Geological investigation and analysis for soil treatment by using vacuum preloading method

VINH, Ta Cong Thanh, Prof. Dr. Dwikorita Karnawati

2010 | Tesis | S2 Teknik Geologi

Ca Mau 2 – 750MW power plant project need to be constructed at the study area, Ca Mau Province, Vietnam especially on the alluvial clay formation with high organic contents, high void ratio, low permeability and the thickness up to 20m. Underneath such clay, it was found a layer of clay-sand with the thickness exceeding 80m. Problem about settlement and time for dissipation the pore water pressure of construction may occur due to the low soil bearing capacity and low permeability. This study was conducted in order to provide the most appropriate method for soil improvement. Geological as well as geotechnical field investigation and laboratory analysis were carried out to support the study. Based on the investigation results, some manual calculations on ratio between coefficient of horizontal and vertical consolidation Ch/Cv and soil consolidation by vacuum preloading method can be performed in order to give the most appropriate design for soil improvement. After calculation step, the Asaoka monitoring method and Plaxis simulation were conducted to recheck the result of calculation. The final result showed a good agreement between manual calculations, Asaoka monitoring and simulation by Plaxis, it described that the installation of vacuum preloading and prefabricated vertical drain (PVD) improved the rate of settlement (Both manual calculation and simulation by Plaxis can obtain the 3.44m of settlement in 5 months). The PVD increased the speed of vertical drainage so increased the speed of pore water pressure dissipation (dissipate all the access pore water from 164 kN/m2 to 0 kN/m2 in 5 months) and decreased the consolidation time (from more than 5 years to 5 months). In addition, the result of calculation the ratio Ch/Cv by Housby and Teh formula in this study showd that this ratio increased according to depth and higher than ratio in Vietnamese standard. So, the ratio Ch/Cv =3 (normally the result equal 2 is used for this ratio in Viet Nam) calculated by Housby and Teh formula was used in manual calculation and input data of Plaxis model and also showed the good result.

Kata Kunci : Soil treatment,Vacuum preloading method