Abstract
<title>Abstract</title> <p>The limestone formation in the Jinan area belongs to a typical karst development zone in northern China. Initially, basic physical tests were conducted on karst fillings from typical sites in the Jinan area. The data indicated that the fillings exhibit moderate expansion potential, with high montmorillonite content being the cause of their expansibility. Further tests were carried out on the expansive karst fillings, including free swelling ratio tests under dry-wet cycles, mercury intrusion porosimetry tests, and triaxial tests. The specimens were subjected to 1, 3, 7, and 11 dry-wet cycles. The findings are as follows: (1) Multiple dry-wet cycles significantly reduce the expansibility of karst fillings. (2) After 11 dry-wet cycles, the total pore volume increased by 83%, with the proportion of large pores rising from 6% to 49%, indicating a significant deterioration in the microstructure of the karst fillings. (3) With an increase in the number of dry-wet cycles, the shear strength decreased noticeably, and the elastic modulus declined exponentially, stabilizing after a reduction of approximately 38% following 3 cycles. The rate of shear strength decline was relatively uniform, with an eventual deterioration of about 40%. Quantitative relationships between elastic modulus, shear strength, and the number of dry-wet cycles were established based on experimental data. Stress paths and effective stress ratio curves revealed a strain-softening effect in the karst fillings after dry-wet cycles, gradually exhibiting ductile failure. As the number of cycles increased, repeated expansion and contraction weakened the cementation between particles, making them more prone to rearrangement and compaction. This led to a 1.3-fold increase in the maximum static pore water pressure during the tests. Based on the results of mercury intrusion porosimetry and triaxial tests, a progressive macro-micro damage evolution pattern was established, revealing the intrinsic correlation between microscopic damage evolution and macroscopic mechanical deterioration of karst fillings under dry-wet cycles. This study provides valuable references for engineering construction in karst areas.</p>