ABSTRACT
The ISP Blue Line is the first underground MRT line constructed in Bangkok. It comprises 22-km-long twin single-track tunnels, 18 stations and a depot. The horizontal alignment mainly follows the right of way of city roads. Construction of the underground structures was implemented under two fast track design-built contracts, each having approximately the same amounts of work. The South Contract involved construction of a twin bored tunnels from the inter-city railway terminal at Hua Lamphong eastwards for 5 km beneath the busy Rama IV road to the Queen Sirikit National Convention Center, then 4.5 km north beneath the narrow business Asoke road, and Ratchadaphisek road ending on the surface near the depot. Works of the North Contract continued for 4.5 km north along Ratchadaphisek road to Lad Phrao road then turned west to Chatuchak Park and finally terminated beneath the Bang Sue
railway station. The 18 stations of the project are as follows:
3 GROUND CONDITIONS
Bangkok is situated on the southern part of the low lying Chao Phraya plain, which extends north from the coast line at the Gulf of Thailand up to approximately 350 km and spans east-westward up to 150 km. The flat topography plain is covered with a thick marine clay layer, which overlies a very thick series of alluvial deposits of alternating stiff to hard clay and dense to very dense sand to gravel. The thick soft clay layer generally extends from the ground surface to a depth of 12 to 15 m. The soft clay which is known as “Bangkok soft clay” has high water content (70-120%), high plasticity, low strength and high compressibility.
