Presentations were made during a workshop session co-sponsored by TC218 - Reinforced Fill Structures (Mechanically Stabilized Earth and Reinforced Soil Slopes) at the 19th ICSMGE Conference held in Seoul, Korea on September 20, 2017. Since this was a paperless session, presenters were asked to prepare 1 page briefings on the subject areas. The briefing provided in this article comes from John Sankey of Terre Armee.
Overview of MSE Walls & Combined Anchor Systems
Prepared by: John E. Sankey, Terre Armee
This presentation was prepared to provide an overview of Mechanically Stabilized Earth (MSE) wall technology as an introduction to the presentations that followed in the TC218 Workshop. The presentation was divided into 6 sections addressing Introduction, Components & Wall Types, Basic Rules of Practice, Applications, Combined Anchor Systems and Conclusions.
The introduction addressed the history of the technology starting with the modern development of MSE walls by Henri Vidal in the late 1960s. The principle is based on development of friction between reinforcing elements and granular fills to develop a stable composite structure.
The basic components of MSE walls are facing panels, steel or geosynthetic reinforcements and select backfill. The combined wall volume serves as the retaining wall structure that retains general backfill behind. The presentation provides an array of facing types (concrete panel, wire mesh and block) and reinforcement elements (steel strips, metallic mesh, geosynthetics strips and geogrid).
Design is commonly determined on the basis of the reinforced width to height ratio of the MSE wall volume. A rule-of-thumb established in practice is the width starting at 0.7H, where ‘H’ is the height of the wall. MSE walls are then designed for internal stability (pullout and tensile resistance of reinforcements) and external stability (sliding, limiting eccentricity, bearing and global). The main advantages of the wall system are its flexibility and ability to accommodate settlements.
Applications are only limited by the imagination of the user. MSE walls have been used in transportation (roads, bridge abutments, railways and airport runways), mine walls, dams and along waterways, protection (environmental containment and military blast walls) and commercial. The common application for roadways and bridges is the basis for codes unique to each country where MSE walls are used.
The availability of sufficient open horizontal space is not always possible and a more recent advancement in MSE walls is to marry it with anchor wall systems. Where the available horizontal space is less than 0.3H, MSE walls can be directly anchored to a backface stabilized by soil nails or rock anchors. Horizontal space available between 0.3H and 0.7H can separate out reinforcements to overlap between those attached to the front facing and the backface forward.
MSE walls are versatile structures that offer over 50 years of superior performance and cost saving. Steel and geosynthetic reinforcements each have their own unique physical and material properties that need addressed in design. More detailed studies are available in the literature and national codes for MSE walls.