Abstract:

In order to study the pore water pressure and deformation characteristics of the soil layer at the bottom of the tunnel under longterm vibration load of metro trains, an effective stress analysis model for crosssection of a typical tunnel on Phase II(eastern extension) of Beijing Metro Line No. 7 is established by using ADINA finite element calculation platform. The dynamic response of watersoil coupling in soiltunnel system at saturated site under the action of upperbound speed driving loads is analyzed. The variation law of pore water pressure in typical location is studied and the settlement caused by metro vibration is predicted. At the same time，the soil laboratory test is conducted on the fine sand of Line No. 7 and the development law of pore water pressure and vertical deformation of soil layer at the bottom of tunnel under the load of metro traffic are further studied. The study results show that: (1) Under longterm train vibration loads, the pore water pressure of soil at the bottom of the tunnel increases gradually, and the increase value decreases with the increase of soil depth. (2) The cumulative excess pore water pressure ratio and cumulative strain of soil increase with the increase of load amplitude. (3) Compared with nonequal consolidated conditions, the excess pore water pressure is larger under the condition of equal consolidation, but the cumulative strain is smaller. (4) The excess pore water pressure and strain caused by train vibration are small, and the excess pore water pressure is sufficient to dissipate during train outage.

Key words: metro tunnel, vibration load, pore water pressure, numerical simulation, dynamic triaxial test