Abstract
Subgrade is a most important part of a pavement structure, which should have a reasonable stiffness modulus and shear strength. CBR (California Bearing Ratio) test is performed to evaluate stiffness modulus and shear strength of subgrade soils. However, CBR test is laborious and time consuming, particularly when soil is highly plastic like Jamshoro soil. In order to overcome this limitation, it may be appropriate to correlate CBR value of soil with its index properties like grain size analysis, Atterberg limits, and compaction characteristics such as MDD (Maximum Dry Density) and OMC (Optimum Moisture Content). This paper expresses the correlations between CBR value of Jamshoro soil and its index properties. SLRA (Single Linear Regression Analysis) and MLRA(Multiple Linear Regression) based Models were utilized. It is seen that MLRA gave better correlations up to R^2 of about 0.984. It is observed that the Soaked CBR value can be predicted with confidence from LL (Liquid Limit), PI (Plasticity Index) and percent finer while the un-soaked CBR value can be obtained from LL, plasticity index and MDD.
Highlights
Pavement design is considered to be the most important parameter in the construction of a road network
It is necessary to evaluate the strength of subgrade soil on which the whole structure of the pavement rests and for this, California Bearing Ratio (CBR) is one of the most widely used methods
Graph is plotted between CBR and IP and a suitable trend line is drawn through the plotted points for obtaining the value of coefficient of determination (R2)
Summary
Pavement design is considered to be the most important parameter in the construction of a road network. It is necessary that the subgrade soil should be properly compacted to fully utilize its strength while carrying the loads of the above layers of pavements as well as the moving loads of traffic [2]. For this purpose, it is necessary to evaluate the strength of subgrade soil on which the whole structure of the pavement rests and for this, CBR is one of the most widely used methods. This method is mainly used to determine the stiffness modulus and shear strength of the subgrade soil and helps in designing the thickness of each layer of Mehran University Research Journal of Engineering & Technology, Volume 37, No 1, January, 2018 [p-ISSN: 0254-7821, e-ISSN: 2413-7219] 177
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