Abstract: To study the mechanical damage characteristics of layered composite rocks, sandstones and mudstones from deep tight reservoirs were selected as research objects. Layered composite class rocks were prepared by similar material model tests. Uniaxial compression tests were conducted and supplemented with Acoustic Emission (AE) and Digital Image Correlation (DIC) systems to obtain physical and mechanical parameters such as strength and elastic modulus of the layered composite rocks. The corresponding law of AE ring count and rock damage evolution was obtained. The damage process of layered composite rock under uniaxial compression was divided into three stages: initial damage, stable damage development, and damage acceleration. In line with the internal damage evolution characteristics of AE and the surface damage evolution of DIC, a damage constitutive model of layered composite rocks based on dual damage factor was established. The strength of sandstone-like rock (rock A) is higher than that of mudstone-like rock (rock B) by 21%, and elastic modulus by 24%; the strength of layered composite rock (AB) is slightly lower than that of rock B by 3%, and elastic modulus by 4%. Rock A is subjected to tensile failure, B to shear failure with single inclined plane, and AB to tensile-shear slip failure along cemented bedding plane or weak parts. The three types of rocks see weak AE in the initial load stage but strongest AE signals at peak stress. Analysis of strain cloud diagrams of the DIC system revealed that the deformation characteristics of the layered composite rock under uniaxial compression were mainly tensile-shear-slip damage. The present model reasonably revealed the damage evolution mechanism of internal structure development and external crack initiation, expansion, and penetration of layered composite rocks under uniaxial compression.

Key words: layered composite rock, similar material, acoustic emission, digital image correlation (DIC), uniaxial compression, mechanical damage characteristics, damage constitutive model