Comparison of consolidation effects by using prefacbricated vertical drain method and sand drain method

DIEU, Chau Quang, Dr. Doni Prakasa Eka Putra, ST.,MT

2010 | Tesis | S2 Teknik Geologi

Sabeco - Quang Ngai Brewery (SQB) project is located in Quang Ngai City, Central of Vietnam and Cai Mep International Terminal (CMIT) project is located in Ba Ria Vung Tau Province, Southern of Vietnam. These both projects lay on areas where the high thickness of soft clay was found from ground surface to the depth of 10 - 13m and 36 – 40m. The constructions set on these areas that have to face the important problems, that are the behaviour of soft clay foundation such as the sinking – emerging or shear failure phenomenon. In addition, the process of consolidation takes much more time to be finished than our expected. In such case, conventional preloading combines with Prefabricated Vertical Drain (PVD) or Sand Drain (SD) method aiming to accelerate that process of consolidation, which was proposed to apply for these research areas. This study has been conducted to analyze geotechnical investigations data in research areas in order to evaluate their effects on consolidation rate and applicability of each method as well as to design the stages of construction to prevent stability problem of foundation. Otherwise, the analysis and comparison of controlling factors of PVD and SD method on consolidation rate will give the best recommendation to choose suitable method for soil improvement in research areas. At last, the applications of Asaoka method and Plaxis finite element method will be helpful in order to check the result of manual calculation of settlement. According to the results of research, the clay consistency controlled the applicability of SD method and PVD method in research areas, it shown that the PVD method are useless with clay that has SPT value higher than 5 blows but SD method can solve such problem due to the different between the installation methods of the mandrel, for instant of SQB project. Engineering properties of soil in CMIT project play an important role to the process of consolidation rate since it caused high of settlement (4.512m) and lower of consolidation process (663 years) due to the application of conventional preloading only. The final results shown the effects of controlling factors of vertical drain on consolidation rate are significant, for example, the consolidation rate will decrease 10% if increase the width of PVD from 100mm to 125mm, and consolidation rate seems increase as geometric progression of 2 if spacing factor increase 0.5m. Thereby, the most appropriate solution for soil improvement in CMIT project can be found out that is PVD method since it saved time (330 days) better than that from SD method (347 days) as well as PVD method gave more advantages than SD method in construction period such as PVD saves time for installation more than SD method, PVD can withstand under lateral displacement of foundation. Finally, the result of Plaxis (4.62m for total settlement) was in good agreement with manual calculation (4.512m for total settlement), Asaoka method (3.84m for primary settlement) also gave a good confirmation for the practicality of manual calculation (3.832m for primary settlement).

Kata Kunci : Sand drain method,Prefabricated vertical drain method