1329 MADRONA AVE Geotech Report 2022-10-25

Subsurface Exploration,Geologic Hazard,and Janowicz Property Geotechnlcal Engineering Report Everett, Washington Preliminary Design Recommendations elements should be provided with suitable corrosion protection, as recommended by the structural engineer. These recommendations assume that the soldier pile wall will be constructed along the upslope property boundary. 11.1 Tiebacks A tieback system consists of drilling behind the soldier pile wall at an angle to the horizontal and installing rods or cables with a grout anchor. Care must be taken to avoid underground utilities. The anchor holes should be drilled in a manner to minimize loss of ground and not endanger adjacent anchors and surrounding subgrades due to subsidence. Tieback anchors must be located far enough behind the soldier pile wall to develop anchorage within a stable soil mass to prevent wall failure or excessive deformation. Commonly, we suggest that this anchorage be obtained behind an assumed failure plane defined by a horizontal line extending a distance equal to H/4 behind the retained excavation at the 'base of the excavation, which then rotates 60 degrees from the horizontal and extends upward to the ground surface. The area between this assumed failure plane and the retained excavation is referred to as the"no-load zone." • The presence of loose, wet soils within the no-load zone will likely require that the tieback holes be cased during drilling to limit ground loss and keep the drill hole open during installation of the tieback tendons. Tieback tendons should be provided with a bond breaker through the no-load zone to prevent load transfer to soils in the no-load zone. The anchor loads are transmitted to the surrounding soil by side friction or adhesion with the soil. The tieback anchors may be tentatively designed for a presumptive allowable unit resistance in the anchor zone of 1,000 psf of anchor surface area for non-pressure-grouted anchors and 2,000 psf for pressure-grouted anchors in very stiff to hard silt soils. Actual load-bearing capacity of tiebacks should be verified after installation, as described below. After tieback test stressing, the tiebacks should be permanently locked off at 100 percent of the design tension load. The rods or cables should transmit the anchor load to the soldier pile in such a manner to avoid eccentric loading. Since the tiebacks are permanent, they should be double-corrosion protected. 11.2 Tieback Anchor Tests • A series of anchor tests must be performed to verify the design and ultimate skin friction or adhesion of the tieback anchors. A common anchor testing program would consist of at least two, 200-percent verification tests of the design or allowable load, plus proof-loading every production anchor to 130 percent of the design load. A common practice is to load an anchor in 10-kip increments held for 5 minutes up to the final load of 200-percent design load,which is held for at least 30 minutes. Measurements of the rod or cable movement should be May 10,2018 ASSOCIATED EARTH SCIENCES,INC. NS/ld-170649E002-2-Pro)ecul261706491KE1WP Page 16