Numerical analysis of the failure process of soil-rock mixtures through computed tomography and PFC3D models

Soil-rock mixture （SRM） is a unique type of geomaterial characterized by a heterogeneous composition and a complicated structure. It is intractable for the continuum-based soil and rock mechanics theories to accurately characterize and predict the SRM＇s mechanical properties. This study reports a novel numerical method incorporating microfocus computed tomography and PFC3D codes to probe the deformation and failure processes of SRM. The three-dimensional （3D） PFC models that represent the SRM＇s complex structures were built. By simulating the entire failure process in PFC3D, the SRM＇s strength, elastic modulus and crack growth were obtained. The influence of rock ratios on the SRM＇s strength, deformation and failure processes, as well as its internal mesoscale mechanism, were analyzed. By comparing simulation results with experimental data, it was verified that the 3D PFC models were in good agreement with SRM＇s real structure and the SRM＇s compression process, deformation and failure patterns; its intrinsic mesomechanism can be effectively analyzed based on such 3D PFC models.

Mechanical Properties of Soil-Rock Mixture Filling in Fault Zone Based on Mesostructure

Soil-rock mixture(SRM)filling in fault zone is an inhomogeneous geomaterial,which is composed of soil and rock block.It controls the deformation and stability of the abutment and dam foundation,and threatens the long-term safety of high arch dams.To study the macroscopic and mesoscopic mechanical properties of SRM,the development of a viable mesoscopic numerical simulation method with a mesoscopic model generation technology,and a reasonable parametric model is crucially desired to overcome the limitations of experimental conditions,specimen dimensions,and experiment fund.To this end,this study presents a mesoscopic numerical method for simulating the mechanical behavior of SRM by proposing mesoscopic model generation technology based on its mesostructure features,and a rock parameter model considering size effect.The validity and rationality of the presented mesoscopic numerical method is experimentally verified by the triaxial compression tests with different rock block contents(RBC).The results indicate that the rock block can increase the strength of SRM,and it is proved that the random generation technique and the rock parameter model considering size effect are validated.Furthermore,there are multiple failure surfaces for inhomogeneous geomaterial of SRM,and the angle of the failure zone is no longer 45◦.The yielding zones of the specimen are more likely to occur in thin sections of soil matrix isolated by blocks with the failure path avoiding the rock block.The proposed numerical method is effective to investigate the meso-damage mechanism of SRM.

Numerical study of soil-rock mixture:Generation of random aggregate structure

The soil-rock mixture(SRM) is highly heterogeneous. Before carrying out numerical analysis,a structure model should be generated. A reliable way to obtain such structure is by generating random aggregate structure based on random sequential addition(RSA). The classical RSA is neither efficient nor robust since valid positions to place new inclusions are formulated by trial, which involves repetitive overlapping tests. In this paper, the algorithm of Entrance block between block A and B(EAB)is synergized with background mesh to redesign RSA so that permissible positions to place new inclusions can be predicted,resulting in dramatic improvement in efficiency and robustness.

基于大型直剪试验的土石混合体剪切带变形特征试验研究

土石混合体介质具有高度非均质性、显著的结构效应与尺寸效应等特点,这使其物理力学特性及其复杂。本文针对土石混合体在剪切过程中剪切带的变形性状与影响因素,采用自主研发的RSM–1000型电机伺服控制大型土工抗剪强度试验系统,考虑不同含石量(0,30%,50%,70%)、上覆压力(50,200,300,400 k Pa)、块石尺寸(L1,L2,L3)3个主要结构控制因素,进行土石混合体剪切变形试验,通过在试样内部钻孔设置铝丝与干灰的方法,监测剪切带特征变化规律。研究结果表明:当含石量小于30%时,块石对试样的变形影响较小,强度主要依赖于砂土强度;当含石量达到50%时,试样内已形成骨架结构,变形受块石的影响突显,强度由块石和砂土共同作用;当含石量达到70%时,试样内已形成块石架空结构。在高含石量与大粒径块石条件下,含贯穿剪切面的块石试样随剪切变形发展,块石发生挤压、翻转现象;剪切面附近分布块石的试样,随剪切变形发展,块石以剪胀作用为主,块石发生挤压、棱角剪断与错动重分布。试样的剪切变形现象可类比由后向前变形的推移式滑坡或由前后向中间变形的复合式滑坡的破坏特征,即后缘坡顶在主动土压力作用下产生裂隙,随之下沉挤密、失稳起滑;前缘坡脚蠕滑变形推移;坡中岩土体发生剪切错动至滑动面渐进扩展破坏,最终剪切面贯通,形成整体破坏。该研究成果对揭示土石混合体滑坡剪切带形成演化规律、破坏模式及土石混合体滑坡的防灾减灾具有重要意义。