Probabilistic analysis of seismic slope stability

The paper presents a reliability-based method that can capture the impact of uncertainty of seismic loadings. The proposed method incorporates probabilistic concepts into the classical limit equilibrium and the Newmark-type deformation techniques. The risk of damage is then computed by Monte Carlo simulation. Random process and RMS hazard method are introduced to produce seismic motions and also to use them in the seismic slope analyses. The geotechnical variability and sampling errors are also considered. The results of reliability analyses indicate that in a highly seismically active region, characterization of earthquake hazard is the more critical factor, and characterization of soil properties has a relatively small effect on the computed risk of slope failure and excessive slope deformations. 1aINTRODUCTION An important step in the slope stability analysis is to identify uncertainties of key design parameter and their statistics. The variability of the various parameters such as material properties, fluctuations of the loads, and the uncertainties of the geometry all contribute the difficulty of evaluating how the slope actually behaves regardless of the computed factor of safety. In spite of extensive effort, there has not been much consensus on how to model these uncertainties systematically, leaving them mostly up to the rather subjective judgments of individual engineers. In the past, there have been numerous studies of the various sources of uncertainty and their impact on the risk of damage of slopes subjected to seismic loading. Most approaches, however, have focused either on material uncertainty or on uncertainty of seismic loading (e.g., Pal et al. 1991; Yegian et al. 1991) partly because of computational convenience, and partly due to the practical difficulty in modeling both material and seismic hazard uncertainties. In this paper, the authors present a reliability-based method that can capture the impact of uncertainty of key material properties and seismic loading in the assessment of seismic slope stability. The uncertainty of seismic loading is approached by generating a large series of hazard-compatible artificial motions, and by using them in subsequent response analyses. The geotechnical variability and sampling errors are also taken into consideration. This approach incorporates probabilistic concepts into the classical limit equilibrium and the Newmark-type deformation techniques. The risk of damage is then computed by Monte Carlo simulation. Finally, the overall impact of uncertainties and their relative significance on seismic stability of slopes will be judged. 2 ENERATION OF HAZARD-COMPATIBLE GROUND MOTIONS Due to the random nature of earthquake motions, the definition of the input excitation is one of the major uncertainties in the seismic response analysis. The stochastic representation of the earthquake motion hazard provides, at least theoretically, a systematic way of representing the infinite number of possible scenarios, which correspond, to a certain level of hazard. A zero-mean process can be represented as: ISGSR2007 First International Symposium on Geotechnical Safety & Risk Oct. 18~19, 2007 Shanghai Tongji University, China