Vibration And Optimization Of Pile Groups

Vertical dynamic impedances of piles and rigid foundations of arbitrary shapes, vertical dynamic interactions between pile groups and raft foundations, optimization of pile groups are studied in the thesis.1. Novak layer method is introduced to obtain the vertical dynamic impedances of both an end-bearing pile and a floating pile in a homogenous stratum. And the vertical dynamic impedances of single pile are analyzed in homogenous elastic soil, inhomogenous viscoelastic soil homogenous viscoelastic soil. At the same time, the factors to influence the impedances of single pile are examined.2. The behaviours of soil layers in a different depth are presented mainly. The pile group and the surrounding soil are discretized into horizontal layers, which meets a plane strain assumption. By means of that the single pile dynamic impedance is developed with a transfer matrix method, the pile-to-pile dynamic interaction factor is derived. Then, the dynamic impedances of rigidly-capped pile groups with due consideration to pile-soil-pile interaction for vertical oscillations are produced.3. In the past many researchers studied dynamic stiffness and damping coefficients of surface and embedded rigid foundations of arbitrary shapes in the elastic homogenous half space. Dynamic stiffness and damping coefficients were obtained by using regularly shaped foundations instead of arbitrarily shaped ones. Obviously, the calculating methods were not perfect. In addition, the two parameters mentioned above were calculated only in the case of asingle foundation. But the cases of two or more foundations were not presented because the interactions between foundations were not considered in all present papers. This thesis eliminates two faults named above by using the assumption of the plane strain and of dynamic foundation-soil interaction factors. The calculating method of dynamic impedances presented by the paper proved to be accurate and practical.4. A dynamic model is accounted for axial vibration between pile groups and raft foundations. It isn t assumed that the raft is a rigid body instead of its flexibility. These new points are completed in the equation of motion of the interaction between pile groups and raft foundations. Then, an example shows that the calculating result with assuming infinitely rigid rafts is not precise, that the stiffness of a raft has an effect on the calculating result.5. Dynamic impedances of pile groups have been studied almost in a same assumption that rigid caps and soil under it do not touch each other in the present papers. The thesis account for the dynamic impedance of pile groups without the aboved-mentioned assumption. So, that the soil under caps affects the caps and piles is discussed. In the thesis, first, the single pile dynamic impedance and the single rigid foundation one are derived in homogeneous elastic media. Then, the pile-to-soil, soil-to-pile and soil-to-soil dynamic interaction factors are defined and worked out. And a simple method for calculating dynamic vertical impedance of rigidly-capped pile groups in homogeneous elastic media is developed.6. Based on the optimizing theory of plural modality method and genetic algorithms, defining the objective function as minimum displacements of caps and minimum deviations of axial force of each pile in pile groups respectively, the optimization of pile groups is derived. And a new design idea is presented for pile-supported structures.