Underground geotechnical engineering is often located in high stress stratum，which is easy to cause disasters such as damage and expansion of surrounding rock，large-scale fracture and swelling.With the implementation of construction，it is inevitable to encounter composite rock with more complex stress distribution and rock mass failure.In view of the deep high in-situ stress and multi-rock complex geological conditions，the servo control testing machine was used to conduct indoor mechanical experiments on composite rock，and the failure process of composite rock under high stress was reproduced，so as to provide reference for the stability analysis of composite rock with different materials.Skarn，serpentine and sandstone were selected as the components of composite rock，and their strengths are 80.25 MPa，83.29 MPa and 87.41 MPa respectively.They have a relatively similar strength relationship with uniform gradient increase，which is convenient to compare the mechanical properties of composite rock.The composite rocks can be divided into two types，one is serpentinite and skarn assemblage，the other is serpentinite and sandstone assemblage.The combination mode is 0°contact surface，the volume proportion of components is the same，and the components with weak strength are located in the upper part of the combination rock.Through uniaxial compression tests，the mechanical properties and failure characteristics of skarn，sandstone and serpentinite in single and composite forms were obtained，including uniaxial compressive strength，peak strain，elastic modulus and failure mode.By comparing the stress-strain curves and the actual failure situation，it can be seen that the composite rock and single rock have similar failure modes，with obvious characteristics of compaction stage，elastic stage，plastic stage and failure stage，and the initiation position and development mode of the initial crack directly determine the final failure mode of the rock sample.Based on the experimental data，it is inferred that there is a quantitative relationship between the compressive strength of a single rock and its composite rock，and this inference was verified.According to the homogenization theory，the composite rock was compared to the ideal series spring model，and the formulas of elastic modulus，peak strain and volume of each component in the composite rock awere deduced by using Hooke’s law.The theoretical results are close to the experimental results.Under the condition of uniaxial compression，the compressive stress on the contact surface of composite rock specimen gradually changes to the tensile stress perpendicular to the compression direction，and the composite rock is mainly shear failure.Under the action of high stress，the deformation phenomena of the two kinds of rocks in the composite rock are not synchronous，and the part with low strength is destroyed first，this shows that in composite rocks，weak facies rocks play a major role in the overall strength of composite rocks.

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