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HomeMy WebLinkAboutSoils Report 06.24.2019ICA Komar & 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 Jmai & Assodates /o SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 37, SPRING RIDGE RESERVE HIDDEN VALLEY DRIVE GARFIELD COUNTY, COLORADO PROJECT NO. 19-7-349 JUNE 24, 2019 PREPARED FOR: MATT JURMU 2906 HAGER LANE GLENWOOD SPRINGS, COLORADO 81601 matt( i anckilaconstruction.com TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS - 1 - GEOLOGY -2- FIELD EXPLORATION - 2 - SUBSURFACE CONDITIONS - 2 - FOUNDATION BEARING CONDITIONS - 3 - DESIGN RECOMMENDATIONS - 3 - FOUNDATIONS - 3 - FOUNDATION AND RETAINING WALLS - 4 - FLOOR SLABS - 5 - UNDERDRAIN SYSTEM - 6 - SITE GRADING - 6 - SURFACE DRAINAGE - 7 - LIMITATIONS - 7 - FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4 - SWELL -CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS Kumar & Associates, Inc. Project No. 19-7-349 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 37, Spring Ridge Reserve, Hidden Valley Drive, Garfield County, Colorado. The project site is shown on Figure 1. The purpose of the study was to develop recommendations for foundation design. The study was conducted in accordance with our agreement for geotechnical engineering services to Matt Jurmu, dated May 31, 2019. A field exploration program consisting of exploratory borings was conducted to obtain information on the subsurface conditions. Samples of the subsoils and bedrock 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, recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION At the time of our study, design plans for the residence were preliminary. The building is proposed in the area shown on Figure 1. We assume excavation for the building will have a maximum cut depth of one level, about 10 feet below the existing ground surface. For the purpose of our analysis, foundation loadings for the structure were assumed to be relatively light and typical of the proposed type of construction. If building loadings, location or grading plans are significantly different from those described above, we should be notified to re-evaluate the recommendations contained in this report. SITE CONDITIONS The property was vacant at the time of our field exploration. The site is vegetated with grass, weeds, and sage brush. The ground surface in the general building area slopes moderately down Kumar & Associates, Inc. Project No. 19-7-349 -2 to the northeast at an approximate 10 percent grade. Maroon Formation sandstone is exposed on the hillside near the lot. GEOLOGY According to the Geologic Map of the Cattle Creek Quadrangle, Garfield County, Colorado, by Krikham, Steufert, Hemborg, and Stelling, dated 2014, the site is underlain by alluvium and colluvium deposits of the Holocene age overlying Maroon Formation. FIELD EXPLORATION The field exploration for the project was conducted on June 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 auger 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 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 and hardness of the bedrock. 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 profiles encountered at the site are shown on Figure 2. Below about 1/2 foot of organic topsoil, the subsoils consist of about 15 feet of stiff to very stiff silty, sandy clay with scattered gravel, underlain by 61/2 feet of dense, silty sand and gravel with cobbles at Boring 1, underlain by weathered sandstone/siltstone. The soils encountered in the borings are similar to the soils encountered at other nearby lots. Laboratory testing performed on samples obtained during the field exploration included natural moisture content and density and percent fines (percent passing the No. 200 sieve). Swell - Kumar & Associates, Inc. Project No. 19-7-349 3 consolidation testing was performed on relatively undisturbed drive samples of the clay subsoils. The swell -consolidation test results, presented on Figure 4, indicate low compressibility under relatively light surcharge loading and minor expansion or compressibility potential when wetted under a constant light surcharge. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at time of drilling and the subsoils were slightly moist. FOUNDATION BEARING CONDITIONS The subsoils encountered at the site possess minor expansion or compressibility potential when wetted. Surface runoff, landscape irrigation, and utility leakage are possible sources of water which could cause wetting. Footing foundations can be used with the accepted risk of movement. Deep foundations, such as drilled piers or micropiles that extend down to dense gravel or bedrock, can be used if the risk of movement cannot be tolerated. We should be contacted if deep foundation recommendations are desired. