On-site supervision measure and analysis of Damaoshan tunnels with large section and small clear-distance

The research on the stability of surrounding rock is carried out during the construction, as per twin-side heading method, of large section and small clear-distance tunnels under complex geological condition; through the on-site supervision measure of internal displacements of surrounding rock, vault settlement, pressure of surrounding rock and stress of bolt in combination with the engineering practice of Damaoshan tunnels. When the pilot tunnels start excavating, the variation trend, characteristics and displacement field of displacement inside surrounding rock should be clarified, as well as the mutual influence of neighboring pilot tunnels in construction, mutual adjusting mechanism between surrounding rock and retaining structure and the reason of smaller distortion measured by vault settlement than the actual distortion of surrounding rock, the stress state of retaining structure, stress of bolt, variation relation of surrounding rock displacement. The supervision results indicate the feasibility of existing construction technology and retaining parameter adopted for fault zone of V-grade surrounding rock section of large section and small clear distance tunnels because of controllable surrounding rock distortion, strong retaining structure, safe storage and stable surrounding rock. The method, analysis and conclusion of research will be valuable experience and for reference in design, construction, supervision and further theoretical research on tunnel engineering under similar condition.