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HomeMy WebLinkAboutSoils Report 01.17.2018H-P�KUMAR Geotechnical Engineering 1 Engineering Geology Materials 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 251, IRONBRIDGE EAGLE CLAW CIRCLE GARFIELD COUNTY, COLORADO PROJECT NO. 17-7-866 JANUARY 17, 2018 PREPARED FOR: MIKE DEER P. O. BOX 2090 GLENWOOD SPRINGS, COLORADO 81602 mikedeer@sooris.net TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - BACKGROUND INFORMATION - 1 PROPOSED CONSTRUCTION - 1 SITE CONDITIONS - 2 - SUBSIDENCE POTENTIAL - 2 - FIELD EXPLORATION - 2 - SUBSURFACE CONDITIONS - 3 - ENGINEERING ANALYSIS _ 3 - DESIGN RECOMMENDATIONS - 4 - FOUNDATIONS - 4 - FOUNDATION AND RETAINING WALLS - 5 - NONSTRUCTURAL FLOOR SLABS - 7 - UNDERDRAIN SYSTEM 7 - SITE GRADING _ g - SURFACE DRAINAGE - 8 - LIMITATIONS - 9 - FIGURE 1 - LOCATION OF EXPLORATORY BORING FIGURE 2 - LOG OF EXPLORATORY BORING FIGURE 3 - SWELL -CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS H-P%KUMAR Project No. 17-7-866 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 251, Ironbridge, Eagle Claw Circle, 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 Mike Deer dated December 11, 2017. We previously conducted a preliminary subsoil study for residences in the Villas North and Villas South parcels of Ironbridge and presented our findings in a report dated February 28, 2014, Job No. 113 471A. A field exploration program consisting of an exploratory boring 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. BACKGROUND INFORMATION The proposed residence is located in the existing Ironbridge subdivision development. Hepworth-Pawlak Geotechnical (now H-P/Kumar) previously conducted subsurface exploration and geotechnical evaluation for development of Villas North and Villas South parcels, Job No. 105 115-6, report dated September 14, 2005, and performed observation and testing services during the infrastructure construction, Job No. 106 0367, between April 2006 and April 2007. The information provided in the previous reports has been considered in the current study of Lot 251. PROPOSED CONSTRUCTION Development plans for the lot were not available at the time of our study. The proposed residence is assumed to be a two-story wood frame structure with a structural slab foundation H-PiKUMAR Project No. 17-7-866 -2 - and no basement or crawl -space. A post -tensioned slab foundation has been used to support the existing residences in this area. Grading for the structure is assumed to be relatively minor with cut and fill depths on the order of a few feet or less. We assume relatively light foundation loadings, typical of the proposed type of construction. When the building loadings, location and grading plans have been developed, we should be notified to re-evaluate the recommendations contained in this report. SITE CONDITIONS The proposed residence is located on the west side of the Villas South parcel overlooking the 18th Green. The natural terrain prior to development in 2006 sloped down to the east at about 5 to 7% grade. The subdivision in this area was elevated by filling on the order of 15 to 20 feet above the original ground surface to create a relatively level building site with a moderate slope down along the west side to the 18th Green. Vegetation consists of grass and weeds. SUBSIDENCE POTENTIAL. Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the subject site. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some massive beds of gypsum and limestone. The Eagle Valley Evaporite is known to be associated with sinkholes and localized ground subsidence in the Roaring Fork River valley. A sinkhole opened in the cart storage parking lot east of the Pro Shop located to the north of the Villas South parcel in January 2005. Other irregular bedrock conditions have been identified in the affordable housing site located to the west of the Villas North parcel. Indications of ground subsidence were not observed in the Villas development area that could indicate an unusual risk of ground subsidence, but localized variable depths of the debris fan soils encountered in the previous September 14, 2005 geotechnical study in the Villas development area could be the result of past subsidence. In our opinion, the risk of future ground subsidence in the Villas North and South project area is low and similar to other