循环荷载下淤泥质粉质粘土强度弱化特性试验研究
发布时间：2018-08-31 19:43
【摘要】：随着越来越多的近海工程投入建设,工程深水化、大型化的发展对软粘土地基的稳定性提出了更高的要求。而软粘土孔隙比大,含水率高,强度低,在波浪等循环荷载作用下强度弱化效应显著,若设计中没有预留足够的安全储备,结构物就可能因地基失稳出现过量的沉降或滑移,造成巨大的经济损失。针对以上问题,本文以烟台港淤泥质粉质粘土为研究对象,以围压、初始静偏应力、动应力、循环次数和固结度为试验变量,进行了大量动三轴试验,综合分析多因素影响下的淤泥质粉质粘土的循环弱化特性。主要工作如下:1、针对累积孔压及累积变形,进行了多因素影响下的动力循环试验,分析了围压、初始静偏应力、循环动应力和循环次数对淤泥质粉质粘土累积孔压及累积变形发展的影响,并基于试验结果建立了改进的双曲累积孔压计算模型和累积塑性应变计算模型。2、针对循环强度弱化,进行了多因素影响下的循环后不排水剪切试验,分析了不同围压、初始静偏应力、循环动应力和循环次数下淤泥质粉质粘土的循环后不排水强度弱化规律。进而运用改进的等效超固结比公式将孔压规律和强度弱化规律结合起来,得到适用于整个动态循环过程的正常固结土强度弱化时程计算模型。对模型进行了试验验证,同时说明了模型的适用范围。3、分析了淤泥质粉质粘土的强度弱化机理。通过试验发现土体存在临界动应力比0.5,当动应力比小于0.5时,累积孔压的增长是强度弱化的主要原因;而当动应力比大于0.5时,土体结构破坏是强度弱化的主要原因;当动应力比等于0.5时,强度弱化的产生是累积孔压和结构破坏共同作用的结果。4、针对固结度的影响,进行了不同固结度下的动三轴试验,分析了土体固结程度对于淤泥质粉质粘土循环后不排水强度弱化的影响,即不排水强度随着固结度降低线性下降。同时在已得到的正常固结土(固结度为1)强度弱化模型的基础上,提出固结度弱化因子的概念,建立了考虑土体固结度影响的强度弱化时程计算模型。5、通过大型有限元软件ABAQUS,将得到的多因素强度弱化时程计算模型应用于烟台港防波堤数值模型的动力计算当中。分析循环弱化效应以及土层固结程度对于防波堤结构产生的影响,并提出有效的工程建议。
[Abstract]:With more and more offshore projects being put into construction, the development of deepwater engineering and large-scale engineering puts forward higher requirements for the stability of soft clay foundation. But the soft clay has high porosity ratio, high moisture content and low strength, and the weakening effect of strength under the action of wave and other cyclic loads is obvious. If there is not enough safe reserve in the design, the structure may have excessive settlement or slip due to the foundation instability. Causing enormous economic losses. In view of the above problems, a large number of dynamic triaxial tests were carried out on silty clay in Yantai Port, taking confining pressure, initial static deflection stress, dynamic stress, cycle number and degree of consolidation as experimental variables. The cyclic weakening characteristics of silty clay under the influence of many factors are comprehensively analyzed. The main work is as follows: 1. For cumulative pore pressure and cumulative deformation, the dynamic cycle test under the influence of many factors is carried out, and the confining pressure and initial static deflection stress are analyzed. The effects of cyclic dynamic stress and cyclic times on the cumulative pore pressure and cumulative deformation development of silty clay are studied. Based on the experimental results, an improved hyperbolic cumulative pore pressure calculation model and a cumulative plastic strain calculation model. 2, aiming at the weakening of cyclic strength, an improved hyperbolic cumulative pore pressure calculation model and a cumulative plastic strain calculation model are established. The undrained shear tests under the influence of many factors were carried out, and the weakening rule of undrained strength of silty clay under different confining pressure, initial static deflection stress, cyclic dynamic stress and cyclic times was analyzed. Furthermore, the improved equivalent overconsolidation ratio formula is used to combine the pore pressure law with the strength weakening law, and a normal consolidation soil strength weakening time history model suitable for the whole dynamic cycle process is obtained. The model was tested and verified, and the applicable range of the model was explained. The strength weakening mechanism of silty clay was analyzed. When the dynamic stress ratio is less than 0.5, the increase of cumulative pore pressure is the main reason of strength weakening, and when the dynamic stress ratio is greater than 0.5, the failure of soil structure is the main reason of strength weakening. When the dynamic stress ratio is equal to 0.5, the strength weakening is the result of the combined action of cumulative pore pressure and structural failure. According to the influence of consolidation degree, dynamic triaxial tests are carried out under different consolidation degrees. The influence of soil consolidation on the weakening of undrained strength of silty clay is analyzed, that is, the undrained strength decreases linearly with the decrease of consolidation. At the same time, on the basis of the strength weakening model of normal consolidated soil (consolidation degree is 1), the concept of consolidation degree weakening factor is put forward. A strength weakening time-history model. 5, which takes into account the influence of soil consolidation, is established. The multi-factor strength weakening time-history model is applied to the dynamic calculation of the breakwater numerical model of Yantai Port by using the large-scale finite element software ABAQUS,. The effect of cyclic weakening and soil consolidation on breakwater structure is analyzed, and some effective engineering suggestions are put forward.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU447
