Three-Dimensional Numerical Analysis Of Seismic Responses Of Micropiles In Liquefiable Soils

Serious damages to pile foundation induced by earthquake liquefaction are observed in many history earthquake cases. Micropile is a new type pile foundation. Up to recent, aseismic safety and seismic responses has not yet fully recognized, especial to the seismic performances of micropile found on the liquefiable soils. Now the engineers always use the seismic design method of normal pile foundation for the micropile. Therefore, in order to provide a rational reference for seismic design of micropiles and investigate the mechanism of pile-soil interaction, the research on the seismic responses of micropile in liquefiable soils is of great importance.Based on the fast Lagrangian analysis of continua, FLAC3D, three numerical simulation models in which the inclination degree of micropiles are 0°, 15°, 25°, respectively, were constructed to investigate the performances of micropile in liquefiable soils subjected to seismic loading and self-weight loading. The principles of accelerations of ground and pile, the lateral displacements, the bending moments of the pile and the express pore water pressure in the ground with different boundary conditions are discussed. Moreover, the pile-soil interaction mechanism is further investigated. Some interesting results are reached as shown in the following:1) The maximum bending moment of the micropile occurs at 1/3 pile length from surface.2) The seismic responses of micropile of different pile inclination and same input wave are different. The bigger the inclination degree of micropile, the smaller the lateral displacement at the pile head is.3) The growth value of the express pore water pressure is smaller in the pile groups than outside the piles during earthquakes.4) The acceleration amplitude in the ground decreases with decrease of buried depth. Liquefiable layer absorbs the main seismic wave energy during shaking.5)Seismic waves intensity plays real on acceleration and excess pore water pressure responses. 6)The lateral displacement of pile top increases with increasing earthquake intensity.The results will provide useful consults for the seismic design of micropiles on a liquefiable foundation.