Research progress and prospect of laboratory test of rock spalling  in deep hard rock roadway

The excavation of a deep hard rock roadway or tunnel is easy to induce a spalling roughly parallel to the excavation surface of surrounding rock,which seriously affects the stability and safety of deep engineering. The formation of spalling are related to the lithology and stress environment of deep rock before excavation and the stress paths experienced by surrounding rock during roadway excavation. Laboratory test is an important method to study the spalling of deep surrounding rock,and the key to obtaining the spalling characteristics and scientifically revealing the formation mechanism of spalling is to perform laboratory test research according to the stress conditions and stress paths during excavation of deep hard rock roadways. The development of test equipment and the progress in spalling laboratory research were mainly introduced from three aspects according to the varied sample types used in the laboratory test on spalling:solid cuboid sample spalling test,sample with a prefabricated hole spalling test and “loading first and then interanal holing” spalling test. The problems existing in the laboratory similation tests on spalling were summarized,and the prospects of laboratory research into spalling were put forward:①Developing the 3D printing materials comparable to rocks for the large-scale roadway excavation model test of deep rock mass;②Developing a large-scale and high-toning true triaxial test system that can truly simulate the stress conditions and stress paths of surrounding rock,so as to simulate the roadway excavation process in a three-dimensional stress environment;③Developing the monitoring technology and software that can display the real-time deformation,fracture and stress state of surrounding rock. On this basis,to carry out the laboratory simulation test on roadway spalling combined with numerical simulation,summarize the characteristics and evolution law of spalling,obtain the specific quantitative indexes of spalling,establish a spalling criterion with key indexes,and reveal the formation mechanism of spalling in deep surrounding rock.