On the mechanism of inrush hazards when Denghuozhai Tunnel passing through granite contact zone

•The inrush hazards of Denghuozhai Tunnel with depth of 175m are introduced.•Three essences for the occurrence of inrush hazards are summarized.•Albitized, sericitized and clayinitized alteration in the contact zone is revealed.•The main controlling factors of alteration are magmatic evolution process.