Crack Characteristic and Permeability Change of Compacted Clay Liners with Different Liquid Limits under Dry-Wet Cycles

The crack characteristic and permeability change in six compacted clay liners (CCLs) under dry-wet cycles were studied. Results show that as soil liquid limit (LL) increases, the crack block (CB) number, crack ratio (CR), and crack length (CL) of the CCLs increase under the dry state. The CB sizes of all the six CCLs correspond to normal distribution. A piecewise linear relationship exists between crack parameters and soil LL, and the slope at LL< 50 is larger than the slope at LL >50. The size of the representative elementary volume (REV) of cracked CCL decreases linearly with the increase in soil LL when LL< 50. The linear fitting result is REV = 90.5 – 1.6 LL, whereas REV change is inconspicuous with a mean value of approximately 10 cm when LL >50. The sample size of the CCLs for the permeability test must be larger than REV. Before and after three dry-wet cycles, the permeability ratio (K₃/k₀) initially increases and eventually decreases as soil LL increases, and LL at the peak value ofK₃/k₀is 36.1%. However, linear relationships exist between permeability D-value (K₃ − k₀) and soil LL in a semilog coordinate system when LL< 50%, whereas the change in the permeability D-value is inconspicuous with a mean value of approximately 1.67 × 10⁻⁸ cm/s when LL >50%. The volume and mean width of unclosed cracks are two main factors that determine the increase in permeability after dry-wet cycles. After three dry-wet cycles, these factors decrease as soil LL increases, thereby reducing the permeability D-value.

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