Effects of freeze-thaw treatment on the dynamic tensile strength of granite using the Brazilian test
基于巴西试验的冻融循环处理对花岗岩动态拉伸强度的影响
Cold Regions Science and Technology, Volume 155, November 2018, Pages 327-332
Chuanju Liu, Hongwei Deng, Huatao Zhao, Jian Zhang
摘要：The deterioration mechanism and dynamic tensile properties of rock subjected to the effects of freeze-thaw cycles are investigated in this study. Brazilian disc granite specimens are treated by 0, 30, 60, 90 and 120 freeze-thaw cycles. Freezing and thawing temperatures are −20 °C and 20 °C respectively. The microscopic damage in the rock samples induced by freeze-thaw treatment is detected by the nuclear magnetic resonance (NMR) technique. T2 spectrum and magnetic resonance imaging (MRI) are used to analyze the effect of freeze-thaw cycles on the pore structure of rock samples. Brazilian splitting tests are performed by a split Hopkinson pressure bar (SHPB) system to measure the dynamic tensile strength of granite and to investigate the effect of freeze-thaw cycles on the dynamic tensile strength and the dynamic mechanical behavior. A formula for dynamic tensile strength prediction considering loading rates and freeze-thaw cycles is presented to quantify the results. The dynamic failure process of specimen is observed by a high-speed camera, it was found that the rock materials were more susceptible to damage and deteriorate after freeze-thaw treatment compared with the untreated rock.
A unified model for frost heave pressure in the rock with a penny-shaped fracture during freezing
冷冻期间硬币型断裂岩石冻胀压力的统一模型
Cold Regions Science and Technology, Volume 153, September 2018, Pages 1-9
Xianjun Tan, Weizhong Chen, Hongyuan Liu, Luyu Wang, Andrew Hin Cheong Chan
摘要：In order to investigate the mechanisms of rock deterioration at low temperature, a unified model for frost heave pressure in the rock with a penny-shaped fracture during freezing was proposed, in which the main influencing factors can be classified into four groups: 1) the mechanical properties of ice and rock (Ei, υi, Es and υs); 2) the external loading conditions (q and λ); 3) shape characteristic of the fracture (η); and 4) effective volume expansion coefficient (βe). The model attempts to unify the volume expansion theory, water immigration theory and combination theory. Validation was carried out, and the comparisons indicated that the proposed model can accurately reflect the variation of the frost heave pressure. Parametric sensitivity analyses were performed to examine the effect of various parameters and to improve the understanding of the damage of fractured rock mass subjected to frost heave. The results showed that βe is the most important parameter that affects the magnitude of frost heave pressure, apart from it, the mechanical properties of ice (Ei and υi) are also crucial, and then is the parameters of Es, q and η. Relatively speaking, υs and λ have little influence. Besides, some discussions were given to the newly defined variableβe, which is a crucial parameter that can unite the three existing frost heave mechanics of rock.
Effects of curing temperature on shear behaviour of cemented paste backfill-rock interface
养护温度对膏体充填岩石界面剪切性能的影响
International Journal of Rock Mechanics and Mining Sciences, Volume 112, December 2018, Pages 184-192
Kun Fang, Mamadou Fall
摘要：Understanding the shear behaviour of the interface between rock and cemented paste backfill (CPB) is critical for the cost-effective geotechnical design of underground CPB structures. Curing temperature is one of the key factors that can affect the shear behaviour and resistance of the CPB-rock interface. However, no studies have been performed to investigate its effects on the shear behaviour of the interface between rock and tailings backfill that is undergoing cementation. The main objective of this study is to therefore experimentally study the effects of three different curing temperatures (2 °C, 20 °C, and 35 °C) on the shear behaviour and strength of the CPB-rock interface. The obtained results show that higher curing temperatures (up to 35 °C in this study) can increase the rate of cement hydration and self-desiccation, thus increasing the peak shear stress at the interface between early age CPB and rock. However, the sample cured for a longer time of 28 days at a higher temperature of 35 °C has a lower shear strength than that cured at a lower temperature of 20 °C. This lower shear strength is due to the crossover effect, which is the phenomenon of temperature inversion in the strength of cementitious materials. The findings presented in this paper will contribute to a better assessment of the stability of backfill structures and a better design for them.
