Prediction of Jacking Forces and Pipe Drive Lengths in Rock: Design and Constructability Aspects

摘要

Jacking forces required to advance pipe string in rocks are primarily controlled by the self-weight of the pipe, cutting resistance at the face, rock load induced friction around the pipe circumference and resistance to machine advance from a loosened rock wedge at the front face of the advancing pipe bore. This paper discusses application of analytical and finite element approaches to predict jacking forces in rock strata, which varied from medium strong to strong jointed blocky rock mass for a 3.8 km long gravity sewer in Brisbane, Australia. In stronger and distinctly jointed rock mass, the number of joint sets, their spacing and orientation with respect to the pipe alignment were found to be key factors influencing the rock loads on the pipe. Detailed interpretation of site investigation and testing data was undertaken to estimate strength, hardness and spatial properties of the rock mass and discontinuities. Combined effect of pipe self-weight friction, and resistance at the face and around the pipe were assessed to determine safe and economic length of jacking drives.