High temperature alters the internal microstructure of rocks and consequently changes the physical and mechanical properties of rocks. Many studies have been carried out to examine the transformations in the microstructures of rocks under high temperature through near infrared spectroscopy (NIR), Raman spectroscopy, or thermo gravimetric analysis (TGA). The current review synthesizes the data from a number of literatures and summarizes the major transformations of silica rocks under high temperature. The analysis shows that silica rocks starts to lose the water adsorbed in open pores upon heating at about 150 °C. At 200-300 °C, the reaction between SiOH (silanole) in the rocks generates new Si-O-Si bonds as well as H2O, and decreases the open pores. The rocks undergo volume expansion at >550 °C, and the volume contracts and forms new micro pores or cracks which play an important role in the evacuation of the water., Jishi Geng, Qiang Sun, Yuchun Zhang and Yuliang Zhang., and Obsahuje bibliografické odkazy
In order to quantitatively study the influence of temperature and confining pressure on brittle plasticity of granite, this paper reviews previous studies regarding quantitative calculation methods for the brittle-plastic behaviors of rocks and their mechanical characteristics under high temperatures and confining pressures. Combining the experimental results for temperatures and confining pressures with theoretical calculations of brittleness and plasticity allowed quantitative calculations and evaluations for the brittleness and plasticity of granite to be obtained. The main conclusions are as follows. (1) High temperatures lead to a transformation of granite from brittle failure to plastic failure. Comparing six conventional empirical equations from the literature, the B3 and B6 can more accurately describe the relationship between the brittleness and temperature of granite. (2) When the confining pressure σ3 is less than 20 MPa, the internal pore structure and fractures of granite are re-compacted and reduced, which gradually increases its brittleness. With the increasing confining pressure, the pore structure changes again after exceeding 20 MPa. This initiates new cracks, which ultimately leads to a decrease of the granite brittleness. (3) The abrupt temperature for the brittle-plastic transformation of granite is approximately 800 °C, and the brittle-plastic transformation of granite is mainly affected by temperature and not the confining pressure.
Permeability plays an important role in the field of geotechnical engineering. Under high temperature and high pressure condition, the physical-chemical and structure properties (such as decomposition, oxidation, dehydration, evaporation, phase transition etc.) of rock have obviously changing, which are significant affected the rock permeability. In order to analyze the influence of temperature and confining pressure on the permeability of rock (sandstones, siltstones and conglomerates) data for permeability was obtained from the literature. The results indicate that temperature and confining pressure have great influence on the permeability of rock, especially for sandstone. There is a threshold temperature and when the heating temperature is lower than the threshold temperature, the permeability of sandstone gradually increases with an increase in temperature. When the heating temperature is higher than 300 ºC (especially 400 ºC), the permeability rapidly increases. The permeability of sandstone decreases gradually with the confining pressure increases. This study of the relationship between rock permeability and temperature and confining pressure lays a foundation for investigations of multi-disciplinary issues regarding high temperatures and high pressures and it can be used for the study of petroleum storage and safe nuclear waste disposal., Zhenlong Ge, Qiang Sun and Wenping Li., and Obsahuje bibliografii