Numerical Analysis of Induced Mechanism of Rockbursts in Tunnels

ABSTRACT: Rockburst is a sudden and violent failure characterized by the breaking up and expulsion of rock from its surroundings. Tunnel rockbursts pose a significant threat to the safety of excavation operations, leading to property damage and tunneler casualties. Buckling has been identified as one of the primary mechanisms causing rockbursts. Furthermore, it has been observed that rockburst can be induced by a seismic event or ambient blasting when stress waves reach the free surface of the underground opening. This paper aims to study numerically the induced mechanism of tunnel rockbursts based on the dynamic buckling of rectangular thin plates. When a rock stress wave travels toward a tunnel sidewall, it decomposes into horizontal and vertical components. The horizontal stress propagates to and reflects from the free surface, creating a rectangular thin plate of rock on the surface. The vertical stress activates parametric resonance in the rectangular thin plate, leading to the induction of a tunnel rockburst. An example of tunnel sidewall rockbursts from the Jinping II project is presented to parametrically study the effect of stress wave amplitude and frequency, static and dynamic components. Based on the mechanism analysis, measures are proposed to alleviate the hazard of tunnel rockbursts. 1. INTRODUCTION Horizontal extended underground structures can be categorized based on the purpose of the completed structure into two types: (i) Tunnels: Extended, flat, or only slightly sloping underground cavities with excavated cross-sections exceeding 20 m2. Primarily designed for road or rail transport, each tunnel features two openings to the surface. However, in some hydropower projects such as Jinping I and II in China, there are tunnels that have only one opening to the surface due to harsh conditions. (ii) Adits, drifts, or galleries: Extended underground cavities, either horizontal or sloping at angles less than 25° to the horizontal, with relatively small diameters. These structures accommodate pipes or cables, provide access, and serve as auxiliary structures during the construction phase or for permanent use. Often, they have only one opening to the surface (Maidl et al, 2013). The present paper is concerned with rockbursts in either tunnels, adits, drifts, or galleries.