3D-effects in total stability evaluations

Abstract: This master’s dissertation has been performed in cooperation with Tyréns and the Dept. of Construction Sciences, LTH. We have investigated if it is possible to increase the total stability for excavations with retaining structures and if each side of an excavation could be treated as a separate 2D-case with additional theories to approximate its 3D-effects. End-surface theories from the Commission on slope stability (CSS) report 3:95 could possibly be used to consider 3D-effects although they are originally created for slopes without structural support. Neither is there any information regarding the interaction between these separated 2D-systems. The intention of this master’s dissertation is to validate that these theories mentioned can be used and that it is reasonable doing so. It is done by evaluating three different kinds of systems namely > Generalised sloped excavations where corners and thus interactions between sides are introduced into the model but without structure to examine end-surface- and additional 3D-effects where the applied theories are valid. > Generalised excavation with retaining structure to determine corner-, end-surface- and structural effects. > The theories evaluated are then applied to a real life case with material- and structural parameters evaluated from the Västlänken project. Here the possibility of excavating a 70x70x15 m (length, width, depth) is investigated. For all of the modelling steps; analytical and numerical calculations have been performed, where Slope/W has been used to aid the analytical calculations and Plaxis- 2D and 3D have been used for 2D and 3D modelling. Evident in the results assembled in this work is that 2D-analytical calculations underestimates the total stability (FS) for an excavation when compared to numerical calculations. Applying the end surface theory from CSS report 3:95 generates results similar to the ones generated by 3D modelling, but on the safe side. This final comparison was made without considering the stabilising effect that can be accounted for due to the retaining structural connections in the corners.