The failure mechanism of tunnel is more complex under the high geostress and high ground temperature action for deep hard rock tunnel. Loading-unloading triaxial tests on granite under different temperatures were carried out. The complete stress-strain curves of rock，mechanical parameters of rock，and macro failure types under different temperature conditions were analyzed in detail. The results show that there is a temperature threshold value of 60 ℃–100 ℃. The failure is from ductile to brittle with the temperature increase if the temperature does not exceed the threshold value. Temperature enhanced the brittle damage of hard rock. Shear is the dominant failure mode with the temperature increase. Then based on the test，thermo-mechanical coupling calculation was carried out. The thermal effect of excavation unloading for hard rock tunnel was calculated by using a brittle constitutive model and energy release rate index. The mechanical response to tunnel excavation was analyzed under different ground temperatures. The plastic zone，stress index and energy release value were compared quantitatively under different ground temperatures. The calculation showed that temperature increase would make rockburst intensity increase，and shear zone increase. The result of calculation and test data is consistent，and the analysis could benefit the understanding of brittle failure under high ground temperature.

According to the results of marble loading and unloading tests，marble failure characteristics and energy evolution under different stress paths are studied. Results show that the absorbed total energy  of conventional triaxial compression is higher than that of uniaxial compression. The release velocity of elastic strain energy under conventional triaxial compression is slower than that of uniaxial compression after peak strength. The energy storage limit of conventional triaxial compression is higher than that of uniaxial compression. The peak strength and peak strain increase with the initial confining pressure increasing. Marble failure mode transfers from tension-shear failure to shear failure. The absorbed total energy  and elastic energy increase. But the dissipated energy   has no significant change. Confining pressure has no significant effect on the rate of   and  . The peak strength and peak strain decrease with the unloading velocity increasing. Marble failure mode transfers from shear failure to tension-shear failure. The absorbed total energy  and elastic energy   decrease. But the dissipated energy has no significant change. Unloading velocity has no significant effect on the rate of   and  . The absorbed total energy and peak strength are in a linear relationship. The energy storage limit and peak strength are also in a linear relationship.

Digital core establishment，as an ideal model to study the physical and mechanical properties of rock, provides an undifferentiated numerical simulation. However，high level of accurate and efficient modeling restricts the promotion of digital core reconstruction technology. The traditional methods are time-consuming and laborious in processing CT slice based scanning data，due to limited number of scanning layers and the pore-fracture recognition depending on the traditional threshold segmentation algorithm. Taking coal as an example，the artificial intelligence recognition is introduced to realize the recognition of four micro phase states of pore，fracture，high-density mineral and coal matrix，and the fractal reconstruction is carried out for filling in information gaps. Data sets of four micro phase states are established and enhanced based on micro CT scanning，and a labelling software is developed for effectively distinguishing four kinds of micro-phases of materials. Especially for improving the efficiency and precision of identification，the FCN architecture is optimized and the Crack-FCN network structure is proposed，which has few network layers and low error rate. Moreover，the Potrace algorithm is introduced to quantitatively calculate fracture area，length and width，and the centerline extraction algorithm is introduced to effectively determine the complex topology. Considering the fractal similarity of fractured surface and to solve the problem of missing information between two adjacent CT slices，a fractal reconstruction algorithm is developed dependent on the local self-similar property and then optimized to improve the computational efficiency. Compared to the line interpolation and cubic spline interpolation，the fractal interpolation is more effective to describe the local roughness，and more importantly，the accuracy of intelligent recognition will continue to be improved with the continuous enhancement of data-set. This paper breaks through the traditional view and introduces the FCN into construct digital core of rock，and provides new technical support for the efficient and accurate establishment of numerical modelling.

Compressed air energy storage(CAES) is a kind of large-scale energy storage technology that is expected to be commercialized. As an underground gas storage engineering structure，the newly-excavated hard rock cavern has attracted much attentions due to its wide adaptability and practicability. Compared with traditional underground engineering，underground rock caverns for compressed air storage face many new challenges due to the periodic high internal pressure and temperature during the course of operation. Recently，great advances about the construction and operation of compressed air energy storage in hard rock caverns have been made by researchers around the world. It is thus imperative to systematically review the progress in this direction，which can help engineers to better understand the development of such emerging energy storage technology in practice. Firstly，the basic principles and scientific problems of compressed air energy storage are described. Secondly，the research progress related to construction and operation is summarized，including airtight performance of sealing structure，thermal transition process of surrounding rock-lining-sealing layer-air during the process of inflation and deflation，uplift failure of the rock mass，and plug stability. Besides，several key scientific and technological issues which need to be further studied are discussed.

The research on rockburst could be traced back to the first half of the 18th century. Since then，although a great deal of scientific achievements have been published，this topic is still an outstanding problem worldwide so far. As an overall review，this paper presents first some background information relating case histories，research methodologies etc. at home and abroad. And then，the criteria and classification of rockburst commonly used at home and abroad are described. The forecast and prediction of rockburst phenomena are discussed too. After that，the rockburst control，including stress relief drilling，water injecting，anchoring etc. are overviewed. Finally，a key case history related to the rockburst phenomena occurring in the auxiliary adit of the Jinping II Hydropower Station is described emphatically. On the basis of analyzing the previous information，some practical methods for classification，prevention and mitigation of rockburst are proposed.