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HomeMy WebLinkAboutSoils Report 08.29.2018H-PKUMAR Geotechnical Engineering 1 Engineering Geology Materiels Testing 1 Environmental 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax: (970) 945-8454 Email: hpkglenwood@kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT FW -5, THE FAIRWAYS ASPEN GLEN DEVELOPMENT GOLDEN BEAR GARFIELD COUNTY, COLORADO PROJECT NO. 18-7-525 AUGUST 29, 2018 PREPARED FOR: KEVIN EVERSON C/O RM CONSTRUCTION ATTN: BLAKE PILAND 5030 COUNTY ROAD 154 GLENWOOD SPRINGS, COLORADO 81601 blake@buildwithrm.com TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS - 2 -1 SUBSIDENCE POTENTIAL - 2 - FIELD EXPLORATION - 3 = SUBSURFACE CONDITIONS , - 3 - FOUNDATION BEARING CONDITIONS - 4 - DESIGN RECOMMENDATIONS - 4 - FOUNDATIONS - 4 - FOUNDATION AND RETAINING WALLS - 5 - FLOOR SLABS - 6 - UNDERDRAIN SYSTEM - 7 - SURFACE DRAINAGE - 7 - LIMITATIONS - 8 - REFERENCES -9- FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4 AND 5 - SWELL -CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS H-P-KUMAR Project No. 18-7-525 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot FW -5, The Fairways, Aspen Glen Development, Golder Bear, Garfield County, 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 agreement for geotechnical engineering services to Kevin Everson dated August 16, 2018. 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 Development plans were not available at the time of our study and we understand our findings will be considered in the lot purchase. For our study, we assume the residence will be typical of this area and be a 1 and 2 -story, wood frame structure above a partial or full basement level. Ground floors could be structural above crawlspace or slab -on -grade. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 10 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. When building location, grading and loading information have been developed, we should be notified to re-evaluate the recommendations presented in this report. H-P�KUMAR Project No. 18-7-525 -2 - SITE CONDITIONS The lot was vacant and vegetated with grass and weeds at the time of our study. Willows are located along the golf course pond near the southwest corner of the lot. The ground surface slopes gently down to the north with about 2 feet elevation difference across the general building area. Fairway 2 is located along the west side, Golden Bear roadway is along the east side and vacant lots border the south and north sides of the lot. SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen development. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some massive beds of gypsum and limestone. There is a possibility that massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the lot. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. During previous studies in the area, broad subsidence areas and several sinkholes were observed scattered throughout the Aspen Glen development, mainly to the east of the Roaring Fork River (Chen -Northern, 1991 and 1993). These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the lower Roaring Fork River valley. The nearest sinkhole was mapped about 900 feet north of Lot FW -5. Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities was encountered in the subsurface materials; however, the exploratory borings were relatively shallow, for foundation design only. Based on our present knowledge of the subsurface conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of future ground subsidence on Lot FW -5 throughout the service life of the proposed residence, in our opinion, is low; however, the owner should be made aware of the potential for sinkhole development. If further investigation of possible cavities in the bedrock below the site is desired, we should be contacted. H-P%KUMAR Project No. 18-7-525 -3 - FIELD EXPLORATION The field exploration for the project was conducted on August 20, 2018. 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 -45B drill rig. The borings were logged by a representative of H-P/Kumar. 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. SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils, below about 1/2 foot of topsoil, consist of very stiff to stiff, sandy silt and clay to sandy clay down to depths of 81/2 and 12 feet overlying dense, slightly silty sandy gravel and cobbles with boulders. