深部人工冻结黏土加卸载颗粒流模拟研究
发布时间：2018-08-31 13:09
【摘要】：深厚表土层冻结法凿井技术的核心是确保冻结壁和井壁的安全,而深部人工冻土的工程特性与冻结壁、井壁安全密切相关。在冻结壁形成和开挖过程中,深部人工冻土分别经历了加载和卸载过程,因此系统深入地认识深部人工冻土的加卸载力学特性,对于科学合理地设计冻结壁和井壁有重要意义。深部黏土由于特殊的赋存环境,具有显著的结构性。深部原状黏土经重塑后冻结,结构发生改变,进而导致深部原状与重塑人工冻结黏土宏观力学特性表现出差异性。因此有必要从微观尺度上刻画出深部原状与重塑人工冻结黏土的结构,研究加卸载条件下两种不同结构冻结黏土的宏细观力学特性,这将有助于从本质上认识深部人工冻土的力学特性,并为冻结壁和井壁设计提供科学依据。本文主要开展了以下研究工作:(1)通过对深部原状和重塑黏土SEM图像数字化处理,定量分析了两者微观结构,在此基础上构建了深部重塑和原状人工冻结黏土的颗粒流模型。系统地分析了颗粒流模型中微观参数的力学效应,结合室内三轴试验资料,引入支持向量机预报模型Lib SVM对微观力学参数进行了标定。(2)在不同温度和围压条件下,分别对深部重塑和原状人工冻结黏土颗粒流模型进行了不同模式的加卸载数值仿真试验。分析了深部重塑和原状人工冻结黏土的强度与变形规律,以及微观结构的演变规律。(3)在室内制备了深部重塑人工冻结黏土试样,分别进行了不同温度和围压条件下的三轴加卸载试验,分析比较了数值计算和室内试验结果。通过上述研究,得出主要结论如下:(1)根据IPP图像处理结果,深部重塑人工冻结黏土的颗粒体面积主要集中在1002?m,颗粒体角度主要分布在50°~70°之间,孔隙率为0.25。深部原状人工冻结黏土的颗粒体面积也主要集中在1002?m,颗粒体角度主要分布在10°~50°之间,孔隙率为0.24。经过微观力学效应分析,结合室内三轴试验资料,引入支持向量机模型得到的微观参数能够很好地反应深部人工冻结黏土的力学性质。(2)深部重塑人工冻结黏土在加载阶段应变随时间的增大而增大,等侧压力系数加载阶段的应变变化显著大于等压加载和变侧压力系数加载阶段;深部原状人工冻结黏土在加载阶段的应变随时间变化规律与重塑土相同,区别在于各个阶段结束时的时间和相应应变小于重塑土。在恒轴压卸围压模式下,应变随着时间显著增大;在恒围压卸轴压模式下,应变随着时间显著减小。(3)深部重塑人工冻结黏土在等侧压力系数加载阶段应变随偏应力的增大呈线性增长。在恒轴压卸围压模式下,深部重塑人工冻结黏土应变随偏应力的增大而增大,应力-应变关系为应变硬化型;恒围压卸轴压模式下,应变随偏应力的减小而减小,应力-应变关系也为应变硬化型。(4)深部原状人工冻结黏土在等侧压力系数加载阶段应变随偏应力的变化规律与重塑黏土相同,在恒轴压卸围压模式下,深部原状结黏土应变开始时随着偏应力的增大而增大,到达峰值强度之后应变随着偏应力的减小而减小,应力-应变关系呈应变软化型。恒围压卸轴压模式下,应变随偏应力的变化规律与重塑黏土相同。(5)加载结束后,深部重塑人工冻结黏土的结构呈“腰鼓状”;深部原状人工冻结黏土的结构呈“劈裂状”,二者均可以看到接触力链。恒轴压卸围压模式下卸载结束后深部重塑人工冻结黏土的“腰鼓状”处的直径相比于加载阶段结束时更大,试样高度更低,接触力链更完整;原状黏土的劈裂处的裂隙更大,接触力链中出现剪切面。恒围压卸轴压模式下卸载结束时的试样形态与恒轴压卸围压模式下的相反。卸载结束时,温度对峰值强度和弹性模量的影响呈线性关系,温度的影响效应大于围压。(6)通过室内三轴加卸载试验,得到卸载路径下不同围压、冻结温度条件下土体的应力-应变关系、强度值和弹性模量,获得了围压、冻结温度对冻土强度、弹性模量和割线模量的影响程度,发现冻结温度的影响效果大于围压。(7)深部重塑人工冻结黏土室内试验结果显示,在加卸载阶段应力-应变曲线特征和试样破坏形态与数值计算结果基本相同。恒轴压卸围压试验条件下,室内试验得到的强度比数值计算结果低4%,弹性模量高24%;恒围压卸轴压试验条件下的室内试验强度比数值模拟结果的强度低5%,弹性模量高15%。
[Abstract]:The core of shaft sinking technology by freezing method in deep and thick surface soil is to ensure the safety of frozen wall and shaft wall. The engineering characteristics of deep artificial frozen soil are closely related to the safety of frozen wall and shaft wall. Unloading mechanical properties are of great importance to the design of frozen wall and shaft lining scientifically and reasonably. Deep clay has remarkable structural properties due to its special environment. Deep undisturbed clay freezes after remodeling, and its structure changes, which leads to the difference of macroscopic mechanical properties between deep undisturbed clay and remolded artificially frozen clay. It is necessary to characterize the structure of deep frozen clay and reconstruct the structure of artificially frozen clay on the micro-scale, and study the macro-and Micro-Mechanical Properties of frozen clay with two different structures under loading and unloading conditions, which will be helpful to understand the mechanical properties of deep artificial frozen soil in essence and provide scientific basis for the design of frozen wall and shaft lining. The following research works are carried out: (1) By digitizing the SEM images of undisturbed and remolded deep clays, the micro-structures of the two kinds of clays are analyzed quantitatively. On this basis, the granular flow model of artificially frozen deep remolded and undisturbed clays is constructed. The micro-mechanical parameters were calibrated by the support vector machine prediction model Lib SVM. (2) Under different temperatures and confining pressures, different loading and unloading numerical simulation tests were carried out on the deep remolded and in-situ artificially frozen clay particle flow models. The strength and deformation laws of the deep remolded and in-situ artificially frozen clay were analyzed. (3) Artificial frozen clay specimens were prepared in laboratory, and triaxial loading and unloading tests were carried out at different temperatures and confining pressures. The results of numerical calculation and laboratory tests were compared. The main conclusions are as follows: (1) According to the results of IPP image processing, deep remodeling was carried out. The granular area of artificially frozen clay mainly concentrates on 1002? M, the angle of granular body mainly distributes between 50 degrees and 70 degrees, and the porosity is 0.25. The area of deep artificially frozen clay mainly concentrates on 1002? M, the angle of granular body mainly distributes between 10 degrees and 50 degrees, and the porosity is 0.24. The Micro-Parameters obtained by