PREDICTIVE MODEL OF UNCONFINED COMPRESSIVE STRENGTH FROM INDEX PROPERTY OF LATERITIC SOILS. (CASE OF DILLA TOWN)

Abstract

In Dilla large buildings and important infrastructures are often supported by lateritic soils. Lateritic soils are anisotropic and heterogeneous. Geotechnical engineers concerned on lateritic soils are attempting to develop specific empirical equations to predict more reliable results needed for the design. As this study is one avenue towards developing specific predictive models, lateritic soil samples were taken and laboratory tests were conducted to meet its objective. Twenty disturbed and twenty undisturbed samples were taken from ten different randomly selected borrow pits having four-meter depth with in the town and various laboratory tests including Atterberg’s limits, natural moisture contents, in-place unit weight, specific gravity and unconfined compressive strength were performed on the soil samples. Regression analysis have been done and various linear relationships between unconfined compressive strength and index properties were investigated and predictive equations estimating unconfined compressive strength from index properties were developed. Among the developed models, two comparatively better models having determination coefficients of 0.866 and 0.927 with standard error of less than 0.0005 are selected and validated. A model with 0.866 determination coefficient is given by qu = -421.843- 4.191wn + 40.870γins. While, a model with 0.927 determination coefficient, qu= 1.1𝑒 0.282𝛾𝑖𝑛𝑠 is exponential and got a better accuracy on prediction during validation using control test result. The equations are valid for a natural moisture content in a range of 19% to 35% and in-situ unit weight in a range of 12 kN/m3 to 20.6 kN/m3 .