Probability-based Risk Research Articles

Probability-Based Risk Assessment Applied to Slope Stability Analysis in Reclamation of an Open-Pit Mine

This paper discusses the use of a probability-based analysis incorporating expected value methodology in the evaluation of slope stability issues during the reclamation of the Spenceville Mine, a flooded, open-pit mine dating from the mid-1800s. Site conditions, necessitating the use of this analysis, are discussed. Resulting data and analyses are presented as an example of the methodology, rather than as an isolated case history. The study resulted in an estimate for the probable volume of material that would fail into the open pit in the course of reclamation. This expected failure volume is a function of the failure mode, the probability of occurrence of each failure mode, the probability of failure of each failure geometry, and the maximum volume of material that could be incorporated into a failure. The resulting value for expected failure volume was not intended to serve as a deterministic solution for individual slope stability problems, but as an index to guide the reclamation team in proactively addressing slope stability concerns. Results of the study were used to determine an appropriate slope monitoring plan, to guide construction activities and designs, and to dictate safety precautions for personnel working in and around the open pit during the de-watering and backfill phases of the reclamation process. A discussion of conditions and events observed during, and immediately following, de-watering of the pit is presented to illustrate differences between analytical predictions and actual conditions. In general, the ability of probability-based analysis to highlight areas of slope stability hazard within the mine was validated by the general agreement between prediction and the actual types and locations of failures observed during the reclamation process.

Managing incomplete knowledge: Why risk management is not sufficient

The Project Management Institute’s Guide to the Project Management Body of Knowledge (PMBOK) underpins many initiatives to improve project management practice. It is widely used for training and underpins the development of competency standards. Because of its fundamental importance, the PMBOK should be critically reviewed. This paper agues for an expansion of the PMBOK Guide’s risk management knowledge area to include a wider perspective of incomplete knowledge. The PMBOK Guide deals with uncertainty through the traditional use of probability theory, however the underpinning assumptions of probability theory do not always apply in practice. Furthermore, probability-based risk management theory does not explain important aspects of observed project management practice. This paper discusses an expanded framework of incomplete knowledge, including: an expanded concept of uncertainty that acknowledges ignorance or surprise, where there is no prior knowledge of future states; imprecision arising from ambiguity (fuzziness) in project parameters and future states; and, human limitations in information processing. The paper shows the expanded framework explains observed project-management practice more thoroughly than the probability-based framework. The conclusion reached is that “management of incomplete knowledge” provides a better theoretical foundation for improving project management practice. To substantiate this, a promising new approach based on “real options” is also discussed.

Assessment and Repair of Offshore Platform Applications to Bay of Campeche Facilities

Abstract In 1995 hurricanes Opal and Roxanne passed through Bay of Campeche (BOC). Opal did not cause any noticeable damage. Roxanne, on the other hand, was the most severe hurricane recorded in the Bay of Campeche in this century. Its anomalous behavior and the resulting extreme environmental conditions did considerable damage. PEMEX implemented a rapid repair program and was able to bring tile production back to its normal levels within two months. Subsequently, PEMEX, jointly with Instituto Mexicano del Petro´leo (IMP), launched an extensive program to inspect, assess, and repair the facilities. Results of the initial assessments indicated that the assessment parameters, as well as the metocean criteria utilized, were not suitable for Bay of Campeche. A detailed risk study considering the site-specific conditions and requirements was performed. Utilizing probability-based risk assessment techniques, a new criteria, known as the “transitory criteria,” was developed. The transitory criteria was then used to reassess the platforms and pipelines in the southwest marine region of BOC. Critically damaged platforms were identified for repair. The scope of repairs included jacket structural members and support framing for deck facilities. An overview of various techniques used for repairs of the underwater jacket structural members and joints is given. Different underwater repair methods are discussed. Repairs of both jacket and deck damages caused by hurricane Roxanne are presented as examples. The repair methods used are based on currently available technology and they will provide practical examples for economical platform repair in shallow, warm water environments. [S0892-7219(00)01101-8]

