ROADWAY SETTLEMENT CHARACTERISTICS ON MEKONG DELTA FOR VARIOUS LANDFORMS

Abstract

The road network in the Mekong Delta faces challenges due to its low-lying topography and extensive layers of soft clay. These deposits, reaching depths of up to 25 m, are found in backswamp/swamp, sand dune, and mangrove marsh landforms. These soils generally have low total unit weight, high water content, and high compressibility. They are problems for road construction, and soft ground treatment must be applied. This study utilized data from 53 boreholes to assess the consolidation characteristics of each landform. According to the typical highway embankment construction, the primary consolidation showed the highway settlement in the ranges 186–1,174 mm, 107–1,049 mm, and 537–1,364 mm for the backswamp/swamp, sand dune, and mangrove marsh, landforms, respectively. These settlements exceed the maximum level of 250 mm for allowable settlement at 5 years post-construction. To address this issue, the prefabricated vertical drain (PVD) method is proposed as a solution to expedite settlement. PVDs, designed with 12–14 m, 10–12 m, and 14–16 m for the backswamp/swamp, sand dune, and mangrove marsh landforms, respectively, and a spacing of 1 m, accelerated the consolidation process, resulting in consolidation percentages of 87–92% within a notably shortened timeframe of 3 months through preloading. Upon completion of the preloading period, the remaining settlement ranges were 54–130 mm, 27–83 mm, and 67–170 mm for the backswamp/swamp, sand dune, and mangrove marsh landforms, respectively, which are all within the permissible limit (250 mm). These findings are important, as they offer valuable insights for the future planning, preliminary design, and construction of highway embankments, emphasizing the importance of incorporating PVDs as an effective measure in mitigating settlement issues.