CORRELATION BETWEEN CBR AND MINI SPT VALUES OF STABILISED SOIL

Abstract

Subbase course is used under flexible pavements primarily to increase the load carrying capacity of the pavement by distributing the load through a finite thickness of pavement. Since subbase lies below the base course, it can be of lower quality and generally consists of locally available materials. The subgrade is the foundation layer which eventually support all the load coming on to the pavement. The performance of the pavement is effected by the characteristics of the subgrade. Subbase and subgrade are not always strong and stable to support traffic load and required improvement in their properties. Flyash is a waste product and lime is also easily available. Hence stabilization is carried out by the lime flyash in order to increase the strength and stability of subgrade soil. They are also used in foundation for low cost buildings. The prime objective of pavement design is to determine the thickness of different layers so that the pavement structure can bear the load without any distress. CBR is the most popular method of flexible pavement design. CBR test in laboratory is carried out in accordance with IS: 2720 (Part XVI) - 1979 to obtain the reliable and reproducible results. However, this test is not effective upto significant depth. In order to overcome this drawback, the standard penetration test (SPT) may be carried out to explore the soil properties upto any depth. The Mini SPT is quite handy equipment and can be carried to the field easily. In the present study, the lab CBR and Mini SPT values of stabilised soil have, been correlated under identical conditions of test. Both CBR Mini SPT were carried . _ _ out in laboratory under soaked and unsoaked condition. The analysis of test results have shown that a linear relationship exists between CBR and mini SPT value of stabilised soil. The correlations have been developed between soaked and unsoaked values of N and CBR and also between dry density, CBR and N-values. Such correlations are very useful for design engineers and can avoid long period of soaking the sample in water before test. iii