It is generally accepted that the uniaxial compressive strength(UCS)and P-wave velocity of rocks tend to decrease simultaneously with increasing temperature.However,based on a great number of statistical data and syst...It is generally accepted that the uniaxial compressive strength(UCS)and P-wave velocity of rocks tend to decrease simultaneously with increasing temperature.However,based on a great number of statistical data and systematic analysis of the microstructure variation of rocks with temperature rising and corresponding propagation mechanism of elastic wave,the results show that(1)There are three different trends for the changes of UCS and P-wave velocity of sandstone when heated from room temperature(20C or 25C)to 800C:(i)Both the UCS and P-wave velocity decrease simultaneously;(ii)The UCS increases initially and then decreases,while the P-wave velocity decreases continuously;and(iii)The UCS increases initially and then fluctuates,while the P-wave velocity continuously decreases.(2)The UCS changes at room temperaturee400C,400Ce600C,and 600Ce800C are mainly attributed to the discrepancy of microstructure characteristics and quartz content,the transformation plasticity of clay minerals,and the balance between the thermal cementation and thermal damage,respectively.(3)The inconsistency in the trends of UCS and P-wave velocity changes is caused by the change of quartz content,phase transition of water and certain minerals.展开更多
In perennially frozen or seasonally frozen soil regions,freeze-thaw cycling adversely impacts the mechanical properties of rock mass,resulting in landslides,rock erosion,and other geological disasters.The microscopic ...In perennially frozen or seasonally frozen soil regions,freeze-thaw cycling adversely impacts the mechanical properties of rock mass,resulting in landslides,rock erosion,and other geological disasters.The microscopic damage evolution law of loaded sandstone under the freeze-thaw cycle is analyzed by conducting Nuclear Magnetic Resonance(NMR)and uniaxial compression acoustic emission(AE)experiments.The experimental results have shown that:(1)Freeze-thaw cycling increases sandstone's internal pores,enlarges the pore size,and modifies the original pore distribution.(2)The damage due to freeze-thaw cycling is positively correlated with the initial damage to the rock,and the damage on the rock surface is more severe than inside the rock sample.(3)Freeze-thaw cycling negatively impacts the mechanical properties of sandstone,and the elastic deformation stage of sandstone gradually decreases as the number of freeze-thaw cycles increases and gradually transitions from brittle failure to ductile failure.(4)The characteristic parameters of AE ringing count and accumulated energy can reveal the severity of freeze-thaw damage and the dynamic evolution process,and the damage development rate exhibits abrupt changes at critical moments.After five freeze-thaw cycles,the damage development rate rises suddenly,as manifested by a sharp increase in the frequency and energy of AE events.High-energy AE events frequently occur during the rapid expansion period of damage,which can be adopted as an essential reference for damage propagation and aggravation.展开更多
Based on the Kangding Tunnel No.2 project,this study analyzes the heat exchange between air and the rock mass surrounding the tunnel under wind flow by the finite difference method.The influence of factors on the temp...Based on the Kangding Tunnel No.2 project,this study analyzes the heat exchange between air and the rock mass surrounding the tunnel under wind flow by the finite difference method.The influence of factors on the temperature field of a tunnel in cold regions,including ventilation and initial conditions,is investigated.The results show that:1)The lower the air temperature,the greater the wind speed,the larger the rock mass temperature influence circle and the greater the frozen depth;2)When the wind speed is less than 3 m/s,its change has an obvious impact on the rock mass temperature;3)For every drop of 5C in air temperature,the frozen depth increases by about 5 m,indicating that the air temperature is an essential factor affecting the rock mass temperature regime;4)The higher the initial rock mass temperature is,the smaller the influence circle on the rock mass is.And to a certain extent,it determines the temperature distribution in the rock mass within a specific range from the wall surface.展开更多
基金This work was supported by the National Natural Science Foundation of China(Grant No.41772333)the program of State Key Laboratory of Frozen Soil Engineering(Grant No.SKLFSE201713)the Shaanxi Province New-Star Talents Promotion Project of Science and Technology(Grant No.2019KJXX-049).
文摘It is generally accepted that the uniaxial compressive strength(UCS)and P-wave velocity of rocks tend to decrease simultaneously with increasing temperature.However,based on a great number of statistical data and systematic analysis of the microstructure variation of rocks with temperature rising and corresponding propagation mechanism of elastic wave,the results show that(1)There are three different trends for the changes of UCS and P-wave velocity of sandstone when heated from room temperature(20C or 25C)to 800C:(i)Both the UCS and P-wave velocity decrease simultaneously;(ii)The UCS increases initially and then decreases,while the P-wave velocity decreases continuously;and(iii)The UCS increases initially and then fluctuates,while the P-wave velocity continuously decreases.(2)The UCS changes at room temperaturee400C,400Ce600C,and 600Ce800C are mainly attributed to the discrepancy of microstructure characteristics and quartz content,the transformation plasticity of clay minerals,and the balance between the thermal cementation and thermal damage,respectively.(3)The inconsistency in the trends of UCS and P-wave velocity changes is caused by the change of quartz content,phase transition of water and certain minerals.
基金supported by the National Natural Science Foundation of China(42277172,42177144,42077274,51774231,41702339)Funded by the Natural Science Basic Research Program of Shaanxi Province(2020JZ-53).
文摘In perennially frozen or seasonally frozen soil regions,freeze-thaw cycling adversely impacts the mechanical properties of rock mass,resulting in landslides,rock erosion,and other geological disasters.The microscopic damage evolution law of loaded sandstone under the freeze-thaw cycle is analyzed by conducting Nuclear Magnetic Resonance(NMR)and uniaxial compression acoustic emission(AE)experiments.The experimental results have shown that:(1)Freeze-thaw cycling increases sandstone's internal pores,enlarges the pore size,and modifies the original pore distribution.(2)The damage due to freeze-thaw cycling is positively correlated with the initial damage to the rock,and the damage on the rock surface is more severe than inside the rock sample.(3)Freeze-thaw cycling negatively impacts the mechanical properties of sandstone,and the elastic deformation stage of sandstone gradually decreases as the number of freeze-thaw cycles increases and gradually transitions from brittle failure to ductile failure.(4)The characteristic parameters of AE ringing count and accumulated energy can reveal the severity of freeze-thaw damage and the dynamic evolution process,and the damage development rate exhibits abrupt changes at critical moments.After five freeze-thaw cycles,the damage development rate rises suddenly,as manifested by a sharp increase in the frequency and energy of AE events.High-energy AE events frequently occur during the rapid expansion period of damage,which can be adopted as an essential reference for damage propagation and aggravation.
基金supported by the National Natural Science Foundation of China(42177144,42077274,51774231,42277172)Funded by the Natural Science Basic Research Program of Shaanxi Province(2018JQ4026,2020JZ-53).
文摘Based on the Kangding Tunnel No.2 project,this study analyzes the heat exchange between air and the rock mass surrounding the tunnel under wind flow by the finite difference method.The influence of factors on the temperature field of a tunnel in cold regions,including ventilation and initial conditions,is investigated.The results show that:1)The lower the air temperature,the greater the wind speed,the larger the rock mass temperature influence circle and the greater the frozen depth;2)When the wind speed is less than 3 m/s,its change has an obvious impact on the rock mass temperature;3)For every drop of 5C in air temperature,the frozen depth increases by about 5 m,indicating that the air temperature is an essential factor affecting the rock mass temperature regime;4)The higher the initial rock mass temperature is,the smaller the influence circle on the rock mass is.And to a certain extent,it determines the temperature distribution in the rock mass within a specific range from the wall surface.
