Jacking Force and Productivity Analysis of Pilot Tube Microtunneling Installations

Abstract

Trenchless technology is a group of techniques whose utilization allows for the repair, rehabilitation, and installation of underground infrastructure with minimal excavation. Pilot tube microtunneling (PTMT) is a trenchless technology in which new wastewater pipelines may be installed at precise line and grade over manhole-to-manhole distances. Generally, PTMT is accomplished with the implementation of three distinct phases: (1) jacking of pilot tubes to achieve line and grade, (2) jacking of casing along the pilot bore and rotation of augers to excavate a borehole slightly larger than the product pipe, and (3) jacking of product pipe directly behind the last casing. Understanding the mechanisms affecting PTMT productivity rates and jacking forces is a valuable tool that can assist designers and contractors with risk abatement. This paper outlines the instrumentation and monitoring process used to record jacking frame hydraulic pressures during seven PTMT installations. Cyclic patterns detected in the data enable the productivity rates for each PTMT phase to be determined and critical tasks associated with each phase to be identified. Variations in depth of cover, drive length, pipe diameter, and localized ground conditions allow for trends in jacking forces to be recognized. Jacking force behavior throughout each drive was compared to existing jacking force predictive models developed for the closely related pipe jacking and microtunneling methodologies because there are no currently developed predictive models to represent PTMT installation behavior.