【作者】 郭莹；

【导师】 栾茂田；

【作者基本信息】 大连理工大学 ， 水工结构工程， 2003， 博士

【摘要】 土工建筑物与地基中土体的初始应力状态是复杂多样的，在主应力大小发生变化的同时，主应力的方向也在不断地变化。在如此复杂的初始应力状态下，当进一步承受波浪、地震等复杂循环荷载作用时，土的动力特性与本构关系将变得更加复杂。因而在实验室研制、开发能够模拟复杂初始应力条件和复杂循环剪切荷载状态的先进土工设备，并依此进行复杂波浪荷载环境或地震荷载条件下土的动力特性研究，是深入研究复杂荷载条件下土工建筑物与地基的静、动力响应与稳定性分析的基础与前提。这一问题不仅是土动力学与岩土地震工程研究中至关重要的基本课题，而且也是海洋平台等重大工程设施设计中首要解决的实际问题。 本项研究力图能够考虑多种复杂初始固结条件与多种循环荷载条件及其组合影响，为研究复杂应力条件下土体的动力特性与本构关系，研制与开发静、动三轴—扭剪多功能剪切试验设备，发展实用的试验测试技术。并在此基础上，针对福建标准砂，着重系统地研究主应力方向对饱和砂土在多种复杂循环荷载条件下动力特性的影响，探讨了动力变形特性与应力—应变关系及动强度与孔隙水压力增长规律和残余应变发展模式，从而为土工动力稳定评价发展合理而实用的分析理论与计算方法提供了必要的试验基础。开展这项研究不仅对促进土动力学与海洋土力学学科的发展奠定坚实的试验基础具有很强的理论意义，而且对于改进重大工程结构及地基设计具有较大的实际参考价值。 为了研究波浪与地震等复杂荷载条件下土的动力变形与强度特性，必须研制与开发能够实施复杂应力路径试验的先进的土工设备。在对设备设计有关的各类问题进行了广泛而深入研究的基础上，根据学校211工程重点学科“海洋和近海工程”建设计划，全面提出了这种设备的各种功能要求和技术参数，由日本诚研舍株式会社进行具体设计并加工制造，共同研制与开发了“土工静力—动力液压三轴—扭转多功能剪切仪”。进而完成了该设备的调试和运行及完善工作，该设备能够实现均等固结、多种不同初始条件下的非均等固结、K₀固结等多种复杂固结条件，静、动三轴拉压剪切与静、动扭转剪切以及静、动耦合剪切等多种静力与循环剪切的复杂应力路径试验，而且能够同时满足土的动力变形特性与动强度及孔隙水压力等特性两方面研究的精度需要，具有相当广泛的适用性。试验结果表明：竖向—扭转双向耦合循环剪切试验能够较好地模拟主应力轴连续旋转的复杂应力路径条件；采用内置式的荷载传感器和微小位移传感器，能够显著地提高试验测试精度。通过变化两向荷载的幅值、相位差和频率绘出的理想应力路径可以看出，该设备还能够实现更多种复杂应力路径的剪切试验，为开展更系统、深入的研究工作打下了良好的基础。 利用新研制的多功能剪切仪，在均等固结条件和不同的三向非均等固结条件下，进行了循环三轴和循环扭剪、不同应力路径的竖向与扭转双向耦合循环剪切等12种类型循环剪切试验，采用内置于三轴室的轴力及扭矩双出力传感器和非接触式微小位移传感器测量荷载与位移，系统地研究了在复杂应力条件下饱和松砂的动力变形特性，包括应力一应变关系与动剪切模量、动等效变形模量和阻尼比变化规律，探讨了不同应力状态对松砂动力变形参数的影响。试验结果表明:均等固结条件下，应力一应变关系基本上不受循环剪切荷载方式的影响:石崛沪残或G/’G。一冷关系与循环荷载方式无关;不同循环剪切条件下的最大动剪切模量参数粉、nG和动变形模量参数概、nE基本一致;阻尼比随应变幅值的变化规律基本不受循环荷载剪切方式影响。因而，在均等固结条件下的复杂循环荷载条件基本上可以采用简单应力条件下所取得的动力变形参数。在非均等固结条件下，初始大主应力方向角对应力一应变关系、动模量和阻尼比随应变幅值的变化规律以及动变形模量参数掩、彻均具有较显著的影响;初始偏应力比的影响并不显著;各种应力路径试验所获得的剪切模量参数基本相近，而得到的变形模量稍有差别与初始大主应力方向角有关。但是采用弹性力学理论由变形模量换算得到的剪切模量与试验直接得到的剪切模量存在差别。 针对饱和松砂（Dr=30%），分别在均等固结条件下和具有不同初始大主应力方向角的三向非均等固结条件下，分别进行了单独循环竖向、单独循环扭剪以及三种藕合循环应力路径等14种循环剪切试验。通过系统的分析分别研究了初始主应力方向、振动中主应力方向变化和振动荷载模式对松砂动强度的影响。研究表明:在均等固结条件下，振动中主应力方向不同变化方式对松砂的动强度具有较显著的影响;在均等固结和三向非均等固结条件下，圆形祸合循环剪切试验所得到的动强度普遍低于循环扭剪试验所得到的动强度，相对降低量约在10一30%之间;初始主应力方向对松砂的动强度具有非常显著的影响，随着初始大主应力方向角的增加，动强度降低;在循环扭剪和圆形祸合剪切两种类型的循环剪切试验中，松砂动强度随初始大主应力方向角的增大而非线性地降低的规律有所不同。主应力方向交替突变的不同循环应力路径在均等固结条件下的动强度普遍低于非均等固结条件下的动强度;?更多还原