本文编号：2215980
[Abstract]:With more and more offshore projects being put into construction, the development of deepwater engineering and large-scale engineering puts forward higher requirements for the stability of soft clay foundation. But the soft clay has high porosity ratio, high moisture content and low strength, and the weakening effect of strength under the action of wave and other cyclic loads is obvious. If there is not enough safe reserve in the design, the structure may have excessive settlement or slip due to the foundation instability. Causing enormous economic losses. In view of the above problems, a large number of dynamic triaxial tests were carried out on silty clay in Yantai Port, taking confining pressure, initial static deflection stress, dynamic stress, cycle number and degree of consolidation as experimental variables. The cyclic weakening characteristics of silty clay under the influence of many factors are comprehensively analyzed. The main work is as follows: 1. For cumulative pore pressure and cumulative deformation, the dynamic cycle test under the influence of many factors is carried out, and the confining pressure and initial static deflection stress are analyzed. The effects of cyclic dynamic stress and cyclic times on the cumulative pore pressure and cumulative deformation development of silty clay are studied. Based on the experimental results, an improved hyperbolic cumulative pore pressure calculation model and a cumulative plastic strain calculation model. 2, aiming at the weakening of cyclic strength, an improved hyperbolic cumulative pore pressure calculation model and a cumulative plastic strain calculation model are established. The undrained shear tests under the influence of many factors were carried out, and the weakening rule of undrained strength of silty clay under different confining pressure, initial static deflection stress, cyclic dynamic stress and cyclic times was analyzed. Furthermore, the improved equivalent overconsolidation ratio formula is used to combine the pore pressure law with the strength weakening law, and a normal consolidation soil strength weakening time history model suitable for the whole dynamic cycle process is obtained. The model was tested and verified, and the applicable range of the model was explained. The strength weakening mechanism of silty clay was analyzed. When the dynamic stress ratio is less than 0.5, the increase of cumulative pore pressure is the main reason of strength weakening, and when the dynamic stress ratio is greater than 0.5, the failure of soil structure is the main reason of strength weakening. When the dynamic stress ratio is equal to 0.5, the strength weakening is the result of the combined action of cumulative pore pressure and structural failure. According to the influence of consolidation degree, dynamic triaxial tests are carried out under different consolidation degrees. The influence of soil consolidation on the weakening of undrained strength of silty clay is analyzed, that is, the undrained strength decreases linearly with the decrease of consolidation. At the same time, on the basis of the strength weakening model of normal consolidated soil (consolidation degree is 1), the concept of consolidation degree weakening factor is put forward. A strength weakening time-history model. 5, which takes into account the influence of soil consolidation, is established. The multi-factor strength weakening time-history model is applied to the dynamic calculation of the breakwater numerical model of Yantai Port by using the large-scale finite element software ABAQUS,. The effect of cyclic weakening and soil consolidation on breakwater structure is analyzed, and some effective engineering suggestions are put forward.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU447
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