Sea Works: Case History

Algeria, Jen Jen – Interventions on the docks of the metallurgical harbour E-mail


Interventions regarding the docks of the new metallurgical harbour of Jen-Jen.

In the years 1986-1990 a number of circular infrastructural cassions for the new metallurgical harbour of jen-jen were built on behalf of Ministère des Travaux Publics—Wilaia . The development of the docks reached a length of 2.300 m and a total number of 126 cassions with a changeable height between 12 and 19,50 m. The cassions with two different diameters, 22 and 15 m along the outside main wall that is 40 cm thick have at the bottom of the wall an expansion base to rest the cassion. The prefabrication installation was made by means of two wharfs 30 metres far from the dock of the service harbour on the depth –5,00 and underwater paddocks made with levelled riprap at increasing different depths. On the wharfs the cassions were prefabricated up to a height of 6,50 m; the following prefabrication steps (n° 1 for the cassions up to 14 m high and n° 2 for taller cassions) were performed on the above mentioned underwater paddocks at a depth of –5,60 during the superelevation operations and to 12,20 for the taller ones. The handling of the monoliths during the different steps, being without a slab, was performed by means of a special pontoon with a catamaran hull and lifting system with computerized controlled winches built by Grandi Lavori Fincosit, with a lifting power up to 1.200 tons. The cassions were plunged at different depths between –11,30 and –19,00 on a levelled riprap bed. After arranging the cassions the pre-compression of the vertical diwidag rods was performed, they were entered into the wall and used as a bearing during the handling of the shaft. The filling of monoliths with selected inert materials and the upper sealing by means of a concrete slab completed the work.