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HomeMy WebLinkAboutSoils Report 03.24.2017H-PKUMAR Geotechnical Engineering 1 Engineering Geology Materials Testing I Environmental 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax: (970) 945-8454 Email: hpkglenwood@kumarusa.com Office Locations: Parker, Glenwood Springs, and Summit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 80, SPRINGRIDGE RESERVE ELK RIDGE DRIVE GARFIELD COUNTY, COLORADO PROJECT NO. 17-7-233 MARCH 24, 2017 PREPARED FOR: JOE KORONKIEWICZ P.O. BOX 45 SILT, COLORADO 81652 (L=elody 03 (AD yahoo. corn) ................................................................ az 2- .;:.. :;:� .................... TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS ... - 2 - FIELD EXPLORATION - 2 - SUBSURFACE CONDITIONS - 2 - DESIGN RECOMMENDATIONS - 3 - FOUNDATIONS - 3 - FOUNDATION AND RETAINING WALLS - 4 - FLOOR SLABS - 5 - UNDERDRAIN SYSTEM - 5 - SURFACE DRAINAGE - 6 - LIMITATIONS - 6 - 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 H -P 3 KUMAR Project No17-7-233 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located at Lot 80, Springridge Reserve, Elk Ridge 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 general accordance with our agreement for geotechnical engineering services to Joe Koronkiewicz dated March 14, 2017. Hepworth-Pawlak Geotechnical previously performed a preliminary geotechnical study for the subdivision and reported their findings February 26, 2001, Job No. 101 126 and updated the study in a report dated June 22, 2004. 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, design recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION The proposed residence will be one and two story wood frame construction with an attached garage. The house will be above a crawlspace. Garage floor will be slab -on -grade. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 6 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. H-PkKUMAR Project Nol7-7-233 -2 - SITE CONDITIONS The residence will be located in the lower southwestern part of the building envelope. Vegetation consists of grass and weeds with scattered stands of scrub oak above the building site. The ground surface slopes steeply down to the west at grades of 14 to 25 percent in the building area. An abandoned irrigation ditch is located below the building area. FIELD EXPLORATION The field exploration for the project was conducted on March 15, 2017. Three exploratory borings were drilled at the Iocations shown on Figure 1 to evaluate the subsurface conditions. The borings were advanced with 4 inch diameter continuous flight augers powered by a track - mounted CME 45 drill rig. The borings were logged by a representative of H-P/Kumar. Samples of the subsoils were taken with a 2 inch I.D. spoon sampler. The sampler was driven into the subsurface materials 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 conditions encountered at the site are shown on Figure 2. The subsoils, below about six inches of topsoil, consist of about 2 feet of weathered sandstone underlain by very hard sandstone bedrock. Drilling in the sandstone bedrock with auger equipment was difficult due to its hardness and cemented conditions with depth and drilling refusal was encountered in the formation. Laboratory testing performed on samples obtained from the borings included natural moisture content and density and percent finer than sand size gradation analyses. Results of swell - consolidation testing performed on a relatively undisturbed drive sample of weathered sandstone, H-PtKUMAR Project No17-7-233 -3 - presented on Figure 4, indicate low to moderate compressibility under conditions of loading and wetting. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at the time of drilling and the subsoils and bedrock were moist to slightly moist with depth. 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 on the natural bedrock materials. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed weathered sandstone or sandstone bedrock should be designed for an allowable bearing pressure of 2,000 psf. Footings placed entirely on hard bedrock can be designed for an allowable bearing pressure of 4,000 psf. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be Less than 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 10 feet. Foundation walls acting as retaining structures should also be designed to resist lateral earth pressure as described below in the "Foundation and Retaining Walls" section. H -Pt KUMAR Project No17-7-233 -4- 5) All topsoil and any loose or disturbed soils and bedrock should be removed and the footing bearing level extended down to the undisturbed bedrock materials. The exposed soils in footing area should then be moistened and compacted as needed. 