Establishment of damage statistical constitutive model of loaded rock and method for determining its parameters under freeze-thaw condition

冻融条件下受载荷作用岩石损伤统计本构模型的建立及其参数确定方法

Cold Regions Science and Technology, Volume 160, April 2019, Pages 31-38

Wen Fang, Nan Jiang, Xuedong Luo

摘要：It is of great significance to analyze and predict the deformation characteristics of rock engineering materials by establishing a universal damage constitutive model under freeze-thaw and loading conditions. Based on the study of statistical damage constitutive model founded under freeze-thaw and loading condition, analytical expressions of the model parameters and characteristic parameters in the stress-strain curves (i.e., elastic modulus, stress and corresponding strain at the peak point) were established under specific freeze-thaw cycles. Then, an attenuation model that complies with Newton's material cooling law was introduced to develop the relationship among elastic modulus, stress at peak point and freeze-thaw cycles. Thirdly, the formula of the peak strain under different freeze-thaw cycles was proposed by exploring the correlation between the peak strain of stress-strain curves and freeze-thaw cycles. Therefore, the determination method of the unified model parameters under different freeze-thaw cycles is proposed, then, statistical damage constitutive model under freeze-thaw and loading conditions is generalized, and the freeze-thaw mechanics test with marble was performed to verify the rationality of the model. The results show that stress-strain curves described by presented model under different freeze-thaw cycles have a good agreement with the experimental curves, especially at the peak strength point. The results can provide theoretical reference for the study of rock mechanical properties under different freeze-thaw cycles

Damage constitutive model of single flaw sandstone under freeze-thaw and load

冻融及荷载条件下的单裂纹砂岩损伤本构模型

Cold Regions Science and Technology, Volume 159, March 2019, Pages 20-28

Yani Lu, Xinping Li, Andrew Chan

摘要：The deterioration of mechanical properties subjected to freeze-thaw action is a determining factor for natural rock masses in cold region engineering. Taking four cases of flaw sandstone as the research object, freeze-thaw cycles experiments and triaxial compression tests were conducted to analyze the mechanical properties after 0, 20, 40 and 60 freeze-thaw cycles. The damage evolution equation of freeze-thaw sandstone under load is established based on the Lemaitre strain equivalent principle and continuum damage mechanics theory. In this regard, the damage model was developed to predict the degradation of triaxial compression strength for single flaw sandstone samples, it takes into account pre-existing cracks, confining pressure, freeze-thaw action and load. The results show that the sandstone damage consists of factors mentioned above, the coupled damage variable acquired from the proposed method well agree with the actual condition, and the damage constitutive model validations are given through comparisons between the calculated and the measured.

Deterioration and strain energy development of sandstones under quasi-static and dynamic loading after freeze-thaw cycles

冻融循环后准静态和动态载荷作用下的砂岩劣化及应变能演化

Cold Regions Science and Technology, In press, accepted manuscript, Available online 17 January 2019

Jian Zhang, Hongwei Deng, Abbas Taheri, Bo Ke, Chuanju Liu

摘要：Rocks in cold regions are often exposed to extreme temperature change, and different loading conditions, therefore, will be subjected to deterioration. In this study, the deterioration of sandstone after freeze-thaw (F-T) cycles under quasi-static and dynamic loading conditions is investigated. In doing so, physical and mechanical properties of sandstone samples were studied after 20, 60, 100 and 140 F-T cycles. An increase in porosity and decrease in P wave velocity demonstrated a degradation in physical properties after F-T cycles. In addition, peak strengths of specimens were observed to be higher in the dynamic loading conditions as compared with the quasi-static conditions; while Young's modulus almost remained constant. Furthermore, a decay model was used to predict the deterioration of sandstone under different loading conditions and F-T cycles. Finally, the effects of F-T cycles on a brittleness and strain energy development were investigated. It was observed that rock became more brittle in the pre-peak regime after F-T cycles. It also demonstrated strain energies including the pre-peak, the peak, the post-peak and the total strain energies decrease after F-T cycles while variations of elastic strain energy with F-T cycles doesn't show any conclusive trend. Correlations between porosity and strain energies implied that porosity is a key factor in strain energy development for this kind of sandstone except that of elastic strain energy.

A damage model for frost heaving pressure in circular rock tunnel under freezing-thawing cycles

冻融循环下圆形岩石隧道冻胀力损伤模型

Tunnelling and Underground Space Technology, Volume 83, January 2019, Pages 401-408

Hongyan Liu, Xiaoping Yuan, Tiancheng Xie

摘要：The failure of rock tunnel lining in cold region involves the evaluation of frost heaving pressure in surrounding rock. Although many theoretical models of frost heaving pressure have been proposed, the combination effect of reduction in rock elastic modulus and increase of rock void ratio due to freezing-thawing cycles has not been considered. For this issue, on basis of the elastic model for frost heaving pressure in the circular tunnel surrounding rock, this study establishes the relationship between the rock elastic modulus and the number of freezing-thawing cycles based on fracture mechanics and mesodamage theory. Thereafter, we propose the damage model for frost heaving pressure by considering the combination of rock elastic modulus and void ratio. It is assumed that frost heaving pressure mainly occurs when water in microcracks is frozen into ice. The calculation example shows that frost heaving pressure gradually increases and tends to be a constant with increasing the number of freezing-thawing cycles. It indicates that the proposed model is capable of calculating the variation of frost heaving pressure with the number of freezing-thawing cycles.

A study on the physical index change and triaxial compression test of intact hard rock subjected to freeze-thaw cycles

冻融循环条件下完整坚硬岩石物理指数变化及三轴压缩试验研究

Cold Regions Science and Technology, Volume 160, April 2019, Pages 39-47

Wang Liping, Li Ning, Qi Jilin, Tian Yanzhe, Xu Shuanhai

摘要：For a long time, experimental studies on frost weathering of rock has been concentrated on soft rock to medium-hardness rock, and research on intact hard rock is relatively less common. Combined with specific engineering projects, taking fine sandstone (UCS = 114.8 Mpa) and coarse sandstone (UCS = 104.1 Mpa) as representatives for intact hard rock, the physical parameters and the triaxial compression mechanical characteristics subjected to different freeze-thaw cycles are studied in this paper. The results show that under freeze-thaw cycling, the intact hard rock still has obvious attenuation. The porosity of the two sandstones increases, and there is a good linear fit with the freeze-thaw cycles. Under the same confining pressure, the triaxial compressive strength of the two sandstones decreases with an increase in freeze-thaw cycles, and an exponential decay relation is expressed. The friction angle φremains constant, and there is a good exponential decay relationship between the cohesive force C and the freeze-thaw cycles. The related conclusions can provide some references for hard rock engineering.