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HomeMy WebLinkAboutSoils Report.pdf Hepworth-Paw•lak Geotechnical, Inc. 5020 County Road 154 Glenwood Springs,Colorado 81601 Phone:970-945-7988 HEPWORTH-PAWLAK 70-9 5- HEPWORTH-PAWLAK GEOTECHNICAL Fax:970-945-8454 email: hp eaf'hpgeotech.co SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE 3090 BOOTH CREEK DRIVE LOT 8, BLOCK 3, VAIL VILLAGE 11TH FILING VAIL, COLORADO JOB NO. 115 240A JUNE 30, 2015 PREPARED FOR: ART REIMERS C/O BERGLUND ARCHITECTS ATTN: KEEGAN WINKELLER P.O. BOX 2378 VAIL, COLORADO 81658 keegsn&r,bergiundarchitects.com • Parker 303-841-7119 • Colorado Springs 719-633-5562 • Silverthorne 970-468-1989 TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS - 2 FIELD EXPLORATION - 2 - SUBSURFACE CONDITIONS FOUNDATION BEARING CONDITIONS - 3 - DESIGN RECOMMENDATIONS - 4 - FOUNDATIONS - 4 - FOUNDATION AND RETAINING WALLS - 5 - FLOOR SLABS (NON-STRUCTURAL) - 6 - UNDERDRAINSYSTEM - 7 - SURFACE DRAINAGE - 7 - LIMITATIONS - 8 FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4 AND 5 - GRADATION TEST RESULTS TABLE 1 -SUMMARY OF LABORATORY TEST RESILTS TABLE 2-SUMMARY OF WATER LEVEL MEASUREMENTS PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located at 3090 Booth Creek Drive, Lot 8, Block 3, Vail Village 1 lth Filing, 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 Art Reimers do Berglund Architects dated June 1, 2015. 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 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 proposed residence design was not available at the time of our study. In general, the existing residence shown on Figure 1 will be razed and a new residence constructed in its place. We assume the new residence will be a two story structure above a basement level with slab-on-grade floor. The garage will be at the main level and could also be underlain by basement. Grading for the structure is assumed to be relatively minor with cut depths between about 5 to 10 feet. The excavation for the basement area will be impacted by shallow groundwater conditions and excavation dewatering will be needed. The feasibility of long term site dewatering with subsurface drainage or designing the lower level to resist water intrusion and buoyancy is in consideration. We assume relatively light foundation loadings, typical of the proposed type of construction. Job No. 115 240A Gtech 2 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. SITE CONDITIONS The lot is occupied by a two story residence. The ground surface is relatively flat in the front part of the lot with a gentle slope down to the north. Gore Creek flood line borders the south side of the lot roughly 10 feet below the building area with a moderate slope down from the residence and back patio. Vegetation generally consists of landscape grass, bushes and scattered evergreen and aspen trees. FIELD EXPLORATION The field exploration for the project was conducted on June 5, 2015. Two exploratory borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. The borings were cased with slotted PVC pipe for groundwater level monitoring and permeability testing for groundwater flow monitoring and excavation dewatering evaluations. The borings were advanced with 4-inch diameter continuous flight augers powered by a truck-mounted CME-45B drill rig. The borings were logged by a representative of Hepworth-Pawlak Geotechnical, Inc. The boring locations were limited to the north side of the lot as shown on Figure 1. Samples of the subsoils were taken with 1% inch and 2 inch I.D. spoon samplers. The samplers were 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. 