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HomeMy WebLinkAboutSoils Report.pdfSUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED ADDITON TO EXISTING HOUSE AND RV STORAGE/GREENHOUSE STRUCTURE 2621 COUNTY ROAD 100 CARBONDALE, COLORADO 81623 JOB NO. 114 230A JUNE 30, 2014 PREPARED FOR: LARRY & LISA SINGER 2621 COUNTY ROAD 100 CARBONDALE, COLORADO 81623 lssiinvec fki con[cast net TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION -1- SITE CONDITIONS -2- FIELD EXPLORATION -2- SUBSURFACE CONDITIONS 3 - FOUNDATION BEARING CONDITIONS - 3 - DESIGN RECOMMENDATIONS FOUNDATIONS - 4 - FLOOR SLABS - 4 - UNDERDRAIN SYSTEM - 5 - SURFACE DRAINAGE - 5 - - 6 - LIMITATIONS 6 - FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 5 - 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 proposed additions to the current residence and a new RV Storage/Greenhouse Structure located at 2621 County Road 100, east of Carbondale, 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 you dated June 9, 2014. 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 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 addition to the existing residence is an attached two story addition on the east side of the residence and the RV Storage and Greenhouse Structure will be located southwest of the existing residence. The attached addition to the house will have a slab - on -grade or a structural floor over a crawlspace and be of similar construction to the existing residence. Ground floors for the RV Storage and Greenhouse Structure will be slab -on -grade. Grading for the additions is assumed to be relatively minor with cut depths between about 2 to 4 feet. We assume relatively light foundation loadings,' typical of the proposed type of construction. Job No. 114 230A Geetech -2 - 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 site is currently occupied with a single family residence located in the middle of the lot. The lot is bounded to the north by the Roaring Fork River, to the south by County Road 100 and to the east and west by adjacent residential Lots. A small outbuilding is located northeast of the residence and adjacent to the Roaring Fork River. The lot is relatively flat with a slight slope down to the north. Shallow irrigation trenches cross the southwest portion of the site. Vegetation on the Iot consists of grasses, shrubs and mature trees. FIELD EXPLORATION The field exploration for the project was conducted on June 19, 2014. 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 Geoteclmical, Inc. Samples of the subsoils were taken with a 1% inch 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 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. Job No. 114 230A -3 - SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils consist of about 4 to 6 inches of topsoil overlying silty sandy gravel with cobbles and boulders. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and boulders and drilling refusal was encountered in the deposit. Laboratory testing performed on samples obtained from the borings included natural moisture content and gradation analyses. Results of gradation analyses performed on small diameter drive samples (minus 1 /z inch fraction) of the coarse granular subsoils are shown on Figure 4. The laboratory testing is summarized in Table 1. Free water was encountered in Boring I at 7 feet at the time of drilling and at 4'h feet when checked 12 days later. Boring 2 caved at shallow depth during auger removal and a water level check was not possible. The 5 foot sample from Boring 2 was wet. Subsoils above the water table were slightly moist to moist. FOUNDATION BEARING CONDITIONS Foundations bearing on the natural granular soils encountered in our exploration should be feasible for support of the proposed structure with some risk of movement. All topsoil, any fill, and all loose or disturbed materials should be removed from the building area and the foundation excavations extended down the natural relatively dense granular soils. Groundwater was encountered in our exploration at relatively shallow depth and may impact foundation construction and dewatering of' foundation or utility trench excavations may be necessary. Job No. 114 230A Gatech -4 - DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we recommend the building additions and RV Storage/Greenhouse Structure 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 2,500 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 should also be designed to resist a lateral earth pressure. 5) Any existing fill, topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the relatively dense natural granular soils. The exposed soils in footing area should then be moistened if needed and compacted. If water seepage is encountered, the footing areas should be dewatered before concrete placement. Job No. 114 230A Gtech -5- 6) A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FLOOR SLABS The natural on-site 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. 