Research On Design Method Of Double Lining In High-Fill Open Cut Tunnel Of High-Speed Railway

High-speed railway network of China is extending into southwest mountainous area rapidly. Due to the geological situations of southwest region, the number of tunnels under construction and in the plan receives an substantial increase. Considering factors like environmental protection of portal area and city planning, building open cut tunnels at the portal and then backfilling it with silt from tunnel construction would be a wise choice, which lead to an increase of the number of open cut tunnels with high fill. However, high fill open cut tunnel lacks clear design specifications. The calculation of its soil pressure, selection of structure form and smart step during construction still need to be researched deeply.Based on a high fill open cut tunnel construction project in Fengdu, Chongqing Municipality, field test and numerical simulation as well as theoretical derivation has been done to study the issues said above. The achievements are as follows:(1)The variation of soil pressure during the filling process is discovered. Correction coefficient method of calculating vertical soil pressure as well as the range of correction coefficient has been given.(2) Formula of calculating vertical soil pressure has been given, which is derived from Marston theory and Elastic theory. This formula is proved both by field test and numerical simulation, and it should be suitable for further use.(3)Soil pressure can be affected by structure form and stiffness. Rigid foundation especially with great thickness has been proved as an essential element that leads to great increase of soil pressure of open cut tunnel.(4) Characteristics and rules of forces of open cut tunnel with double lining are discovered. Open cut tunnel with double lining are proved to be safer than the traditional one, especially in situations of facing disadvantageous load.(5)The construction opportunity of inner lining does great effect on the final stress state and the safety of structure. Structure is safer when inner lining are built at last.Based on diverse methods and theories, some achievements has been reached for further use in designing and construction of high fill open cut tunnels.