A shaking table-based experimental study of seismic response of shield-enlarge-dig type's underground subway station in liquefiable ground

Abstract

In instances where earthquakes with large magnitude occur, liquefaction-induced lateral deformation of ground has caused thorough destruction to the underground structure of urban rail transit. A sequence of shaking table experiments was conducted on shield-enlarge-dig type's subway station structure in liquefiable ground exposed to the near field earthquake and the far field earthquake. Outcomes of these experiments are discussed in items of foundation deformation, pore water pressure, acceleration response, dynamic soil pressure, and macroscopic failure of model structure. The measured data infers that, when subjected to a high intensity earthquake, the model structure generates an upward movement relative to the foundation. The difference between the soil pressure above and below the structure is the internal cause of the liquefaction-induced uplift of the structure. The shear deformation to the soil layer of the foundation happened, and the displacement peak values of the left and right pendula were asymmetric. The acceleration response and its amplification coefficient in the model foundation gradually increases towards the surface from the bottom as a result of a low intensity earthquake, but for medium and high intensity earthquakes, the acceleration response decreases first and then increases. A notable phenomenon of high frequency filtering and low frequency amplification ensued during the seismic wave propagation from the bottom to the surface of soil. For the same depth of measuring points in foundation soil, the time when the pore-pressure ratio reaches the peak lags behind the time when the acceleration reaches the peak, and the hysteresis is more intense with a rise in magnitude of ground movement. The response spectrum of a low intensity earthquake is characterized by low period accumulation and amplification, while the response spectrum of medium and high intensity is characterized by moves from short period to long period and multi-peaks. The pore pressure accumulation of the model foundation experienced a change process of “rapid growth and slow dissipation,” and the time period of its sharp increase was consistent with that of the sharp increase of the acceleration arias strength. The existence of the underground structure notably inhibits an increase in pore water pressure. The earthquake damage mechanism of the underground subway station of shield-enlarge-dig type in liquefiable ground occurred in three phases: shear failure occurred on the column and damaged the opening position and spandrel of the tunnel; connection parts of the side wall and roof exhibited tensile damage; and the underground structure collapsed.