Il progetto Tehran Shomal Freeway in Iran è una nuova autostrada per collegare la capitale Teheran con la città di Chalus nel Mar Caspio nel nord. La lunghezza totale è di 121 km.
Il tracciato autostradale ha più di 30 tunnel gemelli doppie corsie. Il Tunnel Alborz sarà il più lungo di questi con una lunghezza di 6400 m
Di seguito la descrizione del progetto preliminare:
1-INTRODUCTION
The Tehran Shomal Freeway project in Iran is a new freeway to connect the capital Tehran with the city of Chalus at the Caspian Sea in the North. The total length is 121 km.
The freeway alignment has more than 30 twin tunnels for double lanes. The Alborz Tunnel will be the longest of these with a length of 6400 m at an altitude of 2400 m. The maximum overburden is in the range of 850 m.
The service tunnel is located between the main tunnel tubes and it has been used for site investigation, drainage and as access for the main tunnel construction.
LEGECO, in this first phase, developed a preliminary construction project, through acquiring and structuring the project data, project study and context analysis, disarticulation of the intervention in working elements and construction phases. It has been also established an initial work program, studying various options for building, production cycles, their relationships and interdependencies, programming techniques of the linear and reticular work. Therefore LEGECO studied a detailed list of necessary resources: construction equipment and machines, general services and construction facilities.
2-DESIGN REVIEW
A review of design drawings and schemes has been done and it leaded to definition of different cross sections to be used in Alborz Main Tunnel Excavation to face the following issues:
- squeezing behaviour of rock masses under high overburden;
- multiple fault zone associated with severe instability of the crown;
- karstic zone in evaporitic rocks;
- high water flow associated with running soil;
- high concentration of gas.
Trough a comprehensive analysis of all geomechanical and monitoring data collected during and after excavation of the service tunnel, we have defined a reliable geomechanical model. Following this activity, through numerical modeling and state of the art practice application, we have defined and dimensioned the support and lining section types to be applied to in order to provide face and profile stabilization at short and long term.
The cross sections chosen must be applied along 6400 m of Main Tunnels length in the following way:
- section Ab1 (to be applied for a total length of about 401 m);
- section Ab2 (to be applied for a total length of about 4667 m);
- section Ab3 (to be applied for a total length of about 495 m) requires
- preliminary stabilization works on the arch of tunnel (micropiles) before excavation can commence;
- section Ab4 (to be applied for a total length of about 837 m) requires preliminary stabilization works both on the arch and the face of excavation (fiberglass bolting) before excavation itself can commence.
All types of sections involve the use of rock bolts and steel archees with different steps, covered by a welded wire mesh and spritz-beton.