introducing support vector machine model can well reflect the mechanical properties of deep artificially frozen clay. (2) The strain of deep remolded artificially frozen clay increases with time in loading stage, and the strain change of loading stage with constant lateral pressure coefficient is significantly greater than that of isobaric loading and lateral pressure. In the constant axial compression unloading confining pressure mode, the strain increases significantly with time; in the constant confining pressure unloading axial compression mode, the strain increases with time; in the constant confining pressure unloading axial compression mode, the strain increases with time. (3) The strain of deep remolded artificially frozen clay increases linearly with the increase of eccentric stress at the loading stage of constant lateral pressure coefficient. The stress decreases and the stress-strain relationship is also strain-hardening. (4) The strain changes with the deviatoric stress in the loading stage of constant lateral pressure coefficient are the same as that in the remolded clay. The strain decreases with the decrease of deviatoric stress, and the stress-strain relationship is strain softening. Under the constant confining pressure unloading axial compression mode, the strain changes with the deviatoric stress is the same as that of the remolded clay. (5) After loading, the structure of the deep remolded artificially frozen clay is "waist-drum" and the structure of the deep artificially frozen clay is "waist-drum". After unloading under constant axial pressure, the diameter of the waist drum of the artificially frozen clay is larger than that at the end of the loading stage, the specimen height is lower, and the contact force chain is more complete. At the end of unloading, the influence of temperature on peak strength and modulus of elasticity is linear, and the effect of temperature is greater than that of confining pressure. (6) Through indoor triaxial loading and unloading test, the conditions of different confining pressure and freezing temperature under unloading path are obtained. The influence of confining pressure and freezing temperature on the strength, elastic modulus and secant modulus of frozen soil was obtained. It was found that the effect of freezing temperature on the strength, elastic modulus and secant modulus of frozen soil was greater than that of confining pressure. (7) Laboratory test results of deep remolded artificially frozen clay showed that the stress-strain curve characteristics and test results at the loading and unloading stage. Under the condition of constant confining pressure unloading, the strength of laboratory test is 4% lower than that of numerical calculation, and the modulus of elasticity is 24% higher. Under the condition of constant confining pressure unloading, the strength of laboratory test is 5% lower than that of numerical simulation, and the modulus of elasticity is 15% higher.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TD265.3
本文编号：2215080
[Abstract]:The core of shaft sinking technology by freezing method in deep and thick surface soil is to ensure the safety of frozen wall and shaft wall. The engineering characteristics of deep artificial frozen soil are closely related to the safety of frozen wall and shaft wall. Unloading mechanical properties are of great importance to the design of frozen wall and shaft lining scientifically and reasonably. Deep clay has remarkable structural properties due to its special environment. Deep undisturbed clay freezes after remodeling, and its structure changes, which leads to the difference of macroscopic mechanical properties between deep undisturbed clay and remolded artificially frozen clay. It is necessary to characterize the structure of deep frozen clay and reconstruct the structure of artificially frozen clay on the micro-scale, and study the macro-and Micro-Mechanical Properties of frozen clay with two different structures under loading and unloading conditions, which will be helpful to understand the mechanical properties of deep artificial frozen soil in essence and provide scientific basis for the design of frozen wall and shaft lining. The following research works are carried out: (1) By digitizing the SEM images of undisturbed and remolded deep clays, the micro-structures of the two kinds of clays are analyzed quantitatively. On