Strength deterioration of karst fillings under dry-wet cycles: Testing and modeling study

The strength of karst fillings is vital for the safety of tunnels in large-filled karst areas. Karst fillings in areas with seasonal rainfall often experience dry-wet cycle environments, which have a deteriorating effect on their strength and threaten the safety of underground projects such as tunnels. In this study, direct shear tests of dry samples (samples with the moisture con -tent of w(1) ) and wet samples (samples with saturated moisture content) at different dry densities (p(d)), the number of dry-wet cycles ( n ), and the lower-bound moisture content of dry-wet cycles ( w(1) ) were performed to analyze the deterioration rule of c and F of karst fillings. The causes of the strength deterioration of karst fillings were explained based on scanning electron microscopy tests. The deterioration rate was fitted using an exponential function, and a karst filling strength deterioration model (KFDM) was developed that integrated three influencing factors. The KFDM was used through FLAC3D to predict the deformation and safety coefficient of tunnels under dry-wet cycles. The following results were obtained: (1) dry-wet cycles had a significant degrading effect on c and F, and p(d) and w(1) had an important influence on the degradation; (2) the KFDM accurately predicted the c and F values of karst fillings after dry-wet cycles; and (3) the tunnel deformation and safety coef-ficient exhibited cyclic changes during dry-wet cycles. The deformation increased gradually at increasing n , and the safety factor increased in the opposite direction. These results provide insights into the prediction of the deformation and safety coefficient of tunnels in large-filled karst areas and can aid in developing long-term maintenance strategies to ensure safety.