Bearing Resistance of Inextensible Grid Reinforcements

Reinforced earth walls have widely been applied instead of concrete gravity-type retaining walls, because of easiness for its execution and economical efficiency. The strip-type reinforcements usually need to use clean sands and gravels of relatively high quality as backfill materials to generate required frictional resistance. For example, the ideal backfill materials are clean granular soils with less than 15 % of smaller particle diameter than 0.074 mm (Bergado et al. 1996). Such a limitation in backfill materials sometimes prevents to apply them, because of lack of ideal backfill materials. In contrast, the grid-type reinforcements have not such a severe limitation in back fill materials, because they have more pullout resistance than strip-type reinforcements, even in backfill materials of lower quality. To establish the reasonable design method of grid-type reinforcements, the authors have elucidated the pullout mechanism of steel grid reinforcements based on pullout test results (Matsui et al. I996a, b, c). In this paper, the authors try to elucidate the bearing mechanism of the steel grid reinforced earth and propose an equation to estimate the bearing resistance based on the Prandtl's failure mechanism. Then, the applicability of the proposed equation is checked through comparison with available pullout test data. PROPOSED EQUATION BASED ON PLASTICITY THEORY When a steel grid reinforcement is pulled out from confined soils, the ultimate bearing resistance per unit width of each transverse member is given by Eq.(I), which is based on the modified form of Terzaghi-Buisman bearing capacity equation of footing foundation.