本文關(guān)鍵詞：顆粒材料的級配相關(guān)臨界狀態(tài)力學特性模擬　出處：《上海交通大學》2014年博士論文　論文類型：學位論文

  更多相關(guān)文章： 顆粒級配 臨界狀態(tài) 砂土 細觀力學 離散單元法 有限單元法

【摘要】：巖土工程中顆粒材料的級配變動會在很大程度上影響材料在臨界狀態(tài)下的承載能力,可能引發(fā)結(jié)構(gòu)物的大變形甚至導(dǎo)致整體失穩(wěn)。因此,研究顆粒級配變動對材料臨界狀態(tài)特性的影響很有必要。通過室內(nèi)實驗結(jié)合數(shù)值試驗,研究了不同初始級配對顆粒材料臨界狀態(tài)力學特性的影響;建立顆粒級配與材料臨界狀態(tài)的關(guān)系,并將其引進彈塑性本構(gòu)模型,模擬顆粒級配變化引起的力學問題。(1)綜合大量室內(nèi)實驗,研究了玻璃球和Hostun砂隨顆粒級配變化的力學特性,得出臨界狀態(tài)與顆粒級配的關(guān)系。結(jié)果表明相同初始密實度材料的不排水剪切強度和相變偏應(yīng)力比隨著材料不均勻系數(shù)Cu的增加而降低,并在Cu達到10以后趨于穩(wěn)定。通過二階功分析指出顆粒級配對顆粒材料的不穩(wěn)定性有很大影響,隨著Cu的提高材料的靜態(tài)液化潛能提高,變得更加不穩(wěn)定。試驗總結(jié)出顆粒材料臨界狀態(tài)參數(shù)隨顆粒級配指標Cu變化的非線性規(guī)律。在e-p'平面上臨界狀態(tài)線的位置和斜率隨著顆粒級配的拓寬而降低,在Cu達到10以后兩者皆趨于穩(wěn)定。在q-p'平面上顆粒材料的臨界狀態(tài)線則是一條直線,不受級配的影響。(2)數(shù)值試驗拓展分析了多個應(yīng)力路徑下顆粒材料級配相關(guān)的力學響應(yīng)。分析結(jié)果表明在相同加載條件下,材料的剪脹性隨著顆粒級配的拓寬而下降,出現(xiàn)從剪脹到剪縮的轉(zhuǎn)變;材料的不排水抗剪強度隨著級配的拓寬而下降。試驗結(jié)果進一步確認了臨界狀態(tài)參數(shù)與顆粒級配指標cu的非線性關(guān)系,不受排水條件和拉壓剪切模式的影響。在e-p'平面上的臨界狀態(tài)線是唯一的,并隨著級配的拓寬而下移;q-p'平面上的臨界狀態(tài)線則為直線,與級配無關(guān)。(3)基于細觀力學分析,證明了顆粒材料臨界狀態(tài)線在e-p'平面上隨顆粒級配移動以及在q-p'平面上呈直線且與級配無關(guān)的內(nèi)在機理。由平均配位數(shù)的演變規(guī)律表明,顆粒材料在不排水剪切狀態(tài)下較之排水剪切具有更高的不穩(wěn)定性。在臨界狀態(tài)下平均配位數(shù)與平均有效應(yīng)力的關(guān)系是唯一的,并隨顆粒級配的拓寬而下移。應(yīng)力-組構(gòu)-接觸力分析顯示,臨界狀態(tài)下顆粒材料的各個細觀組構(gòu)各向異性分量對細觀應(yīng)力比的貢獻程度相同,且與圍壓和級配無關(guān),從而證實了在q-p'平面上顆粒材料的臨界狀態(tài)線呈直線,且與級配無關(guān)。(4)通過引入顆粒級配指標與臨界狀態(tài)的非線性關(guān)系,建立了顆粒材料的級配相關(guān)彈塑性本構(gòu)模型。該模型可以描述任意顆粒級配材料的排水和不排水力學響應(yīng)。與已有考慮級配效應(yīng)的本構(gòu)模型進行對比,指出不同模型預(yù)測效果差異的主要原因是臨界狀態(tài)參數(shù)與級配指標的關(guān)系不同。通過數(shù)值試驗得出現(xiàn)有級配指標(cu和ig)都無法準確地描述顆粒材料級配相關(guān)的力學性能。提出了一個綜合cu和ig優(yōu)點的級配新指標igu并將其用于改進本構(gòu)模型。模擬驗證表明改進的本構(gòu)模型能夠更好地模擬任意級配顆粒材料的力學特性。(5)對本構(gòu)模型進行有限元二次開發(fā),用于分析可破碎地基土上淺基礎(chǔ)的承載力問題。將本構(gòu)模型編譯成umat子程序,通過abaqus模擬淺基礎(chǔ)的承載力問題。分析結(jié)果得出顆粒破碎引起了地基承載力的降低;隨著地基土初始顆粒級配的拓寬,基礎(chǔ)下壓引起的顆粒破碎逐漸減弱,承載力下降趨勢減弱。綜上,本文的研究成果可為砂性土的本構(gòu)研究、細觀力學分析等提供借鑒,給顆粒級配變化引起的巖土工程問題提供有益的分析手段和借鑒。
[Abstract]:Graded granular materials in geotechnical engineering changes will affect the bearing capacity of the material in the critical state to a great extent, may lead to large deformation structures and even lead to overall instability. Therefore, it is necessary to study the particle size changes on critical state characteristics of materials. Based on the results of numerical experiments through indoor experiment, influence research different initial gradation on mechanical properties of granular materials in critical state; establish relationship between gradation and material critical state, and the introduction of elastoplastic constitutive model, mechanical problems caused by simulation of particle gradation change. (1) a comprehensive laboratory experiment, mechanical properties change with the particle size distribution of sand glass ball and Hostun the relation between the critical state and particle size distribution. The results show that the initial density of materials of undrained shear strength and the transformation ratio of deviatoric stress coefficient Cu with inhomogeneous material increase With the decrease in Cu, and reached 10 after the stable. By the two order power analysis that has great influence the particle size distribution of granular material instability, with the increase of static liquefaction potential of Cu to improve the material, become more unstable. Experiment shows that the nonlinear law of granular materials critical state parameters with the change of particle size distribution index Cu the critical state line in e-p'plane position and slope decreases with widening of particle size distribution in Cu, reaching 10 after both tend to be stable in the q-p' plane. The