Geotechnical Alliance Fast-Tracks the Johor Bahru RTS Hub with Buttressed Diaphragm Walls

The RTS Link is an international cross-border Rapid Transit System that will connect Malaysia’s second largest city, Johor Bahru, and Woodlands MRT station in Singapore, crossing the Strait of Johor. The RTS link has only two stations, with the Malaysian terminus at the newly built Bukit Chagar station, which will have its own immigration, customs and quarantine (ICQ) facilities. The joint Operator aims to have up to 10,000 passengers per hour in each direction, with only five minutes to clear immigration and five minutes travel time for the 4 km railway line. 

Bukit Chagar four-storey station will be co-located within a Transit-Oriented Development (TOD) with a transport hub and property developments around the station. Malaysia Rapid Transit System (MRTS), who is the developer and owner of the civil infrastructure for the Malaysian section of the RTS Link, has awarded in March 2025 the construction of the TOD to Sunway Group.

The first section of the TOD includes a multi-storey car park, with drop-off and pick-up facility and direct connection to the Immigration Customs and Quarantine Complex. This first section, including the 12m deep basement, is expected to be completed as soon as November 2026, at same time as RTS expected opening.

The second section of the TOD includes a retail mall, a podium and 4 high-rise multi-purpose towers, which will soon become a landmark for Johor Bahru skyline.

To complete the 12m deep 3-level basement, Sunway Construction had reviewed a top-down solution and a strutted excavation, both being time-consuming and not compatible with the very tight schedule. Geotechnical Alliance was contacted at early stage by Sunway to explore any alternate solution that would save time. GA proposed some cantilever open excavation using diaphragm wall supported by a long buttress for each panel. Despite being significantly more costly, this solution was adopted by Sunway because it was able to save some precious months on the overall construction program.

The main design criteria for the buttress diaphragm wall was to meet the maximum deflection of 0.5%. Design was performed with 3D finite element model and checked by Soletanche Bachy central Design Office with our in-house “Paris” software. After optimization, the standard diaphragm wall panel was set to 1.00m thick and 6.50m long, supported by a 1.00m x 6.50m buttress, both elements being around 30m deep.

The buttress enables open excavation till final level without any strut or anchors. After the tower base slab is cast, which is the critical task on overall program, the top part of the buttress will be demolished before casting the shallower two basement slabs. 

Despite being slightly less efficient, this buttress design was favored compared to the T-panel solution (where the diaphragm wall and the buttress are cast together and equipped with a single T-shape steel cage) because it does not require lifting operation with 2 cranes to install T-shape cages.  The 6m long plane steel cage required for each D-wall panel is assembled at the trench location from two pieces of 3m cages and installed with a single crawler crane.

Thanks to the detailed design prepared at tender stage and to the goodwill of the project team, and despite last-minute changes by the Architect on the tower base slabs position and depth, the first diaphragm wall panel was cast in April 2025, ahead of schedule. Since, Geotechnical Alliance team had mobilized resources and ramped up quickly to reach more than one panel per day.

The architectural changes have increased significantly the work quantities, amounting eventually to 30,200m3 of concrete in 187 panels (diaphragm wall and buttress). Yet, Geotechnical Alliance was able to complete this job within the initial time frame: the last diaphragm wall panels were cast in October 2025 and the capping beam completed in November 2025.  

The bulk excavation of the TOD basement started in November and reached the final level at Tower 1 lift pit in January 2026. The deflection of the retaining wall observed with the inclinometers is so far consistent with the design forecasts. The infrastructure RC works can now start, while the excavation will continue along the other towers.