Abstract:

In order to investigate the strength degradation characteristics of surrounding rock at inverted arch of tunnel under the coupling action of train load and groundwater, the influences of different factors, i. e. train load, groundwater pressure, surrounding rock grade, etc. , on the practical loss of surrounding rock are analyzed by PFC simulation; and the calculation formula for particle loss rate is obtained. Meanwhile, the degradation characteristics of surrounding elastic modulus and peak strength are discussed, and the calculation formula for strength parameters after degradation is obtained. The study results show that: (1) The particle loss volume of surrounding rock is positively correlated to the surrounding rock integrity, train load and groundwater pressure; and the surrounding rock integrity affects the particle loss volume of surrounding rock greatly, followed by train load and groundwater. (2) The relationships among particle loss rate, atrain load and groundwater pressure is quadric; and the calculation formula for particle loss rate of surrounding rock is proposed. (3) The elastic deformation phase gradually disappeared and the range of plastic deformation gradually expanded with the increased ration of particle loss, which indicates the gradual transition from elastic-plastic to plastic. (4) With the particle loss rate increase, the elastic modulus and peak strength of surrounding rock decrease exponentially; and the calculation formula for degenerated strength parameters is obtained.

Key words: train load, groundwater, tunnel, surrounding rock degradation, particle loss, discrete element