Rehabilitation & Tunnel Widening

1km rail tunnel named after the nearby village of White Ball built by Brunel (opened 1844 on the Great Western Main Line). Victorian brick-arch lining, which has deteriorated over the years including weathering and chemical reaction from the sulphurous steam trains. A refurbishment scheme was required to make it fit for purpose which was planned through various phases. The early phases of the project involved installation of the RAM Arch System and wire mesh to prevent loose bricks from falling on to the tracks. In latter phases of the refurb - the subject of the CAT3 check - sprayed concrete applied to cover the RAM Arch system coupled with rock bolts with butterfly plates were used to hold the concrete lining.

The Puerto Suello Tunnel is a 400 m long single-track rail tunnel in San Rafael, California and was constructed in 1879. The 4.9 m wide and 6.8 m high tunnel was partially destroyed by a fire in 1961, was rebuilt for freight service in 1967 and closed in the mid-1980s. The tunnel was acquired by SMART in 2003, who retrofitted and then reopened it for commuter rail service in 2017.

The ground overburden above the tunnel reaches a maximum of 45 m and the tunnel was constructed using cut-and-cover and mined construction methodologies.

A major collapse during construction of the Thierre Tunnel in 2009 led government officials to call on NATM experts to come up with an innovative fix for the 5.6km, two-lane twin tunnel, which is part of the new Reshen Kalimash Motorway. Recommended stabilisation measures by the Dr. Sauer/iC JV such as backfilling, ribs and fibre shotcrete were implemented and halted creep movements. An alternative design was developed and replaced the original horseshoe profile by an ovoid shape. Pre-treatment, excavation works and support installation were accompanied by extensive monitoring.

The brick lined tunnel constructed by Mark Brunel between 1825 and 1841 was the first to be bored underwater using a shield and comprised a twin arch tunnel, 375m in length, with cross passages every 5.5m. The new lining has been designed to minimise the removal of existing structural brickwork and has a similar shape with cross passages to match the original tunnel. The reinforced concrete/shotcrete lining includes steel fibres to increase the strength and durability of the lining. A waterproof membrane has been installed around both tunnels and the cross passages between the structural brickwork and the new concrete lining.

The original tunnel was built in 1865 as a 12 ft wide (4 m) single-track rail tunnel. It was widened in 1873 to 25 ft (8 m) double-track with a 26 in-thick (66 cm), brick-lined horseshoe design. After several structural repairs, mainly for spalling bricks, it was finally closed in the early 1960s. More than 30 years later the Port Authority of Allegheny County saw benefits in adapting the former railroad alignment and right of way to its new bus way connection between downtown Pittsburgh and the new Pittsburgh International Airport. A NATM value engineered proposal in the tunnel refurbishment contract provided US $ 2 mil cost savings compared to the original bid. The redesign was based on elevating the tunnel alignment so that the future tunnel crown could be excavated in better ground conditions and on changing the proposed horseshoe to a "rounded" cross section. This combined with the utilization of the NATM allowed a 40 % reduction in shotcrete thickness, a 22 % reduction in concrete lining thickness and the elimination of the reinforcement in the final lining. Furthermore, the NATM proposal eliminated pre-excavation grouting (200,000 bags of cement) and over 10,000 rock bolts while reducing lining thickness. During tunneling up to three headings were excavated simultaneously, one from each portal and one started within the tunnel, averaging a total excavation progress of 15.4 ft (4.7 m) /24h day. Following waterproofing, the concrete lining was completed 16 month after beginning of the reconstruction.

The Bergen Tunnel on the New Jersey Transit network is a double track, horseshoe shaped rail tunnel, built in the 1870s, passing through fractured diabase. Over time, water ingress has caused operational problems. In 2000 the owner decided to undertake major structural rehabilitation. The brick lining was stripped out and the original profile was enlarged to take a new reinforced in-situ concrete lining and drainage system. Old ventilation shafts were backfilled. Two large openings were retained for tunnel ventilation, emergency access and to house new power and electrical substations.