本文選題：黃土　切入點(diǎn)：非飽和土　出處：《長(zhǎng)安大學(xué)》2016年博士論文　論文類(lèi)型：學(xué)位論文

【摘要】：黃土是典型的非飽和土,黃土的非飽和本構(gòu)模型是黃土工程特性研究的一個(gè)重要方向。本文采取了陜西涇陽(yáng)南塬L5黃土,開(kāi)展了系統(tǒng)地試驗(yàn)研究。陜西涇陽(yáng)南塬黃土地層剖面出露完整,剖面可見(jiàn)S0到L9全部地層,受農(nóng)業(yè)灌溉影響,該黃土塬北緣滑坡發(fā)育,且屬于典型黃土層內(nèi)滑坡。此次試驗(yàn)所取L5試樣(Q2)位于該處滑坡的主要剪切帶,為典型的非飽和結(jié)構(gòu)性黃土。本文通過(guò)試驗(yàn)取得了該黃土的物理力學(xué)參數(shù),建立了能夠反映黃土變形特性的非飽和本構(gòu)模型,開(kāi)展的主要工作如下:(1)將L5原狀樣和分層擊實(shí)所得重塑樣分別配制8%、11%、15%、20%和25%五個(gè)不同含水率,采用常規(guī)三軸儀在100 kPa、200 kPa、300 kPa、400 kPa和500 kPa五個(gè)不同圍壓下進(jìn)行CD試驗(yàn)。試驗(yàn)結(jié)果表明有效穩(wěn)態(tài)摩擦角與含水率無(wú)明顯相關(guān)性,基本為一穩(wěn)定值。含水率低于塑限時(shí),有效穩(wěn)態(tài)粘聚力隨含水率增大而顯著降低;當(dāng)含水率高于塑限時(shí),有效穩(wěn)態(tài)粘聚力不再隨含水率的增大而降低,趨于一穩(wěn)定值。(2)利用三軸CD試驗(yàn),結(jié)合Fredlund SWCC壓力板儀測(cè)得的土水特征曲線,分析了Fredlund、Bishop和Lu Ning三種非飽和土強(qiáng)度表達(dá)式中的強(qiáng)度參數(shù)。其中Bishop和Fredlund強(qiáng)度公式中的參數(shù)χ和υb必須利用土水特征曲線確定;而Lu Ning強(qiáng)度公式中的吸應(yīng)力與含水率的關(guān)系,可通過(guò)不同含水率常規(guī)三軸試驗(yàn)確定,這回避了基質(zhì)吸力測(cè)定的不便,便于在工程實(shí)際中推廣應(yīng)用。(3)根據(jù)不同含水率不同圍壓原狀和重塑土常規(guī)三軸CD試驗(yàn)所得變形和強(qiáng)度參數(shù)變化規(guī)律,得到不同含水率下L5原狀和重塑試樣的理想彈塑性模型,并對(duì)模型的適用性進(jìn)行了驗(yàn)證,并結(jié)合對(duì)應(yīng)含水率下原狀及重塑土的K0固結(jié)試驗(yàn)結(jié)果,對(duì)Duncan-Chang非線性彈性模型中的μ的表達(dá)式進(jìn)行修改,得到了原狀及重塑黃土非飽和非線性彈性模型的表達(dá)式,并進(jìn)行了驗(yàn)證。(4)通過(guò)對(duì)初始孔隙比相同的L5重塑和原狀試樣進(jìn)行不同含水率的固結(jié)試驗(yàn),發(fā)現(xiàn)在半對(duì)數(shù)坐標(biāo)系下不同含水率試樣的膨脹回彈線相互平行,固結(jié)壓縮線的直線段也相互平行,壓縮線的斜率λ較膨脹回彈線κ更陡;相同應(yīng)力條件下,試樣的初始含水率越高,孔隙比越小;相同應(yīng)力條件下,原狀土相對(duì)應(yīng)重塑土而言能保持更大的孔隙比。(5)本文基于修正劍橋模型,通過(guò)半對(duì)數(shù)坐標(biāo)下非飽和重塑樣與飽和重塑樣固結(jié)曲線的關(guān)系,引入非飽和狀態(tài)變量ρss代表相同平均骨架應(yīng)力下非飽和與飽和狀態(tài)重塑樣孔隙比的差值。并結(jié)合超固結(jié)狀態(tài)變量ρe推導(dǎo)出了能夠反映非飽和重塑黃土超固結(jié)特性的本構(gòu)模型。(6)基于黃土非飽和重塑本構(gòu)模型,引入結(jié)構(gòu)性狀態(tài)變量ρst代表固結(jié)試驗(yàn)半對(duì)數(shù)坐標(biāo)系中相同平均骨架應(yīng)力和飽和度下原狀與重塑黃土孔隙比的差值,推導(dǎo)出了更夠反映結(jié)構(gòu)性的適用于原狀黃土的非飽和本構(gòu)模型。
[Abstract]:Loess is a typical unsaturated soil, and the unsaturated constitutive model of loess is an important direction in the study of loess engineering characteristics. A systematic experimental study has been carried out. The profile of the loess layer in the southern plateau of Jingyang, Shaanxi Province, is completely exposed, and all strata from S0 to L9 can be found in the section. The landslide in the northern margin of the loess plateau is developed under the influence of agricultural irrigation. The L5 sample Q2), which is located in the main shear zone of the landslide, is a typical unsaturated structural loess. The physical and mechanical parameters of the loess are obtained by experiments. An unsaturated constitutive model which can reflect the deformation characteristics of loess is established. The main work is as follows: (1) eight different moisture contents are prepared from L5 undisturbed sample and remolded sample from stratified compaction, respectively, of 8% and 25%, respectively. The CD test was carried out under five different confining pressures of 100kPa200kPa200kPa300kPa400 kPa and 500kPa300KPA by conventional triaxial apparatus. The experimental results show that there is no obvious correlation between the effective steady-state friction angle and the moisture