Mechanical properties and instability analysis of concrete specimens with horizontal holes of different diameters

Uniaxial compression tests were carried on 12 concrete specimens with six different diameter holes using a rigid test machine, and the stress–strain relationship was analyzed in different hole diameter specimens. The effects of different hole diameters on specimen compression strength, elastic modulus, and Poisson’s ratio were studied, and the failure form and instability mode of concrete specimens with holes of different diameters were evaluated. The results show that the larger the compression strength of the specimen, the larger the axial and horizontal strains. As the hole diameter increased from 0 to 50 mm, the compression strength and elastic modulus reduced. The decreasing trend slowed down, and the relationships between the hole diameter and compression strength, and elastic modulus could be represented by negative liner functions. The Poisson ratio of the specimen increased in waves with the increase in hole diameter from 0 to 50 mm. A crack in the concrete specimen with 0–20 mm diameter hole started at the upper and lower diagonal angles of the hole wall; a crack in the concrete specimen with 30–50 mm diameter hole started at the left and right parts of the hole wall. The instability mode of concrete specimens with horizontal holes of different diameters was divided into shear dislocation instability and planar splitting instability.