Extensive and thick permeable strata are found beneath many reservoir sites. The leakage problem in these reservoirs can be effectively solved by constructing a full geomembrane liner design. However, applying this particular solution for the reservoir induces novel engineering problems. The air bulging produced beneath the geomembrane results in geomembrane rupture and causes a renewed leakage in reservoirs. The groundwater level may be relatively low during construction because of seasonal variation and dewatering. Geomembranes isolate pore air from the atmosphere, and a significant amount of air is trapped in the pores of the unsaturated soil above the groundwater level. The rise in the groundwater level or the compression of soil decreases pore-air volume and increases pore pressure, thereby causing air bulging to occur and prompting the ultimate destruction of the geomembrane. The presence of air bulging beneath the geomembrane is studied in the design process of the Datun Reservoir in Dezhou City, Shandong Province, China. Investigation results reveal that a rise in the groundwater level significantly influences the air bulging beneath the geomembrane. The French drain is set to prevent air bulging beneath the geomembrane from occurring. The 75-m French drain spacing is not reasonable because the air pressure beneath the geomembrane will result in air bulging. A comparison among French drains with spacings of 25 m and 50 m indicates that the original design comprising French drains spaced 50 m apart is reasonable and economical.

In excavated earth structures (e.g. Deep Excavation, Cut slope, and Underground Construction etc.) unloading is the most predominant factor that affects on the behavior of soil mass. Although in engineering practice, loading mode is usually applied without really considering the influence of unloading factor; and shear strength parameters are often deduced from the conventional triaxial compression test. There are some doubts when applying the shear strength characteristic to analyze the stability of unloading cases. In this study, a comparison in soil shear strength between loading and unloading modes was pointed out, which was based on two series of tests for remoulded clay conducted on the Advanced Stress Path Triaxial Testing System. The test results showed that the quantities of shear strength in both cases were almost the same, but there were some discrepancies between them in the stress-strain and excess pore pressure characteristics.

The permeability characteristics of expansive soil have a significant impact on slope stability. This study investigates the permeability evolution of three expansive soils (B, GW, GB) with distinct swelling potentials (68%, 42%, and 28%) under repeated wet–dry cycles, combining laboratory falling-head tests and in situ four-ring infiltrometer measurements. The results demonstrate that the permeability coefficient increases consistently with cycle number. The high-expansivity soil (B) exhibited the most pronounced change, with permeability increasing from 10⁻⁶ cm/s to 10⁻³ cm/s after five cycles, whereas the low-expansivity soil (GB) remained stable. A significant specimen size effect was observed in initial permeability, which stabilized beyond a critical infiltration area of 1102.7 cm². However, this size dependence diminished after three cycles due to extensive cracking and structural homogenization. Crack density analysis further confirmed microstructural stabilization at sample diameters between 32 and 38 cm, validating the adopted in situ seepage diameter of 37 cm. Linear regression revealed greater discrepancies between laboratory and in situ permeability values in high-swelling soils. Empirical formulas incorporating wet–dry cycles were developed to accurately predict in situ permeability, providing practical tools for engineering design and risk assessment.