Evaluation of rock mass deformation modulus in the field: A self-loading deformation test

Accurate evaluation and appropriate selection of deformation parameters are crucial for investigating the engineering behavior of rock mass. Based on the Nanshankou Pumped Storage Power Station project, self-loading in situ tests were carried out to determine the deformation modulus of rock mass. Embedding an anchor head within the rock mass eliminates the need for conventional reaction devices. Additionally, five wave velocity boreholes were drilled to a depth of 1.60 m around the loading plate, and P-wave velocities were measured at 0.2 m intervals. A quantitative relationship between the rock mass deformation modulus and P-wave velocity was established through exponential and power function fitting, and three types of pressure-deformation curves were identified: concave-down, concave-up, and linear. The power function shows a stronger correlation than the exponential model, and its correlation coefficient increases with P-wave velocity measurement depth. Furthermore, the discrete element method (DEM) was employed to investigate the effects of bedding plane and anchor hole size on rock mass deformation and failure mode. Numerical results show that the presence of an anchor hole markedly reduces the specimen’s peak strength, with greater reductions occurring as the hole diameter and depth increase. Cracks are primarily distributed above the anchor hole, with a distinct “V-shaped” shear band developing along its base. Furthermore, when the dip angles of the bedding plane are θ = 0°, 30°, and 90°, the specimen’s peak strength is governed by both the rock mass and the weak planes. In contrast, the steep inclination of the plane ( θ = 60°) leads to a pronounced reduction in peak strength, which is then primarily controlled by the properties of the weak planes.