Experimental study on the monitoring of rockburst in tunnels under dry and saturated conditions using AE and infrared monitoring

The brittle failure behaviors of hard rock exposed by tunnelling in a moist environment are of great significance. A serials of laboratory experiments of sandstone tunnel models were conducted to investigate the influence of water contents on rockburst. The rock models contained three different water contents. The rockburst process was monitored by the acoustic emission (AE) monitoring system and infrared thermal imager monitoring system. The rockburst patterns, the AE distribution and average infrared radiation temperature (AIRT) were captured during the compression process. The AE parameters (AE event rate and AE energy rate) and the temperature parameters of the tunnel models with different water content were analyzed. The water softens the rocks and reduced their mechanical parameters (such as the elastic modulus and peak strength), and the tunnel model in the saturated state exhibited a lower dynamic failure rate, leading to quicker static failure. The rockburst of the saturated tunnel model generated more AE events and was more damaged in the early loading period, and then demonstrated a weaker dynamic fracturing. The quiet period of AE event rate and the sharply increasement of AE energy rate can be regarded as the precursor to rockburst on the time-scale. The water also promoted the effects of infrared radiation temperature of the saturated models. The sudden change of the temperature of the tunnel walls can be used as the precursor to rockburst on the space-scale. The knowledge of the influence of the moisture state on the rockburst will improve the design and construction of deep tunnels.