Slope stability modeling and analysis of T-wall subjected to hurricane loading

In the aftermath of Hurricanes Katrina and Rita in 2005, significant damages to the Hurricane Protection System (HPS) were observed in the New Orleans, Louisiana and Mississippi Gulf Coast areas. Pile supported T-walls are one of the most important components of the HPS in the New Orleans area and its vicinity. Due to the unsatisfactory performance of some of the HPS measures, during the above hurricanes, the New Orleans District of the U.S. Army Corps of Engineers and others have undertaken an extensive investigation and re-evaluation of the design criteria of the T-walls from the perspective of its stability against future hurricane loadings. These resulting guidelines are being incorporated in the Hurricane and Storm damage Risk Reduction Guidelines (HSDRRG, 2007). The stability analysis and modeling of T-walls are significantly different from the stability analysis of other structures. They must be analyzed for unbalanced loads arising from the stability analysis which are assumed to be carried by the supporting piles beneath the wall and the analysis should not consider any water load acting directly on the structure, as these loads are presumed to be carried by the supporting piles. Historically, the U.S Army Corps of Engineers had generally relied upon the simplified Method of Planes (MOP) slope stability analysis of T-wall, which satisfies only force equilibrium. However, their recent evaluation revealed that MOP is not very suitable for the stability modeling and analysis of T-walls. Thus, there is a need for a comprehensive slope stability modeling and analysis procedure based on total limit equilibrium (such as Spencer's method of analysis) that can be incorporated in the new design guidelines. MOP can then be retained as a design check for the results obtained using Spencer's analysis. In this paper, a comparative evaluation of the slope stability analyses of T-walls are presented using the above two distinct approaches of slope stability analysis. In addition, the effect of optimization of the failure surfaces on the stability analysis results is investigated in detail. Numerical example of a typical T-wall stability analysis using the two different procedures is presented to demonstrate the above procedures. The findings have indicated that the MOP analysis appeared to be conservative compared to the total limit equilibrium method.