1610 SE EVERETT MALL WAY Geotech Report 2022-10-25

Subsurface Exploration, Geologic Hazard, and Krebs Property Preliminary Geotechnical Engineering Report Everett, Washington Preliminary Design Recommendations 14.0 ROCKERY CONSIDERATIONS It is our understanding that conceptual plans may include the use of rockeries to provide grade separation at the site. At this time, the height and locations of rockeries are not known. In our opinion, rockeries may be used to face cut slopes in the native lodgement till sediments. It is our understanding that the proposed rockeries would consist of a single tier with a maximum height of approximately 8 feet. The rockeries will face a cut slope. Rockeries may be used to face cut slopes in the native lodgement till sediments; however, rockeries are not engineered structures, and should not be used in place of retaining walls. Rockery quality depends largely on the skill of the builder. Although rockeries are commonly used, they should be considered a long-term maintenance item. Care must be exercised in selecting a rock source since some of the material presently being supplied is soft and disintegrates in a relatively short period of time. Samples of rock can be evaluated by AESI prior to their use in rockeries. The following notes present additional rockery considerations. The contractor should also confirm that his rockery configuration conforms with current applicable local and county specifications. A) The base the rockery should be started by excavating a trench to a minimum depth of 12 inches below subgrade into firm, undisturbed soil. If loose, soft, or disturbed materials exist at the base rock location, they should be overexcavated and replaced with free-draining sand and gravel or crushed rock. This backfill material should be compacted to a minimum of 95 percent of the modified Proctor maximum density using ASTM:D 1557 as the standard. The gradation of the sand and gravel should be such, that of the material passing the No. 4 sieve, not more than 5 percent by weight should be finer than the No. 200 sieve. B) Rockeries higher than 5 feet shall be constructed of rocks of graduated sizes from 5- man to 3-man, from bottom to top. Rockeries of 5 feet or lower shall be constructed of 4-man to 3-man rocks, from bottom to top. C) The rock material should all be as nearly rectangular as possible. No stone should be used that does not extend through the wall. The rock material should be hard, sound, durable, and free from weathered portions, seams, cracks, or other defects. The rock density should be a minimum of 160 pcf. D) Rock selection and placement should be such that there will be minimum voids in the exposed face of the wall; no open voids over 8 inches across in any direction. The rocks should be placed in a manner such that the longitudinal axis of the rock will be perpendicular to the rockery face. Each rock should be placed so as to lock February 13, 2007 ASSOCIATED EARTH SCIENCES, INC. TJP/Id-KE070023A1-Projects120070023IKEIWP Page 14