A slope stabilisation solution was required along the N2 National Route in the Western Cape.
The project
The project came about due to a slope stability problem on a 55m long embankment of the N2 national route, 104km East of Cape Town.
Circular crack failure was observed at the road surface as a result of a movement of the road embankment fill.
We entered into a contract with the South African National Roads Agency for the ground improvement (installation of jet grouting columns), roadworks (pavement rehabilitation) and drainage improvement (installation of concrete culverts).
The challenge
The geotechnical investigation showed that the slope failure had occurred as a result of water ingress and percolating piping of water through the underlying fill.
This fact led to a design incorporating jet grouting columns, not only to stabilise the slope and roadway, but also to act as a grouting operation to fill the cavities where piping had taken place.
The solution
186 no. jet grout columns were set out in a grid of 2.5m x 2.5m. The column depth varied between 3m and 14m depending on the in-situ mudstone horizon. The column diameter of 800mm with a mushroom head of 1 200mm on the upper meter was verified through the installation of various test columns in different soil conditions.