本文關(guān)鍵詞：波浪作用下原狀軟粘土動(dòng)力特性與微觀結(jié)構(gòu)關(guān)系試驗(yàn)研究　出處：《浙江大學(xué)》2013年碩士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 飽和軟粘土 波浪荷載 動(dòng)力特性 主應(yīng)力軸旋轉(zhuǎn) 掃描電鏡 微觀結(jié)構(gòu)

【摘要】：隨著海洋資源的開發(fā)與海洋空間的利用,在海床軟土地基上修建了越來越多的海工建筑物,這些設(shè)施在建設(shè)和使用過程中長期受到波浪荷載的作用,與此同時(shí),波浪荷載所引起的巖土工程問題受到了越來越多的關(guān)注。許多學(xué)者對波浪荷載下飽和粘土的動(dòng)力特性做了大量的研究,但研究成果大多以動(dòng)三軸試驗(yàn)為主,無法模擬波浪荷載下主應(yīng)力軸連續(xù)循環(huán)旋轉(zhuǎn)的復(fù)雜應(yīng)力路徑。另外,以往對于土體特性的研究多停留在宏觀力學(xué)的角度上,對引起宏觀動(dòng)力反應(yīng)的土體微觀結(jié)構(gòu)尚缺乏系統(tǒng)的研究,因此,要想全面了解復(fù)雜應(yīng)力路徑下的土體特性,就必須在宏觀力性試驗(yàn)的基礎(chǔ)上,系統(tǒng)深入地開展土體微觀結(jié)構(gòu)變形和破壞機(jī)理研究,揭示土體微觀結(jié)構(gòu)參數(shù)與宏觀力學(xué)特性之間的關(guān)系。 本文在以往研究的基礎(chǔ)上,利用浙江大學(xué)5Hz空心圓柱扭剪儀,模擬波浪荷載下海床地基土體單元的實(shí)際受力條件,對飽和軟粘土的動(dòng)力特性進(jìn)行研究,采用掃描電鏡(SEM)和PCAS微觀定量分析系統(tǒng),對軟土固結(jié)過程及循環(huán)加載前后的土體微觀結(jié)構(gòu)變化特征進(jìn)行定性和定量研究,并分析宏觀特性與微觀結(jié)構(gòu)變化之間的關(guān)系。本文主要工作和研究成果如下： (1)分別開展了不同循環(huán)應(yīng)力比和不同頻率下的主應(yīng)力軸連續(xù)旋轉(zhuǎn)循環(huán)剪切試驗(yàn)。試驗(yàn)結(jié)果表明：循環(huán)應(yīng)力比和頻率對循環(huán)荷載作用下土體的孔壓特性、應(yīng)變特性和動(dòng)模量的衰減特性均有較大的影響。與動(dòng)三軸試驗(yàn)結(jié)果相比,受主應(yīng)力軸連續(xù)旋轉(zhuǎn)的影響,土體孔壓累積、應(yīng)變發(fā)展及模量衰減速度均較快,試樣破壞時(shí)孔壓曲線沒有明顯的拐點(diǎn)也沒有達(dá)到穩(wěn)定狀態(tài),破壞所需的循環(huán)次數(shù)大幅減少,同樣循環(huán)次數(shù)時(shí)土體軟化程度更高,土體臨界循環(huán)應(yīng)力比由0.5減小到0.2左右,動(dòng)強(qiáng)度降低了35%-40%。 (2)通過一維壓縮固結(jié)試驗(yàn)對土體的壓縮特性及其微觀孔隙特征的變化規(guī)律進(jìn)行研究,得到了微觀結(jié)構(gòu)特征參數(shù)隨固結(jié)壓力的變化規(guī)律,發(fā)現(xiàn)土體壓縮性能的變化與微觀結(jié)構(gòu)參數(shù)的變化具有密切的相關(guān)性,揭示了土體受力變形的微觀機(jī)理,進(jìn)而達(dá)到研究和預(yù)測土體壓縮變形的目的。 (3)對循環(huán)加載前后及試樣破壞后剪切帶內(nèi)外土體微觀結(jié)構(gòu)進(jìn)行研究,從微觀層面上揭示了動(dòng)荷載下的土體微觀結(jié)構(gòu)變形和破壞機(jī)理。循環(huán)剪應(yīng)力作用下,孔隙破碎的同時(shí)兼并生長,這是剪切帶上“褶皺”現(xiàn)象的微觀本質(zhì),剪切帶上多數(shù)孔隙排列方向與剪切帶方向一致,不同試樣破壞時(shí)的孔隙尺度及其分布規(guī)律相差不大對應(yīng)宏觀上的臨界軸向破壞應(yīng)變水平也基本一致。靜荷載和動(dòng)荷載下土體微觀結(jié)構(gòu)變形機(jī)理不同,動(dòng)荷載下土體微觀結(jié)構(gòu)的變化比靜力條件下復(fù)雜的多。循環(huán)應(yīng)力比和頻率對土體微觀結(jié)構(gòu)變化的影響存在差異,微觀結(jié)構(gòu)參數(shù)隨循環(huán)應(yīng)力比的變化有一定的規(guī)律性,隨頻率的變化規(guī)律性不明顯。
[Abstract]:With the development of marine resources and the utilization of ocean space, more and more marine structures have been built on the soft soil foundation of the seabed. These facilities have been subjected to wave loads for a long time in the process of construction and use, at the same time. The geotechnical engineering problem caused by wave load has been paid more and more attention. Many scholars have done a lot of research on the dynamic characteristics of saturated clay under wave load, but the research results are mostly dynamic triaxial test. It is impossible to simulate the complex stress path of continuous cyclic rotation of principal stress axis under wave load. There is no systematic research on the microstructure of soil mass which causes the macroscopic dynamic response. Therefore, in order to fully understand the characteristics of soil under complex stress path, it is necessary to base on the macroscopic force test. In order to reveal the relationship between soil microstructure parameters and macroscopic mechanical properties, the deformation and failure