An Analysis On The Seismic Response Of Running Tunnel In Liquefiable Soils

With the fast development of our country, the construction of subway has walked in a golden stage of development. Our country locates in the circum-pacific earthquake zone and the seismic activity is frequent and strong. According to the current earthquake intensity zoning map, most city of our country locate in the earthquake region. So the problem with the seismic design of subway becomes more and more visible.The outlay of running runnel takes a big part in the total investment of subway project. Whether the design of tunnel is reasonable or not will bring great effects on the cost of the project. At present, little research has been made on the seismic response of running tunnel in liquefiable soils in our country. Although engineers and technicians have to adopt some special design schemes and engineering measures when the tunnel runs across the liquefiable soils, they lack for the corresponding theoretical rules. So there is great practical significance to make a further study on theearthquake damage mechanism of running tunnel and find better design methods.A great deal of calculation on the seismic response of running tunnel in liquefiable soils is made by employing the finite difference method. Some conclusions with practical application value were made and the knowledgement of research status in this field was deepened. The main contents of this paper are as follows:First, the present status of subway construction in our country and the cognition of seismic design of running tunnel were briefly introduced. Problems such as the earthquake, liquefaction of sand soil, characteristic of earthquake disaster and research status of running tunnel were also described.Secondly, the finite difference numerical simulation software FLAC 2D used in the thesis was recommended and the various factors involved in the numerical model were also presented. Thirdly, physical conditions and modeling process were introduced in detail. The influence of liquefaction behavior on the results was also analysed. It is found that soil liquefaction problems should be considered in the analyss of the seismic response of running tunnel in liquefiable soils.Then, the influence factors on the seismic response of running tunnel in liquefiable soils, such as concrete labeling, density, thickness and buried depth of the tunnel, were analysed. Some significant conclusions were obtained as follows:(1) Increasing the concrete labeling in subway running tunnel project can control the internal force of the structure, and the structure failure induced by oversize internal force can be also avoided.(2)The influence of concrete labeling change on the structure displacement is not notable. The traditional opinion that the tunnel deformation can be reduced by only increasing the concrete labeling is not advisable.(3)With the increasing of liner density, the response of structural internal force was enhanced, the structural displacement and the excessive pore pressure of surrounding soil were also increased. So the smaller of liner density, the better of tunnel stability. In order to enhance the seismic performance of the tunnel, we should choose some light liner materials.(4) When the thickness of the liner reaches to a certain extent, the utilization ratio of concrete strength is gradually decreased. It has great practical significance to determine the optimal thickness of the liner by considering various factors.(5)The rise of running tunnel induced by soil liquefaction can be reduced by increasing the buried depth of the tunnel. So increasing the buried depth of the tunnel is helpful to the enhancement of its seismic stability.Finally, seismic response of running tunnel between FuChun Road station and QiuTao Road station were also analysed, which locates in saturated sandy and silty soils. Some valuable conclusions were also obtained.