Integrated Risk Analysis for Dam Safety
Date Issued
2007
Date
2007
Author(s)
HSU, Yung-Chia
DOI
en-US
Abstract
Taiwan, located in Southeast Asia, frequently encounters typhoons and earthquakes. By receiving increasing attention from the public, dam safety has become an important issue. Many researchers have reported that overtopping, seepage, and piping are the main causes of dam failures. This study takes Shihmen Dam as a case study of three potential failure modes: overtopping induced by flood and wind events, slope instability due to seepage under steady and transient states, and permanent displacement due to earthquakes.
The overtopping model accounts for the uncertainties involved in hydrological observations and flood frequency models. The annual maximum (AM) and monthly maximum (MM) series models are considered; each model considers the Gumbel, Lognormal, and LogPearson type III distributions. A proposed sampling method replicates the sample set of peak flow rate and wind speed. Reservoir routing incorporates operation rules, wind setup, and run-up models and is used to evaluate dam overtopping risk with the input of the peak flow rate and wind speed sampled by the proposed sampling method.
Determining the locations of the phreatic water table under steady reservoir water levels is the first step of slope stability analysis. Results of seepage analysis are then treated as initial conditions in the stability analysis of earth dams. The slope stability model for seepage under steady and transient states is used to assess the reliability of slopes of Shihmen Dam. Monte Carlo sampling (MCS) is used to reproduce the parameters associated with soil strengths, and to evaluate the reliability of the slope stability of Shihmen Dam.
A probabilistic model is used to assess the permanent displacement induced by earthquakes. This model is verified by the simulated results through time domain double integration on 26 real earthquake motions on rock sites. The ground motion is modeled as a portion of a stationary random process defined by a Kanai-Tajimi spectral density function. In addition, 38 sets of ground motion parameters on rock sites and 11 time history records observed at Shihmen are also used to portray the variability of ground motion parameters. Moreover, the uncertainty of the critical acceleration is also accounted in this study by considering the variability of soil strengths. This model has been proved to yield the best estimate of the distributional properties of permanent displacement.
The probabilities of the three failure modes are then integrated through the system reliability algorithm, which yields the overall risk of Shihmen Dam. The occurrence of three failure modes investigated in this study does not necessarily lead to structural failure of Shihmen Dam. For example, the occurrence of dam overtopping does not necessarily result in dam collapse. Thus, the probabilities of the three failure modes should not be treated as the probability of dam collapse.
Subjects
風險分析
水壩溢頂
滲流
地震
壩坡穩定性分析
壩坡位移
可靠度分析
Dam safety
overtopping
flood frequency
slope stability
seepage
permanent displacement
uncertainty
earthquakes
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-96-D91521012-1.pdf
Size
23.31 KB
Format
Adobe PDF
Checksum
(MD5):1e883f37c04759aa802ac9dd1ccbecd2