【摘要】：黃土狀粉質(zhì)壤土是第四系上更新統(tǒng)沖積層(a1Q3)的一種巖性土,其地層特征為灰黃色,以粉粒為主,粘粒含量較低,屬于級配不良土。飽和黃土狀粉質(zhì)壤土主要表現(xiàn)為強度低,變形大,自穩(wěn)性差、降水困難,給現(xiàn)場施工造成極大的安全隱患,因此系統(tǒng)的研究該土的固結(jié)、強度、卸載和蠕變特性具有重要的現(xiàn)實意義。本文結(jié)合南水北調(diào)中線穿黃工程退水洞施工,通過現(xiàn)場調(diào)查、室內(nèi)試驗和模型試驗對黃土狀粉質(zhì)壤土進行試驗研究,得到如下結(jié)論： (1)固結(jié)試驗得到固結(jié)系數(shù)隨著固結(jié)壓力增大,先增大后減小,在固結(jié)壓力200kPa時得到最大固結(jié)系數(shù),平均值為6.56×10-4cm2/s。因此在工程中要充分考慮固結(jié)壓力對固結(jié)系數(shù)的影響。 (2)直剪試驗研究了不同含水率和抗剪強度的關(guān)系,當(dāng)含水率大于20%時,粉質(zhì)壤土的抗剪強度極低,當(dāng)含水率減至20%以下時,抗剪強度顯著增長,說明降水至20%以下能夠有效提高土體抗剪強度；試驗同時得到該土含水率降至20%后,即使繼續(xù)增大豎向壓力,含水量也幾乎不再發(fā)生損失,因此選擇合理的降水方案值得關(guān)注。 (3)為了研究隧道開挖應(yīng)力狀態(tài)下黃土狀粉質(zhì)壤土的力學(xué)性質(zhì),進行了三軸卸載試驗。試驗表明粉質(zhì)壤土破壞主應(yīng)力隨著含水率的增大成對數(shù)下降,軸向應(yīng)變成對數(shù)增長。 (4)蠕變試驗選取含水率15%的黃土狀粉質(zhì)壤土,試驗得到的破壞主應(yīng)力只有三軸快剪時的2/5,可見施工中時間效應(yīng)不可忽略；同時得到該土等時關(guān)系曲線形式類似于鄧肯張模型,計算時不宜選用線性流變模型。 (5)為模擬隧洞降水、開挖,進行了模型試驗,驗證了常規(guī)井點降水措施難以實現(xiàn)退水洞施工所要求的降水效果；由于含水量達(dá)到或接近飽和,開挖后掌子面下緣出現(xiàn)析水、滲流現(xiàn)象。在滲透和圍土應(yīng)力釋放作用下,土體呈現(xiàn)流塑狀,產(chǎn)生溜坍破壞。驗證了粉質(zhì)壤土在開挖后,含水量局部聚集,發(fā)生瞬時強度喪失,表現(xiàn)出流塑狀的破壞機理。
[Abstract]:Loess silty loam is a kind of lithologic soil of Quaternary Upper Pleistocene alluvial layer (a1Q3). Its stratigraphic characteristics are grayish yellow, mainly silt and low clay content, so it belongs to poorly graded soil. The saturated loess silty loam is mainly characterized by low strength, large deformation, poor self-stability and difficult precipitation, which causes great safety hidden danger to the field construction, so the consolidation and strength of the soil are systematically studied. Unloading and creep characteristics have important practical significance. In this paper, the loess silty loam is studied by field investigation, laboratory test and model test in combination with the construction of the backwater tunnel in the middle line of South-to-North Water transfer Project. The results are as follows: (1) the consolidation coefficient increases first and then decreases with the increase of the consolidation pressure, and the maximum consolidation coefficient is obtained at the consolidation pressure 200kPa, with an average of 6.56 脳 10 ~ (-4) cm ~ (-2) / s. Therefore, the influence of consolidation pressure on consolidation coefficient should be fully considered in engineering. (2) the relationship between different moisture content and shear strength is studied by direct shear test. When the moisture content is larger than 20, the shear strength of silty loam is very low. When the moisture content is reduced to less than 20%, the shear strength increases significantly, which indicates that the shear strength of the soil can be improved effectively by precipitation below 20%, and when the moisture content of the soil is reduced to 20%, the vertical pressure will continue to increase. Water content is almost no longer lost, so it is worth paying attention to choose a reasonable precipitation scheme. (3) in order to study the mechanical properties of loess silty loam under tunnel excavation stress, triaxial unloading test was carried out. The results show that the principal stress of failure of silty loam soil decreases logarithmically with the increase of moisture content, and the axial value should be logarithmic increased. (4) the loess silty loam with 15% moisture content is selected for creep test. The failure principal stress obtained from the test is only 2 / 5 of that of the triaxial fast shear, which shows that the time effect can not be ignored in construction. At the same time, the isochronous curve of the soil is similar to that of Duncan's model. The linear rheological model should not be used in the calculation. (5) in order to simulate the tunnel dewatering and excavate, the model test is carried out, which verifies that the conventional well point dewatering measures are difficult to achieve the dewatering effect required by the dewatering tunnel construction; Due to water content reaching or near saturation, water evolution and seepage appear in the lower edge of the face after excavation. Under the action of seepage and stress release, the soil presents fluid-plastic shape and collapses. It is verified that the local water content of silty loam is accumulated and the instantaneous strength is lost after excavation, which shows the mechanism of fluid-plastic failure.
【學(xué)位授予單位】：石家莊鐵道大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TV554;TV221.2

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