Fault induced rock bursts and micro-tremors – Experiences from the Gotthard Base Tunnel

Abstract

During the construction of the Faido Multifunction Station of the Gotthard Base Tunnel, a previously unknown and unanticipated major tectonical fault has been encountered. Upon completion of the advance through the fault, systematic and major rock burst events occurred in the competent Gneiss rock mass adjacent to the fault.The Swiss Earthquake Service (Schweizer Erdbebendienst – SED) observed an increase of microtremors in the vicinity of the tunnelling site, in a region where usually very low seismic activity is present. As a consequence, the seismic monitoring grid has been enhanced in the project area, allowing reliable pin-pointing of the microtremor hypocenters and examination on the interaction with the tunnel advance and the observed rock burst events.Due to the vast amount of scientific work with regard to rock burst causes, classification, prediction and mitigation, this publication deliberately abstains from trying to add yet another set of relationships and/or classification schemes. Instead, a case study is presented, with the peculiarity that excellent seismic monitoring and very well documented rock mass conditions are seamlessly available, allowing direct correlation and insight into the interaction between seismicity and strike-slip rock bursts. In addition, the results of a dynamic analysis performed in UDEC, with excitation wave data and rock mass parameters calibrated on the field measurements, are presented. They allow greater understanding of the events caused by seismicity-induced rock burst phenomena.The experiences with prediction and mitigation of rock burst are shown, leading to conclusions with regard to efficient and safe tunnelling in rock-burst prone rock masses.