Indian Geotechnical Conference – 2010, GEOtrendz December 16–18, 2010 IGS Mumbai Chapter & IIT Bombay CBR Predicted by Index Properties for Alluvial Soils of South Gujarat Patel, Rashmi S. Desai, M.D. 1 Design Engineer Visiting Professor e-mail:swtrashmi@gmail.com e-mail:earthmdd@yahoo.co.in Techfab India Industries Ltd., Mumbai 1 SMFE, AMD, SVNIT, Surat ABSTRACT California Bearing Ratio (CBR) is a commonly used indirect method to assess the stiffness modulus and shear strength of sub grade in pavement design. However; it is always difficult for transportation engineers to obtain representative CBR value for design of pavement. Type of soil is not the only parameter which affects the CBR value, but it also varies with different soil properties possessed by the soil. A method is proposed for correlating CBR values with the Liquid Limit, Plastic Limit, Plasticity Index, Optimum Moisture Content, and Maximum Dry Density of cohesive soils of various zones of Surat city of Gujarat state. These tests are much more economical and rapid than CBR test. The type of soil found in Surat region is mainly Alluvium which consists of clay, sand, silt. 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. A study evolved to find the correlation between CBR values with soil index properties that are suitable for Surat city. Comparison is done between the experimental results and calculated results. Statistical Analysis is carried out using SPSS Software version 13.0 and programming language. Finally equations are derived for CBR unsoak and soak conditions which are applicable to the local region where the soil properties are within the specified ranges. The correlation can be used with experience for determining CBR value using basic soil properties for no of samples at 100m interval & checked by few CBR test representing a similar range of CBR.. 1. INTRODUCTION Indian road network consist of 33 lakh km. and is second largest in the world. India has large and extensive transportation system. About 65% of freight and 80% passenger traffic is carried by the roads. Number of vehicles has been growing at an average pace of 10.16% per annum over the last five years. Roads may be classified into: National Highways, State Highways, Major District Roads and other Roads (Urban, Village & Panchayat Roads). Geotechnical engineering should play one of the most important roles in early stage of Planning and Design of Infrastructure, due to the fact that incorrect geotechnics can result in unreasonably high cost. For the design of pavement CBR value is one of the important parameters.CBR value can be measured directly in the laboratory test in accordance with IS 2720 part 16 on soil sample acquired from site. Laboratory test takes at least four 4 days to measure the CBR value for each soil sample. Civil engineers always encounter difficulties in obtaining representative CBR value for design of pavement. CBR value is affected by the type of soil and different soil properties. An attempt has been made to correlate the CBR with soil properties. It can be the alternate method for the time consuming tests. These tests are much economical and rapid than CBR test. This paper gives and over view to obtain a correlation between CBR values with soil index properties that is suited for Surat City. It may be used for other alluvial deposits judiciously and after check tests. 2. EXPERIMENTALWORK The soil samples were collected from six different zones of Surat City, two samples from each zone. These zones are North Zone, South-East Zone, East Zone, South Zone, South-West Zone, and West Zone. The selected soil sample are tested for CBR value, optimum moisture content, maximum dry density, particle size distribution, plastic limit, liquid limit plasticity index, and shrinkage limit. These tests were performed according IS code specifications.