Limiting equilibrium, closed-form elastic, and numerical plastic analyses of stability of earth wall reinforced with grouted rebar nails and cable anchors

Abstract

Detailed rigorous analyses for nail-reinforced excavation faces are not available. Limiting equilibrium, closed-form elastic, and numerical plastic analyses were accordingly developed as alternatives for the design of a 12 m deep excavation. It is shown that the nails subject the monolith to constant horizontal compressions equal to active pressures for the limiting equilibrium and elastic analyses. The corresponding boundary condition on the front surface is shown to be more accurate than considering the support as an anchored bulkhead in classical terms. In addition to the compressions induced by the reinforcement, the rear surface is considered to be subject to active pressures and to active pressures net of the cohesion of the retained mass as alternative loadings in the limiting equilibrium and elastic analyses. It is shown that a reliable design result could be obtained for this case by considering the rear surface to be subjected to active pressures net of 50% of the cohesion of the retained mass in addition to the horizontal compressions induced by the nails. The factors of safety against shearing failure at the toe and heel exceed unity, those for the limiting equilibrium analysis being more divergent than those for the elastic and plastic analyses. Otherwise, the various analyses gave similar factors of safety. The horizontal displacements determined from the elastic analysis for active pressures net of the cohesion of the retained mass corresponded closely to that actually observed under stable conditions. Those determined from the plastic analysis underestimated the observed displacements. The horizontal displacements determined from the plastic analysis for a simulated condition of failure compared closely with that observed. Key words : limiting, equilibrium, elastic, numerical, plastic, analysis, earth, wall, nails, anchors.