Belfast Sewers Project Makes First BreakthroughThe GBP100 million Belfast sewers project involves work to upgrade the existing sewer networks and the construction of a large diameter drainage tunnel to increase stormwater capacity. There are approximately 1,800 km of sewers covering a catchment area of 42 square kilometres. The older central area of Belfast is currently served by two large diameter brick sewers which date back to 1888 and a third concrete sewer which was commissioned in the 1970s.The scheme represents a commitment for Northern Ireland (NI) Water to providing Belfast with a sewerage network that has been designed by the highest industry standards to last well into the 21st century. This system will accommodate the expanding city and its drainage needs, significantly reducing the risk of flooding and the pollutant load from the sewerage system on the River Lagan and its tributaries by 85% of present levels. The implementation of the Belfast sewers project will result in the closure of a significant number of the existing combined sewer overflows, which will reduce the pollutant load from the sewerage system on the River Lagan and its tributaries by 85% of present levels.The Belfast sewers project includes the construction of a 9.5 km tunnel, the upgrading of 19 kilometres of existing sewers, the provision of 26 new stormwater storage tanks and more than 500 sewer repairs. Throughout each stage of this programme, a range of advanced technologies have been employed to ensure that the initiative runs safely and efficiently. Structural repairs to 500 sewers commenced in April 2005 and construction work on the tunnel commenced in early 2006. Following completion of the tunnel, further strengthening of the network will involve the upgrading of 19 kilometres of sewer. The programme is due for completion in late 2009.The tunnelling work is the final part of the Belfast sewers project and will provide the required increased capacity in the sewerage system. Capable of holding vast overflows of stormwater (up to 18.2 million litres), the tunnel is up to four metres in diameter and laid at a depth of up to 30 metres. It will follow two routes, from Glenmachan Street near the M1 and from Ormeau Park, converging in the city centre at Cromac Street. It will then proceed to a pumping station at Belfast wastewater treatment works in Duncrue Street, beside the M2.NI Water awarded the stormwater management works contract to Morgan Est and Farrans Construction in September 2006. Under the terms of the deal, the companies will design, build, test and commission the tunnel. The contract also involves the construction of a 16 cu m/sec capacity terminal pumping station housed inside a 40 m-diameter underground structure, a new 6,000 cu m stormwater tank and a marine outfall. NI Water's appointed project managers are consulting engineers Atkins supported by their associates Faithful and Gould. Visit www.niwater.com, www.morganest.com and www.atkins.com The tunnel and pumping station are 40 metres below sea level, the deepest excavation ever in the Belfast area. The route of the tunnels was determined by ground conditions, the availability of sites for the tunnel shafts and other logistical constraints. There are 22 shafts on the tunnel route, varying in depth and diameters from 10 m to 40 m deep and from 2 m to 38 m in diameter. Shaft No. 16, in which the terminal pumping station will be constructed, is 40 m deep and 38 m wide.Nearly 1.5 km long and 40 metres below ground, a key section of Belfast's deepest tunnel was completed on 21st April, 2008 as the tunnel boring machine made its breakthrough at Duncrue Street. The breakthrough is a key milestone in this vital project. This section of tunnel is the longest completed stretch of the Belfast sewers project. The project is one of the biggest civil engineering infrastructure projects in the UK. The Lovat earth pressure balance TBM called 'Lucille' has cut through at a rate of nine metres per hour since June last year. The TBM was specifically selected for this work to ensure that tunnelling on such a large and complex scale could be delivered swiftly, accurately and safely without disturbing surrounding soil. The TBM is 4 m in diameter. The tunnel is covered with precast concrete segments, six per ring, each 1.2 m wide. The precast rings and accessories are supplied from Morgan Est's own manufacturing plant in Ridham, Kent. Visit www.lovat.comThe geology of Belfast is very challenging and consists of weak estuarine clay (sleech) overlying sand, gravels, upper and lower glacial till, sandstone, and intrusions of dolerite dykes. Water can be present at many different levels in the strata at pressures of 4 bar. There have been many consultations with customers and utilities to ensure the minimum of inconvenience, service diversions and traffic management.The remaining sections of tunnels are 2.4 m and 1.8 m diameter. The first section will be constructed using a 2.4 m diameter TBM and the 1.8 m section by pipe jacking. Click uk/46 for more. 20/08.