Research and Application of In-Situ Reconstruction and Expansion of Sanfang Tunnel

In order to solve the problem that the diseases of old railway tunnels in our country seriously affect the safety of train operation. Taking the Sanfang Tunnel project of the down line of the Tumen-Jiamusi Railway， which was built under the shallow-buried conditions of grade V rock mass during the Japanese occupation period as an example， four disease treatment schemes were adopted： simple disease treatment scheme， new tunnel detour on the left side， new tunnel detour on the right side， and in-situ expansion tunnel. The advantages and disadvantages of four schemes were compared and analyzed， as well as their applicable conditions. The excavation method of detecting the voids and loose accumulations behind the lining， performing advanced radial grouting and advanced small pipe support， and then cutting the existing lining in stages and sections was adopted. Manual or mechanical excavation was carried out， and static blasting was used when necessary. The tunnel on the upline was monitored to reduce the impact on the nearby upline tunnel and ensure its operational safety. The arch top and ground surface sedimentation analysis of the tunnel's excavation step by step was conducted using the MIDAS finite element software. Then， proposing to use in-situ tunnel expansion and discussing its feasibility. result The results show that under the same geological and construction technology conditions， the optimal position relationship is that the original tunnel is located below the new tunnel.