Gulf Construction Online - Paschal sets pace for expressway

Scaffolding & Formwork

The channel duct ... four bottom plates form the base for the box culverts.

Paschal sets pace for expressway

Paschal’s systems are being put to the test in the sultanate, where they are being utilised in the construction of a 300-km-long expressway that runs across wadis.

01 December 2011

PASCHAL teams from Europe, the Middle East and India have put their heads together in facilitating the construction of a 300-km multi-lane expressway that will connect Oman’s capital Muscat with Sohar, two of the Sultanate’s largest cities located in the northeast on the Gulf of Oman.

The project is challenging in many respects, chief among them being the wadis, across which the expressway will be built, according to Paschal-Werk G Maier spokesman Frank Gerigk.

'The construction of the expressway has begun at Sohar and runs to the southeast. There are many places where the future expressway cuts across the alluvial deltas of wadis that run down from the mountain ranges; they are several kilometres across at their widest point,' he explains.

These wadis pose a direct challenge to the construction companies, he says. 'Soil conditions are irregular, temporal and local variations of the rivers and their force are unknown and can only be determined statistically. A typical feature of these rivers is their varying bed load, which includes all types of sediments, ranging from giant boulders to fine sand plus any other objects that may be found in a wadi. This depends on the water’s energy: it is at a maximum close to the mountains and at a minimum in the alluvial deltas. In the deltas, up to a dozen wadis may be found running side by side.'

Wadis are dry river beds with steep banks that may lie dry for years or even decades but are prone to flash floods during heavy rains.

The entire carriageway, elevated several metres, will cross the wadis. The substructure consists of parallel tubular culverts made of on-site concrete, allowing the passage of water.

Numerous base plates lying side by side, each 36 m long and made of on-site concrete, form the foundation of the structure. Slightly elevated 20-cm-wide wall foundations placed at 3-m intervals are being built alongside the wadis and at right angles to the direction of the traffic. Slight gradients lead up on either side of these foundations, thus forming shallow U-profiles. In this way, the main flow is maintained in the profile’s centre and unwanted lateral sedimentation by detritus is avoided.

A typical construction site extends over 2 to 3 km and employs up to 1,400 workers who are housed in camps. There are two work shifts a day of 12 hours each, with work being carried out round the clock. Due to high daytime temperatures, concrete work is done mainly during the night hours.

'Work crews on several construction sites are working simultaneously now, erecting so-called box culverts on the base plates. These are inconspicuous concrete boxes used for the construction of traffic routes worldwide. If several of these boxes are lined up in series, they form a canal with a top-cover. If they are placed parallel and topped with a tarmac, they form a trafficable dam with tubes that are open-ended on either side. These boxes can be manufactured on site or sourced as pre-fabricated modules. NCC of Hyderabad, India, the contractor on the project, decided to manufacture the concrete modules on site,' Gerigk says.

Formwork carriage ... light movable scaffolding and orange-coloured modular formwork panels.

Formwork

With a limited quantity of formwork, it is more effective to cast the boxes side by side rather than in an in-line fashion, creating only two external walls but several internal walls. Formwork drawings and procedures have been developed by Paschal Werk G Maier of Steinach, Germany. Paschal Technology India, based in Hyderabad, supplied a formwork carriage, which offers an 80-sq-m formwork surface with a length of 12.50 m, with a forming cycle of 12 m (length) by 2 m (height, minus gradients) by 3 m (width). Four of these carriages were placed side by side.

The formwork system deployed for the walls and the slabs (both 20 cm thick) was the Modular/GE Universal formwork.

Four bottom plates, each 36 m long, form the base for the box culverts. The expressway will traverse the culverts at a right angle. A typical feature of the box culverts is the slanted slabs, which mirror the bottom slants. The dismantling panels, which are integrated here, are indispensable for formwork panels that are cast-in-place in confined building spaces, allowing them to be removed. 'These dismantling panels, with their well-defined slanted slabs and bottoms, are special components which were custom-made by Paschal Concrete Forms Company in Manama, Bahrain,' Gerigk says.

For each forming cycle, the formwork panels were folded and all four carriages were simply shifted in the desired direction and aligned again in parallel fashion, he adds.

The three-cycle sections, 36 m in length, forming the substructure for the expressway, were thus built safely, conveniently and quickly.

'It will take a number of years to complete the expressway and this will offer ample opportunities to deploy the carriage,' says Gerigk, adding that he is pleased with the 'successful co-operation' between the individual Paschal locations on the project.

After concrete curing ... the carriage is moved away to allow the formwork to be cleaned.

Modular

Modular/GE Universal formwork is one of the most widespread and successful formwork systems worldwide, according to Gerigk.

'Due to an extensive range of panel heights and widths available, this range is the most versatile formwork system,' he says. 'For example, for a panel height of 125 cm, the following widths are available: 100, 75, 60, 50, 45, 43, 40, 37, 35, 33, 30, 25, 24, 20, 15, 12, and 10 cm while the filler pieces are available in widths of 6, 5, 4, 3, 2, and 1 cm. Formwork may be fitted within 1 cm to the required architecture. This eliminates the need for complex final adjustments which cost time, money and labour. Panels are compatible with each other in horizontal and vertical positions. An extensive range of accessories such as corners and hinges, supplements the portfolio. The panels are capable of withstanding the pressure from fresh concrete (35 kN/sq m), which is sufficient for most applications on medium-rise structures. The GE large-size panels accept pressures of up to 60 kN/sq m.'

Paschal-Plan light, the relevant formwork software for such applications, runs on any type of PC and is available in a number of languages. Supplied by Planitec of Steinach, Germany, it is one of the most reliable software programs on the market, says Gerigk.

In central Europe, Modular is mainly deployed for foundation work, craneless sites, shafts, stair wells, polygonal components, columns, beams and prefabricated concrete parts. It is used anywhere where standard formwork systems are too unwieldy, for example, for finely stepped or angular building components.

In most other parts of the world, it is being deployed as easy-to-use standard wall shuttering for plants, industrial structures, residential buildings and even high-rise structures.

Modular has 15-mm-thick plywood, which consists of 11 layers, suitable for nailing, from sustainable Finnish birch cultivations. The frame consists of a sturdy high-quality steel-grid, which is easy to clean and repair.

'It is by no means unusual to find that Modular is still in use after 25 years and thousands of field applications with only occasional repairs. Investment in a branded product has been worthwhile for these contractors,' Gerigk concludes.

With its base in Bahrain and branches in Dubai and Abu Dhabi, Paschal Concrete Forms continues to support and serve the construction companies in the GCC countries.

Paschal’s Bahrain office was established in 1997 to meet with the growing demand and to provide its clients with professional and efficient service. The company last year opened its 3,200-sq-m purpose-built covered facility over a 5,600-sq-m plot of land at Salman Industrial City (BIIP) in Hidd, Bahrain.