冻土抗剪强度的数值回归模型研究及其在冻土工程中的应用
发布时间：2018-11-02 10:09
【摘要】：冻土主要分布于我国中北部地区及青藏高原地区,主要分为多年冻土和季节性冻土,冻土是由土颗粒、水、冰、空气组成的四相复杂体系,其“冬冻夏融”的特点使冻土地区土体情况更为复杂。我国有大量土木工程修建于冻土地区,对冻土的物理力学特性如强度认识不足会导致潜在的冻土工程风险。 本文以Mohr-Coulomb抗剪强度准则为基础,着重研究冻土的抗剪强度指标(粘聚力c和内摩擦角φ)与温度、含水率、冻融循环、围压及动荷载等因素的关系,并针对不同土类建立了相应的冻土抗剪强度拟合公式。在此基础上,以哈齐高铁路基为研究对象,采用Comsol Multiphysics软件进行基于水热场条件下的路基稳定性分析。具体工作内容及创新之处如下： 1、针对冻土抗剪强度进行了系统性的研究综述,总结了冻土抗剪强度随温度、含水率、冻融循环次数、围压及动荷载等因素的变化规律,结果表明：温度越低时抗剪强度越高；初始含水率较高时强度随含水率的增大而减小,初始含水率较低时强度随含水率的增大而增大；抗剪强度随着冻融次数的增加而减小,一定循环周期后趋于稳定；围压的高低与强度的大小呈抛物线关系；动荷载作用下强度大小受温度、围压、频率的共同影响。 2、基于大量的冻土抗剪强度实验数据,采用归纳总结与数据拟合相结合的方法,得出不同因素与抗剪强度参数之间的关系,针对不同土类建立了相应的冻土抗剪强度拟合公式,并对其适用性进行了评述。 3、以哈齐高铁为背景,运用Comsol Multiphysics软件对冻土路基水热场进行数值模拟,得出在低温环境下路基的冻胀深度及冻胀量,且土体内部冻胀量的变化滞后于地表气温的变化；分别以不同月份的水热场为初始状态,基于建立的冻土抗剪强度拟合公式,应用于路基断面不同的土层,分析不同时间点路基的稳定性,得出在气温较低时安全系数相对较高,在冻融循环作用下安全系数会逐渐降低,一定次数后强度趋于稳定的结论。对路基安全系数的因素敏感性进行了研究,高温冻土时,安全系数对温度的敏感性高于含水率,低温冻土时正好相反,同时安全系数对冻融作用的敏感性,随着次数的增加逐渐降低。 本文对冻土抗剪强度随外界因素的变化关系进行了系统性的研究,并采用有限元软件对部分结果进行了验证,相关结论具有一定参考价值。
[Abstract]:The frozen soil is mainly distributed in the central and northern part of China and the Qinghai-Tibet Plateau. It is mainly divided into permafrost and seasonal permafrost, which is a four-phase complex system composed of soil particles, water, ice and air. The characteristics of winter freezing and summer thawing make the soil in frozen soil area more complicated. In China, a large number of civil engineering projects are built in frozen soil regions. Lack of understanding of the physical and mechanical properties of frozen soil, such as strength, will lead to potential permafrost engineering risks. Based on the Mohr-Coulomb shear strength criterion, the relationship between the shear strength index (cohesion c and internal friction angle 蠁) and temperature, moisture content, freeze-thaw cycle, confining pressure and dynamic load of frozen soil is studied in this paper. A fitting formula of shear strength of frozen soil is established for different soil types. On this basis, the stability analysis of high speed subgrade based on water and heat field is carried out by using Comsol Multiphysics software. The specific work contents and innovations are as follows: 1. The systematic research on the shear strength of frozen soil is summarized, and the variation law of shear strength with temperature, moisture content, freeze-thaw cycle times, confining pressure and dynamic load is summarized. The results show that the shear strength is higher when the temperature is lower. When the initial moisture content is high, the strength decreases with the increase of water content, the strength increases with the increase of water content when the initial moisture content is low, and the shear strength decreases with the increase of freeze-thaw times, and tends to be stable after a certain cycle period. The relationship between confining pressure and strength is parabola, and the strength under dynamic load is affected by temperature, confining pressure and frequency. 2. Based on a large amount of experimental data of shear strength of frozen soil, the relationship between different factors and shear strength parameters is obtained by combining induction, summary and data fitting. The fitting formula of shear strength of frozen soil is established for different soil types and its applicability is reviewed. 3. Based on the background of high iron in Hazhi, the hydrothermal field of frozen soil subgrade is simulated by Comsol Multiphysics software. The results show that the depth and quantity of frost heave of roadbed under low temperature environment, and the variation of frost heave of soil lags behind the change of surface air temperature. Taking the hydrothermal field of different months as the initial state, based on the established formula of shear strength of frozen soil, the stability of roadbed at different time points is analyzed, and the safety coefficient is relatively high when the temperature is low. Under the action of freeze-thaw cycle, the safety factor will decrease gradually, and the strength will be stable after a certain number of times. The sensitivity of safety factor of roadbed to temperature is higher than that of moisture content in high temperature permafrost, the opposite is true in low temperature permafrost, and the sensitivity of safety factor to freezing and thawing. As the number of times increases, it decreases gradually. In this paper, the relationship between shear strength of frozen soil and external factors is systematically studied, and some of the results are verified by finite element software. The relevant conclusions have certain reference value.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U213.14;TU445
