The Numerical Analysis And Model Test Research On Geogrid-reinforced And Pile-supported Foundation

The thesis introduced development history, mechanisms of load transfer, theoretical calculation method, application in projects and existing problems of Geogrid-reinforced and Pile-supported Foundation Composite Foundation. In the case of laying different geogrids, altering the relative stiffness of piles and arranging different long-short-piles, through the contrast of the finite element and model test, some variable parameters have been studied, such as the foundation settlements, penetrating-into deformations of piles top, the pile-soil stress ratio, the axial forces of piles and the geogrid strains. The result suggested as follows:(1) Tensioned membrane effect of geigrids can significantly enhance the stress transfer soil to pile, increase the pile-soil stress ratio and reduce foundation settlements and the penetrating-into deformations of piles top. Compared to being placed on the top of the piles, a certain distance above the top of piles (30mm) is better. The pile-soil stress ratios increase, the foundation settlements and penetrating-into deformations reduce with increasing the number of the geogrid layer. But the effect is not obvious. Laid geogrids can also move up the neutral point of pile and reduce negative skin friction resistance area.(2) For flexible piles of the composite foundation, along with the (?) increases, the foundation settlements decrease linearly, but the penetrating-into deformations of piles top and pile-soil stress ratios increase linearly; for rigid piles of the composite foundation, when the modulus is small, their effects are still prominent, but for CFG and concrete piles with larger modulus, improving relative stiffness of piles has no current significance. Increasing the relative stiffness of piles also can enhance the pile-soil stress transfer path, increase axial forces of piles, move up the neutral point of pile and reduce negative skin friction resistance area. Increasing the relative stiffness of piles makes no difference on the changing regularity of geogrid strains. But the corresponding geogrid strain values increase and stress concentration phenomenon is worse as the relative stiffness of piles increasing.(3) In the case of long-short-pile and geogrid-reinforced composite foundation, long piles bear most of loads. Stiffness of the long piles is the principal factor for improving the load carrying capacity of composite foundation. And load-sharing ratios of long piles in the middle are more than those beside. As a result, we can use rigid long piles to improve the load carrying capacity of composite foundation, take advantage of flexible short piles to control the foundation settlements and make full use of soil action, which can enhance effects of foundation treatments and improve economic benefits.