Boring tunnels for rocks and roads |19 March 2018

Getting into Mahé’s belly

Following President Danny Faure’s recent proposal to construct 2 tunnels -- between Cascade and Grand Anse Mahé, and the other between Beau Vallon and English River --  a reader sent us a copy of the following article, which is almost 20 years old, on the idea of building tunnels  under Mahé’s mountains. The article was first published in March 1999 in the Seychelles Unlimited news magazine.  

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Young brains in Seychelles have for some time been pondering over an idea from a quarry expert to dig tunnels through the mountains of Mahé.  Tunnelling will produce rocks for the construction industry, saving the hillsides from the scars of quarry. After the rocks have been dug out the tunnels can be used for roads, water mains, electricity cables and telephone lines. 

In Seychelles the idea of building a tunnel to link the East coast of Mahé to the West coast may be considered to be too far ahead of the present time although there are people, among them bosses of utility companies and managers of quarry sites, who think that such accesses will solve many of Seychelles’ development problems.

The really big obstacle preventing the idea from being tuned into a project is the prohibitive cost of tunnelling.

(In 1998) when the debates started on the type of development  Seychelles and the Seychellois would like to see in the year 2020, the national media received a paper entitled “The Quarry Industry – Year 2000 Plus” from A.D. Hall, formerly general manager of the recently privatized Civil Construction Company Ltd (CCCL). The company has for many years been blasting and crushing granite at quarry sites to supply materials for the booming construction industry. It is gnawing at a solid granite mountain at Providence. 

Hall’s idea is firstly aimed at finding an environmentally-friendly source of granites from within the mountains, to avoid further scarring of the verdant hillsides. The tunnels would merely be the end-product of underground granite blasting.

Hall said in the paper that the quarry at Providence had only a few years of proven rock supply, depending on the country’s requirements, but “certainly insufficient proven rock around the year 2000”.

Readers may quickly dismiss the claim that there is not enough rock on an island made up almost entirely of one solid granite ridge running from North to South. The concern actually is not about supply but rather how much can be removed from the hillsides without causing further damage to the natural environment.

“It is no longer acceptable for companies seeking rocks to drill and blast the nearest boulder at the side of the road. Therefore, where do we go to quarry rock in the year 2000 plus?” Hall asked.

It is true that quarrying companies are encountering tighter environmental regulations – the general public are demanding cleaner air, less noise and have a dislike for open face blasting of rock which in some cases also disturb their routine at home.

United Concrete Products Seychelles (UCPS), the main construction material supplier in the country is fast exhausting a rock quarry at Pointe Larue. It, too, is looking for a new quarry site that is friendly to the environment.

What is to be done?

“I have therefore come to the conclusion that to find this kind of area which can sustain an abundance of rocks for years it is not practicable keeping within the criteria of Seychelles being an environmentally friendly country and therefore other methods of obtaining a source of rock supply should be investigated, as present day excavation is not within the parameters acceptable any longer,” said Hall.

The saying “as solid as the rock of Gibraltar” is popular in British colonial parlance but in actual fact this promontory -- a piece of the United Kingdom on the Spanish Mediterranean coast -- is hollow. Tunnels run through within the mountain.

After all, Mahé is known to be made up of granite that is the hardest in the world. This makes Mahé even more solid than Gibraltar. It therefore qualifies Mahé’s mountains for mining from within to take out rocks for the construction industry.

Geologist Eddie Belle, the managing director of the Seychelles National Oil Company (SNOC), has identified the rock face at CCCL’s Providence quarry as a possible site to start digging out a tunnel. He said a tunnel that would end up somewhere at Barbarons would be just over 3.5 kilometres long.

Companies involved with tunnel projects in Norway and Sweden have been contacted to give a costing for the Providence-Barbarons tunnel idea but there have been no site visits so far.  Based on costing for a 16-kilometre tunnel in Switzerland, a link under the mountain from Providence to Barbarons would be over R600 million.

Selwyn Gendron, a director of Gondwana Granite, said boring tunnels through Mahé’s hard rock is technically possible as has been done in the Alps, Hong Kong, Gibraltar, Norway, Sweden and many other places.

“Yes, it is possible. The technology exists,” said Gendron.

The big constraint, he added, is finding the money to finance it. Gendron said proper surveys need to be done to find the best sites from where the tunnel will begin and end.

The Public Utilities Corporation (PUC) has been presented with tunnel projects to facilitate the transportation of water from abundant sources on the West coast to population centres around Victoria. Stephen Rousseau, the managing director who has just seen the country through a prolonged drought, is trying to realise the company’s objective of supplying over 90 per cent of the population with reliable and regular treated water. In fact, a British company submitted a tunnel project, at a cost of R23 million, to transport water from Grand Anse to the Rochon and La Gogue dams.  Presently PUC is tapping water at Sans Souci and pumping it over the mountain to Rochon.

Tunnelling, said Hall, Belle, Gendron and Rousseau, would provide rock for development and after the debris has been cleared the tunnel could be an access for roads, water mains, electricity cables and telephone lines.

“There is no restriction of size of tunnel. It can take a dual carriageway each way plus an environmentally friendly transport system of railway tramways or mono rail. Water and electricity utilities could also use the facility,” said Hall in his paper.

Tunnelling is a never-ending process, guaranteeing supply of rocks for a long time. Rocks could be dug out of the belly of Mahé from Providence to Barbarons, and from Machabée all the way to Anse Royale. Another tunnel could run from Victoria to Beau Vallon, providing more rocks, a faster road and better access for utilities. The tunnels could intersect at various points inside the mountain, just like in a metro system.

Apart from preserving the environment and getting a new source of rocks for construction, tunnelling brings a host of other benefits. Motorists driving from the East coast to the West coast would travel shorter distances. This would cut down on fuel consumption, there would be less wear and tear. Avoiding going over the mountains would also reduce incidence of pollution from overworking engines. There will be less digging up of roads and clearing away of the natural vegetation to make way for water mains and overhead cables.

Cavities created within the mountains could also serve as storage depots.

People interested in seeing the idea turning into a project say that what is financially dear today may save the country a lot of expenses in the long run. They add that until Seychelles discovers oil the idea will remain one that is for the distant future.

Hall insisted that his idea is not aimed at building tunnels primarily for the sake of getting fast access across Mahé. Tunnels will be the excavations left behind after the mining of rocks for the construction industry.

Once excavated, the tunnels serving the public will have to be fitted with lights and ventilation. These add to the maintenance costs.

Courtesy Seychelles Unlimited magazine, March 1999 issue