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Home My WebLink AboutSoils Report 12.31.2019Kumar & Associates, 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.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado si & Assodat, 30 yaarta sa.somiod o� S'clro wwwia 1989-2019 SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 35, FOUR MILE RANCH 225 MAROON DRIVE GARFIELD COUNTY, COLORADO PROJECT NO. 19-7-705 DECEMBER 31, 2019 PREPARED FOR: DON & DEE MOORE 25 BUCKSKIN CIRCLE NEW CASTLE, COLORADO 81647 dtmooreco(a gmail.com 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 6- UNDERDRAIN SYSTEM - 6 - SITE GRADING - 7 - SURFACE DRAINAGE 7 - LIMITATIONS - 8 - FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4 AND 5 - SWELL -CONSOLIDATION TEST RESULTS TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS Kumar & Associates, Inc. Project No. 19-7-705 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 35, Four Mile Ranch, 225 Maroon 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 agreement for geotechnical engineering services to Don & Dee Moore dated November 25, 2019. 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 Building plans for the lot had not been developed at the time of our study. In general, we assume the proposed residence will be a one- to two-story wood frame structure with a walkout basement level and attached garage located in the building envelope shown on Figure 1. Ground floors could be slab -on -grade or structural over crawlspace. Cut depths are assumed to range between about 3 to 10 feet. Foundation loadings for this type of construction are assumed to be relatively light and typical of the proposed type of construction. If building conditions or foundation loadings are significantly different from those described above, we should be notified to re-evaluate the recommendations presented in this report. SITE CONDITIONS The property is currently vacant. The site grading is mostly natural with minor fills in the northern part of the lot due to the water tank construction located north of the site and minor cut Kumar & Associates, Inc. Project No. 19-7-705 2 and fill grading along the water tank access road along the northwest edge of the lot. The lot slopes down to the southwest at a grade of between around 10 to 15 percent. There is about 15 feet of elevation difference across the building envelope. Vegetation consists of native grass, weeds and sage brush. SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Four Mile Ranch subdivision. 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. 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 35 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. FIELD EXPLORATION The field exploration for the project was conducted on December 6, 2019. 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 Kumar & Associates, Inc. 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 Kumar & Associates, Inc. Project No. 19-7.705 3 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 about 1 foot of topsoil overlying 8 to 10 feet of generally very stiff, silty sandy clay. Dense, clayey sandy gravel with cobbles and probable boulders was encountered at depths of 9 and 11 down to the maximum depths drilled of 15 and 121/2 feet in Borings 1 and 2, respectively. Drilling in the coarse granular soils with auger equipment was difficult due to the cobbles and boulders and drilling refusal was encountered in Boring 2 at 121/2 feet. Laboratory testing performed on samples obtained from the borings included natural moisture content and density. Results of swell -consolidation testing performed on relatively undisturbed drive samples of the silty sandy clay, presented on Figures 4 and 5, indicate low to moderate compressibility under conditions of loading and a minor collapse or expansion potential when wetted under a constant 1,000 psf surcharge load. 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. FOUNDATION BEARING CONDITIONS The upper natural clay soils possess a low bearing capacity and a low collapse or expansion potential when wetted. Shallow spread footings placed on the upper fine-grained soils could have a movement potential and could result in building distress especially where foundations transition different bearing soils. Lower risk options include and extending the footings down to the underlying dense granular soils. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we recommend the building be founded with spread footings bearing Kumar & Associates, Inc. Project No. 19-7-705 -4- on the natural soilsaMMIIIIIINIMIIIIIIIMMIbr the underlying natural dense 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 fine-grained soils should be designed for an allowable bearing pressure ofilMlawith a risk of movement and building distress. Footings placed on a minimum of 3 feet of properly placed and r on the natural dense gravel soils should be designed for an allowable bearing pressure allIllMBased on experience, we expect settlement of footings placed on the natural fine-grained soils could be up to about 1 to 2 inches and footings placed on the dense gravel soils or 3 feet of structural fill could be up to about 1 inch. 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 12 feet. Foundation walls acting as retaining structures should also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining Walls" section of this report. 5) The topsoil and any loose or disturbed soils should be removed from the footing bearing level. The exposed soils in footing area should then be moistened and compacted to at least 95% of the standard Proctor. Structural fill (if used) should be compacted to at least 98% of the standard Proctor density near optimum moisture content and extend to at lea beyond footing edges. 