ABSTRACT
Prefabricated Vertical Drain (PVD) is a composite geosynthetics material which designed to have a high permeability property. It is often used to accelerate consolidation process on a compressible soft soil layer. In order to reach a minimum number of 90% consolidation at the beginning of the building or structure construction project, a certain number of preloading is required. The number of preloading depends on the load that would be acting on the ground in the future. There are several methods of preloading, such as: conventional earth embankment, vacuum with membrane, and membraneless vacuum. In this paper, a test area of 800 m2 located in the north coast of Central Java would be tested using PVD with membraneless vacuum preloading method. An approximately 80-90 kPa of vacuum pressure would be applied during vacuum preloading period. The vacuum pressure successfully reached the edge of the area with almost the same pressure as exerted by the vacuum pump. The difference value of vacuum pressure at the edge with the vacuum chamber are ranging from 2-6 %. At the toe of PVD material, vacuum pressure is about 3% smaller than the vacuum pressure measured on the top of the PVD. After three months of vacuum, the result showed that 70-80% of total predicted settlement was reached. Soil investigation data from before and after vacuum showed that qc value of CPT test was slightly increased whereas SPT value increased by 1.5 times. Laboratory test data showed that the natural water content value decreased by 1-4%, unit weight increased by 4-9%, void ratio value decreased by 10-20%, and shear strength increased by 5-20%. The recorded bouncing potential two months after vacuum was 2-3%.
