考虑软粘土循环弱化效应的重力式防波堤地基承载力分析
发布时间：2018-08-15 11:59
【摘要】：近年来我国港口事业蓬勃发展,呈现出大型化、深水化等特点。大部分建港条件优越的天然海岸线已被开发利用,新建防波堤工程往往需要在自然环境更为不利的海域进行,其波浪条件恶劣,地基也多为软粘土。因此,循环荷载作用下,由于软粘土发生弱化效应而导致地基承载能力下降,影响结构安全使用是亟待解决的问题。为此,本文结合天津港、烟台港软粘土的强度弱化动态规律,研究了波浪循环荷载作用下防波堤结构地基中软粘土的弱化状况,并在此基础上分析了软粘土地基的承载特性。主要工作包括以下几方面内容:1.通过等效超固结比理论,将软粘土的孔压发展模与抗剪强度折减规律结合,拟合得到了软粘土抗剪强度随围压、初始静偏应力、循环动应力以及循环周次变化的弱化规律,该规律反映了软粘土强度在整个动态循环中的弱化过程。2.通过对ABAQUS进行二次开发,编写软粘土材料强度参数随预设场变量变化的USDFLD用户子程序,将软粘土强度循环弱化规律体现在土体材料的两项强度指标内摩擦角?和粘聚力c的动态变化上,使地基中不同位置处各个软粘土材料单元的?、c指标根据单元的动应力水平、静应力水平,随着循环荷载作用周次而发生实时衰减,从而将软粘土强度弱化规律引入有限元模型中。3.通过定义地基承载力折减系数K?,表征考虑软粘土循环弱化时地基承载力的整体降低水平,并拟合得到了K?与波浪动荷载、结构物引起的静荷载以及基床底宽之间的关系。从而由不考虑循环弱化的地基承载力安全系数N WK和地基承载力折减系数K?,可得到考虑循环弱化的地基承载力安全系数WK,进而可利用WK对考虑软粘土弱化的地基承载力进行判别。4.针对半圆型防波堤结构,结合天津港软粘土强度弱化的动态规律,建立了考虑软粘土循环弱化效应的动力有限元模型,分析了波浪循环荷载作用下半圆堤结构地基中软粘土的弱化状况,进一步研究了不同波浪力大小、箱内填砂量、基床底宽、换填厚度等因素对软基弱化的影响。在此基础上,对考虑软基弱化的半圆堤地基承载性能进行了研究,并与未考虑软基弱化的情况进行了对比,发现软粘土循环弱化效应对地基承载力的影响较为显著。5.针对沉箱式防波堤结构,结合烟台港软粘土的强度弱化规律,建立了考虑软粘土弱化效应的有限元模型,研究了不同因素影响下沉箱式防波堤地基中软粘土的弱化状况,分析了软基弱化效应对沉箱式防波堤地基承载能力的影响。
[Abstract]:In recent years, China's port industry has developed rapidly, showing the characteristics of large-scale, deep-water and so on. Most of the natural shorelines with superior construction conditions have been developed and used. The newly built breakwater projects often need to be carried out in the waters where the natural environment is more unfavorable. The wave conditions are bad and the foundation is mostly soft clay. Therefore, due to the weakening effect of soft clay under cyclic load, the bearing capacity of the foundation decreases, and it is urgent to solve the problem of affecting the safe use of the structure. Therefore, combining with the dynamic law of strength weakening of soft clay in Tianjin Port and Yantai Port, this paper studies the weakening state of soft clay in the foundation of breakwater structure under the action of wave cyclic load, and on this basis analyzes the bearing characteristics of soft clay foundation. The main work includes the following aspects: 1. Based on the equivalent overconsolidation ratio theory, the pore pressure development model of soft clay is combined with the shear strength reduction law, and the weakening law of shear strength with confining pressure, initial static deflection stress, cyclic dynamic stress and cyclic cycle time is obtained by fitting the shear strength of soft clay with confining pressure, initial static deflection stress, cyclic dynamic stress and cycle. This law reflects the weakening process of soft clay strength in the whole dynamic cycle. Through the secondary development of ABAQUS, the USDFLD user subprogram of soft clay material strength parameters varying with the preset field variable is compiled, and the weakening law of soft clay strength cycle is embodied in the internal friction angle of two strength indexes of soil material. And the dynamic change of cohesive force c, so that the index of soft clay material elements at different positions in the foundation will decay in real time according to the dynamic stress level and the static stress level of the element, with the cycle of cyclic load acting. Thus, the weakening law of soft clay strength is introduced into the finite element model. By defining the reduction coefficient of the bearing capacity of the foundation, the overall reduction level of the bearing capacity of the foundation considering the weakening of the soft clay cycle is characterized, and the K? The relationship between the load and the wave load, the static load caused by the structure and the width of the base bed. Therefore, from the safety factor N WK of foundation bearing capacity and the reduction factor K of foundation bearing capacity without considering cyclic weakening, the safety factor WK of foundation bearing capacity considering cyclic weakening can be obtained, and then the foundation with soft clay weakening can be obtained by using WK. The bearing capacity is judged. 4. According to the structure of semi-circular breakwater and the dynamic law of weakening the strength of soft clay in Tianjin Port, a dynamic finite element model considering the weakening effect of soft clay circulation is established. The weakening of soft clay in the foundation of semi-circular embankment structure under the action of wave cyclic load is analyzed. The effects of different wave force, sand content in box, bottom width of foundation bed and thickness of replacement fill on the weakening of soft foundation are further studied. On this basis, the bearing capacity of semi-circular embankment foundation considering soft foundation weakening is studied, and compared with that without soft foundation weakening, it is found that the influence of soft clay cyclic weakening effect on foundation bearing capacity is obvious. According to the caisson breakwater structure and the strength weakening rule of soft clay in Yantai Port, a finite element model considering the weakening effect of soft clay is established, and the weakening condition of soft clay in the foundation of sinking box breakwater is studied by different factors. The influence of soft foundation weakening effect on the bearing capacity of caisson breakwater foundation is analyzed.
