Development mechanism of radial chain rockbursts in a deep tunnel excavated by TBM

Abstract

In this work, the concept of radial chain rockbursts (RCRs) was proposed for the first time. As a case study, RCRs that occurred in a deep tunnel excavated by TBM was analyzed. The occurrence process and geological characteristics of the RCRs were described. Though analyzing the microseismic (MS) temporal and spatial evolution characteristics, stress and energy evolution characteristics and fracturing mechanism of the RCRs, the development mechanism of the RCRs was revealed. The following results were obtained: (1) The RCRs is prone to occur under geological conditions with alteration zone and lithologic interface. (2) The time interval of adjacent rockbursts gradually increased, and RCRs exhibited the characteristics of time and space delay. The time interval of adjacent rockbursts was mainly affected by the adjustment of the excavation and support measures, and the stress gradually developed to the deep surrounding rock mass. (3) The stress and energy in the development stage were distributed in the deep surrounding rock mass and were released in the surface layer of surrounding rock mass in the occurrence stage. The apparent stress of the rock mass in the occurrence stage was higher than that in the development stage, and the stress gradually developed to the deeper zone during both the occurrence stage and the development stage. The repeated occurrence of RCRs was mainly controlled by three factors: the mechanical properties of the surrounding rock, stress conditions and multiple local shear slips in the rock mass near the alteration zone that are caused by TBM excavation disturbance. (4) The first two rockbursts were strain rockburst, and the latter two rockbursts were strain-structure slip rockburst that occurred along the alteration zone. The research has a guiding role for construction under similar engineering geological conditions, and provides a basis for the research on warning and mitigation of RCRs.