderate compressibility potential under conditions of loading and wetting. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at the time of drilling or when checked 17 days later and the subsoils were slightly moist to moist. FOUNDATION BEARING CONDITIONS The natural soils encountered on the lot are relatively dense granular soils and suitable for support of spread. footings. The upper fill soils can be erratic and should be removed from below the proposed building. Based on the proposed basement excavation for the new structure, we expect the existing fill and debris from prior site development will be removed but the suitability of the exposed soils should be further evaluated at the time of construction. Groundwater was not encountered in the borings made on the lot and groundwater level rise that could impact the foundation construction is not expected. Job No. 113 222A C�Pfech - 4 - DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface 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. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural granular soils should be designed 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 about 1 inch or less. There could be potential for post-construction settlement under wetted conditions on the order of%2 to 1 inch. 2) The footings should have a minimum width of 16 inches for continuous walls and 2 feet for isolated 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 48 inches below exterior grade is typically used in this area. 4) 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 also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining Walls" section of this report. S) The existing fill, debris, topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the relatively dense natural granular soils. 'The exposed soils in footing area should'then be moistened and compacted. If water seepage is encountered, we should be contacted for evaluation and mitigation methods. Job No. 113 222A GecPtech - 5 - 6) A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FOUNDATION AND RETAINING WALLS Foundation walls and retaining structures which are laterally supported and can be expected to undergo only a slight amount of deflection should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 50 pcf for backfill consisting of the on-site granular soils and retained heights up to about 12 feet. Walls taller than 12 feet should be designed for a uniform earth pressure loading of 25H in psf where H is the retained wall height in feet. Cantilevered retaining structures which are separate from the residence and can be expected to deflect sufficiently to mobilize the full active earth pressure condition should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 40 pcf for backfill consisting of the on-site granular soils. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The pressures recommended above assume drained conditions behind the walls and a horizontal backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain should be provided to prevent hydrostatic pressure buildup behind walls. Backfill should be placed in uniform lifts and compacted to at least 90%of the maximum standard Proctor density at a moisture content near optimum. Backfill in pavement and walkway areas should be compacted to at least 95% of the maximum standard Proctor density. Care should be taken not to overcompact the backfill or use large equipment near the wall, since this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall backfill should be expected, even if the material is placed correctly, and could result in distress to facilities constructed on the backfill. The settlement potential can be reduced by use of a select granular material and compaction to at least 98% of standard Proctor density. Job No. 113 222A C�GCPt�Ch - 6 - The lateral resistance of foundation or retaining wall footings will be a combination of the sliding resistance of the footing on the foundation materials and passive earth pressure against the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated based on a coefficient of friction of 0.45. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 375 pcf. The coefficient of friction and passive pressure values recommended above assume ultimate soil strength. Suitable factors of safety should be included in the design to limit the strain which will occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against the sides of the footings to resist lateral loads should be a granular material compacted to at least 95%of the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS The natural on-site soils are suitable to support lightly loaded slab-on-grade construction. 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 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 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 at least 50% retained on the No. 4 sieve and less than 2%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 granular 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 Job No. 113 222A G86'rtech - 7 - of heavy precipitation or seasonal runoff. Frozen ground during 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 1 foot below lowest adjacent finish grade and sloped at a minimum 1% to a suitable gravity outlet. A drywell (or perforated interior sump pit) can be used for disposal of potential drain water at the sub-basement level. We expect the percolation rate to be on the order of 20 minutes per inch and should be verified at the time of excavation. 