Abstract:

Neogene Pliocene series red beds in Qingyang of Gansu Province, due to special origin, the engineering mechanical properties are different from that of the southern red clay. It is important to systematic study the mechanical characteristics of large crosssection tunnel support structure through the stratum. Taking Qingyang Tunnel of Yinxi Highspeed Railway as the research object, the spatiotemporal distribution characteristics such as internal force of lining structure, surrounding rock pressure, deep displacement for 5-10 m surrounding rock, and convergence deformation of support are obtained through field measurement and finite element simulation. The causes of stress state of liningsurrounding rock composite structure that reflected by field monitoring results are analyzed. In addition, ABAQUS software is used to simulate the process of tunnel excavation so as to contrast and verify the force law of lining structure. The characteristics of crustal stresssurrounding rock pressureinternal force of lining structure in the tunnel of this stratum are obtained. The results show that: (1)The indexes of surrounding rock belong to the critical category of extremely hard soil and extremely soft rock. (2)The surrounding rock of the lining structure at this stratum is with good quality, and the horizontal crustal stress is twice as big as the vertical crustal stress. Therefore, it can be optimized to level ⅢⅣ surrounding rock and increase the lateral force coefficient. (3)The primary support without closure cannot effectively limit the deformation of surrounding rock, and the stress state can be improved by measures such as setting temporary invert. The numerical simulation results are consistent with the field measurement. (4)The severe deformation area is within 1 time hole diameter range from the excavation limit around the cave to the surrounding rock, the deformed areas are mainly at crown. The stress on the invert of inner lining can be effectively reduced by delaying excavation.

Key words: tunnel engineering, large crosssection tunnel, mechanical characteristics, monitoring measurement, finite element simulation