Study on construction mechanical behavior of new tunnel under existing expressway

In recent years, the situation of new tunnels crossing the existing expressway is increasing day by day. The construction stability and subgrade settlement safety of new tunnels crossing the existing expressway are often the key problems in design and construction. By means of three-dimensional numerical simulation, the safety analysis of construction mechanical characteristics of the new Dananshan tunnel crossing the existing expressway and the safety analysis of subgrade settlement caused by the construction of the new tunnel crossing the existing expressway are carried out. The research shows that the maximum vertical displacement of surrounding rock occurs after the completion of secondary lining construction, which is + 12.75mm / - 15.18mm, and the maximum horizontal displacement of surrounding rock occurs after the completion of secondary lining construction of right tunnel, which is + 10.93mm / - 9.61mm, which is less than UN / 3 = 26.7 ~ 40mm, meeting the specification requirements; Through the analysis of the surface settlement of the transverse and longitudinal sections, the maximum settlement occurs on the surface of the top of the tunnel vault respectively, and the maximum surface settlement of the left and right tunnels are 2.93mm and 3.09mm respectively, which is far less than the subgrade settlement reference value adopted in the specification and this paper.