泾阳黄土三轴蠕变特性研究及模型分析

发布时间：2018-03-03 09:51

本文选题：黄土　切入点：三轴蠕变试验　出处：《西北农林科技大学》2015年硕士论文　论文类型：学位论文

【摘要】：随着西部大开发的进行,被广泛作为基础工程建设的建筑材料、建筑环境和载体的黄土,其变形、强度与稳定性随时间变化的流变问题变得很明显。实践证明,许多工程的破坏与失稳问题,如自然边坡和人工边坡的破坏与失稳、基坑开挖临空面的缓慢侧向位移、地基以及路基的缓慢竖向位移、土石坝的变形与失稳、隧道施工及运营时的地表沉降和变形等问题,在大多数情况下并不是在开挖后形成或者工程完工后立即发生的,而是其中土体的应力和变形随着时间的推移不断地调整、变化和发展导致的。因此,仍需进一步全面深入研究黄土的蠕变特性,以期更加丰富和完善黄土蠕变理论,为具体实际工程的设计、施工与稳定性分析提供一定的指导作用,对保证黄土高原地区建筑体的长期安全和正常使用等方面,具有重要的理论和实践意义。基于对前人黄土三轴蠕变特性研究成果的总结与思考,本文将进一步利用SR-6型三联式三轴蠕变仪对陕西省泾阳县某边坡Q3黄土原状样和重塑样进行三轴固结排水蠕变试验研究,着重探讨含水率、围压、偏应力水平、应力路径、初始主应力角以及其耦合作用对蠕变特性的影响,并对试验结果进行整理分析,建立适合该地区黄土的蠕变模型,本文主要研究成果如下:(1)该地区黄土具有明显的蠕变特性,重塑样呈非线性衰减蠕变特性,而原状样呈线性衰减蠕变特性。土样蠕变变形量的大小受偏应力水平、围压以及含水率的影响显著,土样在高偏应力水平、小围压、大含水率的条件下蠕变现象明显且蠕应变较大。(2)不同应力路径下重塑黄土的蠕变规律一致,而在各级偏应力水平下,蠕变变形量差别明显。过量加载后卸载试样的蠕变变形值最大,分级加载试样的蠕变变形次之,分别加载试样的蠕变变形最小。(3)由于分级荷载的非线性累积后效影响,使得Boltzmann线性叠加法和陈氏法两种方法处理实测数据所得结果有所差别,针对分级加载非线性蠕变应尽可能使用陈氏法来处理数据。基于数理统计的方法,依据试验资料建立了适合描述该地区90%压实度重塑黄土在20%~65%偏应力水平下非线性衰减蠕变特性的两种经验蠕变模型,二者各具优点,在实际应用中应综合考虑,以期达到互相验证的效果。(4)利用分级增量循环加载方式对原状黄土粘弹塑性基本规律的分析可知,加载时原状土样所产生的蠕应变由瞬时弹性变形、瞬时塑性变形、粘弹性变形和粘塑性变形四部分组成。卸载后,原状土样产生衰减粘弹性回弹变形,回弹量随着卸荷量的减小,围压的增大,含水率的增大而减小。但由于该地区原状黄土胶结强度较弱以及内部存在不均匀大孔隙,在较低的应力水平下便表现出较强的塑性变形特性,回弹变形不明显,蠕变过程中的粘弹性变形在蠕应变中所占比重较小。加卸荷应力历史对黄土的蠕变变形具有累积效应,将会加大土体的蠕变变形。依据试验资料建立了可以较好地描述该地区原状黄土的三轴线性衰减蠕变特性粘弹塑性9元件蠕变模型,物理意义明确,且模型参数可由Origin软件拟合得到。(5)不同初始主应力角的原状土样蠕变规律一致,当轴向偏应力较小时,初始主应力角对土体的蠕变特性有一定的影响,任意时刻,轴向蠕变变形随着初始主应力角的增大而增大,由于该地区黄土的结构性不明显,总体差别不大。随着轴向偏应力的增大,致使土样的原生结构被压坏,土样本身不再具有结构各向异性,对于不同初始主应力角的土样,其蠕变变形差别减小,且其大小关系没有一定的规律性。
[Abstract]:With the great development of Western China, is widely used as a basis for the construction of the building materials, construction environment and the carrier of loess, its deformation, rheological strength and stability with the change of time become apparent. In practice, many engineering damage and instability problems, such as natural slope and artificial slope failure and instability the excavation of free face, slow lateral displacement, foundation and subgrade slow vertical displacement, deformation of embankment dam and instability, the problem of ground tunnel construction and operation of the settlement and deformation, in most cases is not formed after excavation occurs immediately or after the completion of the project, but the soil stress and deformation with the passage of time is adjusted continuously, the change and development of the cause. Therefore, still need further in-depth study on creep characteristics of loess, in order to enrich and perfect the Loess creep theory for The specific design of practical engineering, the analysis provides some guidance for construction and stability, to ensure the Loess Plateau building long-term safety and normal use, which has important theoretical and practical significance. The summary and thinking of the previous Huang Tusan axial creep characteristics based on research results, this paper will further make use of the three axis creep instrument type SR-6 the triple type experiment on consolidation creep three axis to Jingyang County of Shaanxi province Q3 loess slope undisturbed and remolded samples, focusing on the moisture content, confining pressure and deviatoric stress level, stress path, the initial principal stress angle and the coupling effects on creep properties, and the test results are sorted analysis of creep model is established for the loess area, the main results are as follows: (1) the area of loess has obvious creep properties, the rebuilding is nonlinear creep and attenuation