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Insights into saline soil cracking subjected to drying-wetting cycles

Feng Haoxuan, Xing Xuguang, Su Liuchang, Zhang Chunzhe, Wang Yubo, Li Yibo, Wang Weihua

Acta Geophysica

2025

Vol. 73, no. 1

619--633

Soil salinization has become a global environmental issue, and soil cracking can lead to preferential flows and destabilize the developments of plant-soil system. However, little is known about saline soil cracking, especially under external drying- wetting (D-W) alternations. This study explored how soil salt and continuous D-W cycles affected water evaporation and crack development responding to soil salinity (0, 0.3, 0.6, 1.0, and 2.0%, w/w) and three D-W cycles. Observed findings showed that saline soil water evaporation was smaller than nonsaline soil. Besides, the water evaporation decreased and increased as the soil salinity increased and the D-W cycles progressed, respectively. In addition, soil salt and D-W cycle inhibited and promoted soil cracking, respectively; specifically, the crack area density decreased and increased with increasing soil salinity and number of D-W cycles, respectively. Correlations indicated that the soil salt had overall larger contributions than the D-W cycle to the variations of water evaporation and crack development. Soil salt was negatively correlated with cumulative evaporation, evaporation rate, and crack length density, but was positively correlated with soil moisture; besides, D-W cycle was negatively correlated with soil moisture, but was positively correlated with cumulative evaporation, evaporation rate, crack area density, and crack length density. Mechanism exploration suggested that the salts inhibit surface cracking by promoting inter-microaggregate cementation and clay flocculation and blocking soil macropores; and the D-W cycle promotes surface cracking through the swelling-induced crack healing in the case of hydrophilic clay minerals in contact with water.

Hydrological properties of biochar-amended expansive soil under dynamic water environment and biochar-amended soil’s application in green roofs

Li Muyang, Garg Ankit, Huang Shan, Jiang Mingjie, Mei Guoxiong, Liu Jiaqin, Wang Hao

Acta Geophysica

2024

Vol. 72, no. 2

1055--1065

Biochar is widely used as a soil amendment in green roofs because it can increase the soil’s water-holding capacity, inhibit cracking, and provide nutrients for vegetation. The interaction mechanism between biochar and expansive soil is a significant factor in the performance of green roofs. However, research mainly focused on the hydrological scale (i.e. runoff regulation and rainwater storage), and there is a lack of research on the hydrological properties (i.e. hysteresis of soil-water characteristic curves, changes in soil pore size and pore distribution, formation and development of cracks and swelling-shrinking characteristics) of biochar-amended expansive soils under dynamic water environment. This test was conducted out on soil columns with expansive soil and 5% (by mass) biochar-amended under 5 drying-wetting cycles. The results showed that within the range of water content suitable for plant growth (i.e. between the anaerobic point and wilting point), the hysteresis area of soil-water characteristic curves of the amended soil is smaller than the bare soil at each drying-wetting cycle. The addition of biochar changes the pore size distribution of the soil, reduces the pore size and swelling-shrinking characteristics of the expansive soil, and inhibits the development of cracks. Therefore, the addition of biochar significantly attenuates the hysteresis characteristics of the soil-water characteristic curves of expansive soils, which may improve the stability of the hydraulic performance of green roofs. The results contribute to the understanding of the physicochemical and water properties of biochar-amended expansive soil and provide theoretical support for the application of biochar to green roofs.