Unloading deformations of surrounding rock in jointed roadways

The rock mass in nature often develops joints of different scales under the action of long-term geological tectonic movement, and the stability of surrounding rock of roadways has a great relationship with the development of joints. For the sake of studying the effects of joints on the excavation unloading deformation of surrounding rock of roadways, a series of tests are carried out on the cement mortar surrounding rock specimens with different joint sizes through the excavation unloading model test system developed by the authors. The results show that: (1) The unloading deformations of surrounding rock mainly occur at the unloading stage, and the deformations continue to exist at the maintenance stage, but the joints have no obvious influences on the unloading deformations. At this stage, the unloading deformation degree decreases significantly and gradually becomes stable, with the strain increment of about 100με. (2) Compared with the specimens without joints, the average strain reduction of S-1 and S-2 specimens with joints is more than 70%, which is much higher than S-3. That is, the larger the joint size, the greater the degree of unloading deformations, and the more obvious the unloading effects. (3) The specimens have great differences in strain in different directions, and the tangential strain is greater than the radial strain, especially for the specimens with joints.