Soldier Piles

The lagging in the system is used to retain the soils behind the excavation and transfer the loads to the piles, which are designed and embedded below the excavation a sufficient distance to provide the necessary resistance against sliding and overturning for the retained soil mass. The use of lagging may be avoided provided the retained soil has sufficient cohesion to allow soil arching between the piles. Concrete panels are also used for the lagging in rare cases. Soldier pile walls are very typically used for temporarily vertical support of the ground during basement or cut-and-cover tunnel excavation, until the permanent basement or tunnel walls and slabs are constructed and achieve strength, at which time the permanent foundation walls would take over the excavation support. The basic construction sequence for this type of excavation support involves installing the soldier piles at regular intervals, excavating in small stages and installing the lagging, then backfilling and compacting the void space behind the lagging. Tie-backs can be installed to provide additional wall rigidity. Pile and lagging walls have the advantages of being inexpensive, fast and easy to construct. The major disadvantages of soldier pile walls are that they are permeable and therefore cannot be used in high water table areas without extensive dewatering.