Mechanism of failure and control measures for deep excavation and unloading rock mass

Abstract

In order to study the mechanism of rock mass fracture and instability during deep excavation unloading and support problems, a comprehensive approach was adopted, including on-site investigation, laboratory tests, theoretical analysis, and numerical simulation. True triaxial tests were conducted under different support stresses, including "single-sided lateral unloading—three-way five sided stress—single-sided lateral support—vertical continuous loading". The mechanical behavior, failure mode, AE, and energy evolution characteristics of rocks under excavation unloading and support stress paths were studied, and targeted control measures were proposed. The research results indicate that: (1) As the support stress increases, the peak strength of the unloaded rock during failure increases, the maximum principal strain decreases, and the failure mode changes from tensile shear composite failure to shear failure; (2) As the support stress increases, the total energy U, elastic energy U^e, and dissipated energy U^d at the time of rock failure increase, and the strain energy conversion rate u before the peak increases linearly with the support stress; (3) The anchoring support function of bolts and anchor cables were studied, and a coupled support strategy of "beam arch" load-bearing structure with prestressed anchor rods and anchor cables as the main support was proposed. It was applied on site in the 1211 (1) transportation roadway of Guqiao Mine and achieved good application results.