Cause of Failure Investigation of Masonry Retaining Walls at Logita Bridge Site, Sidama Southern Ethiopia

Civil Engineering

Abstract

A masonry retaining wall supporting the approach embankment of Logita Bridge suffered significant distresses, which led to a dispute between the client, the consultant, and the contractor. As a result, the construction work has been interrupted for a prolonged time causing frustration on all stakeholders. This paper presents the investigation work undertaken to establish the causes of the observed distresses. Based on preliminary investigations, a hypothesis was developed that the observed distresses were due to the choice of ambiguous structural system, use of materials with widely varying stiffness and the sole use of standard stability checks, which failed to verify the complex design. A numerical simulation was undertaken using FLAC 8.1 by assuming elastic behavior for the reinforced concrete and stone masonry parts of the wall and Mohr-Coulomb model for the various backfill materials and foundation. The values of parameters were either adopted directly from code provisions or were estimated using methods specified in relevant codes. The modeling was undertaken for the current construction state as well as the final designed state. The numerical analysis conclusively proves that the distress observed in Logita Bridge retaining wall is caused by development of tensile internal stresses at the face of the wall. If the final wall is constructed, the numerical simulation indicates that structure will collapse, not necessarily from stability of the wall but through deep-seated stability failure through the backfill and foundation.