Retrofit of a Steel-Reinforced MSE Wall

Brian Hall, Alireza Afkhami, Amri Benjamin

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Transportation Geotechnics

ABSTRACT: F A STEEL-REINFORCED MSE WALL Brian Hall, M.Eng., P.Eng., Alireza Afkhami, M.A.Sc., P.Eng. Tetra Tech EBA, Vancouver, BC, Canada Amri Benjamin, M.Eng. Ledcor CMI Ltd., Edmonton, AB, Canada ABSTRACT This paper describes the retrofit of an existing mechanically stabilized earth (MSE) wall where concerns existed that the connection between the steel reinforcing and precast concrete wall facing panels had been compromised. The paper describes the investigations undertaken, outlines design constraints and performance considerations, and discusses design and construction. The paper concludes by briefly discussing retrofit design and construction approaches used on three further MSE walls with similar concerns. The field investigation program included constructing a test strip to characterize the shot rock MSE zone backfill and a field loading test to assess the stiffness of the backfill. After considering a range of approaches that included disassembling and rebuilding the wall, constructing a buttress wall, installing a soldier pile wall, grouting the backfill, and soil nailing, the retrofit finally adopted consisted of soil anchors which applied load through a load distribution concrete wall. RÉSUMÉ es critères de performance ainsi que les défis de prévues pour la mise à niveau future de 3 murs de terre armée qui présente une problématique similaire. Une réplique du mur a été réalisée dans le but de réaliser les essais de terrain. Les essais de terrain visaient à conSoil nail, la solution de mise à niveau retenusoil anchors qui transfère la charge via un mur de béton fondé sur pieux vises. 1 INTRODUCTION This paper describes the retrofit of an existing mechanically stabilized earth (MSE) wall where there were concerns that the connection between the steel reinforcing and precast concrete panels had been compromised. The retrofit was initiated following the collapse of several facing panels on an adjacent section of MSE wall supporting a bridge abutment which had been constructed using similar materials and construction methodology. After the facing panels on the adjacent wall collapsed, the MSE backfill directly behind the facing ravelled backwards by about 0.5 m to 0.9 m, and then reached equilibrium with only minor ravelling. Bridge abutment stability was not compromised. The cause of the distress is outside the scope of this paper, which instead discusses the retrofit of MSE walls where issues at the connection between the steel reinforcing and the facing panel may exist. 2 EXISTING MSE WALL 2.1 Wall Details Figures 1 and 2 show a partial view and a typical cross section of the MSE wall. The wall supports a two lane section of roadway ramp, it is about 300 m long and has a maximum of 8 m high. The precast concrete facing panels are nominally 1.8 m by 1.5 m in size, and the MSE wall steel reinforcing (length approximately 70% of wall height) is placed in layers spaced at about 0.76 m vertically apart. The steel reinforcing is not continuous, but placed in sheets with gaps of about 0.6 m between sheets (coverage ratio of 33%). 2.2 Foundation Conditions The foundation soils consist of about 5 m of very stiff, medium to high plastic clay, overlying firm to stiff silty clay. The groundwater level is approximately 14 m below ground surface. 2.3 MSE Backfill The MSE backfill consisted of owner-supplied crushed basalt shot rock from a stockpile adjacent to the work site. The backfill gradations (see Figure 3) were in accordance with BC Ministry of Transportation and Infrastructure Standard Specifications for Highway Construction (2009) Bridge End Fill (BEF), but tended to be on the coarse side of the specified grading envelope. The fines content (percent passing the 0.075 mm sieve) was variable and up to 8%. The percentage retained on the 19 mm sieve was typically between 40% and 70%. Because the fraction of material retained on the 19 mm sieve was greater than 30% compaction control could not be referenced to the familiar Standard Proctor moisture-density test (ASTM D698).

RÉSUMÉ: FIT OF A STEEL-REINFORCED MSE WALL Brian Hall, M.Eng., P.Eng., Alireza Afkhami, M.A.Sc., P.Eng. Tetra Tech EBA, Vancouver, BC, Canada Amri Benjamin, M.Eng. Ledcor CMI Ltd., Edmonton, AB, Canada ABSTRACT This paper describes the retrofit of an existing mechanically stabilized earth (MSE) wall where concerns existed that the connection between the steel reinforcing and precast concrete wall facing panels had been compromised. The paper describes the investigations undertaken, outlines design constraints and performance considerations, and discusses design and construction. The paper concludes by briefly discussing retrofit design and construction approaches used on three further MSE walls with similar concerns. The field investigation program included constructing a test strip to characterize the shot rock MSE zone backfill and a field loading test to assess the stiffness of the backfill. After considering a range of approaches that included disassembling and rebuilding the wall, constructing a buttress wall, installing a soldier pile wall, grouting the backfill, and soil nailing, the retrofit finally adopted consisted of soil anchors which applied load through a load distribution concrete wall. RÉSUMÉ

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Cite this article:
Brian Hall; Alireza Afkhami; Amri Benjamin (2014) Retrofit of a Steel-Reinforced MSE Wall in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper330,author = Brian Hall; Alireza Afkhami; Amri Benjamin,title = Retrofit of a Steel-Reinforced MSE Wall,year = 2014}