Influence Study On Existing Tunnel Vibration Induced By Blasting Construction Of Under-crossing Tunnel

Drilling and blasting method has become a primary method in excavating hard rock tunnels and short tunnels. The method is economic, flexible and easy to use in construction. However, a strong vibration can be caused to surrounding rock during the excavation, which has become more remarkable in the weak rock construction and lining in the poor situation. Moreover, with the development of the construction of transport infrastructure in recent years, closely spaced parallel tunnel and closely spaced crossing tunnels are increasing. Because the short distance between the new and the existing tunnels, the deformation even damage of surrounding rock and lining structure of the existing tunnel can be caused by vibration during blasting. The corresponding construction strategies can be explored by studying the laws of parameters of the blasting to guarantee the safety of the project and its successful completion. Therefore, influence study on existing tunnel vibration induced by blasting construction of under crossing tunnel has been conducted by numerical simulation in this paper. The corresponding construction strategies have been proposed by combining the engineering example of the second line of Qingdao City Subway. The main work of this paper is as follows:1. Based on the theory of rock blasting and stress wave propagation, the typical three-dimensional numerical model of under-crossing tunnel construction by blasting has been built by using finite element software ABAQUS. The problems of material model, material dynamic parameters, damping parameters, load’s infliction, dynamic boundary conditions, unit selection and grid partitioning involved during the process of establishing model have been solved with a detailed discussion. The reliability of the numerical calculated result of the orthogonal situation has been analyzed by contrasting the existing test result from the view point of energy.2. The blasting safety evaluation index of traffic tunnel has been summarized by referring to a large number of literatures. The maximum vibration velocity and principle tensile stress of the liner are regarded as the indexes to predict the safety of the existing tunnel. Parameters like horizontal distance, vertical distance and the level of the surrounding rock of the direct tunnel have been calculated and analyzed. The location and changes of the maximum vibration velocity and the maximum principle tensile stress of the liner also have been discussed during the parametric analysis.3. Numerical calculated the situation of new tunnel that close beneath and skewing through existing tunnel in the project of the second line of Qingdao City subway. Construction strategies to that situation have been proposed and the two kinds of critical distances in full face blasting construction have been obtained.