【摘要】：凍土的融化固結(jié)沉降是造成寒區(qū)工程病害的主要原因之一。以我國(guó)修建的青藏鐵路和青藏公路為例,近年來的監(jiān)測(cè)數(shù)據(jù)顯示：多年凍土層的融化下沉?xí)鹨幌盗械墓こ滩『?例如：路面開裂、路面凹陷、道路翻漿、涵洞開裂、橋跳以及地基的不均勻沉降等。針對(duì)凍土的融化固結(jié)沉降,研究者進(jìn)行了大量的試驗(yàn)和理論研究。就目前來看,這些工作主要針對(duì)常溫邊界條件下土體的融化固結(jié)特性。在實(shí)際工程中,凍土地基的融化沉降往往伴隨著地表溫度的周期性變化而呈現(xiàn)出季節(jié)性的變化規(guī)律,即：在暖季隨著地表溫度的升高,地基內(nèi)孔隙水融化后在外壓力的驅(qū)動(dòng)下排出,地基沉降持續(xù)發(fā)展；在冷季地基內(nèi)孔隙水凍結(jié),由孔隙水的排出造成的固結(jié)沉降也隨之停止。很明顯,周期溫度邊界條件下土體的融化固結(jié)規(guī)律完全有別于常溫邊界的情況。因而,先前基于常溫邊界的研究結(jié)果并不適用于實(shí)際工程問題�；谶@樣的考慮,本文從試驗(yàn)和理論兩個(gè)方面對(duì)周期邊界條件下凍土的融化固結(jié)規(guī)律及其影響因素進(jìn)行了以下幾方面的研究：(1)根據(jù)實(shí)際工程中邊界溫度變化遵循正(余)弦函數(shù)的規(guī)律,進(jìn)行了不同周期溫度和含水量條件的一維融化固結(jié)試驗(yàn)。研究了融化固結(jié)變形和融化深度隨時(shí)間的發(fā)展變化規(guī)律。試驗(yàn)結(jié)果表明,一維周期溫度邊界條件下土體的融化固結(jié)變形隨時(shí)間的發(fā)展呈現(xiàn)出周期性的發(fā)展規(guī)律,這是區(qū)別于常溫邊界條件的最顯著特征。同時(shí),隨著凍融次數(shù)的增加,周期溫度邊界條件下的融化固結(jié)變形和融化深度均逐漸趨于常溫邊界的情況。(2)基于FLAC數(shù)值軟件建立了適用于周期溫度邊界條件下融化固結(jié)的數(shù)值模擬平臺(tái)。為了避免計(jì)算單元的溫度狀態(tài)反復(fù)改變導(dǎo)致的存儲(chǔ)變量丟失的問題,本文將反復(fù)凍融的區(qū)域始終作為融化區(qū)域,并在該區(qū)域內(nèi)進(jìn)行固結(jié)計(jì)算。對(duì)于反復(fù)凍融的區(qū)域,通過改變其滲透系數(shù)以模擬凍結(jié)和融化狀態(tài)對(duì)排水通道的影響。(3)通過對(duì)比分析一維狀態(tài)下融化固結(jié)變形和融化深度的試驗(yàn)和理論計(jì)算結(jié)果驗(yàn)證了該數(shù)值平臺(tái)的正確性。同時(shí)基于該平臺(tái)計(jì)算分析了融化固結(jié)度隨時(shí)間的變化規(guī)律。結(jié)果表明,融化固結(jié)度呈周期性衰減的變化趨勢(shì)。這是周期溫度邊界條件下,土體融化固結(jié)特性有別于常溫邊界的最顯著特點(diǎn)(常溫條件下,固結(jié)度為常數(shù))。同時(shí),融化固結(jié)度的衰減速率正比于融化固結(jié)率。(4)對(duì)凍土路基的計(jì)算分析表明,凍土路基的周期性融化固結(jié)規(guī)律主要源于周期溫度邊界條件下深層凍土的融化固結(jié),即：在每年的8至11月之間多年凍土層持續(xù)融化時(shí),相應(yīng)的固結(jié)變形也隨之產(chǎn)生。對(duì)比路基沉降的計(jì)算和實(shí)測(cè)結(jié)果表明,本文所建立的針對(duì)周期溫度邊界條件下凍土的融化固結(jié)數(shù)值模擬能夠較好地預(yù)測(cè)凍土路基的周期性融化沉降規(guī)律。因此,該平臺(tái)可以作為計(jì)算實(shí)際寒區(qū)工程問題的可靠工具。(5)凍土路基的融化固結(jié)度隨時(shí)間的發(fā)展呈現(xiàn)出先增大后減小的趨勢(shì)。這表明路基淺層土體在運(yùn)營(yíng)初期已完成固結(jié),后期固結(jié)度的降低主要是深層凍土的融化壓縮所致。進(jìn)一步的計(jì)算分析表明融化固結(jié)度的減小速率正比于凍土路基的融化固結(jié)率。通過擬和分析,路基融化固結(jié)的降低速率和融化固結(jié)率之間存在良好的冪函數(shù)關(guān)系。本研究表明：基于周期溫度邊界條件下凍土融化固結(jié)規(guī)律建立的數(shù)值模擬平臺(tái)能夠較好的預(yù)測(cè)土體的固結(jié)融化規(guī)律；對(duì)于較為理想的一維狀態(tài)和邊界條件復(fù)雜的實(shí)際工程問題,周期溫度邊界條件下土體的融化固結(jié)特性完全不同于常溫邊界的情況；同時(shí)表征土體熱學(xué)和力學(xué)特性的融化固結(jié)率對(duì)土體的融化固結(jié)規(guī)律有著重要影響,在研究周期溫度邊界條件下凍土的融化固結(jié)時(shí)必須加以考慮。
[Abstract]:The thawing and consolidation settlement of frozen soil is one of the main causes of Engineering diseases in cold regions. Taking the Qinghai-Tibet Railway and Qinghai-Tibet Highway built in China as examples, the monitoring data in recent years show that the thawing and subsidence of permafrost layer can cause a series of Engineering diseases, such as pavement cracking, pavement depression, road grouting, culvert cracking, bridge jumping and so on. For the settlement of frozen soil, researchers have done a lot of experiments and theoretical research. At present, these works mainly focus on the characteristics of soil thawing and consolidation under normal temperature boundary conditions. There is a seasonal variation law, that is, in the warm season with the increase of surface temperature, pore water melted in the foundation under the driving of external pressure, the foundation settlement continued to develop; in the cold season, pore water frozen in the foundation, the consolidation settlement caused by the discharge of pore water also stopped. Therefore, the previous research results based on the normal temperature boundary are not applicable to practical engineering problems. Based on this consideration, this paper studies the regularity of thawing and consolidation of frozen soil under periodic boundary conditions and its influencing factors from both experimental and theoretical aspects: ( 