5209 GLENWOOD AVE 2017-04-07 - Laserfiche WebLink

• Revised Redi-Rock Retaining wall Design Western Geotechnical Consultants,Inc. 52XX Glenwood Ave.Property #14 91 2 Everett,WA April 17,2015 that results in the greatest dry density from compaction. We recommend using a relatively clean sand-gravel mix meeting the USCS gradation specifications for GW or SW soils or using ballast meeting the specifications contained in Sec 9-03.9(1)of the WSDOT"Standard Specifications of Road, Bridge and Municipal Constmction". Alternate backfill gradations may be used, subject to approval of the geotechnical engineer. Stability Analyses Stabilizing forces in the design result from the mass of the Redi-RockIMSE and friction between the Redi-Rock/MSE and the foundation soil. Stability analyses were performed using limited equilibrium techniques to analyze the margin of safety against sliding,overturning, internal buckling and global stability. The methods of analyses compute the ratio of forces (or moments) resisting movement, as compared to forces (or moments)tending to cause movement. We analyzed the wall designs for total wall heights tip to 24 feet high with an exposed height of 23 feet, assuming a minimum 1-foot embedment of the lowest block below finished grade, and the wall foundation pad must be constructed within the fresh, hard till. MSE wall sections,where geogrid is used to reinforce the soil,are required for all wall heights greater than 9 blocks high. The length of the geogrid reinforcement increases with the height of the wall. In general,the length of geogrid reinforcement is a minimum of 0.6 times the total height of the wall, except longer grids are required:near the top of the wall,as indicated on the design cross-sections in Appendix B. We analyzed the wall using both static and dynamic conditions. We determined that the static safety factors for sliding and overturning were in excess of 1.5 and 2,0, which represent the minimum safety factors normally used for static stability against sliding and overturning. respectively. Our dynamic analyses assumed a pseudostatic earthquake force equivalent to 20% of gravity. While the dynamic analysis revealed a minimum safety factor for most of the blocks of greater than 1.1, which is the norm by geotechnical engineering standards for dynamic analyses, there is a lower factor of safety for the upper block(s)during such a strong earthquake, which could result in some tilting of these blocks. This was compensated for by increasing the length of the top I to 2 geogrid layers. Bearing capacity for the wall was also analyzed and found to be adequate,assuming the removal of any unsuitable subgrade soil down to hard glacial till, which will require inspection and approved prior to the beginning of the wall construction. Construction Considerations 6