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HomeMy WebLinkAboutPermit Correspondence 1996-12-29 '~ 1 . s OREGON / ',,--GEOTECHNICAL "'-. '" " SERVICES "- ~ December 29, 1996 To: Mr. Steve Jokinen Jokinen Construction 28120 Royal Ave Eugene, OR 97402 (541) 345-1458 CC: Branch Engineering 310 North 5th Street Springfield, OR 97477 (541) 746-0637 Re: Soil and Subgrade Inspection: Duplex at ClitTside Manor, 6291 Aster St, Springfield, Oregon. The purpose of this letter is to record that on December 26, 1996 Oregon Geotechnical Services staff provided inspection of the excavation and site preparation at the above mentioned property, to document conditions of the native soil and subgrade and to provide recommendations for the placement of foundations and drainage at this site. This work was performed by David E. Reich, Certified Engineering Geologist (OR Lie. # E1227) of Oregon Geotechnical Services, 38401 Place Rd., Fall Creek, OR 97438 This work consisted of visual inspection of the building site, subsurface sampling, and manual testing and inspection of the subgrade at the site to verify bearing capacity and assess the soil material. The lot consists of a steep north sloping (35% - 55%) building site, above and to the south of Aster St. The building area had been excavated out of the hill and consists of a pad approximately 60 ft wide by 30 ft deep. The back wall of the excavation consists of two cuts, each approximately 7 feet high, separated by a 4 to 5 foot bench. The lot is accessed by a driveway, cut into the low bank at the north edge of the lot. The existing cuts provided excellent exposure of the subsurface materials and conditions at the site. There is a cat road extending from the end of63rd Street, southwest, up the hill behind the lot. At the time of this investigation, a small stream was flowing down the road above the lot. The surficial soil consists of dark brown sandy silt with rock fragments of basaltic material (field classified as USCS: MH) to a depth of approximately 1'/2 feet below the surface. The surticial soils were moist to wet, soft and above the plastic limit at the time of our investigation. The upper soil unit has medium plasticity, and low toughness, slow dilatency and medium to high dry strength. The surficial soil is underlain by approximately 6.5 feet of brown sandy clay with rock fragments (field classified as USCS: CH). The clay soils were moist to wet, highly plastic and varied in consistency from soft to firm, depending on the degree of saturation. The clay soil unit has high plasticity, and high toughness, no dilatency and high to very high dry strength, Beneath the clay, at approximately 8 teet be/ow the surface, hard basaltic bedrock was encountered, and will provide suitable bearing capacity, little or no reaction to wetting and drying (shrink-swell) C!inside Duplex, 63'. & Aster, 12/96 Oregun Geotechnical St.'1Viees 38401 Place Road, Fall Creek, OR 97438 (541) 937-8747 .,-;:. fi , and minimal long term settlement potential. Water was flowing rapidly out of two seep a~eas in the back cutslope, at approximately 7 feet below the surface. The existing gravel backfill is approximately 6to 12 inches thick, and composed of lY2 inch minus base with % minus, surfacing. Test holes into the gravel showed that..water was was not draining off of the subgrade, and saturating the gravel. The origin of the thick soils at this site can be attributed to a process called soil creep, and although there' is evidence for this creep (bent trees and soil characteristics), there. is no evidence at this time for anyslope stabilityproblerns, However, the water flowing un<;ontrolled in the road above'the lot may lead to saturation of the soils and failure of the cutslope. Recommendations: In order to provide 1) adequate bearing capacity, 2) limited shrink-swell reactions in the clay soil, and 3) long term dniinage and protection from moisture, the following recommendations should be adhered to. , All footing areas that are placed on clay soils should be over-excavated and backfilled with approximately 18 inches compacted crushed rock (l1;2minus for base and % minus or similar for finish). A geotextile fabric barrier should be pLaced between the clay soil and the rock, or alternatively a lift of coarse crushed rock can be placed directly onto the clay, and compacted into the clay soil. . The footing pads for the south side of the house, that will support the back retaining wall appear to have been excavated into basaltic bedrock, and then backfilled with crushed rock to desired gr~de (l Y2 minus for base and % minus or similar for finish). This material will be disturbed to install the necessary drainage, and should be machine compacted when replaced. A perforated drain line (4" perforated ABS or PVC) should be placed on the sub grade at the base of the gravel backfill to provide drainage. The drain can be installed in a trench excavated around the perimeter of the building pad and sloped to drain to the north,.around the sides of the building toward the street. ,Compaction of the gravel should ri'ot be attempted untilthis