Abstract:

The aim of this study was to explore the feasibility of protecting slopes by planting vegetation with or without ground coverings， and to select the best protection strategy for this purpose. The site selected for this research was the silty subgrade slope of the Haian-Qidong Expressway in Jiangsu Province. Different types of vegetation were planted on slopes of <2 m， 2-4 m， and >4 m in height， and different materials were used to cover the soil surface. We determined the effects of the covering materials on the growth and protection effect of the vegetation. In addition， we monitored the above-ground growth and root growth of five plant species. The results showed that the use of a fiber mat or a straw layer as ground coverings encouraged plant growth and improved their protection capacity. Compared with the straw curtain， the fiber blanket showed better ground coverage. Slope protection by vegetation alone was not suitable for slopes of >4 m in height， because the coverage and uniformity of protective plants in this slope section were poor， serious stratification occurred， and alluvial soil was still visible on the slope surface. Compared with plant growth after mixed sowing of multiple grasses and flowers， plant growth was better after mixed sowing of seeds of multiple grass and shrub species， mixed sowing of multiple grass species， and sowing seeds of a single grass species. The plant cover and uniformity was significantly better after mixed planting of grasses and shrubs than after other planting patterns. The combination of grasses and shrubs mutually promoted their growth， resulting in the best slope protection effect. We evaluated five plant root indicators， and found that the indexes of total root length， root surface area， and root volume were higher for Amorpha fruticosa， Lespedeza bicolor， and Cynodon dactylon than for Paspalum notatum and Magnolia multiflora. The suitability of plants for particular areas and their root growth characteristics can be used as the criteria for selection as protective plants. In general， the protection approach of mixed sowing of multiple grass and shrub seeds as well as a fiber blanket as a ground cover was suitable for protection of the silty subgrade slope of the Haian-Qidong Expressway. This approach was suitable for protection of slopes <4 m in height. The mixture of A. fruticosa， L. bicolor and C. dactylon grew best， and formed a strong plant root system that contributed to slope protection.

Key words: expressway, silty subgrade slope, slope protection by vegetation, plant growth, protection effect