Characteristics Of Vibration At Ground Surface And Applications

To eliminate some arguments in the related academic and practical regions, the interface of far-near vibration fields at ground surface, the arrangement of excitation and transducers in a surface wave measurement as well as its application to compound foundations are studied by analytical and numerical methods in this paper.For vibration problems of a homogeneous elastic stratum excited by a surface vertical point force, relationships between the interface of far-near vibration fields and Poisson's ratio of subsoil are studied through a comparison of available analytical solutions and Rayleigh's approximations.To investigate the dynamic characteristics of layered strata and compound foundations with vertical cemented-soil or sand-gravel columns, simplified formula are derived for the axis- symmetric fmite-infmite-elements (FE-IE) coupled solution proposed by Liang GQ & Chen LZ. With the corresponding computer program composed by the author, determinations of the geometric size for finite element domain and parameters for infinite elements are defined through a series of parametrical analysis. The comparison shows that the power-decay function will also lead to dynamic responses of ground with very high precise, when it acts as the displacement function of the second and third infinite elements.With the analytical and numerical solutions mentioned above, the arrangement of excitation and transducers in a surface wave measurement is studied. The result indicates that spacing intervals between the excitation and near-transducer and between the two transducers will both increase with increasing Poisson's ratio of subsoil if P- and S-waves in the received signal are not filtered out. For a dimension-limited construction site, the surface wave measurement will give a lower wave velocity for the deeper soil. Further studies show that the horizontal vibration signal at the ground surface could also be used to get the R-wave dispersion curve.A idealized FE-IE coupled model of compound foundation with continuously circled cemented-soil walls is used for investigating the properties of vibration along the ground surface. Due to the reflection and transmission of reinforcement, it's seen that vibration will quickly decay in the radius direction at some specific frequencies related at least to the spacing interval of two adjacent walls. The computed R-wave dispersion curves illustrate that R-wave velocity of such a compound foundation will be greater than that of natural subsoil at wave length even several times greater than the wall depth. The difference between R-wave velocities of compound foundation and natural subsoil depends also on the width and elastic modulus of the cemented-soil wall and the spacing interval of two adjacent walls, which indicates the difficulty to evaluate the wall depth with the conventional half-wave-length method deduced from the wave theory for horizontally layered strata.The work presented in this paper is a part of the research project "Dynamic Characteristics of Composite Foundations and It's Application", which is financially supported by the National Natural Science Foundation of China with Grant No. 50079027.