6) A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. Kumar & Associates, Inc. Project No. 19-7-705 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 leas...or backfill consisting of the on -site 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 leas "or 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. 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. 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 Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight c-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 Kumar & Associates, Inc. Project No. 19-7-705 6 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 upper fine-grained soils have variable compressibility/expansion when wetted and there is a risk of slab movement and distress if the bearing soils become wetted. Slabs -on -grade can be supported on where needed to reduce the risk of movement such as in living areas of the residence. Structural floors should be used in areas where movement cannot be tolerated. 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 should consist of 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. low-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 Kumar & Associates, Inc. Project No. 19-7-705 7 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 1 %2 feet deep. SITE GRADING 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 and topsoil and compacting to at least 95% of the maximum standard Proctor density. 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 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 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 10 feet from foundation walls. Consideration should be given to the use of xeriscape to limit potential wetting of soils below the foundation caused by irrigation. Kumar & Associates, Inc. Project No. 19-7-705 -8- LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this time. We make no warranty either express or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory borings drilled at the locations indicated on Figure 1, the proposed type of construction and our experience in the area. Our services do not include determining the presence, prevention or possibility of mold or other biological contaminants (MOBC) developing in the future. If the client is concerned about MOBC, then a professional in this special field of practice should be consulted. Our findings include interpolation and extrapolation of the subsurface conditions identified at the exploratory borings and variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountered during construction appear different from those described in this report, we should be notified so that re-evaluation of the recommendations may be made. This report has been prepared for the exclusive use by our client for design purposes. We are not responsible for technical interpretations by others of our information. As the project evolves, we should provide continued consultation and field services during construction to review and monitor the implementation of our recommendations, and to verify that the recommendations have been appropriately interpreted. Significant design 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 J. Robat, P.E. Reviewed by: Steven L. Pawlak, P SJR/kac Kumar & Associates, Inc. • Project No. 19-7-705 20 0 20 40 APPROXIMATE SCALE -FEET 4 19-7-705 Kumar & Associates LOCATION OF EXPLORATORY BORINGS BORING 1 EL. 6197' BORING 2 EL. 6188.5' 1- w w w 0 w J w 6200 6200 6195 6190 6185 6180 6180 //] 36/12 // / 38/12 WC=13.8 DD=112 // moo, 50/3 89/12 // //1 14/12 // 22/12 WC=10.6 / / DD=88 // C.. �o. 62/12 6195 6190 6185 6180 61801 1- w w Z O H w J w 19-7-705 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 LEGEND TOPSOIL, CLAY AND SILT, SANDY, FIRM, MOIST, DARK BROWN, ORGANIC. CLAY (CL); SANDY, SILTY, STIFF TO HARD, SLIGHTLY MOIST, LIGHT BROWN, CALCAREOUS, LOW TO MEDIUM PLASTICITY. GRAVEL (GC); CLAYEY, SANDY, WITH COBBLES AND PROBABLE BOULDERS, DENSE, SLIGHTLY MOIST, BROWN. SUBANGULAR TO ROUNDED ROCK. DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE. DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST. 36/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 36 BLOWS OF A 140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. t PRACTICAL AUGER REFUSAL. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON DECEMBER 6, 2019 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 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 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 D2216); DD = DRY DENSITY (pcf) (ASTM D2216). EE 19-7-705 Kumar & Associates LEGEND AND NOTES Fig. 3 CONSOLIDATION - SWELL 2 0 These test results apply only to the samples tested. The testing report shall not be reproduced, except in full, without the written approval of Kumar and Associates, Inc. Swell Consolidation testing performed in accordance with ASTM D-4546. SAMPLE OF: Sandy Clay FROM: Boring 1 ® 5' WC = 13.8 %, DD = 112 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 1.0 APPLIED PRESSURE — KSF 10 100 19-7-705 Kumar & Associates SWELL -CONSOLIDATION TEST RESULTS Fig. 4 CONSOLIDATION - SWELL 0 —1 — 2 —3 — 4 — 5 — 6 SAMPLE OF: Sandy Clay FROM: Boring 2 ® 5' WC = 10.6 %, DD = 88 pcf ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING These test results apply only to the samples tested. The testing report shall not be reproduced, except In full, without the written approval of Kumar and Associates. Inc. Swell Consolidation testing performed in accordance with ASIM D-4546. 1.0 APPLIED PRESSURE - KSF 10 100 19-7-705 Kumar & Associates SWELL -CONSOLIDATION TEST RESULTS Fig. 5 N 1- J w ce 1- 0) w 0 al g at 0 I— CID Q J LL 0 Q • SOIL TYPE Sandy Clay Sandy Clay II UNCONFINED COMPRESSIVE STRENGTH (psf) ATTERBERG LIMITS PLASTIC INDEX (%) 2 J G o 5 a J PERCENT PASSING NO. 200 SIEVE GRADATION a co J g e cD NATURAL DRY DENSITY (pcf) N 1 88 NATURAL MOISTURE CONTENT (%) 13.8 O ~ II SAMPLE LOCATION DEPTH (ft) BORING —, N