To create more complex soil layers, tools of the Structures mode can be used in addition to boreholes. In this video, we create an excavation volume using surfaces.

Note: we are constantly improving and extending the features and commands available in PLAXIS and, therefore, there are typically more than a single possible strategy to create geometry.
Since PLAXIS Connect Edition, the following two new commands are available may ease the creation of the open excavation: blend and loft.
For further information on these commands, please refer to Blend surfaces video and Loft polycurves video.