1903 W MUKILTEO BLVD Geotech Report 2022-10-25

Dr, Hong Li JN 12084 May 10, 2012 Page 6 use the slurry method if caving soil is encountered. Excessive ground loss in the drilled holes must be avoided to reduce the potential for settlement on the surrounding ground. If water is present in a hole at the time the soldier pile is poured, concrete must be tremied to the bottom of the hole. The upper, very loose soil downslope of the wall would then be removed to a shallow depth of about 5 feet. As excavation proceeds downward, the space between the piles should be lagged with timber, and any voids behind the timbers should be filled with pea gravel, or a slurry comprised of sand and fly ash. Treated lagging is usually required for permanent walls, while untreated lagging can often be utilized for temporary shoring walls. Temporary vertical cuts will be necessary between the soldier piles for the lagging placement. The prompt and careful installation of lagging is important, particularly in loose or caving soil, to maintain the integrity of the excavation and provide safer working conditions. Additionally, care must be taken by the excavator to remove no more soil between the soldier piles than is necessary to install the lagging. Caving or overexcavation during lagging placement could result in loss of ground. Timber lagging should be designed for an applied lateral pressure of 30 percent of the design wall pressure, if the pile spacing is less than three pile diameters. For larger pile spacings, the lagging should be designed for 50 percent of the design load. Shallow failures would still be possible, and failure of the soil beneath the wood lagging would also be possible,and would likely result in some minor ground loss above the wall. If this occurs, the lagging would need to be extended down to the resulting ground surface, and the resulting voids behind the wall backfilled. To minimize the effect of this ground loss, the native, fine grained sand should not be used as backfill material. Soldier Pile Wall Design Soldier pile walls thatare cantilevered or restrained by one row of tiebacks, and that has a level backslope, should be designed for an active soil pressure equal to that pressure exerted by an equivalent fluid with a unit weight of 45 pounds per cubic foot (pcf). This active pressure should be applied to a design height (H) equal to 10 feet. Lateral movement of the soldier piles below the active zone will be resisted by an ultimate passive soil pressure equal to that pressure exerted by a fluid with a density of 350 pcf. No safety factor is included in the given value. This soil pressure is valid only for a level slope of in front of the soldier pile; it acts on two times the grouted pile diameter, Any slopes resulting from ground loss in front of the wall would significantly decrease the passive resistance. The soldier piles should be embedded no less than 20 feet below the existing ground surface at the top of the slope. If slope failures occurring downslope of the wall expose a height greater than 10 feet or cause the soil beneath the 10 foot height, in front of the wall to be sloped, the wall will no longer be stable.. Installing remedial measures, such as tieback anchors or longer piles, could be needed at that point. LIMITATIONS The conclusions and recommendations contained in this report are based on site conditions as they existed at the time of our texploration and assume that the soil and groundwater conditions encountered in the test borings are representative of subsurface conditions on the site.. If the subsurface conditions encountered during construction are significantly different from those GEOTECH CONSULTANTS. INC..