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.

中文翻译：

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砂质土壤和铁路保护区内的正割钻孔桩施工面临的挑战

世界各地城市地区人口密度的持续增长，更加重视地下空间的利用和开发，以满足城市日益增长的需求。由于市区的土地空间有限，世界上许多城市也正在着手整合地铁基础设施，商业开发和住宅等大型建设项目，以满足基础设施日益增长的需求。发展全面而完善的公共交通网络对于实现以人为本的世界级交通系统至关重要。为了增强铁路网络的连通性，换乘站和地下通道的建成是为了连接各条线路，从而使大众捷运（MRT）线路之间的运输可以无缝进行。因此，在不影响现有捷运线运营的情况下，在现有捷运线附近建造新的捷运线变得越来越具有挑战性。这项研究的主要目的是提出克服现有地下MRT链接上方（地下15 m）且与现有地下MRT东西线站相邻的割线钻孔桩（SBP）的方法。由于常规的施工方法不适用于现场条件，因此本文提出了四种不同的技术来在砂土中构造SBP墙。在建造SBP墙的同时，使现有MRT结构的振动和运动保持在允许范围内，新技术获得了成功。从该项目中可以得出结论，可以在沙质土壤中安装SBP，而不会对相邻结构和施工时间表产生重大影响。从这项工作中获得的经验将是无价的，并可作为在人口稠密地区和现有的敏感结构附近逐渐变得不可避免的SBP工程的经验教训。