Analysis Of Excavating Stability And Water Seepage Feature Of Tunnel In Permafrost Region

Research on two key points of Kunlun mountain tunnel of Qinghai-Tibet railway, which are the contradiction of excavation and lining of tunneling in permafrost region and the analysis of water seepage from Kunlun mountain tunnel and corresponding treatment, has been done. The engineering project is introduced firstly. Finite element method (FEM) is applied to simulate different models on the basis of thermodynamic theory. The system of construction control and prediction for excavation of Kunlun mountain tunnel is built up by site-monitoring temperature of wall rock. The water seepage features are presented by tests of ditch flux of the tunnel and ground temperature and ground water table and connectivity, and the validity of computational model of moving boundary is verified at the same time. The application of the computational model of moving boundary theoretically explains why water seepage features of Kunlun mountain tunnel are formed. 1. Excavation and lining of Kunlun mountain tunnel1) The climate law around the tunnel is got for research and construction of the tunnel by analysis of the climate around the tunnel.2) The features of site temperature are got for the analysis of wall rock stability of a tunnel in permafrost region and choosing and controlling different temperature fields for excavation and lining of the tunnel by statistical analyses of climate and construction temperature at Kunlun mountain tunnel. The fractional temperature fields are presented firstly for different programs during construction of tunnel in permafrost region. So construction environment is greatly improved, and the disturbing of tunneling to permafrost is limited to minimum.3) The FEM is applied to simulate different excavation to find probable ground stability by the strength and deformation of wall rock on base of geologic feature and geohydrologic condition of Kunlun mountain tunnel, so a suitable excavating method is selected.4) A finite element model is selected to do a transient heat transfer analysis of wall rock on the base of Kunlun mountain tunnel. Construction process is divided by four phases for fulfilling construction safety. Then a system ofconstruction control and prediction is firstly established to guide construction of Kunlun mountain tunnel. There is no record of tunneling technique about it in permafrost region.2. Analysis of water seepage from Kunlun mountain tunnel1) Moving boundary is redefined, and the essential factors are presented. It is firstly discovered that the erosion of fluid flow to permafrost is far great than that of still water to permafrost. A new method is presented to further understand frozen soil.2) A suitable computational method is created to calculate a thawed depth with moving boundary property. Some programs are made on the basis of a popular finite element program to perform computing a thawing depth with moving boundary property. The factors influencing a thawing depth are discussed, and critical damping distance is the key factor. The program is used to simulate different models. The method theoretically explains the reason why the water seepage features of Kunlun mountain tunnel form.3) The relationship between water seepage distribution and topography is analyzed to find that one of water seepage features is that water seepage distributes under the valleys over the tunnel.4) It is testified by connectivity test that water seepage from the tunnel comes mainly from surface water of No.l and No.2 valleys, and seepage runoff exists between the tunnel and the bottom of two valleys.5) The results of analysis of ground temperature and geohydrologic condition of No.2 valley in Oct to Nov 2003 and Mar to May 2004 shows that an unfrozen ground water runoff exists between the tunnel and the bottom of No.2 valley along the valley at least, and that tunneling affects on permafrost around the tunnel to a certain extent.6) From the analysis of the relationship between water seepage distribution and topography of Kunlun mountain tunnel to the analysis of connectivity test, and the analysis of ground temperature and ground water table observation, the water seepage behaviors of the tunnel and fit treatments are presented.