Abstract: The excavation of foundation pit excavation adjacent to existing tunnel will result in the damage of surrounding soil balance, which would lead to uneven settlement of adjacent tunnel structure, and eventually affect the safe operation of existing tunnel. In order to control the longitudinal deformation of existing tunnel caused by foundation pit excavation, a twostage method based on the Pasternak foundation model is adopted to study the longitudinal deformation of adjacent existing tunnel induced by double foundation pit excavation in soft soil. The results of the simplified theoretical calculation are compared with that of threedimensional finite element numerical simulation, and the comparison results show that the results by the two method coinside with each other well, thus it can be concluded that the simplified analytical method is of high accuracy and simple calculation. In addition, according to the distance between the foundation pit and the tunnel axis, the depth of excavation and the spacing of the foundation pit, the influence of double foundation pit excavation on vertical deformation of adjacent tunnel is analyzed under 3 layouts of double foundation pit parallel to tunnel, double foundation pit vertical to tunnel and double foundation pit oblique to tunnel. The analysis results reflect the law of tunnel deformation. 

Key words: Pasternak foundation model, double foundation pit excavation, existing tunnel, longitudinal deformation, twostage analysis method, numerical simulation