【摘要】：地裂縫是彎曲力與剪切力共同作用的結果,剪性裂縫的產生受土體的抗剪強度的影響,而土體的抗剪強度又與其剪切速率有關。另一方面,與通常建筑荷載作用相比,地下水開采引起土中應力的變化較為緩慢。因此,研究剪切速率對土體抗剪強度的影響,對于地下水開采引起的地裂縫形成機理的研究有重要的意義。本文研究了重塑飽和黏性土在正常固結及超固結狀態(tài)下,直剪儀剪切速率分別為0.02、0.1、0.5、0.8和2.4 mm/min時,剪切位移-剪應力曲線及抗剪強度變化情況。結果表明,剪切速率對剪切位移-剪應力曲線影響明顯,而且對抗剪強度參數,如內摩擦角、黏聚力、殘余內摩擦角、殘余黏聚力影響也較為明顯。對于正常固結土,剪切位移-剪切應力曲線近似為雙曲線,而且擬合良好。初始勁度系數隨著剪切速率的增大而增大,峰值應力隨著剪切速率的增大而減小。對強度參數分析,內摩擦角隨著剪切速率的增大而減小,在不同密度條件下,密度越大,內摩擦角受剪切速率影響作用越明顯。直剪試驗土樣的破壞面形狀受剪切速率的影響,剪切速率越大,破壞剪切面越平整,剪切速率越小,破壞剪切面越粗糙。剪切面越平整,在滑動過程中摩擦系數相對偏小,對應的峰值剪應力越小。剪切面越粗糙,在滑動過程中摩擦系數相對較大,對應的峰值應力越大。對于超固結比為2、3的超固結土樣,剪切位移-剪應力曲線的初始勁度系數隨剪切速率的影響較小,峰值應力隨著剪切速率的增大而減小。剪切速率影響剪切位移-剪應力曲線進而影響強度參數,OCR=3時,內摩擦角隨剪切速率呈隨機性變化,變化范圍較小,黏聚力隨著剪切速率的增大而增大,殘余內摩擦角及殘余黏聚力隨著剪切速率而呈現隨機性變化。剪切速率影響超固結土的剪縮性,在相同法向應力作用下,剪切速率越大,豎向位移越小,表現出明顯的剪縮特性,剪切速率越小,剪縮性越明顯。本文結合Goodman無厚度接觸面單元,利用剪切位移-剪應力曲線的雙曲線模型,推出了基于剪切速率的切線剪切勁度系數公式,為有限元數值模擬提供理論支持。
[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.
【學位授予單位】：南京大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TU411.7

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