Identification of parameters for air permeability of shotcrete tunnel lining using a genetic algorithm

This paper describes an identification process for determination of materia l parameters in a constitutive relationship, describing time dependency of air permeability of shotcrete tunnel lining. A numerical model has been dev eloped to predict the air losses from tunnel face and perimeter walls in co mpressed air tunnelling. Field data from a Tunnel in Germany has been used to verify and calibrate the numerical model. A relationship has been establ ished to describe the variation of the air permeability of shotcrete tunnel lining with time and the technique of parameter identification has been us ed to determine the parameters of this relationship. A genetic algorithm ha s been used in the optimisation procedure. It has been shown that time depe ndency of permeability of shotcrete plays a key role in controlling the air losses in driving tunnels under compressed air with shotcrete as a tempora ry or permanent lining and this time dependency should be taken into accoun t in design. (C) 1999 Elsevier Science Ltd. All rights reserved.