Studying the Correlation between the California Bearing Ratio (CBR) Values with Properties of Soil Sample in Egypt and Their Effect on the Thickness of The Rigid Paving Layers
: Background: For most geotechnical solutions of engineering road structures, the California Bearing Ratio is frequently required. To determine the dimensions of rigid pavements in tropical countries the CBR should be known. It should be used to determine the modulus of soil layer subgrade, by using certain correlations. It is a very important engineering parameter for soil condition for design the flexible and rigid roads thickness. Soil factors such as Atterberg limits, maximum dry density, and optimum moisture content have an impact on CBR values. Extensive experimental testing were conducted on a hundred (100) soil samples collected from various locations around Egypt for this investigation. The study's purpose was to find a relationship between CBR values and soil index characteristics.
Results: This study looked into the possibility to use both single and multiple linear regression analysis to relate CBR values to soil index properties. The results showed that there was a direct relationship between CBR Ratio and MDD with a coefficient of determination of R2 = 0.96, and another correlation between CBR and OMC % with a coefficient of determination of R2 = 0.87. Wile, PI was inversely associated (to a lesser extent) with CBR value. In addition, the results discussion showed that while there was a small difference between the laboratory and predicted CBR in A-1-a, A-1-b, and A-3 types of soil, there was a big difference between the two values in A-2-4 and A-2-6 types of soil.
Conclusions: The results confirmed that the time and efforts will be minimized in estimation of CBR. In addition, the effect of the strength of the soil under the concrete slab on its thickness was investigated in this study. In the AASHTO design equation, he term which expresses soil strength is the modulus of sub grade reaction (K). Using the estimated value of (K) and AASHTO design method for designing the slab thickness has been estimated for each case. Results have been analysed to get the effect of improving the soil strength under rigid pavement.