Pile foundation of piers for Gaženica ferry terminal in Zadar

The Zakládání staveb Co. together with its Zagreb branch took part in realisation of the currently largest project of its kind not only on the Adriatic Riviera, but across the whole Mediterranean area. The project consists in pile foundation of piers in the largest Croatian ferry port in Zadar.

The new port is expected to relieve traffic in the old town centre where the existing passenger port is located. Long time ago traffic volumes in the old town exceeded its capacities from the spatial, marine and functional point of view. Every year, more than 2,7 mil. passengers and 350 000 vehicles pass through the centre, with an 8% increase of annual traffic.

The new port should also become an important intersection for passenger transport and attract more tourists to visit northern Dalmatia and especially its heart, the city of Zadar. Not only will the passengers and cars stop blocking the peninsula with the historical town centre and gas emissions will be reduced, but the new terminal is also planned to accept large cruisers that have been avoiding Zadar so far.

The new location in the suburban industrial area of Gaženica, having direct connection both to the A1 highway and the close Zemunik airport, will also hold a new touristic and business centre providing significant boost to the local economy. The plans involve building a container terminal potentially contributing not only to the urban development but also to the economy nationwide. A new system of ferry lines and a higher number of connections between the mainland and Zadar islands as well as lines to other ports of both Croatian and Italian coasts will allow faster economic development of these areas. After its completion in 2014 the port capacity will allow six local line ferries of 50-150m, three international line ships of 150-200m and three cruisers of 250-350m at one time. A fleet of local fishing boats will also get its modernised port. The total investment costs amount to 263 mil. EUR.

The port is built on an artificially created embankment carried out in the previous construction phases. The passenger, ferry and fishing ports consist of four piers projecting from the mainland into the sea as well as several onshore wharfs. The individual piers are founded on two to five lines of piles allowing seawater to flow through the port without negatively influencing the coastal ecosystem.

The Zakládání staveb Co. has previously realised numerous constructions on the sea, e.g. the latest work in the Gruž port in Dubrovnik. With respect to all experience gained so far this construction has obviously ranked among the most demanding from both technical and organisational point of view, especially considering the fact that preparation time was very short. Because of the fixed working terms it was necessary to use two drilling rigs with appropriate pontoons and controlling mechanization.

Two complete mechanization sets were finally used – drilling rigs Bauer BG36H with the Kobelco crawler crane. Favourable seabed morphology allowed the use of supported „semi jack-up“ pontoons by the Dutch company MPS with dimensions of 24x17x2 m and 24x17x2,44 m, and a displacement of 416 and 580 tons. The pontoons are equipped with 24 m long supporting legs of 762 mm in diameter with hydraulic drive.

Pile foundation of all piers required a total of 359 pieces of piles 1340mm in diameter with the pile footing extended to 1500mm keyed by 3,0–4,5 m into a healthy bedrock. The piles are equipped with a permanent boring casing of 1340/60 mm in diameter. It is keyed by a minimum of 0,5m under the bedrock surface.

The pile foundations had to follow rather strict tolerance requirements: head height of ±5 cm, layout location up to 10cm in all directions from an ideal centre.

Piles are placed according to different grid spacing (10x10 m, 12x12 m, 8x10 m etc.). So called headset beams were concreted in place on adjusted piles; a system of prefabricated reinforced concrete beams was further laid on these headset beams as they were further monolithised in place again with a concreted reinforced concrete slab.

Heavily weathered rock was identified during the drilling works in bedrock, resulting in prolonging the bore depth based on geological supervision requirements. Changes in the rock hardness were significant as well as unpredictable. The bore depth for more than 30% of all piles had to be shortened due to very hard dolomite. On the other hand, the main breakwater area involved places where the bedrock was not hard at all and the construction supervisors commanded bores to be drilled over the layers of soft flysch down to the depth of -31 m.b.s., thus carrying out the largest piles of all here. The pile length varied between 9,80–31,30 m at the average length of 19,5m. An ultrasound integrity test was carried out on all piles.

 

The Zakládání staveb Co. finalised all works on the 359 pieces of piles for piers at the end of September 2012 and handed the construction over having fulfilled all required tolerances as well as quality requirements verified by integrity tests.

 

Volume of works:

Total number of piles: 359 pieces

Total length of piles: 6975 m

Average pile length: 19,5 m (9,80–31,30 m)

Weight of reinforcement (including permanent boring casing): 2 197 125 kg

Volume of concrete: 9855 m³

 

Construction investor: Lučka uprava Zadar (Directorate of the Zadar port)

General contractor: Strabag, d. o. o., Zagreb, Croatia

Pile foundation provided by: Zakladani staveb, Co., Podružnica Zagreb

 

Ing. Ivan Gajski, Zakladani staveb, Co., Podružnica Zagreb

RNDr. Ivan Beneš, Zakládání staveb, Co.

Photo: from the Zakládání staveb, Co. archives