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HomeMy WebLinkAboutSubsoil Study for Foundation Design and Perc Test Result 11.15.18MAR titeatechnitigi Enginearing Engineering. Geology Materials Testing Environmental 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax: (970) 945-8454 Email: hpkglenwood@kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado November 15, 2018 Uriel Mellin 144 Cliffrose Way Glenwood Springs, Colorado 81601 Project No.18-7-634 Subject: Subsoil Study for Foundation Design and Percolation Testing, Proposed Residence, Lot 6, Callicotte Ranch, Pinyon Woods Lane, Garfield County, Colorado Dear Uriel: As requested, H-P/Kumar performed a subsoil study and percolation testing 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 October 17, 2018. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Proposed Construction: The proposed residence will be a one story wood fame structure over a partial basement/partial crawlspace located in the area of Pits 1 and 2 shown on Figure 1. Ground floors are proposed to be structural over crawlspace or slab -on -grade. Cut depths are expected to range between about 3 to 10 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 to the northeast 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 site was vacant at the time of our site visit. The lot slopes moderately down to the east-southeast at about 15% grade. The lot is vegetated with pinyon and juniper trees with an understory of grass and weeds. Scattered basalt cobbles were observed 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 2 - certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. During previous work in the area, a sinkhole was observed about 2,000 feet to the northeast of Lot 6, outside the Callicotte Ranch development. Sinkholes were not observed in the immediate area of the subject lot. 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 6 is low throughout the service life of the residence and similar to other lots 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 general building area and two profile pits in the designated 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 1 to 11/2 feet of topsoil, consist of 1 to 11/2 feet of stiff, silty sandy clay overlying 2 to 31/2 feet of basalt gravel, cobbles and boulders in a highly calcareous sandy silt matrix in Pits 1 and 2. Refusal to backhoe digging was encountered at 6 feet in Pit 1 and at 41/2 feet in Pit 2. Results of Atterberg limits testing performed on a disturbed sample of the sandy silt matrix soils, indicate the matrix soils are a high plasticity silt. 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. Foundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, spread footings placed on the undisturbed natural soil designed for an allowable soil bearing pressure of 2,000 psf can be used for support of the proposed residence. The soils tend to compress after wetting and there could be post -construction foundation settlement. Footings should be a minimum width of 18 inches for continuous walls and 2 feet for columns. Loose and disturbed soils encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural 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 12 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, can be used to support lightly loaded slab -on -grade construction with a differential settlement risk. To reduce the effects of some H-P*KUMAR Project No. 18-7-634 -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 least 95% of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on- site 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 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, crawlspace and basement areas, an underdrain system. be protected from wetting and hydrostatic pressure buildup by 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 11/2 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 capped with about 2 feet of the on-site, finer graded soils to reduce surface water infiltration. H-PKGUMAR Project No. 18-7-634 -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 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 the building. Consideration should be given to the use of xeriscape to limit potential wetting of soils below the building caused by irrigation. Percolation Testing: Percolation tests were conducted on October 23, 2018 to evaluate the feasibility of an infiltration septic disposal system at the site. Two profile pits and three percolation holes were dug at the locations shown on Figure 1. The test holes (nominal 12 inch diameter by 12 inch deep) were hand dug at the bottom of shallow backhoe pits and were soaked with water prior to testing. The soils exposed in the percolation holes are similar to those exposed in the Profile Pits shown on Figure 2 and consist of very gravelly sand and very gravelly sandy loam. Results of gradation analyses performed on