含预制双裂纹试样岩桥贯通模式的数值研究

Numerical study on coalescence mode of rock bridge with double parallel pre-existing cracks

当双裂纹岩体破坏时,不同裂纹之间的应力场会相互作用,岩桥区域会发生贯通。将应变强度准则嵌入到二次开发的扩展离散元UDEC中,模拟了含预制双裂纹试样的拉伸裂纹及剪切裂纹的扩展。数值模拟结果发现双裂纹试样在单轴压缩过程中会出现4种岩桥基本贯通模式:(1)伴随着2条预制裂纹尖端的翼裂纹独立逐渐扩展,但岩桥区域不发生贯通的不贯通模式;(2)在岩桥区域内,主应力场及切应力场集中,产生剪切裂纹贯通岩桥,切应力对贯通起主导作用的剪切贯通模式;(3)在岩桥区域内,主应力场高度集中,岩桥贯通具有瞬时性,拉伸裂纹贯通岩桥的拉伸贯通模式;(4)在拉力与剪力共同作用下,试样达到强度最高峰值后产生的拉剪混合贯通模式。通过与室内试验对比,将应变强度准则运用到数值模拟分析中可以更准确描述细观破坏时应力应变及岩桥贯通的变化,丰富了多裂纹岩样在细观力学中的贯通机理,为研究岩体细观破坏提供数值模拟参考。

In the failure process of rock specimen with double cracks,the stress field between different cracks will interact,and the rock bridge area will coalesce.In the research,the strain strength criterion was embedded into the expanded discrete element program UDEC,which was secondarily developed to simulate the propagation of tensile crack and shear crack of specimens with prefabricated double cracks.According to the results of the numerical simulation,four basic coalescence modes of rock bridges will appear in the double-crack specimen during uniaxial compression:(1)Non-coalescence mode:the wing cracks at the tips of the two prefabricated cracks gradually expand independently,but the discontinuous mode of penetration does not occur in the rock bridge area;(2)Shear coalescence mode:in the rock bridge area,the main stress field and the shear stress field are concentrated,resulting in shear cracks coalescence in the rock bridge.At this time,the shear stress plays a leading role in the shear coalescence mode;(3)Tensile coalescence mode:tensile cracks penetrate the rock bridge,and the rock bridge is highly concentrated by the principal stress field.At this time,the rock bridge penetration has the characteristics of instantaneousness,and the tensile crack penetrates the tensile coalescence mode of the rock bridge;(4)Mixed coalescence mode:under the combined action of tensile force and shear force,the rock bridge gets the mixed tensile and shear coalescence mode after the specimen reaches the highest peak strength.Through comparison with laboratory tests,it is concluded that applying the strain strength criterion to the numerical simulation analysis can more accurately describe the changes of stress and strain and the penetration of rock bridges during mesoscopic failure,and enrich the mechanism penetration of multi-crack rock specimen in mesomechanics.The research provides a reference for numerical simulation in studying the actual engineering of rock mass meso-damage.