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we recommend the residence be founded with spread footings placed on undisturbed natural soils with a risk of movement mainly if the bearing soils are wetted. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural soils can 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 up to about 1 inch. Additional differential movement could be on the order of 1 inch for a limited wetted depth of around 10 feet below footings. 2) The footings should have a minimum width of 16 inches for continuous footings and 24 inches for isolated pads. 3) Continuous foundation walls should be reinforced top and bottom to span local anomalies and limit the risk of differential movement. One method of analysis is Kumar & Associates, Inc. Project No. 19.7.349 4 to design the foundation wall to span an unsupported length of at least 12 feet. Foundation walls acting as retaining structures should also be designed to resist a lateral earth pressure as discussed in the "Foundation and Retaining Walls" section of this report. 4) 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 the exterior grade is typically used in this area. 5) Prior to the footing construction, the topsoil and loose or disturbed soils should be removed and the footing bearing level extended down to competent bearing soils. 6) A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FOUNDATION AND RETAINING WALLS Foundation walls and retaining structures which are laterally supported and can be expected to undergo only a slight amount of deflection should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consisting of the on-site soils and at least 45 pcf for backfill consisting of imported granular materials. 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 and at least 35 pcf for backfill consisting of imported granular materials. 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 areas Kumar & Associates, Inc. Project No. 19.7-349 5 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 a nonexpansive material compacted to at least 95% of the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS The upper natural soils possess variable expansion or compressibility potential and there could be slab movement if the subgrade soils were to become wet. Slab -on -grade construction may be used provided precautions are taken to limit potential movement and the risk of distress to the building is accepted by the owner. A positive way to reduce the risk of slab movement, which is commonly used in the area, is to construct structurally supported floors over crawlspace. To reduce the effects of some differential movement, nonstructural 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. Slab reinforcement and control joints 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 immediately beneath basement level slabs -on -grade. This material should consist of minus 2 inch aggregate with less than 50% passing the No. 4 sieve and less than 2% passing the No. 200 sieve. The free -draining gravel will aid in drainage below the slabs and should be connected to the perimeter underdrain system. Kumar & Associates, Inc. Project No. 19-7-349 -6 Required fill beneath slabs can consist of the on-site soils or a suitable imported granular material, excluding topsoil and oversized rocks. The fill should be spread in thin horizontal lifts, adjusted to at or above optimum moisture content, and compacted to at least 95% of the maximum standard Proctor density. All vegetation, topsoil and loose or disturbed soil should be removed prior to fill placement. UNDERDRAIN SYSTEM Although groundwater 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. Therefore, we recommend below -grade construction, such as crawlspace and basement areas, be protected from wetting by an underdrain system. The drain should also act to prevent buildup of hydrostatic pressures behind foundation walls. The underdrain system should consist of a drainpipe surrounded by free -draining granular material placed at the bottom of the wall backfill. The drain lines should be placed at each level of excavation and at least 1 foot below lowest adjacent finish grade, and sloped at a minimum 1% grade to a suitable gravity outlet. Free -draining granular material used in the drain system should consist of minus 2 inch aggregate with less than 50% passing the No. 4 sieve and less than 2% passing the No. 200 sieve. The drain gravel should be at least 1'/2 feet deep. An impervious liner such as 20 mil PVC should be placed below the drain gravel in a trough shape and attached to the foundation wall above the void form with mastic to keep drain water from flowing beneath the wall and to other areas of the building. SITE GRADING The risk of construction -induced slope instability at the site appears low provided cut and fill depths are limited. We assume the cut depth for the basement level will not exceed one level, about 10 to 12 feet. 