dranige has been established and allowed to drain the standing water out of the gravel. Drainage control at the site should include a standard perimeter drain around the building, and the retaining wall drainage should be constructed as shown in the attached figure: Retaining Wall Drainage Detail. In addition, roof drains (downspouts) should be piped away from the footings, and all storm runoff and surface flow should be directed away from the structure. Ground surfaces and any impervious surfaces should be sloped or designed to drain to the street, and in no case should runoff be allowed to concentrate and flow across the existing cutslopes. Compaction testing will be required by the City for tills greater than 12 inches in thickness. This work will performed by another service provider, or by Oregon Geotechnical Services under separate cover. Cli1fside Duplex, 63<<1 & Asll:r, 12/96 Oregon Geotechnical ServiceS 2 > ~ Based on manual consistency tests on in-place native materials, and the material characteristics as defined by the Unified Soil Classification System and the Unified Rock Classification System, the site is suit;1ble for building, and a bearing capacity of 1000 PSF can safely be used at this site provided the above recommendations are followed, and adequate drainage has been established, and is maintained at the site. Limitations: This report was prepared for the exclusive use of Jokinen Construction and its authorized agents. , This report provides an analysis of soil bearing capacity and general construction recommendations regarding soils and drainage. This report does not provide specific fOtUldation or retaining wall designs or rigorous slope stability analysis. Professional services were rendered in accordance with generally accepted geotechnical services, and using the degree of care and skill ordinarily exercised under similar circumstances by firms or individuals practicing in similar locations. Analysis, conclusions and recommendations included in this report relate to conditions at the time the services were performed. Data was accumulated from overall site reconnaissance and limited subsurface exploration in select locations. In the event that changes in the nature, design or layout of the project are made, the conclusions and recommendations contained in this report shall not be considered valid unless the changes are reviewed arid verified in writing. If there are any questions or comments, please call me at 937..;8747 Sincer~ly, Oregon Geotechnical Services ~'~, David E. Reich, PG, CEG , Attachments ClitTside Duplex, 63'd & Aster, 12196 Oregon Geotechnical Services , Waterproof wall face to avoid dampness ,. '. " r ), ~~~J JOG nl \ s\ Slope surface to drain away from structure Select Fill W~ Geotextile Wrap (Filter Fabric) , , , , , . , , . , , , .' 'I / / / /' / / /' /' /' /' /' /' / /1 /' /' /' / t .; ... /' ,I' '" ,; ,/ ,/ /! / / / I Filter Materia I~ /:' , /' /' /' /' /' /' /' /' /' /' /' /' / /1.; : /' /' /' ... ... '" ". " ./ " ./ ... /' /1 · ' -112" Minimum!---r / / /' / / / / /' / / / ~ ~ ~1 /' /' /' /' / /' /' /' /' /' /' /' /' /' , /' /' /' /' /' /' /' /' /' /' /' /' /' /' , /' / /' /' /' /' /' /' / /' /' /' /' /, ',~ :. "~I ~ 4" Perforated Pip~ / / / / / / / / / / / / / /1 / / /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' / /' / / /' /' /' /' /' /' /' /' / / / / / / / / / / / / / / Corrugated Insulating Board /' /' /' /' /' /' /' /' /' /' /' /' /' /' - ~- , / / /' /' /' /' /' /' /' /' /' /' SLAB /' /' /' /' / /' /' /' /' /' /' /' /' /' /' /' /' /' /' / /' /' /' /' / /' /' /' /' /' /' /' /' /' /' /' / /' /' /' /' /1 / / / / / / / / / / / / / /11' /' /' /' /' / / / / / / / /) 14" Perforated Pivel /' / /' /' / /' / /' / /' V /' /' /' /' /: ,/ /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' / /' /' /' /' /' /' /' /' /' /' / /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' I/'/' /' /' /' /' /' /' /' / /' /' /' / /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' ,1---<\ /' I / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / i, )/ 4" PVC Subgrade Drain /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' /' / / / / / / / / / / / / / / >----f / ~ \t...~/ ) '---"" Perforated drain pipe shall be placed at the base of the wall, as shown, An additional horizontal pipe shall be placed at approx. 1/2 wall height. Perforated Pipe to consisit of PVC or suitable alternative (ABS), 4" minimum diameter, perforated drain line Drain pipes shall be wrapped in filter fabric and bedded in about 4-6" of filter material, prior to burial with backfill A Corrugated Insulating board installed against wall will aid in vertical drainage Fliter Material for use in backfilling behind retaining wall shall consisit of free-draining,open-graded, crushed rock or river gravels Geotextiles (filter fabric) shall consist of woven monofilament or felt fabric consisting of long-chain polymeric filaments such as polypropylene, polyethylene, or PVc. (~ (t?) OREGON RetaininCi Wail' & Draina{;Je betaTi"'. 6291 Aster St, Sl?rin~fjeld, OR Not to Scale DER 12/96 GEOTECHNICAL SERVICES 38401 Place Rd. Fall Creek, OR 97438 '