Pipe Fracture Mechanism

The original pipe bursting application used for replacement of gas mains in the UK, used a pneumatic hammer pulled through the existing pipe using a cable. In this configuration, the tension in the cable was mainly used to keep the bursting head in good contact with the existing pipe thus relying on the hammering mechanism to fracture the existing cast iron pipes. The cable and pulley configuration, the flexible pneumatic supply line and the small diameter of the PE replacement pipe allowed the work to be accomplished with minimal additional excavation and primarily using existing manholes. As the method was applied to sewer pipes in larger diameters, approaches were introduced relying on a static pull and the conical head to burst existing brittle pipes such as clay pipes and unreinforced concrete pipes. Fins are also used on the bursting head to provide stress concentrations to aid in the fracture process. The static pull could be applied using suitable cable mechanisms or using a segmented rod pull system. Today, both static pull and dynamic methods are widely used and the dynamic methods may use pneumatic or hydraulic impact systems. The choice of system depends on the type of host pipe and backfill, job configuration, equipment availability and contractor preference.