Challenging bridge removal in Mexico

14 February 2012

Two 400 tonne capacity crawler cranes lifted each 170 tonne section

Two 400 tonne capacity crawler cranes lifted each 170 tonne section

The Malecon and Mirador bridges spanned an entrance from the Pacific Ocean into the Cuyutlan Lagoon and had to be removed, with minimal environmental impact, as part of the Manzanillo Liquid Gas Storage and Regeneration Terminal, which opened in July 2011. The Lagoon was then dredged to a depth of 18 m (59 ft) to allow the passage of deep-water tankers bringing liquefied natural gas to the terminal, where it is regenerated back into gaseous state and burned to generate electricity.

This new terminal will replace the burning of 1-1.5 million tonnes of coal, improving the air quality of the town of Manzanillo and represents a major step for Mexico's sustainable development and the reduction in carbon emissions.

Soluciones Tecnicas first tackled the Malecon Bridge, which was a 153 m (502 ft) long road/rail bridge that was formed by two concrete beams covered by a 0.5 m (0.7 ft) thick concrete slab, built in five 30 m (98 ft) sections.

A temporary rail/road bridge was first built a few metres away from the Malecon Bridge to allow passage of traffic and trains. The tracks, ballast and sleepers were then removed and an embankment with 0.9 m (3 ft) steel pipe to allow water into the Lagoon was constructed alongside by contractor Coconal. From there Soluciones Tecnicas was able to manoeuvre the power pack and water tanks. The embankment was also used by the cranes allotted to the job to carry out lift operations.

Because of the presence of two 400 tonne capacity crawler cranes, only two longitudinal cuts were necessary to produce three bridge sections, each weighing 170 tonnes. These sections were lifted and moved to the side of the bridge, where they were processed by hydraulic hammers to recover the steel reinforcement. The foundations were then dug out, lifted and processed in a similar fashion.

The contractor then moved on to the Mirador Bridge, which was a road bridge made up of five 30 m sections each consisting of six AASHTO type IV beams with a 200 mm (8 in) concrete slab. The substructure consisted of 1,2 m (3.9 ft) piles supported by 9 x 7 x 1.6 m (29 x 22 x 5.2 ft) footings. The foundations consisted of six 0.6 m (2 ft) piles set 12 m
(40 ft) deep.

As with the first bridge. an embankment was constructed by Coconal alongside the structure from where the work was carried out. The bridge remained open during the initial demolition phase, which saw two longitudinal cuts made in the footings and piles. One lane of the bridge was then closed to traffic and the road surface was cut into sections that included two of the beams. These sections were then craned away and processed alongside the bridge, again using hammers. This removal had to be carried out leaving the remainder of the bridge structure - a single lane - intact and undamaged.

The work was further complicated by the fact that both the bridges also supported pipes, with the Mirador Bridge carrying a water pipe that supplied 60% of the water supply to Manzanillo. This required that they remain undamaged until they were shut down, requiring the initial demolition work to be carried out carefully.

In addition to the two 400 tonne cranes, Solutiones Tecnicas had access to one 300 tonne capacity crane and a 120 tonne unit. Two Cat 320 excavators were used in the concrete processing role and the company also had a wheeled loader and a number of trucks available to material transport.

In all, the two bridges yielded 4,053 m3 (143,130 ft3) of demolition debris, with all rebar being recycled. In addition, there was 1,020 m3 (36,000 ft3) of ballast, 250 railway sleepers and 300 m (985 ft) of railway track.

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