Hydraulics provide a lift to Dutch viaduct project

Edited by the Engineeringtalk editorial team Dec 16, 2002

Hydraulics are playing an important part in the construction of a massive viaduct as part of a major new Dutch rail line.

The Dutch HSL South high speed line currently under construction is one of the largest infrastructure projects of recent years.

Between Schiphol and the Belgian border the HSL Southern comprises 80km of new rail track and no fewer than 170 bridges, viaducts and tunnels.

Part of the HSL South is a through rail viaduct over the A12 at Bleiswijk.

In the meantime many rows of columns (pillars) dominate the skyline.

The "plant" too, where the concrete upper surfaces are laid on which the trains will travel, is in full swing.

The heavy upper surface sections for this high viaduct in the HSL are being cast in situ using a special shuttering system with which 35m of concrete upper surface can be laid at once.

The shuttering system consists of a movable bearing steel structure of horizontal beams, uprights and four separate shuttering elements.

Unusually, the shuttering structure is relocated and raised to the proper elevation in its entirety for each new upper section to be cast using hydraulics.

"In some senses this application is comparable to the hydraulic roller lift that we developed", says Hans Knol of Enerpac.

"With the roller lift it is relatively easy to adjust heavy steel tunnel shuttering systems on both the vertical and the horizontal plane and that is more or less what we are doing here".

The work on the HSL is naturally somewhat more complex.

The upper surface sections are 35m long and 10m wide and weigh some 800t.

The shuttering, and everything connected with it, is of course on the same scale.

Every upper surface section of the HSL is supported at each end by three pillars.

The shuttering structure is supported by the same number of steel uprights that are secured to these pillars during casting.

Under each upright a double-operation hydraulic high tonnage cylinder has been installed with a lifting capacity of 100t and a stroke of 50mm.

These cylinders, powered by 20 Titan pumps from Enerpac with a higher yield, are used to adjust the 160t "plant" to height prior to casting and to allow it to decline slightly after casting to release the structure from the cast and hardened upper surface section.

After the structure has been raised hydraulically to the appropriate height, the uprights are secured on mechanical wedges.

This relieves the cylinders during casting.

The height difference in this case is only about 5cm - just enough to avoid contact with the concrete surface during relocation to the next casting location.

When the concrete upper surface section is completely hard, which takes a week, the shuttering is relocated to the next set of pillars.

The horizontal relocation of the shuttering panels is conducted by steel cables and "long-stroke cylinders".

These cylinders are powered by a pump especially developed for this purpose with a yield of 20litre/min at a maximum operating pressure of 700bar.

The plates are first pulled some tens of centimetres apart in crosswise direction using 20 "hollow plunger cylinders" each with a capacity of 10t and a maximum stroke length of 200mm and developed especially for this purpose.

Each of the four shuttering panels is relocated separately.

After the shuttering structure has been relocated in its entirety to the following section, the shuttering panels are united precisely to form a single unit.

"It is a kind of step-by-step plan", explains Knol.

"One panel is oriented relative to the upright and the others drawn to it one by one.

That's how you obtain one large shuttering system".

During relocation of the various steel elements of the shuttering structures, no bearings or anything similar are used, reliance being placed rather on nothing more than the slide bearing principle.

The shuttering panels are fitted with steel slide plates and the steel beams over which they pass clad with a bronze strip.

The entire structure, including the shuttering panels, is even positioned by eye.

"It's really a pretty simple story", as Knol points out, "but nevertheless efficient".