Sustainable Characteristics of Reinforced Soil Structures - from Ancient Great Walls to Modern GRS Walls

This paper is dedicated to the memory of the Late Dr. Jonathan T.H. Wu in recognition of his outstanding contribution to the field of reinforced soil structures, especially for the geosynthetic-reinforced soil (GRS) structures with close reinforcement spacing. The objective of this paper is to introduce the sustainable characteristics of reinforced soil walls, including carbon emission, durability, ecology, vegetation, and landscape, which are less emphasized in the literature. In this paper, the sustainable/green characteristics of reinforced soil walls, using case examples from the ancient Great Wall to the modern GRS walls, are first discussed. The reasons for the extraordinary durability and stability of the ancient Great Wall, even though it was only reinforced by discontinuous (intermittent) natural materials, are investigated, and the reinforcing mechanism is discussed. A series of limit equilibrium analyses were performed to demonstrate the effect of closely spaced reinforcement on enhancing the system stability (i.e., the factor of safety). The results of this study reveal the reinforcements with close spacing could effectively confine the soil through the friction between the reinforcement and surrounding soil, and generate a moderate apparent cohesion to internally stabilize the soil mass, forming a stable soil-reinforcement composite. The findings above are supported by the pioneering works by Late Dr. Jonanthan Wu, who strongly advocated the superior merits of closely spaced GRS walls. In addition to the mechanical performance, several significant advantages of reinforced soil walls compared with traditional reinforced concrete retaining walls are discussed, with particular highlights in the aspects of the sustainable/green characteristics. The reinforced soil structure, especially with wrap-around facing on which vegetation can grow, is one of the vital green/sustainable geotechnology and is worth promoting and developing for the engineering practice worldwide.