Xiuli Du

Shaking table tests on a three-arch type subway station structure in a liquefiable soil

A series of large-scale shaking table tests were performed to investigate the damage mechanisms of a three-arch type subway station structure in a liquefiable soil experiencing strong motions. Methods to measure the displacement included the vision-based displacement test and the fiber Bragg grating test to measure the strain of the galvanized steel wire. Sand boils, waterspouts, ground surface cracks and settlements, and buoyancy movement of the model structure were observed. When the peak excess pore pressure ratios dramatically increased, the Arias intensity also dramatically increased. The peak acceleration of the model soil also almost coincided with liquefaction of the model soil. The seismic responses of the model structure and the soil were shown to be more sensitive to input motions with larger low-frequency components, the phenomenon of high frequency filtering and low frequency amplification effect of the liquefied soil were observed. The peak tensile strain located at the top and bottom of the center pillars was larger than that obtained at the subarch, while the peak tensile strain at the atrium arch was the smallest. The peak strain at the primary and secondary observation sections were remarkably affected by the spatial effect. The results can provide valuable insight into the seismic investigation of these subway structures.

Nonlinear Response Characteristics of Undersea Shield Tunnel Subjected to Strong Earthquake Motions

ABSTRACT Ensuring the safety of undersea shield tunnels constructed in soft marine deposits that are subject to strong seismic motion represents a major engineering challenge. An example of one such undersea shield tunnel is the 2.70 km-long subsea highway tunnel crossing under the Gulf of Suai in the Rongjiang River Estuary in Shantou, China. Using the generalized response displacement method, the authors developed a nonlinear seismic response analysis of the segmental lining for the 2.7 km-long Suai tunnel. In the proposed longitudinal seismic response analysis, the engineering geology characteristics and nonlinear dynamic behavior of the Suai seabed soil, the nonuniform mesh layout of the free-field site, the artificial boundary conditions and nonuniform seismic input, simulation model, and the parameters of soil-tunnel interaction systems, are considered in detail. Special emphasis is given to the irregular unloading-reloading rules for the stress-strain hysteresis loop, the seismic input at artificial boundary nodes, and the spatial incoherency of ground motions in the seabed site. The opening width at the ring intersegment under simultaneous actions of longitudinal, transversal, and vertical seismic motions is critical for seismic safety. The proposed methodology was deemed conservative, as demonstrated by a comparison with dynamic transient analysis using the three-dimensional finite element method. The results of this pilot study should be of use in the construction of future long subsea shield tunnels in the high seismic intensity region.

Experiment and Analysis of the Seismic Characteristics of Liquefiable Ground under Near-Field and Far-Field Ground Motion

This paper documents a series of large-scale shaking table experiments to investigate the dynamic response of liquefaction soil. Test results are discussed in terms of pore water pressure, earthquake-induced ground settlement, and acceleration of soil. The measured data show that, under strong ground motion, the model foundation was more sensitive to the ground motion whose low frequency component is more.The Arias Intensity of ground motion was associated with the peak of pore water pressure ratio. Under lower peak ground acceleration (PGA) ground motion, the magnification effect of acceleration response spectra appeared at the range of low-period component. However, in higher PGA ground motion, the model foundation shows obviously high frequency filtering characteristic. Observations in this study may serve as basis for engineers and researchers.

Earthquake Analysis of arch Dam Including Dam-Foundation Rock Nonlinear Dynamic Interaction

Publisher Summary nThis chapter proposes an analysis method in the time domain by combining the explicit finite element method and the transmitting boundary. A dynamic analysis method is employed to solve the static responses of arch dams and finally, a combination method is also proposed to calculate the nonlinear responses of arch dams under the actions of static and dynamic load. An arch dam-foundation system is divided into an interior region with dam body and its adjacent near-field foundation with important local topographical and geological features and an infinite far-field foundation region with homogenous and linear features. The interior region is meshed by using the finite element method. The infinite exterior region is simulated by setting a set of artificial boundaries to simulate the propagation of outgoing scatter waves from the interior region to the infinite exterior region. The motions of the nodes of the discrete finite element model in the interior region are calculated by the explicit finite element method and the motions of the nodes at the artificial boundaries are solved by the transmitting boundary.