Abstract:
The influence of the interaction between support fluid and soil, e.g., filter cake formation, on the shear
stress transfer in the soil-concrete interface of diaphragm walls and bored piles is still controversially
discussed. Actual research on the soil-concrete interface using bentonite suspensions indicates that shear
stress transfer is underestimated by existing standards. Investigations on the soil-concrete interface using
polymer solutions are rare. Therefore, complementary field investigations and systematic laboratory
studies were conducted to analyse the soil-concrete interface using both bentonite suspensions and
polymer solutions. Thickness and composition of real-scale filter cakes were investigated on several slurry
wall construction sites, where bentonite suspensions were used. Direct shear tests (60x60 mm²) were
executed for soil-bentonite mixtures with varying amounts of bentonite and different granular fines
representing a realistic bandwidth of in-situ filter cake compositions. Larger direct shear tests (300x300
mm²) with preceding horizontal penetration, subsequent vertical tremie concrete placement, and filter cake
consolidation were performed using both bentonite suspensions and polymer solutions. The results
support the view that shear stress transfer in the soil-concrete interface can be described by a wall friction
angle in a range of 25° to 30° for bentonite suspensions and between 35° and 40° for polymer solutions.