Evaluation of Vibration Characteristics at Improved Soft Ground by Surface Wave Method

Soil improvement becomes important for constructing buildings at soft ground. Casting rigid bodies into the soft ground at periodic distance is known as one of popular approaches for improving soft soil ground. When we construct an establishment over this improved ground, it is crucial to estimate the shear wave velocity on this field in order to evaluate the effect of vibration characteristics. in this study, we propose a new approach combining surface wave method and homogenization method to estimate macroscopic vibration characteristics for the improved ground. to study the effectiveness of this approach, the simulation study is carried out as follows. Firstly, simulated waveforms for the grid-form improved ground model are synthesized by 3D finite difference method. from this simulated waveforms, the dispersion curve of surface waves is then obtained from multichannel analysis of surface waves (MASW). to evaluate whether this dispersion curve represents macroscopic characteristics of treated soft ground properly, simulated waveforms are synthesized by using the homogenized ground model which is made by homogenization method. the dispersion curve for the homogenized model is also evaluated. the homogenization method is based on the assumptions that an intended composite ground is composed of periodic structures and the ratio between the length of intended structure and that of periodic structure is close to zero. therefore, the wavelength of surface waves should be long to some extent in order to represent macroscopic characteristics. We investigated the relation between the wavelength of surface waves and the periodic length of rigid body by comparing the dispersion curve of improved ground model with that of homogenized model. As a result of simulation for various improved models, it is concluded that the surface wave dispersion is consistent with the homogenized model when its wavelength is about twice longer than the periodic length of rigid body.