content, which is basically a stable value, and when the moisture content is below the plastic limit, When the moisture content is higher than the plastic limit, the effective steady-state cohesion decreases no longer with the increase of moisture content, and tends to a stable value. Based on the soil-water characteristic curve measured by Fredlund SWCC pressure plate, the strength parameters of Fredlundbin Bishop and Lu Ning are analyzed. The parameters 蠂 and u b in Bishop and Fredlund strength formulas must be determined by soil-water characteristic curve. However, the relationship between absorption stress and moisture content in Lu Ning strength formula can be determined by conventional triaxial test of different moisture content, which avoids the inconvenience of matrix suction measurement. It is easy to be popularized and applied in engineering practice. According to the variation law of deformation and strength parameters obtained from conventional triaxial CD test of different moisture content and different confining pressure, the ideal elastic-plastic model of L5 undisturbed and remolded specimens under different moisture content is obtained. The applicability of the model is verified, and the expression of 渭 in the Duncan-Chang nonlinear elastic model is modified by combining the K0 consolidation test results of the undisturbed and remolded soils under the corresponding moisture content. The expressions of unsaturated nonlinear elastic model of undisturbed and remolded loess are obtained, and verified by the consolidation tests of L5 remolded and undisturbed specimens with the same initial void ratio. It is found that in the semi-logarithmic coordinate system, the expansion springback lines of samples with different moisture content are parallel to each other, and the straight lines of the consolidation and compression lines are parallel to each other, and the slope 位 of the compression lines is steeper than that of the swelling and springback lines, and under the same stress conditions, The higher the initial moisture content of the sample, the smaller the void ratio; under the same stress condition, the undisturbed soil can keep a larger void ratio for the remolded soil. According to the relationship between unsaturated remolded sample and saturated remolded sample consolidation curve in semi-logarithmic coordinate, The unsaturated state variable 蟻 ss is introduced to represent the difference between unsaturated and saturated remolded void ratio under the same mean skeleton stress. Combining with the overconsolidated state variable 蟻 e, the overconsolidation characteristics of unsaturated remolded loess are derived. Based on the unsaturated remolded constitutive model of loess, The structural state variable 蟻 st is introduced to represent the difference between original and remolded loess void ratio under the same mean skeleton stress and saturation in the semi-logarithmic coordinate system of consolidation test. An unsaturated constitutive model suitable for undisturbed loess is derived.
【學(xué)位授予單位】：長(zhǎng)安大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類(lèi)號(hào)】：P642.131

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