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饱和砂土在液化状态下呈现出非牛顿流体的特性,而常规动力试验要获得稳定的液化状态比较困难。采用塑料砂和相等密度的氯化钠溶液配制成了有效应力接近于0的饱和悬浮塑料砂试样,基于流体力学低雷诺数绕球流动理论并结合粒子成像测速(PIV)技术,开发了饱和悬浮塑料砂流动特性的试验装置。利用紧贴透明模型箱内壁的半球在饱和悬浮塑料砂中运动时塑料砂颗粒的运动来分析其流动特性,并通过拉力与速度的关系计算饱和塑料悬浮砂的表观黏度。试验结果表明,饱和塑料悬浮砂试样是剪切稀化非牛顿流体,可作为液化砂土的相似材料用于液化问题的研究。基于试验中的细观规律,提出了零速度线、剪切区、剪切角、剪切区高度等实用概念。研究表明,拖球速度对剪切角有重要影响,速度越大,剪切角也越大,相应剪切区也越大。剪切区高度反映了拖球运动方向的影响范围,提出拖球试验中应保持球体形心与边界之间的距离要大于6倍球体直径。分析了拖球试验中的孔洞产生机制,提出在拖球和拖管试验中,应降低拖球的运动速度,以符合低雷诺数绕球(管)流动的基本理论。
Saturated sand exhibits non-Newtonian fluid properties in the liquefied state, whereas it is more difficult to achieve a steady state of liquefaction in conventional dynamic tests. A saturated suspension plastic sand sample with effective stress close to 0 was prepared by using plastic sand and sodium chloride solution of equal density. Based on the low Reynolds number flow around the ball fluid theory and the particle image velocimetry (PIV) Suspension of plastic sand flow characteristics of the test device. The flow characteristics of plastic sand particles were analyzed by using the hemisphere close to the inner wall of the transparent model box during the movement of the plastic sand in the saturated suspension plastic sand. The apparent viscosity of the saturated plastic sand was calculated by the relationship between the tension and the velocity. The test results show that the saturated plastic suspended sand sample is shear thinning non-Newtonian fluid, which can be used as a similar material for liquefied sand for liquefaction research. Based on the microscopic law in the experiment, practical concepts such as zero velocity line, shear zone, shear angle and shear zone height are proposed. Research shows that the drag speed has an important impact on the shear angle, the greater the speed, the greater the shear angle, the greater the corresponding shear zone. The height of the shear zone reflects the influence range of the direction of the dragging motion. It is suggested that the distance between the centroid and the boundary of the sphere should be greater than 6 times the sphere diameter in the dragging test. The mechanism of hole generation in towing test is analyzed. It is suggested that the speed of towing should be reduced in the towing and towing tests to meet the basic theory of low Reynolds number flow around the tube.