Erosion Control and Growth Promotion of W-OH Material on Red Clay Highway Slopes: A Case Study in South China

Polyvinyl acetate-based soil stabilization for rock slope ecological restoration

External-soil spray seeding (ESSS) is a method often used for the ecological restoration of bare rock slopes. However, the direct use of ESSS is normally less satisfactory due to the erosion of sprayed soil and low survival rate of the plants on rock slopes. This study proposes a novel approach to addressing this issue through the combined use of ESSS with polyvinyl acetate (PVA) based soil stabilization. The PVA solutions are added to the soil to stabilize soil and improve soil strength while possessing high water and nutrient retention favorable for plant growth. A series of experimental tests on the mechanical properties, water stability, erosion resistance, water retention, and plant growth of the PVA-stabilized soil were conducted to assess the efficacy of the proposed method. The results showed that the proposed method could be promising for rock slope ecological restoration. A proper curing time (e.g., >3 days) was required to achieve beneficial effects of PVA on the soil properties. A shorter curing time would otherwise result in the decrease in the strength with the increased PVA content. It was found that the optimum PVA content was 3% for achieving the maximum water stability, erosion resistance, water retention, and plant growth. The cohesion increased by up to 50% and the internal friction angle increased by 3.5° compared to the natural soil. The disintegration rate of the stabilized soil was generally < 3e-3%/min. The maximum reduction in erosion was up to 83% when the PVA content ≥3%. The mechanisms behind the findings are also discussed.

Using PVA and Attapulgite for the Stabilization of Clayey Soil

Considering that, in the context of the ecological restoration of a large number of exposed rock slopes, it is difficult for existing artificial soil to meet the requirements of mechanical properties and ecological construction at the same time, this paper investigates the stabilization benefits of polyvinyl acetate and attapulgite-treated clayey soil through a series of laboratory experiments. To study the effectiveness of polyvinyl acetate (PVA) and attapulgite as soil stabilizer, a triaxial strength test, an evaporation test and a vegetation growth test were carried out on improved soil with different amounts of PVA content (0, 1%, 2%, 3%, and 4%) and attapulgite replacement (0, 2%, 4%, 6%, and 8%). The results show that the single and composite materials of polyvinyl acetate and attapulgite can increase the peak deviator stress of the sample. The addition of polyvinyl acetate can improve the soil strength by increasing the cohesion of the sample; the addition of attapulgite improves the soil strength mainly by increasing the internal friction angle of the sample. The strength of the composite is greatly improved by increasing the cohesion and internal friction angle of the sample at the same time. The effect of adding materials increased significantly with increasing curing age. Moreover, polyvinyl acetate and attapulgite improve the soil water retention of the soil by improving the water-holding capacity, so that the soil can still ensure the good growth of vegetation under long-term drought conditions. The scanning electron microscopy (SEM) images indicated that the PVA and attapulgite of soil affect the strength characteristics of soil specimens by the reaction of PVA and water, which changes the structure of the soil and, by the interweaving of attapulgite soil particles, acts as the skeleton of the aggregate. Overall, PVA and attapulgite can effectively increase clayey soil stability by improving the cohesive force and internal friction angle of clayey soil.

Disintegration Resistance of Steep-Rocky-Slope Wall-Hanging Soil Based on High-Performance Ester Materials

Ecological restoration is difficult on the steep rocky slopes (SRS) in rainy areas in South China that experience severe soil erosion. The disintegration resistance of steep-rocky-slope wall-hanging soil (SRSWS) is a crucial topic in the field of new ecological restoration. The formation of a transient saturated zone of wall-hanging soil (WS) under high-intensity rainfall can easily lead to soil disintegration. The subsequent rain erosion can cause the loss of growth substrate required for early plants, resulting in a poor greening effect or even landslides. Therefore, improving the disintegration resistance of WS and ensuring the stability of the early-plant-growth environment are at the core of SRS protection. In this paper, structural and static underwater disintegration tests of red soil modified by high-performance ester materials (HEMs) were carried out. According to the damage ratio of the soil structure and the disintegration rate and disintegration amount of red soil, the structural properties and disintegration resistance of improved red soil were quantitatively measured. The results show that absorbent HEMs generally increased the content of water-stable aggregates (WAs) in red soil. However, when the content was excessively large, it destroyed the WAs and accelerated the overall disintegration rate and amount. Based on the structure and disintegration resistance test of red soil, optimal pro-portions of adhesive HEMs of 10 g·m−3 and absorbent HEMs of 80 g·m−3 were obtained. The optimal proportions obtained from the above experiments showed good adaptability and an improvement effect on the structural properties and disintegration resistance of red soil. This solves the problem of the growth substrate required for early plant disintegration and loss in water. This paper provides a theoretical and experimental basis for the ecological restoration of SRSWS with disintegration resistance. It has guiding significance for the steady progress of greening construction on SRS sites.