3.4.1 Seepage through Old Backfilled Canals
The investigation team had hypothesized that there was a possibility of water flowing through the old backfilled canals. The old canals were backfilled during the site preparation with silty sand (with fine content less than 25%) for depth greater than 1.5 m, and the top 1.5 m of the canal was filled with clayey soils. To verify the water-carrying canal, a pit was excavated on 12th February 2007 before the public announcement by the investigation committee. The pit shown in Figure 32 indicated no presence of water in the sand layer, therefore this hypothesis was eliminated. In addition, if the water was originated through the old canals, then the water in the blockage areas should be flowing out during the dry season, but there was no sign of water level reduction in Taxilane T11. Furthermore, it is rather unlikely that the water beneath the pavement could flow from the primary canal at one end through the silty sand of the old backfilled canals.