关键词: 白垩系砂岩, 冻结作用, 变形指标, 破坏特征, 微观结构

Abstract:

To study the effect of both low temperature and loading on the deformation and failure characteristics of water-rich Cretaceous sandstone in Longdong area, the uniaxial and triaxial compression tests and microstructure test on different sandstones (medium and coarse-grained sandstones) under different temperatures (−30, −20, −10, −5 and 25℃) and confining pressures (0, 4, 6 and 8 MPa) were conducted using MTS-815 servo rock mechanics testing machine and scanning electron microscope (SEM). Then the freezing-loading deformation, the failure characteristics and the internal mechanism of saturated Cretaceous sandstone were systematically analyzed. The results show that the pre-peak pore compaction deformation of sandstone samples is significant, and that of medium-grained sandstone is more notable. The decrease in test temperature and the increase in confining pressure can weaken the compaction deformation of samples and increase the rigidity and strength. And the post-peak deformation of samples is accompanied by a significant increase in volume. As the test temperature increases, the elastic modulus E, shear modulus G, and volume modulus K_v of the samples show a nonlinear attenuation trend of first fast and then slow, and these parameters of the medium-grained sandstone are always lower than those of coarse-grained sandstone under the same conditions. But the change laws of Poisson’s ratio m and Lame constant l are opposite. In addition, the relationships between these deformation parameters and test temperature can be well characterized by a unified exponential model. Under the negative temperature condition, the frost heave failure of the medium-grained sandstone is more serious than that of coarse-grained one, mainly in the form of transverse cracking and point-like bulge failure. Moreover, the loading failure mode of frozen sandstone samples is significantly affected by the factors such as lithology, temperature and confining pressure. The internal mechanism of the difference in deformation and failure of the two types of frozen sandstones is determined by their macro- and micro-structure characteristics such as grains and pores. The results obtained in this study are helpful for the development of the soft rock mechanics and the frozen shaft design of the coal mines in western China.

Key words: Cretaceous sandstone, frozen action, deformation parameter, failure characteristics, microstructure