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.