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HomeMy WebLinkAboutSoils & Perc Test Report 03.25.2015Gtech HEPWORTH-PAWL AK GEOTECHNICAL March 25, 2015 Doug Button 3201 B %2 Road Grand Junction, Colorado 81503 (butlonranch a umai1.com) Ilepnorlh-Paw•lak Geotechnical, Inc. 5020 County Road 154 Glenwood Springs, Colorado 81601 Phone: 970-945-7988 Fax: 970-945-8454 Email: hpgeo^a hpgeutech.com Job No.l 14 553A Subject: Subsoil Study for Foundation Design and Percolation Test, Proposed Residence, Parcel 11, Section 21, Broken Yoke Drive, Garfield County, Colorado Dear Mr. Button: As requested, Hepworth-Pawlak Geotechnical, Inc. performed a subsoil study and percolation test for foundation and septic disposal designs at the subject site. The study was conducted in accordance with our agreement for geotechnical engineering services to you dated December 31, 2014. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Evaluation of potential geologic hazard impacts on the site are beyond the scope of this study. Proposed Construction: The proposed residence will be -erre -story wood frame construction above a walkout basement and with an attached garage. Basement and garage floors are proposed to be slab -on -grade. Cut depths are expected to range between about 3 to 8 feet. Foundation loadings for this type of construction are assumed to be relatively Tight and typical of the proposed type of construction. The septic disposal system is proposed to be located southwest of the residence. 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 38.19 acres in size and located south of Broken Yoke Drive. The site is vacant irrigated pasture land and snow cover was about 6 inches at the time of our exploration. Vegetation consists of sage brush, grass and weeds with scattered juniper trees. The property is located on an upland rolling mesa and the ground -2 - surface in the building area slopes slightly too moderately down to the southwest. A large irrigation ditch is located just below the building area and was dry at the time of our exploration. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating five exploratory pits in the building area and two profile pits in the septic disposal area at the approximate locations shown on Figure 1. The logs of the pits are presented on Figure 2. The subsoils encountered, below about 6 inches of topsoil, consist of siltstone/sandstone bedrock. A clayey sand layer was encountered in Pit 5 overlying the bedrock. Silty sandy clay was encountered in Profile Pit 1 to 6 feet overlying the bedrock. Results of swell -consolidation testing performed on a relatively undisturbed sample of silty clayey sand, presented on Figure 4, indicate low compressibility under existing moisture conditions and light loading and a moderate collapse potential when wetted. Results of a USDA gradation analysis performed on a sample of silt loans (minus 3/8 inch fraction) obtained from Profile Pit 1 are presented on Figure 5. The laboratory test results are summarized in Table 1. No free water was observed in the pits at the time of excavation and the soils were slightly moist to moist. Foundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, we recommend spread footings placed on undisturbed siltstone/sandstone bedrock designed for an allowable soil bearing pressure of 3,000 psf for support of the proposed residence. The upper soils tend - to compress after wetting and there could be some post -construction foundation settlement for footings placed on them. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. The upper clayey sand or any sandy clay encountered in the excavation should be removed and the foundation bearing level extended down to undisturbed siltstone/sandstone bedrock. Exterior footings should be provided with adequate cover above their bearing elevations for frost protection or the footings can be insulated in accordance with the 2009 International Residential Code. Placement of footings at least 36 inches below the exterior grade is typically used in this area. 