堆积体直剪试验颗粒流细观数值模拟研究

作为一种非均匀、非均质、多相体系的松散岩土介质,堆积体力学性质的研究颇受国内外众多学者关注和重视。以室内重塑样直剪试验结果为依据,可确定基于现场试验颗粒粒度累积曲线和三维颗粒离散元方法建立的堆积体直剪试验模型土石颗粒细观力学参数。在此基础上进行不同岩性、不同含石量的堆积体直剪试验模拟研究,结果表明:堆积体直剪试验剪切屈服面并非一个平面,而是存在一个带内变形以设计剪切平面为基准呈S形变化的剪切带,块石最大粒径越大剪切面影响范围越广,块石刚度越大剪切面则越粗糙;介质抗剪切强度特性在很大程度上受控于岩块的含量和岩性,块石和块石间的咬合力是造成介质内摩擦角较高的根源;在高围压下介质特性表现为应变硬化、低剪胀率,但不排除表现为剪缩的可能,而在低围压下则容易发生剪胀、软化现象,这与重塑样试验结果基本一致;颗粒摩擦系数与含石量呈二次抛物线递增关系,但剪切过程中应变能随摩擦能增加先升后降;黏聚力随基质颗粒刚度增加而提高,而随充填介质颗粒刚度增加而降低;数值试验与室内试验吻合程度较好表明,该方法可作为工程堆积体确定力学参数的有益补充。

Meso-mechanics research of direct shear test on outwash depositswith PFC method

As an unconsolidated geotechnical media with non-uniform, heterogeneity and multiphase characteristics, the research for mechanical properties of outwash deposits are concerned by scholars. According to the results of direct shear tests on remodeling samples, the soil particle parameter of outwash deposit direct shear tests model based on accumulation curve of particle sizes from tests in situ and 3D discrete element method is established. The results show that the yield surface in tests of outwash deposits is not a flat surface, but a shear band with inner deformation and changes as "S" shape according to the designated shear surface. The greater the maximum diameter is, the wider the shear range is. The shear strength of this media is largely controlled by rock properties and content; the bite force between rocks is the root reason of bigger friction angle. It also indicates that the media presents strain hardening, low shear dilatation rate in high confining pressure and shear contraction probably, it is easy to behave shear dilatation and strain softening in the low confining pressure, which is similar to the test results of remodeling samples. Friction coefficient of particles and rock content approximately presents a increasing relationship of second-degree parabola, but strain energy first increases and then drops with the increasing of frictional energy. In addition, the cohesion will increases with soil stiffness increasing while decrease with rock stiffness increasing. In short, numerical tests coincide with the indoor tests, which indicate that this method can be a beneficial supplement to determine the parameters of engineering deposit body.