Behavior of lubricant injection into over-cutting area for slurry pipe jacking

Slurry pipe jacking is firmly established as a special method for non-disruptive construction of underground pipelines. The advantages of this method have been widely recognized. During the pushing processes, the mud slurry is injected into the face and over-cutting area surrounding the pipes. After completion of the pipeline, the mortar is injected into the over-cutting area in order to provide permanent stability of the surrounding soil. Lubrication can effectively reduce the needed thrust if a discrete layer of the lubricant is maintained between the pipe and the excavated soil. Lower frictional force allows greater jacking lengths to be achieved. Reduction of frictional stress around the pipes is closely related to the efficiency of lubrication injection. The lubricant must be designed to form a layer in the surrounding soil, be pressurized to overcome ground water pressure and stabilize the over-cutting area. Lubricant should fill the complete over-break void to minimize surface settlement. In this paper the frictional force between the pipe surface and lubricant at a soil-pipe interface are considered by looking into some parameters controlling lubrication gel stability. The lubrication gel stability is provided for chemically enhanced lubricant gels against loss of water content. Frictional force is responsible for this loss of water content. During laboratory testing, frictional force is measured directly from the concrete-lubricant interface with different gel stability. Finally, as complementary work, in order to examine the effect on the ambient surroundings of the lubricant, a fundamental investigation is performed and various results are discussed.