Determination of design depth of soil-nailing protection structures

The design depth problem of excavation protection structures is one of controversial issues in the design of foundation pits.Taking the soil-nailing structure for the study,the strength reduction FEM is employed to solve this problem.The design depth of local ultra-deep excavation such as base beams and pile caps in the excavation is studied.Research shows that: the strength reduction FEM can be applied to the limit design of slopes and soil-nailing structures;different local ultra-deep excavation depths,sizes and distances are respectively treated in order that the soil nailing structures are truly designed reasonably,safely and reliably.In the design,the base beam ultra-deep excavation can not be considered,1/2 of the ultra-deep excavation depth can be considered for the caps with 1～3 piles,and the ultra-deep excavation depth should be considered for the caps with many piles.