Model test on mechanical characteristics of surrounding rock during construction process of super-large section tunnel in complex strata

Based on Ganggou tunnel of Jing-hu high-speed connection line road which crossed large fault zones, mechanical characteristics of surrounding rock were studied during the construction process of super-large section tunnels under complex strata. For this purpose, a large-scale three-dimensional assembled geomechanical model test system was designed and developed. The system included stress and strain field monitoring systems based on static data acquisition and a displacement field monitoring system based on raster ranging in order to monitor the mechanical response of surrounding rocks during tunnel excavating. Model tests on mechanics in construction process of super-large section tunnel under complex strata were conducted, and the data of displacement and stress were real-time monitored during testing through the pre-buried monitoring instruments at specific positions in the models. The results indicate that the displacement deformation of both horizontal and subsidence can be divided into three phases: slowly increasing phase, sharply increasing phase and steady state phase. The sharply increasing of horizontal displacement starts earlier than subsidence. Meanwhile, the three phases of stress accumulation, releasing and steady state of stress are also revealed. The research methods and results will guide similar engineering practices.