Field Forced Excitation Tests of Water-Rich Loess Tunnel Subgrade for High-Speed Railway

Water seepage is very serious after excavation in a water-rich loess tunnel and softening and mudding phenomena inevitably occur in the loess foundation. The effects of construction machinery repeated rolling and vibration will lead to drastic decrease of soil bearing capacity and increase of deformation. Although measures for drainage are taken during the construction process, many questions (such as uneven settlement of the track bed, the safety, stability and smoothness of the railway, and the long-term stability of the tunnel) remain to be answered for tunnels built on such foundations under cyclic loading of the high-speed train vibration. To answer these questions, we performed field forced excitation fatigue tests in a water-rich loess tunnel with simulation of high-speed train cyclic vibration. Our work is the first one of this kind, which solved the key issue relating to the long-term stability of water-rich loess tunnels under the excitation of the high-speed train vibration. The test results provide a pilot basis and technical support for the large-section tunnel design and construction under similar conditions. This work has filled the blanks of the water-rich loess tunnel design techniques and parameters.