ABSTRACT
The effective mitigation of landslide risk requires analytical approaches. In qualitative risk assessment, the components of risk, which are hazard, elements at risk and vulnerability, are expressed verbally and the final result is in terms of ranked or verbal risk levels (IUGS 1997). Qualitative risk assessment is subjective in nature. Quantitative risk assessment involves quantification of risk components and computation of risk. The purpose of quantitative risk assessment (QRA) is to calculate a value for the risk to enable improved risk communication and decision-making (Lee & Jones 2004). For landslides, the use of quantitative risk assessment procedures is recommended. Several frameworks for QRA have been proposed by many experts and organizations (e.g. Varnes 1984, Whitman 1984, Einstein 1988, Fell 1994, Wu et al. 1996, Morgenstern 1997, Fell & Hartford 1997, Einstein 1997, Aleotti & Chowdhury 1999, Ho et al. 2000, Roberds 2001, Dai et al. 2002, Nadim & Lacasse 2003, Lee & Jones 2004, IUGS 1997, AGS 2000, NRC Transportation Research Board 1996, GEO 1998). The QRA frameworks have common intention to find answers to the following questions (Ho et al. 2000, Lee & Jones 2004):
1 What are the probable dangers/problems? [Danger Identification]
2 What would be the magnitude of dangers/problems? [Hazard Assessment]
3 What are the possible consequences and/or elements at risk? [Consequence/Elements at Risk Identification]
4 What might be the degree of damage in elements at risk [Vulnerability Assessment]
5 What is the probability of damage? [Risk Quantification/Estimation]
6 What is the significance of estimated risk? [Risk Evaluation]
7 What should be done? [Risk Management]
Depending on the characteristics of a landslide, available data, scale of investigation and nature of consequences, the QRA frameworks may differ. Hazard assessment for a specific slope usually involves probabilistic analysis of the given slope, while hazard assessment for a region generally requires the computation of frequency of the landslides in the region. The probabilistic models used for a specific slope depend on the failure mechanism (flows, falls or slides) and slope material (soil or rock). Furthermore, the characteristics of a landslide and scale of investigation influence the consequence/elements at risk, vulnerability, risk quantification/assessment, risk evaluation and risk management. Two important aspects of QRA for landslides are the lack of wellestablished acceptable risk criteria and methods for
ABSTRACT: Two important aspects of quantitative landslide risk assessment, vulnerability and acceptable risk, are studied as part of a new Integrated Risk Assessment Framework (IRAF). IRAF consists of four steps: data collection, hazard assessment, vulnerability assessment, and risk assessment. Data collection involves obtaining the appropriate data for the hazard, vulnerability and risk assessments. The hazard component integrates the numerical and probabilistic analyses to exploit the added knowledge from the two approaches. A new 3-dimensional framework for quantification of vulnerability is proposed. The fourth component of IRAF is risk assessment, with the computation and evaluation of the risk based on some acceptability criteria. IRAF is implemented for rock slopes. To define an acceptability criterion, published data were collected. Various terminology relating to acceptable risk used in the literature, such as acceptable vs. tolerable, specific vs. total, voluntary vs. involuntary and individual vs. societal, are discussed.
