Experimental study on the influence of structure plane on rockburst of hard rock tunnel under combined dynamic-static loading conditions

Abstract

Dynamic disturbances and structural planes (discontinuities) are of critical importance in influencing the damage of surrounding rock in underground engineering. To explore the rockburst process of structural planes under dynamic disturbances, true triaxial tests with coupled dynamic − static loading considering structural planes and periodic weak disturbances were carried out. Cubic specimens with circular holes and pre − fabricated cracks, simulating structural planes, were used as test objects. The damage and micro − cracking processes of the surrounding rock were monitored by a high − speed camera system and an acoustic emission system under three different disturbance frequency and amplitude conditions (Condition 1: 2 Hz, 40 KN; Condition 2: 6 Hz, 30 KN; Condition 3: 10 Hz, 15 KN). A comparative analysis was conducted on the failure processes, strength characteristics, acoustic emission features, debris fractal characteristics, and damage morphologies of specimens with and without structural planes under the three weak dynamic cyclic disturbance conditions. The main conclusions are (1) During the uniform loading stage, discontinuities change the occurrence time, location, and intensity of rockburst. During the disturbance, the damage of specimens with structural planes mainly occurs on the side without structural planes, and the damage intensity and frequency are lower than those of specimens without structural planes.(2) Both structural planes and disturbances weaken rock masses to some extent. Different disturbance conditions have different impacts on structure − controlled rockbursts. An increase in disturbance amplitude promotes new failures in rock masses, while an increase in disturbance frequency facilitates the expansion and connection of original micro − cracks.(3) The presence of structural planes changes the damage pattern of specimens. More shear cracks are observed in specimens with structural planes. The disturbance exacerbates stress concentration, leading to more severe damage to the rock mass. In practical engineering, construction should avoid discontinuities as much as possible. Grouting and support can effectively reduce the hazards of rockbursts caused by structural planes.