Experimental Investigation of Settlement Induced Bending Moments on Pile Supported T-Walls

T-Walls are pile-supported concrete floodwalls that are part of the New Orleans flood protection system. They are typically founded on long concrete or steel battered piles and include a sheet pile cut off for seepage and gradient control. Since the soils in Southern Louisiana contain soft and compressible silt and clay, these floodwalls need to be designed to resist not only flood loads but also loads produced by consolidation of soft foundation soil under the weight of new fill placed on or near a T-Wall during construction. This is commonly referred to as downdrag and induces additional bending moments on the piles. It is important that the settlement induced bending moments are assessed and understood to ensure that they do not exceed allowable limits. In an attempt to develop a comprehensive T-Wall design procedure that appropriately considers field conditions, the United States Army Corps of Engineers (USACE) New Orleans District partnered with Rensselaer Polytechnic Institute (RPI) and Virginia Polytechnic Institute and State University and jointly developed a research program. A series of centrifuge tests was conducted at the Centrifuge Facility at RPI in order to gain insight into the mechanisms and magnitudes of downdrag-induced bending moments and provide reliable data sets for validation of numerical models. Different pile configurations and fill loading conditions were tested in an attempt to isolate the key parameters of the system response to downdrag forces. This paper describes the experimental methodology and discusses data from two centrifuge tests in view of the effect of an additional row of piles on the Protected Side of the system.