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HomeMy WebLinkAboutFile Documents.845 Meadows Rd.0014.2017 (13).ACBKH -P= KUMAR Geotechnical Engineering I Engineering Geology Materials Testing I Environmental 5020 County Road 154 Glenwood Springs, GO 81601 Phone: (970)945-7988 Fa:: (970) 9458454 Email: hpkglenwood®kumama.com Office Locations: Parker, Glenwood Springs, and Silverlhome, Colorado SUBSOILSTUDY FOR FOUNDATION DESIGN PROPOSED RECEPTION CENTER ADDITION LOT 1A, ASPEN MEADOWS SUBDIVISION 845 MEADOWS ROAD ASPEN, COLORADO PROJECT NO. 16-7-327 OCTOBER 24, 2016 PREPARED FOR: ASPEN MEADOWS RESORT ATTN: BOB STUMPUS 845 MEADOWS ROAD ASPEN, COLORADO 81611 (Bob.stumous@acocnmcadms.mml TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY........................................................................................ DESIGN I - PROPOSED CONSTRUCTION ................... ............................................................................. - I - SITECONDITIONS................................................................................................................... 2 - FIELDEXPLORATION ..................................... ....................................................................... - 2 - -SUBSURFACE SUBSURFACE CONDITIONS.................................................................................................- - 2 - DESIGN RECOMMENDATIONS............................................................................................- LIMITATIONS 3 - FOUNDATIONS..................................................................................................................... 3 - FOUNDATION AND RETAINING WALLS.......................................................................- 4 - FLOORSLABS....................................................................................................................... 5. UNDERDRAINSYSTEM...................................................................................................... 6 - SITEGRADING.................................................................................................................... - 6 - SURFACE DRAINAGE......................................................................................................... 7. DRYWELL.............................................................................................................................. - 7 - LIMITATIONS............................................................................................................................ 7 - FIGURE -FIGURE I - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4 - GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS TABLE II- SUMMARY OF PERCOLATION TEST RESULTS H -P -, KUMAR Project No. 76-7-327 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed reception center addition to be located at lot IA, Aspen Meadows subdivision, 845 Meadows Road, Aspen, 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 Aspen Meadows Resort dated June 16, 2016 and revised August 18, 2016. 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 proposed addition will consist of an enclosed dining area with a new basement below and roof top dining above, a new patio area cantilevered over the sleep slope west of the building and a new retaining wall on the south and east sides. Basement Floor will be slab -on -grade. Grading for the structure is assumed to be relatively extensive with cut depths up to 25 feet. We assume relatively light 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. H -P a KUMAR Project No. 16-7-327 2 - SITE CONDITIONS The existing building is one story wood frame construction above a walkout basement with a patio area and retaining wall on the south side. The site is vegetated with evergreen and aspen trees with brush, grass and weeds. There is a landscaped lawn area on the uphill front part of the site. The front pan of the site is relatively Bat with about an 8 foot cut to the patio area. The grade steepens in the rear and falls sharply down to Castle Creek. An existing pedestrian path is located west and south of the patio area. FIELD EXPLORATION The field exploration for the project was conducted on September 28 and 29, 2016. Two exploratory borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. The borings were advanced with 6 inch diameter percussion casing advancer powered by a truck -mounted CME -55 drill rig. The borings were logged by a representative of H-P/Kumar. Samples of the subsoils were taken with a II: 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. SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils consist of up to 2 feet of topsoil overlying dense, silty sandy gravel with cobbles and boulders down to the maximum depth explored, 41 feel. H -P = KUMAR Project No. 16-7-327 3 - Laboratory testing performed on samples obtained from the borings included natural moisture content and gradation analyses. Results of gradation analyses performed on a small diameter drive sample (minus 1'h inch fraction) of the coarse granular subsoils are shown on Figure 4. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at the time of drilling and the subsoils were slightly moist to moist. DESIGN 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 4,000 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 Poolings should have a minimum width of 16 inches for continuous walls and 2 feel for isolated pads. 3) Exterior footings and footings beneath unhealed 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 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 10 feet. H -P x KUMAR Project No. 16-7-327 -4 - 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. 5) All existing fill, 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. 