Human and Organization Errors in Reliability of Offshore Structures

Abstract This paper addresses human and organization errors (HOE) in the context of quantitative reliability analyses (QRA) that are intended to help improve the quality of offshore structures. A classification of HOE is proposed that addresses individual, organization, equipment/hardware, procedures/software, and environmental considerations. A generic process to address the life-cycle quality characteristics of offshore structures incorporating HOE is discussed. Based on these developments, a probability-based risk analysis is developed that addresses HOE in addition to the structure system aspects. Alternatives for improved management of HOE are discussed including quality assurance and quality control (QA/QC), and design of error-tolerant or “robust” structures. Application of the HOE classification, generic assessment process, QRA formulation, and QA/QC measures are illustrated.

A probability-based approach for predicting HIV infection in a low prevalent population of injection drug users

This article proposes a method for estimating HIV risk in low-HIV-prevalent populations. Allard's risk probability model was used to compute individual risk scores. Based on a sample of 3854 injection drug users (IDUs) who were confidentially tested for HIV at five methadone treatment clinics in Los Angeles County, the following self-reported risk behaviors were used to derive an individual IDU risk score: (i) frequency of injection, (ii) frequency of using uncleaned needles, (iii) number of people sharing a needle, (iv) frequency of needle sharing, and (v) type of needle sharing practice. The overall HIV prevalence for the IDU sample was 2%. The risk score was strongly associated with HIV seropositivity (chi-square = 16.1, p < 0.0001), but only one of the individual IDU risk behaviors (needle cleaning) was significantly associated with HIV seropositivity (chi-square = 10.9, P < 0.001). In addition, the risk score was strongly associated with HIV serostatus for both males and females. For females, however, none of the individual IDU risk behaviors were associated with HIV serostatus. Our findings indicate indicate that when predicting HIV infection in a low-prevalence population, the probability-based risk score makes a statistically significant contribution over individual IDU risk behaviors.

Deriving Forecast Probability Distributions of Harvest‐Time Corn Futures Prices

Preharvest corn price forecasts are typically presented as price ranges or point estimates, while the probabilities associated with alternative grain price forecast scenarios are usually not identified. For example, United States Department of Agriculture (USDA) preharvest price forecasts are typically given as price ranges, while preharvest forecasts from university extension and other private sources are often given as point estimates. When alternative market scenario probabilities are provided, they are often based on rudimentary statistical analysis of historic weather conditions and/or the analyst's intuition rather than on accepted econometric methods. Preharvest grain price probability information would be useful to farmers, grain buyers, and processors in making price risk management decisions. Farmers implicitly make probability judgements regarding the likelihood of alternative supply, demand, and price scenarios as they carry out preharvest grain marketing strategies. All grain buyers and sellers could benefit by knowing the probability of financially-adverse price outcomes. With accurate price forecast probability information, probability-based price risk management strategies could be developed to limit the risk of financial loss to the farmer or the firm. A number of structural models of grain market supply and demand have been developed for forecasting and policy analysis purposes. Examples are found in Houck, Ryan, and Subotnik; Chen; Arzac and Wilkinson; and Westhoff et al. Reduced form equations from these multiple equation systems guide the

Probabilistic study of spoil pile stability in strip coal mines—Two techniques compared

For analysis and design work involving the assessment of slope stability of spoil piles in strip coal mines, it is very useful to adopt an approach based on estimated risk of failure. Studies of several spoil pile failures in Queensland (Australia) have revealed a two-wedge failure mode and it is important that probability-based risk studies are made considering such a failure mechanism. Calculations for failure probability were first made using Monte Carlo simulations and assuming a potential two-wedge mechanism. An alternative procedure based on Rosenblueth's method of estimating moments was then used to compare the results with those based on simulation. Excellent agreement was found and it is recommended that, for practical purposes, the relatively quick Rosenblueth method should be used in estimating the probability of slope failures. The study also confirms the suitability of Normal and Beta distributions in this context in geomechanics.