本文選題：重塑黃土 + 應(yīng)力路徑　； 參考：《長(zhǎng)安大學(xué)》2017年碩士論文

【摘要】：黃土具有疏松多孔、弱膠結(jié)的特殊結(jié)構(gòu),在我國(guó)西北地區(qū)廣泛分布。隨著“一帶一路”西北戰(zhàn)略區(qū)的經(jīng)濟(jì)發(fā)展建設(shè),與黃土相關(guān)的人類(lèi)活動(dòng)日益頻繁,形成了大量黃土堆填邊坡。諸多學(xué)者開(kāi)展有關(guān)黃土的力學(xué)特性研究,基于這一層面解釋成災(zāi)機(jī)理,為黃土地區(qū)的防災(zāi)減災(zāi)工作的開(kāi)展起到積極的作用。為研究黃土堆填體的變形破壞規(guī)律,本文在借鑒前人研究的基礎(chǔ)上,依據(jù)黃土堆填邊坡的受力特征,以重塑黃土為研究對(duì)象,設(shè)計(jì)不同應(yīng)力路徑的三軸試驗(yàn),包括常規(guī)三軸壓縮試驗(yàn)(CTC)、平均主應(yīng)力為常數(shù)的三軸壓縮試驗(yàn)(TC)、減圍壓的三軸壓縮試驗(yàn)(RTC),研究不同應(yīng)力路徑對(duì)重塑黃土力學(xué)特性的影響,并通過(guò)SEM圖像分析微觀結(jié)構(gòu)特征,分析黃土堆填體的破壞發(fā)展規(guī)律,進(jìn)而解析黃土的災(zāi)變力學(xué)行為。得出結(jié)論如下:(1)黃土的強(qiáng)度特性:CTC路徑下重塑黃土表現(xiàn)為應(yīng)變硬化型,TC、RTC路徑下呈應(yīng)變?nèi)跤不?同一固結(jié)圍壓下土體抗剪強(qiáng)度CTC路徑TC路徑RTC路徑。應(yīng)力循環(huán)的加載方式相比單調(diào)加載,土體被壓密,因而抗剪強(qiáng)度稍有提高。(2)黃土的變形規(guī)律:重塑黃土屬于亞穩(wěn)定結(jié)構(gòu)土,在變形破壞過(guò)程中整體表現(xiàn)為體積收縮,CTC、TC、RTC試驗(yàn)路徑的體縮量逐漸減小;對(duì)于同一應(yīng)力路徑,體縮量隨初始圍壓的增大而增大。土體的變形同時(shí)存在剪縮和剪脹兩部分塑性變形,重塑黃土在較低應(yīng)力水平下的加載-卸載-再加載循環(huán)中表現(xiàn)為加載體縮,卸載時(shí)因剪脹部分的恢復(fù)而表現(xiàn)為體縮,較高應(yīng)力水平下則表現(xiàn)為加載體縮卸載體脹。(3)微觀結(jié)構(gòu)特點(diǎn):不同應(yīng)力路徑剪切后,按CTC、TC、RTC順序,顆粒破碎程度依次減小,孔隙含量依次增大。(4)重塑黃土的屈服模型描述:引用殷宗澤提出的橢圓-拋物線雙屈服面塑性模型,依據(jù)試驗(yàn)結(jié)果對(duì)模型參數(shù)取值進(jìn)行調(diào)整,經(jīng)計(jì)算,該模型能夠較好地描述重塑黃土變形特性。(5)黃土災(zāi)變力學(xué)行為分析:在加載作用下,變形初期,土體被壓縮擠密,其強(qiáng)度在一定程度上得到提升,隨著荷載的持續(xù)增加,變形速率平穩(wěn)增大,土體變形至破壞呈漸進(jìn)式發(fā)展,以軸向壓縮變形為主,側(cè)向鼓脹變形較小;對(duì)于側(cè)向卸荷形式的變形行為,卸荷初期,土體維持在相對(duì)穩(wěn)定的狀態(tài),變形量很小,當(dāng)側(cè)向約束減小到一臨界狀態(tài)后,結(jié)構(gòu)失穩(wěn)破壞,短時(shí)間內(nèi)土體變形迅速發(fā)展,變形速率迅速增大。
[Abstract]:Loess has a special structure of porous and weak cementation, which is widely distributed in northwest China. With the economic development and construction of "Belt and Road" northwest strategic area, human activities related to loess become more and more frequent, forming a large number of loess landfills slope. Many scholars have carried out researches on the mechanical properties of loess, based on which the mechanism of disaster formation has been explained, which plays an active role in the development of disaster prevention and mitigation in loess area. In order to study the deformation and failure law of loess landfills, based on the previous research, according to the stress characteristics of loess landfill slope, this paper designs triaxial tests of different stress paths, taking remolded loess as the research object. Including conventional triaxial compression test (CTC), triaxial compression test with constant mean principal stress (TCC) and triaxial compression test (RTC) with reduced confining pressure. The effects of different stress paths on the mechanical properties of remolded loess are studied, and the microstructure characteristics are analyzed by SEM images. The failure and development law of loess landfill is analyzed, and the catastrophic mechanical behavior of loess is analyzed. The conclusion is as follows: (1) the strength characteristics of loess are as follows: (1) the remolded loess under the: CTC path is shown as strain hardening under strain hardening type TCU RTC path, and the soil shear strength CTC path is TC path RTC path under the same consolidation confining pressure. Compared with monotone loading, the loading mode of stress cycle results in the compaction of soil mass, so the shear strength is slightly increased.) the deformation law of loess is that the remolded loess belongs to the substable structure soil. In the process of deformation and failure, the volume shrinkage of CTCU TCU RTC test path decreases gradually, and for the same stress path, the volume shrinkage increases with the increase of initial confining pressure. At the same time, there are two parts of plastic deformation in soil deformation: shear shrinkage and dilatancy. In the load-unload reloading cycle of remolded loess at lower stress level, it is shown as carrier shrinkage, and when unloading, it is shown as bulk shrinkage due to the recovery of shear expansion part. At higher stress level, the microstructural characteristics of the loading carrier are as follows: after shearing with different stress paths, the degree of particle breakage decreases according to the order of CTCU TCU RTC, and the degree of particle breakage decreases in turn after shearing under different stress paths. The yield model of remolded loess is described by increasing porosity content in turn. The plastic model of elliptic-parabola double yield surface proposed by Yin Zongze is quoted. The parameters of the model are adjusted according to the test results, and the model parameters are calculated. The model can well describe the deformation characteristics of remolded loess. (5) Analysis of the catastrophic mechanical behavior of loess: under the action of loading, the soil is compressed and compacted at the initial stage of deformation, and its strength is improved to some extent, and the strength increases with the continuous increase of load. When the deformation rate increases steadily, the deformation to failure of soil develops gradually, mainly axial compression deformation, while lateral bulging deformation is small. For the deformation behavior in the form of lateral unloading, the soil is maintained in a relatively stable state at the initial unloading stage. The deformation is very small, when the lateral constraint is reduced to a critical state, the structure loses stability and failure, the soil deformation develops rapidly in a short time, and the deformation rate increases rapidly.
【學(xué)位授予單位】：長(zhǎng)安大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TU444

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