RESPONSE CHARACTERISTICS OF PORE PRESSURE IN SOILS NEARBY METRO TUNNEL DUE TO TRAIN VIBRATION LOADING

The pore pressure behavior of soils nearby the tunnel of Shanghai Metro Line 9 was investigated chronically. The results show that excess pore pressure generates rapidly when the train vibration loading is applied. The excess pore pressure is about 1.2kPa at arch waist depth. After the last train passes through, the pore pressure starts dissipating. By the time that the last train passes 5minutes, excess pore pressure dissipates 80 percent. The excess pore pressure generated by shield construction is much higher than that of metro vibration. Site testing mainly shows the excess pore pressure dissipation. The distributions of excess pore pressure are as follows:above tunnel vault pore pressure increases with depth; below the tunnel vault, pore pressure reduces as the depth increase; surround the tunnel vault, pore pressure is larger and pore pressure contours are denser.