大理岩孔道试样的强度及变形特性的试验研究

利用中晶和细晶两种大理岩的不同内径孔道大理岩试样,在内孔压力为0时进行常规三轴压缩试验,分析试样内非均匀应力分布对试样承载能力和变形特性的影响。孔道试样的变形特征在轴向变形较小时与完整试样大致相同;在变形较大时孔壁附近材料因最小主应力较低而破坏,承载能力逐步下降。以线弹性力学分析孔道试样的应力状态,假设试样内材料同时达到承载极限,Coulomb准则给出的试样强度是一个偏低的估计,而不是偏高的估计。围压和轴向载荷在给定倾角剪切滑移面上的正压力和剪切力由整体力平衡确定,与孔道存在与否没有关系,孔道只是造成应力分布的不均匀,使试样的承载面积减小,引起围压对强度的贡献增加;另一方面,试样内部的破坏是逐步发生的,达到峰值承载能力时试样由黏结力构成的承载能力随围压、孔径的增大而减小。这两种不同趋势的变化决定孔道试样的强度特征。孔道对试样变形破坏的影响随大理岩结构特征而不同。

EXPERIMENTAL STUDY ON STRENGTH AND DEFORMATION PROPERTIES OF HOLLOW CYLINDRICAL SPECIMENS OF MARBLES

A series of pseudo-triaxial compression tests on hollow specimens of marble with fine and medium crystals without considering inner pressure were carried out to study the effects of nonuniform stresses on the bearing capacity and deformation.There are no essential differences in the deformation behavior between solid and hollow specimens when the axial deformation is small.With the deformation increasing,failure in the hollow specimen starts from the hole wall for the minor principal stress;and the bearing capacity drops off.According to the stress state based on the analysis of linear elastic mechanics and the assumption of failure synchronization in the whole specimen,the strength provided by Coulomb criterion is a smaller estimated one.The strength property of hollow cylinder specimen is influenced by following factors.On the shear failure surface of specimen,normal force and shear force provided by confining pressure and axial load respectively are determined by the balance of the total forces and have no relation with hole.The hole just induces the nonuniform distribution of stresses.The bearing area becomes small for the hole;and the strength provided by confining pressure will increase.On the other hand,the failure in the specimen happens step by step;the bearing capacity of the whole specimen provided by cohesion or material strength will be less than that of the solid specimen,and decreases with confining pressure and inner diameter increasing.The experimental results provide a reference to understand the strength criteria,numerical calculation and failure of tunnel and well.