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HomeMy WebLinkAboutSoils Report 03.12.20191(4-A [ii4ii ar &:bsJ33aRitc.3, Inc. Geotechnical and Materials Engineers and Environmental Scientists 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com An Employee Owned Company www.kumarusa.corn Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit Count Colorado RECEIVED JUS. 1 5 :ul:f GARFIELD COUNTY COMMUNITY DEVELOPMENT SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 75, FILING 2, PINYON MESA PINYON MESA DRIVE GARFIELD COUNTY, COLORADO PROJECT NO. 19-7-141 MARCH 12, 2019 PREPARED FOR: THOMAS LaCOSSE HONEYWELL UOP 25 EAST ALGONQUIN ROAD DES PLAINS, ILLINOIS 60017 (Th o mas.1 acoss a qr� h o n ev w ell.c omj TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS - 1 - SUBSIDENCE POTENTIAL - 2 - FIELD EXPLORATION - 2 - SUBSURFACE CONDITIONS - 3 - FOUNDATION BEARING CONDITIONS - 3 - DESIGN RECOMMENDATIONS - 3 - FOUNDATIONS - 3 - FOUNDATION AND RETAINING WALLS - 5 - FLOOR SLABS - G - UNDERDRAIN SYSTEM - 6 - SURFACE DRAINAGE - 7 - LIMITATIONS - 7 - FIGURE 1 - LOCATION OF EXPLORATORY BORING FIGURE 2 - LOG OF EXPLORATORY BORING FIGURES 3 & 4 - SWELL -CONSOLIDATION TEST RESULTS TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS Kumar & Associates, Inc. Project No. 19.7-141 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located at Lot 75, Filing 2, Pinyon Mesa, Pinyon Mesa Drive, 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 proposal for geotechnical engineering services to Thomas LaCosse dated February 12, 2019. 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. PROPOSED CONSTRUCTION The proposed residence will be a two-story structure with crawlspace or basement. Ground floor will be structural over crawlspace or slab -on -grade for basement. 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. 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 was vacant and vegetated by sagebrush, grass and weeds. The lot was covered with about one foot of snow at the time of field exploration. A storm sewer easement runs along the south property line. The ground surface is mostly natural with minor grading near the road and along the storm sewer. The terrain is hilly and moderately to strongly sloping down to the southwest, becoming steeper towards the west. Kumar & Associates, Inc. Project No. 19-7.141 -2 - SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian Age Eagle Valley Evaporite underlies the Pinyon Mesa Development. These rocks are a sequence of gypsiferious shale, fine-grained sandstone/siltstone and limestone with some massive beds of gypsum. There is a possibility that massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the property. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. During previous work in the area, sinkholes have been observed scattered throughout the lower Roaring Fork River valley. No evidence of subsidence or sinkholes was observed on the property or encountered in the subsurface materials, however, the exploratory boring was 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 at the site throughout the service life of the proposed structure, in our opinion is low, however the owner should be 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. FIELD EXPLORATION The field exploration for the project was conducted on February 20, 2019. An exploratory boring was drilled at the location shown on Figure 1 to evaluate the subsurface conditions. The boring was advanced with 4 inch diameter continuous flight augers powered by a truck- mounted CME -45B drill rig. The boring was logged by a representative of Kumar & Associates, Inc. A planned second boring was not possible at the time of field exploration due to the limited access to our drill rig due to the snow and sloping terrain. Samples of the subsoils were taken with a 2 inch I.D. spoon sampler. The sampler was driven into the subsoils at various depths with blows from a 140 pound hammer falling 30 inches. This test is similar to the standard penetration test described by ASTM Method D-1586. The penetration resistance values are an indication of the relative density or consistency of the subsoils. Depths at which the samples were taken and the penetration resistance values are shown on the Log of Exploratory Boring, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. Kumar & Associates, Inc. Project No. 19-7-141 3 SUBSURFACE CONDITIONS A graphic log of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils consist of sandy silt and clay with scattered gravel, becoming sandier with depth down to the boring depth of 50 feet. Laboratory testing performed on samples obtained from the boring included natural moisture content and density and finer than sand gradation analyses. Results of swell -consolidation testing performed on relatively undisturbed drive samples, presented on Figures 3 and 4, indicate low