The mechanical parameters and failure characteristics of sandstone under compressive-shear stress states provide crucial theoretical references for underground engineering construction.In this study,a series of varied...The mechanical parameters and failure characteristics of sandstone under compressive-shear stress states provide crucial theoretical references for underground engineering construction.In this study,a series of varied angle shear tests(VASTs)were designed using acoustic emission(AE)detection and digital image correlation technologies to evaluate the mechanical behaviors of typical red sandstone.AE signal parameters revealed differences in the number and intensity of microcracks within the sandstone,with a test angle(α)of 50°identified as a significant turning point for its failure properties.Whenα³50°,microcrack activity intensified,and the proportion of tensile cracks increased.Asαincreased,the number of fragments generated after failure decreased,fragment sizes became smaller,and the crack network simplified.Cracks extended from the two cut slits at the ends of the rock,gradually penetrating along the centerline towards the central location,as observed from the evolution of the strain concentration field.Both cohesion(c)and internal friction angle(ϕ)measured in VAST were lower than those measured under conventional triaxial compression.展开更多
The main objective of this work is to propose new mixture response parameters and to compare correlations with rut depths and sensitivity of permanent deformation response parameters based on field extracted cores and...The main objective of this work is to propose new mixture response parameters and to compare correlations with rut depths and sensitivity of permanent deformation response parameters based on field extracted cores and lab-mixed duplicates. A new "mix-confined" test is developed and four new parameters for this test are proposed. Correlation coefficients with rut depths and coefficients of variation (sensitivity) are compared between the four new and two existing parameters. Some parameters are recommended to be used for the newly developed test. The results show that, newly developed test can capture the changes of permanent deformation of asphalt mixtures. Only one new parameter (D1 of Stephen Price model) and one existing parameter (flow number, Fn ) have strong correlations with rut depths of asphalt pavements (R2 greater than 0.7) and have relative small sensitivity (coefficient of variation, COV, less than 30%). For polymer modified asphalt mixtures, the parameter D1 rather than Fn should be used. These findings can be used to check the permanent deformation of asphalt mixture during the mix design.展开更多
Based on mineral component and in-situ vane shear strength of deep-sea sediment, four kinds of simulative soils were prepared by mixing different bentonites with water in order to find the best simulative soil for the...Based on mineral component and in-situ vane shear strength of deep-sea sediment, four kinds of simulative soils were prepared by mixing different bentonites with water in order to find the best simulative soil for the deep-sea sediment collected from the Pacific C-C area. Shear creep characteristics of the simulative soil were studied by shear creep test and shear creep parameters were determined by Burgers creep model. Research results show that the shear creep curves of the simulative soil can be divided into transient creep, unstable creep and stable creep, where the unstable creep stage is very short due to its high water content. The shear creep parameters increase with compressive stress and change slightly or fluctuate to approach a constant value with shear stress, and thus average creep parameters under the same compressive stress are used as the creep parameters of the simulative soil. Traction of the deep-sea mining machine walking at a constant velocity can be calculated by the shear creep constitutive equation of the deep-sea simulative soil, which provides a theoretical basis for safe operation and optimal design of the deep-sea mining machine.展开更多
