Laboratory investigation of backfill erosion around rigid pipes with defective joints

Water infiltration is one of the most significant underlying causes of deterioration in buried rigid pipes, which can bring about erosion voids in the backfill that will increase the severity of the soil loading and produce structural failures. Based on model tests, the effect on the erosion is examined for two infiltration scenarios involving a defective joint. Joint leakage is represented using idealised apertures across the invert. Monitoring of the mass flux of sand, the flow rate of water and the development of visible voids enabled the identification of three successive stages during infiltration erosion: initial leakage, primary erosion and then a metastable state. Initial voids occurred at the elevation near the air-entry head in the backfill, then extended downwards to the wide aperture, while the bridge formed in the narrow aperture limited further erosion and reduced the permeability. A practical framework was proposed and verified to predict the geometry of the void envelopes in the backfill for different experimental scenarios.