松散土石混合体大变形过程应力及其强度特性的试验研究

The characteristic of loose rock-soil mixture can be summarized as unconsolidated and wide grading, conventional large-size triaxial test and also large-scale direct shear test are not appropriate in getting the stress-strain feature and strength indexes of loose rock-soil mixture, because during test process, confining pressure and axial bias pressure will make the sample consolidated and in direct shear test, the failure surface is artificially determined, the original characteristics can’t be reflected and it will make the test result distortion. So far, there’s no system test method in achieving the mechanical properties of loose rock-soil mixture. Cohesionless rock-soil mixture samples from dump slope are collected to make the research, particle size distribution and fractal geometry index are statistics for the rock-soil mixture on the slope, then, according to these original parameters, the preparation method for loose rock-soil mixture test samples is explored. The control factors of relative density, normal stress level and wet/try status are taken into account, and orthogonal experimental plan is designed, mechanical tests are carried out with large-scale stacked-ring shear apparatus, the stress-strain and strength characteristic of loose rock-soil mixture in large deformation process can be achieved initially. For the feature that the strength of loose rock-soil mixture degradation when it’s immersed by water, based on the precision CT scanning apparatus, a series model tests are conducted, by immersion the slope model of loose rock-soil mixture, the whole deformation and failure process inner the model can be captured, combine with result from stacked-ring shear test, the progressive failure stage for loose rock-soil mixture can be distinguished and defined. After that, with the mechanical tests data and CT scanning visualization image, we will use 3D particle flow numerical method to reappear mechanical tests process for its advantage in parallel comparison and repeatability, it’s effective way to explain the law of stress-strain and also the evolution of mechanical chains among particles in large-deformation. The research will provide a reference in improving research method for the mechanical properties of loose rock-soil mixture.

松散土石体具有弱固结、宽级配等特性，常规大三轴和大型直剪试验因存在围压(偏压)固结和破坏面固定等问题，不能很好遵循和反映试样原始特性，导致试验成果失真，目前尚无系统针对松散土石体力学特性研究的测试方法。以排土场无黏性松散土石体为研究对象，对坡面土石体颗粒级配和分形指标进行统计，并以此基准探索松散土石体室内试样制备方法。以相对密度、法向力和干湿状态为控制因素，基于大型叠环式剪仪设计正交试验，研究松散土石体大变形过程强度及应力变化规律。考虑其浸水劣化之特性，依托高精度CT仪开展模型试验，以浸水淹没方式动态捕捉大变形破坏过程试样内部结构演化特性，结合叠环剪试验成果，划分松散土石体渐进破坏阶段。后由CT可视化成果及试样物性指标，开展3D颗粒流数值试验，复现力学试验过程并进行延伸，深入诠释松散土石体强度、应力变形规律以及大变形过程颗粒力链传递规律。研究成果可为完善松散土石体力学特性研究方法提供参考。

松散土石（混合）体具有弱固结、宽级配等特性。常规粗粒土试验过程中诸如击实、固结等对其原始结构特性破坏大，导致室内试验难以客观、真实和全面的反映松散土石体的工程力学特性，特别是大变形过程中的应力变形特性。本课题从探索室内标准化制备松散土石体试样和土石（混合）体无损试验方法两方面入手，结合实际工程中采集的试样，对土石（混合）体开展了一系列的叠环式剪切试验、CT扫描试验以及有限元和颗粒流数值试验，深入研究了松散土石体的水敏感性、大变形过程与演化规律。研究成果可为研究松散土石（混合）体的变形破坏发展过程提供科学依据。主要研究成果如下：.（1）以某高速公路强~中风化板岩开挖料为研究对象，探索出一种室内标准化制备松散土石体试样的方法；用大型叠环剪切试验仪，对三种不同松散状态试样（Dr取0.30，0.35和0.40），在干燥、湿润（表面湿润但孔隙无明水）和浸水三种状态下对其强度指标进行测试。结果表明：松散土石体在干燥状态内摩擦角小于14°，而在湿润或浸没时，其内摩擦角将进一步下降至11°左右。叠环式剪切试验能够较好的诠释土石体在松散状态下低强度和水敏感特性；通过采集剪切过程中不同层位叠环变形数据，全面获取了松散土石体大变形破坏过程剪切带发展和演化规律。.（2）选取某滑坡饱和松散滑带土（低含石量土石混合体）开展研究，探索得到力学试验—CT扫描—数值试验相结合的研究方法，达到了对松散土石混合体进行无损试验并获取力学参数的目的，并为深入研究松散土石混合体（泥石流体）应力变形特性提供了便利。.（3）通过松散土石体CT三轴试验和颗粒流数值试验研究认为：结构的不稳定性是松散土石体的显著特征，无法像密实状态土石体那样形成稳定发展的力链结构直至破坏，这也是其试样制备困难以及力学特性测试复杂的原因之一。