在地下富存裂隙的层状复合岩体中，复杂围压环境和裂隙分布对复合岩体力学性质和损伤破坏具有显著影响。选取由类灰岩和类砂岩组成的含预制单裂隙的复合岩样作为研究对象，通过常规三轴压缩试验，分析不同裂隙位置和围压条件下岩样的力学变形和破坏模式。结果表明：（1）完整复合岩样的强度受砂岩控制，而变形受灰岩限制。（2）随着围压的增加，复合岩样破坏特征由裂隙位置主导转变为由围压主导；复合岩样的体缩受围压的影响，而体胀受裂隙位置的影响。（3）在单轴压缩条件下，裂隙对岩样力学性质的削弱程度最大；当裂隙位于灰岩中时，损伤应力受围压影响最显著，岩样的强度和弹性模量随着裂隙位置的改变（从灰岩、接触面到砂岩）及围压的增加呈现出增加的趋势。（4）灰岩中的裂隙易产生拉伸裂纹，砂岩中的裂隙易产生剪切裂纹；随着围压的增加，复合岩样由拉伸破坏转变为剪切破坏，破坏模式由围压主导。该研究成果对复合岩体工程的安全加固设计具有一定的指导意义。

Composite rocks are widely present in underground geotechnical engineering such as tunnel excavation，mining projects，and oil and gas resource extraction.Composite rocks are formed by the layered accumulation of rocks with disparate properties，and are rich in fissures.The intricate features of these fissures，combined with the distribution of stress，collectively influence the stability of composite rocks，making them prone to disasters such as roof collapse，expansion of surrounding rocks，and significant tunnel deformations.Therefore，investigating the mechanical failure mechanisms of composite rocks under different confining pressures and fissure positions is of paramount importance for effectively preventing disasters in underground engineering construction.Based on the above reasons，this study prepared composite rock samples with pre-existing fissures，conducted triaxial compression tests by varying the fissure positions，and analyzed and summarized the influence of fissure positions and confining pressure on the mechanical behavior and failure modes of composite rock.The main conclusions are as follows：（1）Limestone exhibits the highest strength，while sandstone undergoes the greatest deformation under compression.The mechanical deformation of the intact composite rock sample falls between sandstone and limestone，with its strength controlled by the sandstone portion and deformation restricted by the limestone portion.（2） Under lower confining pressures，the intact rock sample and the one with fissures in limestone exhibit brittle failure，while the one with fissures in the contact zone and sandstone exhibits ductile failure.With the increasing of confining pressure，rock samples generally exhibit ductile failure，and the dominant factor in the failure characteristics shifts from the fissure position to the confining pressure.The volumetric contraction of the rock sample increases with the rise in confining pressure，and the volumetric expansion is minimal when fissures are in sandstone.Volumetric contraction is influenced by confining pressure，while volumetric expansion is influenced by fissure position.（3）In uniaxial compression，unstable crack propagation occurs earliest，and at this point，fissures have the greatest impact on the mechanical properties of the rock sample.In triaxial compression，with a constant fissure position，higher confining pressures result in more stable crack propagation when fissures are in limestone.Simultaneously，the strength and elastic modulus of the rock sample show an increasing trend with the change in fissure position from limestone，through the contact zone，to sandstone.With constant confining pressure，crack propagation is most stable when fissures are in sandstone，and the degradation of the sample is minimal when fissures are in limestone.（4）When fissures are in limestone，tensile cracks dominate，whereas in sandstone，shear cracks predominant.With the increasing of confining pressure，the failure mode of the composite rock sample shifts from tensile failure to shear failure，gradually transitioning from fissure-dominated to confining pressure-dominated failure modes.