Prediction of Pile Setup in Clay

Abstract

Reliable calculations of pile setup times represent a critical parameter in the design of large-diameter pipe piles that are used to anchor offshore tension leg platforms. Predictions of setup times can be obtained by analyses that simulate the changes in effective stresses and soil properties occurring around a single pile during installation and subsequent equilibration of excess pore pressures. Pile installation is modeled using the framework of the strain path method, assuming that there is no plugging of soil within the pipe pile. Changes in effective stresses and soil properties at all stages of the analysis are described by the MIT-E3 soil model, with input parameters derived from laboratory tests on highquality samples. After installation, the analyses solve the radial dissipation of excess pore pressures around the pile shaft and setup of effective stresses in the soil by nonlinear finite element methods. Dissipation times are controlled by the pile aspect ratio (ratio of diameter to wall thickness), in situ effective stress, stress history, and hydraulic conductivity of the clay. This paper illustrates the validation of the proposed setup analyses with data from instrumented model piles and pile shaft elements at two well-documented test sites.