考慮軟粘土循環(huán)弱化效應的重力式防波堤地基承載力分析
發(fā)布時間：2018-08-15 11:59
【摘要】：近年來我國港口事業(yè)蓬勃發(fā)展,呈現(xiàn)出大型化、深水化等特點。大部分建港條件優(yōu)越的天然海岸線已被開發(fā)利用,新建防波堤工程往往需要在自然環(huán)境更為不利的海域進行,其波浪條件惡劣,地基也多為軟粘土。因此,循環(huán)荷載作用下,由于軟粘土發(fā)生弱化效應而導致地基承載能力下降,影響結(jié)構(gòu)安全使用是亟待解決的問題。為此,本文結(jié)合天津港、煙臺港軟粘土的強度弱化動態(tài)規(guī)律,研究了波浪循環(huán)荷載作用下防波堤結(jié)構(gòu)地基中軟粘土的弱化狀況,并在此基礎(chǔ)上分析了軟粘土地基的承載特性。主要工作包括以下幾方面內(nèi)容:1.通過等效超固結(jié)比理論,將軟粘土的孔壓發(fā)展模與抗剪強度折減規(guī)律結(jié)合,擬合得到了軟粘土抗剪強度隨圍壓、初始靜偏應力、循環(huán)動應力以及循環(huán)周次變化的弱化規(guī)律,該規(guī)律反映了軟粘土強度在整個動態(tài)循環(huán)中的弱化過程。2.通過對ABAQUS進行二次開發(fā),編寫軟粘土材料強度參數(shù)隨預設(shè)場變量變化的USDFLD用戶子程序,將軟粘土強度循環(huán)弱化規(guī)律體現(xiàn)在土體材料的兩項強度指標內(nèi)摩擦角?和粘聚力c的動態(tài)變化上,使地基中不同位置處各個軟粘土材料單元的?、c指標根據(jù)單元的動應力水平、靜應力水平,隨著循環(huán)荷載作用周次而發(fā)生實時衰減,從而將軟粘土強度弱化規(guī)律引入有限元模型中。3.通過定義地基承載力折減系數(shù)K?,表征考慮軟粘土循環(huán)弱化時地基承載力的整體降低水平,并擬合得到了K?與波浪動荷載、結(jié)構(gòu)物引起的靜荷載以及基床底寬之間的關(guān)系。從而由不考慮循環(huán)弱化的地基承載力安全系數(shù)N WK和地基承載力折減系數(shù)K?,可得到考慮循環(huán)弱化的地基承載力安全系數(shù)WK,進而可利用WK對考慮軟粘土弱化的地基承載力進行判別。4.針對半圓型防波堤結(jié)構(gòu),結(jié)合天津港軟粘土強度弱化的動態(tài)規(guī)律,建立了考慮軟粘土循環(huán)弱化效應的動力有限元模型,分析了波浪循環(huán)荷載作用下半圓堤結(jié)構(gòu)地基中軟粘土的弱化狀況,進一步研究了不同波浪力大小、箱內(nèi)填砂量、基床底寬、換填厚度等因素對軟基弱化的影響。在此基礎(chǔ)上,對考慮軟基弱化的半圓堤地基承載性能進行了研究,并與未考慮軟基弱化的情況進行了對比,發(fā)現(xiàn)軟粘土循環(huán)弱化效應對地基承載力的影響較為顯著。5.針對沉箱式防波堤結(jié)構(gòu),結(jié)合煙臺港軟粘土的強度弱化規(guī)律,建立了考慮軟粘土弱化效應的有限元模型,研究了不同因素影響下沉箱式防波堤地基中軟粘土的弱化狀況,分析了軟基弱化效應對沉箱式防波堤地基承載能力的影響。
[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.
【學位授予單位】：天津大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：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.
【學位授予單位】：天津大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：U656.2
【引證文獻】
相關(guān)碩士學位論文 前1條
1 胡s砰，
本文編號：2184133
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