The Plaxis users at Wroclaw University focus on soil–structure interaction research, which also covers vertical excavations supported by either steel or reinforced–concrete retaining walls. The wall-construction process uses deep vertical trenches that are filled up with a bentonite suspension (Xanthakos, Hanjal). Displacement and stability analyses of the anchored walls belong to standard calculations and they are reported in many places, including the Plaxis Bulletin. In contrast, the stability analysis of the tentative trench itself, supported by the bentonite liquid, is less popular. Therefore, these aspects are the objective of this article.