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Report e z /'/ ci 7 • • ✓ a r1 s on Testing, Inc. Construction Inspection &Related Tes Geotechnical .Consultu P.O. Box 23814 February 18, 1997 Tgard, Oregon 97281 Phone (503) 684-3460 FAX (503) 684 -0954 CTI JOB NO. 96 -6022 Cascade Communities, Inc. 13535 SE 145th Avenue Clackamas, OR 97015 FINAL REPORT OF EARTHWORK OBSERVATION AND TESTING MOUNTAIN HIGHLANDS III TIGARD, OREGON Reference: MORNINGSTAR PROJECT, SOILS AND GRADING REPORT, Oakley Engineering,Inc., April 28, 1994. Carlson Testing Inc. (CTI), has conducted on -call inspection services for the earthwork at the • above residential development. This final letter briefly summarizes our observations and testing during construction, and the as -built soil conditions to the best of our knowledge. This letter also provides recommendations for foundation design and soil guidelines during • construction of the single - family homes. SITE PREPARATION AND FILL PLACEMENT Based on our visual observations and our density test results, after stripping vegetation and topsoil, engineered fill using on -site soil was moisture - conditioned and placed on the following areas to a maximum depth of approximately 15 feet: Lots 42 to 49 Based on the in -place soil density results and our visual observations, it is our opinion that the engineered fill on the above lots was generally placed in conformance with the standards of the City of Tigard. Lots 26 to 41 and 50 to 52 are cut lots or lots left near natural grade. The backfill placed in the sanitary sewer easement between Lots 46 and 47 and to the laterals was not compacted and has settled more than one foot. STRIPPINGS AND /OR EXCESS FILL Based on our observations, it appears that most of the topsoil strippings material was removed from the site. The strippings p pp�ngs and other unsuitable n through 51 before they were apparently removed. Du ng site I visit n 2-1 -97 i observed that approximately 12 inches of trench spoils and strippin fronts of Lots 42 to 52. There is a 2 to 3 foot high debris pile on g the front of of 33 n the northwest corner. • d CTI 96 -6022 Page 2 of 4 SLOPE STABILITY The original geotechnical investigation for this project was performed by others. CTI engineers observed the base of the fill placed along Lot boundaries 43/44 and 44/45 which included subdrains and were started with quarry run fill material before any soil fill was placed. The subdrains are flowing presently and these fills have performed well this winter compared to nearby natural slopes. We also observed the recent slope repairs on Lots 43, 46 and between Lots 28 and 29. More recently a new failure, initiated by excessive uphill storm runoff has occurred just east of Lot 29. Generally, the slopes near the creek become less stable up- canyon or in the southerly direction. We do not anticipate any stability concerns on Lots 47 through 52. Lots 31 through 34 have fill placed during previous phases and some thin dumped fill by builders; shallow slope creep was noted on Lots 31 and 34. Lots 30 and 35 through 41 will likely require cuts to construct future homes. We recommend that these cuts be made in the summertime to minimize the potential for adversely affecting existing residences above; any cut exceeding 8 feet in depth should be observed by a geotechnical engineer during excavation. The following Lots should definitely require a lot - by-lot geotechnical review: Lots 26 -29 and 42 through 46 We anticipate that Lots 26, and 27, may be founded on spread foundations, with some special considerations. These lots would be more stable with daylight basement homes. Lot 29 may likely be founded on spread foundations with a proper setback from the east slope where a recent failure occurred. Lots 28, and 42 through 46, are more steeply sloping or are very near steep slopes that have a moderate to high probability of failing in the future; these lots may require deep foundations or horizontal anchors to improve stability or they may be founded on spread foundations, subject to a geotechnical engineer's review. HOUSE EXCAVATION GUIDELINES We anticipate deeper than typical foundation excavation depths on most of the lots due to the sloping nature of the site. If excavated material is spread around the lot and is expected to support appurtenant structures such as deck footings and sidewalks, it should be placed, compacted, and tested as engineered fill. Under no circumstances should nonengineered fill be placed without observation over ground sloping steeper than 20 percent, or on flat ground more than 3 feet deep. • • r CTI 96 -6022 Page 3 of 4 STANDARD FOUNDATION RECOMMENDATIONS The proposed residential buildings on simple, relatively flat lots, will likely be founded on shallow spread footings bearing on competent native soils or engineered fill. Spread footing design and construction should generally conform to Chapter 4 of the CABO One and Two Family Dwelling Code (CABO), except where we specifically recommend otherwise. For protection against frost heave, spread footings on nonexpansive soils should have a minimum embedment depth of 12 inches for exterior grades on level ground. The recommended minimum widths for continuous wall footings are tabulated below: Minimum Width for No. of Stories Continuous Footing (floors supported) (in) 1 -story 12 2 -story 15 3 -story 18 We anticipate that the allowable bearing pressure can be taken as 1,500 lb/ft for footings bearing on competent native subsoils or engineered fill to a maximum of 15 kips for column footings. ,For heavier column loads and masonry chimneys, a Soil Engineer should be consulted. The coefficient of friction between on -site soil and poured -in -place concrete may be taken as 0.40. The maximum anticipated total and differential footing movements (generally from soil expansion and /or settlement) are 1 inch and 14 inch over a span of 20 feet, respectively; ref a el !d 1'' Ip +I l i -"- d CTI 96 -6022 Page 4 of 4 CLOSING AND LIMITATIONS . Our reports pertain to the materials tested/inspected only. This letter should be made available to each builder in the development: however, information contained herein is not to be reproduced, except in full, without prior authorization from this office. This letter should not be construed to relieve or lessen the responsibility of the contractor or owner's site representative for this site work, but is provided for the minimum required governmental assurance. Our support was given on an as- needed basis as requested. If conditions are encountered during foundation excavation which differ from this report, then the developer(Cascade Communities,lnc.), the contractor (Clearwater Construction), and CTI should be allowed to review the condition before corrective actions are taken. Corrective work performed by the builder without notifying the above parties will be interpreted as an acceptance of the conditions encountered. Respectfully submitted, CARLSON TESTING, INC. ��� PRpF � � co �NGIKfE si 14743 / OREGON '4f* „tik<• O. %Tow E - x� • James D. Imbrie, P.E. Geotechnical Engineer JLK Attachments: Summary report of in -place soil density tests cc: City of Tigard Clearwater Construction Company