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HomeMy WebLinkAboutSoils Report for Foundation & Perc Test 06.21.2017H-PKUMAR Geotechnical Engineering 1 Engineering Geology Materials Testing 1 Environmental 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax: (970) 945-8454 Email: hpkglenwood@kumarusa.com June 21,2017 Kevin and Gretchen Strom c/o Doug Rager Architect 1780 Snowmass Creek Road Snowmass, Colorado 81654 (ragerarchitect @gmail.com) Office Locations: Parker, Glenwood Springs, and Silverthorne, Colorado Project No.17-7-349 Subject: Subsoil Study for Foundation Design and Percolation Testing, Proposed Residence, Lot 5, Callicotte Ranch, TBD Pinyon Woods Lane, Garfield County, Colorado Dear Mr. and Mrs. Strom: As requested, H-P/Kumar 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 proposal for geotechnical engineering services to you c/o Doug Rager, Architect dated November 1, 2016. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Hepworth- Pawlak Geotechnical, Inc. (now H-P/Kumar) previously performed a preliminary geotechnical study for Callicotte Ranch and reported the findings April 19, 2002, Job No. 101 821. Proposed Construction: The proposed residence will be a one and two story structure above a partial walkout basement and partial crawlspace with an attached garage. The house will be located on the site as shown on Figure 1. Basement and garage floors are proposed to be slab - on -grade. Cut depths are expected to range between about 4 to 10 feet. Foundation Ioadings 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 downhill and east 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. -2 Site Conditions: The lot is vacant. Vegetation consists of a pinion and juniper forest with a sparse ground cover of grass and weeds. The property is located on a south facing hillside. The ground surface slopes down to the south at a grade of about I3 percent in the building area. Numerous basalt cobbles and boulders are visible on the ground surface. Subsidence Potential: Callicotte Ranch 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. A sinkhole has been mapped about 1700 feet northwest of Lot 5. Sinkholes were not observed in the immediate area of the subject lot. The pits excavated for this study were shaIIow, for foundation design only. 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 Lot 5 is low and similar to other Tots 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 1. Pit 2 was dug between the septic area and house and is considered to also be the second profile pit in the septic area. The logs of the pits are presented on Figure 2. The subsoils encountered, below about one foot of topsoil, consist of basalt gravel, cobbles and boulders in a sand and silt matrix. Results of a gradation analysis performed on a sample of slightly silty sandy gravel (minus 3 inch fraction) obtained from Pit 2 are presented on Figure 3. Results of a USDA soil texture gradation analysis performed on a sample of slightly silty sandy gravel (minus 3 inch fraction) obtained from Profile Pit 1 are presented on Figure 4. The laboratory test results are summarized in Table I. 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 granular basalt rock soil designed for an allowable soil bearing H-PviKUMAR Protect No. 17-7-349 slab -on -grade construction, -3 pressure of 2,000 psf for support of the proposed residence The matrix soils tend to compress after wetting and there could be some post -construction foundation settlement. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. Loose and disturbed soils at the foundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural soils. Voids created from boulder removal at footing grade should be filled with compacted road base or concrete. 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 based on an equivalent fluid unit weight of at least 50 pcf for the on-site soil as backfill. Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded 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 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 least 95% of maximum standard Proctor density at a moisture content near optimum. Required fill should be a road base type material. Underdrain System: Although free water was not encountered during our exploration, it has been our experience in mountainous areas 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 and W-PkKUMAR Project No, 17-7-349 -4 - 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 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. 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. 