Quantitative Assessment of Horizontal Directional Drilling Project Risk Using Fuzzy Fault Tree Analysis

Fault tree analysis is regarded as a powerful technique for assessing system reliability. The conventional approach of solving fault trees is based on applying probability theory by assigning probability distributions to basic events and propagating the probabilities to calculate the overall probability of the top event. However, applying this technique, especially in construction projects, entails several difficulties attributed to the lack of sufficient data to estimate the probability distributions for basic events. Thus, risk analysts tend to assume probability distributions of basic events, which adds further uncertainty to the analysis. To overcome these difficulties, this paper presents a simplified approach in which basic events are represented by a possibility distribution, and the possibility distribution of the top event probability is calculated by applying fuzzy arithmetic operations. The method presented herein is demonstrated using a case study to quantify the probability of failure of horizontal directional drilling (HDD). The proposed approach is able to overcome the difficulties of using the conventional approach by relying on linguistic terms rather than assuming probability distributions for basic events.