1) According to the law of sinusoidal (cosine) function of boundary temperature in practical engineering, one-dimensional melting and consolidation tests under different periodic temperature and water content conditions were carried out. The development of melting and consolidation deformation and melting depth with time were studied. At the same time, with the increase of freezing-thawing times, the melting and consolidation deformation and the melting depth under the periodic temperature boundary condition tend to the normal temperature boundary gradually. (2) Based on the FLAC numerical software, a suitable periodic temperature boundary is established. In order to avoid the loss of storage variables caused by repeated changes in the temperature state of the calculation unit, the freeze-thaw region is always regarded as the melt region and the consolidation calculation is carried out in this region. For the freeze-thaw region, the freeze and thaw are simulated by changing the permeability coefficient. (3) The validity of the numerical platform is verified by comparing and analyzing the experimental and theoretical results of the deformation and depth of melting consolidation in one-dimensional state. This is the most remarkable characteristic of the soil thawing and consolidation under the periodic temperature boundary condition (the degree of consolidation is constant at room temperature). At the same time, the attenuation rate of the degree of thawing and consolidation is proportional to the rate of thawing and consolidation. (4) The calculation and analysis of the frozen soil roadbed show that the periodic thawing and consolidation law of the frozen soil roadbed is the main. The thawing and consolidation of deep frozen soil originated from the periodic temperature boundary condition, i.e. the corresponding consolidation deformation occurs when the permafrost layer continues to thaw between August and November of each year. Comparing the calculation of subgrade settlement with the measured results, the numerical simulation of thawing and consolidation of frozen soil under the periodic temperature boundary condition established in this paper can be used to simulate the thawing and consolidation of frozen soil. Therefore, the platform can be used as a reliable tool for calculating practical engineering problems in cold regions. (5) The degree of consolidation of frozen soil roadbed increases at first and then decreases with the development of time, which indicates that the shallow soil of roadbed has completed consolidation at the beginning of operation and consolidation at the later stage. The reduction is mainly due to the thawing compression of deep frozen soil. Further calculation and analysis show that the reduction rate of thawing consolidation is proportional to the thawing consolidation rate of frozen soil roadbed. The numerical simulation platform established under the condition of thawing and consolidation law of frozen soil can better predict the consolidation and thawing law of soil; for the ideal one-dimensional state and practical engineering problems with complex boundary conditions, the thawing and consolidation characteristics of soil under the condition of periodic temperature boundary are completely different from those under the condition of normal temperature boundary; The thawing and consolidation rates of thermodynamic and mechanical properties have an important influence on the law of thawing and consolidation of frozen soils.
【學(xué)位授予單位】：蘭州大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：U416.16;U213.14

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本文編號(hào)：2198839