强结构性黏土力学性状的各向异性效应与主应力轴方向关联性

This proposal is based on Zhanjiang grey clay as an research objective, which is well known for its strongly-structured property, the effects of anisotropy and principal stress axes rotation on the basis of special mechanical behaviors of the soils are systemically investigated. Considering different conditions such as disturbance, unloading hysteresis, creep, loading mode and rate, a series of field measurements of self-boring pressuremeter test, pre-drilling pressuremeter test, borehole shear test and seismic dilatometer test of the soils were precisely conducted, In this research the in-situ response characteristics and time effect of mechanical behaviors of strongly-structured clay soils will be clarified. The intact soil samples of laboratory tests are prepared by controlling the different direction angles, the resonant column tests, triaxial test and consolidation test are carried out as well as the hollow cylinder soil samples are also sheared at different principal stress directions by hollow cylinder torsional shear apparatus at the same time. From the above test results, the strength property and deformation property of the soils are analyzed under the influences of orientation angle of sample preparation and principal stress direction angle while the quantitative characterization method of anisotropic parametric variable, evolution law and mechanical effect is placed forward. On this basis, further cyclic hollow cylinder torsional shear tests of directional loading stress path, pure rotation of principal stress axis stress path and heart-shaped stress path are put into effect so as to understand thoroughly the effects of principal stress axes rotation on dynamic property of the soils under different stress paths of cyclic loading along with the differences from common soft clay so that the anisotropic elastic-plastic boundary surface model will be established. In addition, the effect of anisotropy on the future performance of practical engineering by numerical simulation is evaluated. Most of all this will provide technical support for the potential application of strong structured clay soils and effective prevention for engineering disasters.

本项目以强结构性著称的湛江灰色黏土为研究对象，以考察其独特力学性状的各向异性与主应力轴旋转效应为主线，基于考虑扰动、卸荷滞时与蠕变以及荷载施加方式及速率工况的旁压试验、孔内剪切试验与地震波扁铲试验，阐明其原位力学响应特征与时间效应；通过控制不同方向角制备原状土样，开展共振柱试验、三轴试验与固结试验，并同步进行不同主应力方向角的空心扭剪仪定向剪切试验，分析制样方向角与主应力轴偏转角影响下的强度与变形特性，提出强结构性黏土各向异性状态参量与效应的定量表征方法。在此基础上，进一步开展定向加载应力路径、纯主应力轴旋转应力路径与“心形”应力路径条件下的空心循环扭剪试验，弄清不同循环荷载应力路径下其动力特性的主应力轴旋转效应及其与以往软黏土响应性状的异同，建立该类黏土的各向异性弹塑性边界面模型，结合数值模拟评价考虑其各向异性对工程的后效影响，为发挥土体强结构性的应用潜能与有效预防工程灾害提供技术支撑。

本项目围绕考察强结构性黏土独特力学性状的原位响应特征、各向异性效应与复杂应力条件下动力特性主线，基于孔压静力触探、不同加载速率下自钻旁压试验、自钻旁压蠕变试验与地震波扁铲试验等原位测试，阐明结构性黏土原位力学响应特征与时间效应，分析了其原位力学性质的加载速率效应与蠕变特性，提出了结构性黏土原位刚度衰减特性的表征方法；通过控制不同方向角制备原状土样，开展了渗透试验、无侧限抗压强度试验、固结试验、三轴试验与共振柱试验，分析了各向异性对其渗透、强度、变形与小应变剪切模量等工程性状的影响规律，提出了考虑原生各向异性影响的最大动剪切模量表征方法。开展了结构性黏土平面应变竖向加载和侧向卸载试验及利用改装后真三轴设备进行的平面应变竖向加载试验与剪切带演化过程的数字图像相关(DIC)分析，提出基于广义Mises与Lade-Duncan平面应变强度准则的广义平面应变强度准则，分析并揭示了平面应变条件下结构性黏土的剪切带分布与演化特征。通过等平均主应力不等中主应力系数的静真三轴试验，分析了中主应力系数对其广义剪应力-大主应变关系、有效黏聚力与内摩擦角的影响特征，建立了三维应力下可考虑结构性影响的黏土强度准则。基于结构性黏土不排水动三轴试验与平面应变动力试验，类比分析了轴对称和平面应变状态下结构性黏土的动力响应特征，发现平面应变条件可限制其累积大主应变发展且同时提高其回弹模量，提出平面应变状态下考虑循环偏应力和循环小主应力耦合影响的累积大主应变表达式。利用循环真三轴试验模拟了交通荷载作用下地基土体动应力模式，重点研究了循环大、中和小主应力作用下结构性黏土累积变形规律，分析了循环中主应力系数和循环平均主应力幅值与循环广义剪应力幅值之比对累积变形特征的影响，建立了三向循环荷载下累积大主应变的经验模型。上述研究，可为推进发挥土体强结构性的应用潜能与有效预防工程灾害提供帮助。

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