STUDY OF SOFT CLAY LAYER EFFECTS ON STEEL SHEET PILE WALLS BEHAVIORS USING CONVENTIONAL AND NUMERICAL METHODS

Conventional methods used for the design of sheet pile walls as a retaining system are based on the lateral force equilibrium and proposed equations. Soil is not uniform in depth, sometimes, soft soil layer may exist in various depth and situations. This issue can cause different effects on forces and moments acting on sheet pile and struts during the excavation procedure, compared with status such that soil is uniform in depth. In this study, a deep excavation using the finite element method is analyzed. Excavation's depth is divided into three clayey layers. One of the three layers is soft clay layer whose position ns are modelled in three different situations, top, middle, and bottom. The obtained results are compared with those of the conventional design method. According to the comparative obtained results, it can be concluded that:1. In relatively uniform soil deposits, conventional methods cannot correctly estimate sheet piles maximum bending moment locations.
2. In status in which a soft clay layer exists between two stiff clay layers whose thicknesses of all three layers are the same, bending moment location acting on sheet pile is different from other status and is very close to the conventional method value.
3. By increasing the depth of soft clay layer, bending moments acting on sheet piles are increased, especially in the final stages of excavation. This issue is not considered in the conventional method.
4. When the soft clay layer is a surface layer whose thickness does not exceed the one-third the depth of the excavation, using the conventional method for design practices is conservative.
5. It appears that the conventional method underestimates the forces of struts near excavation depth so that, in the current study, forces of these struts are increased by about 15-70 % in finite element method in comparison with conventional method.Using equivalent cohesion and specific gravity in layered soils cannot consider location effects of different soil layers.