Workability of sand bentonite seawater mixture for construction of seepage cut off wall

• Main Author: Dhanwansyah Dinata
• Other Authors: Yi Yaolin
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Civil engineering
• Online Access: https://hdl.handle.net/10356/163746
• Institution: Nanyang Technological University

Due to climate change, sea levels have continued to rise annually. Singapore, an island city, will be affected by these changes significantly, and the construction of seawalls or dikes could help Singapore to fight against the rise of sea levels. However, the effectiveness of seawalls or dikes is significantly affected by the permeability of soil below it. Most of the coastal area of Singapore comes from reclaimed land using sand as the filling material and has a high permeability, which is vulnerable to the intrusion of seawater. Seepage cut-off wall can be constructed in the sand layer to prevent the seepage of water. Bentonite slurry is commonly mixed with sand to form sand-bentonite mixture during the construction of cut-off wall. During the mixing of sand-bentonite mixture in coastal marine areas, seawater would be inevitably involved and hence the workability of sand-bentonite mixture would be significantly affected. To study the effects of seawater on the workability of sand-bentonite mixture, three types of bentonites, i.e. sodium bentonite, calcium bentonite, and seawater bentonite, were mixed with sand and artificial seawater. The workability, including flowability and bleeding, of the fresh sand-bentonite mixture were tested, and distilled water was used as a control. The results show that the use of seawater causes a significant increase in the flowability and bleeding of sodium bentonite-sand mixture and calcium bentonite-sand mixture, while water type has a less significant influence on the flowability and bleeding of seawater bentonite-sand mixture. This is because the cation exchange induced by seawater addition leads to the decrease in the liquid limit of bentonite, reducing the water retention capacity of bentonite, and hence the flowability and bleeding increase.