Abstract: Mastering the height-diameter ratio effect of rock strength under inclined load is the basis of inclined pillar de sign and stability analysis.Taking red sandstone as the research object,20 groups of rock inclined loading tests with 5 loading angles and 4 height-diameter ratios were carried out by using inclined loading device,and the strength characteristics of rock under each loading condition was obtained.On this basis,the linear function relationship between rock strength and diameter height ratio under inclined loading is established.It is concluded that the intercept and slope of the linear function are different under different loading angles.With the increase of loading angle,the intercept decreases and the slope increases.Finally, based on the Mohr-Coulomb strength theory,the mechanical mechanism of the height-diameter ratio effect is interpreted as a friction "end effect" phenomenon,and this effect is affected by the loading angle.The results show that with the increase of loading angle,the rock presents a single slope shear failure.At the same loading angle,the larger the height-diameter ratio of the specimen is,the lower the strength is.Compared with the uniaxial compression condition,the peak load loss of the rock is more under the combined test scheme with large inclination angle and large height-diameter ratio.The research results are of great significance for revealing the ore/rock dip angle and size effect of rock mass engineering strength such as pillars.

Key words: peak strength,height-diameter ratio,inclined load,end effect