areas of the Roaring Fork River valley where there have not been indications of ground subsidence. FIELD EXPLORATION The field exploration for the project was conducted on December 27, 2017. One exploratory boring was drilled at the location shown on Figure 1 to evaluate the subsurface conditions. The H-P%KUMAR Project No. 17-7-866 -3 - boring was advanced with 4 -inch diameter continuous flight augers powered by a truck -mounted CME -45B drill rig and was logged by a representative of H-P/Kumar. Samples of the subsoils were taken with 1'/8 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 Log of Exploratory Boring, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The subsoils consist of about 6 inches of topsoil overlying around 15 feet of mixed sand, silt, and clay with gravel man placed fill. Slightly sandy to sandy silt with lenses and layers of gravel was encountered at depths from 15 to 50 feet. At a depth of 50 feet, very dense rounded gravel and cobbles (river gravel alluvium) was encountered. Laboratory testing performed on samples obtained from the borings included natural moisture content and percent finer than sand size gradation analyses. Results of swell -consolidation testing performed on a relatively undisturbed drive sample of the natural sandy silt soils, presented on Figure 3, indicates low to moderate compressibility under light loading and a low collapse potential (settlement under load) when wetted. The laboratory testing is summarized in Table 1. No free water was encountered in the boring at the time of drilling and the subsoils were slightly moist to moist. ENGINEERING ANALYSIS The upper 15 feet of soils encountered in the boring consist of fill placed mainly in 2006 as part of the subdivision development. The field penetration tests and laboratory tests performed during the study, and review of the field density tests performed during the fill construction indicate that the structural fill was placed and compacted to the project specified 95% standard H-PtKUMAR Project No. 17-7-866 -4 - Proctor density. Debris fan soils which tend to collapse (settle under constant load) when wetted were encountered below the fill. The amount of settlement will depend on the thickness of the compressible soils and their wetted depth. The settlement potential and risk of excessive building distress can be reduced by compaction of the soils to a certain depth below the foundation bearing level (as has already been done) and by heavily reinforcing the foundation to resist differential settlements. The compaction should also extend beyond to below driveway and utility areas. The compacted soils can consist of the existing structural fill used to elevate the project site. Foundation levels deeper than 5 feet below the existing ground surface on this site are not recommended. Relatively deep structural fills will also have some potential for long term settlement. Proper grading, drainage, and compaction as presented below in the Site Grading and Surface Drainage sections will help reduce the settlement risks. A heavily reinforced structural slab or post -tensioned slab foundation designed for significant differential settlements is recommended for the building support. As an alternative, a deep foundation that extends down into the underlying dense, river gravel alluvium and structural floor slabs could also be used to reduce the settlement risk. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory boring and the nature of the proposed construction, we recommend the building be founded with a heavily reinforced structural slab or post -tensioned slab foundation bearing on at least 15 feet of compacted structural fill in the Villas South parcel. If a deep foundation system is considered for building support, we should be contacted for additional recommendations. The design and construction criteria presented below should be observed for a structural or post - tensioned slab foundation system. 1) A structural slab or post -tensioned slab placed on at least 15 feet of compacted structural fill should be designed for an allowable bearing pressure of 1,500 psf. Post -tensioned slabs placed on structural fill should be designed for a wetted distance of 10 feet but at least half of the slab width, whichever is more. Settlement of the foundation is estimated to be about 1 to 11/ inches based on the H-PtKUMAR Project No. 17-7-866 5_ long-term compressibility of the fill. Additional settlement between about 2 to 3 inches is estimated if deep wetting of the debris fan soils were to occur. Settlement from the deep wetting would tend to be uniform across the building/development area and the settlement potential of the fill section should control the design. 