A discussion of "a simplified prediction method for evaluating tunnel displacement induced by laterally adjacent excavations" by Zheng et al. (2018)

In this short paper, the semi-empirical model introduced by Zheng et al. (2018) for evaluating the tunnel displacements induced by adjacent excavation was extended to a probabilistic model. To this end, the input parameters of the problem were defined as random variables with certain means and standard deviations. A reliability model was then established and solved by the Monte Carlo method. The results showed that the probability of exceedance fell sharply by increasing the tunnel displacement so that the probability of tunnel displacement of larger than 41 mm was less than 5%. Moreover, the reliability sensitivity analysis showed that the excavation depth and tunnel burial depth mostly affected the small range of tunnel displacements between 0.5 and 10 mm. However, the maximum impact of the retaining structure displacement and the horizontal distance of the tunnel from the excavation site were found to fall in medium and large (0.5 to larger than 21 mm) ranges of tunnel displacement. Having the exceedance probability curve presented in this paper, the exceedance probability for any desired value of the tunnel displacement is available, which can be used for safety evaluation and risk assessment of existing tunnels close to the surface excavations.