International Journal of Earth Sciences and Engineering

C. N. V. Satyanarayana Reddy ¹, E. V. Raghava Rao ¹

Affiliations
1 Andhra University, Visakhapatnam, Andhra Pradesh, IN

Abstract

The pavement design and construction stages involve determination of large number of CBR values of sub grade, sub-base and base courses. Civil engineers often face difficulty in quick determination of CBR values as it takes about five to six days’ time. Over the years, many correlation equations for CBR have been developed by investigators in terms of easily determinable soil index properties and engineering properties as variables. Most of the equations developed are based single or double variables and met with limited applicability and success. The estimated value of CBR from correlation equations is largely influenced by the number of variables used in the equations and how the variables are selected. In the present paper, impact of number of variables on correlation equations for CBR of coarse grained soils is studied. The significant influencing variables are identified from scatter diagrams generated between the each of the variables and CBR values of coarse grained soils, based on values of R2 values. Correlation equations of CBR are developed with most significant single variable (MDD), two variables (MDD, GF) and three (multi) variables (MDD, GF, OMC) identified from study through linear and nonlinear regression analysis. The study revealed that correlation equation based on Multiple variable linear regression equation of third degree has high impact (highest R2 value i.e. highest correlation coefficient ) on correlation equations of CBR of coarse grained soils when compared to multiple variable non-linear regression equation, regression equation with two variables and regression equation single variable among linear and non-linear regression equations.

Keywords

Flexible Pavements, CBR, Regression, Correlation Equations, Index Properties, Sandy Soils.

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