3322 BROADWAY COMPASS HEALTH 2025-10-03

Compass Health June 26, 2019 J N 19178 Page 9 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 on neighboring properties. 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. Soldier Pile Wall Design Temporary soldier pile shoring that is 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 30 pounds per cubic foot (pcf). This active soil pressure should be increased by 5 pcf if the shoring is permanent. Traffic surcharges can typically be accounted for by increasing the effective height of the shoring wall by 2 feet. It does not appear that there are existing adjacent buildings will exert surcharges on the proposed shoring wall; however, if future buildings are built on the eastern edge of the western alley, they will surcharge the shoring and should -be accounted for if possible. Slopes above the shoring walls will exert additional surcharge pressures. These surcharge pressures will vary, depending on the configuration of the cut slope and shoring wall. We can provide recommendations regarding slope and building surcharge pressures when the preliminary shoring design is completed. If tieback easements cannot be obtained, it may be necessary to utilize internal braces (rakers) to restrain the soldier piles. Soldier piles restrained by rakers can undergo more deflection than do tied -back or cantilever piles, due to the temporary sloped excavation that is necessary in front of the soldier piles to install the rakers and thrust blocks. This requires that the shoring designer closely evaluate the temporary conditions that exist before raker installation. We should be contacted early in the design process if rakers are necessary, in order to provide the appropriate design considerations. It is important that the shoring design provides sufficient working room to drill and install the soldier piles, without needing to make unsafe, excessively steep temporary cuts. Cut slopes should be planned to intersect the backside of the drilled holes, not the back of the lagging. Lateral movement of the soldier piles below the excavation level will be resisted by an ultimate passive soil pressure equal to that pressure exerted by a fluid with a density of 600 pcf. This soil pressure is valid only for a level excavation in front of the soldier pile; it acts on two times the grouted pile diameter. Cut slopes made in front of shoring walls significantly decrease the passive resistance. This includes temporary cuts necessary to install internal braces or rakers. The minimum embedment below the floor of the excavation for cantilever soldier piles should be equal to the height of the "stick-up." Tied -back soldier piles should be embedded no less than 10 feet below the lowest point of the excavation, including footing and utility excavations. GEOTECH CONSULTANTS, INC.