Study On Failure Behavior Of SDDC Artificial Foundation Due To Water Permeation

Super down hole dynamic consolidation(abbreviation: SDDC)is a new foundation treatment method widely used.However,in recent years,due to the rainfall,irrigation,water leakage and groundwater level changes and other reasons,the artificial foundation accidents after SDDC treatment have occurred frequently,which has led the industry scholars to re-examine it,and even the relevant projects cautiously use SDDC construction method.SDDC construction method has undergone severe tests and doubts.Therefore,based on indoor geotechnical test,direct shear test and triaxial test,the failure mechanism of SDDC artificial foundation(inter-pile soil,plain soil,28-lime soil,37-lime soil)under water is studied in this paper,and the variation law of bearing capacity of SDDC artificial foundation before and after water immersion is analyzed numerically by using finite element analysis software ABAQUS.The following research results were obtained:(1)According to the direct shear test and triaxial test of soil samples,the shear strength of artificial foundation soil samples decreases gradually with the increase of immersion degree.When the degree of compaction is low,the decreasing rate of cohesion of soil samples slows down gradually;when the degree of compaction is high,the decreasing rate of cohesion of test soil samples presents a process of "slow first,fast then slow";therefore,it can be known that the Degree of compaction can effectively improve the seepage of soil,so that the bearing capacity of air foundation can not be reduced more quickly and more in a short time.(2)By numerical analysis of the failure of SDDC artificial foundation under water,it is found that the bearing capacity of the foundation decreases significantly and the settlement increases significantly with the increase of the degree of water immersion.The stress of pile body decreases step by step with the increase of the depth of pile body;meanwhile,with the increase of load,the stress of pile body decreases gradually along the direction of the depth of pile body.In addition,the attenuation curve of foundation bearing capacity is consistent with the attenuation curve of plain soil strength,showing a "first slow,then fast,then slow" change rule,which confirms the accuracy of the simulation results.(3)The numerical analysis of the immersion process of SDDC artificial foundation shows that when the upper load is small,the stress difference between the central pile,the side pile and the corner pile is small;as the load increases step by step,the stress difference between the central pile,the side pile and the corner pile at the same depth gradually increases.When the degree of water immersion is low,the stress of the pile body at the same depth presents that of the central pile > the side pile > the corner pile;when the degree of water immersion increases,the difference of the stress of the pile body at the same depth is very small,and the law of the size of the central pile,the side pile and the corner pile is not obvious;with the increase of the depth,the stress of the pile body and the frictional resistance of the pile side appear negative values,and the pile body produces tension;at the same time,the slope of stress attenuation curve of pile body increases gradually.In addition,with the gradual increase of the degree of immersion,the settlement and settlement difference of the artificial foundation increase gradually,and the local uplift increases gradually.At the same time,the increasing rate of the settlement of the artificial foundation soil increases gradually with the gradual increase of the degree of immersion.(4)By numerical analysis of the influence of SDDC artificial foundation immersion on the upper structure,it can be seen that the raft stress along its length direction is distributed with each row of columns,and the maximum stress occurs at the raft position at the bottom of each row of columns.In addition,with the gradual increase of the degree of immersion,the stiffness of the foundation soil decreases,the restraint of its upper structure decreases,and the secondary stress decreases,so the stress of the upper structure is smaller.When the degree of immersion increases again,the bearing capacity of the foundation soil will be completely lost,and the deformation of the upper structure will be too large,and the overall stress will increase.