Characteristics of surrounding rock pressure of deep tunnel in segment of geological structure development

Based on the measured data of surrounding rock pressure and deformation in the segment of Longxia Railway at Xiangshan extra-long tunnel that is buried deeper than 500 m with high development of geological structure, studied the characteristics of surrounding rock pressure, formation mechanism of the deformation pressure, etc., in the segment of the deep tunnel with high development of geological structure are studied. The research shows that: in the deep segment of tunnel, large deformations happen in the sections with lots of structure planes, folds, reversed faults and little ground water, after the excavation, even though the surrounding rock strength is higher. The larger surrounding rock deformation is contributed by the opening and volumetric dilatancy of the structural planes, which are compacted by the self-weight stress and residual tectonic stress, as the lateral confinement is eliminated after the excavation. For that, great deformational pressure from the surrounding rock may be exerted to the primary support. The surrounding rock pressure in the above segment has the following characteristics: (1) The surrounding rock pressure is greater in the sections with little ground water than the sections with a lot. (2) The surrounding rock pressure largest on the arch crown to the hance in the sections with syncline that developed in the tunnel longitudinal, the nearer to the core of the syncline, the greater the pressure. (3) In the sections developed with folds, the surrounding rock pressure is larger in the direction perpendicular to the fold axis. (4) In the sections developed with reversed fault, the surrounding rock pressure is larger in the side that opposite the fault dip; and the surrounding rock pressure in the position of fault surface is largest in this side, smallest in the other side. (5) The surrounding rock pressure on the lower bench is smaller than that on the upper bench, the longer the time between the excavations, the greater the difference between the pressure.