Rockburst and microseismic activity in a lagging tunnel as the spacing between twin TBM excavated tunnels changes: A case from the Neelum-Jhelum hydropower project

•A rare example of changing tunnel spacing to mitigate rockburst risk was studied.•The reasonable tunnel spacing was derived by microseismic and rockburst data.•Sandstone is more sensitive to the tunnel spacing and rockburst than siltstone.