Displacement Prediction And Parameter Optimization Back Analysis Of Surround Rock Mass Under Shallow And Unsymmetrical Pressure In Tunnel Portal

As a decrease in space of construction and people's requirement of environment protection, several countries pay more attention to the exploitation of underground space, so the 21st century has been predicted as the century of underground space. Nowadays, underground engineering has become the hotspot in research, many ripe theories have been developed in the area of geotechnical mechanics. But, the complexity of rock mass causes some theories out of accord with engineering application, so it is possible to get more research with real engineering.In tunnel engineering, people have always regarded the portal engineering highly and formed a directive method that is"Getting in hurry and getting out slow". The background of this paper is Baima tunnel portal engineeing which encountered shallow and unsymmtrical pressure terrain.In this paper, a monitor method, called triangel monitor method, is recommended in NATM construction.Based monitor data,a gray model has been used to predict displacement of tunnel deformation and its correct result proves the good application in tunnel engineering.Then paper introduces some pop elasto-plastic constitutive relationship used in underground engineering.The parameter of surround rock mass in portal area has been back analyzed by combining ANSYS optimize technology with displacement back analysis method.Finite element method based on Drucker-Prager criterion is used to execute numerical simulation. By the analysis of result the mechanics status and the deformation charactoristic of surround rock mass and consolidation structure,which is under unsymmetrical pressure condition, can be gotten.At last,paper points out the weak point of structure and proposes its prevent way.