本文選題：黃土 + 濕陷性��； 參考：《長(zhǎng)安大學(xué)》2015年碩士論文

【摘要】：黃土的濕陷變形通常是通過(guò)室內(nèi)試驗(yàn)測(cè)得濕陷系數(shù)計(jì)算或原位浸水試驗(yàn)直接觀測(cè)獲得。現(xiàn)場(chǎng)浸水試驗(yàn)結(jié)果準(zhǔn)確,但成本高,時(shí)間長(zhǎng)。絕大部分工程是根據(jù)規(guī)范,使用室內(nèi)試驗(yàn)濕陷系數(shù)來(lái)計(jì)算。然而計(jì)算值和實(shí)測(cè)值之間往往存在很大差異,這一方面是由于濕陷系數(shù)是在飽和狀態(tài)下測(cè)得,而實(shí)際上土體含水量增加到某一值時(shí)即可發(fā)生濕陷;另一方面原位浸水試驗(yàn)結(jié)果表明濕陷變形總量會(huì)隨時(shí)間變化,停滲期也有沉降變形,表明濕陷變形同水分在土體中的入滲有關(guān),忽略時(shí)間因素也會(huì)造成差異。黃土是一種典型的非飽和土,本文根據(jù)非飽和滲透和非飽和變形理論,提出了一種非飽和濕陷變形隨時(shí)間變化的計(jì)算模型。用此模型計(jì)算了黑方臺(tái)地區(qū)自1967年灌溉以來(lái)的年沉降量和累積沉降量,并同相關(guān)文獻(xiàn)資料的得到的沉降量進(jìn)行了對(duì)比。此外還利用顯微鏡對(duì)原狀和不同含水率壓縮后的土樣進(jìn)行了細(xì)觀結(jié)構(gòu)分析,探討了細(xì)觀結(jié)構(gòu)同宏觀物理力學(xué)性質(zhì)的關(guān)系。在黑方臺(tái)非灌區(qū)挖井取樣測(cè)定了土體的基本物理參數(shù)沿深度的分布情況,據(jù)此對(duì)該黃土分層,每層取樣進(jìn)行了不同含水率土樣的側(cè)限壓縮試驗(yàn)和土水特征曲線的測(cè)定,獲得計(jì)算模型所需參數(shù)。建立了非飽和滲透模型,得到每年不同灌溉階段土層孔隙水壓力沿深度的分布情況,獲得差值,進(jìn)行沉降變形的計(jì)算。結(jié)果表明自1967年灌溉以來(lái),累積沉降變形達(dá)1.91m,同取樣點(diǎn)位置處臺(tái)面的下降量2.01m接近;地下水水位上升前,年沉降量較大,其中1967年的沉降變形最大,高達(dá)0.4m,之后逐漸降低;地下水水位開(kāi)始上升后后年沉降量在20-40mm之間波動(dòng),2007年以來(lái)年沉降量在20-30mm之間,這同相關(guān)文獻(xiàn)資料研究成果相一致借助顯微鏡得到了到每層土體原狀樣和900kPa壓力變形穩(wěn)定后不同含水率土體的細(xì)觀結(jié)構(gòu)。原狀樣的孔隙大小和數(shù)量直接決定了土樣的孔隙比和干密度,而孔隙分布特點(diǎn)則影響土體的土水特征曲線,體積含水率相同,大孔隙和中孔隙含量百分?jǐn)?shù)越大,土體基質(zhì)吸力越小。900kPa壓力下變形穩(wěn)定后,隨著含水率的增大,百分?jǐn)?shù)最大的孔徑減小,微孔隙增多。每層不同含水率土體壓縮變形穩(wěn)定后具有相同的孔隙分布特征。反映土體變形的參數(shù)主要受原狀樣孔隙分布影響,大孔隙和中孔隙含量越高,濕陷系數(shù)越大。
[Abstract]:The collapsing deformation of loess is usually obtained by calculating the coefficient of collapsibility measured by laboratory tests or by direct observation of in-situ soaking test. The results of field immersion test are accurate, but the cost is high and the time is long. Most of the projects are based on the code, using indoor test to calculate the coefficient of collapsibility. However, there is often a great difference between the calculated value and the measured value, which is due to the fact that the coefficient of collapsibility is measured under saturated condition, but in fact, when the water content of soil is increased to a certain value, the collapsibility can occur. On the other hand, the in-situ immersion test results show that the total amount of collapsing deformation will change with time, and there will also be subsidence deformation in the impervious period, indicating that the collapsing deformation is related to the infiltration of water in the soil, and neglecting the time factor will also cause the difference. Loess is a typical unsaturated soil. Based on the theory of unsaturated permeability and unsaturated deformation, a calculation model of unsaturated collapsing deformation with time is proposed in this paper. The annual and cumulative settlement in Heifangtai area since 1967 has been calculated by using this model and compared with the results obtained from relevant literatures. In addition, the microstructures of soil samples with different moisture content were analyzed by microscope, and the relationship between microstructures and macroscopic physical and mechanical properties was discussed. The distribution of the basic physical parameters of soil along the depth was measured by well sampling in Heifangtai non-irrigated area. According to the stratification of loess, the lateral limit compression test of soil samples with different water cut and the determination of soil water characteristic curve were carried out in each layer. The required parameters of the calculation model are obtained. The unsaturated permeation model was established, and the distribution of pore water pressure along the depth of soil layer was obtained at different irrigation stages every year. The difference value was obtained and the settlement deformation was calculated. The results show that since the irrigation in 1967, the cumulative settlement deformation has reached 1.91 m, and the decrease of the Mesa at the same sampling point is 2.01m, and the annual subsidence is larger before the groundwater level rises, in which the settlement deformation of 1967 is the largest, up to 0.4 m, and then decreases gradually. After the groundwater level began to rise, the annual settlement fluctuated between 20-40mm, and in 2007, the annual settlement was between 20-30mm, This is consistent with the research results of relevant literature and materials. The microstructures of soils with different moisture content are obtained by means of microscope after each layer of soil is undisturbed and stabilized by pressure deformation at 900kPa. The pore size and quantity of the undisturbed sample directly determine the porosity ratio and dry density of the soil sample, while the pore distribution characteristics affect the soil-water characteristic curve of the soil, the volume water content is the same, the percentage of the macroporosity and the middle pore content is larger. With the increase of water content, the pore size of the largest percentage decreases and the micro-porosity increases after deformation and stabilization under the pressure of .900kPa when the suction of soil matrix is smaller. Each layer of soil with different moisture content has the same pore distribution characteristics after compression deformation and stability. The parameters reflecting soil deformation are mainly affected by the distribution of undisturbed pores, and the higher the content of macropores and mesoporous pores, the greater the coefficient of collapsibility.
【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】：2015
【分類號(hào)】：TU444;TU411

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