Shaking table tests on discrepant responses of shaft-tunnel junction in soft soil under transverse excitations

Due to the special configurations of the shaft-tunnel junction, discrepant responses of the shaft and the tunnel will arise when earthquakes strike. This paper presents shaking table tests addressing this discrepancy and its influence on the structures. The model system is designed to reproduce the relative stiffness and the relative mass of the prototype system. Two site-specific synthetic earthquake motions are adopted as seismic excitations along the transverse direction of the tunnel model. The discrepant responses are revealed by the shaft's and the tunnel's acceleration responses. The extent of discrepancy is quantified by correlation coefficients, and its influence on structural performance is evaluated. Consequently, the longitudinal circumferential-joint extensions and the transverse dynamic strains are raised at the shaft-tunnel junction. While the raised strains are relatively small, the longitudinal circumferential joint extensions pose a threat to structural safety. A simplified model based on the solution for Euler-Bernoulli beam on Winkler foundations is put forward to establish the relation of circumferential-joint extensions and shaft-tunnel relative displacements. Validation of the proposed model is conducted by comparison of test results and analytical results.