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 50 pcf for backfill consisting of the on-site soils and well broken rock. 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 40 pcf for backfill consisting of the on-site soils and well broken rock. 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 near optimum moisture content. Backfill placed in pavement and walkway areas should be compacted to at least 95% of the maximum standard Proctor density. Care should be taken not to overcompact the backfill or use large equipment near the wall, since this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall backfill should be expected, even if the material is placed correctly, and could result in distress to facilities constructed on the backfill. H -P KUMAR Project No17-7-233 -5 - 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 0.40. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 350 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. FLOOR SLABS The natural on-site soils and bedrock, exclusive of topsoil, are suitable to support lightly loaded slab -on -grade construction. 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 and well broken rock 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 bedrock is shallow 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, H -N KUMAR Project No17-7.233 -6- crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. The drains should consist of drainpipe placed in the bottom of the wall backfill surrounded above the invert level with free -draining granular material. The drain should be placed at each level of excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum 1% to a suitable gravity outlet. Free -draining granular material used in the underdrain system should contain less than 2% passing the No. 200 sieve, less than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least 11/2 feet deep. 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 finer graded soils to reduce surface water infiltration. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy irrigation should be located at least 5 feet from foundation walls. LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this time. We make no warranty either express or implied. H-PvKUMAR Project No17-7-233 -7 - 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, H-PKU AR Louis E. Eller Reviewed by: Steven L. Pawlak, P.E LEE/kac H-PkKUMAR Project No17-7-233 5ONIdO8 AaO1VIO1dX3 30 NOI1YDO1 —n 1334-31Y3S 31YWIX0addY Lo LOT 80 � N 0 f / se 11.. z 1- lal z 0 a w J LJ BORING 1 EL. 6367' BORING ; EL. 6369 BORING 3 EL. 6365' --- 6370 6370 PROPOSED FLOOR LEVEL EL=6367.75' — 6365 — 6360 18/6,10/0 we=10.1 DD=116 -200=42 26/12 VyC=6.4 DD=122 25/6,15/0 50/2 6365 — 6360 — — 6355 6355- 17-7-233 H-PvKUMAR LOGS OF EXPLORATORY BORINGS w W W z 0 4 W lag Fig. 2 LEGEND TOPSOIL; ORGANIC SANDY SILT AND CLAY, GRAVELLY, FIRM, MOIST, DARK REDDISH BROWN. 7/ WEATHERED SANDSTONE; SILTY, HARD, MOIST, RED, FRACTURED AND BROKEN. SANDSTONE BEDROCK; VERY HARD, SLIGHTLY MOIST, RED, MAROON FORMATION. 11 RELATIVELY UNDISTURBED DRIVE SAMPLE; 2—INCH I.O. CALIFORNIA LINER SAMPLE. 26/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 26 BLOWS OF A 140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE CALIFORNIA SAMPLER 12 INCHES. PRACTICAL AUGER REFUSAL. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON MARCH 15, 2017 WITH A 4—INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2. THE LOCATIONS or 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 D 2216); OD = DRY DENSITY (pcf) (ASTM D 2216); —200= PERCENTAGE PASSING NO. 200 S'EVE (ASTM D 1140), 17-7-233 H - P -KU MAR LEGEND AND NOTES Fig. 3 .. 0 CONSOLIDATION - SWELL —1 — 2 —3 — 4 1n•N tell I.fvlf gpyl WJ Ln Int �a�yn l� l4d P. Inlnp open W it ,at b nNbdrJti. o.Hp1 in !.1t. r;lhnrt S'l Mllin op7ry.01. I, Mans. 0.4 Apw6atn. Inc 7.01 tARlddltan 11.1'..qq PMlurnM W C....6, 1 .:11. '$7U Q-4540. 17-7-233 SAMPLE OF; Weathered Sandstone FROM: Boring 2 ® 1' WC = 6.4 %, DD = 122 pct -- EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 1.0 APPLIED PRESSURE - NSF 10 100 H-P11KUMAR SWELL -CONSOLIDATION TEST RESULT Fig. 4 H-PKUMAR TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 17-7-233 SAMPLE LOCATION BORING DEPTH 1 (ft) 2 NATURAL MOISTURE CONTENT (%} NATURAL DRY DENSITY GRADATION GRAVEL 1%1 SAND (%I PERCENT PASSING NO. 200 SIEVE ATTERBERG LIMITS UQUID LIMIT (%) PLASTIC INDEX (96) UNCONFINED COMPRESSIVE STRENGTH (PSF) SOIL OR BEDROCK TYPE 10.1 116 6.4 122 42 MEM a Weathered Sandstone Weathered Sandstone