A New Approach for Evaluating the Ductility, Volumetric Stiffness and Permeability of Cut-Off Wall Backfill Materials-Article

Article

Pdf Summary

The study presents a laboratory method for evaluating the ductility, volumetric stiffness, permeability, and healing behaviour of soil–cement and plastic-concrete materials used in dam cut-off walls. These materials lie between rigid concrete, which can crack and create high-permeability pathways, and more ductile soil–bentonite, which has less structural integrity.<br /><br />The procedure combines consolidated-drained triaxial testing with permeability measurements. Saturated specimens made from cement, clay, sand, and water are consolidated, then sheared in small strain increments. Permeability is measured between increments, allowing changes in hydraulic conductivity to be related directly to deformation. The method also provides conventional stress–strain and volumetric-strain data, as well as bulk-modulus estimates.<br /><br />Tests on mixtures with varying cement and clay contents showed that specimens with more cement generally had greater stiffness and more brittle behaviour. More brittle specimens tended to show larger permeability changes during shearing, while more ductile specimens showed smaller changes. All tested mixtures displayed some decrease in permeability over time between shear increments, suggesting a degree of healing. This may result from fine particles clogging cracks or from continued cement hydration, but the cause remains uncertain.<br /><br />The results indicate that tracking permeability during triaxial shearing is an effective additional measure of ductility and can accurately assess very low-permeability materials. The method could help characterize and compare cut-off wall backfill mixes, reducing reliance on conventional stress–strain testing alone. Further research is needed, particularly to understand healing and the unexpected stiffness and ductility of the kaolinite-containing mixture.

Keywords

ductility

volumetric stiffness

permeability

healing behavior

soil-cement

plastic concrete

dam cut-off walls

triaxial testing

hydraulic conductivity

brittleness