【摘要】：凍土主要分布于我國(guó)中北部地區(qū)及青藏高原地區(qū),主要分為多年凍土和季節(jié)性?xún)鐾?凍土是由土顆粒、水、冰、空氣組成的四相復(fù)雜體系,其“冬凍夏融”的特點(diǎn)使凍土地區(qū)土體情況更為復(fù)雜。我國(guó)有大量土木工程修建于凍土地區(qū),對(duì)凍土的物理力學(xué)特性如強(qiáng)度認(rèn)識(shí)不足會(huì)導(dǎo)致潛在的凍土工程風(fēng)險(xiǎn)。 本文以Mohr-Coulomb抗剪強(qiáng)度準(zhǔn)則為基礎(chǔ),著重研究?jī)鐾恋目辜魪?qiáng)度指標(biāo)(粘聚力c和內(nèi)摩擦角φ)與溫度、含水率、凍融循環(huán)、圍壓及動(dòng)荷載等因素的關(guān)系,并針對(duì)不同土類(lèi)建立了相應(yīng)的凍土抗剪強(qiáng)度擬合公式。在此基礎(chǔ)上,以哈齊高鐵路基為研究對(duì)象,采用Comsol Multiphysics軟件進(jìn)行基于水熱場(chǎng)條件下的路基穩(wěn)定性分析。具體工作內(nèi)容及創(chuàng)新之處如下： 1、針對(duì)凍土抗剪強(qiáng)度進(jìn)行了系統(tǒng)性的研究綜述,總結(jié)了凍土抗剪強(qiáng)度隨溫度、含水率、凍融循環(huán)次數(shù)、圍壓及動(dòng)荷載等因素的變化規(guī)律,結(jié)果表明：溫度越低時(shí)抗剪強(qiáng)度越高；初始含水率較高時(shí)強(qiáng)度隨含水率的增大而減小,初始含水率較低時(shí)強(qiáng)度隨含水率的增大而增大；抗剪強(qiáng)度隨著凍融次數(shù)的增加而減小,一定循環(huán)周期后趨于穩(wěn)定；圍壓的高低與強(qiáng)度的大小呈拋物線關(guān)系；動(dòng)荷載作用下強(qiáng)度大小受溫度、圍壓、頻率的共同影響。 2、基于大量的凍土抗剪強(qiáng)度實(shí)驗(yàn)數(shù)據(jù),采用歸納總結(jié)與數(shù)據(jù)擬合相結(jié)合的方法,得出不同因素與抗剪強(qiáng)度參數(shù)之間的關(guān)系,針對(duì)不同土類(lèi)建立了相應(yīng)的凍土抗剪強(qiáng)度擬合公式,并對(duì)其適用性進(jìn)行了評(píng)述。 3、以哈齊高鐵為背景,運(yùn)用Comsol Multiphysics軟件對(duì)凍土路基水熱場(chǎng)進(jìn)行數(shù)值模擬,得出在低溫環(huán)境下路基的凍脹深度及凍脹量,且土體內(nèi)部?jī)雒浟康淖兓瘻笥诘乇須鉁氐淖兓�；分別以不同月份的水熱場(chǎng)為初始狀態(tài),基于建立的凍土抗剪強(qiáng)度擬合公式,應(yīng)用于路基斷面不同的土層,分析不同時(shí)間點(diǎn)路基的穩(wěn)定性,得出在氣溫較低時(shí)安全系數(shù)相對(duì)較高,在凍融循環(huán)作用下安全系數(shù)會(huì)逐漸降低,一定次數(shù)后強(qiáng)度趨于穩(wěn)定的結(jié)論。對(duì)路基安全系數(shù)的因素敏感性進(jìn)行了研究,高溫凍土?xí)r,安全系數(shù)對(duì)溫度的敏感性高于含水率,低溫凍土?xí)r正好相反,同時(shí)安全系數(shù)對(duì)凍融作用的敏感性,隨著次數(shù)的增加逐漸降低。 本文對(duì)凍土抗剪強(qiáng)度隨外界因素的變化關(guān)系進(jìn)行了系統(tǒng)性的研究,并采用有限元軟件對(duì)部分結(jié)果進(jìn)行了驗(yàn)證,相關(guān)結(jié)論具有一定參考價(jià)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.
【學(xué)位授予單位】：北京交通大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類(lèi)號(hào)】：U213.14;TU445

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