samples of the very gravelly sand and very gravelly sandy loam (minus 3 -inch fraction) obtained from Profile Pits 1 and 2 are presented on Figures 4 and 5. The percolation test results are presented in Table 2. Based on the subsurface conditions encountered and the percolation test results, the tested area should be suitable for a conventional infiltration septic disposal system. A civil engineer should design the infiltration 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 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 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 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-PvKUNIR Project No. 18-7-634 -5 - 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, H -P- KUMAR Daniel E. Hardin, P.E. Reviewed by: Steven L. Pawlak, P.E. DEH/kac attachments Figure 1 — Location of Exploratory Pits Figure 2 — Logs of Exploratory Pits Figure 3 — Legend and Notes Figures 4 and 5 — USDA Gradation Test Results Table 1 — Summary of Laboratory Test Results Table 2 — Percolation Test Results cc: Patrick Stukey H-P%KUMAR Project No. 18-7-634 / PROFILE PIT 2 • ,P-1 P-2 P-346, ■ PROFILE PIT 1 25 0 25 50 APPROXIMATE SCALE—FEET 4757.89 67'1S qz 18-7-634 H-P--4:4KUMAR LOCATION OF EXPLORATORY PITS Fig. 1 COlco1e Rene%\ Ere/41,187534-02 Iv C3.dwc 0 5 PIT 1 EL. 6771' WC=12.7 LL=55 P1=8 —200=27 PIT 2 EL. 6761' PROFILE PIT 1 EL. 6761' PROFILE PIT 2 EL. 6762' GRAVEL=49 —I SAND=44 SILT=4 CLAY=3 GRAVEL=37 _r SAND=16 SILT=29 CLAY=18 0 5 — 10 10 18-7-634 H-P--KUMAR LOGS OF EXPLORATORY PITS 1- W w a w 0 Fig. 2 7cne!AF4aelEng\: 87534-02 to LEGEND f TOPSOIL, ORGANIC SANDY SILT AND CLAY, FIRM, MOIST, DARK BROWN. CLAY (CL), SILTY, SANDY, STIFF, SLIGHTLY MOIST, BROWN. BASALT GRAVEL, COBBLES AND BOULDERS (GM) IN A SANDY SILT MATRIX, WHITE, DENSE, SLIGHTLY MOIST, CALCAREOUS. GRAVEL (GM—GC) SANDY, SILTY, CLAYEY, DENSE, SLIGHTLY MOIST, WHITE, CALCAREOUS. PROFILE PIT 2 ONLY. Sl HAND DRIVEN LINER SAMPLE. DISTURBED BULK SAMPLE. t PRACTICAL DIGGING REFUSAL. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON OCTOBER 22, 2018. 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 DIGGING. PITS WERE BACKFILLED SUBSEQUENT TO SAMPLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216); —200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140); LL = LIQUID LIMIT (ASTM D 4318); PI = PLASTICITY INDEX (ASTM D 4318); 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 18-7-634 H-P�KLIMAR LEGEND AND NOTES Fig. 3 e! 1) 2018 Medi, and PtIC6ICI,,..1 -4 N.r.CALVO— 18-7-634 PERCENT RETAINED = co 5 . c<) • i r. - 1 I .1) 8 K > 77 0 JD C ci) > . ...§, 1 1 —i K 0 73 9,1 < 0 rn I— ' • I . 1 I I 1 --t 11 . cn> R rn —I m I (r) 0 r= co , 1 i 2 —I -c. -0 e 171 1 1 , a, 1 1 " .F,1 i i 1 it i < ..z c) < -.. 0 a.a i 1 Z CD< 0 •• .. m 1 —1 M i b C * • USDA GRADATION TEST RESULTS DO 1 —Om . g W r- M U) 0 CD Ai. m cn L, m i= —1 -r. , m DJ cn 6 ITI < m 0 KI in.$ - • . 1 1 : i i I 1 • 1 E 13 T 6 o c' I t 73. o., L_ ., • i , , . . 1 i 0 -. m .2 Z o.) Es 5; ' : • • z "2 OD LE -i. a § PERCENT PASSING . PERCENT RETAINED HYDROMETER ANALYSIS SIEVE ANALYSIS C . TIME READINGS U.S. STANDARD SERIES I CLEAR SQUARE OPENINGS 24 HR 045 MN. 10 20 30 40 50 60 70 80 90 71111 1519N. del. 181111 4 1 MIN. #325 #140 #60 #35 418 #10 #4 3/8° 3/4° 11/2° 3' 5°6' 100 90 70 60 100 .001 .002 .005 .009 .019 045 .106 .025 .500 1.00 2.00 4.75 9.5 19.0 37.5 76.2 152 203 CLAY 18-7-634 DIAMETER OF PARTICLES IN MILLIMETERS V. FINE -I FINE f ME{]d.IM i Cos E IY.♦70AABE1 SMALL 0:vm GRAVEL 37 % SAND- 16 % LAAOE COBBLES SILT 29 % CLAY 18 % USDA SOIL TYPE: Very Gravelly Sandy Loam FROM: Profile Pit 2 @ 3 to 4' H-P--A5KUMAP USDA GRADATION TEST RESULTS 50 40 30 20 10 0 PERCENT PASSING Fig. 5 1 r !SU IVAAN TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No.18-7-634 SAMPLE LOCATION PIT DEPTH 1 Profile Pit 1 Profile Pit 2 (ft) 4-41/2 3-4 3-4 NATURAL MOISTURE CONTENT (%) 12.7 NATURAL DRY DENSITY (pcf) ATTERBERG LIMITS LIQUID LIMIT (%) 5.5 PLASTICITY INDEX (%) 8 PERCENT PASSING NO, 200 SIEVE 27 USDA SOIL TEXTURE GRAVEL (%) SAND, (%) SILT (%) CLAY (%) 49 44 4 3 37 16 29 18 SOIL TYPE Silty Sandy Gravel with Cobbles Very Gravelly Sand Very Gravelly Sandy Loam TABLE 2 PERCOLATION TEST RESULTS PROJECT NO.18-7-634 HOLE NO. HOLE DEPTH (INCHES) 27 22 P-3 24 LENGTH OF INTERVAL (MIN) WATER DEPTH AT START OF INTERVAL (INCHES) 15 Water added 7'/ WATER DEPTH AT END OF INTERVAL (INCHES) 53/4 DROP IN WATER LEVEL (INCH ES) AVERAGE PERCOLATION RATE (MIN./INCH) 53/4 43/4 1 43/4 3%3 74 37/8 3% 1/2 6% 57/8 3/4 57/8 5'/4 15 Water added 6% 57/5 57/ 5%3 6 3/4 3A 24 51/ 41/2 41/2 4 5 1/2 6'/2 5'/ 5/8 5'/e 5'/4 8/ 26 15 Water added 61/4 51/2 3/4 51/2 43/4 3/4 4% 4%3 6 4%3 3% 3/4 8% 7% 7% 61/2 1 17 Note: Percolation test holes were hand dug in the bottom of backhoe pits. Percolation tests were conducted on October 23, 2018. The average percolation rates were based on the last three readings of each test.