The new bypass should be ready before Christmas, but meanwhile the closure of the N2 from Grahamstown to Port Elizabeth two-and-a-half weeks ago after its collapse has made road logistics complicated and expensive. Desiree Schirlinger gets to the bottom of a very costly mistake.
The new bypass should be ready before Christmas, but meanwhile the closure of the N2 from Grahamstown to Port Elizabeth two-and-a-half weeks ago after its collapse has made road logistics complicated and expensive. Desiree Schirlinger gets to the bottom of a very costly mistake.
Roland Thompson, the South African National Roads Agency Limited (Sanral) manager of maintenance and toll for the Southern Region, shed some light on the 25m-long sinkhole on the N2 to Port Elizabeth, 25km from Grahamstown.
“The slip was caused due to the failure of the cut-off berm that is supposed to reroute water to the culverts,” said Thompson.
A berm is the raised embankment around many roads, which acts a buffer between the foundations of the road and water run-off. Its graduated slope helps direct the water to run along to the sides of the roads and to not flow over the top or through the soil underneath.
A culvert is a drainage pipe that runs under roads and acts as an outlet for water to flow through.
“The [failure of the berm]caused the water to build up at the bottom of the berm, creating a weak point,” Thompson said. “The water then tunnelled through the fill [the soil under the N2]due to the high water pressure from all the rains. This small tunnel became bigger and bigger and eventually caused the big slip.”
A road engineer from a private engineering company confirmed what Thompson had said.
The source, who wasn't prepared to go on record until he'd completed a full investigation, said it appeared the water had started pooling on the western side of the N2 road embankment and forged a random pathway flowing through the embankment fill, emerging on the lower/downstream side of the road.
The heavy, persistent rains had led to increased pressure from a greater volume of water flowing through/under the embankment, accelerating the erosion and causing the collapse.
Thompson estimates that the erosion process through the foundation had probably taken only a few hours, depending on the water pressure.
“Once the tunnel was established the slip occurred with in minutes, if not seconds,” he said.
Sanral have confirmed that the R72 between Port Alfred and Kenton is once again open for light vehicles, with three stop-and-go stations. They hope to make the route open to trucks and heavy vehicles later this week.
Thompson said construction of the detour around the N2 slip is on track to be completed early in December.
Buses and delivery trucks have meanwhile been forced to make a costly 225km detour via Bedford to get to from Port Elizabeth to Grahamstown, while engineers estimate that road repairs and construction of the bypass will cost millions.
