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HomeMy WebLinkAboutSoils Report.pdfHEPWORTH -PAWLAK GEOTECHNICAL April 25, 2014 Ty Rice P.O. Box 398 Carbondale, Colorado 81623 I kr,t.itli I .,i\ l.,i t :t•• i., Job No.114 123A Subject: Subsoil Study for Foundation Design and Percolation Test, Proposed Residence, 268 Rose Lane, Garfield County, Colorado Dear Mr. Rice 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 April 18, 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 is beyond the scope of this study. Proposed Construction: The proposed residence will be one story wood frame construction and located on the site as shown on Figure 1. Ground floors are proposed to be structural above a shallow crawlspace. Cut depths are expected to range between about 2 to 3 feet. Foundation loadings for this type of construction are assumed to be relatively light and typical of the proposed type of construction. The septic disposal system is proposed to be located in the rear of the property. 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 was previously occupied with a mobile residence and numerous outbuildings. At the time of our field exploration, the site had been cleared of structures except for the pump house and a shed. Outside of disturbed areas, vegetation consists of grass and weeds with scattered cottonwood trees. The site is located in the Roaring Fork River valley bottom and the ground surface is relatively flat with a slight slope down to the west. There is a shallow depression in the center of the site. An Parker 303-841-7119 • Colorado Spring; 719-033-5562 • Silveri -home 970-40-1989 -2 - existing irrigation ditch crosses the property on the north side. The ditch was dry at the time of our field exploration. Subsidence Potential: The Roaring Fork valley in this 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. Sinkholes have been observed in nearby subdivisions during previous work in the area. Sinkholes were not observed in the immediate area of the subject site. 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 property throughout the service life of the residence is low and similar to other properties in the area but the owner should be aware of the potential for sinkhole development. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits in the building area and one profile pit in the septic disposal area at the approximate locations shown on Figure I. The logs of the pits are presented on Figure 2. The subsoils encountered, below about 2 feet of topsoil or fill, consist of slightly silty sandy gravel with cobbles and small boulders. A one foot thick clay layer was observed in Pit 1 overlying the granular soil. Results of gradation analyses performed on samples of sandy gravel with cobbles (minus 5 inch fraction) obtained from the site are presented on Figure 3. 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 the undisturbed natural soil designed for an allowable soil bearing pressure of 2,500 psf for support of the proposed residence. The natural soils should have low compressibility and foundation settlement should be less than 1 inch. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. Loose and disturbed soils, existing fill and sandy clay encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural granular soils. Exterior footings should be provided with adequate cover above their bearing elevations for frost protection. 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 Gtech -3 - based on an equivalent fluid unit weight of at least 45 pcf for the on-site granular soil 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, exclusive of topsoil and sandy clay, are suitable to support lightly loaded slab -on -grade construction. To reduce the effects of some differential movement, floor slabs (if any) 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: Although free water was not encountered during our exploration, it has been our experience in the area that local perched groundwater can develop during times of heavy precipitation, seasonal runoff or during irrigation season. Frozen ground during spring runoff can create a perched condition. We recommend below -grade construction, such as retaining walls and crawlspace 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 or drywell. 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. Free -draining wall backfill should be -4 - capped with about 2 feet of the on-site, finer graded 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 6 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. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. Percolation Testing: A profile pit and three percolation test holes were excavated on April 18, 2014 at the locations shown on Figure 1. The subsoils exposed in the Profile Pit consisted of about 11/2 feet of topsoil overlying slightly silty sandy gravel with cobbles and small boulders to the bottom pit depth of 8 feet. The results of a gradation analysis performed on a sample of sandy gravel (minus 5 inch fraction) obtained from the Profile Pit are presented on Figure 3. The sample tested has a USDA Soil Texture Classification of extremely gravelly sand. 