A Case Study of Metropolitan Waterworks Authority
Bangkok, Thailand
D.Klahan & B.Vongsa & M.Panaim & P.Traidate & W.Phakjarung
Metropolitan Waterworks Authority, Bangkok, Thailand
ABSTRACT: Metropolitan Waterworks Authority (MWA) has been involving in the construction of underground tunnel using Tunnel Boring Machine (TBM) for more than 30 years. Treated water has been conveyed through the large-scale transmission tunnel networks, with the total length of 187 kilometers, to the distribution pumping stations around and inside the metropolitan boundary. At the outset, the typical tunnel sections, both primary and secondary linings, were designed to be reinforced concrete. Having been in use for long term, there are some leakages detected, which caused severe effect to the road surface and to some extents to the above ground structures. MWA, therefore, launched the tunnel rehabilitation project, comprising of 4 routes, with total length of 14 km, with an aim at surveying the leakage points by employing the so-called Geophysical Surveying Method, filling the voids detected along tunnel alignment with proper materials and installing Steel Pipes (MS-Tube) inside the existing tunnels as secondary lining to strengthen the structure and to increase water pressure resistant capability.
This paper is aimed at describing the method of Tunnel rehabilitation, which has been acceptably and technically proven to be one of the proper solutions for rehabilitation of large-scale tunnel, since it was once successfully adopted in the previous tunnel repair project from Bangkhen Water Treatment Plant to Pradipat Valve Chamber. Such repaired tunnel has been in use well until now without any leakage encountered. Pipes inserted inside of tunnel were electrically welded, then, infilling mortar was grouted into the annulus around the inside of tunnel and outside of inserted pipes, leading to final tunnel section with considerably higher sectional modulus. Some challenges, for example, when performing underground works nearby the MRT Tunnel and preventive measures to cope with which employed FEM analysis in conjunction with installation of a series of geotechnical instrumentation as well as setting out the Trigger Level for monitoring, were also discussed.
Keywords : Tunnel Boring Machine (TBM), Transmission Tunnel, Primary Lining, Secondary Lining, Rehabilitation, Geophysical Method, Steel Pipes, FEM Analysis, Instrumentation, Trigger Level