Using advanced hydro-geological and geo-mechanical finite element simulations, it has been possible to model the behavior of a large slope movement, namely the La Frasse landslide in Switzerland. The slide experiences a permanent movement of about 10 to 15 cm/year in its central part and recurrent crises in its more active lower part. The pore water pressure fields corresponding to the 1994 crisis were first calculated with a hydrogeological model and then implemented in a geo-mechanical model. The various site investigations that were carried out consecutively to the previous crises of the slide or in order to calibrate the numerical model are also presented. The model is finally tuned to assess the efficiency of a drainage gallery. The comparison between the drainage gallery as modeled and as constructed is also presented.