Characterising railway substructure layers for rehabilitation design

Abstract

Paper presented at the 31st Annual Southern African Transport Conference 9-12 July 2012 "Getting Southern Africa to Work", CSIR International Convention Centre, Pretoria, South Africa.

Current railway substructure design methods rely heavily on an accurate assessment of the in-situ material properties, particularly the modulus of the subgrade and substructure layers. This information is used in foundation design models to determine the required cover to prevent deformation and failure of support. This paper presents typical data obtained during a rehabilitation design investigation to accurately evaluate the modulus of the in situ subgrade and substructure layers using Pencel pressuremeter tests, dynamic cone penetrometer tests, deflection measurements through remote video monitoring and lightweight drop-weight tests. Standard soil parameters related to the grading, plasticity and CBR of the investigated materials do not have any direct relationship with the modulus values that were obtained. This is specifically true for sand materials where good or poor CBR and plasticity values can give a misleading indication of the formation modulus.