Pisha sandstone, formed in the Mesozoic Era with an interbed of thick sandstone, sand shale and mudstone, is widely distributed in semi-arid area in Shanxi, Shaanxi province and also in Inner Mongolia Autonomous Region within the Yellow River basin. Because of its low degree of diagenesis, it is as hard as a solid rock when it is dry. However, it becomes soft and almost muddy once exposed to water and is prone to wind and water erosions. Additionally, the Pisha sandstone area is a semi-arid climate with less rainfall, mostly heavy rainfall, strong wind and sand storms, and low vegetation coverage. Therefore, the water and soil loss are extremely serious, the ecological environment is fragile, ant it has a great impact on natural, ecology and environment. Currently, the main measures are engineering and vegetation measures. However, these predominantly used approaches all have some limitations, especially for the slopes, there are no effective measures. Thus, it is necessary and urgent to find a comprehensive control measure to realize the goals of water and soil conservation and ecological restoration in Pisha sandstone area. Based on the study of the characteristics of Pisha sandstone, the mechanism of hydraulic erosion and previous achievements, the technique of soil erosion prevention and vegetation promotion is firstly proposed based on a kind of hydraulic polyurethane (W-OH), and the systematic studies are conducted. The main steps and the precedures conducted in this study were as follows.
1) The basic characteristics of Pisha sandstone were studied systematically. The chemical components, mineral components, particle size distribution, mechanical properties, nutrient composition and micro-structure of Pisha sandstone were investigated and the main reasons for its susceptibility to erosion were analyzed emphatically.
2) A type of hydraulic polyurethane (W-OH) was synthetized and developed. The synthesis conditions, viscosity, curing mechanism of W-OH, the tensile strength, UV durability, microstructure and safety of the consolidation layer were studied, and W-OH was synthetized and the synthesis process and conditions were determined. W-OH can react with water rapidly to form a porous flexible gel with a certain mechanical strength and it is safe both in curing gel and consolidation layer (The weathered Pisha sandstone solidified by W-OH solution).
3) The comprehensive erosion prevention and vegetation promotion performance of consolidation layer were studied systematically, and the functional materials such as polyvinyl alcohol (PVA) and ethylene-vinyl acetate copolymer (EVA) were used in combination with W-OH to increase the consolidation and growth promotion. The experiments including the wettability, permeability of composite materials on Pisha sandstone, mechanical properties, the anti-scourability (water stability index K), microstructure, UV durability, water and fertilizer retention and vegetation wilting were conducted. The mechanism of consolidation, erosion prevention and vegetation promotion was analyzed, and the proper concentration and spraying amount of W-OH and the methods to improve the UV durability of the consolidation layer were obtained.
4) The anti-scourability of the consolidation layer under scouring and rainfall conditions was evaluated. The simulated scouring tests both in lab and field and simulated rainfall tests in lab were conducted. The effects of scouring flow, slope angle, concentration and spraying amount of W-OH on runoff, sediment yield, runoff velocity, Reynolds number (Re) and Froude number (Fr) in simulated scouring tests, and the effects of rainfall intensity, slope angle, vegetation coverage and concentration of W-OH on runoff, sediment yield and slope morphology in simulated rainfall tests were analyzed. The hydraulic erosion process and the relationship between the sediment yield and the influencing factors under rainfall conditions were discussed and obtained by regression and fitting analysis.
5) Field experiments were conducted, the proposed technique of erosion resistance and growth promotion was established and it was extended and applied. The field experiments were conducted in Erlaohu ditch in Zhungeer Banner, Inner Mongolia Autonomous region, China, the measure combined with W-OH and vegetation was applied in an entire typical slope and a control one without treatment by W-OH was designed. Subsequently, the surface morphology changes, sediment yield and vegetation restoration were observed and monitored. A new type of integrated construction equipment was developed and the construction methodology was established. Finally, the extended applications via using the erosion resistance and growth promotion technique in Pisha sandstone area, slope disintegration erosion area, river bank slope in sandy soil area in the middle and lower reached of the Yellow River and roadside slope were carried out.