Systematic Laboratory and Field Study on the Shear Resistance of the Soil-Concrete Interface of Diaphragm Walls and Bored Piles-Video

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The presentation examines how filter cakes formed by support fluids affect shear transfer between soil and concrete in diaphragm walls and bored piles. Field samples showed filter cakes typically 0.3–1.5 cm thick, composed mainly of excavated soil grains, with generally low bentonite content (usually no more than 15%, occasionally up to 20%). Small-scale tests suggested bentonite reduces friction angle, but larger, more realistic tests found higher values: about 30° for bentonite-based filter cakes. Polymer solutions produced very thin, sticky layers and no measurable reduction in friction angle; failure occurred in the surrounding dense sand instead. Overall, the results indicate that current design standards may be overly conservative, especially when they do not account for soil grading and the actual composition of the filter cake. Even without considering surface roughness, measured interface strength was higher than assumptions based on testing pure bentonite would suggest.

Keywords

filter cake

shear transfer

diaphragm walls

bored piles

bentonite