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2004, 11-17 Geotechnical Design EvalZ�����E T Materials Testing • Geotechnical Engineering LETTER OF TRANSMITTAL ATTENTION: Mr. Tom Loasdon COMPANY: PROJECT NAME: 1307 South Center DATE: November 17, 2004 PROJECT LOCATION: Spokane Valley, WA PROJECT #: 204-073 FROM: Paul Nelson (cw) # COPIES DATE, DESCRIPTION 2 11/17/04 Geotechnical Design Evaluation COMMENTS: Thank you for allowing us an opportunity to be of service to you. CC: 1010 N. Lake Road Spokane, WA 99212 (509)534-4411 Fax (509)534-9326 Z0 M ESQ' Materials Testing • Geotechnical Engineering November 17, 2004 Mr. Tom Logsdon:' 10511 East 8th Avenue Spokane Valley, WA 99206 Re: Geotechnical Design Evaluation Proposed Boulder Retaining Wall and Slope 1307 South Center Drive Spokane Valley, Washington Dear Mr. Logsdon, As you requested, we have completed the geotechnical evaluation of the boulder retaining wall and slope at the above -referenced site in Spokane Valley, Washington. The purpose of our services was to evaluate the stability of the as -constructed slope and wall and to evaluate the proposed design for the north portion of the wall. This letter presents the results of our site observations, evaluations, and conclusions. SITE OBSERVATIONS A geotechnical engineer visited the site on November 16, 2004. The existing wall (boulder rockery) extends from the east side of the property west along Beverly Drive and turns to the; north along Center Drive. The boulders along Beverly Drive range in size from approximately 4 to 8 feet in diameter. The rockery has an estimated batter of 2:1 (horizontal to vertical) along this section. The portion of the rockery beginning approximately 15 feet north of the southwest corner of the rockery was constructed steeper (approximately 1.5:1) and the boulder diameters were much smaller, most of which were smaller than approximately 2 feet in diameter. In addition, an open ditch is present along the roadway extending along the toe of the slope from the culvert outlet on the south side of the driveway to the intersection of Beverly and Center Drives. The driveway is present above this portion of the slope. The natural soils and fill soils consisted of coarse, clean, free - draining sands and gravels. These soil types are typical of this area and are reflected on the soil maps from the Soil Survey of Spokane County. 1010 N. Lake Road • Spokane, Washington 99212 • (509) 534-4411 • Fax (509) 534-9326 Geotechnical Evaluation Proposed Boulder Retaining Wall 204-073 Page 2 CONCLUSIONS AND RECOMMENDATIONS Based on our site observations, it is our opinion that the portion of the rockery along the south side of the site to approximately 15 feet north of the southwest corner has been adequately constructed and will provide suitable long-term performance. Regarding the remainder of the rockery, Mr. McCrea indicated that they propose to extend the culvert from the south side of the driveway south along Center Drive past the end of the rockery and bury the pipe. He also indicated that he would remove the boulders from the north portion of the rockery and reuse them to reconstruct the slope. He proposes to move the bottom of the rockery closer to the roadway, lower the driveway grade approximately 1 to 2 feet, reconstruct the slope at a 2:1 (horizontal to vertical) angle, place larger boulders on the slope face, and plant evergreens between the boulders. Based on Mr. McCrea's description and our observations of the site, it is our opinion that the proposed changes to this portion of the rockery will be suitable. By extending the culvert, the potential for water to saturate the toe of the slope will be reduced. Based on the soil types at the site, it is our opinion that a 2:1 slope will be stable. The boulders and vegetation will aid in reducing the potential for erosion. REPORT LIMITATIONS This report has been prepared to assist the planning and design of reconstruction of the rockery at 1307 South Center Drive in Spokane Valley, Washington. Our services consist of professional opinions and conclusions made in accordance with generally accepted geotechnical engineering principles and,practices. This acknowledgement is in lieu of all warranties either expressed or implied. It has been a pleasure being of service to you on this project. If you have any questions or need additional information, please do not hesitate to. call us at your convenience. Sincerely, AIIWest Tes 'ng & Engineering, LLC W� Paul T. 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