1.An alternative approach of assessing California bearing ratio (CBR) value of sub-grade soil respecting Grain Sizes

ABSTRACT

Being the bottom most layer of a road, the sub-grade soil acts as one of the most important load bearing strata on which the design and performance of a pavement depend essentially. Grain size of soil particles play a vital role on strength characteristics of the sub-grade as working recommendations varies significantly regarding project location, depositional environment, drainage conditions etc. respecting varying particle sizes. Generally, California Bearing Ratio (CBR) value is widely used for the evaluation of subgrade strengths. Since this test is an expansive and time consuming one, it is much needed to establish an alternative approach to determine the 𝐶𝐵𝑅 value from some other physical properties of soils which are easy, cheap and low time consuming with limited facilities for laboratory experiments. To confront this, an attempt has been conducted in this study to correlate 𝐶𝐵𝑅 value of sub-grade with some physical properties of soils, such as Fineness Modulus (FM) along with grain sizes (percentage finer than sieves 4.75, 2.36, 1.18, 0.60, 0.3, and 0.15mm). For this purpose, eighteen CBR samples with different FM values are prepared at Optimum Moisture Content and Maximum Dry Density (of the modified AASHTO compaction test). At initial stage, necessary engineering properties of soils, like fineness modulus, grain size distribution, unit weight, dry density, optimum moisture content are determined which also followed by California Bearing Ratio (CBR) test. After that, a correlation is intended to be established in the form of an equation as well as graphical representation of 𝐶𝐵𝑅 value as a function of Fineness Modulus using regression analysis. With the help of those equations and graphical representations, CBR value of soil sample can be predicted in a more easy, cheap and less time consuming manner to classify and evaluate the soil sub-grade using Fineness Modulus and other soil properties, i.e. grain size, 𝑀𝐷𝐷 and 𝑂𝑀𝐶 etc. rather than conventional 𝐶𝐵𝑅 test.