A Case Study in Direct Pipe Thrust Load Prediction

Abstract

The Direct Steerable Pipe Thrusting (DSPT) technique, which includes Direct Pipe®, is considered a hybrid of horizontal directional drilling (HDD) and slurry microtunnelling methods. It is a surface-to-surface trenchless method that involves thrusted installation of steel pipe along a typically curved vertical alignment, similar to HDD. Like slurry microtunnelling, soil excavation is performed using a remote-controlled closed-face slurry tunnelling machine located at the leading end of the thrusted pipe. Publications addressing the prediction of DSPT thrust loads have used calculation methods that are commonly either used to predict HDD installation pull loads or those used to predict linear pipe jacking thrust loads. This paper presents measured thrust forces for five (5) DSPT installations completed in North America in silty and sandy clay and till material with gravels and cobble conditions. The paper compares these measured thrust forces to estimates made using a slightly modified HDD calculation approach and provides commentary on the appropriateness.

Techniques