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 be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 50 pcf for the on-site soil or broken bedrock as backfill. 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 and bedrock, exclusive of topsoil, are suitable to support lightly loaded slab -on -grade construction. To reduce the effects of some Job No.114 553A lgtech -3 - 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 less than 50% passing 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 Ieast 95% of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on-site soils or a suitable imported material devoid of vegetation, topsoil and oversized rock. Underdrain System: Although free water was not encountered during our exploration, it has been our experience where bedrock is shallow that local perched groundwater can develop during times of heavy precipitation, seasonal runoff or irrigation season. Frozen ground during spring runoff can also create a perched condition. We recommend below - grade construction, such as retaining walls 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 1 % 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. Free -draining wall backfill should be capped with about 2 feet of the on-site, finer graded soils to reduce surface water infiltration. Job No. ! I4 553A Gecgtech -4- 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 pavement and walkway areas. A swale may be needed uphill to direct surface runoff around the residence, 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. Percolation Testing: Two profile pits and three percolation test holes were excavated on January 2, 2015 at the locations shown on Figure 1. The subsoils exposed in the profile pits was variable and below about 6 inches of topsoil consisted sandy silty clay to 6 feet overlying siltstone/sandstonc bedrock at Profile Pit l and about 6 inches of sandy silty ' clay overlying the bedrock at Profile Pit 2. The results of a USDA Soil Texture gradation analysis performed on a sample of silt loam (minus 3/8 inch fraction) obtained from the site are presented on Figure 5. No free water or evidence of a seasonal perched water table was observed in the pit and the soils were slightly moist to moist. Percolation test holes were hand dug and soaked with water on January 2, 2015. Percolation testing was conducted on January 3, 2015, by a representative of Hepworth - Pawlak Geotechnical, Inc. The percolation rates varied from 60 minutes per inch to 30 minutes per inch with an overall average of 50 minutes per inch. •The percolation test results are summarized on Table 2. Based on the subsurface conditions encountered and the percolation test results, the tested area should be suitable for an on-site waste disposal system. Due to the shallow bedrock a mounded system may be needed. We recommend the area be further investigated to verify soil conditions in the septic field. We understand that the client is considering another site for the septic system. 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 pits 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 this special field of practice should be consulted. Our findings include interpolation and extrapolation of the subsurface conditions identified at the exploratory pits and variations in the subsurface conditions Job No.l 14 553A GecStech -5 - 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 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 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 engi neer. If you have any questions or if we may be of further assistance, please let us know. Respectfully Submitted, HEPWORTH - PAWLAK GEOTECHNICAL, INC. Louis E. Eller Reviewed by: insuuran,,, 0 fact, Daniel E. Hardin, P.E. = 2 • 34.���F/15 •.