This study investigates the pile foundation of a nuclear power plant situated on medium-soft soil. It employs an improved viscoelastic artificial boundary unit to accurately simulate the boundary conditions of the calculation area. The research utilizes a constitutive model of concrete damage plasticity for the pile foundation and an equivalent linearized model for the soil layer. Through large-scale shaking table experiments and numerical simulations, we explore the internal force distribution within the nuclear power structure's pile foundation and assess the extent of the damage. The results indicate that damage primarily occurs in the medium-soft ground, concentrating in the upper part of the pile and affecting the entire cross-section. Subsequent numerical analyses were conducted after reinforcing the soil layer around the top of the pile. The findings demonstrate that this reinforcement leads to a more uniform and rational distribution of internal forces along the pile, significantly reducing damage. Notably, there is no severe damage extending across the entire cross- after reinforcement. This outcome highlights the potential for improving the force distribution in the pile foundations of nuclear power structures through appropriate soil layer reinforcement. The insights gained from this study provide valuable guidance for the seismic design of nuclear power structures.

Loess is a typical structural soil with properties such as water sensitivity, collapsibility, and seismic vulnerability. The dynamic response of a water transmission pipe crossing a fault zone is highly complex in a loess site. The Hanjiang River to the Weihe River Diversion Project (Phase II) crossing the Weihe fault was selected as the prototype for a shaking table test, through which the responses of acceleration, dynamic stresses, strains, and pore-water pressure were systematically investigated. The acceleration response of a geologic body similar to the experimental model was greatly affected by factors such as fault location, degree of soil saturation, distribution of internal structure, and so on. The acceleration along elevation experienced its highest amplification factor of approximately 2.0, mainly due to seismic waves with frequencies above 2.0 Hz being amplified. To ensure the seismic fortification of the pipeline near the fault belt, it is recommended to utilize an acceleration of 1.2 times within the severe impact zone. This zone involved 36.0 m of the hanging wall and 30.0 m of the footwall, which are approximately 6.0 times and 5.0 times of the fault belt width. It is recommended to use an acceleration of 1.1 times for areas within 200 m from the fault of the hanging wall; refer to the fault-avoiding distance of the seismic design code. The deformation mode of the water pipeline was expansion/shrinkage in the transverse and slight bending in the longitudinal section. The pore-water pressure response demonstrated coupling features of hysteresis, accumulation, and dissipation. The seismic collapsibility modes of the loess at the studied site were generalized into four stages: energy accumulation, state mutation, failure extension, and successive failure. Seismic subsidence could be expressed by adopting a piecewise function with a maximum value of approximately 18.0 cm. Based on the similarity calculation, the maximum seismic subsidence of the prototype can be recommended as 3.6 m. Liquefaction occurred when the input acceleration amplitude reached 0.5g. These shaking table test results provided reasonable parameters for the seismic design and construction of the Hanjiang to Weihe River Diversion Project across this fault.