115 240A GecPtech 3 SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils consist of about 5 to 7 feet of fill overlying loose to medium dense, silty sand and gravel with cobbles down to the drilled depths of about 21 feet. The soils appeared stratified and contained frequent sand layers. The existing fill consists of mixed clay, silt and sand soils with gravel and organics and could vary in type and depth across the property. Laboratory testing performed on samples obtained from the borings included natural moisture content and density, and gradation analyses. Results of gradation analyses performed on small diameter drive samples (minus PA inch fraction) of the natural granular soils are shown on Figures 4 and 5 and summarized in Table 1. Free water was encountered at a depth of about 8 feet in Boring 1 and at about 6 to 7 feet in Boring 1. The groundwater level appears to be close to the adjacent creek level. Water level monitoring results conducted in the temporary casings set in the boreholes are summarized in Table 2. FOUNDATION BEARING CONDITIONS The natural granular soils are suitable to support lightly loaded spread footings with relatively low bearing capacity and relatively low settlement potential. Care should be taken to remove all fill and debris from the existing development. Excavation dewatering will be needed depending on the proposed excavation depth, time of year and water level of Gore Creek. It appears that excavation dewatering such as with trenches and sumps could be feasible for relatively shallow excavation depths. Potential groundwater flow through the building area is proposed to be evaluated by GL&A and will be reported under separate cover. The below grade parts of the new residence will probably need to be protected against groundwater impacts and potential seasonal water level rise. Due to Job No. 115 240A Ge P eech - 4 - the proposed basement depth of the new residence, gravity discharge may not be feasible and pumping at times of high groundwater level or designing the lower level to be watertight could be needed. We can assist with the additional evaluation for excavation dewatering and design of a watertight building lower level when the proposed building construction has been determined. 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 1,500 psf. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. 2) The footings should have a minimum width of 18 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. Job No. 115 240A Gtech - 5 - 5) The existing fill, debris, topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the natural granular soils. Structural fill placed below the building foundation can consist of the onsite granular soils free of organics, debris and rock larger than about 6 inches compacted to at least 98% of standard Proctor density. If water seepage is encountered, the footing areas should be dewatered before concrete placement. 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. 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 placed in Job No. 115 240A Ge Ptech - 6 - 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 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 250 pcf(buoyant condition). 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 (NON-STRUCTURAL) The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab- on-grade construction. To reduce the effects of some differential movement, non- structural 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 6 inch layer of free-draining gravel should be placed beneath basement level slabs to facilitate drainage and connected to the subdrain system (if provided). 