Robust geotechnical design of rock bolts for stability of rock slopes using response surface

Abstract

Stability of rock slopes in many civil engineering projects involves installation of rock bolts for stabilization. Uncertainty in input parameters that determine the stability of rock slopes may lead to uncertainty in evaluating the factor of safety. Design of installed rock bolts must be optimized for safety requirements, cost efficiency and robustness. A design is considered robust if it is least sensitive to variation in input parameters. A well accepted quantity, Signal-to-Noise Ratio (SNR) is selected to be a robustness measure. Factor of safety of slope is evaluated using commercial software Phase2D. General purpose response surface as a surrogate model to Phase 2D simulation is created to model the system response for various designs. Reliability index for all the designs was calculated from the response surface via Monte Carlo simulations. Further analysis was performed on those designs which satisfy a threshold value of reliability index. A simplified Robust Geotechnical Design (RGD) methodology is adopted in which a number of single objective optimizations were performed to locate the position of acceptable design w.r.t. utopia point in a plot of cost vs. robustness. Finally the global knee point is taken to be the optimum design whose distance is minimum from the utopia point.