Abstract
For the Kuching Wastewater Management System Phase 1 project in Kuching, Malaysia, 7·7 km of trunk sewer lines were constructed in the highly fractured, highly weathered Tuang Formation using a pipe-jacking method. The pipelines were founded at depths of up to 35 m below Kuching City, where the majority of the pipe-jacking activities would traverse the Tuang Formation. Jacking forces in highly fractured geology are not well understood as most jacking force models were derived for drives traversing soils. Therefore, a novel method was developed, whereby equivalent rock strength characteristics were interpreted from direct shear testing on reconstituted tunnelling rock spoils. Tangential peak strength parameters, [Formula: see text] and [Formula: see text], were developed from the nonlinear behaviour of the reconstituted spoils and applied to a well-established jacking model to assess arching and development of jacking forces from four documented drives. The back-analysed parameters μ avg and σ EV were used to demonstrate that geology had significantly affected the development of jacking forces. The back-analysis of the studied drives was successfully validated through finite-element modelling. This research shows that the developed parameters [Formula: see text] and [Formula: see text] and the back-analysed parameters μ avg and σ EV can be reliably used to predict jacking forces in highly fractured, highly weathered geology.
Highlights
Rapid urbanisation has seen a rise in the need for buried infrastructure for the transportation of water and waste water
Despite some irregularities at the ends of the modelled pipelines due to end effects, the results showed that the distribution of t1 was uniform all along and around the pipelines for all the studied drives
A reasonable agreement was observed between the reaction forces, SFy, and measured jacking forces, with variations ranging between 15 and 29%
Summary
Rapid urbanisation has seen a rise in the need for buried infrastructure for the transportation of water and waste water. The outer surface of the pipe would only be partially solicited in the accrual of jacking forces These earlier studies provided the motivation for Choo and Ong (2014, 2015) to develop a novel method of assessing jacking forces by subjecting reconstituted tunnelling rock spoils to direct shear tests. This would allow for the development of equivalent rock strength parameters in the absence of intact rock core lengths. These tangential peak parameters could be used in the Pellet-Beaucour and Kastner (2002) jacking force model, as shown in Equations 7 and 8, respectively
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