5) Landscaping which requires regular heavy irrigation should be located at least 10 feet from the building. Consideration should be given to the use of xeriscape to limit potential wetting of soils below the building caused by irrigation. H-PkKUMAR Proiect No. 17-7-349 -5 - Percolation Testing: The soil texture and structure conditions in the proposed septic disposal area were evaluated by excavating two profile pits at the approximate locations shown on Figure 1 and performing percolation testing. The logs of the profile pits are presented on Figure 2. The subsoils encountered consist of topsoil overlying basalt gravel, cobbles and boulders in a sand and silt matrix. Results of a USDA gradation analysis performed on a sample of extremely gravelly sand with cobbles (minus 5 inch fraction) obtained from the site are presented on Figure 5. The soil type based on gradation analysis is 0 due to the rock content. No free water or evidence of seasonal perched water was observed in the pits at the time of excavation and the soils were slightly moist to moist. Percolation tests were conducted on June 8, 2017 to further evaluate the feasibility of an infiltration septic disposal system at the site. Three percolation holes were dug at the locations shown on Figure 1. Test holes were hand dug and soaked with water one day prior to testing. The soils exposed in the percolation holes are similar to those exposed in the Profile Pits. The tests were conducted in the granular soils below the topsoil. The percolation test results are presented in Table 2. percolation test results, the tested area and subsoils should be suitable for a septic disposal system. A civil engineer should design the infiltration septic disposal system. Based on the subsurface conditions encountered in the profile pits and the 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 expressed 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 I, 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 construction appear different from those described in this report, we should be notified at once so re-evaluation of the recommendations may be made. H-PkKUMAR Project No. 17-7-349 -6 - 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, Louis E. Eller Reviewed by: Daniel E. Hardin, P.E i 'ra 2444 LEE/kac /7 • �s f7'r •tip`'; ii[ +`s"� attachments Figure 1 — Loca ii r'i of Exploratory Pits and Percolation Test Holes Figure 2 — Logs, Legend and Notes of Exploratory Pits Figure 3 ®- Gradation Test Results Figure 4 — USDA Soil Texture Gradation Test Results Table 1 — Summary of Laboratory Test Results Table 2 -- Percolation Test Results H-PkKUMAR Prniprt Nn 17.7.QAQ L 17-7-349 LOT 3 3' 3' 3' \ t / LOT 4 i -- \ / \` a -- \f Ib' I 1 \ \\\ \ aRaPosED P 1 \ I \ RESIDENCE 4 AP 2 \\ I r • PIT ,\ ' ,r6;" PIT 1 % p 3 •PRROFI1 LE / \ \ \ % \ \ / \\ .� 3' \<\ \ LOT 5 f / 3' / /.0) ■ r r H-PMKUMAR 7 30 0 30 60 APPROXIMATE SCALE -FEET LOCATION OF EXPLORATORY PITS AND PERCOLATION TEST HOLES Fig. 1 --- 0 10 PIT 1 EL. 6809' a LEGEND PIT 2/PROFILE PIT 2 EL. 6801' �$ +4=79 -� -200=5 PROFILE PIT 1 EL. 6794' 'Z. 0/4 0 0 -� GRAVEL=83 -$ SAND=13 SILT=3 CLAY=1 TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, SLIGHTLY MOIST, BLACK TO DARK BROWN. BASALT GRAVEL, COBBLES AND BOULDERS IN A SAND AND SILT MATRIX, DENSE, SLIGHTLY MOIST, LIGHT BROWN, CALCAREOUS. 0 - DISTURBED BULK SAMPLE. NOTES 0- -- 5- 5-- 10- 10- 1. 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A DEERE 490E TRACKHOE ON JUNE 2 AND 8, 2017. 2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED. 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 THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF DRILLING. PITS WERE BACKFILLED SUBSEOUENT TO SAMPLING. 7. LABORATORY TEST RESULTS: +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422); -200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140); 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 THAN PARTICLE SIZE .002mm. w W la. x 1- a 17-7-349 H-P-KIJMAR LOGS OF EXPLORATORY PITS Fig. 2 PERCENT RETAINED € HYDROMETER ANALYSIS 1 gq33��AA H� TIME READINGS U S STANDARD SERIES I 0 451NIN 15 MIN 60MIN19MlN 4 MIN.1 MI#325 #140 *60 *35 *18 #10 #4 SIEVE ANALYSIS CLEAR SQUARE OPENINGS 3/8' 314' 1 1/2' 3' 5'6' 8' 100 10 20 30 40 50 60 70 80 90 100 001 002 005 .009 .019 .045 106 025 500 100 2.00 DIAMETER OF PARTICLES IN MILOMETERS 90 80 70 60 50 40 30 20 10 4 75 9 5 19.0 37 5 76 2 152 203 0 Cur StT GRAVEL 83 % SAND 13 % SILT 3 % CLAY 1 % USDA SOIL TYPE: Extremely Gravelly Sand with Cobbles FROM: Profile Pit 1 @ 17-7-349 USDA GRADATION TEST RESULTS PERCENT PASSING Fig. 4 H-PKUMAR TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 17-7-349 SAMPLE LOCATION NATURAL MOISTURE CONTENT I (%) NATURAL DRY DENSITY (pcfA ) GRADATION PERCENT PASSING NO. 200 SIEVE USDA SOIL TEXTURE SOIL TYPE PIT DEPTH (ft) GRAVEL l (%) SAND (%) GRAVEL (%) SAND (%) SILT (%) CLAY (%) 2 5 to 6 79 16 5 Slightly Silty Sandy Gravel Profile3 to 4 Pit 1 83 13 3 1 Extremely Gravelly Sand with Cobbles f HOLE NO. P1 P2 P3 HOLE DEPTH (INCHES) 20 H-P�KUMAR TABLE 2 PERCOLATION TEST RESULTS LENGTH OF INTERVAL (MIN) 15 Water added Water added Water added Water added Water added 23 19 15 Water added Water added Water added Water added Water added PROJECT NO. 17-7-349 WATER WATER DROP IN DEPTH AT DEPTH AT WATER START OF END OF LEVEL INTERVAL INTERVAL (INCHES) (INCHES) (INCHES) 7 74/4 43/4 21/4 4' 3 6'/2 31/2 3 53/4 31/2 21/4 4 21/4 1'/4 4 21/4 1% AVERAGE PERCOLATION RATE (MIN./INCH) 4 2 2 43/4 23A 2 15 Water added Water added Water added Water added 4 3 23/4 23/4 6 23/4 1'/4 11/2 11/2 1'/4 11/2 1'/4 11/2 911 10/1 2'/4 33/4 63/4 33/4 3 6'/4 31/4 3 53/4 3 2% 3 1/3 33/4 21/2 11/4 2'/2 6/1 Note: Percolation test holes were hand dug and soaked on June 7, 2017. Percolation tests were conducted on June 8, 2017. The average percolation rates were based on the last two readings of each test.