1209 MADRONA AVE 2016-10-05 - Laserfiche WebLink

Geotechnical Engineering Evaluation NGA File No. 870113 Packer Property March 11,2013 Retaining Walls and Steep SIope Evaluation Page 12 Everett,Washington factor of safety of 2.0. The upper four feet of pile embedment should be neglected when calculating the passive resistance due to the presence of loose material on the slope. Tiebacks General: These systems could include drilled, grouted tiebacks, or mechanically installed anchors such as Manta Ray or Helical anchors. We recommend that one of the anchors be tested to a minimum of 200 percent of the design loads to confirm design values. We recommend that measurements be made by the contractor in the field at the time of tieback installation to verify that tiebacks do not encounter any existing structures or underground utilities. No-Load Zane: The anchor portion of all tiebacks must be located a sufficient distance behind the wall face to develop resistance within a stable soil mass. We recommend the anchorage be obtained behind an assumed no-load zone. The no-load zone is defined by a line extending horizontally from the base of the wall back towards the residence a distance of five feet. The line should then extend up from the base elevation at an angle from the horizontal of 60 degrees. We expect that some undocumented fill may exist beyond the no-load zone. We therefore recommend that the anchors be a minimum of 20 feet long. We recommend that we monitor soil conditions during anchor installation in order to evaluate adequate penetration into competent soils. Soil Design Values: The tiebacks will likely terminate in glacial soils below the walls. For use in design of the anchors, we estimate an allowable grout to soil adhesion of 1,500 pounds per square foot (psf). Load carrying capacities on the order of 10 kips or more could be achieved using 8- to 10-inch diameter helical anchors installed successfully. Load carrying capacities anywhere between 4 and 20 kips could be achieved using Manta Ray anchors installed successfully, depending on the size of the anchor. We recommend, however, that we review anchor design and proposed installation methods. We should also observe anchor installation and testing. Tieback Installation and Testing: The contractor should be responsible for using equipment suited for the site conditions. We do not recommend the use of open-hole methods for the purpose of installing the tiebacks due to the potential for soil caving. Secondary grouting to increase soil adhesion may be used; however, if secondary grouting is used, the anchors should be tested using the methods outlined for the performance testing. NELSON GEOTECHNICAL ASSOCIATES, INC.