Effects of seaweed polysaccharide-based materials on shear strength and permeability characteristics of soils

Abstract: Soil fertility decline is caused by loss of fertile top soil due to water or wind erosion. The decreasing of cultivated land may be caused by urbanization, industrialization, land abuse, soil pollution, salinization and improper agricultural cultivation. The deterioration of soil in the cultivated land has posed a serious threat on the productivity of the land and the food security. The control of soil erosion in the cultivated land is strongly related to the agricultural, environmental, economic and social concerns. New technologies are highly demanding to develop for the control of soil erosion in cultivated land. In the present, chemical measures represented by soil anti-erosion material are the focus of current research. However, the ecological benefits of previous materials are not enough to meet the requirements in the environmentally sensitive areas, such as cultivated land. Seeking new feasible materials with excellent soil anti-erosion and ecological benefits has become the great issue in the key investigation of soil anti-erosion materials. As endogenous substances in soil, the soil polysaccharides have excellent ecological benefits, indicating perfect needs of cultivated land. In this study, a novel kind of soil polysaccharide-based material was added into the soil, thereby to investigate the influence on soil strength and water cycle, with emphasis on its application possibility to prevent and control soil erosion in the sloping farmland. The material was also cheap easy to be industrial produced. The direct shear, disintegration, and permeability tests were selected to explore the relationship between addition amount, curing age, shear strength, permeability, and anti-disintegration effect in soil. The results indicated that the material can be used to enhance the cohesion, indicating that the cohesion was positively correlated with the amount of material addition under the same curing time. At the same addition amount, the cohesion increased with the curing age, where the increase was mainly distributed in the early stage of curing. The internal friction angle increased slightly after the application of materials under different addition amount and curing time, where the increasing of internal friction angle ranged between 5.42% to 7.29%. The anti-disintegration effect was improved with the increase of addition amount, indicating that a small amount addition can achieve excellent performance. The disintegration rate of 0.25% concentration treated group decreased 66.1% of control group after 1-hour curing, and the 1% concentration treated group had no disintegration during 30 min test. The permeability of soil samples first increased and then decreased, with the increasing of material application concentration. The permeability coefficient of soil samples was achieved the maximum at 0.25% concentration treated group (2.86×10-5 cm/s), the minimum at 1% concentration treated group (0.91×10-5 cm/s). All the samples belonged to the medium permeable layer, where to ensure the exchange of water and air for the crop growth. Furthermore, all the experiments demonstrated that the short-term and simple curing can be used to achieve excellent anti-corrosion effect after the application of materials, while, the easy application suitable for the sloping farmland. The Scanning Electron Microscopy (SEM) images showed the materials can form the hydrogel on soil particles surfaces and pores, indicating that the materials can wrap the soil particles in the form of a hydrogel network structure, thereby to enhance resistance to soil corrosion.