不同排水及粉土夹层条件下饱和砂土液化特性研究
发布时间：2019-01-28 17:53
【摘要】：我国是一个地震多发国家,地震所造成的砂土液化问题一直是岩土工程界研究的重点和热点之一。目前针对砂土液化影响因素、影响机理的研究已取得很多成果,并得到了广泛认可。在地震荷载作用下土体内部会产生超孔隙水压力,而实际地层中不同位置的土体受相邻土层渗透性质的影响会导致不同的排水条件,排水条件不同对超孔隙水压力产生、消散和重分布有重要影响。目前关于液化问题的研究大多假定为不排水条件,而场地实际排水条件对土体液化特性的影响一直没有得到充分认识。基于此,本文通过室内动三轴试验对不同排水及粉土夹层条件下饱和砂土的液化特性进行了试验研究。(1)设计了可控制渗透系数大小的排水夹层装置,该装置放置在试样顶部,实现了对试样不同排水条件的控制,为后续试验工作提供了依据。(2)利用动三轴仪进行了不同排水条件下饱和砂土动三轴试验,获得了不同排水和加载模式条件下饱和砂土试样的超孔隙水压发展和应力应变关系曲线。试验结果表明:随着渗透系数比的增加,饱和砂土试样孔隙水压增长速度减缓;双向荷载相较与同幅值的单向荷载作用试样产生的塑性变形大,孔隙水压发展速率快,试样更容易发生液化。试验条件下,渗透系数比大于0.54时饱和砂土试样不液化,小于0.17时试样液化。(3)开展了粉土夹层条件下饱和砂土动三轴试验,获得了不同夹层间距比、不同排水条件下饱和层状砂土试样的超孔隙水压发展和应力应变关系曲线。试验结果分析表明:饱和层状砂土试样,孔隙水压积累速率随着粉土夹层间距比的增大而减小,试样抗液化强度增加;排水条件和双向荷载对饱和层状砂土试样的液化强度影响与均匀砂土试样相似,超孔隙水压在渗透系数比较大和双向加载条件下发展速率快,试样更容易液化。(4)开展了饱和砂土试样液化后剪切试验,获得了液化后饱和砂土试样在不同排水条件下的超孔隙水压力消散和变形曲线。试验结果分析表明:液化后饱和砂土试样的剪切模量随着渗透系数比的增大而增大,即排水条件的提高而增加,相应的液化后试样体积剪缩量减小,而剪切吸水效应增强,试样抗剪强度折减率增大。
[Abstract]:China is an earthquake-prone country. The liquefaction of sandy soil caused by earthquake has always been one of the focal points and hot spots in geotechnical engineering. At present, a lot of achievements have been made on the influencing factors and mechanism of sand liquefaction, which have been widely recognized. Under the action of earthquake, the excess pore water pressure will be produced in the soil body, but the different positions of soil in the actual stratum will be affected by the permeability of adjacent soil layer, which will lead to different drainage conditions, and the different drainage conditions will produce the excess pore water pressure. Dissipation and redistribution have important effects. At present, most of the researches on liquefaction are assumed to be undrained conditions, but the influence of actual drainage conditions on soil liquefaction characteristics has not been fully understood. Based on this, the liquefaction characteristics of saturated sand under different drainage and silt intercalation conditions are studied by dynamic triaxial test in laboratory. (1) A drainage interlayer device with controllable permeability coefficient is designed. The device is placed at the top of the sample, which realizes the control of different drainage conditions of the sample, and provides the basis for the subsequent test work. (2) the dynamic triaxial test of saturated sand under different drainage conditions is carried out by using the dynamic triaxial apparatus. The overpore water pressure development and stress-strain relationship curves of saturated sand samples under different drainage and loading modes were obtained. The experimental results show that with the increase of permeability coefficient ratio, the pore water pressure growth rate of saturated sand samples slows down. Compared with the unidirectional load with the same amplitude, the bidirectional load produces larger plastic deformation, faster development rate of pore water pressure, and the sample is more prone to liquefaction. Under the experimental conditions, the saturated sand samples do not liquefy when the permeability coefficient ratio is greater than 0.54, and when the permeability coefficient ratio is less than 0.17. (3) the dynamic triaxial tests of saturated sandy soils under silt intercalation conditions are carried out, and the different interlayer spacing ratios are obtained. Superpore water pressure development and stress-strain curves of saturated layered sand samples under different drainage conditions. The experimental results show that the pore water pressure accumulation rate decreases with the increase of the interlayer spacing ratio, and the liquefaction strength of the sample increases. The influence of drainage conditions and bidirectional loads on the liquefaction strength of saturated layered sand samples is similar to that of homogeneous sand samples, and the excess pore water pressure develops rapidly under the condition of high permeability coefficient and biaxial loading. (4) the shear tests of saturated sand samples after liquefaction were carried out, and the excess pore water pressure dissipation and deformation curves of saturated sand samples after liquefaction were obtained under different drainage conditions. The experimental results show that the shear modulus of saturated sand increases with the increase of permeability coefficient ratio, that is, with the increase of drainage conditions, the volume shear shrinkage decreases and the shear water absorption effect increases after liquefaction. The shear strength reduction rate of the specimen increases.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU441