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 April 18, 2014. Percolation testing was conducted on April 19, 2014 by a representative of Hepworth - Pawlak Geotechnical, Inc. The percolation rates varied from 6 minutes per inch to 8 minutes per inch with an average of 7 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. A professional civil engineer should design the septic disposal 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 may not become evident until excavation is performed. If conditions encountered during -5 - 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 engineer. 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: Steven L. Pawlak, P.E. LEE/ksw �L_P Nom° Ire 16222 , 1jso ji j-3. � d' •"'nu t X46 0 attachments Figure 1— Loca C' -b' oratory Pits and Percolation Test Holes Figure 2 — Logs of Exploratory Pits Figure 3 - Gradation Test Results Table 1 — Summary of Laboratory Test Results Table 2 — Percolation Test Results cc: Sopris Engineering - Paul Rutledge (prutic�lir Gtech PIT 1 ■ ROSE LANE PROPOSED RESIDENCE 268 ROSE LANE P2 A PROFILE ■ PIT LI A P3 EXISTING WELL 0 ■ PIT 2 APPROXIMATE SCALE 1"=30' 114 123A GecPtech HEPWORTH-PAWLAK GEOTECHNICAL LOCATION OF EXPLORATORY PITS AND PERCOLATION TEST HOLES Figure 1 0 5 10 LEGEND: ti _J PIT 1 P:sr WC= 29.5 DD= 87 - I +4= 79 - - -200= 4 PIT 2 .P PROFILE PIT • +4= 72 - J -200= 6 FILL; sandy silt and clay, some topsoil, firm, moist, mixed brown and black. TOPSOIL; organic sandy silt and clay, firm, moist, black. CLAY (CL); sandy, silty, medium stiff, very moist, brown. GRAVEL (GM -GP); silty, sandy, with cobbles and boulders, dense, moist, brown, rounded rocks. 2" Diameter hand driven liner sample. Disturbed bulk sample. 0 _ 5 10 NOTES: 1. Exploratory pits were excavated on April 18, 2014 with a Cat 320B 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 and elevations 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) +4 = Percent retained on the No. 4 sieve -200 = Percent passing No. 200 sieve 0) lL r o - m 0 114 123A Gmach HEPWORTH-PAWLAK GEOTECHNICAL LOGS OF EXPLORATORY PITS Figure 2 ENT RETAIL It ''ER ENT RETAIN_ it HYDROMETER ANALYSIS TIME READINGS 24 HR. 7 HA 45 MIN. 15 MIN. 60MIN19MIN.4 MIN. 1 MIN 0 10 20 30 40 50 60 70 80 90 100 SIEVE ANALYSIS 200 #100 U.S. STANDARD SERIES 1 #50 #30 #16 #8 #4 CLEAR SQUARE OPENINGS 3/8' 3/4' 1 1/2" 3" 5"6" 8° IW .091 .002 0� .019 037 .074 .150 CLAY TO SILT GRAVEL 79 % 1 300 .603 1.19 236 4.75 95125 190 37.5 762 152 203 127 DIAMETER OF PARTICLES IN MILLIMETERS SAND GROVEL FILE I MEDIA (COARSE SAMPLE OF: Sandy Gravel with Cobbles SAND 17 % FEE I COARSE 000OLES SILT AND CLAY 4 % FROM: Pit 1 at 3 X to 4 Feet 45'AIN. 15 MIN. 60MIN19MIN.4 MIN. 1 MIN 0 HYDROMETER ANALYSIS TIME READINGS 10 20 30 40 50 60 70 80 90 100 .001 .002 .005 .009 .019 .037 .074 .150 #200 #100 SIEVE ANALYSIS U.S. STANDARD SERIES 1 CLEAR SQUARE OPENINGS #50 #30 #16 #8 #4 3/8' 8' CLAY TO SI GRAVEL 72 % 1 90 50 70 60 50 40 20 20 10 100 90 80 70 Z U U 60 d 50 r w U 40 W 0 30 20 10 0 .300 .600 1.18 2.36 4.75 9.512.519.0 37.5 76.2 121/52 203 DIAMETER OF PARTICLES IN MILLIMETERS FEE 1 MEDIA (COARSE SAND 22 % GROVEL FINE 1 ODARSE CCOOLES SILT AND CLAY 6 % SAMPLE OF: Sandy Gravel with Cobbles (Extremely FROM: Profile Pit at 4 to 5 Feet Gravelly Sand) 114 123A Gaigtech Hepworth-P4lwlak Geotechnical GRADATION TEST RESULTS Figure 3 C rn 3 Sc > 0 O r Orn 0 0 O rn rn —Ixn nnz r D r C t.., r z n VEZI MI 'oN 4oC ro b o II SAMPLE LOCATION 4 to 5 w Nm O A 12 x N 02 1 87 0 z 3 �jc r 72 79 GRAVEL (%) GRADATION N J ° o 0 14_ 2 v v 4.12 Q�4n m 8 y,4 Sandy Clay UNCONFINED COMPRESSIVE SOIL OR STRENGTH BEDROCK TYPE (PS9 Sandy Gravel with Cobbles 11 { Sandy Gravel with Cobbles 11 C rn 3 Sc > 0 O r Orn 0 0 O rn rn —Ixn nnz r D r C t.., r z n VEZI MI 'oN 4oC HEPWORTH-PAWLAK GEOTECHNICAL, INC. TABLE 2 PERCOLATION TEST RESULTS 306 NO. 114 123A HOLE NO. HOLE DEPTH (INCHES) LENGTH OF INTERVAL (MIN) WATER DEPTH AT START OF INTERVAL (INCHES) WATER DEPTH AT END OF INTERVAL (INCHES) DROP IN WATER LEVEL (INCHES) AVERAGE PERCOLATION RATE (MIN./INCH) P 1 28 5 Water added Water added Water added Water added Water added 6 3 3/4 2 1/4 5 3/4 4 1/4 1 1/2 6 5 3/4 4 3/4 1 6 1/4 5 1 1/4 6 5 1 5 4 1/4 3/4 6 1/2 5 1/2 1 5 1/2 4 3/4 3/4 P 2 30 5 Water added Water added Water added Water added Water added Water added 6 4 1/2 1 1/2 8 5 1/2 4 1/4 1 1/4 5 1/2 4 1/4 1 1/4 5 3/4 4 3/4 1 5 1/2 4 1/2 1 5 1/2 5 1/2 5 4 1 5 1/2 5 1/2 P 3 28 5 Water added Water added Water added 7 4 3/4 2 1/4 7 6 3/4 5 1 3/4 6 3/4 5 1/2 1 1/4 6 3/4 6 3/4 6 4 3/4 1 1/4 Water added 6 5 1/4 3/4 5 1/4 4 1/4 1 4 1/4 3 3/4 1/2 Note: Percolation test holes were hand dug in the bottom of backhoe pits and soaked on April 18, 2014. Percolation tests were conducted on April 19, 2014. The average percolation rates were based on the last 3 readings of each test.