Research And Analysis On The Model Test Of Stiffened Micropile Under Circulating Load

Micro-pile has been widely used in engineering practice,which can carry load of the static and dynamic in axial or lateral direction, its work behavior involves the interaction between pile, soil and pile cap. The working characteristics of Micro-pile under Lateral load is relatively complex, especially under the lateral circulating load.This paper firstly introduces the latest development situation of the micro-pile at home and abroad,and then introduces the results of research pile under lateral circulating load.The physical model test of single stiffened micro-pile and group stiffened micro-pile were selected in this paper,the hysteretic characteristics and the mechanical characteristics of stiffened micro-pile under circulating load were systematically analyzed. The results showed that, the load-displacement had have the stable hesteretic curve and the characteristics of the stiffness degradation; the separation effect between the micropile and soil was happened in the upper soil under the lateral circulating load, and the force model of micro-pile will change, which change from winkler foundation beam into a cantilever beam gradually. The atrophy phenomenon was found in the hysteresis curve. When the load is lesser, hysteresis curve first showed for spindle shape,with the load increase, the shape of hysteresis curve be formed into the bow, finally into the z shape. At the model test of micro-pile group, the bending moment was happened on the top of the micro-pile while the top of the pile were embedded; under circulating load, the influence depth is smaller than the top of pile were free. The connection with pile and pile cap have significant influence for pile stress condition.Established numerical analysis model of single pile by FLAC3D,which could reflect the deflection of pile and the rule of lateral soil reaction. After determining the parameter is adopted, by changing two factors which are pile body length and pile body stiffness to found the influence law of micro-pile under circulating load. Then establish a model of micro-pile group. To analysis the influence of embedded solid on pile top for the internal force of pile. At the same displacement, with the increase of bending stiffness of micro-pile, the displacement of most value trends down and the maximum bending moment increases; when pile body stiffness reaches a certain value, the bearing capacity increase a little, but the trend of further improving have reduced, horizontal bearing capacity can not get large improvement while increase stiffness blindly. The maximum bending moment was located below the top of the pile with the 0.25m distance of micropile in different aspect ratio. Aspect ratio have no influence with the position of the maximum bending and the dangerous cross-section, and the maximum bending moment have a little change, the maximum bending moment of pile length less influence for maximum, piles of dangerous section has nothing to do with the pile length.