Loading...
HomeMy WebLinkAboutPermit Field Test & Inspection Report 2003-10-10 .... -a K & A Engineering, Inc. P.O, Box 23624, Eugene, OR 97402 521 Market St., Suite B, Eugene, OR 97402 (541) 684-9399 Voice (541) 684-9358 FAX engineering October 10, 2003 Project: 134.03 Stapleton Timber and Excavation 38141 Place Road Fall Creek, OR 97438 Subject: Geotechnical Site Evaluation 458 So. 72"d St. Springfield, OR ,. PURPOSE AND SCOPE , As requested, K & A Engineering, Inc. has evaluated the subject residential building site for suitability to construct a conventional concrete cast-in-place strip and spread footing foundation supporting a conventionally wood-framed one or two-story single-family residence. This evaluation includes recommendations for preparation of the foundation soils to support the foundation. INVESTIGATION AND FINDINGS General Our investigation was conducted at the beginning of excavation operations for foundation preparation. The site is located on a north-facing slope at the end of a cul-de-sac. The natural ground slope varies between 15 and 20%. There are no indications of slope movement on this lot or other residential lots (most of which are presently occupied) adjacent to the site. ~ Subsurface Soils Foundation soils revealed in the excavator consisted of 2 to 4-feet of unspecified loose fills (mostly silts and gravelly silts) over the original ground surface. Soils below the original ground surface consisted of 1 to 3-feet of moist, moderately stiff, brown plastic silts or tan, saturated, highly plastic clays. Soft, weathered tuff underlies the plastic silts and clays Groundwater was not encountered in the excavation, which ranged from 3 to 7 -feet [n depth. SUMMARY AND RECOMMENDATIONS General The existing soils at the site are not suitable for supporting the proposed foundation. The loose fills do not provide a consistent allowable bearing capacity. The underlying native soft plastic silts and clays are highly expansive and would likely present a significant hazard associated with consolidation (settlement) over time. K & A Engineering, IDe, Foundation Preparation To make the site suitable for construction of the proposed foundation, we make the following recommendations. 1. The unspecified fill should be removed from the foundation area. These soils are suitable for landscaping and final grading around the foundation after construction is complete. 2. The underlying plastic sitts and clays should be removed from the site entirely. The site should be prepared so that the underlying weathered tuff is smooth and undisturbed. Benched excavation is acceptable to accommodate the natural slope as long as the benches are horizontal and uniform in grade and width. 3. The foundation area should be brought to the proper grade by placing a coarse select granular fill on the undisturbed weathered tuff to within 6 to 12-inches of final grade, and covered with a fine select granular fill to footing grade. 4. A perimeter footing drain should be installed around the back (uphill) and sides of the foundation to intercept water and route it away from the foundation. 5. We recommend that a crawlspace drain be installed underneath the foundation. This should be installed at the time that the foundation is constructed. Specifications Coarse Select Granular Fill Coarse select granular fill can consist of a well-graded silty-sandy-gravel pit run or a 3 to 5-inch open graded crushed quarry rock. Well-graded pit run should have less than 15% of the material (by weight) passing the no. 200 sieve and no fragments larger than 4-inches. Well-graded pit run should be placed in layers not exceeding 12-inches and compacted with a heavy steel-wheeled vibratory drum roller until there is no significant deflection along the sides of the roller. Moisture content of the pit run should be at or near optimum to avoid pumping of fines from the material and to promote maximum dry density. Quarry rock should consist of durable crushed basatt rock having a uniform gradation in the 3 to 5-inch range. Crushed quarry rock should have 100% fractured faces. Quarry rock should be placed in layers not exceeding 12-inches and well-seated in place with the back of the excavator bucket. Fine Select Granular Fill Fine select granular fill should consist of clean, durable, well-graded material with a maximum particle size of 1 1/2-inches and a maximum of 10% passing the no. 200 sieve. Select granular fill shall be placed in layers not to exceed 12-inches (loose) and mechanically compacted to a dry density exceeding 95% of maximum as determined by ASTM 0698. Footing Drain The footing drain should consist of a 3-inch diameter, continuous perforated pipe placed at the outside of the bottom of the footing. The perforated pipe should be covered on the sides and top with a minimum of 12- inches of %-inch to 1 lh-inch clean drain rock covered with a non-woven geotextile. The footing drain should be routed to the storm drain system and should not be connected to the roof drain system. Project: 134.03 458 So. 72nd St., Springfield, OR Client: Stapleton Timber and Excavation Page 2 of 2 October 10,2003 ~ K & A Engineering, Inc. Crawlspace Drain A minimum of one 3-inch diameter schedule 40 PVC or ABS solid pipe should be placed undemeath the footing at a low point along the front (north) footing to drain any water that may collect in the crawlspace. The crawlspace drain may be connected to the footing drain system north of the foundation. Non-woven Geotextile Geotextile used to separate the native soils from the footing drain should consist of a light to medium-weight needle-punched, non-woven polypropylene fabric having an ADS of 70. The fabric should not have any tears or punctures. Lap the fabric a minimum of 12-inches at the top of the drain rock and at splices. LIMITATIONS OF THIS REPORT This report has been prepared for the exclusive use of Stapleton Timber and Excavation and its design consultants for the subject proposed structure. This geotechnical investigation, analysis, and recommendations meet the standards of care of competent geotechnical engineers providing similar services at the time these services were provided. We do not warrant or guarantee these recommendations, site surface, or subsurface conditions. Exploration test holes indicate soil conditions only at specific locations (i.e. the test hole locations) to the depths penetrated. They do not necessarily reflect soiVrock materials or groundwater conditions that exist between or beyond exploration locations or limits. The scope of our services does not include construction safety precautions, techniques, sequences, or procedures, except as specifically recommended in this report. Our services should not be interpreted as an environmental assessment of site conditions. Thank you for the opportunity to be of service. Please call us if you have questions or need further assistance. Respectfully, EXPIRES l1/kL / ""/ . I Michael Remboldt, P.E. Principle, K & A Engineering, Inc. Project: 134.03 458 So. 7200 St., Springfield, OR Client: Stapleton Timber and Excavation Page 3 of 3 October 10,2003