Expansive Soil Essay

The term expansive soil indicates to soils, which ahs the tendency to swell when their moisture content is allowed to increase. The moisture may come from rain, flooding, leaking water or sewer lines, or from a reduction in surface evapotranspiration when an area is covered by a building or pavement. The term cracking soils is also used for these soils as they have the tendency to shrink and crack when the moisture is allowed to decrease. Soils containing the clay mineral montmorillonite generally show these properties (Komine and Ogata, 1996; Rao and Triphaty, 2003; Sivapullaiah et al. 1996; Wayne et al. 1984).

There are many correlations that are useful in identifying potentially expansive soils. It may also be possible to identify them visually. Visual indications include (Wayne et al. 1984):

1) Wide and deep shrinkage cracks occurring during dry periods

2) Soil is rock-hard when dry, but very sticky and soft when wet

3) Damages on the surrounding structures due to expansion of soil

Expansive soils are mostly found in arid and semi-arid regions of the world. The presence of montmorillonite clay in these soils imparts them swell-shrink potentials (Chen, 1988).

Expansive soils cover nearly 20% of the landmass in India and include almost the entire Decan plateau, Western Madhya Pradesh, parts of Gujurat, Andhra Pradesh, Uttar Pradesh, Karnataka, and Maharastra (Gopal Ranjan and Rao, 1991).

Expansive soils are a worldwide issue that poses many challenges for civil engineers. These are considered a potential natural hazard, which can cause extensive damage to structures if not properly treated. Such soils swell when given an access to water and shrink after they dry out (Al-Rawas et al. 2002).

In general, expansive soils hav...

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...ssification tests

Atterberg limits are usually used for identifying swelling soil. The increase in plasticity index is considered as an indicator of increased swelling potential. Chen (1988) presented a classification of swelling soil based on the plasticity index of the soil as shown in Table 2.1.

Table 2.1 Expansive soil classification based on the plasticity index

PI (%) Swelling potential

0 - 15 Low

10 - 35 Medium

35 - 55 High

55 and above Very High

Classification based on shrinkage index is found to be undependable to predict swelling potential of soil. However, the shrinkage index may be used with plasticity index for identification as shown on Table 2.2..

Table 2.1 Expansive soil classification based on the plasticity index and shrinkage index

PI (%) SI (%) Degree of expansion

< 12 < 15 Low

12 - 23 15 - 30 Medium

23 - 32 30 - 40 High

> 32 > 40 Very High