First and second vacuum-PVD improvement of soft Bangkok clay for the third runway of Suvarnabhumi International Airport Thailand

This paper applies a modified vacuum-PVD system combined with the embankment surcharge and multiple field distributed air-water separation sub-tanks to improve soft Bangkok clay. The system efficiently generated and maintained vacuum pressures from − 80 to -90 kPa at the top of the embankment surcharge. The case study involved the construction of the third runway of Suvarnabhumi International Airport Thailand, which was built on soft Bangkok clay deposits. The back-calculation results of monitored data from the second improvement of the third runway extension were compared with the corresponding results of the first improvement of the taxiway extension, including the evolutions of settlements, excess pore pressures, and flow parameters. The second improvement with 29 kPa surcharge had lower settlements but recorded higher pore pressures and flow parameters. The first improvement with 34 kPa surcharge registered higher settlements but indicated lower pore pressures and flow parameters. The unit weights, water contents, liquid limits, compression indices, and void ratios were reduced. The undrained shear strengths, maximum past pressures, and over-consolidation ratio were increased. Inward lateral movements perpendicular to the surcharge embankment due to higher vacuum pressures than the lower embankment surcharge load were observed. The surcharge embankment combined with the modified vacuum-PVD system using an airtight membrane and horizontal prefabricated drain has been successfully applied to improve soft Bangkok clay.