主应力连续旋转下软粘土非共轴变形特性试验和模型研究
发布时间：2018-08-19 15:36
【摘要】：主应力轴旋转普遍存在于岩土工程中,地基土体经历交通荷载、波浪荷载、多向地震作用等动荷载作用后,作用于土体单元上的主应力方向会产生连续的旋转。主应力轴旋转的影响也早已引起了广大研究者的关注,随着空心圆柱扭剪仪在土工试验中的使用,目前国内外的研究者对主应力轴旋转条件下土体的变形特性和本构模拟方面开展了广泛的研究。主应力轴旋转过程中土体的一个重要特性就是塑性应变增量方向与应力方向不共轴。在实际工程中,如果忽略土体非共轴特性的影响可能会低估土体的变形而使工程设计偏于不安全。但目前有关主应力轴旋转的土体非共轴研究主要还是集中在砂土,应力路径也以主应力轴小幅旋转为主。无论在试验研究还是理论研究方面对于软粘土在主应力轴连续纯旋转条件下的非共轴变形特性的研究还都比较少。合理考虑土体的非共轴特性对准确预测主应力轴旋转条件下土体的变形又至关重要。为此急待丰富与完善考虑主应力轴旋转条件下软粘土非共轴变形特性的研究,以适应软土地区面临的越来越复杂的岩土工程问题。本文在已有研究成果的基础上,分别从试验研究、规律分析总结、模型建立等三个方面开了考虑主应力轴连续旋转影响的软粘土非共轴变形特性研究。给出了计算主应力轴连续旋转条件下软粘土非共轴角的计算模型,基于试验研究结果建立了考虑主应力轴旋转引起的软粘土变形的计算方法。 本文主要研究内容和取得的研究成果如下： 1.通过对杭州原状软粘土和重塑粘土进行的主应力轴大幅(180°)连续纯旋转试验,重点研究了主应力轴连续旋转条件下软粘土的非共轴变形特性。分析软粘土在主应力轴单纯连续旋转条件下变形发展、孔压累积、刚度衰减等规律,并从微观结构层面对主应力轴旋转影响机理进行解释。试验结果发现：(1)定向剪切条件下原状粘土和重塑粘土的非共轴特性都不显著,随着剪应力增加塑性主应变增量方向和主应力方向基本趋于共轴；(2)主应力轴连续旋转条件下原状粘土和重塑粘土存在显著的非共轴特性,非共轴角随着主应力轴的旋转而波动变化,中主应力系数、剪应力水平、循环旋转次数和初始各向异性等对软粘土非共轴特性的影响不显著,土体非共轴特性主要受应力路径的影响和控制；(3)主应力方向的单纯改变会引起原状粘土和重塑粘土显著的塑性变形累积,随着主应力轴的旋转各应变分量也呈波动变化,试样会由于变形的不断累积而破坏。中主应力系数对应变分量的开展规律和试样破坏时的形态有较大的影响。随着剪应力水平的增加,主应力轴单位转幅引起的应变也逐渐增加。应变的变化规律与相应的应力分量变化规律相似,类似三角函数曲线,但应变曲线要滞后应力曲线20°左右；(4)主应力方向纯旋转也会引起原状粘土和重塑粘土试样孔压的显著累积,孔压的累积也随主应力轴的旋转呈波动变化。中主应力系数对孔压累积速率有一定影响。即使剪应力水平很低(q=5kPa,p=150kPa)的条件下,主应力轴纯旋转也会引起孔压显著累积；(5)按常规的设计思路,虽然应力幅值没有达到破坏水平,但是应力方向的单纯改变也会使土体发生破坏,并且主应力旋转对工程设计的不利影响还不仅仅体现在变形的累积上,还表现在孔压累积引起的刚度衰减；(6)从微观结构角度分析,主应力轴旋转引起的土体变形机理可以归结为大主应力旋转剪切对土体微观结构的扰动和破坏,使颗粒发生破碎或重新排列。 2.通过对现有考虑主应力轴纯旋转的土体本构模型的分析总结之后发现只有合理考虑土体非共轴变形特性的本构关系才能较合理地描述试验结果揭示的土体变形规律。为此,本文对考虑主应力轴旋转复杂应力条件下的软粘土非共轴塑性流动特性进行了深入的研究。借鉴边界面模型的理论,基于定向剪切试验研究结果引入椭圆形的原状粘土破坏边界面,考虑非共轴塑性应变增量切向和法向分量的共同耦合影响,建立了考虑中主应力系数、剪应力水平等影响的软粘土非共轴角计算模型。通过与试验结果和计算结果的对比发现,该方法能较好地反映试验研究中得到的粘土非共轴变形规律。 3.在分析总结主应力轴旋转条件下软粘土变形特性的基本规律基础上,结合软粘土的非共轴塑性流动规律,通过应力空间的转换将主应力轴纯旋转应力路径转换为一种加载方式(应变不变量的广义剪分量)。在广义塑性理论的基本框架下建立了计算主应力轴旋转引起的软粘土变形的方法。考虑非共轴的影响对三维条件下Rowe应力剪胀关系进行了的修正,在将主应变增量转换到一般物理空间坐标内时,采用考虑非共轴角影响的塑性应变增量方向角。最后对计算结果和试验结果进行了对比验证,表明通过非共轴修正之后的计算结果与试验结果更吻合。
[Abstract]:The rotation of the principal stress axis is common in geotechnical engineering. The direction of the principal stress acting on the soil element will produce continuous rotation after the foundation soil undergoes dynamic loads such as traffic loads, wave loads and multi-directional seismic actions. At present, researchers at home and abroad have carried out extensive research on the deformation characteristics and constitutive modeling of soil under the condition of principal stress axis rotation. One of the important characteristics of soil under the condition of principal stress axis rotation is that the direction of plastic strain increment is not coaxial with the direction of stress. The influence of non-coaxial characteristics may underestimate the deformation of soils and make engineering design unsafe. However, at present, the non-coaxial study on the rotation of principal stress axis mainly focuses on sandy soils, and the stress path mainly depends on the small rotation of principal stress axis. There are few studies on the non-coaxial deformation characteristics of soft clay under continuous pure rotation. It is very important to consider the non-coaxial characteristics of the soil properly to predict the deformation of the soil under the condition of principal stress axis rotation. On the basis of existing research results, this paper studies the non-coaxial deformation characteristics of soft clay considering the influence of continuous rotation of principal stress axis from three aspects: experimental study, rule analysis and model establishment. Based on the experimental results, the calculation method of soft clay deformation caused by rotation of principal stress axis is established.
