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'arl on Testing, Inc. August 8, 1997 CTI #97-G1106 Construction Inspection & Relat~ Tests C~ot~ch~tc~l Cons~ P.O. Box 23814 'Rgard, Oregon 97281 Phone (5O3) 684-3460 FAX (503) 6844)954 Craig Roberts and Bob AIt(m 24085 and 24075 Butteville Road Aurora, OR 97002 ENGINEER'S RESPONSE TO MARION COUNTY FLOODPI.AIN PERMIT AND ENGINEERING REVIEW ROBERTS AND ALTUN RESIDENCES BUTTEVILLE, OREGON This letter is in response to the county's review of our geotechnical review of slope failure letter dated June 20, 1997. The Roberts and Alton residences are located along the Willamette River and are within the floodplain. Prior to approval, it is our understanding that the proposed slope stabilization work must be shown that it is anchc,-ed in such a manner to prevent flotation, collapse or lateral movement. The stabilization measures must also be shown to be in compliance with Section 178.060(c)(2). From our review of Section 178.060(c)(2)it appears that the only major concern is that the structure does not reduce the volume of the flood plain. Since the stabilization measures will incorporate substantially less volume than what natural slope slid into the river two winters ago, it is our opinion that there is no net volume reduction. The approximate old slope corffigoration as drawn from the homeowners recollections is shown on sheet I attached. The top of the proposed structure is abeet elevation 80 feet MSL. The structure will be a driven row of steel "H' HP10x42 piles emplaced 30 feet deep and retaining a maximum of 10 feet of free draining gravel that is gently sloped. The backfill is lagged between piles spaced 10 feet center to center using Holiowcore 4CF8 extruded concrete panels (4.7 strand). Since the material used have specific gravities much greater than water and no trapped air spaces, flotation or anchoring is not a problem. The geotechnical stabilization of the riverbank is primarily from the gravel emplacement. The soldier piles are placed merely to retain the toe of the gravel. From our check the steel Soil(tier piles have an allowable moment of 78,120 ft-lbs and the actual moment from the lateral gravel load is about 41,574 ft-lbs.,~he holiowcore panels selected have an 2 actual average lateral pressure of about 156 Ib/ft which is acceptable for a span of up to 16 feet. Our calculations are shown in the attached sheets 1 and 2. The panel manufacturers specifications are also attached. If further verification is necessary, such as to determine deflections, then we recommend that a structural engineer be consulted. In our opinion, the proposed structure meets the county requirements and will adequately resist lateral movement, Our reports pertain to the material tested/inspected only. Information contained herein is not to be reproduced, except in full, without prior authorization from this office. If there are any questions, please do not hesitate to contact this office. Respectfully submitted,