【摘要】：深厚表土層凍結(jié)法鑿井技術(shù)的核心是確保凍結(jié)壁和井壁的安全,而深部人工凍土的工程特性與凍結(jié)壁、井壁安全密切相關(guān)。在凍結(jié)壁形成和開挖過(guò)程中,深部人工凍土分別經(jīng)歷了加載和卸載過(guò)程,因此系統(tǒng)深入地認(rèn)識(shí)深部人工凍土的加卸載力學(xué)特性,對(duì)于科學(xué)合理地設(shè)計(jì)凍結(jié)壁和井壁有重要意義。深部黏土由于特殊的賦存環(huán)境,具有顯著的結(jié)構(gòu)性。深部原狀黏土經(jīng)重塑后凍結(jié),結(jié)構(gòu)發(fā)生改變,進(jìn)而導(dǎo)致深部原狀與重塑人工凍結(jié)黏土宏觀力學(xué)特性表現(xiàn)出差異性。因此有必要從微觀尺度上刻畫出深部原狀與重塑人工凍結(jié)黏土的結(jié)構(gòu),研究加卸載條件下兩種不同結(jié)構(gòu)凍結(jié)黏土的宏細(xì)觀力學(xué)特性,這將有助于從本質(zhì)上認(rèn)識(shí)深部人工凍土的力學(xué)特性,并為凍結(jié)壁和井壁設(shè)計(jì)提供科學(xué)依據(jù)。本文主要開展了以下研究工作:(1)通過(guò)對(duì)深部原狀和重塑黏土SEM圖像數(shù)字化處理,定量分析了兩者微觀結(jié)構(gòu),在此基礎(chǔ)上構(gòu)建了深部重塑和原狀人工凍結(jié)黏土的顆粒流模型。系統(tǒng)地分析了顆粒流模型中微觀參數(shù)的力學(xué)效應(yīng),結(jié)合室內(nèi)三軸試驗(yàn)資料,引入支持向量機(jī)預(yù)報(bào)模型Lib SVM對(duì)微觀力學(xué)參數(shù)進(jìn)行了標(biāo)定。(2)在不同溫度和圍壓條件下,分別對(duì)深部重塑和原狀人工凍結(jié)黏土顆粒流模型進(jìn)行了不同模式的加卸載數(shù)值仿真試驗(yàn)。分析了深部重塑和原狀人工凍結(jié)黏土的強(qiáng)度與變形規(guī)律,以及微觀結(jié)構(gòu)的演變規(guī)律。(3)在室內(nèi)制備了深部重塑人工凍結(jié)黏土試樣,分別進(jìn)行了不同溫度和圍壓條件下的三軸加卸載試驗(yàn),分析比較了數(shù)值計(jì)算和室內(nèi)試驗(yàn)結(jié)果。通過(guò)上述研究,得出主要結(jié)論如下:(1)根據(jù)IPP圖像處理結(jié)果,深部重塑人工凍結(jié)黏土的顆粒體面積主要集中在1002?m,顆粒體角度主要分布在50°~70°之間,孔隙率為0.25。深部原狀人工凍結(jié)黏土的顆粒體面積也主要集中在1002?m,顆粒體角度主要分布在10°~50°之間,孔隙率為0.24。經(jīng)過(guò)微觀力學(xué)效應(yīng)分析,結(jié)合室內(nèi)三軸試驗(yàn)資料,引入支持向量機(jī)模型得到的微觀參數(shù)能夠很好地反應(yīng)深部人工凍結(jié)黏土的力學(xué)性質(zhì)。(2)深部重塑人工凍結(jié)黏土在加載階段應(yīng)變隨時(shí)間的增大而增大,等側(cè)壓力系數(shù)加載階段的應(yīng)變變化顯著大于等壓加載和變側(cè)壓力系數(shù)加載階段;深部原狀人工凍結(jié)黏土在加載階段的應(yīng)變隨時(shí)間變化規(guī)律與重塑土相同,區(qū)別在于各個(gè)階段結(jié)束時(shí)的時(shí)間和相應(yīng)應(yīng)變小于重塑土。