LP Consulting Australia Pty Ltd has worked closely with Leda Holdings and Sydney Water to produce a compliant and high quality sewer reticulation system in difficult ground conditions.
The subdivision is located on the corner of Bay Road and Production Road in close proximity to Woolooware Bay and an associated open stormwater channel. The existing Sydney Water sewer was located at a depth greater than 5m below the existing surface.
In order to provide a safe and secure work environment a shoring and dewatering system was implemented during the construction of the sewer reticulation. Figure 1 below presents the shoring boxes and props utilised and the type of ground condition at the invert of the trench.
Figures 2, 3 and 4 present the dewatering system which was implemented throughout the course of the deep construction works. DN 30mm slotted PVC pipes (Figure 3) were inserted at 450mm centers around the edge of the shoring box to a depth of 7m below the surface.
These spears were then connected to a DN 100mm suction line (Figure 2). This suction line was then connected to the dewatering pump (Figure 4) which brought the water level down below the trench base while the sewer reticulation main was constructed.
To protect the delicate mangroves within close proximity downstream of the site the dewatering outlet was placed into a hessian bag to filter any sediment collected by the ground water. Figure 5 presents the dewatering outlet configuration.
The unsuitable ground conditions did not provide a sufficient bearing capacity to support a concrete encased sewer reticulation main. To provide a suitable base the trench was over excavated and a geo-fabric wrapped, 200mm thick blue metal bed was included under the sewer main. Figure 6 presents the blue metal bed being wrapped in geo-fabric.