Research on Load Transfer Character of Pile in Expansive Soil Foundation
|Keywords||Expansive soils Pile Load transfer Pile friction Shear displacement method|
Many engineering examples and studies have shown that, in the expansion land construction projects in the region, using the pile foundation can effectively reduce the impact of expansive soil expansion and contraction changes on the deformation of the upper structure. Expansion of the land base generated due to changes in the water content of the pile the uplift or negative skin friction, causing uplift of the pile, the pile and pile cap Void may even pull off the pile, resulting in damage to structural integrity. According to statistics, the country each year due to expansive soil caused the destruction of a large number of municipal, civil engineering and transportation facilities, the direct economic losses of up to billions of dollars. Therefore, it is necessary to carry out a systematic study is also very urgent expansive soil. Based on the research status at home and abroad on the expansion of the land base in the pile, on the basis of comprehensive analysis, combined with research projects of the National Natural Science Foundation of China, this paper carried out the research work pile load transfer characteristics of expansive soil. By laboratory experiments, model test, the theoretical analysis and numerical simulation method of combining the research, the main conclusions and innovative research results for the following aspects: 1) based on one-dimensional consolidation of laboratory experiments to study the deformation of expansive soil with the time variation of the following results: (1) expansive soil bearing linear expansion rate and the Netherlands linear expansion rate versus time curve is different: the former development process approximation is divided into two stages, in the semi-logarithmic coordinates found hyperbolic relationship; process approximation of the development of the latter is divided into three stages, more suitable for use logarithmic function will be described in the same coordinate. ② expansive soil line shrinkage in double logarithmic coordinates and time almost linear relationship. Further with the corresponding function of the deformation curve fitting, accuracy is very good. On this basis, from the physics point of deformation mechanism of expansive soil depth analysis expansive soil in the pile - soil interaction research laid the foundation for change over time. 2) through improved indoor direct shear apparatus Nanning expansive soil in contact with the concrete surface friction test direct shear explore the vertical pressure, the impact of factors such as moisture content, dry density and mechanical properties of the contact surface. The research shows that: the most important factors affecting the shear stress change is the dry density, the most important factors affecting the residual shear stress change the moisture content. Based on experimental data and the literature, the analysis of the sensitivity of various factors, help to raise awareness and understanding of the expansive soil structure interaction mechanism, and also to deal with expansive soil problems and continue to study the expansion of the soil in the pile - soil interaction basis. 3) through the pile foundation model test, from the the Ps curve, axial force, skin friction, tip resistance and pile side, tip resistance load allocation study and analysis of the expansion of the land base in pile load transfer characteristics simultaneous contrast the similarities and differences of the load transfer expansive soil and clay in a pile, and contribute to a better understanding of the expansive soil pile load transfer law. 4) through the expansion of the model test of the soil pile foundation flooding from deformation and force both explore flooding process in the pile - soil interaction mechanism. Focus on the axial force, lateral friction and the variation of the neutral point, and proposed design pile length can be obtained by solving the positive, negative skin friction balance equation, at the same time get a pile of soil deformation schedule features The experimental and theoretical basis for further pile - expansive soil together the numerical simulation analysis. 5) based on the pile - soil interaction mechanism, the first time the use of shear displacement method were established elastic differential equations for the expansion and contraction of single pile load transfer in the top of the pile load and expansive soils, and the principle of superposition HIGHWAY expansive soil The analytical solution of the single pile load transfer under the foundation expansion or contraction. The results of theoretical analysis and experimental results agree well. 6) on the basis of the above research, the preparation of the corresponding analytical procedures, numerical analysis of the pile in the expansion of the land base load transfer law, the following conclusions and results: with increasing pile length, pile uplift displacement decreases, and the tension increased. ② buried expansion affect deeper below the depth of the small diameter of the pile (d lt; 0.043L) can effectively reduce the displacement of the top of the pile in expansive soil. ③ pile displacement and axial force with the expansion of the Soil and table the amount of expansion increases. ④ the top of the pile load increase will change the direction and size of the pile displacement and axial force; prevent piles required for the upward movement of the top of the pile load is about the maximum tension in the pile were not loads of 2.5 times. ⑤ pile displacement and axial force with flooding extension of time increases, but the increase is getting smaller and smaller, until Expansive Soil stabilized, the pile displacement and axial force will stabilize.