Study On Construction Method Of Bias Section In The Huitougou Tunnel

Huitougou Tunnel is located at Baishan area, Jilin. The Terrains and landforms are complicated and varied with huge altitude difference and broken countries which create unsymmetrical tunnel caves. Extreme dangerous cases would happen at the entrance of the tunnel caves because its loose surrounding rock with crushing dynamic properties, shallow-buried unsymmetrical phenomena contributes as well. Improper construction methods and managements could lead to rock splitting, roof caving and collapsing. For improving the construction quality and better understanding of the process of these cases, Bureau of Highway Construction Jilin cooperated with Jilin University regarding the Huitougou Tunnel as research target to highlight unsymmetrical tunnel crucial construction techniques and methods as followed.(1)This paper firstly summarized the methods for clarifying shallow-buried caves and unsymmetrical tunnels and cited as proof for demonstrating the shallow-buried and unsymmetrical tunnel(The Huitougou phase); Besides, factors on arousing tunnel asymmetric and cave excavation methods on tunnel surrounding rock have been concluded and applied to Huitougou Tunnel..(2)Numerical analysis methods have been applied on Huitougou tunnel. Four common applied excavation methods: Step method, the annular core excavation remain indigenous method, CRD method, single side heading method are compared under numerical analysis on traditional Huitougou shallow-buried unsymmetrical tunnel. The expected tunnel excavation construction method has be proposed.(3)For decreasing the degree of unsymmetrical impact of construction at Huitougou tunnel, this paper analyzed deep-buried tunnel and one side shallow-buried tunnel. Setting unilateral pilot tunnel method as the construction method, simulating and comparing the methods of one side deep-buried excavation and one side shallow-buried excavation. Detailed comparison would be plastic region distribution on surrounding rock, surface and rock settlements, inner pressure about supporting structure. After comparison, the reasonable Huitougou shallow-buried unsymmetrical tunnel construction procedures would be confirmed.(4)Regarding shallow-buried unsymmetrical tunnel, the earliest supporting closure chance play a significant role for tunnel stability. If the supporting fail to take the chance, surrounding rock would exposure at a long period of time which leading to great rock structure deformation and affect the tunnel stability. Numerical methods are applied for tunnel construction method optimization, and proposed sound and reasonable step lengths at step excavation method.