Micro Tunnelling
We invested in the Herrenknecht AVN Slurry based Microtunnelling equipment in 2007 and have completed 26 individual tunnels since. This in-house ability to drive 1200mm, 900mm and 600mm tunnels up to 250m in all soil types from 250MPa rock to 0.0N value silt with our own ‘home-grown’ crew has given great flexibility when working in urban areas especially where underground services are present. The associated slurry separation system consisting of vibrating screens and hydro-cyclones allows the removal of suspended solids down to 50 microns with Centrifuge equipment working below this level down to 0.0 microns. All of these tunnels are driven from shafts which can be precast in our yard. A 600mm diameter tunnel can be launched from a 3.2m internal diameter shaft. The 900mm and 1200mm diameter tunnels can be launched from a 5m internal diameter shaft. Drive lengths are typically 100m for the 600 mm diameter tunnel with 500m (drive length) possible for the 1200mm diameter tunnel using inter-jacks. The management of this system relies on a good working knowledge of ground conditions.

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