The main contents and achievements of this paper are as follows:
1. The non-coaxial deformation characteristics of soft clay under the condition of continuous rotation of principal stress axes are studied by means of large-scale (180 degrees) continuous pure rotation tests of undisturbed soft clay and remolded clay in Hangzhou. The deformation development, pore pressure accumulation and stiffness attenuation of soft clay under the condition of continuous rotation of principal stress axes are analyzed. The results show that: (1) the non-coaxial properties of undisturbed and remolded clays are not significant under the condition of directional shear, and the incremental direction of plastic principal strain and the direction of principal stress tend to coaxial with the increase of shear stress; (2) the undisturbed clays under the condition of continuous rotation of principal stress axis. The non-coaxial properties of clay and remolded clay are significant. The non-coaxial angles fluctuate with the rotation of the principal stress axis. The influence of the middle principal stress coefficient, shear stress level, cyclic rotation times and initial anisotropy on the non-coaxial characteristics of soft clay is not significant. The non-coaxial characteristics of soil are mainly affected and controlled by the stress path. (3) The principal stress is controlled by the stress path. Simple change of direction will cause significant accumulation of plastic deformation of undisturbed clay and remolded clay. With the rotation of the principal stress axis, the strain components fluctuate, and the specimen will be destroyed due to the accumulation of deformation. With the increase of the force level, the strain caused by the unit rotation of the principal stress axis increases gradually. When the shear stress level is very low (q = 5kPa, P = 150kPa), the pure rotation of the principal stress axis will cause significant accumulation of pore pressure. (5) According to the conventional design, although the stress amplitude does not reach the destructive water However, the simple change of stress direction will destroy the soil, and the adverse effect of principal stress rotation on engineering design is not only reflected in the accumulation of deformation, but also in the stiffness attenuation caused by pore pressure accumulation; (6) From the micro-structure point of view, the deformation mechanism caused by the rotation of principal stress axis can be attributed to the large deformation. The rotation and shear of principal stress disturb and destroy the microstructure of the soil, causing particles to be broken or rearranged.
2. Based on the analysis and summary of the existing constitutive models of soils considering the pure rotation of the principal stress axis, it is found that only the non-coaxial deformation characteristics of soils are reasonably considered can the deformation laws of soils revealed by the test results be described. Therefore, the non-coaxial deformation of soft clays considering the complex rotation of the principal stress axis is discussed in this paper. Based on the theory of boundary surface model and the results of directional shear test, the failure boundary surface of elliptical undisturbed clay is introduced. Considering the coupling effect of tangential and normal components of non-coaxial plastic strain increment, the soft clay considering the influence of middle principal stress coefficient and shear stress level is established. Comparing with the experimental results and the calculated results, it is found that this method can well reflect the non-coaxial deformation law of clay obtained in the experimental study.