2) The thickened sections of the slab for support of concentrated loads should have a minimum width of 20 inches. 3) The perimeter turn -down section of the slab 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. If a frost protected foundation is used. The perimeter turn -down section should have at least 18 inches of soil cover. 4) The foundation should be constructed in a "box -like" configuration rather than with irregular extensions which can settle differentially to the main building area. The foundation walls, where provided, should be heavily reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 14 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. 5) The root zone and any loose or disturbed soils should he removed. Structural fill placed below the slab bearing level should be compacted to 98% of the maximum standard Proctor density within 2 percentage points of optimum moisture content. 6) A representative of the geotechnical engineer should evaluate the compaction of the fill materials and observe all footing excavations prior to concrete placement for 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 soils. Cantilevered retaining structures which are separate from the building and H-PtKUMAR Proiect No. 17-7-866 -6 - 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 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. Site walls with a maximum back slope of 2 horizontal to 1 vertical should be designed for an active earth pressure of at least 60 pcf equivalent fluid unit weight. 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. 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 0.35. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 300 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. H-P%KUMAR Project No. 17-7-866 _7_ NONSTRUCTURAL FLOOR SLABS Compacted structural fill can be used to support lightly loaded slabs -on -grade separate from the building foundation. The fill soils can be compressible when wetted and result in some post - construction settlement. To reduce the effects of some differential movement, nonstructural floor slabs should be separated from buildings to allow for 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 relatively well graded sand and gravel, such as road base, should be placed beneath 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 12% 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 of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched condition. We recommend below -grade construction, such as grade change site retaining walls, be protected from wetting and hydrostatic pressure buildup by an underdrain system. An underdrain should not be provided around structural building foundation slabs and separate slabs -on -grade Where installed, 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. H-P-KUMAR Project No. 17-7-866 8 SITE GRADING Extensive grading was performed as part of the existing Villas South development. Additional placement and compaction of the debris fan soils could be needed to elevate the site to design grades and reduce the risk of excessive differential settlements and building distress. In addition. The water and sewer pipe joints should be mechanically restrained to reduce the risk of joint separation in the event of excessive differential settlement. Additional structural fill placed below foundation bearing level should be compacted to at least 98% of the maximum standard Proctor density within 2 percentage points of optimum moisture content. Prior to fill placement, the subgrade should be carefully prepared by removing any vegetation and organic soils and compacting to at least 95% of the maximum standard Proctor density at near optimum moisture content. The fill should be benched into slopes that exceed 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. This office should review site grading plans for the project prior to construction. SURFACE DRAINAGE Precautions to prevent wetting of the bearing soils, such as proper backfill construction, positive backfill slopes, restriction landscape irrigation, and use of roof gutters need to be taken to help limit settlement and building distress. 