The mechanical properties of marble, limestone, and sandstone as well as the stress-strain curve, the varying characteristics of the peak strength, the peak strain and elastic modulus were studied by using the MTS810 Rock Mechanics Servo-controlled Testing System under the action of temperatures ranging from room temperature to 800 . Results show that ℃ (1) the peak strength and elastic modulus of marble fluctuate at the temperature from normal to 400 ; and they decrease gradually over 400 .℃ ℃ (2) With the rise of the temperature, the peak strength and elastic modulus of limestone show downward trend from normal temperature to 200 ;℃ have little change from 200 to 600 ; and decrease sharply ℃ ℃ over 600 . ℃ (3) The peak strength of sandstone shows a downward trend while a little change for elastic modulus at normal temperature to 200 ; and fro℃ m 200 to 600 , the peak strength of sandstone i ℃ ℃ ncreases while a little change for elastic modulus; the peak strength and elastic modulus decrease rapidly at the temperature over 600 .℃ (4) The peak strain of limestone shows little change at normal temperature to 600 , however, the peak strain increases rapidly over 600 ; and for marble and san ℃ ℃ dstone, the peak strain decreases with the rise of the temperature from normal temperature to 200 , ℃ the peak strain increases rapidly over 200℃. The result can provide valuable references for the rock engineering design at high temperature.rock mechanics, high temperature effect, mechanical properties, experimental study It is a new challenge for rock mechanics to deal with rock engineering problems at high temperature. Most rock mass in nuclear waste bury, geothermic exploitation and underground development in big city may undergo high temperature, so rock strength and deformation characteristics under high temperature need to be studied in detail. Related mechanical parameters are the basic foundations for excavation of rock underground engineering, support design and stability analysis of the surrounding rock. The effect of temperature on the physical and mechanical properties of rocks has been an important study topic in rock mechanics. Heuze and Lau et al. [1][2][3] tested a number of rock's deformation modulus, Poisson's ratio, the tensile strength, compressive strength, cohesion and internal friction angle, viscosity, and other parameters and discussed the dependence of lateral pressure and high temperature on thermal expansions as well as the creep characteristics of the rock. Du et al. [4][5][6][7][8] studied the mechanical properties of granite, marble, and sandstone which had been cooled down after experiencing high temperature, and analyzed the variations of stressstrain curve, the peak stress, peak strain, elastic modulus and Poisson's ratio after high temperature. Meanwhile, the mechanical properties of the fused tuff, granite and flow striated tuff-breccia under different temperatures were studied by Zhu et al. [9] using the uniaxial compres-

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Rockburst frequently occurs in deep underground engineering, which poses a threat to safety and causes economic losses. Water injection into surrounding rock masses is an effective method for preventing rockburst, and the moisture content of rocks is significant for assessing the probability of rockburst. However, the majority of studies focus on the relationship between the macromechanical properties of rock masses under static loads and the moisture content of rock masses and seldom explore the impact of moisture variation (under dynamic loads) on the mechanical properties and energy dissipation. In this paper, the mechanical properties and energy dissipation of sandstone with different moisture contents have been experimentally investigated by the split Hopkinson pressure bar (SHPB) test. The test results indicate that the peak strength, dynamic elastic modulus, and unloading elastic modulus of sandstone in dry conditions are considerably larger than those in moisture conditions, and the three parameters linearly decrease as the moisture content increases from 0% to 2.58%. The distribution law of sandstone fragments with different moisture contents has been investigated by sieving test fragments with different grain sizes of grading sieves. The results show that the percentage of large grain size fragments incrementally decreases, and the percentage of small grain size fragments incrementally increases with moisture contents from 0% to 2.58%. When the moisture content ranges from 2.01%∼2.58%, the fractal dimension linearly increases, which indicates that the higher the moisture content is, the larger the dimension of the broken sandstone is. The calculation results for energy indicate that the sandstone energy attains the peak value with 0% moisture content. When the moisture content ranges from 2.01%∼2.58%, the reflected energy increases, and the transmitted energy and dissipated energy linearly decrease. In addition, the surface energy of the sandstone with different moisture contents has been investigated by converting fragments into spheres with the corresponding size. The results indicate that the smallest surface area of sandstone is obtained in dry conditions, but its surface energy in dry conditions is larger than that in moisture conditions. When the moisture ranges from 0% to 2.58%, due to 3% illite and 2% chlorite clay minerals reacting with different proportions of moisture, the surface areas of sandstone fragments linearly increase and the surface energy of sandstone linearly decreases.

The instability of layer-crack plate structure in coal wall is one of the causes of rock burst. In the present paper, we investigate the formation and instability processes of layer-crack plate structure in coal wall by experiments and theoretical analysis. The results reveal that layer-crack plate structure formed near the free surface of the coal wall during the loading. During the formation of the layer-crack plate structure, the lateral displacement curve of the coal wall experiences a jagged variation, which suggests the nonlinear instability failure of the coal wall with a sudden release of the elastic energy. Then, a dynamic model for the stability analysis of the layer-crack plate structure was proposed, which takes consideration of the dynamic disturbance factor. Based on the dynamic model, the criterion for dynamic instability of the layer-crack plate structure was determined and demonstrated by an example. According to the analytical results, some control methods of dynamic stability of the layer-crack plate structure was put forward.