中文摘要：

砂土等天然颗粒材料具有的剪胀性、压硬性、各向异性等特殊力学性质受控于其内部的微细结构及其演化，如何利用试验与数值模拟等手段对砂土细观组构进行量化，对深入研究砂土变形机制尤为重要。基于数字图像相关方法的光学测量技术与土工试验相结合的新手段，通过对直剪仪的可视化改造，开发了能初步实现土体宏细观力学性状联合测量的“砂土变形细观瞬时光学测量系统”，并利用该系统对福建标准砂进行了室内细观直剪试验。随后进行了基于颗粒流软件PFC2D直剪数值试验，提取室内试验还难以获得的细观信息，作为对室内试验的补充。通过对宏观力学性质和位移场、应变场、颗粒定向、速度场、颗粒配位数和接触力链等细观的室内与数值试验结果进行剖析，探讨了砂土力学性质的细观机制。

英文摘要：

Sand, as a kind of typical natural granular material, its special mechanical behaviors, such as compressive hardening, dilatancy, anisotropy, etc., are controlled by the internal meso-fabric and its evolution. How to quantify the meso-fabric by experiment and numerical simulation is essential to further study the deformation mechanism of sand. The optical measurement technique based on relevant digital image methods is combined with soil test; and then a measuring system named “meso instantaneous optical system for sands deformation”, which can preliminarily achieve the macro-and meso-mechanical behaviors of soil, is developed by visually upgrading the shear box. The laboratory meso-diret-shear tests for Fujian standard sand are carried out by using this system. And then, numerical direct shear tests based on the software of particle flow code in two dimensions （PFC2D）are performed; and some meso-information which are difficultly obtained from laboratory test are extracted as its supplement. The test results of macro-and meso-mechanical behaviors including displacement field, strain field, particle orientation, velocity field, coordination number and force chain are compared and analyzed; and then the meso-mechanism of sand mechanical behavior is further studied.