ABSTRACT
The Premprachakorn flood diversion tunnel was the first diversion tunnel shortcut the flooding water from Premprachakorn cannel to Choa Phraya river. The second and third diversion tunnels are now under design and construction period by divert the flood water from Sansab-Ladpro Cannel and Makkasan reservoir to Choa Phraya river, respectively (SECC, 2004). The tunnel has outside diameter of 4.05 m with reinforced concrete segmental lining of 180 mm thick and bored by means of EPB shield. The tunnel was seated in the very stiff silty clay layer alternated with dense silty sand layer at about 20-24 m below ground surface as shown in Figure 2. The tunneling work was started from outlet shaft at Choa Praya river. At station 1 534 from Choa Phaya river, the flood diversion tunnel was bored about 3 m underneath through the existing Bangkok main water supply tunnel as shown in Figure 3.
