Description

Project DE151 upgrades the road network between Upper Changi Flyover and Tanah Merah Flyover in Singapore, to support future traffic from Changi Terminal 5 and surrounding developments. The case study in this session focuses on the MC103 underpass, which crosses beneath the East Coast Parkway (ECP), the main route in and out of Changi Airport. The underpass sits within a 620m depressed road section, with the underpass itself spanning approximately 90m. The design combines bottom-up construction for the depressed road with top-down construction for the underpass, retained by Secant Bored Pile (SBP) walls that serve as both temporary and permanent structures.

Using MIDAS CIVIL NX, a typical underpass cross-section is modelled as a 2D frame — a one-metre strip — with the SBP wall represented as pile springs and the surrounding soil as compression-only springs. Beam end releases are applied at the base slab-to-SBP wall connection to reflect the pinned condition arising from the site's dowel-bar detailing, since full moment continuity cannot be achieved at that interface. Load combinations follow the LTA Civil Design Criteria (LTACDC) and are imported directly between models using the MCT command shell, rather than being recreated manually for each project. For vehicle collision loading on the underpass walls, a plate model is used instead of the frame model, to capture two-dimensional load distribution and local stress concentration around the impact location. Results — including axial force, bending moment, shear force, and spring reactions — are extracted at planned node locations and compiled into a Word-based design report using the Dynamic Report Generator.