critical state line of granular materials is a straight line, is not affected by gradation. (2) numerical analysis of multiple should expand the mechanics of particulate material gradation path of force response. Analysis results show that under the same loading condition, the dilatancy decreases with widening the particle size distribution of materials, from the dilatancy to shear the material does not change; The strength decreases with the gradation of broaden the shear. The experimental results further confirmed the nonlinear relationship between the critical state parameters and particle size distribution index Cu, is not affected by the drainage condition and tension shear mode. The critical state line in e-p'plane is the only, and with the widening of the graded down; the critical state line q-p' the plane is a straight line, and gradation. (3) based on meso mechanics analysis, proved that the granular material critical state line in e-p'plane with the mobile grain size distribution and the inherent mechanism and a linear independent gradation in the q-p' plane is indicated by the evolution of the average coordination number of particles in water compared with the shear shear condition has higher stability. In the critical state of the average coordination number and the relationship between the average effective stress is unique, and with the particle size distribution widened down. The stress group structure Contact force analysis showed that the critical state of each particle material micro structure of anisotropic component of meso stress than the same degree of contribution, and has nothing to do with the confining pressure and gradation, thus confirming the linear critical state line for granular materials in the q-p'plane, and has nothing to do. (4) and graded by nonlinear the relationship between the introduction of particle gradation index and critical state, established a graded granular materials dependent elasto plastic constitutive model. The model can describe arbitrary drainage materials and grading of undrained mechanical response. The effect of the gradation of constitutive model were compared with the existing account, it is pointed out that different models to predict the main reason is the relationship between the difference of the effect critical state parameters and grading index. By numerical experiments, some grading index (Cu and Ig) can not accurately describe the mechanical properties of granular material gradation related. This paper puts forward a comprehensive and Cu The new IGU Ig has the advantages of gradation index and used to the improved constitutive model. Simulation tests show that the mechanical properties of the improved constitutive model can better simulate arbitrary graded granular materials. (5) the constitutive model for finite element analysis can be used to develop two times, breaking ground shallow foundation bearing capacity. The constitutive model is compiled into a UMAT subroutine, the bearing capacity of shallow foundation is simulated by ABAQUS. The results of particle breakage caused by the bearing capacity of foundation soil is reduced; with the widening initial particle size distribution, particle breakage gradually weakened the pressure caused by foundation, weak carrying capacity decreased. In summary, constitutive research the results of this study for the sandy soil, micromechanics analysis provide a reference, to provide useful reference and analysis methods of geotechnical engineering problems caused by changes to particle size distribution.

【學位授予單位】：上海交通大學
【學位級別】：博士
【學位授予年份】：2014
【分類號】：TU41

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