Building a subway is categorically different from building anything else. Elevated rail lines, highways, and airports all involve large-scale civil works — but underground construction operates under a fundamentally different set of constraints. The ground pushes back. Water infiltrates. Every cubic meter of excavated soil has to go somewhere. And the city above continues moving while the work proceeds below.
The Philippines confronted all of these realities when it committed to constructing its first underground rapid transit system. For the Tokyu Tobishima Megawide joint venture (TTM-JV) — the consortium delivering Contract Package 104 of the Metro Manila Subway Project — this is not a theoretical challenge. It is active, ongoing construction beneath one of Southeast Asia’s most congested urban corridors.
This article explains what underground construction of this complexity actually demands: the methods used, the risks managed, and why the engineering approach the TTM-JV brings to CP104 subway works matters for how the Philippines builds infrastructure from here.
Why Underground Construction Is a Different Discipline
Surface construction works with gravity and exposure. Materials come in from above, structures rise upward, and inspections are straightforward. Underground construction inverts most of these conditions.
At depth, engineers must contend with lateral earth pressure, groundwater, and the load of everything built above. In Metro Manila specifically, the soil profile is variable — soft alluvial deposits near riverbanks, harder volcanic material in other zones, and pockets of fill and made ground that behave unpredictably under load. Understanding the ground before breaking it is as critical as the construction itself.
Underground construction also demands a longer geotechnical preparation phase than surface works. Soil boring, in-situ testing, and groundwater monitoring must inform every design decision — from the depth of the station box to the type of tunnel lining used. Errors at this stage are far costlier to correct underground than they are above it.
Station Construction: Cut-and-Cover in a Dense Urban Environment
The two stations in CP104 — Ortigas Station and Shaw Boulevard Station — are built using the cut-and-cover method. This involves excavating from the surface downward, constructing the station box within the open cut, and then reinstating the surface above once the structure is complete.
Cut-and-cover is the most reliable method for building large underground spaces in urban areas with shallow to moderate depths. It allows engineers to work within a controlled open environment rather than inside a confined tunnel bore, which simplifies the construction of wide, multi-level station boxes that need to accommodate platforms, concourses, utilities, and ventilation systems.
In an urban context like Ortigas Center, the cut-and-cover process requires extensive temporary works. Sheet piles or bored pile walls are installed first to retain the surrounding soil before any excavation begins. Internal bracing or tie-back anchors then hold those walls against the pressure of adjacent ground and structures throughout the dig. Each stage of excavation must be carefully sequenced to maintain wall stability and minimize ground movement — settlement of even a few millimeters in the wrong location can affect adjacent foundations.
The Ortigas Station site occupied by the former Metrowalk commercial complex presented specific coordination challenges: clearing a large, developed urban footprint while managing public access around an active business and transport district. Demolition of that structure commenced in September 2025, enabling the excavation phase to proceed.
Tunnel Construction: How TBMs Work and Why They Matter
The approximately 3.4 kilometers of running tunnels connecting the CP104 stations are excavated using tunnel boring machines — TBMs. Understanding how TBMs work explains both the scale of what the TTM-JV is building and why this method is the standard for urban subway construction worldwide.
A TBM is a large cylindrical machine that advances through the ground by rotating a cutter head at its face, breaking the soil or rock while simultaneously installing segmental concrete lining rings behind it. The machine is essentially self-contained: it excavates, installs lining, and conveys the excavated material rearward in a single continuous operation. The precision required in manufacturing those precast concrete tunnel lining segments is one reason why advances in precast construction methodology have direct relevance to underground rail — not just surface works.
In soft urban soils — the conditions present in much of Metro Manila — Earth Pressure Balance (EPB) TBMs are the standard type used. An EPB machine uses the excavated material itself as a pressure medium, filling the cutterhead chamber with a conditioned soil paste that balances the earth and water pressure at the tunnel face. This prevents ground collapse and, critically, controls surface settlement. In a dense urban environment, keeping surface settlement within tolerances of a few millimeters is not optional — it protects the foundations of buildings, utilities, and roads above.
