Introduction

The Limerick Tunnel Project consists of the construction of approximately 10km of dual carriageway with grade separated intersections and includes the Limerick Tunnel under the River Shannon Southwest of the City.
 

	Key Facts
	Start Date	August 2006
	Completion Date	September 2010
	Overall Length	10Km
	Major Interchanges	4
	Number of Structures	17
	Length of Tunnel	675m
	Toll Collection Locations	2
	Volume of Excavation	300,000 m3
	Volume of Fill	3,100,000 m3

Project Details

From the start of the scheme at the N7/N20 Rossbrien Interchange to Bunlicky Lake, a distance of 4.5km, the existing ground levels range from approximately +12.4m to 1.5m above sea level. Over the vast majority of the length the general level is below +2.00m above sea level. There is only one short 300m section where the road alignment is in cut.
The fact that the majority of the existing ground levels are so low (approx +2.0m above sea level) means that most of the mainline has to be built up by over 3m (to a level +5.2m above sea level) to ensure protection from flooding. This will involve the importation of approximately 3.2 million m³ of suitable fill material.
The geological conditions underlying the route corridor present a number of geotechnical issues to be addressed in the design  of the scheme. The major issues are summarised as:

1. Construction of Earthworks Embankments.
2. Structure Foundations.
3. Tunnel Casting Basin (Temporary Works)
4. Immersed Tube Tunnel and Approach Foundations.
5. Source of Fill Material.

The difficult ground conditions present many difficult engineering problems including ground stabilization. In addition to the mainline earthworks, some 500,000m³ will be excavated from the area of the Tunnel casting basin to the north of the River Shannon.
The dredging activity in the River Shannon prior to placing of the immersed tube units will generate an additional 400,000m³ of material which will be suction dredged and placed in lagoons.