�� LEE/ksw '*��ls''+. sevolc,�`t J�igr0a�r p ieti�� attachments Figure 1 — Location of Exploratory Pits and Percolation Test Holes Figure 2 — Logs of Exploratory Pits Figure 3 - Swell -Consolidation Test Results Figure 4 — USDA Gradation Test Results Table 1 Summary of Laboratory Testing Table 2 — Percolation Test Results Job Na 1 14 553A APPROXIMATE SCALE 1'=30' PROFILE PIT 1 ■ A P3 A P2 ■ PROFILE PIT 2 114 553A P1 H PIT 5 PIT 1 ■ ■ 1 650' TO PROPERTY LINE Hepworth—Pawlak Geotechnleal GARAGE PROPOSED RESIDENCE PORCH PIT 3 ■ LOCATION OF EXPLORATORY PITS AND PERCOLATION TEST HOLES 67TO PROPERTY PIT 2 ■ Figure 1 W 0▪ . m 0 0 5 10 - 0 - 5 10 114 553A PIT1 _J PIT 5 PIT 2 WC=4.7 DD=95 -200=28 PIT 3 PIT 4 PROFILE PIT 1 PROFILE PIT 2 5 WC=10.6 GRAVEL=8 SAND=37 SILT=50 CLAY=5 Note: Explanation of symbols is shown on Figure 3. HEPWORTh.PAWLAK GEOTECHNICAL LOGS OF EXPLORATORY PITS 0 5 10 . 0 5 10 Figure 2 LEGEND: b TOPSOIL; organic sandy silt and clay, soft, moist, dark brown. CLAY (CL); silty, sandy to sandy clayey silt, stiff, moist, red, porous, blocky. SAND (SC); clayey, silty, medium dense, slightly moist, brown. SILTSTONE/SANDSTONE/; hard, slightly moist, light brown, thin bedding, dips slightly down to southwest. Wasatch Formation. 2' Diameter hand driven liner sample. Disturbed bulk sample. NOTES: 1. Exploratory pits were excavated on January 2, 2015 with a trackhoe. 2. Locations of exploratory pits were measured approximately by pacing from features shown on the site plan provided. 3. Elevations of exploratory pits were not measured and the logs of exploratory pits are drawn to depth. 4. The exploratory pit locations should be considered accurate only to the degree implied by the method used. 5. The lines between materials shown on the exploratory pit logs represent the approximate boundaries between material types and transitions may be gradual. 6. No free water was encountered in the pits at the time of excavating. Fluctuation in water level may occur with time. 7. Laboratory Testing Results: WC = Water Content (%) DD = Dry Density (pcf) -200 = Percent passing No. 200 sieve Gravel = Percent retained on No. 10 Sieve Sand = Percent passing No. 10 sieve and retained on No. 325 sieve Silt = Percent passing No. 325 sieve to particle size .002mm Clay = Percent smaller then particle size .002mm 114 553A H HEPWORT .PAWL4K GEOTECHNICAL. LEGEND AND NOTES Figure 3 Compression % Moisture Content = 4.7 percent Dry Density = 95 pct Sample of: Silty Clayey Sand From: Pit 5 at 2 Feet Compression upon wetting 0.1 114 553A 1H 1.0 Hepworth—Powlak Gsotachnlcal APPIJED PRESSURE - ksf r 10 100 SWELL -CONSOLIDATION TEST RESULTS Figure 4 HYDROMETER ANALYSIS 1 24 7�� TIME READINGS 1 MIN. 0 45 MIN 15 MIN.60MIN19M N 4 MIN. #325 10 20 30 40 50 60 70 80 90 100 #140 — --.—i ....— a--aa` Sa Sin a.a— laa•I —r ---ter a—lam —a. —a— —wa—= is---i.s =•••••1 Sam! 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MARE GRAVEL mut 1 warm 1 COBBLE; 114 553A GRAVEL 8 % SAND 37 % USDA SOIL TYPE: Silt Loam H Hapworih—Pawlok GeoteehnIcol SILT 50 % CLAY 5 % FROM: Profile Pit 1 at 4 Feet USDA GRADATION TEST RESULTS 80 70 60 5o 40 30 20 10 0 ENT PA , r, Figure 5 Job No. 114 553A cn Z -J 6 UJ � LF! -i• L!! WI't ~ o a 11.1 E 2rjj w FZ z ,• f, Z0Ili 0 LI mn z N 00 N HOLE NO. PI HEPWORTH-PAWLAK GEOTECHNICAL, INC. TABLE 2 PERCOLATION TEST RESULTS HOLE DEPTH LENGTH OF (INCHES) INTERVAL (MIN) 24 15 Water added WATER DEPTH AT START OF INTERVAL (INCHES) 10 WATER DEPTH AT END OF INTERVAL (INCHES) 9 1/4 DROP IN WATER LEVEL (INCHES) 3/4 JOB NO. 114 553A 9 1/4 8 3/4 1/2 10 9 1/2 1/2 9 1/2 9 1/4 1/4 9 1/4 8 3/4 1/2 8 3/4 8 1/2 1/4 8 1/2 8 1/4 1/4 AVERAGE PERCOLATION RATE (MIN./INCH) 60 P2 P3 24 26 15 15 Water added Water added 9 8 1/2 1/2 8 1/2 8 1/4 1/4 8 1/4 7 3/4 1/2 7 3/4 7 1/2 1/4 7 1/2 7 1/4 1/4 7 1/4 7 1/4 7 9 6 3/4 7 1/2 1/4 1 1/2 7 3/4 7 3/4 8 1/4 7 3/4 1/2 7 3/4 7 3/4 7 6 1/2 1/2 6 1/2 6 1/2 6 5 1/2 1/2 60 30 Note: Percolation test holes were hand dug in the bottom of backhoe pits and soaked on January 2, 2015. Percolation tests were conducted on January 3, 2015. The average percolation rates were based on the last two readings of each test.