Examination of Desiccation Cracking Activities of Drying Soil

Cracking is a complex phenomenon in materials like soils. It is a natural process involving weathering, chemical changes and biological. Desiccation cracking significantly affects soil performance. Cracks create a zone of weakness in a soil mass and reduce its overall strength and stability (Miller, 2010). Examples can be found in various geotechnical, agricultural and environmental applications e.g. irrigated land, tailing ponds for mining waste, landfill liners, earth embankment, reservoir beds, etc. (Yesiller et. al., 2010). Considerable work has been done to study experimentally the physical phenomenon of cracking in soils. To explain the development and extent of desiccation cracking several factors are considered including clay content and mineralogy, soil thickness, surface configuration, rate of drying, total drying time etc. (Colina and Roux, 2010). As soil structure is an important property which affects water storage and movement, it is necessary to measure crack size and pattern precisely. Examples of basic crack measurements are reported on several works (Aitchinson and Holmes, 2003. Abedine and Robinson, 2011. Logsdon et. al., 2010). Imaging techniques have also been developed to basic cracking measurement. Guidi used electro-optical determination to estimate size distribution of crack (Lima and Grismer, 2012). Lima also used photographic image analysis to determine soil surface cracking (Logsdon et. al., 2010). Photographic image analysis techniques appeared to be a useful tool to distinguish differences in crack patterns which may be useful characterising soil cracking. This study has been conducted on a soil (Bengawan Ganga Soil) from a flood protection embankment in India. The highly dense desiccation crack network observed in this man made embankment may have an important role in the occurrence of the small progressive failure frequently detected along the embankment. It is considered that in a drying soil, drying causes shrinkage and a crack initiates when the tensile stresses exceed the soil strength. The tensile strength is dependent on the moisture content of the soil and the associated suction. In this paper the influencing factors behind cracking behaviour of soil such as volumetric shrinkage, water retention property of Ganga soil has been investigated experimentally under proper laboratory environment. Accurate measurement of geomaterial parameters of soil shrinkage cracks is not easy by direct measurement. Large measurement error is expectable due to irregular shape and complex cracks pattern. In recent years, image analysis techniques have been used extensively to characterise the crack network with improved accuracy (Guidi et. al., 2008), (Tang et. al., 2008). of cracking on the surface of the soil. This research work is an attempt of development towards standard and improved procedure of laboratory testing using modern technology of cracking behaviour of soil.

The samples have been obtained at the depth on 0.5 m - 1.0 m from the surface. The soil has been classified as inorganic silts of high compressibility and organic clay (Yan et. al., 2012). Some basic properties of the soil are given in table 1. From the clay mineralogy of this soil (table 2), it has found that the clay is rich in Smectite minerals (montmorillonites) which makes the soil highly attracted to absorb water and causing expansion of the material. These kinds of soils develop significant change of volume (contraction) during drying. The kinds of minerals of the clay fraction play a central role on the properties of the soil, such as plasticity and strength (McCloskey et. al., 2008).

All crack parameters were extracted accurately with program algorithm. Finally, skeletonized operation has been performed. Table shows the desiccation test condition parameters. The information extracted from crack patterns in plates is shown in table. The total length of crack was determined by calculating the distance between intersections from skeletonized image. To quantify the amount of cracking, Crack Intensity Factor (CIF) was determined, which is the ratio of the surface area of the cracks to the total surface area of the soil. Clayey soils are mostly used as liner material because of their low permeability. Clayey soils also follow the EPA standards as well. Sometimes, these soils cause a lot of problems for the geo-technical engineers as these soils tend to have high compressibility and poor shear Strength. The variation in the volume is found at a very high level just because of high compressibility and hence, this variation creates a lot of problems for the engineers. But the use of clayey soils has not decreased, it is still used for many purposes like clay liners, stabilization of bore holes etc. So while using this type of soil, its negative aspects are ignored by the engineers and only positive aspects are considered and this soil is used whenever needed. There are many reasons because of which the variation in the volume of clayey soils is observed. One is due to the expulsion of pore water from the voids upon static surcharge. This process is known as consolidation. The other reason of variation is because of the shrinkage in the clay soils while

The soil tends to shrink and the volume of the soil water decreases as a result of drying procedure. Soil tends to crack during desiccation if shrinkage is restrained. There are many applications of the desiccation cracking of clay in the performance of clayey soils. The compressibility of the soil gets affected by the cracks formation. Cracks also affect the strength of soil to re-enter the water in it. So many kinds of applications directly or indirectly are affected by the presence of cracks in the soil. Many type of construction work is done by using the clayey soils because of its property of swelling and drying. Clay tends to shrink during the dry time; as a consequence desiccation cracks are formed.

This work focuses on the study of some relevant factors that affect the behaviour of soils submitted to drying. The experimental research has been performed on samples from Ganga River of India. The following conclusions were derived: 1. The volumetric shrinkage of Ganga soil was found low which is 16.45%. Low shrinkage limit indicates high potential for shrinkage and swelling (Miller, 2010).. 2. The visual observation from the circular desiccation plate test was that all samples produced predominantly sequential, orthogonal crack (cracks that tends to meet at right angles) patterns leading to subdivision of the crack area into smaller cells. 3. The shapes of the crack notes at intersection was always ‘+’ or ‘T’ regardless any experimental condition. Similar observations were found in the work by Tang et. al. (Guidi et. al., 2008). 4. Higher desiccation rate was observed for smaller thickness; non-orthogonal crack patterns evolved at the primary cracking stage and they occurred simultaneously and relatively fast all over the soil surface The higher the number of crack per area the higher was the length and CIF. But the opposite was found in the case of average width of crack.

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Lecturer in Civil Engineering, Department G.B.N. Govt. Polytechnic, Nilokheri, Karnal, Haryana