【摘要】：隨著越來越多的近海工程投入建設(shè),工程深水化、大型化的發(fā)展對(duì)軟粘土地基的穩(wěn)定性提出了更高的要求。而軟粘土孔隙比大,含水率高,強(qiáng)度低,在波浪等循環(huán)荷載作用下強(qiáng)度弱化效應(yīng)顯著,若設(shè)計(jì)中沒有預(yù)留足夠的安全儲(chǔ)備,結(jié)構(gòu)物就可能因地基失穩(wěn)出現(xiàn)過量的沉降或滑移,造成巨大的經(jīng)濟(jì)損失。針對(duì)以上問題,本文以煙臺(tái)港淤泥質(zhì)粉質(zhì)粘土為研究對(duì)象,以圍壓、初始靜偏應(yīng)力、動(dòng)應(yīng)力、循環(huán)次數(shù)和固結(jié)度為試驗(yàn)變量,進(jìn)行了大量動(dòng)三軸試驗(yàn),綜合分析多因素影響下的淤泥質(zhì)粉質(zhì)粘土的循環(huán)弱化特性。主要工作如下:1、針對(duì)累積孔壓及累積變形,進(jìn)行了多因素影響下的動(dòng)力循環(huán)試驗(yàn),分析了圍壓、初始靜偏應(yīng)力、循環(huán)動(dòng)應(yīng)力和循環(huán)次數(shù)對(duì)淤泥質(zhì)粉質(zhì)粘土累積孔壓及累積變形發(fā)展的影響,并基于試驗(yàn)結(jié)果建立了改進(jìn)的雙曲累積孔壓計(jì)算模型和累積塑性應(yīng)變計(jì)算模型。2、針對(duì)循環(huán)強(qiáng)度弱化,進(jìn)行了多因素影響下的循環(huán)后不排水剪切試驗(yàn),分析了不同圍壓、初始靜偏應(yīng)力、循環(huán)動(dòng)應(yīng)力和循環(huán)次數(shù)下淤泥質(zhì)粉質(zhì)粘土的循環(huán)后不排水強(qiáng)度弱化規(guī)律。進(jìn)而運(yùn)用改進(jìn)的等效超固結(jié)比公式將孔壓規(guī)律和強(qiáng)度弱化規(guī)律結(jié)合起來,得到適用于整個(gè)動(dòng)態(tài)循環(huán)過程的正常固結(jié)土強(qiáng)度弱化時(shí)程計(jì)算模型。對(duì)模型進(jìn)行了試驗(yàn)驗(yàn)證,同時(shí)說明了模型的適用范圍。3、分析了淤泥質(zhì)粉質(zhì)粘土的強(qiáng)度弱化機(jī)理。通過試驗(yàn)發(fā)現(xiàn)土體存在臨界動(dòng)應(yīng)力比0.5,當(dāng)動(dòng)應(yīng)力比小于0.5時(shí),累積孔壓的增長是強(qiáng)度弱化的主要原因;而當(dāng)動(dòng)應(yīng)力比大于0.5時(shí),土體結(jié)構(gòu)破壞是強(qiáng)度弱化的主要原因;當(dāng)動(dòng)應(yīng)力比等于0.5時(shí),強(qiáng)度弱化的產(chǎn)生是累積孔壓和結(jié)構(gòu)破壞共同作用的結(jié)果。4、針對(duì)固結(jié)度的影響,進(jìn)行了不同固結(jié)度下的動(dòng)三軸試驗(yàn),分析了土體固結(jié)程度對(duì)于淤泥質(zhì)粉質(zhì)粘土循環(huán)后不排水強(qiáng)度弱化的影響,即不排水強(qiáng)度隨著固結(jié)度降低線性下降。同時(shí)在已得到的正常固結(jié)土(固結(jié)度為1)強(qiáng)度弱化模型的基礎(chǔ)上,提出固結(jié)度弱化因子的概念,建立了考慮土體固結(jié)度影響的強(qiáng)度弱化時(shí)程計(jì)算模型。5、通過大型有限元軟件ABAQUS,將得到的多因素強(qiáng)度弱化時(shí)程計(jì)算模型應(yīng)用于煙臺(tái)港防波堤數(shù)值模型的動(dòng)力計(jì)算當(dāng)中。分析循環(huán)弱化效應(yīng)以及土層固結(jié)程度對(duì)于防波堤結(jié)構(gòu)產(chǎn)生的影響,并提出有效的工程建議。
[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.
【學(xué)位授予單位】：天津大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類號(hào)】：TU447

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