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Home My WebLink AboutSubsoil Study for Foundation Design 03.15.16. ". , ~· ~ech HEPWORTH-PAWLAK GEOTECHNICAL SUBSOIL STUDY Hepworth-Pm\ lak Gc(l(cchnical, Inc. 5020 Oiunr~· RnaJ 154 Glcnwo,.,J Spring~. Color.ido 81601 Phone; 9i0-945-7938 Fax: 970-9.JS-8454 email: hpgco@hpgcotcc..h.wm FOR FOUNDATION DESIGN PROPOSED BARN 404 CORYELL ROAD GARFIELD COUNTY, COLORADO JOB NO. 116 OSOA MARCH 15, 2016 PREPARED FOR: ROBERTO VARGAS 404 CORYELL ROAD GLENWOOD SPRINGS, CO 81601 robertovargasl059@gmail.com Parker 303-841-7119 • Colorado Springs 719-633-5562 • Silverthorne 970-468-1989 ., ! TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY ............................................................................ - 1 - PROPOSED CONSTRUCTION .................................................................................... - 1 - SITE CONDITIONS ....................................................................................................... - 2 - SUBSIDENCE POTENTIAL ......................................................................................... -2 - FIELD EXPLORATION ................................................................................................. -2- SUBSURFACE CONDITIONS ...................................................................................... - 3 - FOUNDATION BEARING CONDITIONS .................................................................. - 3 - DESIGN RECOMMENDATIONS ................................................................................ - 4 - FOUNDATIONS ........................................................................................................ -4- FOUNDATION AND RETAINING WALLS ........................................................... -5- FI...OOR SLABS .......................................................................................................... - 6 - UNDERDRAlli SYSTEM .......................................................................................... - 6 - SURFACE DRAlliAGE ............................................................................................. - 7 - LWITATIONS ............................................................................................................... - 7 - FIGURE 1 -LOCATION OF EXPLORATORY BORINGS FIGURE 2 -LOGS OF EXPLORATORY BORINGS FIGURE 3 -LEGEND AND NOTES FIGURE 4 -GRADATION TEST RESULTS TABLE 1-SUMMARY OF LABORATORY TEST RESULTS ,· .• PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed barn to be located at 404 Coryell Road (County Road 167), 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 Robert Varga s dated March 4, 2016. 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 class ification 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 construction is a 60'x36' barn to be located in the vacant lawn area in front of the existing residence. We assume the proposed barn will be a two-story wood-frame structure with an earth ground floor and slab-on-grade floor in the office area. Grading for the structure is assumed to be relatively minor with cut depths up to about 4 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. Job No. 116 050A .. -2- SITE CONDITIONS The property is currently occupied by a one-story, wood-frame residence and several outbuildings and sheds. Access to the residence is via a shared driveway, and the neighbor's residence is in very near proximity. The site is bordered by residential properties to the north and south, the Roaring Fork River to the west, and Coryell Road to the east. The ground surface across the site and in the proposed building area is relatively level, with the exception of a steep slope at the west side of the property down to the river. The elevation difference across the site about 2 to 3 feet. Vegetation consists mainly of lawn grass, landscaped brush, and willow trees. SUBSIDENCE POTENTIAL The project area is underlain by Pennsylvania Age Eagle Valley Evaporite bedrock. The evaporite contains gypsum deposits. 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 were observed in the Roaring Fork River valley. Sink.holes were not observed in the immediate area of the subject property and no voids were encountered in the exploratory boring. Based on our present knowledge of the site, it cannot be said for certain that sinkholes will not develop. In our opinion, the risk of ground subsidence at the proposed barn through its service life is low and similar to other properties in the area but the owner should be aware of the potential for sinkhole development. FIELD EXPLORATION The field exploration for the project was conducted on March 4 and 7, 2016. 