Improvement of Sri Lankan peaty soil by vacuum consolidation

Abstract

Vacuum consolidation was used to improve highly compressible soft organic soil encountered in the Southern Transport Development Project in Sri Lanka. As this method of soil improvement is used for the first time in Sri Lanka, several trial embankments were built to study the feasibility and the effectiveness of the vacuum consolidation method in improving the Sri Lankan peaty soils prior to adopting the same in main construction work. At the trial embankment sites the founding soil mainly consisted of very soft highly compressible peaty or organic soil layers of thickness varying from 3 to 8 m. The soft layers were improved by a combined vacuum consolidation and surcharging with 5 to 9m high stage constructed embankments to compensate the primary consolidation settlements and to minimize the secondary settlements that can take place during the service life of the road. The improvement in the peaty soil due to the vacuum consolidation was assessed from the data obtained through the field monitoring program and the results obtained from the laboratory and field tests carried out on improved and unimproved ground areas. The obtained data was analyzed to investigate the effectiveness of vacuum consolidation process in improving the properties of Sri Lankan peaty soils. Furthermore, the obtained data was analyzed to quantify the improvement in the strength gain due to vacuum consolidation and compressibility properties of Sri Lankan peaty soils as a results of the over consolidation due to vacuum consolidation process. In addition, some of the already published empirical correlations for Sri Lankan peaty soils were improved by including the data obtained from the field and laboratory testing programme carried out under the present study.