Case History
Geotechnical Aspects of Radès La Goulette Bridge Project (Tunisia)
By Foued Kanoun: Académie Navale Menzel Bourguiba (kanoun.foued@gnet.tn) And Mounir Bouassida: Ecole Nationale d’Ingénieurs de Tunis (mounir.bouassida@enit.rnu.tn)
This paper briefly presents one of the very recent big Tunisian projects that is Radès La Goulette Bridge. This project is accompanied by the construction of the first cable stayed bridge of length 260 m across Tunis channel which connects Tunis City with its north suburb passing first by La Goulette County. The project groups four main lots involving the construction of bridges, highways and reclamation of lake areas. Focus is given on three items. The first one is the in situ and laboratory investigations led for soil characterization. The second item is the description of types of foundations and soil improvement techniques with specific challenges encountered and modern techniques performed during their execution. The third item is related to economical aspects of the geotechnical components which are commented and main conclusions are drawn.
1. Introduction
The owner of project is the Tunisian Ministry of Equipment, Housing and and land Regional Development. The project is managed by the Directorate-General of Highways Department. The project consists in a main bridge construction across Tunis channel for connection between North and South suburbs passing by La Goulette and Rades counties (Figure 1). The project of Rades La Goulette Bridge also includes structures and infrastructures of access toward Tunis City, and North and South suburbs. The project aims at the reduction of traffic intensity within Tunis City centre, keeping in mind that existing infrastructures by means Tunis La Goulette express route, Rades La Goulette ferry connection, the national road N°9 present serious limitations to keep a fluid circulation between La Goulette and Rades suburbs and Tunis City, [10]. The execution of Rades La Goulette bridge project comprises four separated lots: first is the main bridge, second is the south connection of 2.6 km length, third is the interchange in Tunis North Lake, and four is the north connection of 6.5 km length.
Fig.1. Location of the project “Radès-La Goulette” bridge (Red line)
Lot 1: The main bridge: its structure is characterized by a bridge of total length of 260 m, and a total breadth of 23.5 m. The released navigation gauge of the channel has 20 m in elevation and 70 m in breadth.
The bridge is composed of to ways of circulation each offers two line of 3.5 m, a 2m hard shoulder and a central full ground of 2.5m which shelters the two towers and cables. It is a cable stayed bridge an “extradossed” stay Cable Bridge composed by caissons elements made by pre stressed concrete in three continuous spans of 70m, 120m and 70m respective lengths. The pylons of 20 m in height are founded on 2m diameter deep piled foundation of 75 m length.
Lot 2: The South connection: it comprises four sub lots namely: Planning of rotary junction, the construction of two kilometres express route, two ways each with two lanes, the construction of a pre stressed concrete bridge of 180 m length on Rades channel and the construction of a pre stressed concrete bridge of approach (from south side) having 400m length.
Lot 3: The North connection: It comprises the reclamation of about 20 hectares in North Tunis Lake, the deviation of Tunis La Goulette express route along 2.4 kilometres, the construction of a pre stressed caisson bridge of approach (north side) of 720 m length and the construction of the interchange between the main bridge and the express route Tunis La Goulette. Then, these works needed the draining of North Lake for which environmental challenges should be faced, essentially the contamination of the lake’s water by finer of reclaimed zone and the sedimentation of filled material which affects the quality of water. During the reclamation it was observed the formation and migration of mud waves followed by their propagation in the lake, [3]. This problem has been tackled by the installation of geotextile barrier aided by the counter weight flotation technique. Also a reduced intensity of traffic plan was adopted.
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