Sydney Metro Northwest - Design and construction of the Norwest and Castle Hill pedestrian underpass

The Norwest and Castle Hill station pedestrian tunnels are 45 m and 36 m long respectively with the same horseshoe shaped profile with an internal height of 4.7 m and a width of 8.4 m. Under the live roadways ground cover varies between 2.5 m and 4.5 m. Both tunnels will be excavated through overlying fill, residuals soils and Class II to V shales. The construction includes preinstalled canopy tubes over the tunnel arch and fibreglass dowels to stabilise the tunnel face. A one pass synthetic fibre reinforced shotcrete lining will be installed (no lattice girders or steel sets) as permanent support progressively as the tunnel is excavated. The tunnel is fully drained via a drained invert, with a spray on waterproof membrane applied over the tunnel arch to prevent water drips into the tunnel. The final layer of shotcrete over the membrane is for mechanical protection of the membrane and fire resistance. During construction, the tunnel will be monitored both within the tunnel and above the tunnel using convergence readings for in tunnel monitoring and surface settlement road points for surface monitoring.