Assessing the influence of geotechnical uncertainty on existing tunnel settlement caused by new tunneling underneath

Inherent soil variability, measurement error, statistical uncertainty, and transformation uncertainty constitute the four main sources of geotechnical uncertainties. This paper presents a systematic probabilistic analysis framework, through a case study, to assess the influence of geotechnical uncertainty on the existing shield tunnel settlement due to new tunneling underneath. Within this framework, various sources of geotechnical uncertainties are quantified using available Cone Penetration Test data (cone tip resistance) in the studied area, and three scenarios (i.e., pessimistic, neutral, and optimistic scenarios) are considered to incorporate different magnitudes of measurement errors. Through a random field-based 3D numerical simulation, the existing tunnel settlement by construction of a new tunnel is evaluated under the three scenarios. The errors in the settlement prediction are quantified using the monitored settlement data in a probabilistic manner with the assistance of Monte Carlo simulations. Two types of errors in predicting the existing tunnel settlement are identified (positive error, which occurs when the predicted settlements exceed the monitored settlement; and negative error, which occurs when the predicted settlements are smaller than the monitored settlement), and a conditional random field-based numerical simulation is performed. The results indicate that the conditional random field-based numerical simulation significantly reduces the positive error at the junction of the two tunnels, with the largest accuracy improvement of 48% for the pessimistic scenario.