Development of backfilling injection into over-cutting area including lubricant behavior for pipe jacking in deep strata

In Japan when urban infrastructures need to be constructed, the difficulty of utilizing the ground or shallow strata will necessarily lead to the more frequent use of the deep strata. The common construction methods are open-cut, pipe jacking, and shield methods. In recent years a new pipe jacking method has been established that can be adapted to 20 m below the ground or more. Using the method, the drivage machine and the jacking pipe continue to move an underground until the completion of the driving. Therefore an over-cutting area (so-called tailvoid) must be formed to lower the friction between the ground and the pipe. The over-cutting area is filled with lubrications. However, because the stress release of the ground continues to advance when the over-cutting area is formed, there are some challenges required to cope with the stability of the surrounding ground. In order to utilize the pipe jacking method in the deeper strata layers, the theory, analysis and installation of over-cutting area have to be systemized, and such systematic data must be stored. Therefore, the conditions of over-cutting area in the deep pipe jacking method are discussed using numerical analyses. Moreover, a lubricating material comprised of a mixture of surfactant and fly ash was developed for the application of pipe jacking in deep strata.