mechanism of soil microstructure is studied. On the basis of previous research, the dynamic characteristics of saturated soft clay are studied by using the 5 Hz hollow cylindrical torsional shear apparatus of Zhejiang University to simulate the actual stress conditions of the soil element in the sea bed under the wave load. The microstructure of soft soil before and after cyclic loading was studied qualitatively and quantitatively by means of scanning electron microscope (SEM) and PCAS microquantitative analysis system. The main work and results of this paper are as follows: 1) continuous rotating cyclic shear tests of principal stress axis were carried out under different cyclic stress ratios and different frequencies. The experimental results show that the cyclic stress ratio and frequency affect the pore pressure characteristics of soil under cyclic load. Compared with the dynamic triaxial test results, the pore pressure accumulation, strain development and modulus decay rate of soil are faster due to the continuous rotation of the principal stress axis. The pore pressure curve has no obvious inflection point and does not reach a stable state when the specimen is destroyed, and the number of cycles required for failure is greatly reduced, and the softening degree of soil is higher when the same number of cycles occurs. The critical cyclic stress ratio decreases from 0.5 to 0.2 and the dynamic strength decreases from 35 to 40. 2) through one-dimensional compression consolidation test, the variation law of soil compression characteristics and micro-pore characteristics is studied, and the variation law of microstructure characteristic parameters with consolidation pressure is obtained. It is found that the variation of soil compression performance is closely related to the change of microstructure parameters, and the microscopic mechanism of soil deformation is revealed, and the purpose of studying and predicting soil compression deformation is achieved. 3) the microstructure of soil in and out of the shear band before and after cyclic loading is studied, and the mechanism of deformation and failure of soil under dynamic loading is revealed from the micro level, under cyclic shear stress. The microcosmic essence of the "fold" phenomenon in the shear zone is that the pores are broken and grow simultaneously, and most of the pores in the shear zone are arranged in the same direction as the shear zone. The pore size and distribution of different specimens are similar to the macroscopic critical axial failure strain level. The deformation mechanism of soil microstructure is different under static load and dynamic load. The variation of soil microstructure under dynamic load is more complex than that under static condition. The influence of cyclic stress ratio and frequency on the change of soil microstructure is different. The variation of microstructure parameters with cyclic stress ratio is regular, but the variation with frequency is not obvious.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2013
【分類號(hào)】：TU442;TU447

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