MEASUREMENT OF DYNAMIC SHEAR MODULUS AND BEARING CAPACITY OF SUBGRADE LAYER ON A CLAYEY SANDY RESIDUAL SOILS

The knowledge of the in-situ strength and stiffness of the ground is normally required for monitoring

and evaluation of pavement subgrade layer to ensure an adequate margin of safety. In order to estimate

the dynamic stiffness of the pavement subgrade a method called the spectral analysis of surface

wave (SASW) has been developed. The method consists of generation, measurement and processing

of the dispersive Rayleigh waves recorded on two vertical transducers. Subsequently, an inversion

process is carried out to obtain the shear wave velocity versus depth profile of the site from dispersive

Rayleigh wave data. The results presented in this paper showed that the SASW method is able to reliably

determine the seismic parameter, i.e. the dynamic shear modulus of the soil subgrade layer of

the pavement profile. In situ subgrade bearing capacity test using the field CBR test was also carried

out in the same location of the SASW test. An empirical relationship between the CBR and the dynamic

shear modulus from the SASW measurements was also established for bearing capacity measurement

in the pavement system. Results showed that the empirical model is statistically valid with

excellent correlation coefficient.