Challenges in Construction of Secant Bored Piles in Sandy Soil and Within a Railway Protection Zone

Abstract

The continuing growth of population density in urban areas around the world has placed greater emphasis on the utilisation and development of underground space to meet the increasing demands of the city. Due to limited land space available in downtown areas, many cities in the world are also embarking on integration of major construction projects of metro infrastructure, commercial developments and residential estates, etc., to meet the growing demand of infrastructure In land-scarce Singapore, the development of a comprehensive and well-integrated public transport network is important to achieve a people-centric, world-class transport system. To enhance the connectivity of a rail network, interchange stations and underground linkways are constructed to connect the various lines so that transfers between mass rapid transit (MRT) lines can be seamless. Hence, it is becoming more challenging to construct a new MRT line in the vicinity of existing MRT lines without impacting the operations of existing MRT lines. The prime aim of this study is to present the ways to overcome the challenges in construction of secant bored piles (SBPs) above the existing underground MRT linkway (15 m below ground) and adjacent to the existing underground MRT East West Line station. The paper presents four different techniques applied to construct the SBP wall in the sandy soil since the conventional method of construction was not applicable to the site condition. The new techniques were successful as the SBP wall was constructed while keeping the vibrations and movement to the existing MRT structures within the allowable limits. From this venture, it can be concluded that it is possible to install SBPs in sandy soils without any significant impact on adjacent structures and construction timeline. The experience gained from this endeavour will be invaluable and can serve as lessons learnt for SBP works in the densely populated area and in the vicinity of existing sensitive structures which is increasingly becoming unavoidable.