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A special form of mechanically stabilized soil (MSS) wall is modular block wall, which is commonly referred to as a segmental block wall. It is constructed with a brick facing and backfill stabilized by soil reinforcements. A 12-m-high modular block wall was constructed to support the end span of a major bridge structure at a river crossing. The wall consisted of four tiers and a bridge sill beam sat on the top tier, thus giving a total wall height of about 12 m. High density polyethylene (HDPE) geogrids were used as the soil reinforcements. This wall type was selected on the basis of simplicity in construction, ability to accommodate differential settlement, and aesthetics. However, the unusual wall configuration presents a number of engineering challenges, and may not be adequately covered by conventional design calculations. There was a lack of actual performance data for such a wall form. The foundation material at the site is compressible and variable, and there may be interaction between foundation movements and wall behavior. Initial design was conducted using limit equilibrium analysis and simplified numerical modeling. Recognizing the limitations of these calculations, conservative design decisions were made in relation to the reinforcement layout. Furthermore, the wall was instrumented. Field measurements were taken over a long period of time. Field response of the wall revealed movements higher than those expected or predicted by the initial analysis. There were also concerns about reinforcement tension. The challenge is to have a “single analysis” that can “feed” the observed high movements (during working condition) into the prediction of safety margin. A numerical model that could conservatively predict the observed movements and continue to do so until the ultimate design was completed was developed. A parametric study was conducted to better understand the behavior of this wall. |
