Study On Model Test Of Large-Diameter And Over-Length Pile Group In Loess Area

The application of the pile foundation hold a long history .The number of super high-rise buildings is increasing obviously . Aiming at the characteristics of high , heavy and strict control of settlement of these buildings ,large diameter super-long piles has emerged as the times require.At present, the studies of the load transfer mechanism of the super-long pile are still at the initial stage. The design method of super-long pile in the applicable codes and standards is not based entirely on the mechanism of load-bearing and deformation, the conflict often exist between the theory and the reality. The study of the large-diameter over-length pile in the loess area has been mainly to the single pile, systematic research on the over-length pile group was seldom.By means of collecting and reading lots of literature, model test and theoretical analysis, this paper has done a series of studies on the settlement rule and the load transfer mechanism of the large diameter pile group foundation of the loess area, the characteristics of additional stress of the soil under the bearing platform, as well as the cap-pile-soil interaction. Basing on these works,this paper have investigated the influence on the working characteristics of the over-length pile group of the loess area when the groundwater rising. Details including:(1). The model test of the large diameter over-length pile group under the condition of the routine and the groundwater rising has been done in the Geotechnical Engineering Laboratory of the Xi'an University of Architecture and Technology, the parameters of the soil which is used in the model test have been measured by the soil test in the laboratory.(2). By means of model test, this paper studied the settlement rule of the large diameter over-length pile group of the loess area, analyzed the influence on the characteristic of the foundation settlement because of the water content increasing of the bearing stratum and the surrounding soil which is caused by the groundwater rising; By studying of the load transfer mechanism of the super-long pile, this paper gained the distribution law of the axial force, tip resistance and side friction, and researched the influence of the groundwater rising on the load transfer mechanism; According to the test result of the distribution of additional stress under the bearing platform of the lager diameter over-length pile group, this paper got the distribution law and development law of the additional stress of the soil, and also the effecting ofgroundwater on it.(3). Based on experimental data and existing theory, this paper have done initial research on the cap-pile-soil interaction with the lager diameter over-length pile group in the loess area, obtained the characteristic the load sharing between the pile and the bearing platform, the distribution characteristics of the additional stress of the soil under the bearing platform, and also gained the development law of the additional stress causing by the developing of the load and the settlement.