Seismic Analysis Of The T Type Joint Of Underground Utility Tunnels

With the rapid development of comprehensive utility tunnel,it is inevitable to form a cross or T-type utility tunnels in the construction process.Therefore,it is particularly important to study the stress characteristics of T-type utility tunnels under the action of earthquake and the simplified calculation method applicable to engineering design.In this paper,nonlinear time-history analysis method is adopted,and finite element software ABAQUS is used to respectively establish a three-dimensional soil-pipe gallery model of T-type utility tunnel composite pipe gallery vibrating along the two vertical direction.The nonlinear characteristics of soil in earthquake process are simulated by the equivalent linearization method.The truncated boundary of soil layer is treated by viscoelastic boundary.At the same time,the equivalent node force is applied to the truncated boundary to realize the input of seismic load.Elastic-plastic damage model is used to simulate the concrete of composite pipe gallery.The time history analysis method of T-type utility tunnel model is calculated by the above theory.The distribution law of the internal forces in the two vertical directions of the T-type utility tunnel under the action of earthquake is obtained,and the position of the maximum internal forces in the utility tunnel under the action of earthquake is obtained after theT-type joint is set.Then this paper adopts the pseudo-static analysis method to model and calculate,By applying the displacement response of free field to the soil spring connected with the composite pipe gallery under earthquake action,the interaction between soil mass and the utility tunnel under earthquake action was simulated,and the response of the utility tunnel under earthquake action was obtained.Then,the section of the maximum internal force and the position of the maximum internal force on the section of the maximum internal force were analyzed and determined.The results of the quasi-static calculation are compared with the time-history analysis method,which provides a reference for the simplified calculation of the seismic design of the time-history analysis method.Researches show that,T-type joint will increase the internal force of the pipe corridor at the interface to the maximum,and the corner of the junction between the top and bottom plate and the side plate of the section is the section with the maximum internal force.Compared with the unidirectional pipe gallery,the existence of T-type joint has the greatest influence on the bending moment of the utility tunnel where the axial vibration occurs.It has the greatest influence on the axial force of the transverse vibrating utility tunnel.The most unfavorable position of the standard section pipe gallery away from the T type joint is at the junction between the side plate and the bottom plate.The internal force in the vibration condition of the T-type utility tunnels along the axis and the symmetry axis in the same direction is greater than that in the vibration condition along the other vertical axis.The vibration condition along the axis and the symmetry axis of the T-type utility tunnels is the control condition of the seismic design of the T-type utility tunnels.Under the control condition,the quasi-static analysis method can be used as a simplified calculation method of time history analysis method to reflect the internal force distribution trend of T-type utility tunnels.