The shear behavior of rock joints is important in solving practical problems of rock mechanics. Three group rock joints with different morphologies are made by cement mortar material and a series of CNL(constant norma...The shear behavior of rock joints is important in solving practical problems of rock mechanics. Three group rock joints with different morphologies are made by cement mortar material and a series of CNL(constant normal loading) shear tests are performed. The influences of the applied normal stress and joint morphology to its shear strength are analyzed. According to the experimental results, the peak dilatancy angle of rock joint decreases with increasing normal stress, but increases with increasing roughness. The shear strength increases with the increasing normal stress and the roughness of rock joint. It is observed that the modes of failure of asperities are tensile, pure shear, or a combination of both. It is suggested that the three-dimensional roughness parameters and the tensile strength are the appropriate parameter for describing the shear strength criterion. A new peak shear criterion is proposed which can be used to predict peak shear strength of rock joints. All the used parameters can be easily obtained by performing tests.展开更多
[目的]针对水稻秸秆不同含水率下离散元参数标定方法通用性不足导致水稻秸秆还田装备数值模拟误差较大的问题,结合物理试验与仿真试验对不同含水率的水稻秸秆进行试验研究。[方法]通过物理剪切试验建立含水率-剪切力模型;基于水稻秸秆...[目的]针对水稻秸秆不同含水率下离散元参数标定方法通用性不足导致水稻秸秆还田装备数值模拟误差较大的问题,结合物理试验与仿真试验对不同含水率的水稻秸秆进行试验研究。[方法]通过物理剪切试验建立含水率-剪切力模型;基于水稻秸秆物理特征在EDEM中建立以Hertz-Mindlin with bonding为接触模型的水稻秸秆离散元模型,通过Plackett-Burman试验、最陡爬坡试验和Box-Behnken试验筛选出水稻秸秆离散元显著性参数:黏结键半径、单位面积法向刚度、单位面积剪切刚度。[结果]模型决定系数(R^(2))分别为0.986和0.984,模型均显著(P<0.01);基于水稻秸秆的含水率-剪切力模型和剪切力-离散元模型构建含水率-离散元模型,采用物理试验与仿真试验对比的方法得到相对误差小于等于5.4%,验证了模型的可靠性。[结论]所标定的含水率-离散元模型可用于不同含水率水稻秸秆的数值模拟,为水稻秸秆的收获、还田、免耕等环节的装置结构设计和优化提供理论依据。展开更多
土石混合体-基岩接触面是下伏基岩堆积体边坡稳定性的主要控制面,基覆面形态特征是重要的设计内容。为此,开展了不同基覆面形态参数条件下接触面室内大型直剪试验,研究了基覆面形态参数对接触面剪切力学特性的影响,探讨了接触面土石颗...土石混合体-基岩接触面是下伏基岩堆积体边坡稳定性的主要控制面,基覆面形态特征是重要的设计内容。为此,开展了不同基覆面形态参数条件下接触面室内大型直剪试验,研究了基覆面形态参数对接触面剪切力学特性的影响,探讨了接触面土石颗粒运动概化模式,建立了接触面剪切简化的复合幂-指数模型(composite power exponential model,CPE模型)。结果表明:随着粗糙度的增加,接触面抗剪强度不断增大,表观内摩擦角和表观黏聚力分别呈非线性上凸增长和似线性增长趋势,随着锯齿高度的增加,接触面抗剪强度先增大后减小,增加锯齿高度对表观黏聚力的影响较为明显;接触面剪应力-剪切相对位移关系曲线基本呈弱硬化型,土石颗粒骨架密实度随粗糙度的增大而减小,但随锯齿高度的增大呈先增大后减小,接触面土石颗粒运动主要表现为咬合、翻转和滑移,较高法向应力时会发生颗粒破碎和基岩尖端剪切破坏;模型参数k、b和n与无量纲化法向应力σ_(n)/Pa存在线性关系(σ_(n)为法向应力,P_(a)为标准大气压),拟合系数α_(i)(i=1,2)不受基覆面形态参数的影响,拟合系数βi和i分别与粗糙度R和锯齿高度D存在线性关系;简化CPE模型能够很好地模拟出不同基覆面形态参数条件下土石混合体-基岩接触面剪切变形全过程,模型适用性良好,参数的确定方法合理且可行。展开更多
基金Project(52374150)supported by the National Natural Science Foundation of ChinaProject(2021RC3007)supported by the Science and Technology Innovation Program of Hunan Province,China。
文摘The mechanical parameters and failure characteristics of sandstone under compressive-shear stress states provide crucial theoretical references for underground engineering construction.In this study,a series of varied angle shear tests(VASTs)were designed using acoustic emission(AE)detection and digital image correlation technologies to evaluate the mechanical behaviors of typical red sandstone.AE signal parameters revealed differences in the number and intensity of microcracks within the sandstone,with a test angle(α)of 50°identified as a significant turning point for its failure properties.Whenα³50°,microcrack activity intensified,and the proportion of tensile cracks increased.Asαincreased,the number of fragments generated after failure decreased,fragment sizes became smaller,and the crack network simplified.Cracks extended from the two cut slits at the ends of the rock,gradually penetrating along the centerline towards the central location,as observed from the evolution of the strain concentration field.Both cohesion(c)and internal friction angle(ϕ)measured in VAST were lower than those measured under conventional triaxial compression.
基金Project(08Y038) supported by Jiangsu Transportation Engineering Construction Bureau,China
文摘The main objective of this work is to propose new mixture response parameters and to compare correlations with rut depths and sensitivity of permanent deformation response parameters based on field extracted cores and lab-mixed duplicates. A new "mix-confined" test is developed and four new parameters for this test are proposed. Correlation coefficients with rut depths and coefficients of variation (sensitivity) are compared between the four new and two existing parameters. Some parameters are recommended to be used for the newly developed test. The results show that, newly developed test can capture the changes of permanent deformation of asphalt mixtures. Only one new parameter (D1 of Stephen Price model) and one existing parameter (flow number, Fn ) have strong correlations with rut depths of asphalt pavements (R2 greater than 0.7) and have relative small sensitivity (coefficient of variation, COV, less than 30%). For polymer modified asphalt mixtures, the parameter D1 rather than Fn should be used. These findings can be used to check the permanent deformation of asphalt mixture during the mix design.
