Research On Mechanical Characteristics Of Segments And Joints Based On Three-dimensional Discontinuous Contact Model

Shield tunnel lining is assembled from segments, which is its most important characteristic, and the existence of the segment joints makes the shield lining and monolithic lining significantly different in the aspect of stress and deformation properties, especially the joints ofter develop into disease prone points of the tunnel under the repeated train load.Relaying on the subjects supported by the National Basic Research Program of China (973:2011CB013802) and so on, the static and dynamic properties of segments and joints of metro shield tunnel in the normal service and unloading condition caused by a new adjacent foundation pit construction are analyzed in-depth with numerical calculation method. Thesis completed the following contents:(1) Taking a full consideration of the feature of shield tunnel structure, the three-dimensional discontinuous contact model of track bed-segment-surrounding rocks is build, by use of the nonlinear contact theory to simulate segment joint and the interaction between the segment and surrounding rocks as well as track bed. By introducing the infinite-element artificial boundary and train dynamic loading, this model can make dynamic response analysis under the train load in the stress and strain state which is made by static calculation.(2) Based on the three-dimensional discontinuous contact model of track bed-segment-surrounding rocks, the stress and deformation properties of segments and joints under the pressure of surrounding rock and the action of train dynamic load are analyzed. The change rules of the deformation and stress of segment joints, the internal force of joint bolts under the train dynamic load are reached.(3) By adopting multi-scale mixed modeling technology, the change rules of mechanical behaviour of segments and joints with lateral unloading caused by a new adjacent foundation pit construction as well as the control index of the shield tunnel are reached. With the excavation of adjacent foundation pit, the stresses and deformation of segments and joints increase significantly, and when the vertical convergence rate of the lining reaches3.68‰or the horizontal displacement rate of tunnel axis reaches0.53‰, we should pay particular attention to the condition of the shield tunnel. The deformation and stresses of some segment joints reach their limit.(4) The effect of unloading, caused by a new adjacent foundation pit construction, on dynamic characteristic of segments and joints is studied. Before and after lateral unloading, the change rules of dynamic response time-history curves are same, but the lateral unloading enhances dynamic responses of the tunnel, and the effect on segment joints on the side of tunnel near the foundation pit is most significant.