ABSTRACT: A monitoring program employed to measure the support performance of spiles in a recent Canadian tunnel project is presented. Of novelty in this research is the use of a distributed optical strain sensing technique to measure the load distribution of individual spile support members at a spatial resolution of 0.65mm. The distinct challenges and technique developed to instrument the 6-meter long, self-drilling spile members specified by the design are presented. Additionally, the considerations to effectively monitor the instrumented spiles over a 15-meter section of the tunnel are discussed. Selected load profiles are presented for instrumented spiles over one month of monitoring and approximately 36 meters of tunnel advance. Significant correlations between the measured load of each spile using the optical fiber sensing technology and the qualitative assessments made from within the tunnel were found and highlight the necessity of the support installation regulations implemented at the project.

1. INTRODUCTION

The management of increased transportation needs in growing metropolises has led to the development of many new subterranean infrastructure projects to support rail and road transit. In many cases, this situates shallow urban tunnel construction projects within proximity to existing infrastructure. The construction of the Valley Line LRT project in Edmonton, AB is an example of such a project where the disturbance to existing buildings, roadways, and utilities must be minimized during tunnel excavation. A major aspect of this project, therefore, involves restricting excavation induced displacements to predefined levels by implementing ground control measures such as pre-support. Pre-support and/or face- support techniques include, but are not limited to: face bolting, ground freezing, pre-vaults, and umbrella arch techniques. Of interest in this research effort is the spile support member, which falls under the collection of umbrella arch techniques. According to Oke et al. (2014), the umbrella arch is a temporary support system forming a structural umbrella around the excavation from the insertion of longitudinal support members installed from within the tunnel, above and around the crown of the tunnel face. Installed prior to the first pass of the excavation, the umbrella arch provides support to the ground ahead of and at the working facing, as well as the unsupported span immediately behind the working face (i.e., within the tunnel). The latter is a distinguishing feature of the umbrella arch in comparison to other presupport techniques such as face bolting, which may be used in combination with the umbrella arch.

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