Desiccation cracks behaviour of leachate in bentonite - zeolite composite liner

This study tested desiccation crack potential and migration of metals through pure bentonite and bentonite-zeolite composites to determine the best composition of the composite liner. Pure bentonite (B) and bentonite-zeolite composites of 2% (B2), 5% (B5), and 8% (B8) were used as controlled variables. The results showed that the addition of zeolite could not minimize the desiccation behavior in the liner. The value of crack intensity factor (CIF) of each sample B, B2, B5, and B8 was 3.44%, 3.51%, 3.58%, and 3.64%, respectively, indicating a moisture content of 29.95%, 34.54%, 30.88%, and 28.21%, respectively.

A method to predict desiccation crack depth in a compacted clayey soil

Estimation of crack depths due to desiccation of clayey soils is needed to predict changes in mechanical or hydraulic properties in the cracked layer. Desiccation cracks are associated with increasing suction due to moisture loss accompanied by restrained shrinkage, which results in tensile stresses in near surface soil layers. A simple analytical method is presented to predict crack depths in compacted clayey soil due to changes in matric suction with depth. The model equation is based on the Hookean elastic equation relating incremental strain to incremental stress and incorporates two stress state variables including net normal stress and matric suction. Input to the model includes the tensile strength and elastic parameters, and to complete the prediction of crack depth, the suction change profile of interest is needed. The method validity was investigated by comparing predicted crack depths to those observed in soil compacted in a bench scale apparatus for studying desiccation cracking. Tensile strength and elastic properties were determined from tests conducted on soil during desiccation under approximate uniaxial conditions. Predicted crack depths were obtained based on changes in suction interpreted from water content sensors at various depths in the soil bed and compared favorably to observed desiccation crack depths.

Effect of Wetting-Drying Cycles on Desiccation Crack Pattern and Soil Behavior

Cracking, shrinkage, and curling of soils, in general, take place due to drying. These deformations lead to many problems include the development of main paths for water flow and pollutant transport, reduction of soil strength (and impact on other mechanical properties of soils), erosion in slopes, landslides, increase infiltration capacity of the soil and the differential settlement problems. Few studies have investigated the effect of wetting-drying (W-D) cycles on desiccation cracks of soils. The effect of multiple wetting-drying cycles in the cracking behavior was investigated in this research by performing several wetting-drying (W-D) cycles on the initially saturated samples (of pure kaolinite and a mixture of kaolinite with bentonite) under the lab atmosphere (24 ± 1 °C, and 52 ± 2% of RH). The weight of each sample was monitored using a computerized scale (with an accuracy of 0.01 g) connected to the computer. During the test, the water evaporation path with the development of surface cracks and volume shrinkage was monitored by means of digital images. It was observed that the crack patterns changed during the initial cycles, but there was an equilibrium state in the third and fourth W-D cycles. Additionally, it was observed that the main cracks formed in the first dry path were virtually closed after 10 minutes of the second wetting path; in the meantime, small cracks (fissures) were initiated after this wetting process. It was, also, detected that soils with high plasticity required more W-D cycles to reach the equilibrium condition than soils with low plasticity. The results of these experiments are useful for understanding the effect of different seasons on soil behavior.