Effect of particle size and relative density on dynamic resistance and subgrade modulus of clean sand

Abstract

The present study was aimed at developing an alternative indirect method which can be used to determine Relative Density, Initial Tangent Modulus and Modulus of Subgrade Reaction for clean sand of any particle size. To know the height of fall and hole diameter of sand discharging bowl for a desired Relative Density of a specific sand, the air pluviation method was calibrated in the first stage. Then in the second stage sand deposits of different relative densities were prepared in calibration chamber and Dynamic Probing Light (DPL), Dynamic Cone Penetrometer (DCP) tests and Plate Load Test (PLT) were performed on the prepared sand deposit. Correlation between Pindex (rate of penetration in mm/blow) and Relative Density was made from the test results in calibration chamber. Based on the test results, resistance of sand increase exponentially with increasing Relative Density for different mean diameter (D50) of particles but the larger mean diameter of particles of sand shows the higher resistance at same Relative Density than the smaller mean diameter of particles. Correlation among Initial Tangent Modulus (EPLT(i)), Subgrade Modulus (Ks), Relative Density and Pindex was made from the test result in calibration chamber. It was found that Initial Tangent Modulus (EPLT(i)) and Subgrade Modulus (Ks) increases with increasing Relative Density. On the other hand, mean diameter (D50) of particles has large effect on the Initial Tangent Modulus (EPLT(i)) and Subgrade Modulus (Ks). Larger mean diameter (D50) of particle shows the higher value of Initial Tangent Modulus (EPLT(i)) and Subgrade Modulus (Ks) at same Relative Density. Therefore, Initial Tangent Modulus (EPLT(i)) and Subgrade Modulus (Ks) decrease exponentially with increasing Pindex for different mean diameter of particle. In the third stage, the correlation was verified for three dredge fill sites where DCP and DPL results were compared with the result from Sand Cone Method. At the last stage, CBR test was performed at laboratory at field density to make the correlation among CBR value, Relative Density (%) and field Pindex for DPL and DCP. CBR value decreases exponentially with increasing Pindex value for both DPL and DCP. A generalized correlation between Pindex and Relative Density for clean sand of any particle size was found from this study. To determine in situ Relative Density of sand deposit, it is concluded that the proposed method (DCP and DPL) can be used as an alternative indirect method which is suitable up to 2 m depth.