There are two types of segmental shafts linings; the caisson and underpin, which suit major soil conditions and installation methods. The shaft range includes 6m to 25m (internal) diameters, and accessories such as internal cast-in protective linings.
The caisson method is suitable for soft soil conditions, where the shaft can be constructed above ground and pushed down from the surface using jacking force. The soil is then excavated from the inside and the smooth segmental linings are joined together by external fixings. The strong connections bolt together segment-to-segment and ring-to-ring, complete with gaskets, to form a finished shaft lining. The system retains all the benefits of strength, flexibility and speed of erection associated with a bolted ring, whilst providing the client with a safer system of working, by reducing man entry into the shaft and working at heights. The system also optimises site space during construction.
The underpin method maintains the same strength and benefits of the caisson method but is more suitable for hard soil condition where shaft jacking is not feasible. There is never more than one metre of ground open. Grouting between the outside perimeter of the constructed segmental ring and the excavated ground maintains the structural integrity of the shaft.