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 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 5 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 H-P%KUMAR Project No. 17-7-866 -9 - capped with about 2 feet of the on-site soils to reduce surface water infiltration. Surface swales in landscape areas should have a minimum grade of 4%. 4) Roof gutters should be provided with downspouts that discharge at least 5 feet beyond the foundation and preferably into subsurface solid drain pipe. 5) Landscaping which requires regular heavy irrigation, such as sod, should be located at least 10 feet from foundation walls. Consideration should be given to use of xeriscape to reduce the potential for wetting of soils below the building caused by irrigation. 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 boring drilled at the location 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 boring 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 H-P*KUMAR Protect No 17-7-RRf - 10 - of excavations and foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer. Respectfully Submitted, H -P= KUMAR Robert L. Duran, E. I. Reviewed by: a Steven L. Pawlak, RLD/kac H-P*KUMAR Project No. 17-7-866 3 BORING 1 LOT 251 40473 SF. 0.0931 AC. A -pjA S n SLAT L. LSA' ie. SSIbC{PE C Lir C0‘IN t s,� _- 4 alp Are 15 O 15 30 APPROXIMATE SCALE -FEET Lor LACE MACAO LOT 254 42893 S.F. 0.099} AC. 17-7-866 H-p--KUMAR LOCATION OF EXPLORATORY BORING ] Fig. 1 DEPTH -FEET 1'^ 0 — 5 — 10 — 15 20 25 — 30 — 35 40 --- 45 ---- 50 — 55 — - 60 BORING 1 EL. 5995' 50/5 79/12 05=7.6 00=113 - 200=B6 30/12 21/12 WC=3.3 05=130 - 200=15 28/12 WC=5.0 00=111 46/12 25/12 WC=5.2 05=111 - 200=66 57/12 50/3 LEGEND I�.,. TOPSOIL; CLAY AND SILT, SANDY, FIRM, SLIGHTLY M015T, BROWN, SLIC111LY O8509115. FILL; 511.T AND SAND, CLAYEY, SCATTERED GRAVEL AND SANDSTONE FRAGMENTS, HARD, SUGHTLY M0W, TAH. SILT WITH GRAVEL LENSES (GM -ML}; SLIGHTLY SA40Y TO SANDY, VERY STIFF TO HARD/MEDIUM 65009 TO DENSE, SLIGHTLY MOIST, DROWN, SCATTERED COBBLES. ROUNDED GRAVEL AND COBBLES (GP -GM); PROBABLE BOULDERS, , SILTY, SANDY, VERY DENSE, BROWN. 111 DRIVE SAMPLE, 2-1659 I.O. CALIFORNIA LINER SAMPLE. IDRIVE SAMPLE, 1 3/8 -INCH I.D. SPLIT SPOON STANDARD PENETRAIIQN TEST, 50/5 DRIVE SAMPLE BLOW COUNT, 119095 TFS THAT 50 BLOWS OF A 140 -POUND 1169016 FALUHO 30 INCHES WERE REQUIRED TO DRIVE T115 SAMPLER 5 INCHES. NOTES I. THE EXPLORATORY 008190 WAS DRILLED ON DECEMBER 27, 2017 WITH A 4-I9511 DIAOElER CONTINUOUS FLIGHT POWER AUGER. 2. THE LOCATION OF THE EXPLORATORY 80RING WAS MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PUN PROVROEO. 3. THE ELEVATION of THE EXPLORATORY BORING WAS 000416ED 8Y INTERPOLATION BETWEEN CONTOURS ON THE SUBDIVISION PLAN. 4. THE 53950RATORY BORING LOCATION AND ELEVATION SHOULD BE CONSIDERED ACCURATE ONLY 70 THE DEGREE IMPLIED BY THE 151900 65E0. 5. THE UNES BETWEEN MATERIALS 51109N 011 ME EXPLORATORY BORING LOG REPRESENT TH5 APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRAH5161005 MAY BE ORAOUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT THE TIME OF DRILUNG. 7. LABORATORY TEST RESULTS: WC = WATER CQHTEHT (x) OM 0 2216); 0D = DRY DENSITY (PCA (ASTM 0 2216); -200 = PERCENTAGE PASSING 60. 200 SIEVE (ASTM 0 1140). LOG OF EXPLORATORY BORING CO CO 1 sr E. gra SAMPLE OF: Sandy Silt with Gravel FROM: Boring 1 ® 20' WC = 5.0 %, DD = 111 pcf Thier t,I ri+;li.Ip$.e y So 11w ♦omprH tested The lest ep mood O NO not he wprodeced, 4lxe0e in ..then 4 the wr;ti.e approval of K vmq' PRI RafoClate,, Me Swell CeMG ddlien OrImp prfunnimi in OrCar4ance with ASN [I -4,1 1.0 APPLIED PRESSURE - KSF 10 ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING r 100 7-7-866 H -P- KUMAR SWELL—CONSOLIDATION TEST RESULTS Fig. 3 H-PKUMAR TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 17-7-866 SAMPLE LOCATION NATURAL NATURAL GRADATION ATTERBERG LIMITS PERCENT UNCONFINED BORING DEPTH MOISTURE DRY GRAVEL SAND PASSING I LIQUID ! PLASTIC COMPRESSIVE CONTENT DENSITY (%) (%) NO. 200 LIMIT I INDEX STRENGTH j , (f) 4`v} C ale oho PS SIEVE 1 5 7.6 113 88 15 3.3 130 15 I 20 5.0 111 30 5.2 111 66 SOIL TYPE Fine Sand and Silt (Fill) Sandy Silt and Gravel Sandy Silt with Gravel Sandy Silt � � I