this basis, the granular flow model of artificially frozen deep remolded and undisturbed clays is constructed. The micro-mechanical parameters were calibrated by the support vector machine prediction model Lib SVM. (2) Under different temperatures and confining pressures, different loading and unloading numerical simulation tests were carried out on the deep remolded and in-situ artificially frozen clay particle flow models. The strength and deformation laws of the deep remolded and in-situ artificially frozen clay were analyzed. (3) Artificial frozen clay specimens were prepared in laboratory, and triaxial loading and unloading tests were carried out at different temperatures and confining pressures. The results of numerical calculation and laboratory tests were compared. The main conclusions are as follows: (1) According to the results of IPP image processing, deep remodeling was carried out. The granular area of artificially frozen clay mainly concentrates on 1002? M, the angle of granular body mainly distributes between 50 degrees and 70 degrees, and the porosity is 0.25. The area of deep artificially frozen clay mainly concentrates on 1002? M, the angle of granular body mainly distributes between 10 degrees and 50 degrees, and the porosity is 0.24. The Micro-Parameters obtained by introducing support vector machine model can well reflect the mechanical properties of deep artificially frozen clay. (2) The strain of deep remolded artificially frozen clay increases with time in loading stage, and the strain change of loading stage with constant lateral pressure coefficient is significantly greater than that of isobaric loading and lateral pressure. In the constant axial compression unloading confining pressure mode, the strain increases significantly with time; in the constant confining pressure unloading axial compression mode, the strain increases with time; in the constant confining pressure unloading axial compression mode, the strain increases with time. (3) The strain of deep remolded artificially frozen clay increases linearly with the increase of eccentric stress at the loading stage of constant lateral pressure coefficient. The stress decreases and the stress-strain relationship is also strain-hardening. (4) The strain changes with the deviatoric stress in the loading stage of constant lateral pressure coefficient are the same as that in the remolded clay. The strain decreases with the decrease of deviatoric stress, and the stress-strain relationship is strain softening. Under the constant confining pressure unloading axial compression mode, the strain changes with the deviatoric stress is the same as that of the remolded clay. (5) After loading, the structure of the deep remolded artificially frozen clay is "waist-drum" and the structure of the deep artificially frozen clay is "waist-drum". After unloading under constant axial pressure, the diameter of the waist drum of the artificially frozen clay is larger than that at the end of the loading stage, the specimen height is lower, and the contact force chain is more complete. At the end of unloading, the influence of temperature on peak strength and modulus of elasticity is linear, and the effect of temperature is greater than that of confining pressure. (6) Through indoor triaxial loading and unloading test, the conditions of different confining pressure and freezing temperature under unloading path are obtained. The influence of confining pressure and freezing temperature on the strength, elastic modulus and secant modulus of frozen soil was obtained. It was found that the effect of freezing temperature on the strength, elastic modulus and secant modulus of frozen soil was greater than that of confining pressure. (7) Laboratory test results of deep remolded artificially frozen clay showed that the stress-strain curve characteristics and test results at the loading and unloading stage. Under the condition of constant confining pressure unloading, the strength of laboratory test is 4% lower than that of numerical calculation, and the modulus of elasticity is 24% higher. Under the condition of constant confining pressure unloading, the strength of laboratory test is 5% lower than that of numerical simulation, and the modulus of elasticity is 15% higher.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TD265.3
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