Numerical Simulation Of Micro-pile Composite Foundation Model Under Hard And Soft Interbedded Mudstone Geological Conditions

With the vigorous development of urban infrastructure in Nanning,the capital of Guangxi,a large number of high-rise buildings and large-load structures have emerged in Nanning.The basic engineering problems involved in such tall,heavy and large construction(structure)are increasingly complex,and the requirements for the bearing layer are also higher and higher.Because the shallow foundation above the Quaternary loose sedimentary layers could not bear such a large superstructure load,the Tertiary mudstone layers replaced the Quaternary layers as the main foundation bearing layer.Due to the particularity of the formation and occurrence environment of the tertiary mudstone and the interaction of various factors such as the disturbance of human activities in the late period,the test parameters of the mudstone have great discreteness and variability,and the mechanical properties of the mudstone often show great uncertainty and fuzziness in practice.The hard and soft interbedded mudstone or the interbedded mudstone in Tertiary has more complex mechanical properties,and the soft mudstone in the hard and soft interbedded mudstone has a great influence on the strength and deformation of foundation.And interbed of hard and soft mudstone related theoretical research is not mature at present stage,the regional regulations and procedures are rare,if only to use general specification and experience,used blindly dig and pile foundation,makes the bearing capacity of shallow of mudstone is not due to play,and deep foundation pit and the pile foundation construction in the water and the effect of artificial disturbance often makes the hidden trouble of the subsoil in great changes of load-bearing characteristics of mudstone,which brings great difficulties to construction and material waste.In view of this,this paper puts forward the design concept and method of cementing the hard and soft interbedded mudstone foundation with grouting micro-steel pipe piles by dry drilling,and analyzes and studies the engineering characteristics of the micro-pile composite foundation.In this paper,the design of micro-pile composite foundation for a high-rise raft foundation is taken as an example to calculate the appropriate pile length and the calculation depth of foundation settlement.Based on this,four groups of36 pile element foundation models are established.First,the settlement values of four groups of natural foundation and two groups of micro-pile composite foundation were calculated by the layered summation method formula.Then,30 models of 36 pile elements were selected for modeling.Then,the finite element software ABAQUS was used to analyze and verify the results.After the study of the small raft foundation model of pile element is extended to the study of the large raft foundation model,the settlement behavior of the foundation is obtained through the analysis of several large raft foundation models.The results show that the bearing capacity of the composite foundation is improved greatly compared with that of the natural foundation,and the control of settlement and deformation is effective to some extent.Therefore,it is feasible to adopt the grouting micro-steel pipe pile to treat this kind of special ground foundation,and the expected purpose can be achieved.Some rules are concluded that the weaker the uniformity of the natural mudstone foundation is,the more frequent the strength changes,the lower the bearing capacity is,and the greater the settlement deformation is.The uniformity of deep hard and soft interbedded mudstone natural foundation under large raft has little influence on settlement deformation;The strength of the bearing layer at the pile end has a certain influence on the bearing capacity and settlement deformation of the composite foundation.Increasing pile length is more effective in controlling settlement.The difference settlement of foundation is obvious,large in the middle and small in the periphery.It is necessary to pay attention to the design of the strength of micro – pile,etc.so as to provide a reference for engineering practice.