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 Hepworth-Pawlak Geotechnical, Inc. Job No. 116 050A -3- Samples of the subsoils were taken with 1 %-inch and 2-inch l .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 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 8 to 12 inches of topsoil overlying dense, silty sandy gravel with cobbles over medium stiff, silty sandy clay soils at 8 feet in Boring 1. Drilling conditions in Borings 1 and 2 indicated weathered bedrock below 12 and 8 feet, respectively, and extending down to the depths explored of 21and16 feet, respectively. Laboratory testing performed on samples obtai~ed from the borings included natural moisture content, density, and gradation analyses. Results of gradation analyses performed on small diameter drive samples (minus 1 Yz-inch fraction) of the coarse granular soils are shown on Figure 4 . The laboratory testing is summarized in Table 1. Groundwater was encountered in Boring l at a depth of l 0 feet and in Boring 2 at a depth of 12 feet at the time of drilling. FOUNDATION BEARING CONDITIONS Spread footings placed on the natural granular soils can be used for support of the building with some risk of settlement. The topsoil and any existing fill or debris should be completely removed from beneath the proposed barn. Groundwater level may rise during spring runoff, but the level appears deep enough not to affect shallow footing Job No. 116 OSOA -4- construction. A lower risk foundation could consist of piers or piles that extend down into the weathered siltstone bedrock. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings aild the nature of the proposed construction, we recommend the building be founded with spread footings bearing on the natural 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 granular soils should 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 about 1 inch or less. 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 {if any) should also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining Walls" section of this report. 5) All existing fill, topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the natural granular soils. The exposed soils in footing areas should then be moisture adjusted to near optimum and compacted. If water seepage is encountered, we should be contacted for further evaluation. Job No. 116 050A ... - 5 - 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 (if any) 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 45 pcf for backfill consisting of the on-site granular soils. Cantilevered retaining structures which are separate from the addition 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 granular 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. 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 Job No . 116 OSOA -6- 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 .50. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 400 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 that 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 granular soil compacted to at least 95% of the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS The natural on-site granular soils, 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 relatively well graded sand and gravel such as road base should be placed beneath interior slabs for support. 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 debris. UNDERDRAIN SYSTEM It is our understanding the finished floor elevation at the lowest level will be at or above the surrounding grade. Therefore, a foundation drain system is not required. It has been our experience in the area that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a Job No. 116 050A -7- perched condition. We recommend below-grade construction, such as retaining walls, crawlspace and basement areas (if provided), be protected from wetting and hydrostatic pressure buildup by an underdrain and wan drain system. If the finished floor elevation of the proposed structure has a floor level below the surrounding grade, we should be contacted to provide recommendations for an underdrain system. AU earth retaining structures should be properly drained. SURFACE DRAINAGE The folJowing drainage precautions should be observed during construction and maintained at all times after the barn 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 10 feet in unpaved areas and a minimum slope of 3 inches in the first l 0 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 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. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory borings drilled at the locations Job No . 