在恒軸壓卸圍壓模式下,應(yīng)變隨著時(shí)間顯著增大;在恒圍壓卸軸壓模式下,應(yīng)變隨著時(shí)間顯著減小。(3)深部重塑人工凍結(jié)黏土在等側(cè)壓力系數(shù)加載階段應(yīng)變隨偏應(yīng)力的增大呈線性增長(zhǎng)。在恒軸壓卸圍壓模式下,深部重塑人工凍結(jié)黏土應(yīng)變隨偏應(yīng)力的增大而增大,應(yīng)力-應(yīng)變關(guān)系為應(yīng)變硬化型;恒圍壓卸軸壓模式下,應(yīng)變隨偏應(yīng)力的減小而減小,應(yīng)力-應(yīng)變關(guān)系也為應(yīng)變硬化型。(4)深部原狀人工凍結(jié)黏土在等側(cè)壓力系數(shù)加載階段應(yīng)變隨偏應(yīng)力的變化規(guī)律與重塑黏土相同,在恒軸壓卸圍壓模式下,深部原狀結(jié)黏土應(yīng)變開始時(shí)隨著偏應(yīng)力的增大而增大,到達(dá)峰值強(qiáng)度之后應(yīng)變隨著偏應(yīng)力的減小而減小,應(yīng)力-應(yīng)變關(guān)系呈應(yīng)變軟化型。恒圍壓卸軸壓模式下,應(yīng)變隨偏應(yīng)力的變化規(guī)律與重塑黏土相同。(5)加載結(jié)束后,深部重塑人工凍結(jié)黏土的結(jié)構(gòu)呈“腰鼓狀”;深部原狀人工凍結(jié)黏土的結(jié)構(gòu)呈“劈裂狀”,二者均可以看到接觸力鏈。恒軸壓卸圍壓模式下卸載結(jié)束后深部重塑人工凍結(jié)黏土的“腰鼓狀”處的直徑相比于加載階段結(jié)束時(shí)更大,試樣高度更低,接觸力鏈更完整;原狀黏土的劈裂處的裂隙更大,接觸力鏈中出現(xiàn)剪切面。恒圍壓卸軸壓模式下卸載結(jié)束時(shí)的試樣形態(tài)與恒軸壓卸圍壓模式下的相反。卸載結(jié)束時(shí),溫度對(duì)峰值強(qiáng)度和彈性模量的影響呈線性關(guān)系,溫度的影響效應(yīng)大于圍壓。(6)通過(guò)室內(nèi)三軸加卸載試驗(yàn),得到卸載路徑下不同圍壓、凍結(jié)溫度條件下土體的應(yīng)力-應(yīng)變關(guān)系、強(qiáng)度值和彈性模量,獲得了圍壓、凍結(jié)溫度對(duì)凍土強(qiáng)度、彈性模量和割線模量的影響程度,發(fā)現(xiàn)凍結(jié)溫度的影響效果大于圍壓。(7)深部重塑人工凍結(jié)黏土室內(nèi)試驗(yàn)結(jié)果顯示,在加卸載階段應(yīng)力-應(yīng)變曲線特征和試樣破壞形態(tài)與數(shù)值計(jì)算結(jié)果基本相同。恒軸壓卸圍壓試驗(yàn)條件下,室內(nèi)試驗(yàn)得到的強(qiáng)度比數(shù)值計(jì)算結(jié)果低4%,彈性模量高24%;恒圍壓卸軸壓試驗(yàn)條件下的室內(nèi)試驗(yàn)強(qiáng)度比數(shù)值模擬結(jié)果的強(qiáng)度低5%,彈性模量高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.
【學(xué)位授予單位】：中國(guó)礦業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TD265.3

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