Dynamic response of deep tunnel subjected to contour blasting-unloading considering internal free surface radius

Abstract

The dynamic stress response of the surrounding rock in deep tunnels during contour blasting is first derived using elastic statics and dynamics theory alongside Fourier transform methods. This solution uniquely accounts for the effects of lateral stress coefficient, blasting loading, two-dimensional unloading, and the redistribution of static stress fields induced by internal free surfaces. Discrete element numerical simulations are also performed and cross-validated with the theoretical model. The study analyzes and discusses the effects of in-situ stress levels, lateral stress coefficients $k$, and internal radius ratio $\tilde{r} _0$ (ratio of internal free surface radius to tunnel radius) on the failure characteristics and mechanisms of surrounding rocks. The results indicate that increasing $\tilde{r} _0$ can reduce the unloading amplitude, thereby decreasing the dynamic circumferential compressive stress and circumferential cracking induced by unloading, especially under high in-situ stress. Under low stress levels, the maximum dynamic radial compressive stress during blasting decreases, reducing radial compression-shear failure. Simultaneously, the dynamic circumferential tensile stress is also reduced, thereby minimizing blasting-induced radial fractures. However, under extreme lateral stress conditions (k < 0.2), adjusting $\tilde{r} _0$ cannot cause the circumferential stress to exceed the radial stress at the tunnel contour along the maximum principal stress direction. As a result, an ideal contour blasting effect cannot be achieved, and failure continues to propagate radially. In conclusion, the derived dynamic blasting-unloading stress response, in relation to the internal radius ratio, provides theoretical analysis tools for understanding the failure characteristics and mechanisms of surrounding rock during contour blasting, serving as a foundation for optimizing blasting and support design.

Keywords

Dynamic response / Contour blasting / Transient unloading / In-situ stress / P-wave and S-wave / Internal radius ratio

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

CRediT authorship contribution statement

Siyu Peng: Writing - original draft, Visualization, Validation, Software, Methodology, Formal analysis, Conceptualization. Xibing Li: Supervision, Project administration, Funding acquisition. Lisha Liang: Software, Conceptualization. Jingyao Gao: Writing - review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The research was supported by the National Natural Science Foundation of China (Grant Nos. 51927808 and 52434006) and the Postgraduate Innovation Fund Project of Hunan Province (Grant No. CX20200242). The financial supports are gratefully acknowledged.

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