Pumice mineral using as a backfill grout injection in TBM excavations

Shielded full-face tunnel boring machines (TBM) have been used in the mining and construction industry for many years in underground tunnel excavations. There are two important elements of this manufacturing method, which is based on the principle of filling every voids in underground excavations that will meet certain strength values; the first is reinforced concrete structures consisting of precast segments, and the second is backfill injection injected between these segments and the ground cavity. In a tunnel opening in which the excavation-support cycle progresses rapidly, therefore it is desirable to improve the mechanical requirements of the backfill mortar, such as early setting, reaching high early strengths, maximum gap filling, easy pumpability, reducing water permeability into the precast segments, and at an affordable cost. In addition to being an expensive binder, the cement used in backfill mortar also causes CO₂ emissions during its production. All these factors motivate the tunnelling industry to reduce the use of cement in backfill mortar and to seek alternatives. In this direction, the use of different pozzolans as additives to improve the properties of the backfill mortar been examined. In this study, as a pozzolan named pumice was obtained by chemical synthesis from rocks containing high percentage of silica by weight. Cement backfill mortar samples mixed with different proportions of pozzolans at different ratios will be prepared and the optimum pozzolan ratio was be determined by strength tests. With the findings of this research provides to define the suitable pozzolan that’s backfill mortar.