Seismic Dispersion Analysis Feasibility for the Subgrade Investigation: Measurement, Experimental and Numerical Modeling

The study focuses on the feasibility of the seismic guided waves dispersion analysis for investigating the subgrade layer made of a treated soil, in the case of under construction roads, before the shallower pavement layers are built. Such a non destructive geophysical method could help to qualify the project acceptance concerning this earthworks phase. In this context, the issue deals with a two layers medium case where the investigated subgrade, whom the top is the measurement surface, lays above a low velocity zone, i.e. the natural soil. The first feasibility stage involved field experimental measurements. A clearly main mode was extracted from the dispersion diagram and has been inverted to a S wave velocity profile leading to a global information concerning the subgrade. In a second feasibility stage dispersion diagram has been studied through a reduced scale experimental modeling providing a well controlled data set that have been compared with theoretical results firstly calculated without any source effects and secondly by tacking into account the source effects through a new numerical approach. The results show other modes distinguishable in the diagram that could be taken into account in the case of a dispersion diagram inversion.