Lateral Earth Pressure on Lagging Walls
Lateral Earth Pressure
Various theories regarding lateral earth pressure on lagging walls used in excavation support systems are illustrated in Figure 1. In the left diagram, the pressure distribution assumes that the maximum load is applied directly to the soldier piles used in excavation support systems (support by retaining structures, nailing, anchorage, micropiles, top-down, etc.), while the minimum load occurs at the center of the lagging wall.
The right diagram is based on the theory that the pressure acting on the wall is equal to half of the total lateral earth pressure in excavation support systems.
Figure 1. Reduced lateral earth pressure on lagging walls used in excavation support systems (retaining structures, nailing, anchorage, top-down, etc.) based on MacNab’s theory, 2002
Results from Soil Testing
The lateral earth pressure exerted on walls in excavation support systems can be modeled using sliding wedge analysis. Mathematical calculations reveal that this pressure increases with height.
Two-dimensional and three-dimensional finite element analyses show that the primary horizontal arching occurs between two adjacent piles in excavation support systems. In this section, a wall is assumed between the piles.
To account for stress-strain effects, both Mohr-Coulomb and hardening soil models were used. For both models, the results indicate that most of the lateral earth pressure is carried by the piles.
MacNab’s Theory
To estimate the load applied on lagging walls used in excavation support systems, MacNab’s 2002 theory (illustrated in Figure 1, left) suggests a conservative assumption for lateral earth pressure. This conclusion is valid for stiff soils and piles with rigid interaction throughout their length. However, this cannot be generalized to all soil types or all types of piles used in excavation support systems (retaining structures, nailing, anchorage, top-down, etc.).
