Laboratory characterization and discrete element modeling of shrinkage and cracking in clay layer

Abstract

The performance of a variety of geostructures, such as compacted clay liners, earth dams, and pavement embankments, is compromised by soil cracking. Experiments are set up to monitor the drying process of a clay layer under controlled temperature and humidity conditions. The gravimetric water content and images are captured automatically. Volumetric shrinkage of the bentonite sample as well as the crack patterns are determined from images. The monitored volumetric strain development is used to implement the discrete element method (DEM) to simulate the drying shrinkage and desiccation cracking. Model parameters are calibrated through unconfined compression tests on clay specimens at different water contents. This simplified calibration procedure allows characterization of the soil behaviors in the mesoscale and bypass the complex physicochemical processes involved. The initiation and propagation of cracks from the DEM model agree well with the phenomena observed in the laboratory experiments. The influence of boundary constraint and sample thickness on the crack patterns is analyzed, which includes the use of hydrophobic coating to diminish the boundary constraint. Major features of desiccation cracking can be replicated with the computational procedures. Boundary constraint, including surface roughness and strength of boundary layer, is found to significantly influence the final crack patterns.

Drought‐Induced Soil Desiccation Cracking Behavior With Consideration of Basal Friction and Layer Thickness

“…It should be noted that there is an increase in N T with decreasing layer thickness, representing that the number of cracks initiating at the top surface reduces. This effect of layer thickness on soil surface cracking observed in this study is consistent with the results obtained by previous researchers (Costa et al, 2013; Gui et al, 2016; Guo et al, 2018; Lakshmikantha et al, 2012; Lakshmikantha et al, 2018; Zeng et al, 2019). N B gradually exceeds N T as the layer thickness increases, indicating that more cracks develop from the bottom surface.…”

“…For thin layer thickness, these cracks may emerge on the soil top surface and affect the evolution of the surface crack network (Table 2). Thus, with increasing basal roughness, the cracking intensity of the soil top surface increases, which matches with the findings summarized in previous research (Guo et al, 2018; Zeng et al, 2019). For increased layer thickness, although more cracks form at the soil bottom surface because of the frictional force, most of them cannot propagate through the entire soil layer and are not visible from the top surface (Table 2).…”

“…Moreover, with increasing layer thickness, the normal pressure acting on the base increases, resulting in larger frictional force and more crack initiations at the bottom ( N B in Table 2). Previous studies found that increasing layer thickness decreases the crack intensity (Costa et al, 2013; Guo et al, 2018; Lakshmikantha et al, 2012; Sánchez et al, 2014; Zeng et al, 2019), which is concluded based on experimental observation of top surface cracks. To accurately assess soil cracking behavior with various layer thicknesses, cracks that initiate at both top and bottom surfaces should be taken into consideration.…”

“…Previous studies about the effect of basal friction and layer thickness on soil desiccation cracking mainly focus on their influences on the evolution of surface cracking intensity. These works advance our knowledge in the mechanisms of cracking on the soil surface (Costa et al, 2013;Guo et al, 2018;Lakshmikantha et al, 2012;Zeng et al, 2019). However, the initiation and propagation of bottom cracks and how they are correlated with the soil cracking density remain poorly understood.…”

“…The frictional force generated on the base between soil interlayers applies a significant constraint to the upper soil shrinkage and causes the soil desiccation cracking. In previous studies, some scholars found that the basal friction could affect the stress distribution inside the soil and aggravate soil cracking (Amarasiri & Kodikara, 2013;Gui et al, 2016;Guo et al, 2018;Lakshmikantha et al, 2018;Pouya et al, 2018;Rodríguez, 2006;Sima et al, 2014;Vo et al, 2017;Zeng et al, 2019). So far, most prior studies focus on the evolutions of desiccation cracks initiated at the soil top surface.…”