۱- Introduction

۲- Input method of oblique incidence seismic waves

۳- Dynamic contact analysis model of an underground powerhouse structure and the surrounding rock

۴- Numerical application

۵- Summary and conclusions

References

In this work, the impacts of seismic motion incident angles and the rock-structure interaction (RSI) on the seismic response of an underground powerhouse structure of a hydropower station are studied. Based on the viscous-spring artificial boundary condition, the input methods of oblique incidence SV and P waves are presented by transforming the seismic motion into equivalent nodal forces acting on the nodes of artificial boundaries. Based on the explicit central difference method, an explicit dynamic contact analysis method considering the bonding and damage characteristics of the contact face between the surrounding rock and the underground powerhouse structure is also proposed. Consequently, the proposed methods are implemented into an dynamic finite element program and applied to the seismic damage evolution process analysis for the concrete structure of an underground powerhouse, and the results reveal that (1) the stress and deformation response of the underground powerhouse structure caused by seismic excitations are clearly affected by the incident angle and its degree of damages reaches a maximum when the incident angle is 30°; (۲) compared to the case of without the RSI, the damage distribution ranges and the damage coefficient of the underground powerhouse structure are much larger than that in the case of with the RSI; and (3) the contact state of the contact face plays a key role in the dynamic stability of the underground powerhouse structure, and a good contact state can help to reduce the dynamic damage of the underground structure.

Introduction

Southwest China is rich in water resources, with a number of large hydropower stations located there. These hydropower underground powerhouses are generally composed of several long-span and high sidewall caverns that are located in areas of high seismic intensity, which will have a great impact on the overall safety of the hydropower stations if an earthquake disaster occurs. Numerous studies have been conducted to study the dynamic response of underground caverns [1–۷], with many achievements having been obtained. However, the researches have mainly focused on the surrounding rock, while few studies have investigated the dynamic response of the underground structures. The “Wenchuan” earthquake disaster investigation [8,9] showed that the surrounding rock of an underground powerhouse in the earthquake area is generally stable, but the seismic damage to the underground structure is serious, which means that the underground structure is a weak component in the seismic design of an underground powerhouse, and its seismic response characteristics have a high theoretical and engineering significance. The dynamic time history method is an effective method for analyzing the seismic response of complex large-scale structures. The seismic response time history analysis of an underground powerhouse structure mainly includes two aspects: one is the seismic motion input for the finite element model, and the other is the dynamic contact analysis of the surrounding rock and underground structure. It is well known that whether or not the input method of the seismic motion is reasonable will directly affect the accuracy and credibility of the calculation results. In the existing numerical calculations of underground structures, it is mostly assumed that the seismic motion is a vertical incidence from the bottom of the numerical model. In reality, when the epicenter is close to the engineering site of the underground structure, the seismic motion is usually obliquely incident [10]. According to the statistics data of strong earthquake observation records in recent years, it was determined that the incident angle of the seismic motion for a bedrock site is approximately 60° [۱۱,۱۲]. This oblique incidence seismic wave will produce spatial non-uniform effects on the underground structure. Some scholars are currently studying the influence of oblique incidence seismic motion on underground structures. Du et al.