Many of the soils in Ireland are glacial. A common one, which underlies much of Dublin, is lodgement till. This soil, referred to as Dublin Boulder Clay, has a high undrained shear strength, a high stiffness and a stiff low permeability. It also has some sand lenses. Dublin Boulder Clay was encountered during excavations for the Dublin Port Tunnel. A full scale trial excavation and finite element analyses were carried out to determine the stability of the excavations, their stand-up time and the surface settlements behind the excavations. The field tests showed that the failure mechanism consisted of a narrow failure wedge, the length of the stand-up time was shorter than expected and depended on maintaining negative pore water pressures in the slope, and there was very little settlement behind the excavations. The finite element analyses confirmed the results of the field tests. As a result of the information obtained from the field tests and the finite element analyses, it was possible to use an observational approach, observing the presence of permeable layers and monitoring the ground movements, so as to reduce the required number of rows of ground anchors and achieve more economical design.