Dismantling Technology for Temporary Support of Large-span Ventilation Tunnel under Shallow Cover

There are lots of difficulties in the construction of southwest ventilation tunnel.The ventilation tunnel is constructed by CRD method.The dismantling of the temporary support is the key point in the control of the ground surface settlement and the security of the underground pipelines and the surface traffics.The temporary support is dismantled section by section and level by level,so as to guarantee the safety of the construction and the surrounding environment.The dismantling technology of the temporary support is presented in the paper.The dismantling effect is analyzed on basis of the monitoring of the ground displacement.The study shows that: 1) In principle,the range of the temporary support dismantling is up to the span of the tunnel.Sometimes it should be narrowed when it is necessary.2) The ground surface settlement induced by the temporary support dismantling is small,ranging from 5.86% to 18.49% of the total settlement.3) The standard for the temporary support dismantling is established and improved.