The stability of tunnels in grouted fault zones

Tunnel construction in water-bearing fault zones consisting of cohesionless soil has always been prone to difficulties due the risk of sudden and large water and mud inflows, as well as due to the high ground and water pressures prevailing. Deep tunnelling under the protection of injection bodies can be extremely costly. In any specific situation the relevant parameters, which are pre-determined, are the thickness of the fault zone, the mechanical properties of the untreated ground, the in situ state of stress and the water pressure in the fault zone. Parameters which can be altered by the engineer are the tunnel support, the size (i. e. the diameter) and the material properties of the injection body. It is a substantial engineering task to select the economically optimum set of parameters. By means of the computational method developed in this report the tunnel design engineer is assisted in making such selection against the background of clearly defined criteria.