Cracking and water seepage of Xiashu loess used as landfill cover under wetting–drying cycles

Abstract

This paper intends to investigate the anti-seepage characteristics of Xiashu loess used as landfill cover under wetting–drying cycles. A series of tests were performed to systematically evaluate the surface cracks, pores, the hydraulic conductivity and water seepage of the soil under wetting–drying cycles. The cracking tests indicated that the cracking intensity factor (CIF) increased with the number of wetting–drying cycles. After three wetting–drying cycles, the CIF gradually reached a stable value. The influence of the compactness of the compacted clay was significant to cracking. After four drying–wetting cycles, the CIF of compacted clay with relatively low compactness (ρ = 1.65 g/cm3, W 5 = 25 %) was 0.15, and the CIF of compacted clay with higher compactness (ρ = 1.65 g/cm3, W 3 = 21 %) was only 0.06. With the increase in the number of wetting–drying cycles, the accumulated pore volume of the soil particles increased and the maximum pore size was nearly unchanged. After four drying–wetting cycles, the proportion and average diameter of macro-pore in the soil particles were both increased. However, the proportion and average diameter of the meso-pore slightly decreased. Furthermore, the proportion and average diameter of the micro-pores were unchanged. After four wetting–drying cycles, the hydraulic conductivity of the compacted soil was at 8.3 × 10−7–1.5 × 10−5cm/s, which was increased about three orders of magnitude compared with the compacted soil without cracks. The hydraulic conductivity of compacted soil increased linearly as cracks increased. The hydraulic conductivity of compacted soil also gradually increased to a stable value as the pore volume increased. After 1 month of wetting–drying cycles, the cracks of soil with low compactness had extended to a depth of 15 cm below the soil surface while the cracks of soil with higher compactness only reached a depth of 5 cm.