Formation Of Desiccation Cracks Research Articles

Landfill cap models under simulated climate change precipitation: impacts of cracks and root growth

Desiccation crack formation is a key process that needs to be understood in assessment of landfill cap performance under anticipated future climate change scenarios. The objectives of this study were to examine: (a) desiccation cracks and impacts that roots may have on their formation and resealing, and (b) their impacts on hydraulic conductivity under anticipated climate change precipitation scenarios. Visual observations, image analysis of thin sections and hydraulic conductivity tests were carried out on cores collected from two large-scale laboratory trial landfill cap models (∼80 × 80 × 90 cm) during a year of four simulated seasonal precipitation events. Extensive root growth in the topsoil increased percolation of water into the subsurface, and after droughts, roots grew deep into low-permeability layers through major cracks which impeded their resealing. At the end of 1 year, larger cracks had lost resealing ability and one single, large, vertical crack made the climate change precipitation model cap inefficient. Even though the normal precipitation model had developed desiccation cracks, its integrity was preserved better than the climate change precipitation model.

Analysis of polygonal cracking patterns in chloride‐bearing terrains on Mars: Indicators of ancient playa settings

AbstractThe ancient southern highlands on Mars (~3.5 Gyr old) contain > 600 regions that display spectral evidence in the infrared for the presence of chloride‐bearing materials. Many of these locations were previously reported to display polygonal cracking patterns. We studied more than 80 of the chloride‐bearing terrains using high‐resolution (0.25–0.5 m/pixel) images, as well as near‐infrared spectral data, to characterize the surface textures and the associated cracking patterns and mineralogies. Our study indicates that ~75% of the studied locations display polygonal cracks that resemble desiccation cracks, while some resemble salt expansion/thrust polygons. Furthermore, we detect, spectrally, the presence of smectites in association with ~30% of the studied fractured terrains. We note that smectites are a special class of swelling clay minerals that can induce formation of large desiccation cracks. As such, we suggest that the cracking patterns are indicative of the presence of smectite phyllosilicates even in the absence of spectral confirmation. Our results suggest that many chloride‐bearing terrains have a lacustrine origin and a geologic setting similar to playas on Earth. Such locations would have contained ephemeral lakes that may have undergone repeated cycles of desiccation and recharging by a near‐surface fluctuating water table in order to account for the salt‐phyllosilicates associations. These results have notable implications for the ancient hydrology of Mars. We propose that the morphologies and sizes of the polygonal cracks can be used as paleoenvironmental, as well as lithological, indicators that could be helpful in planning future missions.

Position control of desiccation cracks by memory effect and Faraday waves

Pattern formation of desiccation cracks on a layer of a calcium carbonate paste is studied experimentally. This paste is known to exhibit a memory effect, which means that a short-time application of horizontal vibration to the fresh paste predetermines the direction of the cracks that are formed after the paste is dried. While the position of the cracks (as opposed to their direction) is still stochastic in the case of horizontal vibration, the present work reports that their positioning is also controllable, at least to some extent, by applying vertical vibration to the paste and imprinting the pattern of Faraday waves, thus breaking the translational symmetry of the system. The experiments show that the cracks tend to appear in the node zones of the Faraday waves: in the case of stripe-patterned Faraday waves, the cracks are formed twice more frequently in the node zones than in the anti-node zones, presumably due to the localized horizontal motion. As a result of this preference of the cracks to the node zones, the memory of the square lattice pattern of Faraday waves makes the cracks run in the oblique direction differing by 45 degrees from the intuitive lattice direction of the Faraday waves.

Electric-field-induced crack patterns: Experiments and simulation

We report a study of crack patterns formed in laponite gel drying in an electric field. The sample dries in a circular petri dish and the field is radial, acting inward or outward. A system of radial cracks forms in the setup with the center terminal positive, while predominantly cross-radial cracks form when the center is at a negative potential. The laponite accumulates near the negative terminal making the layer thicker at this end. A spring model on a square lattice is used to simulate the desiccation crack formation, with an additional radial force acting due to the electric field. With the radial force acting outward, radial cracks form and for the reversed field cross-radial cracks form. This conforms to the observation that laponite platelets become effectively positive due to overcharging and are attracted towards the negative terminal.