116 050A ... - 8 - indicated on Figure l, 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, HEPWORTH -PAWLAK GEOTECHNICAL, INC. &?Ayrl !bJ.lfW"Y7@ Robyn C. Brown, P.E. Reviewed by: RCB/ksw Job No . 116 050A ' . 116 OSOA SHEDS EXISTING ESIDENCE 404 CORYELL ROAD 'l---...-...("l-FENCE~ ~UTBUILD INGS 1 ----el I BOAJNq 1 I 1--L._ ____ J w CJ z UJ u... BORING2 ~ w > a: 0 CORYELL ROAD APPROXIMATE PROPOSED BARN APPROXIMATE SCALE 1" = 50' ~ LOCATION OF EXPLORATORY BORINGS Figure 1 He worth-Pawlak Geolechnlcol . ' BORING 1 BORING 2 0 0 19/12 30/1 2 } WC -4 8 +4 = 48 5 62/12 -200 -15 75/1 2 5 WC = 7.2 +4 ... 45 -200 = 14 10 6/12 3311 2 10 - Ci) -..... CJ.) a> CJ.) u.. LL I -J:: -J:: E. a a> CJ.) a Cl 15 13/12 74/1 2 15 WC = 108 DD= 120 20 72/12 20 25 25 Note: Explanation of symbols is shown on Figure 3. Figure 2 ~ H worth-Pawlak Geotec:hnlcal LOGS OF EXPLORATORY BORINGS 116 050A LEGEND: TOPSOIL; organic silt with roots, loose, very moist, dark brown. GRAVEL (GM); silty, sandy to very sandy, with cobbles and scattered boulders, medium dense to dense, moist. brown. CLAY (Cl); silty, slightly sandy, medium stiff, moist. brown. WEATHERED SILTSTONE; with gypsum, medium hard to hard, slightly moist to wet , dark gray to black . Eagle Valley Evaporite. 74/12 -- Relatively undisturbed drive sample; 2-inch l.D. California liner sample. Drive sample; standard penetration test (SPT), 1 3/8 inch l.D. split spoon sample, ASTM D-1586 . Drive sample blow count; indicates that 74 blows of a 140 pound hammer falling 30 inches were required to drive the California or SPT sampler 12 inches. Free water level in boring at the time of drilling. NOTES: 1. Exploratory borings were drilled on March 4 and 7, 2016 with 4-inch diameter continuous flight power auger. 2. Locations of exploratory borings were measured approximately by pacing from existing features and a site sketch was prepared in the field. 3. Elevations of exploratory borings were not measured and the fogs of exploratory borings are drawn to depth . 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 transitions may be gradual. 6. Water level readings shown on the logs were made at the time and under the conditions indicated. Fluctuations in water level may occur with time. 7. Laboratory Testing Results: WC = Water Content (%) DD = Dry Density (pc~ +4 = Percent retained on the No . 4 sieve -200 = Percent passing the No. 200 sieve 116 050A ~ Heoworth-Powlok Geotechnlcol LEGEND AND NOTES Figure 3 ' I HYDROMETER ANALYSIS SIEVE ANALYSIS I TIME READINGS I U S STANDARD SERIES I CLEAR SQUARE OPENINGS I 2 .. 1~. 7HR 45 MIN. 15 MJN 60MINl9MIN.4 MIN 1 MIN #200 #100 #50 #30 #16 !118 #4 3/8" 3/4" 1 1/2' 3• 5' 6' 8' 10 0 20 LU z 30 ~ a: 40 1-z 50 w (..) a: 60 w CL 70 80 90 100 .001 .002 005 .009 .019 037 07• 150 300 .600 118 2 311 075 95125190 37.5 76.2 152 203 127 DIAMETER OF PARTICLES IN MILLIMETERS CL.AYTOS!LT :}-.--..Fu'""'1e.---..... -...ll~::::;£D:.\l-IU-... -.......... COAR_S..,..e -1-:-....,F,.....INE,....-.!::GRA:::;IVEl:slo.....,COAAS---e --1: COB~S GRAVEL 48 % SAND 37 % SILT AND CLAY 15 % LIQUID LIMIT - -% PLASTICITY INDEX - -% 100 90 ao CJ 70 ~ (/) (/) eo ct 1- 50 z UJ ~ •O W CL 30 20 10 0 SAMPLE OF: Silty, very sandy gravel FROM : Boring 1 at 2f and 5' (combined) HYDROMETER ANALYSIS SIEVE ANALYSIS HR TIME READINGS I U.S. STANDARD SER IES I CLEAR SQUARE OPENINGS I 24 iR. 7 N 3/8' 3/4" 11/2' 3• 5"6" a• 45 AIN 15 Ml . 60MINl9MIN .4 MIN . 1 M,N #200 #100 #50 #30 #16 #8 #4 100 10 0 20 w z 30 ~ a: 1-z w u a: w CL 40 50 60 70 80 90 100 - 90 80 CJ 70 z Ci5 60 en ct I- 50 z UJ u 40 ffi CL 30 20 10 0 .001 002 005 .009 .0 19 037 0 74 150 .3 00 .600 1.18 2.36 4 75 9.51 2 .5 19.o 37 .5 76 2 12~52 203 DIAMETER OF PARTICLES IN MILLIMETERS CL.AYTO Sol.T •l-'--~.---....----::s~~~o.,,..,....__,==",,,.,,..+•-.....,,,,,,,......~GRA~vn::.:..::.....,,,,,.,==----1' coee~ I f iNE ... EOllJM I COAASE I FINE I COARSE GRAVEL 45 % LIQUID LIMIT • -% SAMPLE OF: Silty sand and gravel 116 050A ~ HEPWORTH-PAWLAK GEart:CHNJCAL SAND 41 % SILT AND CLAY 14 % PLASTICITY INDEX --% FROM : Boring 2 at 5' GRADATION TEST RESULTS Figure 4 HEPWORTH-PAWLAK GEOTECHNICAL, INC. TABLE 1 Job No. 116 050A SUMMARY OF LABORATORY TEST RESULTS SAMPLE LOCATION GRADATION ATTERBERG LIMITS "' NATURAL NATURAL PERCENT UNCONFINED MOISTURE DRY GRAVEL SAND PASSING LIQUID PLASTIC COMPRESSIVE SOIL OR BORING DEPTH CONTENT DENSITY (%) (%) N0.200 LIMIT INDEX STRENGTH BEDROCK TYPE SIEVE (ft) (%) (DCfl (%) (%) (PSF) 1 21/i and 5 4.8 48 37 15 Silty, Very Sandy Gravel (combined) 10.8 120 Weathered Siltstone with 15 Gypsum 2 5 7.2 45 41 14 Silty Sand and Gravel