Study on the safe distance of spatial intersecting tunnel cavern under ground shock

Abstract

The vertical distance of intersection area is an important factor dominating the service performance of spatial intersecting cavern. To obtain the influence of vertical distance on the dynamic response of orthogonal spatial intersecting caverns under ground shock, the plastic region and peak particle velocity (PPV) distribution are investigated by numerical simulation. A finite-dynamic model is established to simulate the mechanical response of the deeply bureid structure subjected to coupled static and dynamic load, with an artifical boundary condition setting method. The results indicate that as the vertical distance decreases, the plastic region in the intersection area gradually merges, while the bolt support at the lower cavern vault effectively suppresses the destruction of the intersection area. The free surface of the lower cavern vault weakens the bottom support conditions of the upper cavern floor structure, resulting in higher PPV when vertical distance is smaller. Conversely, as vertical distance increases, isolation effect of upper cavern on ground shock weakens, leading to an increase and followed by a decrease in PPV at the lower cavern vault and straight wall. Morever, when vertical distance exceeds than 3 times the cavern characteristic size, the lower cavern exhibits dynamic response characteristics of deeply buried single-cavern. when vertical distance within 3 times, there is significant interaction between caverns with inverse relationship between dynamic axial stress on bolts in intersection area and PPV at lower cavern vault. It is recommended to use comprehensive criteria involving PPV and plastic region distribution to evaluate safety performance for spatial intersecting cavern.