【作者】 刘洋；

【导师】 郭莹；

【作者基本信息】 大连理工大学 ， 岩土工程， 2006， 硕士

【摘要】 土的动模量和阻尼比是描述土的动力变形特性的两个基本参数,也是实际工程设计中所需考虑的最主要的动力参数。影响土的动模量及阻尼比等动态特性参数的因素有很多,其中以剪应变幅、有效平均主应力、孔隙比与土的组构（包括试样制备方法）的影响最大。 本次研究使用的仪器是大连理工大学与日本诚研株式会社合作研制的“土工静力—动力液压三轴—扭转多功能剪切仪”,该仪器设置了两套测量系统:一套为内置式的非接触微小位移计及转角计;一套为普通的接触式竖向位移计及转角传感器。为了提高土工测试精度,拓宽应变测试范围,试验中尝试将非接触与接触式竖向位移计与转角计联合使用。这样,同一个试样的动模量随动应变幅值的变化关系曲线可由接触式位移计与非接触式位移计联合测得,既避免了竖向大位移计在微小应变幅下测量不够准确、精度不能满足要求的问题,也避免了小位移传感器测量范围有限的缺点。试验结果表明,这种试验技术能够很大程度地提高了位移的测量精度,从而获得至关重要的微小应变的试验数据。 对于动力变形特性参数的测定,针对粉煤灰和福建标准砂,通过试验探讨了利用循环三轴试验和循环扭剪试验进行动模量阻尼比特性研究的试验技术。本文首先针对采用1个试样通过多次固结的方法代替采用3到4个试样获得全部动模量和阻尼比特性的方法进行了试验研究,探讨了两种试验方法获得试验结果的主要差别;然后采用一级循环加荷结束进行充分排水再施加下一级荷载的逐级消散孔压的间断排水方法与完全不排水试验方法进行了对比,着重研究了不同试验方法所获得的动模量特性与阻尼比特性。研究结果表明:使用一个试样通过改变初始固结压力的方法所获得的试验结果在初始固结压力σ′₃=100kPa、200kPa、300kPa时与采用独立试样分别进行试验的常规方法的结果基本一致,是比较可靠的。这种方法能够确保试验过程中试样成型的稳定性,而且节省拆样、装样以及试样饱和的时间,在很大程度上提高了工作效率。利用逐级消散孔压的间断排水方法所获得的动模量阻尼特性与常规方法的试验结果也十分相近。 为了研究固结应力比对粉煤灰的动模量特性的影响,本文针对相对密实度D_r=60%的粉煤灰进行了固结应力比K_c=1.0、1.5和2.0的循环三轴试验,试验结果表明:不同固结应力比条件下的动弹性模量E～ε关系曲线,随着动应变幅值的增大,动弹性模量呈现一致的衰减趋势;当K_c=2.0时各级初始固结压力下的最大动弹性模量值有下降趋势。更多还原

【Abstract】 Dynamic modulus and damping ratio, the two main parameters describing dynamic deformation of soil, are of great importance in the analysis of soil layer and its seismic response. The two parameters are determined by many factors, of which effective mean principal stress, void ratio and structure of soil are the most important factors.The apparatus used in the experiments, soil static and dynamic universal triaxial and torsional shear apparatus, is made by Dalian University of Technology and Seiken Inc., Japan. In this apparatus, two measuring systems are equipped: one is un-touched displacement sensor and corner sensor installed in the triaxial cell, the other is touched displacement and corner sensor. In order to improve the precision of experiment, both the un-touched and touched displacement sensor are used together. The curve that dynamic modulus of the sample varies with the amplitude of dynamic strain can be obtained simultaneously by touched displacement sensor and un-touched displacement sensor, avoiding the disadvantage that the vertical large displacement sensors is inaccurate under small strain amplitude and the measure range of small displacement sensors is narrow.In this paper, the methods and techniques that dynamic modulus and damping ratio are measured by cyclic triaxial tests and cyclic torsional tests are discussed. Through comparing the dynamic deformation behavior measured by conventional methods with results coming respectively from the test 1, i.e. sample under three different mean effective confining pressures and test 2, i.e. sample under dissipating pore water pressure frequently, the damping ratio property and the methods by which dynamic modulus and maximum dynamic modulus are measured are studied. The conclusion is that the results from testl agree with those from conventional methods when initial confining pressure σ₃ equals 100kPa, 200 kPa or 300 kPa. Furthermore, this method can guarantee the stability of the sample during experiment and effectively decrease the time of making and saturating samples. The comparison also shows that dynamic modulus and damping ratio from test 2 is close to results from conventional methods.In order to explore the effect of fly ash consolidation stress ratio on its dynamic modulus, cyclic triaxial tests are performed on fly ash whose relative density of D_ris 60%, under the condition that consolidation stress ratio K_c equalsl.0, 1.5 and 2.0 respectively. Result shows that, as illustrated by the curve of E^ε, under different consolidation stress ratio, the dynamicmodulus decreases consistently as the amplitude of dynamic strain increases. When consolidation stress ratio Kc equals 2.0, the maximum dynamic modulus under different initial consolidation stress is descending.更多还原