Anomalous Seepage Flows and Piping in Oje-Owode earthdam: Granular filter-drain media as controlling measure

Abstract

There was loss of water at Oje-Owode dam embankment through seepage. Evidence of some degrees of fracturing and seepage at the dam toe been reported. Previous results showed that the dam embankment was permeable and anomalous seepage occurred at the toe. This study, therefore attempted the application of locally sourced granular filters, precisely, stone dust from quarry, to model the control of seepage and piping at the toe of the dam embankment. Coarse soil samples were collected from quarry site as selected granular filters. Granite stones of sizes ½ - ¾ inch were selected as the drain samples. These were subjected to particle size analysis, compaction tests, specific gravity; and constant head permeability test. Numerical analyses were also carried out to generate flow lines, seepage rates and velocity vectors of the dam. The results of the simulated flow net showed a seepage value of 3.8066 x 10^-8 m³/s per width, while total seepage at maximum phreatic level and at full length (896m) of dam axis was 3.4107 x 10^-5 m³/s. This indicated loss of water from dam toe through seepage. The velocity vector contours showed flow directions and maximum velocity magnitude of 3.6 x 10^-8m/s in the direction of decreasing heads. The modelled filter-drain installed at dam toe controlled the anomalous seepage water and prevented piping as though it were a horizontal drain. The flow lines were controlled at coordinate points (36.25m, 0.56m) and remained horizontal through the filter media, until it exited the dam at the toe at coordinate points (41.88m, 0.59m), which is relatively a save point for collection. The modelled filter-drain media installed at dam toe controlled the anomalous seepage water and prevented piping.

Keywords: Oje- Owode dam, Piping, Granular Sand filter, Numerical analyses, Seepage