Comparison of Jacking Load Models for Trenchless Pipe Jacking

Pipe jacking is a trenchless technology method of installing pipes under existing facilities such as roads and railroads. Predicting jacking forces is important for planning, design, and construction phases of these types of projects. The jacking forces dictates shaft or pit locations, thrust block or backstop design, jacking equipment, use of intermediate jacking stations, and pipe bearing capacity. Accurate estimation of jacking forces depends on several site and project parameters, such as soil and site conditions, lubrication, size of overcut and steering corrections. Excessive jacking forces can damage the pipe, instable the thrust block, and may stop project progress. There are different methods of calculating jacking loads presented by researchers and industry organizations. By using different models, a discrepancy can be observed in results, which make precise estimation questionable. It can be concluded that analytical and empirical models are based on certain assumptions and field data, and more research is required. For example, ASCE 27 recommends using experimental values to calculate frictional forces and do not consider the face pressures. Other researchers have considered detailed analysis of soil conditions at the face and recommended including project specific conditions such as pipe depth and bore stability. This paper presents an analysis of literature and provides a framework for design engineers to refer to applicable guidelines for planning pipe jacking operations. A conceptual case study is provided to illustrate the differences.