Influence of the schistous structure of gneiss on the rockburst of Qinling tunnels in China

Two extra-long tunnels, with two tubes each, were excavated in a corridor of about 200 m in Qinling Mountain in the central part of China, for railway and road lines from Xi'an to Ankang, respectively. During tunnel excavations, severe rockbursts have occurred in several gneiss sections. The rockburst features indicate the pronounced effect of the fabric of the schistous structure of gneiss on the strength and deformation characteristics of intact rocks. The analysis on the geological conditions in terms of initial geostatic stress, rock strength and the occurrence of the gneiss foliation planes indicates that the schistous structure of gneiss is in favor to the severe rockburst in the section of magmatic gneiss with large overburden. The influence of anisotropic feature of the gneiss on the rockburst becomes significant on the condition that a large initial principal stress is nearly parallel to the foliation planes and the foliation structure composed mainly of biotite and quartz provides a weak plane to brittle failure.
QC 20190320