Instability risk assessment of expressway construction site above an abandoned goaf: a case study in China

In recent years, more and more expressways have been built above the abandoned goaf. It is of great significance for safe operation of expressways to assess the instability risk of construction site above the abandoned goaf. In this study, a risk assessment model with seven main assessment factors is established for expressway construction site instability based on the fuzzy theory. According to the residual subsidence under different working conditions, the influence mechanism of these main factors on stability is revealed, and the weights of assessment factors are acquired using the grey correlation analysis. The membership degrees of qualitative factors are determined by Delphi method, and the membership degrees of quantitative factors are determined by establishing membership function. The built model is used for Wuyun expressway. The results show that the expressway construction site is basically stable, and the geotechnical grille is applied to improve the anti-deformation ability of Wuyun expressway. Finally, the subgrade subsidence is monitored for 811 days to prove the reliability of assessment result and the effectiveness of subgrade treatment indirectly. This research can provide technical support for risk assessment of similar engineering projects.