Project Showcase - Dural

Job at Hand

We received a call about reconstructing a failed keystone retaining wall that lines the circumference of a large dam. After inspecting I was informed the wall was standing for 20 years and came down after a huge downpour of rain. The section that came down was 25metres in length and 1.6metres in height, this section was also receiving quite a lot of run off from surface water from around the acreage property as it all was directed to the dam. The surface water was evidently sitting behind the retaining wall and there was nothing in place to redirect sub surface water either. I was surprised the wall was standing for this much time as there were quite a few other issues such as the wall being constructed with no batter, no footing and lack of aggregate behind the wall just to state a few.

We began to design a solution to address all issues and after given the approval we commenced work.
Our proposal was to reconstruct the retaining wall with a reinforced concrete footing also adding dowels into the footing where the first course would sit. Filling the block and 300mm behind with aggregate, a further 1.4metres from the face of the wall to be compacted crushed sandstone with every 2 courses having geogrid reinforcement. To address the surface drainage we proposed concrete pits with 300mm pipes running through the retaining wall and for the sub-surface drainage we installed agg-lines running into the pits.

Challenges

This project was inside a dam which resulted in draining the dam low enough to get the excavator inside, there was always a slurry layer that made things difficult to move the excavator around. The walls were fairly steep which made entering and existing difficult at times. We needed big amounts of material for the project which a bogey could not enter the job due to soft ground beneath the manicured turf so this resulted in much more loads of smaller trucks. We had more turf to lay then anticipated because of the soft ground the trucks would leave large divots. The project was delayed a month due to much rain and even when we had the dryer days the ground was still holding much water.