New design methods for sheet pile cellular structures

Traditional methods commonly used to design sheet pile cellular cofferdams and bulkheads were developed in the 1940's and 1950's and are based on semi-empirical approaches. The traditional methods are limited because they do not explicitly incorporate soil-structure interactions, they do not predict deflections, and they are based on assumed failure plane orientations. In recent years, two-dimensional and three-dimensional finite element models have been developed to study the behavior of cells constructed at two project sites. Additionally, cells constructed at 11 project sites have been instrumented to quantify movements and sheet pile tensions.

This investigation focused on combining the instrumentation measurements with finite element parametric studies in an effort to improve the existing design procedures. Sheet pile tensions were investigated by performing axisymmetric analyses of cell filling and developing correlations between computed tensions and cell geometry, foundation conditions, and sheet pile characteristics. To study the response of cells to lateral loading, a new crosswall model that simulates sheet pile slippage was implemented for plane-strain analyses. Cell deflection trends were investigated by performing analyses of lateral loading and developing correlations between computed deflections and cell geometry, cell fill characteristics, applied load level, and foundation conditions. The analyses were verified by measurements collected for the instrumented cells. Internal shearing mechanisms were investigated by performing plane-strain analyses of cells loaded by extreme lateral pressures and observing element failure plane orientations.

The results of the study indicate that main cell sheet pile tensions depend on the amount of arching within the cells, foundation conditions, the degree of available interlock slack, and the method used for cell filling. Common wall sheet pile tensions are furthermore influenced by arc cell fill lateral pressures and by arc cell sheet pile tensions transferred through the wye pile. During lateral loading, cell deflections increase with increasing values of a newly defined parameter termed "characteristic head". During extreme lateral loading, vertical shear planes were computed to develop within the cell fill along the dredgeline and along the inboard sheet pile wall.