Evaluation of Pipe-Jacking Forces Based on Direct Shear Testing of Reconstituted Tunneling Rock Spoils

The installation of underground trunk sewer lines in the Tuang formation of Kuching City, Malaysia, used trenchless technology in the form of the pipe-jacking method. The evaluation of pipe-jacking forces mainly involves empirical models developed for soils, with rather limited considerations for drives through weathered rock. Therefore, a novel approach is proposed to evaluate strength parameters by reconstituting and subsequently shearing scalped tunneling rock spoils in the direct shear apparatus. The direct shear results are then applied to a well-established pipe-jacking force model, which considers arching theory. The outcomes indicate that the backanalyzed frictional coefficients mu(avg) are not only reliable but also related to their surrounding geologies because of soil-structure interaction. This study also highlights the significance of lubrication and effect of rock arching in assessing jacking forces. The successful characterization of reconstituted tunneling rock spoils in this paper has shown potential use in assessing jacking forces during microtunneling works. (C) 2015 American Society of Civil Engineers.