考虑颗粒破碎后堆石料的临界状态特性与边界面本构模型研究

A large number of high earth-rockfill dams are currently under construction or to be constructed in the western part of China. These dams may be subjected to combined loading from earthquake and water reserved behind the dam, which may lead to particle breakage of rockfill material with its gradation changed. The potential influence of such particle breakage and gradation change on the stress-strain behaviors of rockfill material is becoming an area of much research interest. A series of specimen vibration tests will be carried out in this research project to investigate the particle breakage behaviors of soil specimens prepared using various vibration loads and frequencies. Large-scale triaxial compression tests will also be conducted to examine the stress-strain behaviors of those specimens after vibration tests. Experimental results are expected to illustrate the effect of the particle breakage on soil’s critical state line. The breakage index will then be incorporated into soil’s critical state equations. With that, a three-dimensional breakage-dependent critical state surface will be proposed for rockfill material. In line with the change of critical state surface, the dilatancy equation and plastic modulus has to be modified. These will eventually lead to a development of new constitutive model of rockfill material in the framework of bounding surface plasticity. Moreover, a subroutine will be developed to code the newly developed model into finite element software. Its application will be exemplified through numerically modelling an actual rockfill dam to investigate its deformation and stability. The findings generated from this research project can play a useful role in illustrating the deformation mechanism of rockfill material after particle breakage and ensuring the stability of the dam during its later operation.

我国西部地区正在规划和建设一大批高土石坝，这些高土石坝将面临强震和高压力作用，从而引起坝体中的堆石料产生颗粒破碎，进而导致堆石料的级配曲线发生较大变化，而这种变化对堆石料的应力变形特性以及对坝体后期运行的影响是一个值得深入研究的课题。本项目拟通过试样振捣试验和大型三轴剪切试验，研究试样制备过程中不同振捣荷载和频率下的破碎率和破碎后试样的应力变形特性；根据试验结果研究破碎量对临界状态线的影响，并将破碎指标引入到临界状态线方程中，提出一种与破碎相关的三维临界状态面；在边界面塑性理论框架下，依据所提出的与破碎相关的三维临界状态面，修正剪胀方程和塑性模量，建立边界面本构模型；将该模型开发到有限元程序中，结合土石坝实际工程构建数值分析模块，分析土石坝震后的变形和稳定性。研究成果对阐明破碎后堆石料的变形特性及揭示其力学机理具有重要的理论意义，对评价颗粒破碎后坝体后期运行稳定性问题具有重要的实际意义。

采用试验研究及理论研究等研究方法，对高土石坝材料—堆石料在复杂应力条件下强度变形特性和颗粒破碎特性开展了系统的研究，在临界状态理论及状态相关塑性理论框架下，建立了考虑颗粒破碎的堆石料本构模型。主要取得的成果包括：依托高土石坝实体工程，选取典型筑坝堆石料开展了大型三轴剪切试验研究，研究了初始比容对于临界状态线位置的影响；堆石料内部孔隙变化主要是颗粒的相互运动和颗粒本身的破碎，针对堆石料等大颗粒破碎特点，提出了一个新的相对破碎指标；针对粗粒料在压缩和剪切过程中产生颗粒破碎导致粗粒料临界状态线向下移动的特点，提出了三维临界状态面，建立了考虑颗粒破碎的状态参数；结合剪胀方程的基本条件，提出了考虑颗粒破碎和状态相关的剪胀方程，建立了考虑颗粒破碎的堆石料状态相关塑性本构模型；基于分数阶微积分理论，对于在循环荷载下的粗粒土力学特性，提出了适用于粗粒土的分数阶本构模型；基于能量守恒理论，开展了粗粒土的剪胀和能量耗散的研究，提出了一个考虑颗粒破碎的塑性流动法则，得到了粗粒土能量耗散的变化规律；统一了边界面塑性模型在二维应力空间和三维应力空间中的塑性模量参数，使其对于同种材料塑性模量参数保持一致；开展了堆石料真三轴试验，研究了中主应力比对于临界状态线的影响，建立了关于中主应力比的三维临界状态面；针对目前常用的剪胀方程不能用于一般应力状态，提出了堆石料的三维应力剪胀方程；针对两种不同的堆石料，提出了考虑中主应力比和初始围压的非线性回归模型；同时研究了不同剪切模式对于堆石料强度-剪胀关系的影响。本项目的研究成果对阐明破碎后堆石料的变形特性及揭示其力学机理具有重要的理论意义。