1707 SCENIC DR SNO CO PUD Geotech Report 2022-10-25

� northwest corner of the 115kV yard along the Interurban trail. Structurally reinforced slops, such as Tensar's SierraScape� retaining wall system, can have a vegetated face and be inclined from 1H:1V to 1/2H:1V and be blended into the adjacent slopes. For preliminary design purposes,the length of the reinforcing materials is typically 70 to 90 percent of the wall height. The length generally depends on the soil type used for backfill, backslope conditions, and the competency of the foundation soils. MSE walls can be used in cut (less economical) or fill (more economical) areas where existing structures or right-of-way constraints do not preclude accomplishing an open cut excavation for construction. Construction of these walls will require a foundation width approximately equal to 70 to 90 percent of the wall height. MSE walls may be designed to reuse the on-site soil in the dry summer months, which may be a benefit to the project; however, imported gravel borrow is commonly used in the reinforcement zone. We recommend that the walls be designed using imported gravel borrow in the reinforcement zone in accordance with WSDOT Standard Specification 9-03.14(4) Gravel Borrow for Geosynthetic Retaining Wali. We recommend GeoEngineers complete the design of the MSE walls and prepare specifications or review these documents to make sure they are prepared in accordance with our recommendations. Soldier Pile Wails Soldier pile walls are suitable for use in either cut or fill wall sections. The soldier pile wall system for cut sections consists of drilling and grouting soldier beams and then excavating in front of the wall. Cantilever soldier piles are generally adequate for walls less than 15 feet in height. Treated timber is typically used for lagging when permanent wall facing is added. This type of structure involves the least amount of disturbance to the ground surface behind the wall. The sequencing of a fill section soldier pile wall is slightly different than a cut section wall, since the wall is constructed and backfilled from bottom to top rather than top to bottom. However, local contractors have used this wall system numerous times in fill situations and have equipment to facilitate installation of all the elements. We recommend the following parameters for design purposes: ■ Design using the equivalent fluid pressure and seismic pressures for reinforced concrete cantilevered walls, as described above. ■ For fill walls, backfill during wet weather should consist of gravel borrow, and backfill during dry weather should be either gravel borrow, or select borrow, or suitable on-site soils in order to permit compaction to reach the required density. ■ Drainage measures should be incorporated into the design of the wall. Gravity Walis Gravity walls such as crib walls, gabions, unreinforced Ultra Block, and bin walls may also be considered. These wall systenis act as gravity retaining structures. Construction of this type of wall requires a base width approximately equal to half of the wall height and this type of wall usually has a face batter of about 1H:4V. The units are backfilled with compacted granular soil. These walls should be designed with back drainage. TY�e required temporary cut slope and width of the structures should be considered in planning and design. GEOENGINEERS� October24,2014 Page 18 Fle No.�482-027-02