Investigations On Source Characteristics And Propagation Laws Of The Ground Vibration Induced By High Dam Flood Discharge

The hydropower engineering project with high dam and large reservoir capacity is the need of comprehensive utilization of water resources. With the development of high dam construction, vibration problems induced by flood discharge of high dam are increasingly prominent. Due to the high drop height, the flow fluctuating loads generated by the enormous water energy will induce vibration of the discharge structures, as well as other hydraulic structures. This vibration can be transmitted from the superstructure to the dam foundation, and then to the ground, which can influence the safe of nearby structures and be harmful to the surrounding environment the neighboring residents when it reaches a certain magnitude. However, previous studies are mainly focused on the flood discharge-induced vibration safety of hydraulic structure itself. Very few studies have looked at the vibration on complex dam site and nearby ground. This paper is aimed at investigations on the characteristics of vibration sources and propagation laws as well as prediction the ground vibration induced by high dam flood discharge under broadband flow fluctuating loads-multi vibration sources excitement. The results are as follows:(1) The causes of ground vibration induced by high dam flood discharge are investigated. A prototype observation system is used to analyze the effect of micro-tremor acts on the ground under background vibration conditions, assess the characteristics of ground dynamic and natural vibration as well as investigate the vibration distribution and the local site amplification effect.(2) The vibration sources characteristics of ground vibration induced by high dam flood discharge are analyzed. And the Time-wavelet power spectrum(TWPS) and the Cross wavelet transform(XWT) techniques are introduced. The results show that the time-wavelet distribution can reflect the magnitudes and changes of flow fluctuating energy, which helps identify the primary cause of ground vibration and examine the energy of the vibration sources and its change. The XWT reveals the changing characteristics of two signals both in the time and frequency domains, which can establish the spatial relationship between multi-vibration sources and ground vibration. Then, the correlation characteristics of different source in time- frequencyspace domain and the contribution of each vibration sources are analyzed, respectively.(3) The propagation laws of ground vibration are analyzed. The “multi-vibration sources- discharge structure- foundation- ground” finite-infinite element coupling dynamic model is developed. This model solves the problems of vibration wave propagation in infinite domain and the problems in large complicated field simulation well. The calculated results agree well with the prototype observation ones. Through the finite-infinite element coupling model and the vibration source analysis results, the propagation(attenuation, amplification) laws of ground vibration in complex valley along the downstream direction induced by broadband flow fluctuating loads-multi vibration sources are examed. Based on this, the effects of each source on the ground vibration and its propagation characteristics are also investigated.(4) The establishing method of ground vibration prediction system is studied. The ground vibration prediction system based on “noise correction” transfer function with multi-sources combined input is developed according to the vibration sources characteristics and propagation laws of ground vibration. The result shows that the system is able to accurately predict the intensity and frequency spectrum of ground vibration, which solves the multi-sources combined input system prediction problems. At the same time, an improved filtering method based on ensemble empirical mode decomposition(EEMD) and wavelet threshold is proposed. The method possesses attractive properties such as strong noise reduction ability, keeping the useful vibration signal completely. Therefore, it provides an effective support for the accurate prediction of ground vibration.In a word, during discharging of high dam, the flow fluctuating loads are generated and applied on different discharging structures, which can all cause the ground vibration. Different sources show different vibration characteristics, while all the sources can influence each other. The contributions and the propagation(attenuation, amplification) laws of each source are different under different discharge ways and different soil composition. The ground vibration prediction method based on the vibration sources characteristics and propagation laws of ground vibration can accurately predict the ground vibration in both time domain and frequency domain, which provides the basis for designers to select reasonable flood discharging way, with strong practical significance.