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HomeMy WebLinkAbout03333 1 Hepworth- I'awlak Geoteclmical, Inc. � �/��(/�► V V� 5020 County Road 154 Glenwood Springs, Colorado 816111 Phone: 970 - 945 -7988 • Fax: 970 - 945 -8454 hpgeo ©hpgeolech.com March 21, 2000 Lonnie and Anita Bones 1041 Heritage Drive Carbondale, Colorado 81623 Job No. 100 227 Subject: Subsoil Study for Foundation Design and Percolation Test, Proposed Residence, Lot 6, Teller Springs, County Road 109, Garfield County, Colorado. Dear Mr. and Mrs. Bones: 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 February 28, 2000. 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 two story wood frame structure located in the eastern (downhill) portion of the lot as shown on Fig. 1. Ground floors will be structural over crawlspace or a slab -on -grade basement level. Cut depths are expected to range between about 4 to 8 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 about 40 to 50 feet to the northwest of the proposed building area. 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 field work. The property is a previously irrigated field. An irrigation ditch transects the middle portion of the lot. The ground surface is relatively flat with a slight slope down to the east. There is about 2 to 3 feet of elevation difference in the proposed building area. A steep slope down to a lower terrace and the Roaring Fork River is located to the east of the lot. The lot is vegetated with sagebrush, grass and weeds. • Lonnie and Anita Bones March 21, 2000 Page 3 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 soils, excluding oversized rock, as backfill. Floor Slabs: The natural on -site soils, exclusive of topsoil, are suitable to support lightly loaded slab -on -grade construction. The upper clay soils appear expansive when wetted which could result in some floor slab heave. The clays could be removed to prevent potential heave. 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 can consist of the on -site gravels devoid of vegetation, topsoil and oversized rock. Underdrain System: Although free water was not encountered during our exploration, it has been our experience in area 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 9rawlspace and basement areas, be protected from wetting and hydrostatic pressure _ buildup by an underdrain system. An underdrain should not be needed for crawlspace areas shallower than about 3 feet provided a positive surface slope is maintained around .the building and the exterior wall backfill is properly compacted . 4 r 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. H -P GEOTECH • Lonnie and Anita Bones March 21, 2000 Page 4 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 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: Percolation tests were conducted on March 16, 2000 to evaluate the feasibility of an infiltration septic disposal system at the site. One profile pit and three percolation holes were dug at the locations shown on Fig. 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 one day prior to testing. The soils exposed in the percolation holes are similar to those exposed in the Profile Pit shown on Fig. 2 and consist of about 1 foot of topsoil and 2 feet of sandy silty clay overlying slightly silty sandy gravel with cobbles and scattered boulders. The percolation test results are presented in Table II. The percolation test results indicate an infiltration rate between 7 and 13 minutes per inch with an average of 9 minutes per inch. Based on the subsurface conditions encountered and the percolation test results, the tested area should be suitable for a conventional 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 Fig. 1, the proposed type of construction and our experience in the area. Our findings include interpolation and extrapolation of the subsurface conditions identified at the exploratory pits and variations in the subsurface conditions H -P GEOTECH • . I HYDROMETER ANALYSIS I SERE ANALYSIS I TIME READINGS U.S. STANDARD SERIES 1 CLEAR SQUARE OPENINGS 24 HR. 7 HR 45 MN. 15 MIN. 60 MN.10 MN. 4 MIN" 1 MN. /200 /I00 00 /30 116 /6 /4 3/6'1/2'3/4' 1 I/2' 3' S'6' 6 Q 100 1 so I 10 w ; 20 70 30 I 0 Z 60 4 0 Z (71 I 1-- a n ce F- F Z S0 1 w W w I 0 a w d a so 40 30 I 70 20 I , .... 60 I I 90 10 I I 100 0 .001 .002 .005 .000 .010 .037 .074 .150 .300 .600 1.16 2.36 4.75 9.5 19.0 37.5 76.2 12752 203 DIAMETER OF PARTICLES IN MILLIMETERS DIAY To SIL 1 N sANO 1 _ EA'YEL coARSE i COSOI.Es GRAVEL 68 % SAND 22 % SILT AND CLAY 10 % LIQUID LIMIT % PLASTICITY INDEX SAMPLE OF: Slightly Silty Sandy FROM: Pit 2 at 3 to 4 Feet Gravel with Cobbles 100 227 I H E WO ECHNIC PAWLAK 1 GRADATION TEST RESULTS I Fig. 4 ,( rn 6 ƒ o g �„ , / \\ ) /] | � 2 z 2|■ 2 \ 4 ] g 2 j \ + I e | o |2 §__ $§/ _ƒ _ . J$g |■§§ _ 0 E } | |;° ° . R.. o & �. R \ \ 05 \ I w | « 2 1 . l,r §`L . , § §| { , t / r c2E , a