Impact of undrained deformation on the hydraulic conductivity of cement-bentonite barrier material

Alzayani, Nuha Jamal (2019). Impact of undrained deformation on the hydraulic conductivity of cement-bentonite barrier material. University of Birmingham. Ph.D.

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Abstract

Cement-bentonite (CB) slurry is used to construct non-structural underground barriers of low hydraulic conductivity (i.e. 10-9 or less) for retarding fluids migration in groundwater and waste containment systems. The hardened CB barrier material (after 7 days of curing) has brittle nature with strain-softening behaviour post-peak strength up on undrained loading. Therefore, cracking at small strains (ranging from 0.6% to 1.4%) might have a negative impact on the hydraulic conductivity of the CB barrier.
This research aimed to investigate the unknown relationship between the undrained deformation response and hydraulic conductivity of CB in the triaxial cell. This was investigated using a CB mixture comprising of 80% GGBS as a cement-replacement material under triaxial unconsolidated-undrained loading expected to occur during short-term curing ages (i.e. for specimens cured up to 90 days). A bespoke testing methodology that combines undrained shearing with hydraulic conductivity measurement was developed.
The increase of CB hydraulic conductivity from the order of 10-9m/s up to 10-6 m/s was confirmed to happen after exceeding the undrained peak strength. Therefore, undrained deformation need to be prevented throughout the whole service life of a CB barrier (regardless of the curing age and effective stress achieved) to avoid compromising its low hydraulic conductivity requirement.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):