Investigation of Uplift Pressures on a Drainage Shaft Using ANSYS SOLID185 Elements and Drucker-Prager Failure Criterion for the Surrounding Rock Stratum

Abstract

This paper presents an assessment study conducted to investigate the structural condition of a drainage shaft that is part of a very large aqueduct system located in the Northeastern United States. A comprehensive three-dimensional finite-element model was generated to simulate the hydrostatic uplift pressures the shaft is subjected to. The behavior of the steel shaft cover, anchor rods, other connecting elements, and the surrounding granite rock stratum are analyzed. The finite-element model covers a large cylindrical region with a radius of 32 m around the shaft centerline to a depth of 15.2 m. The rock material was modeled on the Drucker-Prager failure criterion since the von Mises criterion is not perfectly suited for modeling the yielding of a frictional material like granite rock. A condition assessment study like the one described in this paper required an extensive finite-element model created with comprehensive software like ANSYS to investigate the load and stress distribution of uplift forces through the elements of the shaft to ensure structural integrity. The special features of ANSYS SOLID185 elements are a good fit for the simulation of the nearly incompressible rock stratum of this study. SOLID185 elements with advanced capabilities such as fracture parameter calculations, stress stiffening, creep, nonlinear stabilization, and linear perturbation are used to model the rock. Since a structural condition assessment of a drainage shaft modeled with ANSYS SOLID185 finite elements have not been discussed in detail in a technical publication before, this paper fills that gap. (C) 2019 American Society of Civil Engineers.