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and boulders and drilling refusal was encountered in the deposit. 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 relatively undisturbed drive samples of the silt and clay soils, presented on Figures 4 and 5, indicate low compressibility under conditions of light loading and natural moisture content. The samples showed variable expansion (Boring 1 at 21/2 feet) or compression (Boring 2 at 5 feet) when wetted. 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. H-P-KUMAR Project No. 18-7-525 -4 - FOUNDATION BEARING CONDITIONS The upper silt and clay soils have variable load capacity and movement potential, mainly when wetted and use of mitigation methods to reduce the movement risk appears warranted. The underlying dense granular soils have moderate load capacity and low settlement potential. Partial or total removal of the silt and clay soils and replacement with compacted structural fill to a maximum depth of around 5 feet could also be used to achieve relatively low settlement potential. The suitability of the silt and clay soils to support building foundations and floor slabs should be further evaluated at the time of construction. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, on the natural granular soils or compacted structural fill. we recommend the building be founded with spread footings bearing 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 or compacted structural fill should be designed for an allowable bearing pressure of 2,500 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 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 36 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-PvKUMAR Project No. 18-7-525 -5 - 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) The topsoil, silt and clay soils and any loose disturbed soils should be removed down to the relatively dense natural granular soils. The exposed soils in footing area should then be moistened and compacted. Structural fill placed to reestablish design bearing level should consist of a relatively well graded granular soil (such as road base) excluding organics and rock larger than 6 inches compacted to at least 98% of standard Proctor density at near optimum moisture content. The structural fill should extend laterally out beyond the footing edges a minimum distance of one-half the fill depth below the footing. 6) A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions and test structural fill for compaction. 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 55 pcf for backfill consisting of the on-site fine-grained soils. Cantilevered retaining structures (if any) 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 50 pcf for backfill consisting of the on-site fine-grained soils. Backfill should not contain organics, debris or rock larger than about 6 inches. 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. H-P-MKUMAR Project No. 18-7-525 -6 - Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum standard Proctor density at near optimum moisture content. Backfill placed 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. A relatively well graded granular material such as road base and compaction to at least 98% of standard Proctor density could be used to limit the settlement potential. 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 400 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, exclusive of topsoil, can be used to support lightly loaded slab -on -grade construction with a risk of movement and distress. The movement potential can be reduced by replacing at least 2 feet of the silt and clay soil below slab areas with structural fill such as road base. 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 H-P1KUMAR Project No. 18-7-525 -7 - 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 soils or imported 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 the area and where there are clay soils that 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. 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. 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 11/2 feet deep. An impervious membrane such as 20 mil PVC should be placed beneath the drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils. The liner can be omitted where the footings bear directly on the natural gravel soils. 