characteristics of undisturbed A kind of linear attenuation creep characteristics. The amount of creep deformation is affected by the deviatoric stress level, confining pressure and the influence of moisture content significantly, soil samples under high deviatoric stress level, low confining pressure, creep phenomenon of high moisture conditions and the creep strain significantly larger. (2) under different stress paths consistent heavy plastic loess creep law, and at all levels of deviatoric stress, creep deformation is obviously different. Excessive loading unloading creep deformation value of the specimen, the deformation of the specimen creep loading times, respectively. The minimum creep loading deformation of the specimen (3) due to the cumulative load after effect of nonlinear classification, the Boltzmann linear superposition method and Chen's method two methods of processing the measured data the results vary, according to the classification of load nonlinear creep should as far as possible to use Chen's method to process the data. Based on mathematical statistic method, on the basis of the experimental data was established. He described the area 90% degree of compaction loess in 20%~65% should be two kinds of partial empirical creep model nonlinear stress attenuation creep characteristics, two have their own advantages, should be considered in practical application, in order to verify the effect of each other. (4) analysis by using multi-step incremental cycling loading method on undisturbed loess viscoelastic plastic the basic rule that generated undisturbed loading creep strain by instantaneous instantaneous elastic deformation, plastic deformation, visco elastic and visco plastic deformation of four parts. After unloading, undisturbed attenuation of viscoelastic rebound deformation, the springback decreases with unloading confining pressure increases, the increase of the water content decreases. But because the area of loess and weak cementation strength within the inhomogeneous pore, at low stress level will show the characteristics of strong plastic deformation, the springback deformation is not obvious, creep Viscoelasticity deformation in the process of a smaller proportion in the creep strain. Loading and unloading of loess creep deformation history has a cumulative effect, will increase the creep deformation of soil. According to the test data set up can be used to describe the three axis linear loess attenuation creep characteristics of visco elastic plastic element 9 creep model, clear physical meaning, and the model parameters can be obtained by using the Origin software. (5) different initial principal stress consistent undisturbed creep force angle, axial deviatoric stress is small, the initial principal stress to a certain extent, the creep characteristics of angle on the soil at any time, the axial creep deformation increase with the initial angle of principal stress, because the area of structural loess is not obvious, is not very different. With the increase of axial deviatoric stress, resulting in the primary structure of soil samples were crushed, the soil itself is no longer with the structure To the opposite sex, the creep deformation of soil samples with different initial main stress angles is reduced, and the relation between their size and size is not regular.

【学位授予单位】：西北农林科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU411

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