Study On Mechanical Properties Of Ram-compacted Piles With Bearing Base In Clay Bearing Layer

Ram-compacted piles with bearing base is a new type of pile foundation,which have the advantages of high bearing capacity,short construction period,good pile quality,environmental protection and low cost.In order to make ram-compacted piles with bearing base more widely used,it is necessary to clarify the bearing mechanism,load transfer mechanism,factors affecting the bearing capacity.However,when the spacing of ram-compacted piles with bearing base is not suitable,the lateral earth pressure generated during the formation of the rammed body will seriously affect the quality of adjacent piles.It causes the separation of the pile body from the hard concrete body.Such accidents occur frequently in the construction process.In order to avoid such accidents,this paper studied the optimal pile spacing of ram-compacted piles with bearing base in the clay bearing layer.Reasonable suggestions were put forward for the design and construction of ram-compacted piles with bearing base.Based on the engineering project of a coastal city,this paper applied the methods of finite element analysis and theoretical analysis.A large number of engineering practice rules were combined to study ram-compacted piles with bearing base.The main research contents are as follows:(1)The three-dimensional finite element model of the ram-compacted piles with bearing base and the soil around the pile was established by using ABAQUS software and the correctness of the model was verified by comparing the numerical simulation results with the field test results.(2)Under vertical loads,the mechanical properties of the ram-compacted piles with bearing base were analyzed by numerical simulation.The distribution law of axial force of the pile,the distribution law of frictional resistance at the side of pile,the distribution of total resistance at the end of pile and the influencing factors of vertical bearing capacity were studied.It is verified that ram-compacted piles with bearing base belong to end-bearing pile.In view of the length and diameter of the pile in this project,reasonable suggestions were put forward.The optimal rammed body diameter of the ram-compacted piles with bearing base is 800~1000mm.(3)Under horizontal loads,the mechanical properties of the ram-compacted piles with bearing base were analyzed by numerical simulation.The variation laws of horizontal displacement,bending moment,shear force,deformation of soil around the pile and the influencing factors of horizontal bearing capacity were studied.It is concluded that the ram-compacted piles with bearing base belong to long elastic pile.By changing the diameter of the rammed body,the horizontal bearing capacity of the ram-compacted piles with bearing base in this project can not be significantly improved,However,when the ram-compacted piles with bearing base is short,increasing the diameter of the rammed body can greatly reduce the horizontal displacement and significantly improve the horizontal bearing capacity.(4)Under combined loads,the mechanical properties of the ram-compacted piles with bearing base were analyzed by numerical simulation.The bearing behaviors of the pile under combined horizontal and vertical loads were studied.(5)Combined with the stress diffusion theory,the mutual disturbance of the rammed body was considered,it is concluded that the rammed body will move upward and outward,when ram-compacted piles with bearing base is disturbed by the surrounding pile.The optimal pile spacing of the ram-compacted piles with bearing base in this project is 2.4m.On this basis,by gradually changing the diameter of the rammed body,the analytical relationship between the optimal pile spacing in the clay bearing layer and the diameter of the rammed body was obtained.