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 Kumar & Associates, Inc. Project No. 19-7-349 7 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 It will be critical to the long term performance of the foundation to keep the bearing soils dry. The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) Excessive wetting 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 areas and to at least 90% of the maximum standard Proctor density in landscape 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. 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. 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 data obtained from the exploratory borings drilled excavated 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 Kumar & Associates, Inc. Project No. 19.7-349 8 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 to be different from those described in this report, we should be notified at once so 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 of 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. Project Manager Reviewed by: Steven L. Pawlak, SJR/kac Kumar & Associates, Inc. Project No. 19.7.349 Rea — Ridden VoRq\Drafting \197 Zoz' 35 et 250• Building • X863\e Envy tPa 9` -,9 • \\ IBM Elevation \ N. 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NN. \ `eoR NG\t \ \ s \ \ \ \ \ \ \\,, .,\ \� \ �\ \I\ \ \ \\ \\y \\\ L • N \ \ \ \ \ \ \ �y \ `\ ., \\\\ \\ \ \ ,\ \ \\\\\\ \ I \ N\\ CS\ \ \ \ \ \see' \ -0•\\— \\\\\\Ital\ \ \\\ \ \` \ \\\ \\\`\\\ \\ 652 \ \ \ \\ \\\\\\ \ \ \ \ \.\'-N \ \ e \\ N ` \\ � e°\ \ ` 515\ ` 7_-- 6523.'1 • \ \ \ \\ \; Envelope \ -\ 0,078- 5.0 U Emmenen 25 0 25 50 APPROXIMATE SCALE—FEET priv e S k5 valley 50.0mei OrlvPer er R lonBB 077 •dden 19-7-349 I Kumar & Associates LOCATION OF EXPLORATORY BORINGS 1 Fig. 1 0 5 10 I -- w w — w 15 20 25 BORING 1 EL. 6516' // //] 14/12 / WC=12.4 / DD=116 // //] 26/12 / WC=6.1 / DD=113 -200=59 64/9 50/2 50/1 BORING 2 EL. 6507' / // // // //] // // 0-1 16/12 11/12 WC=12.5 DD=114 25/12 WC=5.2 DD=120 -200=46 50/12 50/1 0 5 10 15 20 25 30 30 19-7-349 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 s — N ea,r, Vc!!ey\o LEGEND TOPSOIL; CLAYEY, SAND AND SILT, ORGANIC, FIRM, MOIST, DARK BROWN. CLAY (CL); SILTY, SANDY, SCATTERED GRAVEL, STIFF TO VERY STIFF, SLIGHTLY MOIST, REDDISH BROWN. SAND AND GRAVEL (SM—GM); SILTY, COBBLES, DENSE, SLIGHTLY MOIST, REDDISH BROWN. WEATHERED SANDSTONE/SILTSTONE BEDROCK; HARD TO VERY HARD, SLIGHTLY MOIST, RED. MAROON FORMATION. DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE. 11/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 11 BLOWS OF A 140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON JUNE 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); —200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D1140). 19-7-349 Kumar & Associates LEGEND AND NOTES Fig. 3 !ley \Drattb g\197349 49 Subsoil Stu CONSOLIDATION - SWELL CONSOLIDATION - SWELL 1 0 — 1 — 2 —3 1 0 — 1 — 2 —3 10 APPLIED PRESSURE - KSF 10 100 SAMPLE OF: Sandy Silty Clay FROM: Boring 1 ® 5' WC = 12.4 %, DD = 116 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING I 1 ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 10 APPLIED PRESSURE - KSF 10 100 1.0 APPLIED PRESSURE - KSF 10 100 19-7-349 Kumar & Associates SWELL—CONSOLIDATION TEST RESULTS Fig. 4 SAMPLE OF: Sandy Silty Clay FROM: Boring 2 © 5' WC = 12.5 %, DD = 114 pcf 1 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 ASTM D-4546. 1.0 APPLIED PRESSURE - KSF 10 100 19-7-349 Kumar & Associates SWELL—CONSOLIDATION TEST RESULTS Fig. 4 Ca• W E N h das co 4) I CO C at!'c o L � C be U t6 1%07 - Ill Project No. 19-7-349 SOIL TYPE Sandy Silty Clay Very Sandy Silty Clay Sandy Silty Clay Very Silty Clayey Sand II UNCONFINED COMPRESSIVE STRENGTH (psf) ATTERBERG LIMITS PLASTIC INDEX (%) LIQUID LIMIT (%) PERCENT PASSING NO. 200 SIEVE 01 46 GRADATION a co J g e NATURAL DRY DENSITY (pcf) O M 114 120 W J ce Z 1-yz o Z 2 U 7t. vin cin in II SAMPLE LOCATION DEPTH (ft) V) NO BORING N