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. Job No. 115 240A Gtech - 7 - 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 Free water was encountered at shallow depth and it has been our experience that the water level will rise during spring runoff and local perched groundwater can develop during times 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 unless the lower level is designed to be watertight and to resist buoyant forces. Where provided, 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 above the 100 year flood level of Gore Creek. The basement underslab gravel should be frequently connected to the perimeter foundation drain with interior lateral drains. 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 2 feet deep. SURFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 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 Job No. 115 240A Gatech - 8 - 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 6 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 about 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. 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 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 borings 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 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 Job Na 115 240A Gtech - 9 - 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. "\A L. ` —.4 .„ rear., .` a. • • `10_.y 04 .90. ` * -o N.` ' +i i 62 22 1* ., . Steven L. Pawlak, P.E. Reviewed b : t . ! .;�.�§ ,aJ ''if ae Ce\- - - \lieu j1/4.::...... ‘''' ------ .....jk. Daniel E. Hardin, P.E. SLP/ksw cc: Berglund Architects-Keegan Winkeller(keegan@berglundarchitects.corn) Job No. 115 240A APPROXIMATE SCALE 1" = 30' BOOTH CREEK DRIVE os BENCH MARK:TRANSFORMER SLAB; ELEVATION =8307.8',AS GIVEN. • BORING 2 BORING 1 • - 8310 EXISTING RESIDENCE 3090 BOOTH CREEK DRIVE LOT 7 (TO BE REMOVED) / I LOT 9 I 8370 1 _ 8305 \ LOT 8 OOV 100 eE C;FV0 a(JD 0 GORE CREEK 115 240A � �Hpp�� C7Qp7,1@Cf'1 LOCATION OF EXPLORATORY BORINGS Figure 1 Hepworth—Pawlak Geotechnical BORING 1 BORING 2 ELEV.= 8307.8' ELEV.= 8307.9' _ 8310 8310 __ EXISTING FLOOR LEVEL=8309.6' 8305 ' 12/12 6/12 8305 8/12 3 �#,,p' 8/12 WC=11.0 — _ '' DD=101 8300 200=22 3 0 rio — io 8300 m o — ,tf'e, 7/12 • 5/12 EL tiliF WC=10.7 +4=14 c +4=35 • -200=16 g °' _ 8295 200=3co w — oil 8295 m w rii 5/12 - 2/6,50/3 — +4=25 +4=27 — tl: ? -200=25 • -200=32 8290V _g 8290 3/12 4' 20/12 a▪ , 8285 8285 Note: Explanation of symbols is shown on Figure 3. I 115 240A GeHp,ech I LOGS OF EXPLORATORY BORINGS I Figure 2 Hepworth—Pawlak Geotechnical LppEGEND: (� FILL; mixed clay, silt and sand with organics, scattered gravel, very moist, dark brown. 4 SAND (SM); silty, gravelly, loose to medium dense,wet, brown. SAND AND GRAVEL (SM-GM); silty, scattered cobbles, loose to medium dense, moist to wet with depth, brown. Relatively undisturbed drive sample; 2-inch I.D. California liner sample. IDrive sample; standard penetration test (SPT), 1 3/8 inch I.D. split spoon sample,ASTM D-1586. 8/12 Drive sample blow count; indicates that 8 blows of a 140 pound hammer falling 30 inches were required to drive the California or SPT sampler 12 inches. 0,3 Free water level in boring and number of days following drilling measurement was taken. r Indicates 2-inch diameter factory slotted PVC pipe installed in boring to depth shown. 24 NOTES: 1. Exploratory borings were drilled on June 5, 2015 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 instrument level and refer to Bench Mark shown on Figure 1. 