3. On the basis of analyzing and summarizing the basic deformation characteristics of soft clay under the condition of rotation of principal stress axis, combined with the non-coaxial plastic flow law of soft clay, the pure rotation stress path of principal stress axis is transformed into a loading mode (generalized shear component of strain invariant) by stress space transformation. A method for calculating the deformation of soft clay caused by the rotation of principal stress axis is established. Considering the influence of non-coaxiality, the stress-dilatancy relationship of Rowe under three-dimensional condition is modified. When the principal strain increment is transformed into general physical space coordinates, the direction angle of plastic strain increment considering the influence of non-coaxial angle is adopted. The experimental results are compared and verified. The results show that the non-coaxial correction is more consistent with the experimental results.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU44;TU411
本文编号：2192094
[Abstract]:The rotation of the principal stress axis is common in geotechnical engineering. The direction of the principal stress acting on the soil element will produce continuous rotation after the foundation soil undergoes dynamic loads such as traffic loads, wave loads and multi-directional seismic actions. At present, researchers at home and abroad have carried out extensive research on the deformation characteristics and constitutive modeling of soil under the condition of principal stress axis rotation. One of the important characteristics of soil under the condition of principal stress axis rotation is that the direction of plastic strain increment is not coaxial with the direction of stress. The influence of non-coaxial characteristics may underestimate the deformation of soils and make engineering design unsafe. However, at present, the non-coaxial study on the rotation of principal stress axis mainly focuses on sandy soils, and the stress path mainly depends on the small rotation of principal stress axis. There are few studies on the non-coaxial deformation characteristics of soft clay under continuous pure rotation. It is very important to consider the non-coaxial characteristics of the soil properly to predict the deformation of the soil under the condition of principal stress axis rotation. On the basis of existing research results, this paper studies the non-coaxial deformation characteristics of soft clay considering the influence of continuous rotation of principal stress axis from three aspects: experimental study, rule analysis and model establishment. Based on the experimental results, the calculation method of soft clay deformation caused by rotation of principal stress axis is established.
The main contents and achievements of this paper are as follows:
1. The non-coaxial deformation characteristics of soft clay under the condition of continuous rotation of principal stress axes are studied by means of large-scale (180 degrees) continuous pure rotation tests of undisturbed soft clay and remolded clay in Hangzhou. The deformation development, pore pressure accumulation and stiffness attenuation of soft clay under the condition of continuous rotation of principal stress axes are analyzed. The results show that: (1) the non-coaxial properties of undisturbed and remolded clays are not significant under the condition of directional shear, and the incremental direction of plastic principal strain and the direction of principal stress tend to coaxial with the increase of shear stress; (2) the undisturbed clays under the condition of continuous rotation of principal stress axis. The non-coaxial properties of clay and remolded clay are significant. The non-coaxial angles fluctuate with the rotation of the principal stress axis. The influence of the middle principal stress coefficient, shear stress level, cyclic rotation times and initial anisotropy on the non-coaxial characteristics of soft clay is not significant. The non-coaxial characteristics of soil are mainly affected and controlled by the stress path. (3) The principal stress is controlled by the stress path. Simple change of direction will cause significant accumulation of plastic deformation of undisturbed clay and remolded clay. With the rotation of the principal stress axis, the strain components fluctuate, and the specimen will be destroyed due to the accumulation of deformation. With the increase of the force level, the strain caused by the unit rotation of the principal stress axis increases gradually. When the shear stress level is very low (q = 5kPa, P = 150kPa), the pure rotation of the principal stress axis will cause significant accumulation of pore pressure. (5) According to the conventional design, although the stress amplitude does not reach the destructive water However, the simple change of stress direction will destroy the soil, and the adverse effect of principal stress rotation on engineering design is not only reflected in the accumulation of deformation, but also in the stiffness attenuation caused by pore pressure accumulation; (6) From the micro-structure point of view, the deformation mechanism caused by the rotation of principal stress axis can be attributed to the large deformation. The rotation and shear of principal stress disturb and destroy the microstructure of the soil, causing particles to be broken or rearranged.
2. Based on the analysis and summary of the existing constitutive models of soils considering the pure rotation of the principal stress axis, it is found that only the non-coaxial deformation characteristics of soils are reasonably considered can the deformation laws of soils revealed by the test results be described. Therefore, the non-coaxial deformation of soft clays considering the complex rotation of the principal stress axis is discussed in this paper. Based on the theory of boundary surface model and the results of directional shear test, the failure boundary surface of elliptical undisturbed clay is introduced. Considering the coupling effect of tangential and normal components of non-coaxial plastic strain increment, the soft clay considering the influence of middle principal stress coefficient and shear stress level is established. Comparing with the experimental results and the calculated results, it is found that this method can well reflect the non-coaxial deformation law of clay obtained in the experimental study.
3. On the basis of analyzing and summarizing the basic deformation characteristics of soft clay under the condition of rotation of principal stress axis, combined with the non-coaxial plastic flow law of soft clay, the pure rotation stress path of principal stress axis is transformed into a loading mode (generalized shear component of strain invariant) by stress space transformation. A method for calculating the deformation of soft clay caused by the rotation of principal stress axis is established. Considering the influence of non-coaxiality, the stress-dilatancy relationship of Rowe under three-dimensional condition is modified. When the principal strain increment is transformed into general physical space coordinates, the direction angle of plastic strain increment considering the influence of non-coaxial angle is adopted. The experimental results are compared and verified. The results show that the non-coaxial correction is more consistent with the experimental results.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU44;TU411
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