Currently, the thickness design method for ecological soil covers used in northwest China is based on the practice of non-humid regions in north America, which is complicated, involves various parameters, and fails to consider the different meteorological conditions between northwest China and north America. To solve this issue, on the basis of the monsoon climate of northwest China, the feature that the precipitation during the non-growing period of vegetation should not exceed 20% of the total annual precipitation, as well as the water retention characteristics of ideal cover soils that the ratio of the field capacity to the wilting point K ≥ 1.44, the thickness design method for ecological soil covers used in northwest China is simplified. The numerical program Vadose/W is utilized to analyze the hydraulic responses of the loess monolithic cover and the loess-gravel capillary barrier cover designed with the proposed simplified method in the year of maximum precipitation. The results indicate that the capillary barrier effect significantly prevents the migration of water from the loess layer to the gravel layer, resulting in the capillary barrier cover having better anti-seepage performance than the monolithic cover. The anti-seepage performance of the two covers decreases with the decrease in the ratio of the field capacity to the wilting point of the loess (i.e., K). When K ≥ 1.35, the two covers can meet the local anti-seepage requirements, thus preliminarily verifying the reliability of the proposed simplified method.

The long-term safety of geological disposal for high-level radioactive waste relies critically on the effective retardation of radionuclide migration by geological barriers. Given the characteristics of radionuclide migration processes at large spatiotemporal scales, hypergravity experiments and multi-scale numerical simulations have become essential tools for investigating long-term seepage and solute transport behaviors in fractured media. Research progress in hypergravity testing techniques for seepage and solute migration in fractured rock masses, similarity theories for hypergravity tests of fractured rock masses, and long-term safety evaluations of geological barriers was reviewed. To address current challenges such as the integrated preparation of micron-scale matrix and fracture systems, similarity theories for complex rough fractures, and coupled thermal-hydrological-mechanical-chemical (THMC) processes, future research should focus on the integrated printing of micro-fracture and pore structures, similarity theories for natural rough fracture structures in hypergravity experiments, multi-process response mechanisms, and full-process simulations spanning ten-thousand-year timescales.