Construction risk probability assessment of shield tunneling projects in karst areas based on improved two-dimensional cloud model

Tunnel construction in karst areas presents significant risks due to the complex geological environment and inherent uncertainties. Existing risk assessment methods often struggle to adequately capture and quantify these uncertainties, leading to potentially inaccurate evaluations. This study addresses this gap by developing a novel risk assessment system specifically for shield tunnel engineering in karst areas. This system combines a risk index, considering both frequency and consequence dimensions, with four probabilistic models for quantifying risk levels. These models, based on the spatial geometric characteristics of the two-dimensional cloud model, simulate a large number of outcomes of risky decisions under the influence of uncertainties. Applied to the Guiyang Metro Line 3 construction project, the models effectively determined risk levels, with the Comprehensive Cloud Envelope Model (CCEM) demonstrating high precision and the Comprehensive Cloud Oval Model (CCOM) excelling in computational efficiency. Comparative analysis with existing 2D and 1D cloud models highlights the advantages and wider applicability of the proposed methodology for risk evaluation and control in complex geological environments.