Strength Evaluation of Soil Subgrade Using In-situ Tests

Abstract

Flexible pavements in many countries including India are designed on the basis of laboratory California Bearing Ratio (CBR). During construction to ascertain that the design stipulations are met with, one has to check in-situ CBR. For testing in-situ CBR, undisturbed samples are taken and are then tested in the laboratory. Collection of undisturbed sample from soil subgrade that is essentially non-plastic in nature, is near to impossible and further more determination of CBR is a time consuming and sensitive to many parameters, such as relative density, particle size, texture, moisture content and confinement pressure etc.. Thus, during execution stage, it becomes very difficult to ascertain whether the design stipulation has been achieved or not. In this study an effort has been made to evaluate the subgrade strength by conducting in-situ tests using Dynamic Cone Penetrometer (DCP) and Light Weight Deflectometer (LWD) on various locations shown in (Figure 1), of an under-construction road, that is on the service bank of Sirhind Canal, in Punjab, India. The road is tested at fifteen different locations; representative samples of soil were collected from all the fifteen locations and tested in the laboratory for Grain Size Analysis, Atterberg Limits (Liquid Limit, Plastic Limit), Maximum Dry Density (MDD), Optimum Moisture Content, and Laboratory CBR at 97 percent of modified MDD, to find correlations.