Predicting Performance of Pipe Culverts Buried in Soil, Phase 1 : Interim Report

An analytical tool based on the finite element method has been developed to analyze buried culvert problems in a realistic fashion. Segments of a curved bar with three degrees of freedom (normal, tangential and rotational) at each end have been used to simulate a thin pipe where nodal moments are important. Triangular, isoparametric elements with one curved boundary (to fit the shape of pipe), and three midside nodes have been used to represent the soil. A special type of interaction element with zero thickness has been used between pipe and soil to simulate interface behavior, including slip and/or the inability to resist tensile stresses. Nonlinear, anisotropic soil properties have been accounted for. Actual test data are used as input for soil properties. A computer program was written to include all the aspects mentioned above, and example problems were solved to demonstrate its versatility and to investigate the influence of such factors as non-linear soil properties, relative stiffness of pipe and soil, inclusion of weak materials near the spring line, and construction procedures. The present program is applicable only for analysis of two-dimensional problems transverse to the pipe in which the state of stress either in the soil mass or in the pipe does not approach failure.