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 1 Meet deep. SITE GRADING The risk of construction-induced slope instability at the site appears low for relatively shallow cuts and fills up to about 10 to 12 feet deep. Fills should be limited to about S to 10 feet deep. Embankment fills should be compacted to at least 95% of the maximum standard Proctor density near optimum moisture content. Prior to fill placement, the subgrade should be carefully prepared by removing all vegetation and topsoil and compacting to at least 90% of the maximum standard Proctor density. The fill should be benched into slopes that exceed 20% grade. SURFACE DRAINAGE. Care should be taken to keep the bearing soils dry and Iimit the potential for settlement induced by wetting below the building. The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: Job No. 113 222A GLcGtech - S - 1) Inundation of the 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 95%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. 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. Free-draining wall backfill should be capped with at least 2 feet of the on- site finer graded soils to reduce surface water infiltration. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping that requires regular heavy irrigation and sprinkler heads should be kept at least 10 feet from the building foundation. LIMITATIONS This study 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 obtained from the exploratory borings drilled 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 contaminants (MOBC) developing in the fixture. 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 borings and variations in the subsurface conditions may not become evident until excavation is performed. If conditions Job No. 113 222A G rkech - 9 - 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. 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 strata and testing of structural fill by a representative of the geotechnical engineer. Respectfully Submitted, HEPWORTH - PAWLAK GEOTECHNICAL, INC. f Steven L. Pawlak, P. 115222 Reviewed by; �q •� Daniel E. Hardin, P.E. SLP/ksw Job No. 113 222A C(�'trtech APPROXIMATE SCALE 1" = 301 TRACT D r _ 8250 f PROPOSED POOL 828`' LOT 1 / • BORI 2 LOT 3 EXISTING RESIDENCE PROPOSED I �p I LOT 2 RESIDENCE i BORING 1 "260 / 026 EXISTING PARKING AREA - -- f PTARMIGAN ROAD 113 222A HEPWORTH•PAWLAK� GEOTECHNICAL Cw LOCATION OF EXPLORATORY BORINGS Figure 1 I BORING 1 BORING 2 ELEV.= 8259' ELEV.= 8256' 8260 8260 7 X 8255 12/12 X 8255 WC=6,9 X DD=115 X -200=20 6/12 WC=13.3 8250 DD=111 28/12 8250 WC=6.8 (3) H DD=105 .2) 28/12 Wc=6.8 8245 DD=109 15112 8245 WC=7.8 DD=118 APPROXIMATE LOWEST LEVEL 7/12 WC=20.6 8240 DD=102 16/12 8240 - WG=10.6 200=64 DD=119 d . r 36112 L 8235 8235 Note: Explanation of symbols is shown on Figure 3. r 113 222A LOGS OF EXPLORATORY BORINGS I-Figure 2 _11 11— I He 97-P&..I.k eG--Ct..thn 11 1 1 LEGEND: FILL; man-placed silty clayey sand with scattered gravel and cobbles, loose, slightly moist to moist, dark brown. QJ SAND (SM-SC); silty, clayey, scattered gravel and cobbles, clay layer at 14'in Boring 2, medium dense, slightly moist to moist with depth, mixed brown. d . GRAVEL AND COBBLES (GM); possible boulders, sandy, silty, clayey, dense, moist, brown. Relatively undisturbed drive sample; 2-inch I.D. California liner sample. 28/12 Drive sample blow count; indicates that 28 blows of a 140 pound hammer falling 30 inches were required to drive the California sampler 12 inches. 12 Indicates 2"diameter slotted PVC pipe installed in boring to depth shown. NOTES: 1. Exploratory borings were drilled on June 26, 2013 with 4-inch diameter continuous flight power auger. 2. Locations of exploratory borings were measured approximately by pacing from features shown on the site plan provided. 3. Elevations of exploratory borings were obtained by interpolation between contours shown on the site plan provided and checked by instrument level. 4. The exploratory boring 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 boring logs represent the approximate boundaries between material types and transitions may be gradual. 6. No free water was encountered in the borings at the time of drilling or when checked 17 days later. Fluctuation in water level may occur with time. 7. Laboratory Testing Results: WC = Water Content (%) DD = Dry Density (pcf) -200 = Percent passing No. 200 sieve H 113 222A @C]'"� LEGEND AND NOTES Figure 3 He worth—Pawlak Geotechnicci Moisture Content= 10.6 percent Dry Density = 119 pof Sample of: Silty Clayey Sand with Gravel From: Boring 1 at 19 Feet 0 1 Compression upon 2 wetting c 0 U 2 3 CL E 0 U 4 5 6 0.1 1.0 10 100 APPLIED PRESSURE-kst 113 222A ~ Bch SWELL-CONSOLIDATION TEST RESULTS Figure 4 He worth—Pawlak Geotechnfcol Moisture Content 13.3 percent Dry Density= ill pcf Sample of: Silty Clayey Sand with Gravel (Fill) From: Boring 2 at 4 Feet 0 1 Compression upon 2 1 11 wetting L 3 Q O U 4 5 6 7 8 9 10 11 12 0.1 1.0 10 100 APPLIED PRESSURE-ksf 113 222A He worth-Pawlak Geotechnical SWELL-CONSOLIDATION TEST RESULTS Figure 5 N r r w a. z° .c 0Y 3 3 5 o � � � 78 '8 b ,� cn v� rn co r i � rA ai ai a�i ai >0 > �, u V U U U U U V Wax E:mo paUl C3.2 N �� Z J ,a Q W w L) g O)m V a w UJ z i- m n U F 0 w W 0 a 9a ) (F YW9 f-0 Q J O Zzoo LU w Q Q 2N0 N ably a LL z O a 0 Q o o Q. a LU _ CO 0 > : 0 N Z a JLF Z L o 0� 00 00 M 00 4R a 00 'c tc N Zzo z = IL LU V � O Lu I IL Z a 2 0