Analytical Stability Checks for Diaphragm Wall Trenches and Boreholes Supported by Polymer Solutions

Abstract

Polymer solutions are increasingly used as supporting fluids for the temporary stabilization of diaphragm wall trenches and boreholes. However, analytical stability checks as they are common practice for geotechnical structures like retaining walls or slopes are rarely performed in these cases. Fundamental considerations for such stability checks will be presented here. For trenches and boreholes supported by bentonite suspensions analytical stability checks have proven themselves over a long time. Based on this concept, characteristics of hydraulic support by polymer solutions will be described in detail. The focus will be on the derivation of the time-dependent penetration length of a polymer solution into the surrounding foundation soil and of the hydraulic gradient over this penetration length which correlates with the efficiency of hydraulic support. Findings of other references dealing with three-dimensional failure body geometry, layered soils etc. may be combined with the approach in this paper as the hydraulic gradient around the trench or borehole is always required for such investigations. Unlike trial trenches or boreholes (typical in construction practice) analytical stability checks allow to evaluate relevant parameters for a specific application and to determine a level of safety for a given system. Such calculations should therefore complement trials on site.