黄土状粉质壤土工程性质试验研究

发布时间：2018-09-12 18:08

【摘要】：黄土状粉质壤土是第四系上更新统冲积层(a1Q3)的一种岩性土,其地层特征为灰黄色,以粉粒为主,粘粒含量较低,属于级配不良土。饱和黄土状粉质壤土主要表现为强度低,变形大,自稳性差、降水困难,给现场施工造成极大的安全隐患,因此系统的研究该土的固结、强度、卸载和蠕变特性具有重要的现实意义。本文结合南水北调中线穿黄工程退水洞施工,通过现场调查、室内试验和模型试验对黄土状粉质壤土进行试验研究,得到如下结论： (1)固结试验得到固结系数随着固结压力增大,先增大后减小,在固结压力200kPa时得到最大固结系数,平均值为6.56×10-4cm2/s。因此在工程中要充分考虑固结压力对固结系数的影响。 (2)直剪试验研究了不同含水率和抗剪强度的关系,当含水率大于20%时,粉质壤土的抗剪强度极低,当含水率减至20%以下时,抗剪强度显著增长,说明降水至20%以下能够有效提高土体抗剪强度；试验同时得到该土含水率降至20%后,即使继续增大竖向压力,含水量也几乎不再发生损失,因此选择合理的降水方案值得关注。 (3)为了研究隧道开挖应力状态下黄土状粉质壤土的力学性质,进行了三轴卸载试验。试验表明粉质壤土破坏主应力随着含水率的增大成对数下降,轴向应变成对数增长。 (4)蠕变试验选取含水率15%的黄土状粉质壤土,试验得到的破坏主应力只有三轴快剪时的2/5,可见施工中时间效应不可忽略；同时得到该土等时关系曲线形式类似于邓肯张模型,计算时不宜选用线性流变模型。 (5)为模拟隧洞降水、开挖,进行了模型试验,验证了常规井点降水措施难以实现退水洞施工所要求的降水效果；由于含水量达到或接近饱和,开挖后掌子面下缘出现析水、渗流现象。在渗透和围土应力释放作用下,土体呈现流塑状,产生溜坍破坏。验证了粉质壤土在开挖后,含水量局部聚集,发生瞬时强度丧失,表现出流塑状的破坏机理。
[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.
【学位授予单位】：石家庄铁道大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TV554;TV221.2

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