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. Water level readings shown on the logs were made at the time and under the conditions indicated. Fluctuations in water level may occur with time. 7. Laboratory Testing Results: WC = Water Content(%) DD = Dry Density (pcf) +4 = Percent retained on the No.4 sieve -200 = Percent passing No. 200 sieve 115 240A H CI'1 LEGEND AND NOTES Figure 3 Hepworth—Pawlak Geotechnical HYDROMETER ANALYSIS ISIEVE ANALYSIS HR TIME READINGS U.S.STANDARD SERIES I CLEAR SQUARE OPENINGS 45 MIN.15 MIN .60MIN19MIN.4 MIN. 1 MIN. #200 #100 #50 #30 #16 #8 #4 3/8" 3/4" 1 1/2" 3" 5"6" 8" 0 190 10 1 90 20 1 W 60 _CI Z 30CD I 70 Z CC 40 Q En I— Z 50 W So Z LU0 CC 60 0 d n. 70 I 40 FE I 3o 80 i 20 ..../..7 90 I' I 10 100 .001 .002 .005 .009 .019 0 .037 .074 .150 300 .600 1.18 2.36 4.75 9.5125 19.0 37.5 76.2 152 203 DIAMETER OF PARTICLES IN MILLIMETERS 127 CLAY TO SILT SAND MEDIUMGR44£L I COARSE FINE COARSE COBBLES GRAVEL 35 % SAND 57 % SILT AND CLAY 8 % LIQUID LIMIT % PLASTICITY INDEX % SAMPLE OF: Slightly Silty Sand and Gravel FROM: Boring 1 at 10 Feet HYDROMETER ANALYSIS I SIEVE ANALYSIS I 24 7 HR TIME READINGS U.S.STANDARD SERIES I CLEAR SQUARE OPENINGS 40 5 MIN.15 MIN.60MIN19MIN.4 MIN. 1 MIN. #200 #100 #50 #30 #16 #8 #4 3/8" 3/4" 1 1/2" 3" 5"6" 8" I 100 10 1 90 20 0 in Z 30 ' I 80 CD Fa— 1 70 Z CC 40 I Q Z 50 I 60 0_ 0 I 50 W CC 60 0 D I 40 w 70 I 80 I 30 1 20 90 I 10 100 I .001 .002 .005 .009 .019 .037 .074 .150 .300 .600 1.18 2.36 4.75 9.5125 37.5 76.2 19.0 12152 203 DIAMETER OF PARTICLES IN MILLIMETERS 7 CLAY TO SILT SMIB FIN MEDIUM I COARSE 11111mE I ppq .11a COBBLES GRAVEL 25 % SAND 50 % SILT AND CLAY 25 % LIQUID LIMIT % PLASTICITY INDEX % SAMPLE OF: Silty Sand with Gravel I FROM: Boring 1 at 15 Feet g �'�'eI"1 115 240A GRADATION TEST RESULTS IFigure 4 Hepworth—Pawlak Geotechnical I HYDROMETER ANALYSIS I SIEVE ANALYSIS TIME READINGS U.S.STANDARD SERIESSIEVE CLEAR SQUARE OPENINGS 45 MIN.15 MIN.60MIN19MIN.4 MIN. 1 MIN. #200 #100 #50 #30 #16 #8 #4 3/8" 3/4" 1 1/2" 3" 5"6" 8" 0 / I o0 i 10 — 1 so A 7� 0 20 80 Z 30 CD Q o Z CO C 40so Q.Q Z 50 so Z W 0 60 0 a 40 f w 70 d 30 80 20 90 10 100 0 .001 .002 .005 .009 .019 .037 .074 .150 .300 .600 1.18 2.36 A75 9.5 125 19.0 37.5 76.2 152 203 DIAMETER OF PARTICLES IN MILLIMETERS 127 CLAY TO GLT SAND GRAVEL FINE I MEDIUM I COARSE FINE I COARSE COBBLES GRAVEL 14 % SAND 70 % SILT AND CLAY 16 % LIQUID LIMIT % PLASTICITY INDEX % SAMPLE OF: Silty Sand with Gravel FROM: Boring 2 at 10 Feet HYDROMETER ANALYSIS I SIEVE ANALYSIS q TIME READINGS U.S.STANDARD SERIES I CLEAR SQUARE OPENINGS I 24 M.15 MIN.60MINI9MIN.4 MIN.1 MIN. #200 #100 #50 #30 #16 #8 #4 3/8" 3/4" 1 1/2" 3" 5"6" 8" I . 100 10 90 20 I 80 LLi Z 30 i CD Q I 70 z F 40 CO 60 d Z 50 i H U 50 LLLJ 0 60 / U LLL •••'°°°°°...°°...°°°°' J 40 W 70 0 30 80 20 90 10 100 0 .001 .002 .005 .009 .019 .037 .074 .150 .300 .600 1.18 2.36 4.75 9.51a519.0 37.5 76.2 12752 203 DIAMETER OF PARTICLES IN MILLIMETERS CLAY TO SILT SAND FINE I MEDIUM I COARSE FINE GRAVEL ICOARSE COBBLES GRAVEL 27 % SAND 41 % SILT AND CLAY 32 % LIQUID LIMIT % PLASTICITY INDEX % SAMPLE OF: Silty Sand with Gravel FROM: Boring 2 at 15 Feet H 115 240A CI'1 GRADATION TEST RESULTS Figure 5 Hepworth—Pawlak Geotechnical s \ k \ \ k nt to � (yr ± 5 ± ± ± - § g g § > 2 « > « .0 , ® '0G 3 no / »— Q 7 ` » ƒ \ 2 3 \ — @ ± 7 y 7 \ \ ( to Li \ - \ / 11 y ƒ m w H LU cc< 0 / \ 5 \ e § ) \ - N °C) zp f2 ± / N [ \ 2 / • � N 0 N I \( 0 cc \ z % In « B , § Z cc 0 z Ln Li 0 N 7 I © © 2 Q 2 & o w \ ce (±9 .—cn HEPWORTH-PAWLAK GEOTECHNICAL, INC. TABLE 2 SUMMARY OF WATER LEVEL MEASUREMENTS JOB NO. 115 240A Depth Below Ground Surface (ft) Casing Location Depth 6/8/15 6/10/15 6/17/15 6/23/15 6/30/15 (ft) Boring 1 20 8.6 7.7 8.5 8.6 8.0 Boring 2 18.1 7.9 6.1 6.0 5.9 6.3