粗粒土的离心模型试验与数值模拟

岩土工程数值计算中粗粒土常采用邓肯-张本构模型,为了验证该模型在轴向加载、卸载、侧向加载等复杂应力路径条件下的适用性,进行了粗粒土的三轴试验获取其力学特性及本构模型参数;根据相似性原理制作了堆石坝的离心模型试样,并采用与三轴试验同样级配与粒径的粗粒土进行复杂应力路径的堆石坝离心模型试验,试验中通过改变离心加速度模拟加载、卸载,利用上游蓄水模拟坝体的侧向加载;采用ABAQUS对离心模型试验进行三维数值模拟,并研究了模型箱侧壁摩擦系数与土体的初始应力对数值结果的影响。通过比较离心模型试验与数值模拟成果,表明土体的初始弹性模量对计算结果影响较大,初始应力应选择自重作用下的应力场;邓肯-张本构模型能较好地描述堆石坝的加载应力路径,而模拟卸载应力路径有一定的差异,需要改进邓肯-张本构模型中卸载模量的确定方法。

Centrifuge model test and numerical simulation of coarse-grained soil

Duncan-Chang constitutive model is commonly used in the numerical analysis of the geotechnical problems related to coarse-grained soils. To explore the applicability of this model under complex stress path conditions including axial loading, unloading and lateral loading, a series of triaxial tests is conducted on coarse-grained soils to determine their mechanical properties and constitutive parameters. Based on the principle of similarity, the centrifugal models of a rockfill dam are prepared, and the centrifuge model test of a rockfill dam under complex stress path conditions is performed using the coars-grained soil with the same gradation and particle size in triaxial tests. The tests are conducted by changing the centrifugal acceleration to simulate loading and unloading conditions, and using the upstream impoundment to simulate the lateral loading. A three-dimensional numerical analysis of the centrifuge model test is performed using software ABAQUS. The effects of the sidewall friction and the initial stress conditions are studied. It is shown that the initial elastic modulus of soil can significantly influence the calculated results and the initial stress should assume the stress under the action of gravity in numerical simulations. Duncan-Chang constitutive model can better describe the behavious of the coarse-grained soil under the loading stress path than under the unloading stage; and thus the unloading modulus need to be determined with a proper method.