![]() The survey prisms were fixed to the rails at 2 m intervals along all three railway tracks (400 prisms were used in total). The three railway tracks were monitored using three robotic scanning theodolites and the accuracy of the readings were very high as the prism targets were less than 50 m away from the monitoring stations. Early strength measurements of the shotcrete were taken onsite and the next excavation cycle could not commence until a strength gain of 6 MPa was achieved. In tunnel displacement, monitoring consisted of convergence taping and optical survey target readings.Īn interesting apparent anomaly in the monitoring data was noted between the 1 mm (only) settlement of the in-tunnel crown and the up to 15 mm surface settlement (surface settlements were generally in the range of 5 to 8 mm). ![]() The excavation/shotcrete support cycle advanced in 1, 1.3 or 1.5 m increments depending on the geology, shotcrete strength and the displacement monitoring data. The 12 m long canopy tube arrays had a 3 m overlap and their installation was staggered relative to the 12 m long face dowels byĤ.5 m. A repeated grid pattern of thirty-five grouted 12 m long fibre glass dowels ensured tunnel face stability. Apart for the initial steel canopy tubes, no other steel support is installed in the driven tunnel (a first for Australia and perhaps in the world for such a shallow cover tunnel under live railway tracks). Finite element (FE) analysis calculated the stresses in the synthetic fibre reinforced shotcrete lining and was also used to assist in predicting surface settlements. The ground is predominately Ashfield shale rock with either fill or highly weathered shale at or above the tunnel crown. The tunnel excavation dimensions are 7 m in height and 9 m in width and has a horseshoe shaped profile with the ground cover varying between 2.5 to 3.5 m above the tunnel crown. The underpass is designed for diesel hauled freight trains up to 1.5 km in length. The single track North Strathfield Rail Underpass (NSRU) consists of two dive structures either end of a 148 m long shallow cover driven tunnel. A shallow cover tunnel was excavated under live railway tracks just south of North Strathfield Railway Station, Sydney.
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