This article was presented at Malaysian Geotechnical Conference, Malaysian Geotechnical Conference, 14-16 March 2004, Petalingjaya, Kuala Lumpur, which was written by S.A. Rosyidi (LATEI’s staff), M.R.Taha (Professor, UKM Malaysia) and K.A.M. Nayan (Lecturer, UKM Malaysia).


The knowledge of the in-situ strength and stiffness of the ground is normally required for the design monitoring and evaluation of highway pavement so as to ensure an adequate margin of safety. In order to estimate the stiffness of the pavement foundation a method called the spectral analysis of surface wave (SASW) has been developed. Stiffness parameters from the shear and Young’s modulus derived from the SASW measurements are obtained at a small strain level of <0.001%. At this strain level the soil is linearly elastic and the use of elastic theories is thus justified. The method consists of generation, measurement and processing of the dispersive Rayleigh waves recorded from two vertical transducers. Subsequently, the dispersive data are inverted and the shear wave velocity versus depth of the site is obtained. The results presented in this paper showed that the SASW method is able to determine reliable stiffness parameters of the subgrade layer of the pavement profile. In situ subgrade bearing capacity test using the dynamic cone penetrometer (DCP) was also carried out in the same location of SASW test. The DCP results showed the 8 kg hammer blows per penetration depth corresponding to soil strength of subgrade layer. An empirical relationship between the DCP value and the soil stiffness from SASW measurements was also established for practical applications.

Keywords: SASW, shear modulus, shear wave velocity, pavement subgrade layer

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