Study On Working Behaviour Of Composite Foundation Of Geogrid And Rammed Soil-cement Tappered Column With Lateral Constrain Under Cyclic Loading

As the composite foundation treated with geogrid and rammed soil-cement tapered pile with lateral constraint structure has good working characteristics,it’s very significant to study its performance under cyclic loading.On the basis of summarizing the research situation at home and abroad and sponsored by NSFC（51108716）,studied the working behaviors of reinforced cushion and the composite foundation of geogrid and rammed soil-cement tapered piles with lateral constraint structure under cyclic loading through a method that combines model test in laboratory and FLAC^3D numerical analysis,the main contents and conclusions as follows:（1）Based on the laboratory model test of reinforced cushion with soft foundation under cyclic loading,discussed the regularity of the foundation settlement characteristics with cyclic times and cyclic stress ratio under different thickness cushion and geogrid layers.The results show that,when the cyclic times is less than the critical cyclic times,the settlement of soft soil increases nonlinearly with the increase of cyclic times,but the settlement of soft soil tends to be stable along with the increase of cyclic times.In the same condition,the settlement of soft foundation decreases with the increase of the thickness of cushion or geogrid laying layers.（2）Based on the results of laboratory model tests of the composite foundation of geogrid and rammed soil-cement tapered piles with lateral constrain under cyclic loading.Discussed the influence law of the lateral constraint,wedge of pile,reinforced cushion,cyclic times and other parameters on the settlement or stress of pile tip and soil.Obtained the law of the axial force of pile along the depth and cyclic times.Experiment results show that,under cyclic loading,the composite foundation working behaviors will be improved by adding to the lateral constrain,laying geogrid and adopting rammed soil-cement tapered piles;and the settlement difference between pile and soil is nonlinearly increases first and then tends to be stable with the increase of cyclic times;the axial force of soil-cement tapered piles first increases then decreases with the increase of depth,the maximum axial force of pile lying in 1/4position of pile length,axial force of pile shows the same tendency with increase of the cyclic times,but the amplification is decreased.（3）Established the calculation model of composite foundation by using FLAC^3D,and verified the rationality and reliability of the numerical model by the laboratory model test results.Considered the influence of related design parameters on the working behavior of composite foundation,analyzed the influence law of the position and modulus,rammed soil-cement tapered pile distance,wedge angle and on settlement performance of composite foundation under cyclic loading.The optimum design parameters of composite foundation have been obtained as follows:the modulus of constraint pile ranges from 50 MPa to 500 MPa,the optimum wedge angle of rammed tapered pile ranges from 0.48° to 2.2°,the modulus of rammed soil-cement pile ranges from 60.67 MPa to 606.7MPa.