Tanteen Traffic Tunnel

General

This preliminary engineering report is for a bypass tunnel as an alternative to a coastal ring road to provide a connection between the southern Tanteen Area and the northern St. John’s River Area of St George’s.

 This bypass tunnel would provide an enormous and sustainable relief to the environmental situation around the Carenage area of St George’s and enhance the potential of this area to become the major tourist attraction.

 If this tunnel can be realized it will add a significant improvement to living and traffic conditions in the centre of town. It would also be possible to use the present Sendall Tunnel as a much needed, safe pedestrian walkway. The access to the hospital could still be realized utilizing the Toute Bagay restaurant approach with the benefit of improved traffic conditions.

 The advantages of the tunnel are to:

  • Get the traffic out of St George’s.
  • Preserve the Carenage waterfront.
  • Provide a quick link between the Port and Lagoon Areas and River Road and onto the West Coast Highway.
  • Take heavy traffic off the present narrow, steep and winding route from Lowther’s Lane and San Souci Road.
  • Reduce travel distance and time.
  • Provide utility service links if required.
  • Involve minimal disruption during construction.
  • Provide a hurricane shelter.

It is envisaged that the tunnel would operate as a toll road.

 

SUMMARY

On the invitation of Zublin Grenada Ltd., the Caribbean Tunneling Consortium, a group of five engineers with extensive tunneling, mining and construction experience, have prepared a Preliminary Design for the proposed road tunnel to by-pass the Carenage waterfront of St George’s and provide a safe convenient route for heavy traffic currently using the narrow, winding over-hill route along Lowther’s Lane and Sans Souci Road.

A conceptual tunnel route, from Tanteen Road in the south to River Road, just east of Gretna Green, was identified in a brief report prepared by one of the CTC group members

in Jan 2004. This route has been reviewed and found to be the most practical and economic option. The alignment has been refined using topographical data available from

the 1977 DOS topographical maps and visual site inspections. The proposed cross section has been designed to conform to current basic UK Highways Authority standards.

The design includes details of the approach roads and roundabouts required to connect the tunnel to the existing Tanteen Road and River Road. Improvements to the roads leading to these points have not been considered and may need to be reviewed by the Government Highways Department. Due the restricted space, and the bend in the St. John’s River, at the north approach road, it will be necessary to include some retraining works to a short section of the river as part of the tunnel project. It has been assumed that

the tunnel will operate as a Toll Tunnel and provision has been made for a toll plaza in the south approach road. The Tunnel Operation / Service Building will also be located at the south end.

The tunnel will be 625 metres (2,050 feet) long with 40 metres of approach road at the north end and 190 metres at the south end having an overall length 860 metres (2,820 feet or 0.53 miles). Use of the tunnel will be restricted to vehicular traffic only. There will be a speed limit of 30mph. The cross section will allow for two lanes of traffic, with clearance for two large container vehicles to pass in opposite directions (overtaking in the

tunnel should not normally be allowed), and a narrow footpath on either side for emergency use. This length of tunnel will only require minimal mechanical ventilation for occasional and emergency use. Back ground lighting will be provided together with signing and signaling. Emergency facilities will include refuge niches, fire fighting equipment, telephones and CCTV connected to the Service Building and a local police or

fire station.

The ground conditions are considered to be good and should not present any major problems for tunneling using conventional tunneling equipment. At this stage it has been

assumed that the conditions will be 50/50 relatively soft volcanic tuff and hard rock. The

site investigation is essential to confirm this. There is a large area at the south end that will be used as the primary works site. Excavation will be carried out northwards from this site. Spoil will be transported to proposed reclamations in the Lagoon area. The tunnel will be lined with sprayed concrete. It will not be 100% watertight and any appreciable leaks will be controlled and channeled into the tunnel drainage system. Simple reinforced concrete arched portal structures will be constructed at either end of the tunnel using shotcreting techniques.

 It is estimated that the overall project period would be in the order of 27 months. This is divided into a pre-construction, investigation and design phase, of about 5 months and a construction period of about 22 months. 

Caribbean Tunnelling Consortium
St George’s Bypass Tunnel, Grenada October 2004

 

PRELIMINARY DESIGN REPORT

The estimated Budget Cost for the tunnel, approaches and M & E works is £10.92M (approx. US$19.7 at current exchange rates). Of this £320,000 (US$576,000) is for pre-construction investigations and designs and £10.6M (US$19.1M) for the construction contract. This will need to be reassessed in light of the site investigation report and the final outline design and specification. This estimate assumes that project will be exempt from all duties and taxes. It is proposed that a Design and Construction type Contract should be used for the construction works.