A quantitative study on the amount of water-retaining agent based on adhesive-modified red bed weathered soil

Engineering activities can lead to serious soil erosion problems in red bed areas. To overcome their loose structure, low strength and poor water retention, the red bed weathered soil needs to be modified with adhesives and water-retaining agents. At present, on the premise of applying adhesive, there are few studies on the mechanism of water retention agent to improve soil, and the amount of water retention agent in practical engineering is mainly determined by experience, lacking reliable quantitative basis. Herein, the effects of water-retaining agents on soil quality were quantitatively studied in red bed weathered soil modified by a fixed amount of adhesive. By using shear, permeability, porosity and plant growth tests, we show that the shear strength of the modified soils decreased slightly with increasing resin content, while permeability, porosity and water retention increased, and the growth of plant roots was promoted. Additionally, the processes by which these soil agents improve water retention were investigated, and the control mechanism of the optimum addition amount of water-retaining agent based on the soil water storage and aggregate size was revealed by scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) images, and the optimal water-retaining resin dosage for red bed weathered soil modification is proposed. This study provides a quantitative basis for determining water-retaining agent dosage in the red bed areas of South China and similar areas.