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The geo-structures embedded in the multiple variable strata could be significantly affected by the geological uncertainty. The quantitative evaluation of geological uncertainty and its influence on the structural safety of embedded tunnels are seldom studied in the past. This paper aims to analyse the effect of geological uncertainty on the structural performance of tunnel using the proposed stochastic geological modelling framework. The geological uncertainty is characterized using an improved coupled Markov chain model based on sparse limited boreholes. A mapping approach is presented to solve the mesh asymmetry problem between the simulated strata and the numerical tunnel model. The tunnel structural performance analysis is then conducted based on the combined model considering the geological uncertainty and tunnel structure. A geological uncertainty index (GUI) is proposed to quantitatively evaluate the level of uncertainty of each borehole and the whole site. The effect of the borehole layout scheme on uncertainty evaluation of factor of safety of tunnel structure is investigated by a large number of stratigraphic realizations. Boreholes collected from Norway with relatively more considerable variability and from Shanghai with relatively more minor variability are adopted as case studies to illustrate the proposed probabilistic analysis framework. The results show that the boreholes with larger GUI values and closer to tunnel locations have a greater weight to affect the embedded tunnel structural performance in uncertain geological strata. [ABSTRACT FROM AUTHOR]

Geological uncertainty is common in nature due to complex depositional processes as one layer appears to be randomly embedded in neighbouring layers. However, the geo-structures could be significantly affected by the geological uncertainty, often simulated using the coupled Markov chain (CMC) model. The objective of this study is to develop an improved CMC method by enhancing the rationality of determining the horizontal transition probability matrix (HTPM) in the CMC model to simulate complex multi-layer strata based on limited borehole data. This difficulty of determining HTPM is solved by combining the vertical transition count matrix and intermediate horizontal matrix with Walther's law. The effectiveness of this method is evaluated by the artificial HTPM and virtual boreholes. Boreholes collected from Norway are adopted to illustrate the proposed method for HTPM estimation. Estimating the HTPM has been dramatically enhanced for the improved CMC model and is not sensitive to the borehole layout schemes. The error of HTPM between estimated and actual strata is less than 3% for different borehole schemes. A matching rate indicator is defined to evaluate the accuracy of the simulated results. The results show that the proposed method has good performance and robustness. An optimizing design approach for the borehole location and number is presented to minimize the uncertainty of the stratum simulation based on the information entropy. • An improved CMC method is developed to simulate complex multi-layer strata. • The approach is validated and illustrated using both real and artificial boreholes. • A matching rate indicator is defined to evaluate the accuracy of simulated results. • Optimation for borehole location and number is presented based on information entropy. [ABSTRACT FROM AUTHOR]