Experimental Study On Uplift Bearing Characteristics Of Post Grouting Micro Steel Pipe Pile For Transmission Line Tower

Different from the foundation of industrial and civil buildings,the transmission line tower foundation is subjected to wind load,wire tension and other load forms all the year round,the control load is usually uplift load.The traditional cast-in-place foundation can not fully meet the requirements of "quality,speed and quality" of urban power grid construction in the new era because of its large construction area and long construction period.Micro steel pipe pile has the advantages of fast construction speed,flexible layout and high bearing capacity,which has a broad application prospect in transmission line tower foundation engineering.But at present,this kind of foundation is widely used in building reinforcement,foundation pit support and other projects,most of the research mainly considers the compression,bending and other situations,and the research on uplift is rare.Therefore,based on the mechanical characteristics of the transmission line tower foundation and considering the effect of uplift force,this paper studies the uplift bearing characteristics of a new type of post grouting micro steel pipe pile with cone end and enlarged bottom.In this paper,a new type of post grouting micro steel pipe pile with cone end and enlarged bottom is the research object,combined with a variety of test methods to reveal its uplift bearing characteristics.Firstly,the field uplift bearing capacity tests of grouting and non grouting test piles are carried out,and the effect of grouting on the uplift bearing capacity of micro steel pipe piles is analyzed;Then,through the field sampling,the macro characteristic test and micro structure test are carried out to fully understand the mechanical characteristics of the pile-soil interface,and fundamentally grasp the uplift bearing mechanism of the post grouting micro steel pipe pile;Combined with 3D scanning and 3D printing technology,through pouring out cement blocks with the same roughness and remolded soil samples,the overlapping ring shear test is carried out,and the shear failure mode of pile-soil system is analyzed;Finally,based on the results of field static load test,numerical simulation method is used study the influence of different factors on the bearing characteristics of post grouting micro steel pipe pile.he main conclusions of this paper are as follows: the load displacement curve of micro steel pipe pile before and after grouting changes from steep drop type to slow change type,the plastic deformation characteristics are enhanced,and the uplift bearing capacity of micro steel pipe pile before and after grouting is significantly improved;From the change of shear strength parameters and micro level analysis,this is because the infiltration of grout after grouting makes the soil structure more compact and the cohesion increases significantly,forming a certain range of "cement soil",so as to improve the bearing capacity of pile foundation;After grouting,there are two contact surfaces of steel pipe pile cement consolidated body and cement consolidated body soil around the pile,and there are four potential shear failure modes;The results show that the uplift bearing capacity of post grouting micro steel pipe pile increases linearly with the increase of steel pipe wall thickness,and decreases with the increase of belled width;the pre imposed horizontal load will reduce the uplift bearing capacity of post grouting micro steel pipe pile.The research results provide reference for the design and application of micro steel pipe pile in transmission line engineering.