基于超大型三轴仪的堆石料尺寸效应试验研究

Rockfill material is the main building material of geotechnical structures (such as artificial island, roadbed and embankment). The strength and deformation of rockfill material are mainly obtained by conventional triaxial test. Due to the lack of the super large-scale apparatus, the rockfill material commonly used in large civil engineering must be scaled in laboratory test, and the influences of particle size on the strength and deformation are not yet clear. Scale effect is one of the main problems in structural analysis for large civil engineering. In order to solve the problem, the first super large triaxial apparatus (specimen diameter: 800mm, 1000mm) has been built in Dalian University of Technology in China. Combining with a series of the triaxial apparatuses (specimen diameter: 300mm) developed since 1990s, a multiple-scale triaxial research platform with its auxiliary equipment has already been built to provide significant technical support for the deep and systematical research on the scale effect in rockfill material. The boundary effect induced by friction constraints will be found out firstly, and then the scale effect of particle morphology and mechanical characteristics of rockfill material will be revealed. On this basis, the scale effect of shear strength, modulus, particle breakage and dilatancy will be discussed by the relations between the microscopic parameters of the particles and the macroscopic parameters of the fraction. The model parameters of modulus and shear strength will be modified to reflect the scale effect, and more reasonable scaling method and criteria will be proposed to evaluate the scale effect of rockfill material. The research will not only have great importance on providing reliable parameters to conduct numerical simulation for large civil engineering but also provide theoretical basis and experimental data for improving the constitutive model for rockfill material.

堆石料是大型土工构筑物（如人工岛、路基、堤坝等）的主要建筑材料，三轴试验是测试其强度和变形指标最广泛的方法，但由于试验仪器尺寸的限制，堆石料只能大比例缩尺后进行试验研究，对其缩尺前后强度和变形特性的变化规律和机理的认识尚不清楚，一直都是困扰工程设计和安全评价的难题。本项目拟联合申请人近期成功研制的国内第一个超大三轴仪(试样直径800mm、1000mm)和上世纪90年代起研制的大型三轴仪(试样直径300mm)，在探明试样边界约束对变形和强度的影响基础上，揭示堆石料单颗粒形状及其力学特性的尺寸效应，进而阐明堆石料强度、变形模量、颗粒破碎及剪胀特性的尺寸效应机理，建立颗粒细观与粒组宏观参数之间的定量关系以及考虑堆石料尺寸效应的变形和强度参数的修正方法，并提出合理的堆石料缩尺标准和方法。研究成果为发展堆石料本构模型提供理论基础和试验依据，对提高土工构筑物变形预测和安全评价可信度具有十分重要的意义。

筑坝材料的最大粒径可达800~1000mm，然而常规大型三轴仪所允许进行试验的最大粒径仅为60mm，只能进行大比例缩尺后的试验研究，缩尺的比例可达到10倍以上。缩尺后材料力学性质与原型材料的差异（即缩尺效应）一直都是工程和学术界关注的热点。为此，本项目针对堆石料的缩尺效应特性进行了系统性的研究，首先对国内首台超大型三轴仪进行了调试及校准，并提出了超大型三轴试验的具体试验方法，包括超大型三轴试验的制样步骤以及具体试验过程。在此基础上，揭示了堆石料的静动力缩尺效应特性，为构建考虑缩尺效应的本构模型提供了试验依据。最后采用本项目试验成果和发展的计算软件GEODYNA对深厚覆盖层上最高的阿尔塔什面板坝工程的变形进行了预测，与实际监测数据对比表明，基于本项目的考虑缩尺效应的广义塑性模型参数计算结果与实测值在分布规律及量值上均吻合良好，研究成果为解决因传统三轴试验缩尺效应导致的计算误差提供了重要的试验依据。