直剪试验剪切速率对黏性土强度影响试验研究
发布时间：2018-12-06 17:49
【摘要】：地裂缝是弯曲力与剪切力共同作用的结果,剪性裂缝的产生受土体的抗剪强度的影响,而土体的抗剪强度又与其剪切速率有关。另一方面,与通常建筑荷载作用相比,地下水开采引起土中应力的变化较为缓慢。因此,研究剪切速率对土体抗剪强度的影响,对于地下水开采引起的地裂缝形成机理的研究有重要的意义。本文研究了重塑饱和黏性土在正常固结及超固结状态下,直剪仪剪切速率分别为0.02、0.1、0.5、0.8和2.4 mm/min时,剪切位移-剪应力曲线及抗剪强度变化情况。结果表明,剪切速率对剪切位移-剪应力曲线影响明显,而且对抗剪强度参数,如内摩擦角、黏聚力、残余内摩擦角、残余黏聚力影响也较为明显。对于正常固结土,剪切位移-剪切应力曲线近似为双曲线,而且拟合良好。初始劲度系数随着剪切速率的增大而增大,峰值应力随着剪切速率的增大而减小。对强度参数分析,内摩擦角随着剪切速率的增大而减小,在不同密度条件下,密度越大,内摩擦角受剪切速率影响作用越明显。直剪试验土样的破坏面形状受剪切速率的影响,剪切速率越大,破坏剪切面越平整,剪切速率越小,破坏剪切面越粗糙。剪切面越平整,在滑动过程中摩擦系数相对偏小,对应的峰值剪应力越小。剪切面越粗糙,在滑动过程中摩擦系数相对较大,对应的峰值应力越大。对于超固结比为2、3的超固结土样,剪切位移-剪应力曲线的初始劲度系数随剪切速率的影响较小,峰值应力随着剪切速率的增大而减小。剪切速率影响剪切位移-剪应力曲线进而影响强度参数,OCR=3时,内摩擦角随剪切速率呈随机性变化,变化范围较小,黏聚力随着剪切速率的增大而增大,残余内摩擦角及残余黏聚力随着剪切速率而呈现随机性变化。剪切速率影响超固结土的剪缩性,在相同法向应力作用下,剪切速率越大,竖向位移越小,表现出明显的剪缩特性,剪切速率越小,剪缩性越明显。本文结合Goodman无厚度接触面单元,利用剪切位移-剪应力曲线的双曲线模型,推出了基于剪切速率的切线剪切劲度系数公式,为有限元数值模拟提供理论支持。
[Abstract]:The ground crack is the result of bending force and shear force. The shear crack is affected by the shear strength of soil, and the shear strength of soil is related to the shear rate. On the other hand, the variation of soil stress caused by groundwater mining is slower than that of normal building loads. Therefore, it is of great significance to study the influence of shear rate on the shear strength of soil, and to study the formation mechanism of ground fissure caused by groundwater exploitation. In this paper, the shear displacement-shear stress curve and shear strength of remolded saturated clay under normal and overconsolidated conditions are studied when the shear rates of the direct shear apparatus are 0.02 ~ 0.1 ~ 0.50.0.8 and 2.4 mm/min, respectively. The results show that the shear rate has an obvious effect on the shear displacement-shear stress curve, and the influence of the shear strength parameters, such as the angle of internal friction, the cohesion force, the residual internal friction angle, and the residual cohesion force, is also obvious. For normal consolidated soil, the shear displacement-shear stress curve is approximately hyperbolic and fitted well. The initial stiffness coefficient increases with the increase of shear rate, and the peak stress decreases with the increase of shear rate. For the strength parameter analysis, the internal friction angle decreases with the increase of the shear rate, and the higher the density is, the more the internal friction angle is affected by the shear rate under different density conditions. The shape of failure surface of direct shear test soil is affected by shear rate. The larger the shear rate is, the more flat the failure surface is, the smaller the shear rate is, and the rougher the failure shear surface is. The more flat the shear plane is, the smaller the friction coefficient is and the smaller the peak shear stress is. The more rough the shear surface is, the larger the friction coefficient is and the greater the corresponding peak stress is during the sliding process. For the overconsolidated soil samples with an overconsolidation ratio of 2 ~ 3, the initial stiffness coefficient of the shear displacement-shear stress curve has little effect on the shear rate, but the peak stress decreases with the increase of the shear rate. The shear rate affects the shear displacement-shear stress curve and then the strength parameter. At OCR= 3, the angle of internal friction changes randomly with the shear rate, and the range of variation is small, and the cohesive force increases with the increase of shear rate. The residual internal friction angle and residual cohesion change randomly with shear rate. The shear rate affects the shear shrinkage of overconsolidated soil. Under the same normal stress, the larger the shear rate, the smaller the vertical displacement, and the more obvious the shear shrinkage is, the smaller the shear rate is, the more obvious the shearing shrinkage is. By using the hyperbolic model of shear displacement-shear stress curve, a tangent shear stiffness coefficient formula based on shear rate is presented in this paper, which provides theoretical support for finite element numerical simulation.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU411.7
本文编号：2366419
[Abstract]:The ground crack is the result of bending force and shear force. The shear crack is affected by the shear strength of soil, and the shear strength of soil is related to the shear rate. On the other hand, the variation of soil stress caused by groundwater mining is slower than that of normal building loads. Therefore, it is of great significance to study the influence of shear rate on the shear strength of soil, and to study the formation mechanism of ground fissure caused by groundwater exploitation. In this paper, the shear displacement-shear stress curve and shear strength of remolded saturated clay under normal and overconsolidated conditions are studied when the shear rates of the direct shear apparatus are 0.02 ~ 0.1 ~ 0.50.0.8 and 2.4 mm/min, respectively. The results show that the shear rate has an obvious effect on the shear displacement-shear stress curve, and the influence of the shear strength parameters, such as the angle of internal friction, the cohesion force, the residual internal friction angle, and the residual cohesion force, is also obvious. For normal consolidated soil, the shear displacement-shear stress curve is approximately hyperbolic and fitted well. The initial stiffness coefficient increases with the increase of shear rate, and the peak stress decreases with the increase of shear rate. For the strength parameter analysis, the internal friction angle decreases with the increase of the shear rate, and the higher the density is, the more the internal friction angle is affected by the shear rate under different density conditions. The shape of failure surface of direct shear test soil is affected by shear rate. The larger the shear rate is, the more flat the failure surface is, the smaller the shear rate is, and the rougher the failure shear surface is. The more flat the shear plane is, the smaller the friction coefficient is and the smaller the peak shear stress is. The more rough the shear surface is, the larger the friction coefficient is and the greater the corresponding peak stress is during the sliding process. For the overconsolidated soil samples with an overconsolidation ratio of 2 ~ 3, the initial stiffness coefficient of the shear displacement-shear stress curve has little effect on the shear rate, but the peak stress decreases with the increase of the shear rate. The shear rate affects the shear displacement-shear stress curve and then the strength parameter. At OCR= 3, the angle of internal friction changes randomly with the shear rate, and the range of variation is small, and the cohesive force increases with the increase of shear rate. The residual internal friction angle and residual cohesion change randomly with shear rate. The shear rate affects the shear shrinkage of overconsolidated soil. Under the same normal stress, the larger the shear rate, the smaller the vertical displacement, and the more obvious the shear shrinkage is, the smaller the shear rate is, the more obvious the shearing shrinkage is. By using the hyperbolic model of shear displacement-shear stress curve, a tangent shear stiffness coefficient formula based on shear rate is presented in this paper, which provides theoretical support for finite element numerical simulation.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU411.7
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