| The exploration of hot dry rock geothermal—a kind of new cleaning energy resource—involves numerous foundational and technological subjects, such as geonomy, thermodynamics, rock mass mechanics, deep drilling technology, material science, testing technology in deep earth, etc. There are lots of problems in the process of exploring geothermy needing solving and studying, such as high depth holes drill, distortion of holes after drill, hydraulic fracturing,the transfixion between drill holes and cracks, the design of artificial reservoir and the control of the temperature field in it, etc. The rock cracking under high temperature is called the heat cracking. With the need of practical engineering application, the cracking rules of rocks under high temperature and triaxical stress need to be studied.Aiming at the above problems, this paper adopted the acoustic emission experiment under triaxical stress, acoustic emission experiment and penetrability experiment, CT scanning experiment and the contrasting studies of the senior scholars' works, the research on the heat cracking rules of the rocks under triaxical stress have been studied and the corresponding research findings are as follow:1) Acoustic emission experiment on jumbo sized (φ200×400mm) granitesample has been made under high temperature and invariable triaxical stress(axial pressure 860KN and confining pressurel150KN) by the use of 20MNservo controlled triaxial rock testing system of high temperature and highpressure. The main findings include:(1) Through the noise experiment, the noise in acoustic emission experiment has been confirmed, and the size of character parameter and its transformation laws have been analyzed.(2) The appearance of the acoustic emission is brought by the partial energy accumulation and release inside of the rocks, the interior structure of which has gained obvious changes with the influence of pressure and temperature. Meanwhile, the temperature's threshold value when heat cracking happens to the granite is around 110℃to 120℃.(3) In the first stage of the experiment with the normal temperature from 24℃to 60℃, the acoustic emission was caused mainly by the conformity and adjustment of the original crannies under the triaxical stress rather than by the heat cracking of the rocks. In the middle stage of the experiment with the temperature around 260℃acoustic emission brought about heatedly, when with the relative centralization of the energy the interior structure of the rocks suffered from bigger destruction or there were bigger transfixion crannies coming into being.(4) Under the invariable triaxical stress, as the temperature goes up, the acoustic emission phenomenon, so called cracking rules, can be divided into 5 stages: the conformity stage of the original rock crannies at the normal temperature from 24℃to 60℃; Still stage of the acoustic emission before the heat cracking between 60℃and 120; The acoustic emission of heat cracking stage 120℃and 260℃; Still stage of the acoustic emission after the large-scale heat cracking between 260℃and 340℃; Hypo-heat cracking beginning stage after 340℃. In the original rock state, the heat cracking is an alternant and continual process in which the energy centralizes and releases.2) The main findings as follow have been revealed by the contrasting research on the acoustic emission experiment and the penetrability experiment under the same conditions, the contrasting research on the results acquired from the acoustic emission experiment and the CT experiment of the sample splice up after the acoustic emission experiment as well as the senior scholars' works.(1) The change of the penetrability is linked to the characteristics of the crannies happening in every heat cracking stages inside of the rocks, and those of seepage channels as well as the seepage network. At the same time, these characteristics have been discussed. The phenomena of jump and suck-up in the experiment were produced by the block of the seepage channels.(2) By the contrast of acoustic emission and penetrability experiment, it was found that the laws of acoustic emission correspond with that of penetrability and the crack laws of rocks have been concluded. In the scale of the testing temperature, the crack stage can be divided into 3 stages: Low seepage and no heating stage from the normal temperature to 120℃;Heat cracking stage with frequently increasing penetrability between 120℃and 260℃; No heat cracking stage with increased penetrability between 260℃and 300℃. Compared with the laws of acoustic emission, there is hysteresis quality in penetrability laws.(3)3 models in the heat cracking of the rocks have been put forward: tiny cranny, single macro cranny and cranny network. The transformation laws and characteristics of the 3 models under the impact of heating have been discussed in details. The real heat cracking of the rocks in this experiment was the combination of one or several of the 3 models.(4) The validity of the series of conclusions put forward above has been validated by systematical CT experiment and Chen Yong's study.
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