A tunnel is definitely better than a bridge

By: Edgar Mana-ay

CONNECTING Iloilo City to Guimaras has been a dream for many decades. Just imagine the ease of travel to Guimaras, and vice versa, if there is a bridge or a tunnel connecting the two islands.

In the past decades of planning this connection, NOBODY HAS THOUGHT OF A TUNNEL to connect the Island of Guimaras to Iloilo City, all minds were set on building a BRIDGE.

This dream of Guimaras-Iloilo connectivity is again resurrected in the “BUILD, BUILD, BUILD” Program of Pres. Duterte wherein the National Economic Development Authority (Neda) announced that 27.156 billion pesos has been earmarked for the Construction of Panay Guimaras, Negros (PGN) Islands Bridges.

This is part of the 77 billion pesos capital expenditure for Western Visayas alone under the Public Investment Program (PIP) from 2017 until the end of DU30 term in 2022. This very ambitious PIP which embodies the “Build, Build, Build” program will cost about 8 trillion pesos of infrastructure for the duration of DU30’s term.

Which is better – a bridge or a tunnel? All advantages are in favor of a TUNNEL over a BRIDGE connection to Guimaras. Foremost of all is cost. Ask any construction engineer worth his salt and has the experience on both tunnel and bridge construction, he will tell you that constructing a tunnel is cheaper by 30 percent than a bridge especially for long and high spans over seawater.

A tunnel is an all-weather passage even during typhoons when the bridge cannot be used. A bridge between Iloilo City and Guimaras will pose navigational hazards to large seafaring vessels, it might even limit passage thru for large ocean-going vessels just like the two Mactan bridges in Cebu and the San Juanico Bridge connecting Samar and Leyte.

When I was with Petron Tacloban many years ago, I was always concerned with the bridge clearance of San Juanico Bridge, especially during high tide because the large oil tankers of Petron cannot pass through.

A classic example of the superiority of a tunnel over a bridge is “D CHUNNEL”, or the CHANNEL TUNNEL, the 51-kilometer long tunnel linking Folkestone Kent in the United Kingdom to Coquelles, Pas-de-Calais in Northern France under the English Channel. This is a TWO single-track train rail system where passengers, cars and cargo trucks are shuttled back and forth in two large tunnels each about 6 meters wide by 4 meters tall and separated in between with a small service tunnel of about 4 meters wide. The electric service trains are operating at a speed of 160 km. per hour.

“D CHUNNEL” allows up to 400 EURO STAR trains to pass through the tunnel each day carrying an average of 50,000 passengers, 6,000 cars, 180 coaches and 54,000 tonnes of freight. Shuttle trains are 775 meters long, equivalent to 8 soccer fields place end to end. It takes only 31 minutes to travel from England to France using the Channel Tunnel.

Before a tunnel is constructed especially under the sea, a very exhaustive hydro-geology study is made of the sea bed and the ground strata underneath to determine which strata is the safest from water intrusion and at the same time provide the least construction cost. In the case of the English Channel it was found out there is a 30-meter chalk marl strata at an average of 50 meters below the sea bed of the English Channel that connects England to France. This is further confirmed by the chalk outcrop of cliffs on both sides of the Channel.

Chalk is a form of bio-clastic limestone (skeletal limestone) that are formed on the seafloor by the precipitation and accumulation of microscopic marine organisms such as encrusting algae and other shell-forming organism and buried for millions of years. Since this chalk marl contains 60 percent clay (the ancient environment where it settled), it was the excellent strata for a tunnel passage because it has a low permeability not to allow water to come in and at the same time it is not so hard for a tunneling operation.

It’s a very short distance between Iloilo and Guimaras and since the geology of both Guimaras and shoreline of Iloilo is purely sedimentary, then offhand, we can conclude that tunneling between the two islands will not be expensive. In Hong Kong the subway transit system accounts for 80 percent of the traffic in Hong Kong but the geology of Hong Kong is mostly volcanic, hence their tunnels are blasted by explosives thru hard rocks and therefore very expensive.

Many years ago Atlas Copco Sweden, a supplier of tunneling equipment, sent this writer to observe tunneling operations in Hong Kong as a representative of PNOC Coal Corporation.

Hopefully, this article on tunneling will be an eye and mind opener for our politicians and economic planner in whose hands lies the power in connecting Iloilo to Guimaras.  For according to George Bernard Shaw: “One man who has a mind knows it can always beat ten men who haven’t and don’t.”

Note: The author is the hydro-geology consultant of the municipality of Pavia and a retired drilling manager of PNOC.