North-south highway link: should we brace for disaster?
Professor Simon Mitchell, Guest Columnist
A north-south route connecting Kingston to the North Coast Highway is undoubtedly an important step in the development of Jamaica. Yet this project has met numerous problems. The leg from Linstead to Moneague has been particularly troublesome, and eventually resulted in the contractors, Bouygues, pulling out from Jamaica.
Now the three legs, Caymanas-Linstead, Linstead-Moneague, and Moneague-Steer Town, have been taken over by China Harbour, and while I wish it luck with its venture, I feel that serious questions regarding the geological issues of the route of the highway must be raised.
HIGHWAY LEG 1
The first leg of the north-south route begins at Caymanas and heads off towards the golf club, where it climbs on to the hill, across a few faults, west of the club. From here, the road will descend on to the alluvium to the northeast of Spanish Town, cross the Rio Cobre and then skirt along the western margin of the Bog Walk gorge. Several faults in the north of this area render potential issues to the roadway, but depend on the exact route taken.
Further north, the route intersects the Cavaliers-Crawl River Fault Zone, a major active fault that crosses Jamaica, and here we have our first major problem. The planned route for the road descends to the interior valley to the west of Bog Walk along one of these fault zones.
Often we think of faults as a single surface, but here, this is not the case - for along this whole descent, the limestones are so weak and fractured that a machete can be thrust easily into them up to the hilt. Should you build embankments on so steep a hillside with such weak rocks? No!
From here, the proposed road runs off towards Linstead across alluvial deposits, which pose no serious threat.
HIGHWAY LEG 2
From Linstead, the highway has to negotiate the hills to the north, and this is the major problem that Bouygues faced. A series of faults uplift Cretaceous volcanics in this area, which have been covered by landslide deposits. The landslide deposits are up to 40m thick, and constructing a road across this presents major problems.
Loading the deposits, creating cuttings or even building a bridge would lead to disaster if the landslide deposits started moving, if triggered by heavy rains or even an earthquake.
From this point, the road moves on to white limestone, with few issues, and is virtually complete.
HIGHWAY LEG 3
Leg 3 leads from Moneague to the north coast road. It does cross certain features (e.g., the so-called Duanvale Fault), but few would appear to be of great engineering significance.
What should we learn from Highway 2000?
Highway 2000 was planned with little or no geological input, and consequently the route taken has not been evaluated geologically. One only needs look at the new leg from Sandy Bay to May Pen to see this. The westbound leg of this new leg is already closed because the road has collapsed. Geologically, this is built not on white limestone, but on the May Pen Beds, which are unconsolidated and can collapse.
THE WAY FORWARD
With these lessons, Jamaica must use its scientific knowledge. In the past, geology was not seriously considered, whether from private sources, from the University of the West Indies, or from the Mines and Geology Division, and this has cost the country significantly in terms of money, planning and the development of projects.
It is very clear that this needs to change. I would promote that for every major infrastructure project, there MUST BE an independent geological survey to identify the problems associated with the project and mitigate the impacts. Also, such surveys need to be reviewed by other qualified scientists as part of the process. These are critical issues which the Government of Jamaica needs to look at.
While I wish for a safe construction of the north-south link, I must say that to ignore the geology will lead to disaster! I would not want to see the next small earthquake or the next heavy rains lead to the collapse of our new highway - particularly if I was driving on it at the time.