Reliability-Based Design of Base Stability for Wide Excavations in Clay with Consideration of Model Bias

Abstract eng:
Design equations for base heave stability in clay are typically simplified and may have conservative bias for design safety. In this study, three popular base heave design equations are calibrated based upon real case histories with wide excavation. It is found that modified Terzaghi's method is nearly unbiased, while Bjerrum and Eide's and slip circle methods are biased to the conservative side. The model uncertainty associated with Bjerrum and Eide's method is the lowest, while that associated with the slip circle method is the highest. The reliability levels for design code regulations are verified, and reliability-based design charts are provided as shown in Fig. 1. It is revealed that the recommended FSs for modified Terzaghi's and Bjerrum-Eide methods in design codes (FS = 1.5 and 1.2 respectively) provide safety level higher than that for slip circle method (FS = 1.2).

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