1907 W MUKILTEO BLVD 2021-11-15 - Laserfiche WebLink

l I Pearson Property Slope Stabilization NGA File No 945216 1907 West Mukilteo Boulevard February 19,2016 Everett,Washington Page 9 " !• anchors such as helical anchors. We recommend that five percent of the anchors, but no less than two anchors, be treated as performance anchors and be tested to a minimum of 200 percent of the design loads. The soil creep characteristics would be evaluated during these tests. We recommend that the foundation embedment of the residence and utilities within the yard area be verified by the contractor and measurements made in the field at the time of tieback installation to ensure tiebacks do not encounter the existing residence, or underground utilities. No-Load Zone: 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 bonded portion of the tiebacks, or the helical anchor helicies,be placed a minimum of 15 feet beyond the face of the wall. 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) can be used for grouted anchors. Load carrying capacities on the order of 10 kips or more could be achieved using 8- to 10-inch diameter helical anchors installed successfully. We recommend 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. In the case of the helical anchors, the contractor should determine the torque values required to achieve the desired capacity. However, the anchors should advance a minimum of 20 feet from the face of the wall and two anchors be tested to confirm design capacities. Two anchors should be performance tested to 200 percent of the anchor design capacity. The performance test should consist of cyclic loading in increments of 25 percent of the design load, as NELSON GEOTECHNICAL ASSOCIATES,INC.