compressibility under light loading at natural moisture content and low to The laboratory testing is summarized in Table 1. moderate expansion potential when wetted. No free water was encountered in the boring at the time of drilling or and the subsoils were slightly moist. FOUNDATION BEARING CONDITIONS The natural sandy silt and clay soils possess low bearing capacity and variable swell or settlement potential mainly when wetted. A shallow foundation placed on these soils will have a risk of movement if the soils become wetted and care should be taken in the surface and subsurface drainage around the house to prevent the soils from becoming wet. It will be critical to the long-term performance of the structure that the recommendations for surface grading and drainage contained in this report be followed. The amount of movement, if the bearing soils become wet, will mainly be related to the depth and extent of subsurface wetting but may result in settlements of around 1 to 2 inches which could cause building distress. Mitigation methods such as removing and replacing the bearing soils as compacted structural fill should be used to support the proposed house with a lower nsk of movement. 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 spread footings bearing on a minimum of 6 feet of compacted structural fill below garage and crawlspace Kumar & Associates, Inc. Project No. 19.7-141 _4 footings and 3 feet of compacted structural fill below basement level footings movement, mainly if the bearing soils become wet. with a risk of The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the compacted structural fill should be designed for an allowable bearing pressure of 1,500 psf. Based on experience, we expect initial settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. Additional differential movements of about 1/2 to 1 inch could occur if the bearing soils are wetted. 2) The footings should have a minimum width of 20 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 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 topsoil, sub -excavation depth and any loose or disturbed soils should be removed below the foundation area. The exposed soils in footing areas after sub -excavation should then be moistened and compacted. Structural fill should consist of low permeable soil (such as the on-site sandy silt and clay soils) compacted to at least 98% of standard Proctor density within 2% of optimum moisture content. The structural fill should extend laterally beyond the footing edges equal to at least 'h the fill depth below the footing. 6) A representative of the geotechnical engineer should evaluate the fill placement for compaction and observe all footing excavations prior to concrete placement to evaluate bearing conditions. Kumar & Associates, Inc. Project No. 19.7-141 -5 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 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 45 pcf for backfill consisting of the on-site fine-grained soils. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The pressures recommended above assume drained conditions behind the walls and a horizontal backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain should be provided to prevent hydrostatic pressure buildup behind walls. Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum standard Proctor density at a moisture content near optimum. Backfill in pavement and walkway areas should be compacted to at least 95% of the maximum standard Proctor density. Care should be taken not to overcompact the backfill or use large equipment near the wall, since this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall backfill should be expected, even if the material is placed correctly, and could result in distress to facilities constructed on the backfill. Backfill should not contain organics, debris or rock larger than about 6 inches. 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 325 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 Kumar & Associates, Inc. Project No. 19.7-141 -6 - 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 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 movement risk similar to the foundation if the underlying soils are wetted. To reduce the effects of some differential movement, floor slabs should be separated from all bearing walls and columns with expansion joints which allow unrestrained vertical movement. Floor slab control joints should be used to reduce damage due to shrinkage cracking. The requirements for joint spacing and slab reinforcement should be established by the designer based on experience and the intended slab use. A minimum 4 inch layer of free - draining gravel should be placed beneath basement level slabs to facilitate drainage. This material should consist of minus 2 inch aggregate with at least 50% retained on the No. 4 sieve and less than 2% passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95% of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on-site 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 clay soils are present 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 and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. An underdrain should not be provided around slab -at -grade garage and shallow crawlspace areas to help limit potential wetting of bearing soils from shallow water sources. The drains should consist of drainpipe placed in the bottom of the basement 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 or sump and pump. Free -draining granular Kumar & Associates, Inc. Project No. 19-7-141 7 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 11/4 feet deep. An impervious membrane such as 30 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. SURFACE DRAINAGE Proper surface grading and drainage will be critical to keeping the bearing soils dry and limiting building movement. 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 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. 5) Landscaping which requires regular heavy irrigation 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 Kumar & Associates, Inc. Project No. 19-7.141 -8 - 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 of excavations and foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer. Respectfully Submitted, Kumar & Associates, Inc. Shane M. Mello, Staff Engineer Reviewed by: Daniel E. Hardin, P.E SMM/kac cc: Scott Dillard (scottdilI�ci aiI.com) Kumar & Associates, Inc. Project No. 19.7-141 ila-cd CS, 242,1N-111,0tf N -111,0m APPet.CAPO,INn-Y-.A, 5.61.1 VAy. wlcku-101KNI1111,y1e.[ CO sa}eloossy'9 JeWn) ONId08 AdOlVe101dX3 JO N011V00TI 133d-31 VDS 31'VWIX021ddY Cn Cn C7 1 f L II OA/. grel Wltr - 6.y MO;' :- - 0 — 5 –- 10 15 LJ La _ - — 20 a— w --- 25 — 30 35 - 40 BORING 1 EL. 6193' LEGEND l CLAY AND SILT (CL–ML); SANDY TO VERY SANDY WITH DEPTH, SCATTERED GRAVEL WITH DEPTH, STIFF TO VERY STIFF, SLIGHTLY MOIST, LIGHT BROWN. DRIVE SAMPLE, 2–INCH I.D. CALIFORNIA LINER SAMPLE. 9/ 12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 9 BLOWS OF A 9/12 140–POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. 14/12 WC=6.3 DD=105 27/12 WC=8.6 DD=111 29/12. WC=8.7 DD=109 – 200=91 35/12 WC=3.4 DD=115 52/12 46/12 WC=3.9 DD=132 – 200=55 NOTES 1. THE EXPLORATORY BORING WAS DRILLED ON FEBRUARY 20, 2019 WITH A 4–INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2. THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATION OF THE EXPLORATORY BORING WAS OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED. 4. THE EXPLORATORY BORING LOCATION AND ELEVATION SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED, 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOG REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING 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). 1 55/12 J WC=2.5 DD=124 –200=34 40- 45 50 DEPTH -FEET 19-7-141 Kumar & Associates LOG OF EXPLORATORY BORING Fig. 2 CONSOLIDATION SAMPLE OF: Sandy Silt and Clay FROM: Boring 1 © 5' WC = 6.3 %, DD = 105 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING Throe seal reeune Opp2 only to U. . omptea S.W. Oho I.aUnp import . hon not b reprodueed, e.eepi .n lull, without the written epprmrel of Kyrner end /a.oclotea, Inc Swell t ws dation IwoI�np periowo.ba rn dens. with ASYA4 D—*S4 1 0 APPLIED PRESSURE - KSF 10 100 19-7-141 Kumar & Associates SWELL—CONSOLIDATION TEST RESULTS Fig. 3 3 z f of 2 CONSOLIDATION CONSOLIDATION - SWELL 0 —1 — 2 — 3 1 0 — 1 —2 — 3 10 APPLIED PRESSURE — KSF 10 100 II SAMPLE OF: Sandy Silt and Clay FROM: Boring 1 ® 10' WC = 8.6 %, DD = 111 pcf EXPANSION PRESSURE UNDER UPON CONSTANT WETTING 10 APPLIED PRESSURE — KSF 10 100 10 APPLIED PRESSURE — KSF ID 100 19-7-141 Kumar & Associates SWELL—CONSOLIDATION TEST RESULTS Fig. 4 SAMPLE OF: Sandy Silt and Clay FROM: Boring 1 © 20' WC = 3.4 %, DD = 115 pcf EXPANSION UNDER CONSTANT -411thou PRESSURE UPON —�^— WETTING I..4 ...wit. epyy ' to 11,. pnlp].. (tiled. th. Linn* report .M�1 nM . r.prod+.CM. �.e.pl in fug. Dof Meo Iga,w.W.d1 ckrRlen I A �I Cun1rn.sshSgThqVe.In 10 APPLIED PRESSURE — KSF ID 100 19-7-141 Kumar & Associates SWELL—CONSOLIDATION TEST RESULTS Fig. 4 11 -F -A nuuwr a lf.1 uUrdleS, IUG. Geotechnical and Materials Engineers and Environmental Scientists kumarusa.com TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Prosect No.19-7- SAMPLE LOCATION NATURAL MOISTURE CONTENT re) NATURAL DRY DENSITY (pcn 1 GRADATION 1 PERCENT PASSING NO. 200 SIEVE 1 ATTERBERG LIMITS UNCONFINED COMPRESSIVE STRENGTH (Psfl SOIL TYPE BORING DEPTH (ft) GRAVEL (%) SAND (%) LIQUID LIMB (%) PLASTIC INDEX CYO 1 T 5 6.3 105 Sandy Silt and Clay 10 8.6 111 I Sandy Silt and Clay 15 20 8.7 3.4 109 115 ! I 91 Slightly Sandy Silt and Clay Sandy Silt and Clay 30 3.9 132 55 Sandy Silt and Clay with Gravel 40 2.5 124 34 Clayey Silty Sand with Gravel