Study On Entrance Technology Of Highway Tunnel Portal In Special Zones

Entrance of highway tunnel is generally strong weathering zone, where the rock isbroken. In particular, when entrance of tunnel is in special zone, such as undercrossing theexisting road, steep slope, the rock is shallow buried, bias pressure, covering thin layer, and ispoor to become arch. When the constrution of tunnel portal is in special zone, how to choose areasonable way into hole, reduce engineering investment, shorten the construction period, andat the same time to strengthen the mechanism of formation damage, which is need toaddressed urgently.This paper introduces a variety of support and excavation methods in the entrance ofmountain tunnel, summed up the characteristics of these methods and construction techniques,and compared the advantages and disadvantages. Under the construction of Xianglianshantunnel in Zhejiang Provice, with the use of finite element software MIDAS/GTS to establishthe basis of the actual terrain model, the model is construction of umbrella arch method，pipe roof pre-reinforcement,ring excavation leaving core soil, CD mothod, CRD mothod,twin-side heading method. It is to study on the vertical deformation and the plastic zonedistribution and development of II Highway, rock deformation, the characteristics of rockstress,early support stress from the calculation results of model. Researching ways into holeof Xianglianshan tunnel to influence II Highway and rock, with considering economic factor,the simulation results show that umbrella arch method, pipe roof pre-reinforcement,twin-side heading method is optimal act.Under the construction of Huashan tunnel in Zhejiang Provice, with the use of finiteelement software MIDAS/GTS to establish the basis of the actual terrain model, the model ispipe roof pre-reinforcement,ring excavation leaving core soil, CD mothod, CRD mothod,twin-side heading method. It is to study on the plastic zone distribution and development ofrock, rock deformation, the characteristics of rock stress,early support stress from thecalculation results of model. Researching ways into hole of Huashan tunnel to influence rock,with considering economic factor, the simulation results show that pipe roofpre-reinforcement, twin-side heading method is optimal act.The conclusions of this paper, provide a technicalbasis for guidance in the excation ofXianglianshan tunnel and Huashan tunnel. So the two methods has extensive applicability inspecial zone tunnel portal construction.