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 oversized rock. UNDERDRAIN SYSTEM Free water was encountered during our exploration and will likely fluctuate with river levels, heavy precipitation and seasonal runoff. Frozen ground during spring runoff can also create perched conditions. We recommend below -grade construction, such as retaining walls and crawlspace areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. If a crawlspace is constructed for the addition, shallow seasonal groundwater may impact the crawlspace area and a sump with an adequate pump may be necessary. Slab -on -grade construction should not require an underdrain system. If installed, 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% grade to a sump and pump. Free -draining granular Job No. 114 230A ~Ptech -6 - 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 additions have 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 10 feet in paved areas 4) Roof downspouts and drains should discharge well beyond the limits of all backfill and foundation areas. 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 fixture. If the client is concerned about MOBC, then a professional in this special field of practice should be Job No. 114 230A Gtech -7 - 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 GEOC James A. Parker, P.E., P.G. Reviewed by: P).4()0(4,L... Daniel E. Hardin, P.E. JAP/ ksw cc: Jeff Dickenson — bio pace y:'so ris,net Job No. 114 230A GLZtech 1 1, BRIDGE. APRIL 1, 2014 ;33. 4ArCMP INV:6 4).97 114 6'9 _— j tft) 6254 WING FORK INV: 6248.53 132 CONCRETE /• RETAINING WALLS, HEADGATE & 48`CMP PECK 6"CMP fNV:62 5.55 VER Z2 1 125 tit! 12 CONCRETE r PATIO 142 .143 PROPOSE=[) v ADDITION LOCATION 1-7,6• -------100.1'( TIE) SEPTIC TANK LIDS s)U CCPD mV: s2 .06 BUILDING ENVELOPE AND 100—YEAR FLOODPLAIN LIMIT PER RECEPTION NO. 394271 4'PVC r S1UB • to • D1C6_ e..r ASONI1 . SiORY M / SIDED HOUSE 2621 C.R.100 .z�; II . 9D1 ti'., i; - i LOT 2 ' ,` - :oo-bACRES',, 1 ' i 4 /0 • GRAVEL • DRIVE r 49. 1 �y'`y 1 tal i 11 11( B INV: 625 64 �: r;:M;_.. II I' /NV•62 4.34; C'. 1 r i / x7 ' 1IIIj 1 %'6255-/ / 6%1'4 ' fal �V•�" �5 .62 i - —60> ib ./. r, - . ) ;.,3137 30'. %34 :r; L;iERM91E _ lf. ...1111_ 25.3.19 ;1 /: / f 114 230A f IEPWORTH•PAWLAK GEOTECHNICAL. LED `ff A MAP TEJJo. 7) • g. 1i':•'f r—�1 1.49' 39-W e2ssY "COUNT Y I OAD LOCATION OF EXPLORATORY BORINGS FIGURE 1 Elevation - Feet 6260 6255 6250 6245 BORING 1 ELEV.- 6254' 48/12 WC = 4.0 +4=51 -200=8 21/12 BORING 2 ELEV.— 6256' 40/12 29/12 WC=8.3 +4=55 -200=9 Note: Explanation of symbols is shown on Figure 3. 6260 6255 6250 6245 Efevation - Feet 114 230A GLZtech ?.2404U1J:eawi r,FnTFrN01lrai LOGS OF EXPLORATORY BORINGS FIGURE 2 LEGEND: 48/12 0, 12 T TOPSOIL; silty sand with gravel, roots, slightly moist, brown. GRAVEL (GM); silty, sandy, with cobbles and boulders, medium dense to dense, moist to wet, brown. Drive sample; standard penetration test (SPT), 1 3/8 inch I.D. split spoon sample, ASTM D-1586. Drive sample blow count; indicates that 48 blows of a 140 pound hammer falling 30 inches were required to drive the SPT sampler 12 inches. Free water level in boring and days after drilling measurement was taken. Depth at which boring had caved when measured after drilling. Practical drilling refusal. NOTES: 1. Exploratory borings were drilled on June 19, 2014 with 4 -inch diameter continuous flight power auger. 2. Locations of exploratory borings were measured approximately by pacing from features shown on the site plan provided. 3. Elevations of exploratory borings were obtained by interpolation between contours shown on the site plan provided and checked by instrument level. 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 (%) +4 = Percent retained on the No. 4 sieve -200 = Percent passing No. 200 sieve 114 230A ech • LEGEND AND NOTES FIGURE 3 RCENT RETAINE i� HYDROMETER ANALYSIS I SIEVE ANALYSIS TIME READINGS U.S. STANDARD SERIES I CLEAR SQUARE OPENINGS 45MIN.1 7401 IN.60MIN19MIN.4 MIN. 1 MIN. /11200 #100 #50 7/30 1/16 #8 #4 3/8" 3/4' 1 1/2" 3" 5i'6" 8" 0 10 20 30 40 50 60 70 80 90 100 93 FA 70 Z rn s3 w Z W U 4O w 30 20 0 100 001 002 005 .009 CLAY TO SILT .019 .037 .074 .150 300 600 118 2.36 DIAMETER OF PARTICLES IN MILLIMETERS FINE GRAVEL 51 LIQUID LIMIT % SAMPLE OF: Slightly Silty Sandy Gravel SAND 4.75 9.5 12.5 190 GRAVEL 375 0 76.2 152 203 127 COBBLES SAND 41 % SILT AND CLAY 8 % PLASTICITY INDEX % FROM: Boring 1 at 2 Feet ME0894 ICOARSE FINE I COARSE HYDROMETER ANALYSIS I SIEVE ANALYSIS I 24 -IR. 7 HR TIME READINGS U.S. STANDARD SERIES I CLEAR SQUARE OPENINGS 45 NIH. 15 MIN. 60MIN19MIN.4 MIN. 1 MIN. #200 #100 #50 #30 416 #8 #4 3/8" 3/4" 1 1/2" 3" 5'6' 8" 100 10 20 30 40 50 60 70 80 90 100 0 .001 .002 .005 .009 .019 .037 .074 .150 .300 .600 1.18 2.36 4.75 9.512 519.0 37.5 76.2 721752 203 DIAMETER OF PARTICLES IN MILLIMETERS 90 80 C3 70 60 4 50 U 40 w 0_ 30 20 10 CLAY TO SILT GRAVEL 55 % LIQUID LIMIT SAMPLE OF: Slightly Silty Sandy Gravel SANG FINE I MEDIUM I COARSE GRAVEL FINE 1 COARSE COBBLES SAND 36 % SILT AND CLAY 9 % PLASTICITY INDEX % FROM Boring 2 at 2 and 5 Feet Combined GeStech GRADATION TEST RESULTS 114 230A H FIGURE 4 Job No. 114 230A W Z fa 'Op- Q0. z0N J 0 z 0 Q 2 O 0 3 Z O M 0. LL to SAMPLE LOCATION w 0 O 2 0 O OD Slightly Silty Sandy Gravel 00 ON v h m 00 rr