Laws of water migration and settlement at interface in loess filled areas under rainfalls

The new-old interfaces and those with different compaction degrees often cause disasters such as piping, collapse, landslide, uneven settlement and crack in the duration of gully control and land creation projects in the Loess Plateau areas. The relevant physical models are established to reveal the laws of water migration and settlement at interface in loess filled areas under rainfalls. The results show that: (1) The velocity of rainwater seepage increases as the compaction degree of fill decreases. The volumetric moisture content and pore water pressure under low compaction degrees fill increase and decrease sharply near the peak. Besides, the pore water pressure has obvious hysteresis. (2) The wetting front has an obvious transition zone near the interface, where a rainwater dominant flow channel is available. (3) The total settlement of soils is nonlinearly related to the fill height above the interface. Besides, the local incline of the upper edge of the interface with different compaction degrees is much larger than that of the lower edge of the interface, and the maximum local incline appears near the upper edge of the interface. (4) The difference in settlement between soils correlates positively with the difference in compaction degree between the two sides of the interface. Meanwhile, the trend of failure at the interface becomes larger as the difference in compaction degree between the two sides of the interface increases. (5) The large settlement of fill and uneven settlement of soils are often accompanied by surface cracks, and the largest crack appears near the upper edge of the interface with different compaction degrees in soil fill area. Therefore, increasing the compaction degree of fill soils is of great significance for reducing the uneven settlement and preventing the cracks at interface in gully control and land creation projects.