The Design and Construction of Ocean Outfall Diffuser for Samut Prakarn Wastewater Management

The Ocean Outfall Diffuser system is a mechanism for transmitting and dispersing of treated wastewater from the shore to the ocean through a submarine pipeline. Based on the Terms of Reference for the contract, the original concept envisaged a gravity flow pipeline to be installed below the seabed. Among several alternatives proposed for the construction of the Outfall Diffuser system, the inverted tunnel siphon constructed by a tunnelling technique is preferred. The inverted tunnel diffuser system comprises (1) an onshore shaft and an offshore shaft, located 2,620 m apart;

(2) a segmental tunnel with an inside diameter of 2.6 m, connecting the two shafts at the elevations of -26.0 and -23.0 m MSL, respectively; (3) a submarine pipeline (diffuser header) with an inside diameter of 2.6 m, extending 613.5 m in length from the offshore shaft; and (4) 100 risers spaced equally on top of the diffuser header, extending 0.7 m above the seabed for dispersing the treated wastewater to the ocean. The design, analysis and the construction procedures of the onshore and offshore shafts, submarine pipeline, and temporary structures for launching the onshore and offshore shafts are presented in this paper.