The $1.1 Billion Engineering Marvel: Inside South Asia’s First Underwater Tunnel

The $1.1 Billion Engineering Marvel: Inside South Asia’s First Underwater Tunnel

Building roads underwater used to be the domain of speculative fiction, but modern civil engineering has officially reshaped that reality in South Asia. Passing beneath the Karnaphuli River in Chittagong City, Bangladesh, the Bangabandhu Sheikh Mujibur Rahman Tunnel stands as a landmark megaproject. Officially inaugurated on October 28, 2023, by Prime Minister Sheikh Hasina, the $1.1 billion underwater tunnel bridges a long-standing developmental divide in Bangladesh’s primary port city, turning complex geological hurdles into a high-speed artery for international trade.

The Chittagong Dilemma: Why Go Underwater?

Chittagong City (officially known as Chattagram) serves as the economic heartbeat of Bangladesh. Home to the country’s largest seaport, it handles the vast majority of Bangladesh’s import and export volumes. Despite its commercial significance, the city historically suffered from severe spatial inequality caused by the Karnaphuli River dividing it into two distinct halves.

• The Thriving Western Bank: Heavily developed, hosting the main urban center, commercial districts, and seaport facilities.

• The Neglected Eastern Bank: Isolated from the main city, lacking high-capacity road infrastructure and relying almost exclusively on slow, congested ferry routes.

As Chittagong planned major expansions—including the Bay Terminal and the Matarbari Deep Sea Port—the reliance on ferry crossings created an unsustainable bottleneck. Building a traditional high-level bridge posed severe risks: it could disrupt maritime traffic entering Chattagram Port, interfere with operations of the Bangladesh Navy, or contribute to heavy siltation in the Karnaphuli River bed.

Constructing a tunnel deep beneath the riverbed emerged as the definitive solution to preserve the river’s naval and commercial utility while establishing a seamless overland route.

Financing and Strategic Partnerships

To realize a megaproject of this scale, Bangladesh partnered with international stakeholders for both capital and technical expertise:

• Funding Structure: The project carries a total cost exceeding $1.1 billion, heavily supported by soft loans from the Export-Import Bank of China (Exim Bank of China).

• Construction & Management: The project contract was awarded to the China Communications Construction Company Limited (CCCC). Construction officially commenced in December 2017 under the leadership of Project Manager Yu Jingtao.

• Urban Development Model: The project adopted China’s “One City, Two Towns” urban planning model—modeled after Shanghai—aiming to balance urban growth by developing the Eastern Bank into a modern hub equal to the Western Bank.

Overcoming Bay of Bengal Geology

Engineers encountered formidable soil conditions in the Bay of Bengal estuary, where soft, water-logged silt and complex sediment layers made conventional excavation impossible.

To overcome these underwater conditions, CCCC deployed a massive Slurry Shield Tunnel Boring Machine (TBM) specifically customized for the project:

• TBM Scale: Featuring a cutting diameter of 12 meters, it was tailored to carve through delicate sub-river strata safely.

• Depth Parameters: The tunnel was excavated at depths ranging from 18 to 31 meters beneath the Karnaphuli River bed.

• Structural Engineering: The bored tunnel consists of precast concrete ring segments engineered to withstand high hydrostatic pressure from the river and tides above.

Key Infrastructure Specifications

The project extends far beyond the underwater section itself, incorporating a multi-modal highway network to integrate into existing regional routes smoothly.

Local & Regional Economic Impact

The opening of the Karnaphuli Tunnel fundamentally alters the economic topography of southern Bangladesh. By cutting travel times across Chittagong to mere minutes, it unlocks significant opportunities across several key sectors: