**1. Introduction**

The instability problem of the tunnel face has occurred during the construction of several tunnels in the world (STEFANO Tunnel 1984, TASSO Tunnel 1988, VASTO Tunnel 1991, recognition gallery of St Martin-de-La Porte 2001). This problem has been reported many times in Algeria (Algiers Metro Tunnel 2000, Djebel El Kantour Tunnel in Skikda 2010 and Djebel El Ouhach Tunnel in Constantine 2011). Several studies have been conducted in this regard: [1–3], and various stabilization techniques of tunnels face were used:


The tunnel face is located at kilometer point (KP 230 + 586.5), which is located inside the tunnel of «Djebel El Kantour". The main problem in this tunnel is the instability of the face which was reported since the beginning of the project, especially in northern the tunnel because of two key factors: the quality of the ground (Marly sandstone clay) and low coverage. In this research finite element simulation were conducted using the software ANSYSE in order take into account the staged

#### *Slope Engineering*

construction technique for better estimation the vertical and longitudinal deformations, as well as the failure mechanisms to the front of the tunnel face.

To solve this problem, many techniques have been used to stabilize the face, but the technique did not yield the expected results. Therefore, the prime contractor applied a new technique called the Fiberglass Technique (FIT). However, it proved inadequate in this case, due to its high cost and the limited effectiveness. This is mainly due to the poor mastery of the excavation method, which in turn, was not suitable to this type of rocks. In this study, we try to demonstrate, via a numerical modeling tool, the relationship between the attack section and the deformation field on the Tunnel face.