【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】：U656.2
[Abstract]:In recent years, China's port industry has developed rapidly, showing the characteristics of large-scale, deep-water and so on. Most of the natural shorelines with superior construction conditions have been developed and used. The newly built breakwater projects often need to be carried out in the waters where the natural environment is more unfavorable. The wave conditions are bad and the foundation is mostly soft clay. Therefore, due to the weakening effect of soft clay under cyclic load, the bearing capacity of the foundation decreases, and it is urgent to solve the problem of affecting the safe use of the structure. Therefore, combining with the dynamic law of strength weakening of soft clay in Tianjin Port and Yantai Port, this paper studies the weakening state of soft clay in the foundation of breakwater structure under the action of wave cyclic load, and on this basis analyzes the bearing characteristics of soft clay foundation. The main work includes the following aspects: 1. Based on the equivalent overconsolidation ratio theory, the pore pressure development model of soft clay is combined with the shear strength reduction law, and the weakening law of shear strength with confining pressure, initial static deflection stress, cyclic dynamic stress and cyclic cycle time is obtained by fitting the shear strength of soft clay with confining pressure, initial static deflection stress, cyclic dynamic stress and cycle. This law reflects the weakening process of soft clay strength in the whole dynamic cycle. Through the secondary development of ABAQUS, the USDFLD user subprogram of soft clay material strength parameters varying with the preset field variable is compiled, and the weakening law of soft clay strength cycle is embodied in the internal friction angle of two strength indexes of soil material. And the dynamic change of cohesive force c, so that the index of soft clay material elements at different positions in the foundation will decay in real time according to the dynamic stress level and the static stress level of the element, with the cycle of cyclic load acting. Thus, the weakening law of soft clay strength is introduced into the finite element model. By defining the reduction coefficient of the bearing capacity of the foundation, the overall reduction level of the bearing capacity of the foundation considering the weakening of the soft clay cycle is characterized, and the K? The relationship between the load and the wave load, the static load caused by the structure and the width of the base bed. Therefore, from the safety factor N WK of foundation bearing capacity and the reduction factor K of foundation bearing capacity without considering cyclic weakening, the safety factor WK of foundation bearing capacity considering cyclic weakening can be obtained, and then the foundation with soft clay weakening can be obtained by using WK. The bearing capacity is judged. 4. According to the structure of semi-circular breakwater and the dynamic law of weakening the strength of soft clay in Tianjin Port, a dynamic finite element model considering the weakening effect of soft clay circulation is established. The weakening of soft clay in the foundation of semi-circular embankment structure under the action of wave cyclic load is analyzed. The effects of different wave force, sand content in box, bottom width of foundation bed and thickness of replacement fill on the weakening of soft foundation are further studied. On this basis, the bearing capacity of semi-circular embankment foundation considering soft foundation weakening is studied, and compared with that without soft foundation weakening, it is found that the influence of soft clay cyclic weakening effect on foundation bearing capacity is obvious. According to the caisson breakwater structure and the strength weakening rule of soft clay in Yantai Port, a finite element model considering the weakening effect of soft clay is established, and the weakening condition of soft clay in the foundation of sinking box breakwater is studied by different factors. The influence of soft foundation weakening effect on the bearing capacity of caisson breakwater foundation is analyzed.
【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】：U656.2
【引证文献】
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1 胡s砰，
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