Site-based research in pipe jacking—objectives, procedures and a case history

Abstract

This paper provides an introduction to the programme of field monitoring of pipe jacking undertaken at Oxford University, as part of a major research programme initiated and funded by industry in collaboration with the Engineering and Physical Sciences Research Council. In the first half, the need for research is discussed, the objectives of the work introduced, and the reasons for the use of site monitoring to achieve these objectives presented. The instrumentation developed for this purpose, and the methods of planning and execution of the site work, are described, and brief details given of the five schemes monitored during the first stage of fieldwork. The second half of the paper is a case history of the first instrumented scheme, involving a pipe jack at shallow depth in stiff glacial clay. Results presented include measurements of. total jacking force; local shear and normal stresses and pore water pressures at the pipe-soil interface; deviations in line and level of the pipe line, and consequent misalignment angles at the pipe joints; and the magnitude and distribution of joint pressures between pipes. The instrumentation generally performed very well, so that only minor modifications were needed for later schemes. Pipe-soil interaction was found to be complex, affected by ground type, excavation technique and the presence of free water within the tunnel bore; however, two simple theoretical models were found to give calculated values for pipe jacking resistance in reasonable agreement with measured values. Pipe line alignment was shown to be very important in determining pipe barrel load paths and pipe joint pressure distributions. No evidence was found for any significant changes to alignment either due to continued movement of the pipes, or to pipe line straightening under load. The alignment was thus defined by the accuracy of steering of the tunnelling shield.