TBM tunneling is not a simple mechanical process. Advancing through variable ground requires constant adjustment of face pressure, penetration rate, and conditioning material. Crossing beneath structures with sensitive foundations demands additional monitoring and, in some cases, pre-treatment of the ground ahead of the machine. The operational expertise required to run a TBM effectively in urban conditions is one of the core technical contributions the Japanese partners in the TTM-JV bring to this project. How global engineering innovation gets verified on the ground — at the project level, not just in principle — is something our teams track actively across every site.
Depth, Right-of-Way, and the Urban Subway Planning Reality
One of the defining characteristics of the Manila subway’s construction timeline is the right-of-way challenge. Acquiring surface rights in a dense, built-up city is slow and legally complex. The DOTr’s response to persistent right-of-way disputes was to authorize deeper alignment in affected areas — at depths reaching up to 47 meters below the surface in some sections.
Greater depth creates its own engineering demands. Deeper stations require longer escalator banks, more complex vertical circulation, and higher pumping requirements for drainage. The structural design of the station box must account for significantly greater lateral and vertical earth pressures. TBM performance in deeper, potentially harder or more variable ground conditions may also differ from shallower sections.
These are not unusual complications in underground rail construction — every metro system in a dense city navigates them. But they underscore why underground construction requires a level of technical planning and adaptive engineering capability that surface projects simply do not.
Why the Joint Venture Model Is the Right Structure for This Work
The Tokyu Tobishima Megawide joint venture is structured around the technical requirements of the project, not just the contractual requirements of ODA-funded procurement.
Tokyu Construction leads as head contractor, drawing on its experience with underground rail construction in Japan — including the redevelopment of Shibuya Station, one of Tokyo’s most complex underground interchange environments. Tobishima Corporation contributes deep civil engineering expertise, including involvement in major tunneling projects such as the Tokyo Bay Aqua-Line and the Seikan undersea railway tunnel. These are not adjacent credentials — they are directly applicable to the methods being used in CP104.
Megawide Construction provides the local execution infrastructure: procurement networks, regulatory navigation, workforce, and project management capacity built through large-scale Philippine infrastructure delivery. The company’s experience building the Mactan-Cebu International Airport, PITX, and multiple rail packages under the NSCR demonstrates the organizational scale required to execute a project of this complexity. That foundation is built on a deliberate commitment to first-world engineering in the Philippines — the standards and methodologies that make technically demanding projects executable. Underground construction adds a new technical layer, and the TTM-JV structure ensures that layer is covered by the most experienced parties available.
The result is a joint venture where capability distribution matches work scope distribution. That alignment is what makes complex international infrastructure projects succeed.
What This Means for Philippine Construction Capability
The Philippine construction industry has built expressways, airports, bridges, and elevated rail systems at scale. Underground construction is the technical frontier it has not yet crossed at the metro system level — until now.
CP104 is a live transfer of underground construction methodology into the Philippine industry. Filipino engineers and construction professionals working within the TTM-JV are gaining direct experience with TBM operation, deep excavation management, underground station construction sequencing, and the geotechnical monitoring systems required to execute safely at depth. That knowledge does not leave when the project ends. It complements the kind of exposure our teams actively pursue — such as exploring future-ready construction techniques through technical visits abroad — to ensure that what we bring to projects like CP104 reflects where the industry is heading.
For Megawide Construction specifically, CP104 completes a rail capability matrix that spans at-grade, elevated, and underground construction. That range positions the company as a comprehensive rail infrastructure contractor — not a specialist in one mode, but an construction company in the Philippines capable of delivering across the full spectrum of rail project types that the country’s infrastructure pipeline requires. It is a result of sustained investment in research and development that translates directly into expanded execution capability.
Conclusion
Underground construction is demanding precisely because the margin for error is smaller and the consequences of mistakes are greater than in surface works. The methods used in CP104 — cut-and-cover station construction, EPB TBM tunneling, deep excavation with retained walls — are proven globally but technically complex in execution.
The engineering behind the Philippines’ first subway is not incidental to the outcome. It is the outcome. Getting it right requires the right methods, the right partners, and the right level of technical commitment to every phase of the work.
For full project details on Megawide Construction’s role in CP104, including scope, contract, and project status, visit the MMSP CP104 project page.
