The Load Bearing Characteristic Of The CFG Pile Composite Foundation Under Large Oil Tan In Saturated Loess Ground Treatment

West crude oil & product pipeline works is another important construction project afterwards West-East natural gas transmission project at the beginning of 21 centuries in West China. This paper serve one major project of the pipleline works namely Lanzhou Terminal 15×10~4m~3 large oil tanks as engineering background. Based on saturated loess, theoretical study and Engineering Practice of Cement-flyash-gravel(CFG) pile composite foundation for saturated loess treatment is Introduced.Firstly, this paper has summarized the saturated loess and the development and research of ground treatment in large oil tanks. It also has retrospective studied the application, development research of CFG pile composite foundation and the deformation of foundation under oil tank due to preloading by water filling method. Meantime, the reinforcement mechanism of CFG Pile in loess is also mentioned.Secondly, the engineering geological characters of the project are analyzed in detail, the construction technique and the design parameters of the CFG pile composite foundation such as the length, diameter, spacing and plane layout of piles are determined according to the conventional method. The quality of the CFG pile and the effect of reinforcement are analyzed according to the field test, the laboratory test and the low strain reflection wave test results. The feasibility and validity of CFG pile composite foundation under large oil tan in saturated loess is also verified.Thirdly, by organizing and analyzing the field measurement data, the annular wall foundation settlement deformation, the settlement of CFG pile composite foundation, the pore water pressure and the stress distribution of pile and soil under load by water filling method are analyzed according to the test results. There is differential settlement under the tank. The stress of pile under the center of tank is largest, the stress of pile under the annular wall foundation takes second place, the stress of pile between them is small. The stress of soil changes not necessarily. Because of the permeability of cobble layer under losses, the evanescence of the pore water pressure resulted of external loads is accelerated, and the change range of the pore water pressure in the process of preloading is small.As we all know, there are a number of influence factors of the CFG pile composite foundation's load bearing properties, such as: load level,, the thickness and material of cushion layer, the length and compression modulus of pile, etc. Moreover, the cushion layer technology is a core one in CFG pile composite foundation. It is able to adjust the pile-soil stress ratio and to achieve pile-soil work unitarily. Ultimately, using ADINA finite element to analysis the above-mentioned influence factors of the CFG pile composite foundation's characteristics of bearing capacity and subsidence. Research indicates that the above-mentioned factors exercise a great influence on the distribution of pile stress and side friction. Research also indicates that the pile-soil stress ratio has respective relation with the above-mentioned influence factors.Along with engineering construction development, The general loess distribution area will has a new construction high tide. So the research of the losses treatment, especially the saturated loess treatment and its construction methods are an important subject. It has wide application future. It would make great contribute to engineering if we discover the subject actively.