Clay interaction with liquid and supercritical CO2: The relevance of electrical and capillary forces

Caprocks with significant clay content are candidate seal layers for CO2 geological storage. Changes in electrical and capillary forces are expected when CO2 invades the water saturated pore space. Sedimentation experiments conducted to explore the response of kaolinite and montmorillonite to deionized water, brine, heptane, liquid CO2 and supercritical CO2 show that both montmorillonite and kaolinite aggregate when submerged in CO2 and the final porosity in CO2 is smaller than in brine. Differences in dielectric properties between CO2 and water, and ensuing implications on van der Waals attraction and double layer repulsion explain the observed phenomena. On the other hand, capillary effects induced by the water–CO2 interface are corroborated by clay–water paste desiccation experiments conducted using supercritical CO2: water dissolution into the surrounding CO2 causes suction and capillary contraction, the invasion of the CO2–water interface into the sediment, and the formation of desiccation cracks. Volume contraction and crack initiation are consistent with the sediment response within an effective stress framework. Altered electrical forces and emergent capillary forces lead to coupled chemo-hydro-mechanical phenomena in seal layers that could facilitate CO2 breakthrough and advection through high porosity caprocks; related phenomena are identified in the reservoir rock. Additional studies are needed to further assess coupled phenomena when the interparticle distance is a few monolayers of water.

Capillary Fracturing in Granular Media

We study the displacement of immiscible fluids in deformable, noncohesive granular media. Experimentally, we inject air into a thin bed of water-saturated glass beads and observe the invasion morphology. The control parameters are the injection rate, the bead size, and the confining stress. We identify three invasion regimes: capillary fingering, viscous fingering, and "capillary fracturing," where capillary forces overcome frictional resistance and induce the opening of conduits. We derive two dimensionless numbers that govern the transition among the different regimes: a modified capillary number and a fracturing number. The experiments and analysis predict the emergence of fracturing in fine-grained media under low confining stress, a phenomenon that likely plays a fundamental role in many natural processes such as primary oil migration, methane venting from lake sediments, and the formation of desiccation cracks.

Desiccation mechanism for formation of giant polygons on Earth and intermediate-sized polygons on Mars: Results from a pre-fracture model

We present a pre-fracture incrementally non-linear elastic–hydric model to constrain the models of formation of giant (spacing of 20–300m) desiccation cracks on Earth, and possibly intermediate sized (80 to 350m) polygonal networks of cracks located in many impact craters on Mars which have been interpreted to form by desiccation as opposed to thermal contraction (El Maarry et al., 2010). The results of the model show that tensile stresses rise monotonically with desiccation. However, in soils with diffusivities below 10−4m2/s, it is not possible to generate high enough stresses to cause fracturing. On the other hand, intermediate values between 10−2 and 10−4m2/s create optimum conditions for the formation of cracks at the time scales suggested for the formation of giant desiccation polygons on Earth. Our model clearly shows that for typical diffusivity values of clayey soils with a considerable amount of smectites enough stress can build up to stimulate cracking of various spatial scales. These results corroborate earlier assumptions that giant desiccation polygons on Earth occur through lowering of the water table rather than surface evaporation. Extending the model to Mars shows that soils would crack within similar diffusivity limits but in slightly longer periods of time owing to the lower gravity. Finally, a model for formation of desiccation cracks on Mars is presented that shows that two main conditions need to be fulfilled for desiccation cracks to occur under current martian climatic conditions, namely, that the thermal and soil diffusivity conditions 1) allow for the formation of an unsaturated zone with a considerable thickness while at the same time 2) limiting the growth of the permafrost downward which would disrupt the cracking process.

