The start point of this paper is to figure out the deformation mechanism of existing pipelines induced by shield tunneling using the system energy technique instead of the general namely mechanical balance method. The existing pipeline is simplified as an Euler-Bernoulli beam on the Pasternak foundation which can deform continuously. After giving the displacement function referring to the Rayleigh-Ritz method， the energy expressions of each component in the elastic foundation beam system are achieved， and then the total potential energy equation about pipeline deformation is obtained. Based on the principle of minimum potential energy， the theoretical method is derived to assess the pipeline deformation by employing a variational method to solve the governing equation. The rationality of the proposed method is verified by comparing the calculated results with those of the simulation results of the finite element software （FEM） and the monitoring data from the engineering project in the published literature. Then， the parameter analysis on the bending stiffness， cross angles and ground loss is conducted to figure out their influence on the deformation of the pipeline. The results show that with the increase of the bending stiffness of the existing pipeline and the crossing angle between the new and existing structures， the deformation of the pipeline decreases. However， the deformation increases as the ground loss increases. The proposed method can quickly evaluate the impact of tunnel excavation on existing pipelines.
