Geo-spatial Variability of Physiographic Parameters and Landslide Potentiality - Semi-quantitative Approaches for Landslide Assessment and Prediction - page 83

2.3.3.1 Volumetric Expansion

Soil Survey Standard Test Method was applied to measure volumetric expansion
of the soil. This method outlines the procedure for the determination of the free
swell of a disturbed soil on wetting. This test measures the free swelling of a
disturbed soil (ground and sieved finer than 0.425 mm) on wetting from air-dry to

saturation. The swell is calculated on a volumetric basis using a modi cation of

the Keen-Raczowski Test. The soil samples having at least 150 g of the material
passing a no 36 BS Sieve (0.425 mm) were collected from 50 different locations
of the Shivkhola watershed and prepared according to the procedure for testing
(Keen and Raczowski 1921 ). To calculate the percentage volumetric expansion
(VE), the following equation was applied.

W 3 W 2

VE

ðÞ¼

W 1

100 ð 2 : 2 Þ

W 4

where, W 1 = weight of volume expansion box (g); W 2 = weight of the weighing tin
(g); W 3 = weight of wet expanded soil + tin (g); and W 4 = wet of wet residual
soil + box (g).

2.3.3.2 Water Holding Capacity

Simply de ned soil water holding capacity is the amount of water that a given soil

can hold for crop use. Soil texture and organic matter are the key components that
determine soil water holding capacity. In terms of soil texture, those made up of
smaller particle sizes, such as in the case of silt and clay, have larger surface area.
The larger the surface area the easier it is for the soil to hold onto water so it has a
higher water holding capacity. Sand in contrast has large particle sizes which results
in smaller surface area. The water holding capacity for sand is low. Soil organic
matter (SOM) is another factor that can help increase water holding capacity. Soil
organic matter has a natural magnetism to water. By using Keen-box and oven,
water holding capacity of soil was assessed applying the following equation.

total water in the wet soil
oven dry weight of the total soil

Water holding capacity of soil ¼ 100 ð 2 : 3 Þ

2.3.3.3 Porosity of the Soil

Porosity or pore space refers to the volume of soil voids that can be filled by water

or air. It is inversely related to bulk density. To calculate porosity, bulk density and
particle density were determined applying Keen-box method. The oven dry weight
of a unit volume of soil inclusive of pore spaces, called as bulk density. Generally
soil with low bulk density provides good physical condition. The bulk density of