Study Of Earth Pressure Acted On Tunnel Portal Structure

Tunnel portal is principal part of tunnel structure, it's safety should not be gnored. Active earth pressure is the main load acted on tunnel portal . it's a key actor in tunnel portal design. In this paper . active earth pressure of tunnel bortal is studied by means of numerical simulation, limit analysis and limited ength space earth pressure theory. So the new earth pressure calculation nethod of tunnel portal is carried out. Then based on the new method and the basic theory of structure reliability . reliability design formulas are carried out. The contents of this thesis are as follows:1. By using three-dimensional contact element, three-dimensional finite analysis on typical tunnel portals are studied with tunnel lining soil contact :unnel portal-soil contact and tunnel lining -tunnel portal contact. So the rules of earth pressure distributing along the length and the height of tunnel portal are carried out. The earth pressure action point and the rules of earth pressure variation with tunnel portal-soil friction angle can also be obtained.2. Based on soil plasticity and upper-bound analysis theory, the earth pressure intensity formula distributing along the tunnel portal length, general earth pressure formula and earth pressure action point formula are derived. And earth pressure of typical tunnel portals is calculated with such formulas. The results show that the fracture angle and general earth pressure acted on per unit length of tunnel portal are less than which calculated with coulomb theory.3. Based on limited length space earth pressure theory, the idea of tunnel portal's space earth pressure is putted forward. The tunnel portal earth pressure is divide into two parts at tunnel lining height, the earth pressure intensity-formula at upper part, below part, general earth pressure formula and earth pressure action point formula are derived. The example shows that the tunnel portal length and tunnel lining make earth pressure acted on tunnel portal difference from which acted on normal retaining wall.4. The new earth pressure calculation method of tunnel portal is carried out. The example shows that the new method match to engineering practice moreexactly.5. Based on the new method and the basic theory of structure reliability . the reliability of typical tunnel portals is calculated. So the object reliability index and partial coefficients in each limit state formula are obtained. And limit state design formulas that can be applied into tunnel portal practice are also acquired.