11-01-1990 - Re: Design of Timber Retaining Walls

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IEFERICKSON . ENGINEERING Consulting Engineers November 1, 1990 Jim Speich Aspen Landscape Inc. P.O. Box 834 Wayzata, MN 55391 RE: Design of Timber Retaining Walls at the Walker Residence in Orono, MN Dear Mr. Speich: I have completed the design of the retaining walls for the project referred to above. There are three cross-sectional drawings enclosed. Two of the drawings are for traditional header-and-deadman timber walls and one is for a timber wall reinforced with earth anchors. Also enclosed is a detail drawing showing how to connect the earth anchors to the timbers that make up the face of the wall. This design specifies Minuteman 650I earth anchors. If you decide to substitute Duckbill earth anchors instead, the equivalent model is 138-DB 1. Please check with me before substituting any other type or model of earth anchor. All of the hardware used to construct this wall should be hot- dip galvanized steel. The design specifies that the first two feet of soil behind the wall must be clean, free-draining sand. This will help prevent the buildup of water behind the wall, one of the major causes of wall failures. The design also specifies that a 6-inch layer of high-clay content soil should be placed on the top of the backfill. This will help keep water from entering the soil behind the wall. It is extremely important that the backfill soil be thoroughly compacted. I recommend that you use a vibrating plate compactor and compact the soil in lifts of not more than 1 foot. Finally, if you have any questions at all about this design,please feel free to call me at 929-6791. Thank you very much for allowing Erickson Engineering to provide the engineering design on this project. Sincerely, ERICKSON ENGINEERING COMPANY oseph A. Arsenault Enc. Erickson Engineering Company 3340 Republic Avenue St. Louis Park, Minnesota 55426 (612)929-6791