To provide a method for evaluating the soundness of a foundation structure based on the vibration data by excitation of a superstructure.

As shown in the figure, in this method, for the structure consisting of the superstructure 1 and the foundation structure 3, a vibration test is performed to the superstructure 1 and its vibration data is measured by a sensor part 5. The vibration data is analyzed by a data record-analysis system 9 and the soundness of the foundation structure 3 is evaluated. In a first technique, the shear rigidity G and the shear strain of the ground are calculated from the vibration data, the sheer rigidity GO of the ground of an initial level and the shear rigidity G' of a design level are calculated from these values, stable calculation is carried out to a structural model of a structure considering the ground spring constant determined from the shear rigidity G', and the soundness of the foundation structure is evaluated. In a second technique, the limit value G' (L) of the shear rigidity is determined assuming deformation of the ground and the foundation, and the soundness is evaluated by comparing the analytical natural frequency at the limit value and the natural frequency of actual measurement.