Correct understanding of rock dilatation plays a non-negligible role in the safety of rock engineering and the efficiency of geological resources extraction. Although the significance of dilatation under quasi-static loading or unloading conditions is well-studied, its behavior under dynamic loads remains poorly understood. This is largely because conventional dynamic testing system fails to capture the volumetric strain evolution of rock under confinement. This study develops a transparent confining chamber in SHPB system with which high-speed 3D-DIC is capable of measuring both axial and circumferential strain history of dynamically compressed rock. The progressive failure stages and volumetric change of red sandstone under confining pressure of 3.5 MPa and strain rates of 129∼292 s were studied and compared with those in quasi-static case. Results show that, the normalized stress thresholds of crack initiation and dilatancy in dynamic cases are much smaller than those in the quasi-static one. The volumetric variation of soft rock is characterized by four distinct stages: elastic contraction, pre-peak dilatancy, strain-softening dilatancy and strain-recovery dilatancy. The pre-peak elastic contraction is negligible compared to the post-peak dilation, and the ultimate dilation observed in dynamic compression is significantly greater than that in quasi-static compression. Increasing strain rate delays the onset of dilatancy, decreases the dilatant rate but remarkably extends the strain-softening dilatant process which is dominant in total dilation. A rate-dependent piecewise model incorporating key strain thresholds and a dilatancy rate factor was established to characterize the dynamic dilatancy behavior. The research results provide a new insight and possible method in dilation prediction for underground engineering subjected to dynamic loading.

中文翻译：

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动载下软岩剪胀行为试验研究


正确认识岩石膨胀对于岩石工程的安全和地质资源开采的效率有着不可忽视的作用。尽管对准静态加载或卸载条件下膨胀的重要性进行了充分研究，但对其在动态载荷下的行为仍知之甚少。这主要是因为传统的动态测试系统无法捕获岩石在约束下的体积应变演化。本研究在 SHPB 系统中开发了一个透明的限制室，高速 3D-DIC 能够测量动态压缩岩石的轴向和周向应变历史。研究了围压3.5 MPa、应变速率129∼292 s下红砂岩的渐进破坏阶段和体积变化，并与准静态情况进行了比较。结果表明，动态情况下裂纹萌生和剪胀的归一化应力阈值远小于准静态情况下的裂纹萌生和剪胀应力阈值。软岩的体积变化具有四个不同的阶段：弹性收缩、峰前剪胀、应变软化剪胀和应变恢复剪胀。与峰后膨胀相比，峰前弹性收缩可以忽略不计，动态压缩中观察到的最终膨胀明显大于准静态压缩中的最终膨胀。增加应变率会延迟膨胀的开始，降低膨胀率，但会显着延长在总膨胀中占主导地位的应变软化膨胀过程。建立了结合关键应变阈值和剪胀率因子的速率相关分段模型来表征动态剪胀行为。 研究成果为动荷载下地下工程膨胀预测提供了新的见解和可能的方法。