6) A representalive 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 45 pcf for backfill consisting of the on-site granular soils for walls up to 12 feet high. Walls taller than 12 feet should be designed for a uniform earth pressure of 23H in psf where H is the wall height in feet. Cantilevered retaining structures which are separate from the addition 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 pavement and walkway areas should be compacted to at least 95'% of the maximum standard Proctor density. H -P —' KUMAR Project No. 167-327 -5 - 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 0.50. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 450 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 compacted to at least 95% of the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS 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, 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 forjoint spacing and slab reinforcement should he established by the designer based on experience and the intended slab use. A minimum 4 inch layer of Gee - 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. H -P —, KUMAR Project No. 167927 -6- UNDERDRAIN SYSTEM Although free water was not encountered during our exploration, it has been our experience in the area that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can also create a temporary perched condition. We recommend below -grade construction, such as retaining walls 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 I% to a suitable gravity outlet. 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 192 feet deep. SITE GRADING The basement excavation will he extensive and there is a risk of construction -induced slope instability at the site. We expect excavation sides will be sloped to a safe slope or retained with shoring to maintain cut slope stability- 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, topsoil and existing fill and compacting to at least 95% of the maximum standard Proctor density. The fill should be benched into the portions of the hillside exceeding 20% grade. Permanent unretained cut and fill slopes should be graded at 2 horizontal to 1 vertical or flatter and protected against erosion by revegetation or other means. The risk of slope instability will be increased if seepage is encountered in cuts and Flatter slopes may be necessary. If seepage is encountered in permanent cuts, an investigation should be conducted to determine if the seepage H -P � KUMAR Project No. 16-7-327 -7 - will adversely affect the cut stability. This office should review site grading plans for the project prior to construction. SURFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at all times after the addition has been completed: I) 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 about 2 feet of the on-site soils to reduce surface water infiltration. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. DRYWELL We understand that a drywell will be used for site runoff detention and disposal. The Natural Resources Conservation Service has identified four hydrologic soil groups (HSG) in the Aspen area and the site is located in Type B soil having a moderate infiltration rate. Results of a percolation test performed at Boring 1 am shown on Table Il. The groundwater level and bedrock are generally known to be relatively deep in this area. 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. H -P � KUMAR Project No. 16-7-327 IE 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 I, 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 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, H -Pk KUMAR LVE. Iter Reviewed by: Daniel E. Hardin, LEElksw cc: Jim H -P a KUMplt Project Na. 16-7J27 ® 'r BONING 1• /' -V. r} I. o R ::..`. h.......... yP PROPGSEG ATIO BUILDING h y g g A �� L 4 4P Ld BUILDING . ( BORING 2 �1 f(� • g.0 _ yM --------- Is o Is sa APPROXIMATE SCALE -FEET �I 16-7-327 I H-P�-tKUMAR I LOCATION OF EXPLORATORY BORINGS I Fig. 1 BORING I BORING 2 EL 7862' EL 7852' 7865 7865- -7855 7855- - _APPROXIMATE MAIN 1 25/0 FLOORLEVEL=7854' - 784518/5.20/0 0 --APPROXIMATE LOWER 7845 — FLOORLEVEL=7844.8' n 64/12 28/6.20/0 WC=4.3 +4=28 -200=6 27/12 7835 7835 — 25/0 2 5/0 0 0 r --7825 7825 — 50/6 7815 7815 — 17805 25/0 7805 H -PIWIMAR 16 -7-327 LOGS OF EXPLORATORY BORINGS Fig. 2 LEGEND ® TOPSOIL; ORGANIC SANDY SILT AND CLAY, DARK BROWN. GRAVEL AND COBBLES (GM -GP); SLIGHTLY SILTY, SANDY. BOULDERS. DENSE, SLIGHTLY MOIST, BROWN, ROUNDED ROCK. DRIVE SAMPLE; STANDARD PENETRATION TEST (SPT), 1 3/8 INCH I.D. SPLIT SPOON SAMPLE, ASTM D-1586. 25/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 25 BLOWS OF A 140 -POUND HAMMER FALLING 30 INCHES WERE REOUIRED TO DRIVE THE SPT SAMPLER 12 INCHES. NOTES 1. THE EXPLORATORY BORINGS WERE GRILLED ON SEPTEMBER 28 AND 29. 2016 WITH AN 8 -INCH DIAMETER ODEX CASING AND PERCUSSION HAMMER. 2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED. 4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE UNES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING. 7. LABORATORY TEST RESULTS; WC = WATER CONTENT (X) (ASTM 0 2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422); -200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140). I6-7-327 LEGEND AND NOTES I Fig. 3 N,LYa15 aD I. •° '• N' nv DIUAETCA OF PARTICLES IN MILLIMETERS,' CLAY 70 SILT SANG GRAVEL LORRIES FINE MEDIUM C01R$E EINE COiRSE GRAVEL 36 Y. S.ND 66 % SILT AND CLAY 6 % UOIND LIMIT PLA91O7r INDEX SAMRE OF: SIIppIIT SIIIY Sane eM GmrN FROM: II 1 O 20- E d S N' I. x mow... .I Tx a; TMAI,A H-P=KUMAR 16-7-327 GRADATION TEST RESULTS Fig. 4 N,LYa15 HIM H-R�KUMAR TABLE 2 PERCOLATION TEST RESULTS PROJECT NO. 16-7-327 HOLE NO. HOLE DEPTH (INCHES) LENGTH OF INTERVAL (MIN) WATER DEPTH AT START OF INTERVAL (INCHES) WATER DEPTH AT ENDOF INTERVAL (INCHES) DROP IN WATER LEVEL (INCHES) AVERAGE PERCOLATION RATE (MINJINCH) B-1 84 2 46% 41% 6 0.4 0.7 0.7 0,9 0.5 0.3 0.4 0.5 0.6 0.7 41% 38% 3 35/: 35% 3 36% 33% 2% 33% 29% 3% 29% 23 6% 23 18% 4% 18'f. 14% 4 14% 11 3% 11 8 3 Note: The percolation test was conducted in the 6 -inch diameter borehole following drilling on September 29, 2016.