The MRT Orange Line is a crucial expansion of Bangkok’s public transport system, designed to connect the city centre to the eastern districts and alleviate traffic congestion.

Arup was appointed by Italian-Thai Development Ltd as their preferred partner to work on the detailed design of the East Section between Hua Mak and Khong Ban Ma stations. This section includes about 4km of twin bored tunnels, three underground stations, three ventilation shafts and a cut-and-cover tunnel. It runs through the city’s busiest roads, with one station under a flyover and several canal crossings requiring temporary or permanent diversion.

Our scope of work included track and tunnel alignment, geotechnical, tunnelling, structural, civil, MEP, fire, tunnel ventilation, building services, station planning and architectural design.

Our involvement in the East Section began at the tender stage, where we provided multidisciplinary design services for three separate contract packages. This early involvement enabled us to incorporate valuable lessons learnt to enhance project execution.

To facilitate construction, we used more detailed basic designs and advanced modelling tools to quickly address potential issues and optimise designs before construction. We tackled basal instability during underground station excavation with an innovative bay-by-bay approach, avoiding costly ground treatments and ensuring safety. We also developed a holistic fire safety strategy for underground stations, tunnels and ancillary ventilation buildings, utilising computational modelling to optimise evacuation and smoke control systems.

Enabling fast-track construction

In Thailand, the design-to-construction timeline is often rapid, with minimal gaps in between. Designs are frequently reviewed, approved and promptly handed over to construction teams for immediate implementation.

To enable this rapid pace of construction, Arup used slightly more detailed basic designs that provided a solid foundation for construction to begin while allowing flexibility for incorporating other essential disciplines such as mechanical and electrical and ventilation designs. 

We also relied on cutting-edge modelling and simulation tools to identify potential issues and optimise designs before construction began.

Innovating excavation approach

During the excavation of the underground station, one of the major challenges was the potential of basal instability. Gaps in the Second Stiff Clay were found through ground investigation information. The gaps could allow upward water flows from the underlying Second Aquifer Sand, posing a threat to the excavation.

To address this challenge, a bay-by-bay excavation approach was adopted along the cofferdam. The 250m long station was divided into bays of various lengths, and the excavation process was carefully managed and coordinated to ensure an adequate Factor of Safety against basal heave. As a result, significant cost savings were achieved by avoiding the need for extensive and expensive ground treatment works.

Ensuring fire and life safety

We also delivered a holistic fire safety strategy for the underground stations, tunnels and ancillary ventilation buildings, based on international fire code NFPA 130, to address and prevent major fire safety issues.

We adopted advanced computational modelling analysis to verify emergency evacuation patterns and smoke spread analysis to advise on the optimal smoke control system design for different smoke zones, including long adits with limitations in headroom and complex configurations. 

Our use of advanced technologies and innovative solutions helped ensure that the fire safety systems meet the highest standards of safety and efficiency.