Abstract: This paper presents a case history of a comparative evaluation of soil properties before and after the pretreatment of a fast land reclamation site for a petroleum project site in the coastal area. The pre-fabricated vertical drain with surcharging preloading method was used as the pretreatment method in this soft soil site with thick and un-even thickness peaty soils. The soil improvement results were evaluated by the in-situ tests and laboratory tests on samples collected from the site before and after the pretreatment. The laboratory test items included, void ratio, coefficient of compression and compression modulus and the in-situ testing methods are, Standard Penetration Tests (SPT), Cone Penetration Tests (CPT) value shear test and dilatometer test. The results indicate that the site predominantly consists of peaty clayey soils and the void ratio in the cohesive soils reduced significantly after the pretreatment with an average reduction of 24.6%. The coefficient of compression has an average reduction of 23.7%. The modulus of compression has an average increase of 5.5 times. The in-situ test results also indicate that the shear strength of the subsurface soil has a significant increase, at various locations, these increase are, 4.1, 3.9 and 1.29 time, respectively.

Key words: soft ground, site pretreatment, insitu testing, prefabricated vertical drain method, effect evaluation