Shaking table tests on shaft-tunnel junction under longitudinal excitations

Shaking table tests are conducted to study the discrepant responses of shaft-tunnel junction. The cases with transverse excitations are introduced in a previous paper, while the current paper mainly addresses the responses under longitudinal excitations. A brief introduction is provided on the design of the tests. Data of accelerations, dynamic strains, and circumferential-joint extensions are presented in four cases. Two white-noise cases are conducted to evaluate dynamic characters of the model system as well as examine repeatability of the test results. Two synthetic-earthquake-motion cases are conducted to study the seismic responses of the shaft-tunnel junction under natural earthquakes of different intensities. As revealed by the acceleration data, the shaft and the tunnel have exhibited quite different dynamic characters under longitudinal excitations. The extent of shaft-tunnel discrepancy is statistically quantified by correlational method. Although transverse strains of the tunnel are slightly elevated at the shaft-tunnel junction, absolute values of the strains remain in a lower range which is below 65 mu epsilon. However, the discrepant responses have caused tensile deformations of the tunnel, which eventually lead to significant circumferential-joint extensions near the shaft. A simplified analytical model is proposed to establish the relationship between the discrepant responses and the longitudinal deformations of the tunnel. At the end, testing data from the transverse-excitation and the longitudinal-excitation cases are compared. In both cases, the shaft-tunnel relative displacement and the soil-tunnel relative stiffness are considered as the two key factors.