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8 CHAPTER 1 INTRODUCTION AND RESEARCH APPROACH PROBLEM STATEMENT developed by Tatsuoka and his associates at the University of Tokyo. These GRS bridge-supporting structures were Soil is generally weak in tension and relatively strong in constructed in two stages. The first stage involves con- compression and shear. The concept of reinforcing a soil structing a wrapped-faced GRS wall with the aid of gabions, mass by incorporating a material that is strong in tensile and the second stage involves casting in-place a full-height resistance is similar to that of reinforced concrete. The rein- reinforced concrete facing over the wrapped face. Field forcing mechanisms of reinforced soil and reinforced con- measurement has shown that these structures experienced lit- crete, however, are somewhat different. In reinforced soil, tle deformation under service loads and have performed far the bonding between the soil and the reinforcement is derived better than conventional reinforced concrete retaining walls from soil-geosynthetic interface friction, and in some cases and abutments in the 1995 Japan Great Hansin earthquake also from adhesion and passive resistance. Through the inter- that measured 7.2 on the Richter scale (Tatsuoka et al., 1997). face friction, the reinforcement restrains lateral deformation Most recently, Tatsuoka and his associates developed a pre- of the soil next to the reinforcement and therefore increases load-prestress technique to improve the performance of the the stiffness and strength of the soil mass. GRS bridge-supporting structures (Tatsuoka et al., 1997; Over the past two decades, geosynthetic-reinforced soil Uchimura et al., 1998). Despite their success, the "rigid" (GRS), a reinforced soil mass that uses layers of geosynthet- facing GRS bridge-supporting structures have only found ics as reinforcement, has been employed in the construction applications in Japan, mostly because of their cost and of many earth structures, including retaining walls, embank- longer construction time compared to GRS walls with a ments, slopes, and shallow foundations. In actual construction, "flexible" facing. GRS structures have demonstrated many distinct advantages GRS bridge-supporting structures with a flexible facing over their conventional counterparts. GRS structures are typ- have been the subject of several studies (e.g., Gotteland et al., ically more ductile, more flexible (hence more tolerant to dif- 1997; Adams, 1997; Ketchart and Wu, 1997; Miyata and ferential settlement), more adaptable to low-quality backfill, Kawasaki, 1994; Werner and Resl, 1986; and Benigni et al., easier to construct, and more economical. They also require 1996), and recently have seen actual applications in the less overexcavation. United State and abroad, including the Vienna railroad In recent years, applications of the GRS technology to embankment in Austria (Mannsbart and Kropik, 1996), the bridge-supporting structures have gained increasing attention. New South Wales GRS bridge abutments in Australia (Won Depending on the facing rigidity, GRS bridge-supporting et al., 1996), the Black Hawk bridge abutments in Colorado, structures can be grouped into two types: "rigid" facing and (Wu et al., 2001), and the Founders/Meadows bridge abut- "flexible" facing structures. A "rigid" facing is typically a ments in Colorado, (Abu-Hejleh et al., 2000). These struc- continuous reinforced concrete panel, either precast or cast- tures have shown great promise in terms of ductility, flexi- in-place. A "flexible" facing, on the other hand, typically takes bility, constructability, and costs. the form of wrapped geosynthetic sheets, dry-stacked con- Figure 1-1 shows the schematic diagram of a typical GRS crete modular blocks, timbers, natural rocks, or gabions. In bridge abutment with a segmental concrete block facing. The contrast to a "flexible" facing, a "rigid" facing offers a sig- abutment has four major components: (1) a GRS load-bearing nificant degree of "global" bending resistance along the wall (the lower wall), (2) a back wall (the upper wall), which entire height of the facing panel, and thus offers greater resis- may or may not be a reinforced soil wall, (3) a bridge sill, tance to "global" flexural deformation caused by lateral earth i.e., a footing to support bridge loads, and (4) a segmental con- pressure exerted on the facing. crete block wall facing. The bridge sill can be either integrated Since 1994, the Japan Railway has constructed a large with the upper wall face (referred to as an "integrated sill") or number of full-height concrete facing GRS bridge abut- isolated from the upper wall as a separate footing (referred to ments and piers (Tateyama et al., 1994; Kanazawa et al., as an "isolated sill"). The bridge sill shown in Figure 1-1 is an 1994; Tatsuoka et al., 1997) using a rigid wall GRS system integrated sill.