Cross Island Line achieves first breakthrough on Singapore's largest bored tunnel

Construction works on the MRT's Cross Island Line (CRL) reached a new milestone on Sept 11, as the Land Transport Authority (LTA) achieved the first of four tunnel breakthroughs on the line, marking the completion of excavation for a tunnel between stations in the vicinity of Tampines North and Defu.

Beyond the milestone, the project also is the largest bored tunnel built in Singapore to date, LTA said in a news release on Thursday (Sept 24).

In conventional MRT projects, two tunnels are typically bored using regular-sized tunnel boring machines (TBMs).

However, for the CRL, a large-diameter TBM measuring approximately 12.6 metres in diameter was used.

"This allows both MRT tracks to be accommodated within a single tunnel instead of two separate tunnels," the authority explained.

What this means, LTA said, is that overall land take can be reduced, which can be beneficial in land-scarce urban areas.

"By accommodating both tracks within one tunnel, it reduces the overall tunnel corridor required compared with conventional twin-bored tunnels, providing greater flexibility for future underground and surface developments."

Another benefit of the single large tunnel is the reduced need for cross-passages between tunnels, which are typically required for emergency access.

Innovations to overcome challenges

Boring a single large tunnel comes with challenges, LTA said.

These include the need for higher-capacity muck removal, handling and transportation systems to maintain efficient tunnelling operations, as the larger TBM generates a substantially greater volume of excavated material.

To ensure safe and efficient excavation, LTA's project team developed solutions such as an accessible cutterhead design that allows cutter tools to be replaced under normal atmospheric conditions instead of in a compressed-air environment.

Compressed-air environments are typically used to counter surrounding groundwater and soil pressure, helping to keep the excavation face stable and prevent collapses.

LTA said the project team also equipped the TBM with systems that provide real-time monitoring of cutter wear and enhanced soil-conditioning capabilities to support safe and efficient excavation.

While the tunnel breakthrough marks the completion of excavation for this stretch, there remains "substantial work" inside the tunnel before railway systems can be installed, LTA highlighted.

"The next stage includes constructing the centre wall that will separate the eastbound and westbound tracks within the tunnel," the authority said.

To improve productivity, LTA said it will be using a precast centre wall system instead of the conventional cast-in-situ method, which requires extensive manual work.

To do this, a specially designed erection gantry equipped with a robotic arm will be used to handle, position, and install the precast centre wall panels.

"This reduces the manpower required and the amount of labour-intensive activities within the tunnel environment and enhances construction safety," LTA said.

A similar robotic arm was previously used during tunnel-strengthening works on the Circle Line, where it helped install more than 300 inner and outer steel rings.

When fully completed, the Cross Island Line will be Singapore’s eighth and longest fully underground MRT line. It will span around 67km, linking major hubs such as Changi, Punggol Digital District, Jurong Lake District, and Tuas.

It is expected to have a daily ridership of at least 600,000 in the initial years, growing to around one million over time.

9 月 11 日，地铁跨岛线 (CRL) 的建设工程迎来新的里程碑，陆路交通管理局 (LTA) 完成了该线路四条隧道中的第一条，标志着淡滨尼北站和德福站附近车站之间的隧道挖掘工作完成。

陆路交通管理局周四（9月24日）在一份新闻稿中表示，除了这一里程碑之外，该项目也是新加坡迄今为止建造的最大盾构隧道。

在传统的地铁工程中，通常使用常规尺寸的隧道掘进机（TBM）掘进两条隧道。

然而，对于 CRL，使用了直径约为 12.6 米的大直径 TBM。

“这样一来，两条地铁轨道就可以容纳在一条隧道内，而不是两条独立的隧道里，”有关部门解释说。

LTA表示，这意味着总体土地占用量可以减少，这对于土地稀缺的城市地区来说是有益的。

“通过在同一隧道内容纳两条轨道，与传统的双孔隧道相比，所需的隧道总长度有所减少，为未来的地下和地面开发提供了更大的灵活性。”

单一大型隧道的另一个好处是减少了隧道之间横向通道的需求，而横向通道通常是紧急情况下需要的。

创新应对挑战

陆路交通管理局表示，开凿一条大型隧道面临诸多挑战。

这包括需要更高容量的泥土清除、处理和运输系统来维持高效的隧道掘进作业，因为更大的隧道掘进机会产生更大体积的挖掘材料。

为了确保安全高效的挖掘，LTA 项目团队开发了诸如易于操作的刀盘设计等解决方案，使得刀具可以在正常大气条件下更换，而不是在压缩空气环境中更换。

压缩空气环境通常用于对抗周围的地下水和土壤压力，有助于保持开挖面的稳定性并防止坍塌。

LTA表示，项目团队还为TBM配备了可实时监测刀具磨损情况和增强土壤改良能力的系统，以支持安全高效的挖掘作业。

陆路交通管理局强调，虽然隧道贯通标志着该段隧道挖掘工作的完成，但在安装铁路系统之前，隧道内部仍有“大量工作”需要完成。

“下一阶段包括建造中央墙，将隧道内的东西向轨道分隔开来，”有关部门表示。

为提高生产效率，陆路交通管理局表示将采用预制中心墙系统，而不是传统的现场浇筑方法，后者需要大量的人工操作。

为此，将使用配备机械臂的专门设计的安装龙门架来搬运、定位和安装预制中心墙板。

“这减少了隧道环境中所需的人力和劳动密集型活动的数量，并提高了施工安全性，”陆路交通管理局表示。

类似的机械臂此前曾在环线地铁隧道加固工程中使用过，当时它帮助安装了 300 多个内外钢环。

建成后，跨岛线将成为新加坡第八条也是最长的全地下地铁线路。它全长约67公里，连接樟宜、榜鹅数码区、裕廊湖区和图阿斯等主要枢纽。

预计初期几年日均客流量至少为 60 万人次，随着时间的推移，将增长到约 100 万人次。