ABSTRACT
A 4m high earth embankment was constructed out of compacted residual granite soil to form a reservoir to contain spills of waste water at a sewage treatment works outside Johannesburg. No spillway was provided. The dam was overtopped and a 15m wide break formed. Repair of the dam incorporated a drop inlet spillway with an outlet pipe and a pressure relief drain pipe. The residual soil was again used for the embankment earthfill. Precautions were taken in the design of the various components of the works and in the specification of the construction procedures because of the high erodibility of the soil. Despite all this, on first filling of the reservoir a piping failure occurred through the embankment. Investigation of this second failure revealed a number of deficiencies in the detailing and in the execution which could have contributed to the failure.
