Study On The Influence Factors Of Compressive Bearing Behavior Of Root-Caisson Foundation

The root-caisson foundation is a new form of bionic foundation,which is based on the caisson foundation and combined with the design philosophy of the variable cross-section foundation.Root holes are reserved in the wall of a well,and then jacking roots with multi-head push device,at last,pouring concrete to the gap between the caisson wall to make roots and the caisson form a whole.In this paper,the indoor model test and numerical simulation are used to analyze the stress characteristics of the root-caisson foundation under vertical load.The main research work and related achievements are as follows:(1)The vertical loading tests of caisson and root-caisson foundation were carried out,and the vertical load-displacement,internal force of wellbore and earth pressure at well end of caisson were monitored.The results show that compared with the caisson foundation,the root-caisson foundation can effectively improve the bearing capacity and reduce the settlement of the foundation.(2)The influence of different root layers,root position,root number,root length,section form and root inclination angle on the vertical stress characteristics of root-caisson foundation were discussed.The results show that the reasonable increase of the number and length of roots and the reduction of the radial distance between roots of the same layer can expand the influence range of the root on the soil,effectively improve the bearing performance of the foundation,and reduce the settlement.When the roots are arranged along the bottom of the well,the reaction force of the bottom soil is large,and the supporting effect of the soil on the foundation is better,compared with the overall arrangement of the roots,the bearing capacity of the foundation is larger.Compared with the circle root section form,the square root section form can improve the bearing capacity of the foundation.Compared with the inclined arrangement of root,the horizontal projection surface of horizontal arrangement of the roots increase,the compaction effect on the lower soils is strengthened,and the vertical bearing capacity is greater.(3)Using digital image processing technology obtain the variation regulation of soil displacement field around the caisson.The results show that with the increase of load,the vertical displacement of soil at the well end of caisson is the largest,and the horizontal displacement field with conical distribution is formed below the well end.The failure mode of the caisson foundation in the sand is local shear failure.(4)The numerical model of root-caisson foundation under vertical load is established by FLAC3D finite difference software,and the displacement field change of the root-caisson foundation and the stress characteristics of the root are analyzed.The results show that the position near the wellbore on the root has the largest force,and the force decreases gradually along the radial direction.When the load is small,the upper roots of the caisson bear most of the load,and its root has a relatively large degree of deflection.With the increase of the load,the load sharing ratio of the middle and lower root continues to increase,and the corresponding deflection degree of the root increase.Appropriately increasing the layer of roots,the number of root in the same layer,the length of root and arranging the roots along the bottom of the well can improve the load proportion shared by the roots of the root-caisson foundation,so as to improve the overall bearing capacity of the root-caisson.