Extensive instrumentation has been installed at Bell Common Tunnel to monitor the performance of a propped embedded retaining wall and the behaviour of the stiff clay in which it has been constructed. Earth and porewater pressures, ground and wall movements, and roof loading have been monitored during the construction period. The deformations and stresses measured at each stage of construction are presented and the performance of the wall is discussed. Un systeme important d'instrumentations a ete installe au tunnel de Bell Common pour controler le comportement d'un mur de soutenement encastre et celui de l'argile raide dans laquelle il a ete construit. Pendant la periode de construction on a controle les pressions du sol et de l'eau interstitielle, les mouvements du sol et du mur et le chargement du mur. L'article presente les deformations et les contraintes mesurees a chaque etape de la construction et analyse le comportement du mur.