宽级配土离心试验地基模型落雨法分层机制与数值模拟

Numerical simulation of layered phenomena and mechanism of wide-graded soil deposits using pluviation method for centrifuge tests

落雨法因其在模型制备过程与自然条件下砂土沉积过程相似,因而成为土工离心试验地基模型常用的模型制备手段,但是有关落雨法研究主要集中于相对密实度控制,而对于分层现象关注较少,尤其宽级配土。针对宽级配土落雨法制备过程出现的分层现象,利用PFC3D数值模拟软件,探讨了落雨法制备过程分层现象的物理机制和出砂口落距、移动速度、宽度对分层现象的影响。结果表明:在真空介质中,粗细颗粒不出现分层现象;而在非真空介质中,粗、细颗粒出现了分层现象,原因为非真空环境下粗、细颗粒下落过程中产生了相对速度差,内在机制为粗、细颗粒半径不同受到平均表面流体阻力不同,从而造成不同粒径颗粒分离现象;随环境介质密度的增加,粗、细颗粒在下落过程中更易于发生分离,出砂口落距、移动速度和流量对分层现象具有一定程度影响。

Because it is similar to the process of sand deposition under natural conditions,the sand pluviation has become a common method of model preparation for foundation models in geotechnical centrifugal tests.However,the researches on the sand pluviation mainly focus on the control of the relative density,and pays little attention to the layered phenomenon of sand,especially for wide-graded soils.Aiming at the layered phenomenon of sand in the preparation process of wide-graded soils by the sand pluviation method,the physical mechanism of layered phenomenon of sand in the process of rain preparation and the influences of falling distance,moving speed and width of sand outlet on the layered phenomenon of sand are discussed by using the PFC3D numerical simulation software.The results show that there is no layered phenomenon of coarse and fine particles in vacuum medium.In the non-vacuum medium,the coarse and fine particles have layered phenomena of sand,because the relative velocity difference occurs during the fall of the coarse and fine particles in the non-vacuum environment.The internal mechanism is that the average surface fluid resistance of the coarse and fine particles is different due to the different radii of the coarse and fine particles,resulting in the separation of particles with different particle sizes.With the increase of the density of the environment medium,the coarse and fine particles are more easily separated during the falling process,and the falling distance,moving speed and flow rate of the sand outlet have a certain influence on the layered phenomenon of sand.