Soil conditioning in tunnelling involves modifying the ground as it is excavated to make its properties suit the operation of the tunnelling machine, chiefly when working in earth-pressure-balance (EPB) mode. Lubrication in pipe jacking involves injection of a lubricant around the pipes to reduce the frictional resistance as the pipes are driven through the ground. The two effects can combine, for instance when pipe jacking behind an EPB machine, or because soil conditioning also has important lubricating actions. The traditional material for both purposes has been bentonite, but recent years have seen the introduction of polymer materials and foams as alternatives or additives to bentonite.
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