Long-Short Piles Composite Foundation Stress And Settlement Analysis

In the recent years, with the research about the foundation treatment technology and composite foundation theory deepening at home and abroad, the new foundation treatment way of long-short-pile composite foundation is developed. Just according to the pile which is rigid and flexible combined way, the long-short-pile composite foundation treats foundation. Not only can coordinate the pile soil deformation, reasonable play its bearing capacity, but also it can optimize the design of the scheme, save the investment, shorten the time limit for a project and so on. At present, for the new type of composite foundation, theory research fall behind the practice, and the understanding of the basic mechanical properties is not enough in-depth and comprehensive.Take advantage of the unity of the rigid long pile and the rigid or semi-rigid pile or the flexible short pile, the technology treat the ground synthetically, and also it lays down the flexible cushion so that the long pile-long pile-earth-pile cap act together. Generally speaking, the short pile mainly carries on processing to the soil body, enhances the supporting capacity of ground. The long pile not only can increase the ground supporting capacity, but also it can control the whole settlement which is more important. This foundation approach, in fact, is a new type of foundation approach developed by our country’s engineers and technicians who consider Chinese national conditions and constantly sum up experience of the past.The theory of long-short-pile composite foundation falls far behind the project practice. In order to study the distortion characteristic and sedimentation analysis of the long-short-pile composite foundation, using the FLAC3D finite element analytical procedure, this article establishes the model of long-short-pile composite foundation, and carries on numerical simulation of the long-short-pile composite foundation about the distortion character, in order to provide the rationality theory basis of this kind of compound ground form, and strengthen further the understanding for its mechanism and the promoted application.Based on the foundation of the fundamental model, this article analyzes the distortion characteristics of the long-short-pile composite foundation by changing the load value, pile’s module, pile’s body length, cushion thickness. Through the analysis and the fundamental research, the conclusion is followed:Firstly, the maximum stress points appear on the top of short pile, and the stress decreases along the depth.Secondly, an important feature of the stress of long pile along depth is that the point of maximum stress is not on the top of long pile, but in a certain depth under the top of long pile. The stress of pile gradually increased along the depth upon this point while decrease below it.Thirdly, with the length of long pile increasing, the settlement of long pile and short pile decreases corresponding, the stress of long pile will increase, but the rate of increase is getting smaller and smaller, showing that there is an effective pile length of long-pile body.Fourthly, as modulus of long pile increases, the settlement of pile cap, long pile and short pile decreases, but the rate of decrease is getting smaller and smaller. The stress of long pile gets greater and greater, showing that the stress concentration of long pile is more obvious and the load on the long pile is greater.Fifth, with the thickness of layer increasing, the settlement of long pile also increases; the maximum stress of pile cap and long pile decreases, but the changes is more and more indistinct.An engineering case is analyzed, compared the theoretical calculation results with the monitor in site, the close results testify the applicability of the long-short-pile composite foundation, and have important engineering value in further analysis and application to the long-short-pile composite foundation.