AbstractsEngineering

The increasing need for regional development has led engineers to find safe ways to construct the infrastructure of transportation on soft soils. Soft soil is not able to sustain external loads without having large deformations. The geotechnical properties of soft soil which is known for its low bearing capacity, high water content, high compressibility and long term settlement as well. In pavement engineering, either highway or runway as an infrastructure, a pavement encompasses three important parts namely traffic load, pavement and subgrade. Traffic load generated from tire pressure of vehicle and/or airplane wheels are usually around 550 kPa even more on the surface of the pavement. Pavement generally comprises granular materials with unbounded or bounded materials located between traffic load and subgrade, distributing the load to surface of subgrade. One of the promising soil improvement techniques is a piled embankment. When geosynthetics layer is unrolled over piles, it is known as geosynthetics supported piled embankment. Particularly in deep soft soil, when piles do not reach a hard stratum due to large thickness of the soft soil, the construction is an embankment on floating piles. Furthermore, because of different stiffness between piles and subsoil, soil arching effect would be developed there. By using Finite Element analysis, some findings resulted from experimental works and several field tests around the world as field case studies are verified. Some important findings are as follows: the stress concentration ratio is not a single value, but it would be changed depending on the height of embankment, consolidation process of subsoil, surcharge of traffic load, and tensile modulus of geosynthetics as well. Ratio height of embankment to clear piles spacing (h/s) around 1.4 can be used as a critical value to distinguish between low embankment and high embankment. When geosynthetics is applied to reinforce a pavement/embankment, the vertical distance of geosynthetics layers and number of geosynthetics layers depend on the quality of pavement material. The lower layer of geosynthetics withstands a tensile stress higher than upper layer. Primary reinforcements for geosynthetics in piled embankments are located at span between piles with maximum strains at zones of adjacent piles. Traffic load that passes through on the surface of the pavement can reduce the soil arching, but it can be restored during the off peak hours. Settlements of embankments on floating piles can accurately be modelled using the consolidation calculation type, whereas the end-bearing piles may be used the plastic calculation type. Longer piles can be effectively applied to reduce a creep. By applying length of floating piles more than 20% of soft soil depth, it would have a significant impact to reduce a creep on a deep soft soil.