Challenges in Urban Transit Tunnelling - Circle Line Stage 5 Experience

Rama Venkta1,a, Simon Hoblyn1,b, Khalid Mahmood2,c and S Mahatma2,d

1Land Transport Authority, Singapore.

2AECOM Singapore Pte Ltd, Singapore.


This paper presents the challenges faced during the planning, design and construction of the bored tunnels for Circle Line Stage 5 (CCL5) Mass Transit System in Singapore. Circle Line is a 33km long fully underground rail transit system. Circle Line stage 5 is the last stage of the Circle Line with about 3.3km long twin bored tunnels and 600m single track and overrun tunnels. In land scarce Singapore, most of the rail transit alignments are generally below the roads and cut through the residential and commercial built-up areas. The circle line alignment underwent several reviews and refinements to avoid sensitive buildings and utilities, however constraints still required the tunnels to run underneath sensitive shallow founded shop houses, a substation, a 9 story R/C pile founded building as well as a 6 story building with a basement under construction. In addition the twin tunnels were required to run in close proximity to each other, the pile foundations of adjacent elevated viaducts, a sensitive high power substation, cable tunnels and other significant structures. This paper discusses the development of the alignment at some of these sensitive locations, design checks for ensuring the stability of the buildings, structures and utilities, the supervision of the tunnelling works and monitoring of the buildings and structures. The lessons learnt during the tunnelling works have also been presented in this paper.

Keywords: Bored tunnel, Circle line, Urban infrastructure.

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