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. H-P1KUMAR Project No. 18-7-525 -8- 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 covered with filter fabric and 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. 5) Landscaping which requires regular heavy irrigation should be located at least 5 feet from foundation walls. 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 moldor 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 H-P%KUMAR Project No. 18-7-525 -9 - 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 -P KU MAR Steven L. Pawlak, Reviewed by: Daniel E. Hardin, P.E. Sj.,P/kac oLL REFERENCES Chen -Northern, Inc., 1991, Preliminary Geotechnical Engineering Study, Proposed Aspen Glen Development, Garfield County, Colorado, prepared for Aspen Glen Company, dated December 20, 1991, Job No. 4 112 92. Chen -Northern, Inc, 1993, Geotechnical Engineering Study for Preliminary Plat Design, Aspen Glen Development, Garfield County, Colorado, prepared for Aspen Glen Company, dated May 28, 1993, Job No. 4 112 92. H-Pk4KUMAR Project No. 18-7-525 BENCHMARK: MANHOLE RIM EL. 100' ASSUMED GOLDEN BEAR ®4^F—yam ...M.M•+ +• eel LOT FW 6 i 1 1 1 a BORING 1 LOT FW 5 NOT TO SCALE 18-7-525 2ND FAIR WAY H-PtiKUMAR BORING 2 1 1 +w.••=ms LOCATION OF EXPLORATORY BORINGS Fig. 1 0 5 10 15 18-7-525 BORING 1 EL. 101' 21/12 WC=6.B DD=115 9/12 WC=10.1 DD=94 -200=67 50/4 H-P---*KIJMAR BORING 2 EL. 103' 19/12 15/12 WC=6.9 DD=94 19/12 WC=7.2 DD=113 -200=66 LOGS OF EXPLORATORY BORINGS 0 0 DEPTH -FEET 10 15- Fig. 2 LEGEND TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, SLIGHTLY MUISI, BROWN. SILT AND CLAY (ML—CL); SANDY, VERY STIFF TO STIFF, SLIGHTLY MOIST, BROWN, SLIGHTLY POROUS AND CALCAREOUS. /F1 GRAVEL AND COBBLES (GM—GP); SLIGHTLY SILTY, SANDY, PROBABLE BOULDERS, DENSE, SLIGHTLY MOIST, MIXED BROWN, ROUNDED ROCK. RELATIVELY UNDISTURBED DRIVE SAMPLE; 2—INCH I.D. CALIFORNIA LINER SAMPLE. DRIVE SAMPLE; STANDARD PENETRATION TEST (SPT), 1 3/8 INCH I.D. SPLIT SPOON SAMPLE, ASIM 0-1586. 21/12 DRIVE SAMPLE BLOW COUNT. INDICATES [HAI 21 BLOWS OF A 140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE CALIFORNIA OR SPT SAMPLER 12 INCHES. I PRACTICAL AUGER REFUSAL. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON AUGUST 20, 2018 WITH A 4—INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 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 MEASURED BY HAND LEVEL AND REFER TO THE BENCHMARK ON FIG. 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 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 (%) (ASTM D 2216); DD = DRY DENSITY (pcf) (ASTM D 2216); —200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140). 18-7-525 H-P45KUMAR LEGEND AND NOTES Fig. 3 F 5 s s J CONSOLIDATION - SWELL 3 2 0 —1 —2 —3 18-7-525 f0 H-PtiKUMAR APPLIED PRESSURE - KSF 10 SWELL -CONSOLIDATION TEST RESULTS 100 Fig. 4 SAMPLE OF: Sandy Silty Clay FROM: Boring 1 ® 2.5' WC = 6.8 %, DD = 115 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING .4 �.1 e _ — 4---- — — —...� — Th... test mull. tippy tiny to 1M' Oionotoi t..ted. Tn. falling .wart oTeO not 110 eep}advCed, on pt in M. .IU.oul p.. .:H,n npp.wal al Humor and Anacleto., Inc. S..II =doiGnn�ria p.elmn a M occwaw.c. �ih u o—+S.E. 18-7-525 f0 H-PtiKUMAR APPLIED PRESSURE - KSF 10 SWELL -CONSOLIDATION TEST RESULTS 100 Fig. 4 2 0 J —2 W 3 N CONSOLIDATION —4 —6 8 —10 —12 18-7-525 H-P-KUMAR SWELL—CONSOLIDATION TEST RESULTS Fig. 5 SAMPLE OF: Sandy Silt and Clay FROM: Boring 2 ® 5' WC = 6.9 %, DD = 94 pcf ��J-E ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING -. Th.m teat results apply only to In. wimples teated. T. Luting report shall ,,o1 In ropra_,,v. a,c pt in fuU. r'iFoul the • nIl.. arp•c.al el Kumon and Aaaocialea. Inc 5..11 Consolidation tasting pMarm.d In occordanc. Mtn ASTY 0-4346. 1 Q APPLIED PRESSURE - KSF 10 1flfl 18-7-525 H-P-KUMAR SWELL—CONSOLIDATION TEST RESULTS Fig. 5 H-PI<UMAR TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 18-7-525 SAMPLE LOCATION NATURAL MOISTURE CONTENT (%) NATURAL DRY DENSITY (Fact) GRADATION PERCENT PASSING NO. 200 SIEVE ATTERBERG LIMITS UNCONFINED COMPRESSIVE STRENGTH (Psf) SOIL TYPE BORING DEPTH (ft) GRAVEL (%) SAND (%) LIQUID LIMIT (%) PLASTIC INDEX (%O 1 21/2 6.8 115 Sandy Silty Clay 5 10.1 94 67 Sandy Silt and Clay 2 5 6.9 94 Sandy Silt and Clay 10 7.2 113 66 Sandy Silt and Clay