Dublin Port Tunnel Xiaowei Jin, Xinni Wang, Mingqiu Mao

Introduction in Dublin, Ireland connects to the M1, part of the M50 relieves surface road congestion in Dublin city center the twin tunnels June 2001–2006, €752 million

Geological condition Bedrock in the Dublin area is a thin to medium interbedded homogenous grey argillaceous limestone and calcareous shale. Over much of the city, it is overlain by glacial deposits, known as Dublin boulder clay.

Geological condition Boulder Clay has a widespread distribution across central Dublin. It has traditionally been divided into two strata, an upper Brown Boulder Clay and a lower Black Boulder Clay for engineering purposes, the upper unit being a weathered facies of the lower. These sediments can vary greatly in thickness, from a few metres to upwards of 20m. The till contains water-bearing lenses of sand and gravel.

Problems The changing geology, boulder clay, limestone, clay, sands and gravels, can cause differential settlements The excavation influences onto the adjacent roads the diaphragm walls need to be supported as the depth of the excavation A comprehensive drainage system is needed

Overview The tunnel is built in five section: Two bored section Two “cut and cover” section A specialised pipe jacked section

Solution1 TBM Two TBMs are adopted TBM1 Progress per day10 to 12m average length2.6km geologyCarboniferous limestone Volume spoil excavated0.5 million cubic meters

Solution1 TBM TBM2 Progress per day2 to 3m average length800m geologyDublin boulder clay Volume spoil excavated71,000 cubic meters

Solution2 Cut and Cover The “cut and cover” sections: -The southern section is 500m long at Fairview -The northern section is 1500m from Whitehall Church to Shantalla

Solution2 Cut and Cover To secure the sides of the excavation two separate measures are employed -the construction diaphragm -the use of a combination of soil nailing and shotcreting

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