CORRELATION OF CBR WITH INDEX PROPERTIES OF SOIL

California bearing ratio (CBR) test is performed to determine the stiffness modulus and shear strength of sub grade which is used for the design of flexible pavement of runways of the airfields, village roads, highways etc. The sub grade provide the foundation for the pavement material and should be well compacted to utilise its full strength. The sub grade strength is related to the CBR value of the soil. The CBR test according to IS: 2720 is performed by static penetration test procedure. The CBR test is laborious and time consuming and must always be performed on molded soil samples. It is always difficult for engineers to obtain accurate CBR values of the soil. The CBR values depend on the type of soil as well as other soil properties. In this research work it is tried to establish a relation between different index properties of soil and CBR value so as to obtain accurate CBR values in less time by using ANN and MLR analysis. As the results obtained are satisfactory, CBR value of soil depends on many factors like maximum dry density (MDD), optimum moisture content (OMC), liquid limit (LL), unconfined compressive strength, percent fines etc. In this study an attempt has been made to correlate soaked CBR value with percent fines, LL, MDD and OMC of 11 soil samples collected from different locations of two districts in Punjab, India. This research work is done on SW-SM type (Well graded sand containing silt) soil. The tests are performed in laboratory to obtain the CBR value experimentally and on the other hand the correlation is established in the form of an equation of CBR as a function of different soil properties by the method of regression analysis. It has been observed that the predicted values are in the domain of experimental values and the results indicated a strong correlation with value of R 2=0.844 for soaked CBR was obtained.