Desiccation cracks in saturated fine-grained soils: particle-level phenomena and effective-stress analysis

The formation of desiccation cracks in soils is often interpreted in terms of tensile strength. However, this mechanistic model disregards the cohesionless, effective-stress-dependent frictional behaviour of fine-grained soils. An alternative theory is explored using analyses, numerical simulations based on an effective-stress formulation, and experiments monitored using high-resolution time-lapsed photography. Results show that desiccation cracks in fine-grained sediments initiate as the air–water interface invades the saturated medium, driven by the increase in suction. Thereafter, the interfacial membrane causes an increase in the local void ratio at the tip, the air-entry value decreases, the air–water interface advances into the tip and the crack grows. The effective stress remains in compression everywhere in the soil mass, including at the tip of the desiccation crack. This crack-growing mechanism can explain various observations related to desiccation crack formation in fine-grained soils, including the effects of pore fluid salt concentration, slower crack propagation velocity and right angle realignment while approaching a pre-existing crack, and the apparent strength and failure mode observed in fine-grained soils subjected to tension. Additional research is required to develop a complementary phenomenological model for desiccation crack formation in coarse-grained sediments.

Numerical modelling of desiccation cracking

AbstractThe ability to model and predict the formation of desiccation cracks is potentially beneficial in many applications such as clay liner design, earth dam construction, and crop science, etc. However, most studies have focused on statistical analysis of crack patterns and qualitative study of contributing factors to crack development rather than prediction. Because it is exceedingly difficult to capture the nonlinear processes during desiccation in analytical modelling, most such models handle crack formation without considering variation of material properties with time, and are unattractive to use in realistic modelling. The data obtained from laboratory experiments on clay soil desiccating in moulds were used as a basis to develop a more refined model of desiccation cracking. In this study, the properties, such as matric suction, stiffness and tensile strength of soil, and base adhesion, could be expressed approximately as functions of moisture content. The initial conditions and the development of suction due to desiccation and the varying material properties were inputted to UDEC, a distinct element code, using its internal programming language FISH. The model was able to capture some essential physical aspects of crack evolution in soil contained in moulds with varying lengths, heights, and materials of construction. Extension of this methodology is potentially beneficial not only for modelling desiccation cracking in clay, but also in other systems with evolving material properties such as concrete structures and road pavements. Copyright © 2010 John Wiley & Sons, Ltd.

Animal burrowing and associated formation of large desiccation cracks as factors of a rapid restoration of soil cover in flooded farmlands

The burrowing activity of annelids controls the spatial pattern and rapid formation of large desiccation cracks in the river flood-derived mud cover in recently inundated farmland areas in northwestern Anatolia, Turkey. The phenomenon is confirmed by laboratory experiments imitating the natural floodplain conditions.

Model Experiment on Leachate Migration Through a Clayey Soil

Clayey soils are commonly used as liners and cover materials for leachate containment in landfills. Some of these clayey soils tend to be expansive and, after long-term exposure to alternating cycles of dry and wet climatic conditions, develop desiccation cracks which induce a secondary permeability that may result in migration of fluids through them. A model experiment was conducted in the laboratory to study the extent of formation of desiccation cracks and to investigate the changes in soil chemistry after its interaction with the “leachate.” A large quantity of a clayey soil was subjected to repeated cycles of drying and wetting in a specially designed experimental set-up, in which the climatic variables were simulated by using heat lamps, electric fans and water. After the formation of desiccation cracks, the soil surface was flooded with a “leachate” of known chemical composition and the permeate was recovered from the soil through lysimeters, built at various depths in the soil mass. Chemical analyses revealed that some adsorption of Cu, Mn, Cr, Zn, and Fe occurred during the passage of “leachate” through the cracks in the soil mass. On the other hand, Mg, Ca, and Al were released by the soil upon reaction with the “leachate.” The maximum depth of desiccation crack formation was observed to be limited to 19.1 cm (7.5 in.).

Ichnologic note

Scratchings, forming two partial scratch circles, surround a narrow, filled tube probably formed by a plant stem. The scratchings are interpreted to have formed as follows: Water currents carrying sediment onto a floodplain swirled around the plant leaves, etching out partial scratch circles on the sediment surface. Later settling of the finest material resulted in a veneer of mud filling the scratch circles. Drag marks on the bedding surface were formed by the same processes. Later drying of the mud resulted in the formation of desiccation cracks.