By Paul Colbert
When completed in the 2030s, Singapore’s Cross Island Line will be the island nation’s eighth Mass Rapid Transit system. A better understanding of the underground helped the team driving phase two of this project navigate complex sub surface conditions, many stakeholders and a nature reserve.
Phase two of Singapore’s Cross Island Line (CRL2) is constructed underground close to biodiversity areas as well as residential and commercial buildings. This 15km section, includes six stations set to open from 2032. It will improve commuter connectivity and shorten travel times to and from the western part of the island.
The subsurface conditions added further complexity to the project. The CRL2 alignment crosses uneven terrain with diverse ground types, including fill, fluvial sand, clay, marine clay, residual soil, and undulating rock. About half of the route is on granite rock, the rest on sedimentary rock like sandstone, siltstone, and mudstone.
Additionally, the planned excavations were near high-rise residential and commercial buildings, busy roads, high voltage cables, and deep tunnel sewer systems. All these factors together presented a particularly challenging combination of hurdles and risks for the professionals involved including how to manage so much data and communicate it clearly to stakeholders.
Rendered image of CR17 Station distinguishes area that above and below rockhead
(Image: Arup)
Making the unseen understood
TanSje Ting Tan, Geotechnical team lead for lead consultants Arup, said it was vital to understand the ground conditions in “exhaustive detail” for such a large and multidisciplinary project.
Manually managing and inputting such large amounts of data, including digitising field records, cleaning lab test data, and creating 2D profiles, would have been extremely time-consuming and repetitive for multiple sites, she said.
Illustration showing the geological formations intersected by the proposed tunnel alignment and the estimated volume of tunnel spoil
(Image: Arup)
“We learned from the past,” Tan said. “To reduce the number of hours spent on manual data entry, we introduced Leapfrog Works—initially assisted by gINT and later by OpenGround as part of Arup’s global migration to the new solution. This approach also enabled engineers to more thoroughly investigate the geotechnical risks associated with deep excavation and tunnelling.”
Including underground stations and tunnels in Leapfrog visualisations of expected geological formations helped engineers identify gaps in geological information and risks associated with stability and settlement.
In the end, the task, which would traditionally have taken the time of six geotechnical engineers, was achieved by just two.
Geological section of CRL2 alignment at Sin Ming Road developed using Leapfrog (Image: Arup)
Sustainable solutions, satisfied stakeholders
Part of the project analysis involved sensitivity studies to reduce the impact on the biodiversity areas. Leapfrog’s capability to present a 3D ground model helped stakeholders comprehend the challenges involved and develop a well-rounded design that balanced efficiency and effectiveness.
Tan said the Leapfrog 3D ground model of the tunnel alignment was able to estimate the volume of tunnel spoil in various scenarios and predict the volume of reusable material for sustainability assessment.
Tan also believes Leapfrog significantly reduced the effort required to produce ground level and rock surface contours when compared to traditional methods of identifying the vertical coordinates from one borehole to another in drawing related tools.
“It’s approximately 90% more efficient than traditional methods,” estimates Tan.
This also meant the structure impact assessment could be supported by more accurate settlement contour information, and therefore be more refined.
Bentley’s MicroStation was also a valuable tool for conveying ideas to clients and stakeholders.
An example of the use of MicroStation into 3D visualisation as part of the concept study of new CR17 connections to existing Clementi MRT station (Image: Arup)
By recognising the possible impact and construction risks, this ensured that all stakeholders were aware of any hazards and could collaborate to minimise them.
The reference design saw an enhancement in both detail and usefulness. Initially, 15 analysis sections were planned; however, the integration of Python automation in PLAXIS increased efficiency, enabling the submission of 24 sections.
This improvement allowed the team to perform additional design analyses at critical locations that required more thorough examination. The more detailed and refined design not only reduced risks but also optimised designs, resulting in further cost savings, according to Tan.
Bentley’s collaborative ProjectWise platform enabled “seamless coordination” among the many multidisciplinary teams. It streamlined the planning and execution process to deliver critical infrastructure that met the needs of all stakeholders, even under a wide range of challenges.
90%
greater efficiency in structural impact assessment
~70%
up to 70% improvement in analysis task efficiency
10%
project cost saving due to reduced work hours
“Automation and digital technologies have significantly improved accuracy and efficiency in this project,” Tan said. “With such a large dataset of geological information across a 15km long project, and over 20 multidisciplinary stakeholders, the team must communicate and juggle comments and opinions into designs in multiple stages.”
Tan said the team had learned a lot during the CRL2 project that would change how they worked in future.
“The use of digital tools such as those offered by Seequent and Bentley will lead us to a higher level of project performance, provide a positive impact on environmentally sustainable practices, and result in socioeconomic gains.”