本文選題：微重比 + 土體胞元模型�。� 參考：《華南理工大學(xué)》2016年博士論文

【摘要】：土體介質(zhì)是地質(zhì)循環(huán)作用下由固體顆粒、孔隙液體和孔隙氣體組成的多相地質(zhì)材料,土體不同尺度土顆粒之間形成的復(fù)雜微細(xì)觀結(jié)構(gòu)和組構(gòu)以及各相物質(zhì)之間的相互協(xié)作用,導(dǎo)致土體在不同尺度結(jié)構(gòu)層次呈現(xiàn)不同的物理機制和力學(xué)響應(yīng),突顯土體強度和變形特性的多層次耦合和跨尺度演化效應(yīng)。本文以黏性土為研究對象,采用理論分析和試驗研究相結(jié)合的方法探討土體介質(zhì)的多尺度耦合力學(xué)特性,理論分析主要是闡述土體介質(zhì)不同尺度結(jié)構(gòu)層次上力學(xué)機制的多樣性和耦合性并建立能夠模擬和預(yù)測土體介質(zhì)多尺度耦合力學(xué)特性的力學(xué)模型和本構(gòu)關(guān)系;試驗研究則主要是呈現(xiàn)土顆粒粒徑和相對含量對土體抗剪強度的影響規(guī)律并求解力學(xué)模型和本構(gòu)關(guān)系的微細(xì)觀計算參數(shù)。在這兩個方面的工作基礎(chǔ)之上,綜合分析具有多尺度分層次理論框架的力學(xué)模型和本構(gòu)關(guān)系中微細(xì)觀計算參數(shù)的物理意義并通過試驗結(jié)果評估理論的適用性和有效性。最后,將提出的多尺度研究框架與傳統(tǒng)土力學(xué)強度理論相結(jié)合,以詳細(xì)解釋土體介質(zhì)強度特性的顆粒尺度效應(yīng)。本文開展的研究工作和取得的研究成果主要有以下幾個方面:(1)通過分析不同尺度土顆粒之間各種力場的相互作用效應(yīng),提出微重比的概念,定量計算土顆粒之間的范德華力和庫侖力等微觀作用力,建立土顆粒微重比與其粒徑的關(guān)系,計算結(jié)果表明,當(dāng)土顆粒粒徑小于10μm時,反映黏聚效應(yīng)的微觀力相互作用十分顯著,隨著土顆粒粒徑的繼續(xù)增加,反映摩擦效應(yīng)的重力作用開始顯現(xiàn)。因此,土顆粒的微重比可作為劃分基體顆粒和加強顆粒的客觀物理依據(jù)。(2)根據(jù)不同尺度土顆粒相互作用產(chǎn)生的黏聚和摩擦物理效應(yīng),構(gòu)建能夠反映土體內(nèi)部材料信息和顆粒特征信息的細(xì)觀土體胞元,以協(xié)調(diào)微裂紋密度和應(yīng)變梯度分別描述土體的微細(xì)觀結(jié)構(gòu)變形特征,利用不同尺度層次間的能量平衡原理和幾何變形相容性條件建立能夠模擬和預(yù)測土體介質(zhì)多尺度耦合力學(xué)特性的土體胞元模型,比較土體胞元模型對土體屈服應(yīng)力的預(yù)測結(jié)果與試驗結(jié)果,初步證實了土體胞元模型的適用性和有效性,在此基礎(chǔ)之上,導(dǎo)出具有多尺度分層次理論框架的土體增量本構(gòu)模型,以此對無側(cè)限壓縮試樣的塑性應(yīng)變分布進行分析,結(jié)果表明,基于土體胞元模型的增量本構(gòu)關(guān)系能夠有效地描述土體力學(xué)特性的顆粒尺度效應(yīng)和多尺度耦合機制。(3)制備一系列具有不同加強顆粒組合和基體液性指數(shù)的土體胞元模型試樣,分別進行直接快剪試驗和三軸壓縮試驗。試驗結(jié)果呈現(xiàn)了加強顆粒粒徑和體分比對土體抗剪強度的影響規(guī)律:當(dāng)加強顆粒體分比小于0.271時,土體的抗剪強度隨加強顆粒粒徑和體分比的變化而改變:對于三軸固結(jié)/不固結(jié)不排水剪切試驗,土體的抗剪強度隨加強顆粒的粒徑減小和體分比增加而顯著提高;對于直接快剪試驗,土體的抗剪強度隨加強顆粒體分比的增加而提高,但隨加強顆粒粒徑的變化而基本保持不變。當(dāng)加強顆粒體分比大于0.318時,無論是三軸壓縮試驗還是直接快剪試驗,土體的抗剪強度不再隨加強顆粒體分比的變化而改變,呈現(xiàn)加強顆粒增強效應(yīng)的臨界現(xiàn)象。土體胞元模型的理論與試驗研究表明,加強顆粒體分比增加誘發(fā)土體細(xì)觀組構(gòu)發(fā)生物質(zhì)相變是加強顆粒體分比增強效應(yīng)出現(xiàn)臨界值的根本原因。(4)結(jié)合土體胞元模型的理論分析與試驗研究,土體力學(xué)特性顆粒尺度效應(yīng)的作用機制可以解釋為:基體與加強顆粒之間的不相容變形,微觀上導(dǎo)致協(xié)調(diào)微裂紋的產(chǎn)生,細(xì)觀上誘發(fā)土體胞元應(yīng)變梯度的出現(xiàn),協(xié)調(diào)微裂紋密度和應(yīng)變梯度則增加了單位體積土體中消耗或儲存的能量,進而使土體的變形阻力增大,宏觀上表現(xiàn)為土體具有更強的變形性能和更高的抗剪強度。(5)在土體胞元模型的基礎(chǔ)上,考慮了土體胞元內(nèi)部加強顆粒的轉(zhuǎn)動梯度對土體強度特性的影響,推導(dǎo)體現(xiàn)土體介質(zhì)力學(xué)特性顆粒尺度效應(yīng)的屈服應(yīng)力計算公式,結(jié)合傳統(tǒng)土力學(xué)強度理論,建立多尺度Mohr-Coulomb強度準(zhǔn)則,根據(jù)試驗結(jié)果繪制其屈服軌跡并與傳統(tǒng)Mohr-Coulomb強度準(zhǔn)則的屈服軌跡進行比較,結(jié)果表明,多尺度Mohr-Coulomb強度準(zhǔn)則能夠較好地模擬和預(yù)測土體介質(zhì)強度特性的顆粒尺度效應(yīng)和多尺度耦合機制,而且可以較好地與傳統(tǒng)土力學(xué)強度理論相結(jié)合。
[Abstract]:Soil medium is a multi-phase geological material composed of solid particles, pore liquid and pore gas under the action of geological cycle. The complex microstructure and structure of soil particles in different scales and the interaction between each phase matter, resulting in different physical mechanism and mechanics of soil in different scale structure levels. In response, the multi-layer coupling and cross scale evolution effect of soil strength and deformation characteristics are highlighted. In this paper, the multi-scale mechanical properties of soil medium are discussed by combining theoretical analysis with experimental research. The theoretical analysis is mainly about the mechanical mechanism of soil body medium at different scale structure levels. The mechanical model and constitutive relation can be established to simulate and predict the mechanical properties of multi scale coupling in soil medium. The experimental study is mainly about the effect of the particle size and relative content of soil on the shear strength of soil and the calculation parameters of the mechanical model and the constitutive relation in the two aspects. On the basis of the work, the mechanical model of the multi scale hierarchical theoretical framework and the physical meaning of the calculation parameters in the constitutive relation are synthetically analyzed and the applicability and effectiveness of the theory are evaluated through the experimental results. Finally, the proposed multi scale research framework is combined with the traditional soil strength theory to explain the soil medium in detail. The research work and results obtained in this paper mainly include the following aspects: (1) by analyzing the interaction effects of various force fields between different scales of soil particles, the concept of micro gravity ratio is proposed, and the microcosmic forces such as Vander Ed Ley and Coulomb force between soil particles are calculated