桩-土界面扭剪剪切与直剪剪切的差异性研究
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摘要
直剪试验在剪切过程中桩-土的剪切面积逐渐减小,导致垂直应力发生偏心,剪应力不能保持均匀分布,并不能反映土体的实际软弱剪切面,而扭转剪切能够保持剪切过程中桩-土的接触面积始终不变,避免了垂直应力发生偏心。针对新出现的界面扭剪试验和常规直剪试验在桩-土界面研究中的差异,探讨了两种剪切方式下的桩-土界面的摩擦特性,设计了桩-土界面摩擦单元,并基于相同剪切速率和桩-土界面接触条件,进行不同含水率和法向应力下的扭剪试验和直剪试验。试验结果表明扭剪和直剪试验的不同之处为:(1)扭转剪切的桩-土界面剪切强度为直剪剪切强度的1.5～2.1倍,扭剪剪切的剪应力达到最大值后会呈现出不同程度的软化或保持基本不变,而直剪剪切的剪应力表现为硬化趋势;(2)同一法向应力下,随着含水率的增加,扭剪试验的极限剪切位移逐渐增加而直剪试验的极限剪切位移呈现出微弱的降低;(3)直剪剪切界面摩擦角明显低于同条件下扭剪剪切的界面摩擦角。试验结果可以为桩-土界面研究中扭剪试验和直剪试验剪切强度的转换提供参考。
The shear stress of the pile-soil decreases during the shearing test, resulting in the eccentricity of the vertical stress, the shear stress can not be evenly distributed, and can not reflect the actual weak shear surface of the soil, and the torsional shear can be maintained During the shearing process, the contact area of the pile-soil is always the same, which avoids the eccentricity of the vertical stress. In this paper, the friction characteristics of pile-soil interface under two kinds of shear modes are discussed in view of the differences in the intermittent torsional shear test and the conventional direct shear test. Torsional shear test and direct shear test under different water content and normal stress were carried out based on the same shear rate and pile-soil interface contact conditions. The results show that the torsional shear and the direct shear test are as follows: 1) The shear strength of the pile-soil interface is 1.5～2.1 times of the shear shear strength, and the shear stress of the torsional shear reaches the maximum 2) Under the same normal stress, with the increase of water content, the ultimate shear displacement of the torsional shear test is gradually increasing, and the shear stress of the shear shear is shown in the same direction. And the friction shear angle of the shear shear interface is significantly lower than that of the torsional shear under the same conditions. The test results can provide a reference for the torsional shear test and the shear strength of the shear shear test in the pile-soil interface study.
The shear stress of the pile-soil decreases during the shearing test, resulting in the eccentricity of the vertical stress, the shear stress can not be evenly distributed, and can not reflect the actual weak shear surface of the soil, and the torsional shear can be maintained During the shearing process, the contact area of the pile-soil is always the same, which avoids the eccentricity of the vertical stress. In this paper, the friction characteristics of pile-soil interface under two kinds of shear modes are discussed in view of the differences in the intermittent torsional shear test and the conventional direct shear test. Torsional shear test and direct shear test under different water content and normal stress were carried out based on the same shear rate and pile-soil interface contact conditions. The results show that the torsional shear and the direct shear test are as follows: 1) The shear strength of the pile-soil interface is 1.5～2.1 times of the shear shear strength, and the shear stress of the torsional shear reaches the maximum 2) Under the same normal stress, with the increase of water content, the ultimate shear displacement of the torsional shear test is gradually increasing, and the shear stress of the shear shear is shown in the same direction. And the friction shear angle of the shear shear interface is significantly lower than that of the torsional shear under the same conditions. The test results can provide a reference for the torsional shear test and the shear strength of the shear shear test in the pile-soil interface study.
引文
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[2] Clough G W,Duncan J M.Finite element analyses of retaining wall behavior.Journal of Soil Mechanic and Foundation Division,ASCE,1971,97(12):1657-1673.
[3] 龚辉,赵春风,陶帼雄,等.应力历史对黏土-混凝土界面剪切特性的影响研究[J].岩石力学与工程学报,2011,30(8):1712-1719.
[4] 李永辉,王卫东,黄茂松,等.超长灌注桩桩-土界面剪切试验研究[J].岩土力学,2015,(07):1981-1988.
[5] 卢廷浩,王伟,王晓妮.土与结构接触界面改进直剪试验研究[J].沈阳建筑大学学报(自然科学版),2006,(01):82～85.
[6] 胡黎明,马杰,张丙印,等.粗粒料与结构物接触面力学特性缩尺效应[J].清华大学学报(自然科学版),2007,(03):327-330.
[7] 俞培基,秦蔚琴.在共振柱仪上研究接触面的动力变形特性[J].水利学报,1995,(01):81-85.
[8] 尚文昌,刘俊伟,李晓玲,等.桩-土界面剪切机理试验研究进展及新型界面剪切仪的研制[J].青岛理工大学学报,2016,(02):8-12.
[9] SHAHROUR I,REZAIE F.An elastoplastic constitutive relation for the soil-structure interface under cyclic loading[J].Computers and Geotechnics,1997,21(1):21-39.
[10] 殷宗泽,朱泓,许国华.土与结构材料接触面的变形及其数学模拟[J].岩土工程学报,1994,(03):14-22.
[11] Yin Z Z,Zhu H,Xu G H.A Study of deformation in the interface between soil and concrete.Computers and Geotechnics,1995,17:75-92.
[12] 李立云,杜修力,李亮.土与结构界面接触问题研究进展评述[J].力学进展,2009,(05):588-597.