Damage evolution mechanism and constitutive model of freeze- thaw yellow sandstone in acidic environment
酸性环境下的黄砂岩冻融损伤演化机理与本构模型
Cold Regions Science and Technology, Volume 155, November 2018, Pages 174-183
Dengxing Qu, Dengke Li, Xinping Li, Yi LUO, Kun Xu
摘要：The study on the damage evolution mechanism of freeze-thaw of rock sample in acidic environment is of great theoretical and practical significance to the analysis and prevention of freeze-thaw disasters in cold area. Taking the yellow sandstone as the research object, the freeze-thaw cycle experiments, the NMR system experiments, the chemical composition analysis experiments and the uniaxial compression experiments under acidic environments with different pH are carried out to analyze the physical and chemical characteristics of the yellow sandstone. The damage evolution equation and constitutive model of rock are studied based on statistical strength theory, Lemaitre strain equivalent assumption and damage mechanics. In this paper, the damage evolution equation of chemical freeze-thaw sandstone under load is established. The damage correction coefficient is introduced to modify the total damage of chemical freeze-thaw sandstone under load. The constitutive model is deduced and the model parameters are deduced by the combination of theoretical derivation and experiment. The results show that the rock damage is the result of the coupling of freeze-thaw cycles and acid erosion, and the freeze-thaw cycle is the main reason and acidic erosion is the secondary reason. The experimental parameters are brought into the constitutive model, and the reliability of the model under uniaxial stress is verified by comparing with the experimental curve.
Degradation of physical and mechanical properties of sandstone subjected to freeze-thaw cycles and chemical erosion
冻融循环和化学侵蚀环境下的砂岩物理力学性能衰减
Cold Regions Science and Technology, Volume 155, November 2018, Pages 37-46
Jian Zhang, Hongwei Deng, Abbas Taheri, Bo Ke, Xiangru Yang
摘要：Rocks are often exposed to chemical erosion and extreme temperature changes in cold regions. In this study, the deterioration of sandstone is investigated under rapid freeze-thaw (F-T) cycles. To do so, physical and mechanical properties of sandstone specimens immersed in different chemical solutions were studied after 10, 20 and 30 freeze-thaw cycles. It was found that after applying freeze-thaw cycle specimens' mass, tensile strength and point load strength decrease at different extent while porosity increases. Coupled effects of chemical erosion and freeze-thaw cycles were observed to have a destructive damage on physical and mechanical properties. In this regard, the samples experienced deterioration at different extend when immersed in different chemical solutions. The maximum deterioration was observed for samples being immersed in NaOH solution, followed by that of NaCl solution, H2SO4 solution and pure water. Finally, a decay function model is used to further investigate the variations of splitting tensile strength and point load index with freeze-thaw cycles and predict deterioration of rock integrity.
An experimental study of a freeze-thaw damage model of natural pumice concrete
天然浮石混凝土冻融损伤模型实验研究
Powder Technology, Volume 339, November 2018, Pages 651-658
Xiaoxiao Wang, Yao Wu, Xiangdong Shen, Hailong Wang, Changwang Yan
摘要：This paper presents the experimental studies of the natural pumice concrete freeze-thaw damage model based on Cai Hao's Model and Powers' hydrostatic pressure hypothesis. The hydrostatic pressure calculation and testing methods are improved by the application of a theory of fatigue damage mechanics and a more accurate description of the physical properties of natural pumice concrete. A hydrostatic pressure calculation model was established for natural pumice concrete through simplification of the system. The model was then verified by experiments. Cryogenic nuclear magnetic resonance (NMR) was then applied to samples. Finally, a freeze-thaw damage model for natural pumice concrete was developed. The experimental results indicate that the freeze-thaw damage model, which uses the relative dynamic modulus of the elasticity loss Dof the natural pumice concrete as a physical damage index, can effectively provide theoretical support for the study of freeze-thaw damage mechanisms affecting natural pumice concrete.