本文编号：2305723
[Abstract]:The frozen soil is mainly distributed in the central and northern part of China and the Qinghai-Tibet Plateau. It is mainly divided into permafrost and seasonal permafrost, which is a four-phase complex system composed of soil particles, water, ice and air. The characteristics of winter freezing and summer thawing make the soil in frozen soil area more complicated. In China, a large number of civil engineering projects are built in frozen soil regions. Lack of understanding of the physical and mechanical properties of frozen soil, such as strength, will lead to potential permafrost engineering risks. Based on the Mohr-Coulomb shear strength criterion, the relationship between the shear strength index (cohesion c and internal friction angle 蠁) and temperature, moisture content, freeze-thaw cycle, confining pressure and dynamic load of frozen soil is studied in this paper. A fitting formula of shear strength of frozen soil is established for different soil types. On this basis, the stability analysis of high speed subgrade based on water and heat field is carried out by using Comsol Multiphysics software. The specific work contents and innovations are as follows: 1. The systematic research on the shear strength of frozen soil is summarized, and the variation law of shear strength with temperature, moisture content, freeze-thaw cycle times, confining pressure and dynamic load is summarized. The results show that the shear strength is higher when the temperature is lower. When the initial moisture content is high, the strength decreases with the increase of water content, the strength increases with the increase of water content when the initial moisture content is low, and the shear strength decreases with the increase of freeze-thaw times, and tends to be stable after a certain cycle period. The relationship between confining pressure and strength is parabola, and the strength under dynamic load is affected by temperature, confining pressure and frequency. 2. Based on a large amount of experimental data of shear strength of frozen soil, the relationship between different factors and shear strength parameters is obtained by combining induction, summary and data fitting. The fitting formula of shear strength of frozen soil is established for different soil types and its applicability is reviewed. 3. Based on the background of high iron in Hazhi, the hydrothermal field of frozen soil subgrade is simulated by Comsol Multiphysics software. The results show that the depth and quantity of frost heave of roadbed under low temperature environment, and the variation of frost heave of soil lags behind the change of surface air temperature. Taking the hydrothermal field of different months as the initial state, based on the established formula of shear strength of frozen soil, the stability of roadbed at different time points is analyzed, and the safety coefficient is relatively high when the temperature is low. Under the action of freeze-thaw cycle, the safety factor will decrease gradually, and the strength will be stable after a certain number of times. The sensitivity of safety factor of roadbed to temperature is higher than that of moisture content in high temperature permafrost, the opposite is true in low temperature permafrost, and the sensitivity of safety factor to freezing and thawing. As the number of times increases, it decreases gradually. In this paper, the relationship between shear strength of frozen soil and external factors is systematically studied, and some of the results are verified by finite element software. The relevant conclusions have certain reference value.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U213.14;TU445
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