Nonlinear Finite-Element-Based Investigation of the Effect of Bedding Thickness on Buried Concrete Pipe

Abstract

The pipe-soil interaction is studied by using the finite-element software ABAQUS/CAE Version 6.5-1 as a symmetric model of embankment installation to study the effect of bedding property and thickness on pipe-soil interaction with increase in the height of fill. A three-dimensional (3D) finite-element method (FEM) model of the concrete pipe and surrounding soil is developed. The FEM model is capable of simulating material, geometric, and contact nonlinearities which employs a nonlinear incremental solution algorithm. Several different element types and mesh sizes were tested to obtain the optimum converged mesh. These elements include eight-noded linear brick (C3D8R) and six-noded linear triangular prism (C3D6) for modeling of the concrete pipe and surrounding soil. The behavior of the 3D model is investigated by varying the pipe diameter, backfill height, bedding thickness, and bedding material. Three material constitutive relationships of soil involving in the model are gravelly sand and sandy silt. To study the effect of bedding thickness on the pipe wall, due to the increment of backfill soil depth, contact elements were employed in the interface between each two regions. The lateral boundaries and model length were also studied for the converged solution. A parametric study was conducted to study the effects of bedding thicknesses. The results showed that the increase in bedding thickness reduces tensile stress at crown, spring line, and especially invert of the pipe wall depending on the material property. This means the change in material property and compaction level has a greater effect on the reduction of tensile stresses than the effect from the variation of bedding thicknesses. Also, materials with lower bedding stiffness (high deformability characteristics) cause greater reduction in induced stresses. This study shows that for commonly used bedding material (coarse grained gravelly sand), the effect of the increase in bedding thickness has a minimal effect on stress reduction of the pipes studied.