Prediction of Soil Water Characteristic Curve Based on GSD and PI for Red Clay and Expansive Soils Found in Addis Ababa
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Date
2013-09
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Addis Ababa University
Abstract
Many researchers have done researches on unsaturated soil mechanics worldwide to bring the
unsaturated soil mechanics in to practices. Among those researches some of them focused on
simplifying the complex and expensive testing mechanism by developing models which can be
used to predict the unsaturated soil parameters from basic soil prosperities such as Grain Size
Distribution (GSD) and Plasticity Index (PI) along with the saturated shear strength parameters.
Soil water characteristic curve (SWCC) was proved to have good relationship with the
unsaturated soil parameters. In this study an attempt was made to check whether those developed
models would work for expansive and red clay soils found in Addis Ababa.
Using the model developed by Fredlund and Xing (1994) along with the correlation equation
given by Perera et.al (2005), family of SWCC for soils found in Addis Ababa has been plotted. It
was observed that the family of SWCC plotted was out of the widely referenced family of curves
developed by Zapata et.al (2000) to some extent. Even though the family of curves seems to be
out of the range provided by Zapata et.al (2000), the model gave good prediction for the
unsaturated shear strength parameter Φb.
The percentage error between the measured values of unsaturated shear strength parameter Φb in
previous researches of Habtom (2010) and Getaneh (2010) with predicted unsaturated shear
strength parameter Φb in this study was compared.
For red clay samples the percentage error lie in the range 2.07 to 6.37% for suction ranges of
36.67 to 52.9 kPa and at lower suctions of 16.75 and 21.5 kPa the percentage error ranges from
11.42 to 25.39% .
For expansive soil samples for suction of 23.1 and 32.9 kPa, the percentage error is in the range
from 3.86 to 6.13%. For suction values of 14.5 and 52 kPa the range of error is about 9.45 to
13.40% and for suctions of 38.8 and 48.6 kPa the error lies between 18.94 and 38.84%.
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Keywords
Soil Water Characteristic, GSD, PI, Expansive Soils, Red Clay