Experimental Study On Effect Of Coating On Negative Friction Resistance Of Steel Pipe Piles

In the pile foundation project,when there is a large surface area piled on the ground and the groundwater level suddenly drops,the pile will produce an upward displacement with respect to the soil,and the negative friction resistance problem will emerge,which often affects the safety of the pile foundation.In the project,load preloading method,electroosmosis method,casing method,coating method and other measures are often used to reduce and eliminate the negative friction resistance on the pile side.Coating methods are widely used due to their economy and effectiveness.At present,there is still a great deal of deficiencies related to the specific application of the coating method in engineering practice.To determine the type,thickness,and application range of the coating in practical applications,and to fully understand the effect of the loading For the performance of coated single piles and coated piles,DSJ-2 type electric quadruple strain and other direct strain shears are used.The commonly used pile materials(concrete,steel and wood)and different coating materials(petroleum pitch)are used in the project.A series of soil-structure and soil-coating-structure interfacial friction tests were performed on a variety of coating thicknesses(1mm to 5mm).Based on the test results and finite element analysis,the friction properties of the soil and the different structures at the contact interface,the vertical bearing behavior of the single-pile steel pipe under different loading conditions,and the coating application range of the coated steel pipe piles were studied.The main conclusions are as follows:(1)The friction coefficient between soil and structure is influenced by the structure,coating and coating thickness.The asphalt coating can significantly reduce the shear stress on the contact interface,and it should be used as a friction reducing coating.When the coating is the same type,the friction coefficient at the contact interface is basically consistent.(2)Applying asphalt coating on the surface of pile body from pile top to around 0.6l area(negative friction zone),the negative friction resistance,pile driving load and axial force of pile body can be reduced significantly.The negative friction resistance of the single pile on the single pile side is affected by the number of friction system,the range of coating and the load grade of the coating.(3)Under the condition of corner piles and side piles,the effect of maximum axial force reduction of piles has been very significant,reaching about 10%.The results of the comprehensive test and the finite element analysis put forward the following suggestions for the engineering practice: the best effect of applying the oil asphalt coating on the side of the0~0.6l area below the surface of the pile to reduce the negative friction resistance of the pile side.