Micro-tunnelling in congested urban areas: A case study of level crossing removal project

Abstract

This paper presents a case study for a 275m length pipe-jacked concrete sewer line, installed under an existing road using trenchless techniques as part of level crossing removal works in Melbourne, Victoria. Due to high vehicular traffic in the area and to avoid congestion, micro-tunnelling was chosen as a suitable method for laying the pipe. Based on borehole data and seismic survey information, the tunnel was predominantly installed through a geological interface containing residual soils and weathered volcanic basalt where core stones or ‘floaters’ could be present. Based on the ground conditions and a risk and cost benefit assessment undertaken by the Client and microtunnelling contractor, an Earth Pressure Balanced (EPB) TBM method was selected. The launch shaft was designed to retain lateral earth pressure using a trench box. A conventional thrust block was constructed to facilitate pipe jacking. The location of the shaft was just 2m from the edge of an existing building. To mitigate risk and to ensure the performance was within the design requirements, soil-structure interaction analysis of the launch shaft was undertaken to predict building settlement and conduct an impact assessment. During pipe jacking works, ground monitoring was carried out at regular intervals along the drive, at the shaft location and along the building edge. The roof awning of the existing building was modified to accommodate the launch shaft and reinstated to the original configuration after pipe jacking works were completed. This paper provides insights into the design and construction challenges of microtunnelling projects in dense urban environments containing high traffic and nearby buildings.

Techniques