Whole-process deformation laws and determination of stability criterion of surrounding rock of tunnels based on statistics of field measured data

Deformation of the surrounding rock during the whole excavation process is the basic premise to understand the evolution mechanism of interaction between the supports and the surrounding rock, which is also an important reference for stability evaluation of the surrounding rock and design of the supports. On the basis of collecting the deformation of the surrounding rock during the whole excavation process of 40 tunnels and underground projects, the whole process deformation and its key nodes, the distribution laws of deformation rate and deformation acceleration of the surrounding rock and the influencing factors are systematically analyzed. The results show that the advance deformation and basically stable deformation of the surrounding rock increase with the construction speed and decrease with the excavation radius, while the corresponding displacement release rates have no obvious correlation. With the increase of the surrounding rock, the advance deformation and basic stable deformation increase, and the corresponding displacement release rate decreases instead. By improving the Hoek’s formula, the whole-process deformation of the surrounding rock is fitted, and the goodness of fitting is above 0.95, which can provide a basis for the solution of loss displacement. The deformation rate of the surrounding rock first increases and then decreases with time, while the deformation acceleration shows the characteristics of "sinusoidal curve", both of which change significantly with tunnel radius and construction speed. According to the analysis results, it is pointed out that the deformation rate of the surrounding rock is small and the deformation duration is long for the large-section tunnels under unfavorable geological conditions, and the deformation acceleration should be taken as the main index to judge the stability of the surrounding rock. Furthermore, the determination method for deformation acceleration threshold is given.