EFFECT OF GYPSUM CONTENT ON SOIL - W ATER CHARACTERISTIC CURVE AND UNSATURATED HYDRAULIC CONDUCTIVITY IN SOIL

Abstract

A laboratory experiment was conducted to study some hydraulic properties such as soil-water characteristic curve, specific water capacity and hydraulic conductivity, for a soil contenting 5 to 502 g gypsum.kg-1 soil, for wide range of water content from residual water content 0r at soil-water potential 1500 k Pa to the saturated conditions 0s The soil-water characteristic curve was estimated, and the equation of van Genuchten (32) was used to determine the best-fit parameters a, n and m for experimental data of soil-water characteristic curve. Unsaturated hydraulic conductivity was calculated from the values of soil-water potential and the values of u, n, and m, by using a closed¬form integral equation which it is suggested by van Genuchten (32). The results showed that volumetric water content were changed with gypsum content changing under each different water potential. At soil-water potential 0.1 kPa the saturated water content was increased from 0.442 to the 0.442 cm 3. cm-3 when gypsum content was increased from 32 to the 502 g gypsum.kg-1 soil. But at soil-water potential 1500 kPa the residual water content was decreased from 0.255 to the 0.089 cm3.cm-3 with increasing gypsum content from 64 to the 502 g gypsum.kg-1 soil. The effect of these variations reflected on the calculated values of unsaturated hydraulic conductivity. The values of unsaturated hydraulic conductivity were increased from 1.29X10-4 to the 2.29xl0-2 em.min" with increasing gypsum content from 5 to the 502 g gypsum.kg-1 soil, at high water content. But at residual water content ( 0 = 0r ) the values of unsaturated hydraulic conductivity were decreased from 4.94x10-8 to the 6.36xl0-11 cm.min-1 with increasing gypsum content from 64 to the 502 g gypsum.kg-1.soil,