GE-34 design of retaining walls accounting for paramatric uncertainties

Abstract

Eurocode 7 had been introduced to supersede British Standards and used in geotechnical designs of civil engineering works in Singapore’s construction industry since 2015. It employs limit state design by applying partial factors to characteristic parameter values to achieve the appropriate degree of reliability. However, uncertainties are unavoidable in geotechnical engineering and they arise from various aspects including geotechnical properties, loadings, design methodologies and so on. Hence, a complementary reliability-based design approach to Eurocode 7 is introduced and analyzed in this research project. Reliability-based design is based on computing reliability index (β) to reveal reliability level and probability of failure for designs. It explicitly reflects the combined effects of parameters’ uncertainties and correlation structures. Among various methods to compute reliability index, a practical and conceptually simple spreadsheet based first-order reliability based method (FORM) (Low and Tang, 2007) is used by the author for analyses at Microsoft Excel platform. Additionally, a computer simulation program @RISK to run Monte Carlo Simulation is demonstrated. It provides a simple and convenient way to practitioners to access the reliability analyses and provides additional check to reliability-based design as a safety measure. This research project illustrates retaining wall cases on embedded wall and anchored sheet pile wall with Eurocode 7 design approach, reliability-based design approach and Monte Carlo Simulation. Calibration of EC7 partial factors are studied and compared with the ratios of mean values to design point values from reliability based design. Sensitivity of design parameters to different case configurations is addressed. Additionally, probabilistic methods to determine characteristic values are studied and discussed. Results from different approaches are generally in line and it is demonstrated that design approaches of Eurocode 7 are aiming at sufficiently safe design. While EC7 is conceptually easy for practitioners to apply, reliability design approach and Monte Carlo Simulation can be adopted to provide additional checks and insights to uncertainties of parameters and ensure sufficient reliability is obtained.