Fracturing mechanism of pre-damaged granite induced by multi-source dynamic disturbances in tunnels

Abstract

To elucidate the fracturing mechanism of deep hard rock under complex disturbance environments, this study investigates the dynamic failure behavior of pre-damaged granite subjected to multi-source dynamic disturbances. Blasting vibration monitoring was conducted in a deep-buried drill-and-blast tunnel to characterize in-situ dynamic loading conditions. Subsequently, true triaxial compression tests incorporating multi-source disturbances were performed using a self-developed wide-low-frequency true triaxial system to simulate disturbance accumulation and damage evolution in granite. The results demonstrate that combined dynamic disturbances and unloading damage significantly accelerate strength degradation and trigger shear-slip failure along preferentially oriented blast-induced fractures, with strength reductions up to 16.7%. Layered failure was observed on the free surface of pre-damaged granite under biaxial loading, indicating a disturbance-induced fracture localization mechanism. Time–stress–fracture–energy coupling fields were constructed to reveal the spatiotemporal characteristics of fracture evolution. Critical precursor frequency bands (105–150, 185–225, and 300–325 kHz) were identified, which serve as diagnostic signatures of impending failure. A dynamic instability mechanism driven by multi-source disturbance superposition and pre-damage evolution was established. Furthermore, a grouting-based wave-absorption control strategy was proposed to mitigate deep dynamic disasters by attenuating disturbance amplitude and reducing excitation frequency.

1. Introduction

The stability of rock masses is critical to ensure safety during both construction and service periods of deep-buried tunnels. Rockburst is defined as a dynamic rock mass disaster and is recognized as a sudden failure phenomenon caused by the release of internal energy [1]. Time-delayed rockburst, characterized by its prolonged incubation period and difficulty in monitoring, is regarded as a severe challenge to the safe operation of deep-buried tunnels [2]. The catastrophic mechanism of excavation-induced rock mass failure triggered by multi-source dynamic disturbances under high in-situ stress in deep environments remains to be fully clarified [3].

Stress-induced failure of surrounding rock is widely recognized as a critical factor affecting the safety of deep drill-and-blast tunnel excavation [4–6]. The use of blasting as an excavation method creates a larger excavation-induced damage zone compared to tunnels constructed using the TBM method, leading to varying levels of damage within the stress adjustment zone of the surrounding rock [7]. Researchers have identified several key factors contributing to the brittle failure of surrounding rock, including rock mass properties (e.g., rock strength, joints, or faults), in-situ stress conditions (magnitude and orientation), and excavation parameters [8]. Brittle failure in deep tunnels is primarily caused by stress concentrations exceeding rock strength, while external dynamic disturbances such as TBM excavation and blasting further weaken already stressed rock, accelerating damage and degradation [9,10]. Previous studies have often underestimated the changes in mechanical properties of surrounding rock under weak excavation-induced disturbance. Notably, multi-source dynamic disturbances are capable of accelerating failure in surrounding rock subjected to tangential stress concentrations.