and the soil is established. The relationship between the particle microweight ratio and the particle size shows that when the particle size is less than 10 m, the micro force interaction which reflects the cohesive effect is very significant. With the continuous increase of the particle size of the soil, the gravity action reflecting the friction effect begins to appear. Therefore, the micro weight ratio of the soil particles can be used as a matrix particle and a strengthening particle. (2) in accordance with the physical effects of cohesive and friction produced by the interaction of soil particles in different scales, a mesoscopic soil element can be constructed which can reflect the information of the material and the characteristics of the particles in the soil. In order to coordinate the micro crack density and strain gradient, the microstructural deformation characteristics of the soil are described respectively, and the different scales are used to make use of the different scales. Based on the principle of energy balance and the compatibility condition of geometric deformation, the soil cellular element model which can simulate and predict the multi scale coupling mechanical properties of soil medium is established, and the prediction results and experimental results of soil cell element model on soil yield stress are compared, and the applicability and effectiveness of the soil cellular element model are preliminarily confirmed. The soil incremental constitutive model with multi scale hierarchical theoretical framework is developed to analyze the plastic strain distribution of unconfined compression specimens. The results show that the incremental constitutive relation based on the cellular element model can effectively describe the particle size effect and multi-scale coupling mechanism of soil mechanical properties. (3) a series of materials are prepared. The experimental results show that the influence of particle size and body ratio on the shear strength of soil is enhanced by direct fast shear test and three axial compression test. As for the three axis consolidation / unconsolidated undrained shear test, the shear strength of the soil increases significantly with the increase of the particle size and the volume ratio. For direct fast shear test, the shear strength of the soil increases with the increase of the particle ratio, but it is basically guaranteed with the increase of particle size. When the particle ratio is greater than 0.318, both the three axis compression test and the direct fast shear test, the shear strength of the soil no longer changes with the increase of the particle ratio, and presents the critical phenomenon of strengthening the particle enhancement effect. The fundamental reason for strengthening the critical value of the particle ratio enhancement effect is the phase transition of the meso microstructure of the soil. (4) combining the theoretical analysis and experimental study of the soil cell element model, the mechanism of the particle size effect of the soil mechanical properties can be explained as: the incompatible deformation between the matrix and the strengthening grain, and the microcosmic coordination micro The occurrence of the crack is induced by the microcrack density and the strain gradient, which increases the energy consumed or stored in the unit volume soil, and then increases the deformation resistance of the soil. On the macroscopic view, the soil has stronger deformation property and higher shear strength. (5) in the soil element model of soil mass On the basis of this, the influence of the rotational gradient of the soil element on the strength characteristics of the soil is considered, and the formula of yield stress is derived, which embodies the particle size effect of the mechanical properties of the soil. In combination with the traditional soil mechanics strength theory, the multi scale Mohr-Coulomb strength quasi rule is set up. The yield trajectory of the Mohr-Coulomb strength criterion is compared. The results show that the multi-scale Mohr-Coulomb strength criterion can better simulate and predict the particle size effect and multi scale coupling mechanism of soil medium strength characteristics, and it can be better combined with the traditional soil mechanics strength theory.
【學(xué)位授予單位】：華南理工大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TU43
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本文編號：2087995