Desiccation crack

In addition to being potentially less costly to construct, ET covers have the potential to provide equal or superior performance compared to conventional cover systems, especially in arid and semiarid environments. In these environments, they may be less prone to deterioration from desiccation, cracking, and freezing/thawing cycles. ET covers also may be able to minimize side slope instability, because they do not contain geomembrane layers, which can cause slippage.5-42 43... 

Fig. 2.3 Enhanced recharge through parts of high conductance in soil, alluvium, and nonconsolidated rocks (1) gravel in buried streambeds (2) open desiccation cracks (3) old desiccation cracks filled with coarse material (4) animal holes (5) plant roots.

Such a concretion (shown in thin section in Fig. 3.1.10 and bisected as in Fig. 3.1.11) is believed to have existed initially as an organic gel in a quiet muddy marine sediment. The entrapment of a crab in such a slimy mess is believed to be coincidental, because a fossil crab is not always present (Stenzel, 1934). The irregular fractures are believed to represent subsequent shrinkage [desiccation ( )] cracks which are now partially filled with pyrite, suggesting initial anaerobic petrification. More or less contemporaneously with fracturing, the phosphatization supposedly took place. 

Sandstone- and mudstone-siltstone facies are slightly bioturbated, mostly as single vertical to horizontal burrows some finely laminated mudstone units are non-bioturbated. Desiccation cracks, filled with very fine sand, are common. Desiccation has also given rise to disturbed primary lamination. Massively carbonate-cemented beds and concretions of 2-3 cm occur in both the sandy and the muddy sediments. Root structures are rare. The overall high resistivity and low N/G ratio of the middle member reflects the extensive carbonate cementation in sandstones. 

The overall depositional environment of the Middle Lunde Member represents a distal alluvial plain or terminal basin (Nystuen et al 1989 Steel Ryseth, 1990 Nystuen Fait, 1995). Depressed areas were flooded by ephemeral sheet floods, leaving blankets of sand, silt and mud of high lateral extent. During certain periods these depressions could turn into shallow temporal lakes in which laminated, current-ripple laminated and wave-ripple laminated mud and silt aggraded. Drying up of these shallow lakes gave rise to frequent desiccation cracks, distorted lamination and mud flakes. The episodic flooding promoted the infiltration of suspended clay particles into the sand blankets. 

Desiccation cracks may extend to depths of 2 m in expansive clays and gape up to 150 mm. The suction pressure associated with the onset of cracking is approximately pF 4.6. The presence of... 

In a series of experiments, slabs of clay were compacted in the lab and then trimmed to produce cylindrical test specimens. One sample of the clay was compacted and then trimmed for a test specimen immediately, while the other was allowed to desiccate for a period of time before being trimmed. The one that desiccated had tiny cracks as a result of the desiccation process, and was much more permeable than the soil that had not been desiccated. As confining stress increased, the hydraulic conductivity decreased because the soil was compacted into a less porous condition. 

Although the sample that was cracked from desiccation was obviously more permeable, at a very high stress the hydraulic conductivities were essentially identical. With enough confining pressure acting on the soil, the cracks that had existed earlier closed up completely so that the soil was no longer highly permeable. 

Pedoturbation is the constant internal turnover of soil material. Vertisols are churning heavy clay soils with a high proportion of swelling 2 1 clay minerals (FAO, 2001). These soils form deep wide cracks from the surface downward when they are desiccated, which happens at least once in each year. 

Cracked Gas Drying. Ethylene and propylene are two of the most important petrochemical raw materials today. They are manufactured by a thermal cracking of ethane, propane, or naphtha. One of the important separation-purification steps in the production of ethylene and propylene is removal of water before low temperature separation. Although alumina has been the most commonly used desiccant in drying cracked gas in the past, 3A molecular sieve adsorbents have an overall economic advantage 32), and many cracked gas plants are using the 3A molecular sieves today. 

After polishing, the specimens were stored in a desiccator until testing. Once mounted in the specimen holder, the specimen was scanned for fibers that were spaced a minimum of 2 /rm and a maximum of one half of their diameter from the nearest neighbor. Matrix conditions near the fiber of interest were also considered. Fibers near voids, cracks, or surface damage or those fibers that showed a pre-existing interfacial crack were rejected. Once a suitable fiber end was located, its diameter and distance to the nearest neighbor were entered for data reduction purposes. 

Figure 4. Crack length as a function of time for mild steel primed at 34% RH and bonded with PES and placed in a desiccator at room temperature.

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