基于复杂应力路径饱和砂土动力试验的本构模型研究

发布时间：2018-04-12 14:45

本文选题：空心圆柱扭剪仪 + 主应力轴旋转　；参考：《浙江大学》2015年硕士论文

【摘要】：砂土在含主应力轴旋转的复杂应力作用下的应力应变特性是当今岩土工程研究的热点与难点,有着较高的理论价值与工程价值。尽管考虑复杂应力作用的本构模型研究广受重视,但是至今国内外仍未有一个广受认可的相应的本构模型。本文基于试验数据分析,以Manzari临界状态双面弹塑性模型为基础架构,在一定的理论推导与假设的基础上,提出了一个可以考虑主应力旋转作用的本构模型。本文主要取得了如下的成果： (1)基于复杂应力路径作用下饱和砂土动力试验的结果,分析了饱和砂土在不同应力路径(动三轴、动扭剪、圆形路径、椭圆路径)作用下的变形特性。其主要的规律为：动三轴加载作用下,试样的累积变形趋势为径向与环向均匀压缩,试样轴向不断拉伸；动扭剪荷载作用下,试样在扭剪应力作用平面内均匀拉伸,而在垂直于该平面的径向则不断压缩；试样的偏差正应力一偏差正应变滞回曲线具有较为统一的形状,应变滞后特性不明显,应力与应变几乎同时达到峰值,扭剪应力—扭剪应变曲线有着相同的规律；当有效球应力小于某一特定值时,试样的残余孔压累积速率加快,试样的应变发展也明显加快,这一临界有效球应力近似为20kPa。 (2)对主应力旋转平面内应变增量主方向的规律进行了较为细致的分析,得到的主要结论有：定义应变增量主方向与主应力方向的夹角为非共轴角(基于总应变,而非塑性应变),则非共轴角随着振次的增加而不断减小；在各应力分量的极值处(应力路径的极点处),应变增量方向几乎与应力路径相切,也即应变增量方向与应力增量方向一致；在达到液化之前的大部分振次内,应变增量方向与应力增量方向都近似位于同一个象限内；在达到液化之前,仅有很小的一段区间内,非共轴角能减小至零。基于此,本文提出了一个非共轴角的简化计算模型。 (3)对Manzari临界状态双面弹塑性模型做了简要的介绍,对其做了一定的修改与优化,并且对将该模型应用于不排水循环问题的可行性进行了分析。提出了将该本构模型运用于不排水加载的变形协调迭代计算方法。基于静力加载试验,确定了模型的主要参数。运用该模型对砂土的静力三轴压缩试验(排水),循环三轴加载试验(不排水)分别进行了变形预测,验证了该模型的适用性。 (4)在优化的临界状态双面弹塑性模型基础上,增添了考虑主应力旋转作用的功能。运用双面弹塑性模型考虑正应力增量引起的塑性变形,然后再将扭剪应力增量引起的附加变形纳入其中。扭剪应力增量引起的附加变形采用广义塑性理论的思想,直接根据试验规律而给出加载强度、流动方向与塑性模量。附加变形分为偏应变与体应变,两者的比例关系借鉴Yunming Yang所提出的公式。运用新提出的模型预测了不同应力路径作用下砂土的变形趋势,结果表明该模型能大致预测出各应变分量及孔压的发展趋势,而对于试样在较大振次时的变形预测则不甚理想,同时该模型也无法预测试样液化后的大变形,这表明该模型具有一定的适用性,也存在一定的局限性。
[Abstract]:In the sand with the rotation of principal stress axes complex stress strain characteristics under the action of force is a hotspot and difficulty in geotechnical engineering research, has theoretical value and engineering value. Although high considering complex stress constitutive model of wide attention at home and abroad, but so far there has not been a wide approved by the corresponding constitutive model. Based on the analysis of the test data, the critical state of Manzari double elastoplastic model based architecture based on theoretical derivation and some hypotheses on the proposed one can consider the main mode should be the constitutive force of the rotating role. This paper mainly achieved the following results:
(1) complex dynamic test results of saturated sand under the action of stress path based on the analysis of the saturated sand under different stress paths (three axis, dynamic torsional shear, circular path, elliptical path) deformation characteristics under the action. Its main rule: three triaxial loading, the cumulative deformation trend test as a kind of radial and circumferential uniform axial compression, constant tensile specimen; dynamic torsional shear loads, the specimen in the shear plane uniform tensile, and radial direction perpendicular to the plane is continuously compressed; sample deviation of normal stress is a deviation strain hysteresis curve with uniform shape, strain hysteresis is not obvious, the stress and strain peak almost at the same time, shear stress and shear strain curves have the same rules; when the effective stress is less than a certain value, accelerate the accumulation rate of residual pore pressure of the specimen, the specimen strain The development is also speeded up, and the critical effective ball stress is approximately 20kPa.
(2) the main direction of incremental principal strain plane rotation law for a more detailed analysis, the main conclusions are: the definition of included angle of strain increment direction and the principal stress direction for non coaxial angle (based on the total strain and plastic strain), non coaxial angle with increasing vibration time decreases; in the extreme should force components (poles should be the path of force), strain increment and stress path direction almost tangent, i.e. strain increment and stress increment direction direction; at most before liquefaction vibration times, strain increment and stress increment direction direction approximately in the same quadrant; in just a little before liquefaction, a range of non coaxial angle can be reduced to zero. Based on this, this paper puts forward a calculation model of non coaxial angle is simplified.
(3) Manzari on the critical state of double elastoplastic model is briefly introduced. The modification and Optimization on the model, and the application of analysis on feasibility of undrained cyclic problem was put forward. The constitutive model is applied to the deformation coordination of iterative undrained loading calculation method based on the static loading test, the main parameters of the model were determined by static test. The model of sand three axial compression (drainage), cyclic loading test of three axis (undrained) of deformation prediction, verify the applicability of this model.
(4) in the optimization of the critical state of double elasto-plastic model, add considering principal stress rotation function. Using double elastoplastic model considering plastic deformation is caused by the stress increment, then the torsional shear stress increment caused by the additional deformation should be included. Torsion shearing deformation the stress increment caused by the thought of generalized plasticity theory, according to the rules given directly test loading intensity, flow direction and plastic modulus. The additional deformation is divided into partial strain and volume strain, the ratio between two reference Yunming Yang proposed a new formula. Using the model to predict the deformation trend of different stress paths under the action of sand, the results show that the model can roughly predict development trend of strain components and pore pressure, and for the prediction of deformation in large sample vibration frequency is not ideal at the same time, the model can predict the sample solution The large deformation after the transformation shows that the model has certain applicability, and there are some limitations.

【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU441;TU411

【参考文献】