【摘要】：飽和砂土在靜力和動力荷載作用下,具有壓硬性、剪脹性、應(yīng)變硬化和應(yīng)變軟化等特點�？紤]狀態(tài)參數(shù)的影響,研究飽和密砂和中密砂土在剪應(yīng)力作用下的變形特性,建立飽和砂土的彈塑性模型已經(jīng)是近年來國際巖土工程界的重要研究領(lǐng)域和研究方向,具有重要的學(xué)術(shù)價值和實踐意義。本論文在國內(nèi)外大量試驗結(jié)果的基礎(chǔ)上,以北京市自然科學(xué)基金資助項目(8112024)、北京市教委科技發(fā)展計劃項目(KM200910009008)為依托,對飽和密實和中密砂土在靜力荷載作用下的變形特點和剪脹規(guī)律開展了系統(tǒng)和深入的研究工作。取得的主要研究成果如下： (1)論述了密實砂土和中密砂土剪脹性的特點和影響剪脹的因素。通過對已有試驗結(jié)果的分析和整理,考慮密實砂土和中密砂土體變過程的特點,提出應(yīng)關(guān)注這類砂土的相轉(zhuǎn)換臨界狀態(tài)點,簡稱為相變點。并進(jìn)一步指出相變點是這類砂土變形過程的一個關(guān)鍵狀態(tài)。諸多試驗表明,在相變孔隙比和相變圍壓構(gòu)成的平面上,二者呈直線關(guān)系,也即相變線方程是線性變化的。因此,本文建立了呈線性變化特征的相變線方程或數(shù)學(xué)表達(dá)式。并以相變線作為參照標(biāo)準(zhǔn),以相變孔隙比為具體參照量,提出了新的狀態(tài)參量表達(dá)式和新的剪脹比計算公式。這一狀態(tài)參量綜合考慮了應(yīng)力水平和材料狀態(tài)的影響。結(jié)合相變孔隙比和臨界狀態(tài)孔隙比,利用狀態(tài)參量的概念可以較為準(zhǔn)確地判斷砂土在初始時和任意時刻的剪脹趨勢。以此為基礎(chǔ)建立的砂土的彈塑性模型即可以較真實地反映土的體積先剪縮后剪脹的變化全過程和變形特性。 (2)對于砂土,其剪脹比不能被視為應(yīng)力比的唯一性函數(shù),這一點與黏性土不同。因為砂土的剪脹比不僅與三軸應(yīng)力變量q和p'有關(guān),而且還與材料的內(nèi)部狀態(tài)有關(guān),即土的密實程度有關(guān)。在顆粒破碎前,按照這一思路建立砂土的剪脹性模型可以突破以往的一些障礙,以契符合土體受力和變形的實際情況。本文建立的剪脹比計算公式,考慮了材料狀態(tài)的影響,把具有不同密度的同一類砂處理為一種砂而不是兩種砂,可以較好地描述剪縮和剪脹兩種體積變化過程。 (3)本文基于前面建立的飽和砂土的考慮狀態(tài)參量影響的剪脹比計算公式,實現(xiàn)和達(dá)到了考慮材料狀態(tài)對剪脹比影響的目標(biāo)。在此基礎(chǔ)上,提出了一種能真實地反映密實砂土和中密砂土體積變化過程的砂土彈塑性本構(gòu)模型,僅用一組模型參數(shù)即可以描述同一種砂土在不同初始密度和不同圍壓條件下的應(yīng)力應(yīng)變特性。 (4)進(jìn)行了系列飽和砂土實驗。通過與各種初始狀態(tài)和加載條件下砂土相應(yīng)的實驗數(shù)據(jù)的比較,證明該模型具有較好的模擬能力。
[Abstract]:Saturated sand under static and dynamic loads has the characteristics of compression hardness, dilatancy, strain hardening and strain softening. Considering the influence of state parameters, it is important to study the deformation characteristics of saturated sand and medium-dense sand under shear stress and to establish the elastic-plastic model of saturated sand. On the basis of a large number of experimental results at home and abroad, the deformation of saturated and medium-dense sands under static loads is studied in this paper, which is supported by the Beijing Natural Science Foundation (8112024) and the Beijing Education Commission's Science and Technology Development Program (KM200910009008). The characteristics and dilatancy laws have been studied systematically and thoroughly.
(1) The characteristics of dilatancy and the factors affecting dilatancy of compacted sand and medium-dense sand are discussed. Based on the analysis and collation of the existing experimental results and considering the characteristics of deformation process of compacted sand and medium-dense sand, the critical state point of phase transition of this kind of sand is proposed, which is called phase transition point for short. A key state in the deformation process. Many experiments have shown that there is a linear relationship between the phase change pore ratio and the phase change confining pressure on the plane formed by the phase change pore ratio and the phase change pore ratio. A new expression of state parameter and a new formula for calculating dilatancy ratio are proposed for concrete reference. The state parameter takes into account the effects of stress level and material state. Combining phase change void ratio and critical state void ratio, the concept of state parameter can be used to judge the dilatancy of sand at the beginning and at any time accurately. The elastic-plastic model of sandy soil based on this model can truly reflect the whole process and deformation characteristics of soil volume change after shear dilatancy.
(2) For sands, the dilatancy ratio can not be regarded as the unique function of the stress ratio, which is different from clay because the dilatancy ratio of sands is not only related to the triaxial stress variables Q and p', but also to the internal state of the material, i.e. the compactness of the soil. The formulas for calculating the dilatancy ratio are established in this paper. Considering the influence of material state, the same kind of sand with different densities is treated as one kind of sand instead of two kinds of sand, which can better describe the volumetric variations of shear shrinkage and dilatancy.
(3) Based on the formulas for calculating the dilatancy ratio of saturated sands considering the influence of state parameters, this paper achieves and achieves the goal of considering the influence of material state on the dilatancy ratio. On this basis, a sand elastic-plastic constitutive model which can truly reflect the volumetric variation process of compacted sands and medium-dense sands is proposed. The model parameters can describe the stress-strain characteristics of the same sand under different initial density and confining pressure.
(4) A series of saturated sand experiments are carried out. The model is proved to have good simulation ability by comparing with the corresponding experimental data of sand under various initial conditions and loading conditions.
【學(xué)位授予單位】：北京交通大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2013
【分類號】：TU441

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本文編號：2176706