Analytical study of minimum cover required for thermoplastic pipes used in highway construction

Abstract

This paper presents an analytical study on the minimum cover required for corrugated high-density polyethylene and polyvinyl chloride pipes used for under-roadway (cross drain) applications in highway construction. As state highway agencies have only recently begun allowing plastic pipes for cross drain applications, there has been little rigorous analytical research into the minimum cover required for safe traffic load applications using thermoplastic pipes. Furthermore, there is considerable variability among the minimum cover requirements specified by state departments of transportation. The objective of this study was therefore to evaluate the minimum cover required for safe use of thermoplastic pipes for cross drain applications under AASHTO live loads. Analyses were carried out using the finite element method based on a 2D plane strain formulation and nonlinear soil models. Both deflection and stress criteria were evaluated. In general, the required minimum cover resulting from this study was found to be in agreement with most currently used criteria when based upon H25 loading oriented transverse to the pipe; however, significantly higher minimum cover requirements result when the loads are oriented parallel to the pipe.