FFP在黏土中贯入过程的CFD模拟  

CFD SIMULATION ON THE PENETRATION OF FFP INTO UNIFORM CLAY

作　　者：刘君[1] 张雨勤 Liu Jun;Zhang Yuqin(State Key Laboratory of Coastal and Offshore Engineering,Dalian University of Technology,Dalian 116024,China)

机构地区：[1]大连理工大学海岸与近海工程国家重点实验室,大连116024

出　　处：《力学学报》2018年第1期167-176,共10页Chinese Journal of Theoretical and Applied Mechanics

基　　金：国家自然科学基金资助项目(51479027;51539008)

摘　　要：圆锥静力触探法(cone penetration test,CPT)广泛应用于土的抗剪强度测试中.在此基础上发展的自由落体式贯入仪(free fall penetrometer,FFP),依靠自由下落获得的动能和自身重力势能贯入土中,不需要借助外部加载装置,提高其使用的便捷性.但在动力贯入过程中FFP与土的相互作用更为复杂,涉及到土体的率效应和拖曳阻力等的影响.因此,对FFP各项受力和相关参数的准确分析有助于提高其实用性以及测量的准确性.作者采用基于计算流体动力学(computational fluid dynamics,CFD)的分析软件ANSYS CFX 17.0模拟FFP在均质黏土中的贯入过程,借助动网格的大变形分析方法模拟FFP贯入过程中的运动边界问题.提出了薄层单元法模拟FFP与土体的界面摩擦接触行为.在CFD模拟中,土体材料采用非牛顿流体来模拟,其剪切强度受土体切应变率的影响(即土体的率效应).通过模拟贯入仪以不同的速度在黏土中贯入的过程,研究FFP的端部阻力和侧壁阻力与贯入速率、土体强度和密度、界面摩擦系数以及率效应参数之间的关系,建立了端部承载力系数、端部和侧壁率效应参数及拖曳系数的表达式,并提出了土体不排水抗剪强度的预测方法,为FFP测试数据的解析提供依据.The cone penetration test(CPT)has been widely used to measure the soil undrained shear strength.On the basis of CPT,the free fall penetrometer(FFP)is developed to improve the test efficiency,which penetrates into soil by its kinetic energy gained from free fall in the water/air column and potential energy.However,the soil-FFP interaction is rather complex,which refers to the shear strain rate effect and drag force.Therefore,it is necessary to analyze the forces acting on the FFP accurately to improve its practicability and the accuracy of soil strength measurement.The FFP penetration procedure in uniform soils was simulated in the present study by using the commercial software ANSYS CFX 17.0,which is based on the computational fluid dynamics(CFD)approach.The dynamic mesh approach was applied to simulate the moving boundary.The thin layer element method was proposed to simulate the FFP-soil interaction.In the CFD simulation,the soil was modeled as non-Newtonian fluid and the shear strain rate effect was considered.Different FFP velocities,soil strengths and densities,interface frictional coefficients and shear strain rate parameters were considered to investigate their effects on the bearing and sleeve resistances of FFP.The fitted formulas of the cone bearing capacity factor,the strain rate parameters and drag coefficients for the cone and sleeve were established based on the present numerical results.In addition,the process to estimate the undrained shear strength of clayed soils was put forward,which may be beneficial for analyzing the recorded data from FFP.

关 键 词：自由落体式贯入仪 土体率效应 拖曳阻力 承载力系数 土性测试 计算流体动力学 

分 类 号：TU470.3[建筑科学—结构工程]