1903 W MUKILTEO BLVD Geotech Report 2022-10-25

Dr. Hong Li JN 12084 May 10, 2012 Page 5 website, the mapped spectral acceleration value for a 0.2 second (Ss) and 1.0 second period (Si) equals 1.2g and 0.4g, respectively. The site soils have a low potential for seismic liquefaction because of the absence of near-surface groundwater. CLOSELY SPACED PILE STABILIZATION The piles would be constructed by setting steel H-beams or rebar cages in drilled holes and grouting the spaces between the steel reinforcements and the soil with concrete for the entire height of each drilled hole. It is possible that the holes could be drilled without casing, but the contractor should be prepared to case the holes or use the slurry method if caving soil is encountered. Groundwater was observed during our investigations. If water is present in a hole at the time a soldier pile is poured, concrete must be tremied to the bottom of the hole. Pile Design The piles should be spaced no more than 3 feet edge-to-edge, so that the soil above the theoretical failure plane can arch between the piles if a landslide occurs. The piles should be designed for an active soil pressure equal to that pressure exerted by an equivalent fluid with a unit weight of 45 pcf for a total depth of 15 feet beginning at the top of existing ground. This active soil pressure should be assumed to act over the center-to-center pier spacing. An ultimate passive soil pressure equal to that pressure exerted by a fluid with a density of 350 pcf will resist the lateral movement of the piles below the 15-foot depth. For long-term conditions, a safety factor of 1.5 should be applied to the passive soil pressure for the design. The minimum pile length should be 35 feet. These design considerations are illustrated on Plate 4. SOLDIER PILE WALL As discussed in the GENERAL section, as a more economical, shallow slope protection, a smaller wall could be constructed. Two types of steel beam, cantilevered pile walls are feasible. This section presents design considerations for either driven or drilled cantilevered soldier pile walls. Since the most suitable choice is primarily dependent on a number of factors under the contractor's control, we suggestthat the contractor work closely with the structural engineer during the shoring design. As discussed above, the construction of this type of retaining structure would protect only the rear yard area from shallow failures occurring near the top of the steep slope, and would not protect the property or existing house from deep-seated landslides occurring near the interface of the upper loose soils and underlying dense soils. Soldier Pile Installation Soldier pile walls would be constructed by one of two methods: setting steel H-beams in a drilled hole and grouting the space between the beam and the soil with concrete for the entire height of the drilled hole, or by driving the beams into the ground using a hydraulic hammer. If the drilling method is chosen, due to the loose nature of the upper sands, and the possibility of groundwater, the drilling contractor should be prepared to case the holes or GEOTECH CONSULTANTS.INC.