Study on correlation between TBM tailings gradation and granitic gneiss surrounding rock stability

In the process of double-shield TBM excavation, it is difficult to directly observe and test the characteristics of the surrounding rock. In this paper, the screening test of the different type tailings in the wet state was carried out to obtain the gradation curve and curve evaluation index. Combining with the excavation parameters and the surrounding rock characteristics of the tailings, a comprehensive analysis was carried out to establish the evaluation system among with the tailings gradation characteristics, lithology characteristics and excavation parameters. The results showed that: Sparsely fissured rock: the tailings are extensional fractures, the tailings gradation curve is inverse “ S ” type and gentle, and the evaluation index value: (1.50 > lg( Cu ) > 1.35), (1.90 > C c > 1.10). Broken surrounding rock: the curve is “ L ” type and steep, the content of coarse particles is much more than that of fine particles and (1.10 > lg( Cu ) > 1.00), (2.60 > C c > 2.40). Fractured rock: the curve is “ Step ” type, the tailings particles lack the middle particle size, the minerals are mostly weathered, (2.15 > lg( Cu )> 1.95), (0.09 > C c > 0.07). The research results have good applicability to the surrounding rock stability evaluation of the example tunnel, which verifies the feasibility of the method.