Shaking Table Experiment Research Of Group Pile In Liquefiable Soil

In recent years, the worldwide earthquake disasters resulted in a large number of people injuries and property loss. Buildings, bridges and roads were destroied by earthquake. The phenomena made people pay more attention to the seismic performance of a variety of structures. As a common phenomenon in earthquake disasters, soil liquefaction has been researched long ago and made some achievements. In the engineering field, it is a common earthquake destruction that the pile foundation loss bearing capacity due to soil liquefaction. At present, the theory of pile foundation seismic design is obviously lagging behind the practical needs of the project, especially in the part of anti-liquefaction design, people has not found the suitable methods for practical project design. The research has focused on laboratory tests and numerical simulation. Laboratory tests mainly include such as triaxial tests, centrifugal machine tests and shaking table test, which are largely dependent on theory and experience in static conditions. It is still not deep enough for the research of pile-soil cooperation under the dynamic action. After understanding and researching at home and abroad, relying on the financial suppoting from Shanxi Province, the laboratory tests of the pile group effect in liquefying soil were conducted. To study the improvement of liquefaction effect of saturated sand foundation under the condition of different pile spacing between piles and the changes of pile tip resistance after shaking:1. Natural foundation, in the process of soil vibration which is from beginning to complete liquefaction, the greater the depth, the greater the excess pore water pressure. In the same moment, pore pressure ratio decreases with depth increases, and the used time increases with the depth decreases. The liquefaction begins to happen in upper, and then happens in the deeper soil with time move, at last, the whole soil layer will liquefy. 2. The saturated sand improved by pile foundation with3D pile spacing vibrate after12s or15s, excess pore water pressure increase gradually and pore pressure ratio increase, too. The liquefaction beginning time of saturated sand at-5cm,-30cm and-50cm is separately later than natural ground for10s,9s and10s, the complete liquefaction time for11s,9s and10s. It is shown to us that3D spacing pile reinforces the saturated sand in some way to delay vibration.3. For the saturated sand improved by pile foundation with3.5D pile spacing, the liquefaction beginning time of saturated sand at-5cm,-30cm, and-50cm is separately later than natural ground for4s,2s,3s, the complete liquefaction time for5s,3s, and5s. For the saturated sand of4D pile spacing, the liquefaction beginning time of saturated sand at-5cm,-30cm, and-50cm is separately later than natural ground for2s, Is, Is, the complete liquefaction time for4s, Is, and3s. It is shown to us that3.5D and4D spacing pile can also reinforce the saturated sand, but less effective than3D4. The types of piles are divided into middle pile, side pile①, side pile②and corner pile according to its position in pile foundation. In vibration, the resistance of pile changes regularly, the middle one increases slowly from beginning and then fast; the corner one is opposite, and the two side ones are somewhere in between.