本文编号：2417141
[Abstract]:China is an earthquake-prone country. The liquefaction of sandy soil caused by earthquake has always been one of the focal points and hot spots in geotechnical engineering. At present, a lot of achievements have been made on the influencing factors and mechanism of sand liquefaction, which have been widely recognized. Under the action of earthquake, the excess pore water pressure will be produced in the soil body, but the different positions of soil in the actual stratum will be affected by the permeability of adjacent soil layer, which will lead to different drainage conditions, and the different drainage conditions will produce the excess pore water pressure. Dissipation and redistribution have important effects. At present, most of the researches on liquefaction are assumed to be undrained conditions, but the influence of actual drainage conditions on soil liquefaction characteristics has not been fully understood. Based on this, the liquefaction characteristics of saturated sand under different drainage and silt intercalation conditions are studied by dynamic triaxial test in laboratory. (1) A drainage interlayer device with controllable permeability coefficient is designed. The device is placed at the top of the sample, which realizes the control of different drainage conditions of the sample, and provides the basis for the subsequent test work. (2) the dynamic triaxial test of saturated sand under different drainage conditions is carried out by using the dynamic triaxial apparatus. The overpore water pressure development and stress-strain relationship curves of saturated sand samples under different drainage and loading modes were obtained. The experimental results show that with the increase of permeability coefficient ratio, the pore water pressure growth rate of saturated sand samples slows down. Compared with the unidirectional load with the same amplitude, the bidirectional load produces larger plastic deformation, faster development rate of pore water pressure, and the sample is more prone to liquefaction. Under the experimental conditions, the saturated sand samples do not liquefy when the permeability coefficient ratio is greater than 0.54, and when the permeability coefficient ratio is less than 0.17. (3) the dynamic triaxial tests of saturated sandy soils under silt intercalation conditions are carried out, and the different interlayer spacing ratios are obtained. Superpore water pressure development and stress-strain curves of saturated layered sand samples under different drainage conditions. The experimental results show that the pore water pressure accumulation rate decreases with the increase of the interlayer spacing ratio, and the liquefaction strength of the sample increases. The influence of drainage conditions and bidirectional loads on the liquefaction strength of saturated layered sand samples is similar to that of homogeneous sand samples, and the excess pore water pressure develops rapidly under the condition of high permeability coefficient and biaxial loading. (4) the shear tests of saturated sand samples after liquefaction were carried out, and the excess pore water pressure dissipation and deformation curves of saturated sand samples after liquefaction were obtained under different drainage conditions. The experimental results show that the shear modulus of saturated sand increases with the increase of permeability coefficient ratio, that is, with the increase of drainage conditions, the volume shear shrinkage decreases and the shear water absorption effect increases after liquefaction. The shear strength reduction rate of the specimen increases.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU441
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