Abstract

Characterizing the temperature-dependent shear mechanical responses of rock masses under constant normal stiffness (CNS) boundary conditions is of crucial importance for evaluating the stability and performance of deep underground projects. This paper experimentally analysed the shear mechanical properties and dilatancy deformation of sandstone exposed to high temperature with respect to various initial normal stresses under a constant normal stiffness. The results indicate that the developed thermally induced defects cause the porosity of sandstone to increase by 42.48% in a temperature range of 25–800 °C, while the P-wave velocity, unit weight and fractal dimension of pores are reduced. A typical shear failure process including a fracture surface generation process and a shear slipping process of surface asperities is identified. Due to the formation of fracture surfaces, both the normal displacement and normal stress curves show notable sudden drops. The peak shear strength, residual shear strength and terminal normal stress all display an exponential variation with temperature, i.e., initial fluctuations or a slight increase, then a dramatic decrease, achieving a threshold temperature of 400 °C. The secant peak shear stiffness declines by 43.79–70.48% in a temperature range of 400–800 °C due to enhanced ductility and decreasing peak shear strength. With increasing initial normal stress, both shear strength and terminal normal stress increase, but the terminal normal displacement decreases by 52.68–57.37% due to weakened dilation effects. The normal stress–shear stress variation paths are plotted, and the apparent internal friction angle decreases with temperature. Two representative failure patterns, including shear off of surface asperities and edge spalling of the rock matrix, are identified. Both the shear area and mass loss ratios of the sheared rock samples increase with both temperature and initial normal stress due to weakened shear strength and strong shear dilation inhibition effects.

Article Highlights

1. 1.

   Temperature-dependent shear properties of sandstone under CNS conditions.

2. 2.

   Identifying a typical shear failure process of intact sandstone samples.

3. 3.

   Evaluating the dilatancy deformation with various initial normal stresses.

中文翻译：

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在恒定法向刚度边界条件下暴露于高温的砂岩的剪切力学响应

摘要

在恒定法向刚度（CNS）边界条件下表征岩体的温度相关剪切机械响应，对于评估深层地下工程的稳定性和性能至关重要。本文通过实验分析了在恒定法向刚度下，高温下砂岩在各种初始法向应力作用下的剪切力学性能和剪胀性。结果表明，在25–800°C的温度范围内，发达的热致缺陷导致砂岩孔隙度增加42.48％，而P波速度，单位重量和孔隙的分形维数减小。确定了典型的剪切破坏过程，包括断裂表面产生过程和表面粗糙的剪切滑动过程。由于断裂表面的形成，法向位移和法向应力曲线均显示出明显的突然下降。峰值抗剪强度，残余抗剪强度和终端法向应力均随温度呈指数变化，即初始波动或略有增加，然后急剧下降，达到了400°C的阈值温度。由于增强的延性和降低的峰值剪切强度，在400–800°C的温度范围内，割线峰值剪切刚度下降了43.79–70.48％。随着初始法向应力的增加，抗剪强度和终端法向应力均增加，但由于扩张效应减弱，终端法向位移降低了52.68-57.37％。绘制了法向应力-剪切应力变化路径，并且表观内摩擦角随温度降低。确定了两个代表性的破坏模式，包括表面粗糙的剪切和岩石基质的边缘剥落。剪切岩石样品的剪切面积和质量损失率均随温度和初始法向应力的增加而增加，这是由于剪切强度减弱和剪切膨胀抑制作用强所致。

文章重点

1. 1。

   在中枢神经系统条件下，砂岩的温度相关剪切特性。

2. 2。

   确定完整砂岩样品的典型剪切破坏过程。

3. 3。

   用各种初始法向应力评估剪胀性变形。