In the low-lying parts of The Netherlands challenging ground conditions are often encountered. Thick layers of soft material such as peat and clay are present and pile foundations into deeper sand layers are required when objects are constructed that have to transfer significant loads to the subsurface without inducing settlement (differences). This also counts for pile foundations of wind turbines which, apart from compression and tension loads also are subjected to horizontal loading. The horizontal translational stiffness is an important and depending on the wind turbine manufacturer governing aspect in the required dimensions of the pile foundation (number and type of piles). In order to improve this horizontal translational stiffness, the foundation designer usually opts for the use of battered (raked) piles. The basic principle is that the axial stiffness of the pile will, in this way, contribute to the horizontal stiffness of the foundation as a whole. The verification of wind turbine requirements usually involve the use of generally accepted analytical 2D methods, simplifying the more complex 3D effect, to model the interaction between soil-pile and the group effect for closely spaced piles. Although the analytical model generally provides good results, investments can reduce significantly when only a small amount of piles can be saved upon. Also the effort in the field is reduced when using vertical piles...