【Abstract】 The initial stress conditions for soil elements beneath the foundation under the building are usually rather complex. Before subjected to complicated cyclic loading induced by ocean wave and earthquake shaking, the principal stresses of subsoil element under the different places of building are not equal generally on three directions. The initial direction angle of maximum principal stress axe changes. Under this condition, the dynamic behavior of soils and the constitutive relation are very complicated. It is necessary to develop the experimental apparatus that can simulate complex condition of initial consolidation and cyclic shear and use it to investigate the correlation problem. It is not only basic problems of dynamic soils and geotechmcal earthquake engineering, but also the problems that have to solve for important project.In order to simulate complex stress path influences combined by initial consolidation condition and shear loading, the soil static and dynamic universal triaxial and torsional shear apparatus is developed. The effect of direction of principal stress on dynamic characteristic of saturated Fujian standard sand under complex stress condition is studied, such as dynamic deformation behavior of small strain, the relation of stress and strain, dynamic strength and the variations of pore water pressure and remaining strain. The findings based on this fundamental study will be instructive for improving design of important structures and foundation subjected to complex loading.On the basic of investigating the many problems about the design of the apparatus, the function demands and skill parameters are proposed. The apparatus is designed and newly facilized in Dalian University of Technology under the cooperation of Seiken Inc., Japan. The debugging and running of the complex and big apparatus has been finished. This apparatus can reproduce isotropic consolidation, anisotropic consolidation with different initial conditions, K consolidation. It can be used for complex stress conditions and stress path including static and dynamic triaxial test, static and dynamic torsional test, the cintinuous rotation of principal stress axes and can be used to perform various soil experimental tests of sands or clays. It is fulfilled the precision requirement for small strain behavior and large strain behavior. The results of experiment indicated that it is possible for this apparatus to simulate the complex stress path including rotation of principal stress axes. The precision of experiment can be improved by using with the loading sensors and small displacement sensors installed in the triaxial cell. It can be made out that the apparatus can realize many other kinds cyclic shear tests of stress path by changing the amplitude of vibration, phase difference and frequency of two cyclic loading.The apparatus is used to perform experimental tests of sand subjected to simple triaxial shear, simple trosional shear and verticalandtorsional coupling cyclic shear with different stress path. 12 types of test are perfomed under isotropic consolidation and third-directional anisotorpic consolidation with different effective consolidation pressures, different initial direction angle of principal stress, different initial deviator stress ratio to study the dynamic modulus and damping ratio behavior of small strain of sand under complex stress condition. The experimental results for different combination of various relevant parameters are reportedand systematically analyzed. It is shown through comparative studies that the relations between stress and strain and the variations of damping ratio with strain under isotropic consolidation are not influence by the manner of cyclic loading, the relations of E/E or G/Go~X/r also. The parameters of and are consistent under different cyclic shear test, E and 獷 too. Under anisotropic consolidation, it has been shown that the initial orientation of principal stress axes has a considerable influence on relations between stress and strain, the variations of modulus and damping更多还原