基金Project(51274251)supported by the National Natural Science Foundation of China
文摘Based on mineral component and in-situ vane shear strength of deep-sea sediment, four kinds of simulative soils were prepared by mixing different bentonites with water in order to find the best simulative soil for the deep-sea sediment collected from the Pacific C-C area. Shear creep characteristics of the simulative soil were studied by shear creep test and shear creep parameters were determined by Burgers creep model. Research results show that the shear creep curves of the simulative soil can be divided into transient creep, unstable creep and stable creep, where the unstable creep stage is very short due to its high water content. The shear creep parameters increase with compressive stress and change slightly or fluctuate to approach a constant value with shear stress, and thus average creep parameters under the same compressive stress are used as the creep parameters of the simulative soil. Traction of the deep-sea mining machine walking at a constant velocity can be calculated by the shear creep constitutive equation of the deep-sea simulative soil, which provides a theoretical basis for safe operation and optimal design of the deep-sea mining machine.
基金Project(41130742)supported by the Key Program of National Natural Science Foundation of ChinaProject(2014CB046904)supportedby the National Basic Research Program of China+1 种基金Project(2011CDA119)supported by Natural Science Foundation of Hubei Province,ChinaProject(40972178)supported by the General Program of National Natural Science Foundation of China
文摘The shear behavior of rock joints is important in solving practical problems of rock mechanics. Three group rock joints with different morphologies are made by cement mortar material and a series of CNL(constant normal loading) shear tests are performed. The influences of the applied normal stress and joint morphology to its shear strength are analyzed. According to the experimental results, the peak dilatancy angle of rock joint decreases with increasing normal stress, but increases with increasing roughness. The shear strength increases with the increasing normal stress and the roughness of rock joint. It is observed that the modes of failure of asperities are tensile, pure shear, or a combination of both. It is suggested that the three-dimensional roughness parameters and the tensile strength are the appropriate parameter for describing the shear strength criterion. A new peak shear criterion is proposed which can be used to predict peak shear strength of rock joints. All the used parameters can be easily obtained by performing tests.
文摘[目的]针对水稻秸秆不同含水率下离散元参数标定方法通用性不足导致水稻秸秆还田装备数值模拟误差较大的问题,结合物理试验与仿真试验对不同含水率的水稻秸秆进行试验研究。[方法]通过物理剪切试验建立含水率-剪切力模型;基于水稻秸秆物理特征在EDEM中建立以Hertz-Mindlin with bonding为接触模型的水稻秸秆离散元模型,通过Plackett-Burman试验、最陡爬坡试验和Box-Behnken试验筛选出水稻秸秆离散元显著性参数:黏结键半径、单位面积法向刚度、单位面积剪切刚度。[结果]模型决定系数(R^(2))分别为0.986和0.984,模型均显著(P<0.01);基于水稻秸秆的含水率-剪切力模型和剪切力-离散元模型构建含水率-离散元模型,采用物理试验与仿真试验对比的方法得到相对误差小于等于5.4%,验证了模型的可靠性。[结论]所标定的含水率-离散元模型可用于不同含水率水稻秸秆的数值模拟,为水稻秸秆的收获、还田、免耕等环节的装置结构设计和优化提供理论依据。
文摘土石混合体-基岩接触面是下伏基岩堆积体边坡稳定性的主要控制面,基覆面形态特征是重要的设计内容。为此,开展了不同基覆面形态参数条件下接触面室内大型直剪试验,研究了基覆面形态参数对接触面剪切力学特性的影响,探讨了接触面土石颗粒运动概化模式,建立了接触面剪切简化的复合幂-指数模型(composite power exponential model,CPE模型)。结果表明:随着粗糙度的增加,接触面抗剪强度不断增大,表观内摩擦角和表观黏聚力分别呈非线性上凸增长和似线性增长趋势,随着锯齿高度的增加,接触面抗剪强度先增大后减小,增加锯齿高度对表观黏聚力的影响较为明显;接触面剪应力-剪切相对位移关系曲线基本呈弱硬化型,土石颗粒骨架密实度随粗糙度的增大而减小,但随锯齿高度的增大呈先增大后减小,接触面土石颗粒运动主要表现为咬合、翻转和滑移,较高法向应力时会发生颗粒破碎和基岩尖端剪切破坏;模型参数k、b和n与无量纲化法向应力σ_(n)/Pa存在线性关系(σ_(n)为法向应力,P_(a)为标准大气压),拟合系数α_(i)(i=1,2)不受基覆面形态参数的影响,拟合系数βi和i分别与粗糙度R和锯齿高度D存在线性关系;简化CPE模型能够很好地模拟出不同基覆面形态参数条件下土石混合体-基岩接触面剪切变形全过程,模型适用性良好,参数的确定方法合理且可行。
