Experimental Study On Stability Of Large Diameter Steel Pipe Pile Under The Condition Of Surrounding Soil Excavation

With the continuous advance of China's urbanization process,many existing buildings due to lack of underground parking lot and other facilities,the use of functional defects has become increasingly prominent,the development of both the construction and utilization of underground space has attracted more and more attention.In the case of the existing building,the original pile foundation or the new pile foundation should be used to bear the load of the existing building.In the process of excavating the soil around the pile,the stability of the pile foundation is obviously reduced.Steel pipe pile foundation is one of the most common forms of pile foundation.It is of great significance to study the stability of steel pipe pile by means of large scale model test.In order to carry out the model test,the 2.5m×2.5m×3.0m geotechnical model box was designed and manufactured.The utility model is composed of a vertical steel plate which is surrounded by the periphery and a horizontal hoop which is connected with the periphery through bolts.The angle steel of the four big horns of the model box is fixed with the adjacent vertical steel plate through bolts,and the temporary skeleton of the model box can be formed,and the soil filled in the box can be prevented from leaking along the joint of the two steel plates.This paper presents the design method of the vertical steel plate,the horizontal hoop and the connecting bolt of the model box.In this paper,the stability of the pile body under the condition of soil excavation of large diameter steel pipe pile is studied.Through model experiments,(1)of the soil around the pile in the pile and the supporting conditions than the load strain variation of different excavation;(2)by changing the radius of gyration,eccentric distance,support position of steel pipe pile,the number of support,support stiffness,excavation ratio and other factors,obtained the pile buckling ultimate load and the analysis of different factors on the stability of the pile body;(3)reliabilityverification group proposed virtual fixed point theory in large scale steel pipe pile under the condition;(4)the calculation method of pile bearing load to verify the proposed.Based on the test data analysis shows that(1)when the axial compression,the maximum strain near the pile end,eccentric compression,close to the maximum strain at the top of pile;load in a certain range,the strain of the pile and the support strain is linear,the supporting strain is 1/4~1/5 times the pile should be changed,in the destruction of at times the value generated mutation;(2)for large scale steel pipe pile,the stability of the virtual test fixed point method and numerical research group proposed a consistent,verify the reliability of the virtual fixed point method;(3)when the excavation is small,the buckling failure point now pile soil near the contact surface,with the excavation ratio the increase of the failure location gradually close to the pile top;(4)the bearing capacity of eccentric compression of pile body has great influence,the offset is 40 mm and 80 mm,the ultimate load on axial compression,were reduced by 50% and6 5%;(5)applying the level of support can significantly improve the ultimate load of pile,the pile support set in the central role to improve the ultimate load is more significant,that weak link close to the middle position close to the pile body;(6)the excavation is small,the radius of gyration increases,increase the ultimate load of steel piles(8)method is proposed to calculate the ultimate pile load of steel pipe pile,through to verify the reliability of this calculation method and experimental comparison.