Experimental Study On Interfacial Strength Weakening Mechanism Of Steel Casing And Concrete Piles Core

After the completion of the Three Gorges Project,the role of the Yangtze River"golden waterway" has been further play,inland shipping developing steadily.Since the wharf construction in the reservoir area facing special geological environment and complex hydrological conditions,such as deepwater,large water level difference,shallow overburden or bare rock,new overhead port commonly use steel casing rock socketed pile foundation.Since the current steel-concrete composite pile design theory imperfect.Load transfer characteristics and joint stress by steel casing and core concrete is quite scarce.It combines with the "twelfth five-year plan" of the National Science&Technology Pillar Program of China about "the key technology research of maritime project construction of permanent backwater region of the Three Gorge",carry out the Push-out test,the interfacial shear test to study steel-concrete interface shear bond performance and load distribution mechanism.The main work and results of this paper as following.1.Obtain the average bond strength and the residual bond strength after repeated Push-out test.By 8 group Push-out test,in the range of four mortar strengths,the average bond strength increasing linearly,and the average bond strength exponentially increased.P-S curve of repeated Push-out test shows a linear development,residual bond strength mainly friction.As the plastic deformation of steel casing,P-S curve shows difference between before and after.2.Obtain the bonding strain and bond stress along the axial distribution of the specimens.Before the peak point P-S curve,bonding strain and bond stress along the specimen axial negative exponent distribution;In or close to a peak point,the bond stress redistribution occurs,bonding strain tend to be linear distribution,more average bond stress along the axial distribution of the specimens.3.Theoretical derivation to determine the axial load distribution coefficient and combining with the test data for each load stage steel liners and the pile core mortar assume their respective proportion of axial load.Steel ratio,the lower or pile core concrete elastic modulus is smaller,the greater the axial pressure distribution coefficient of concrete.According to the different methods of loading,to calculate the two steel liners rock-socketed pile the actual service condition of the axial load transfer length.4.Improve the steel liners rock-socketed pile steel-mortar interface shear test apparatus,considering the effects of parameters such as interface roughness and normal stress design for 36 groups.Comparison of the flat type,concave,convex interface in T-S curve and the difference of shear failure mode.All specimens were analyzed characteristics of T-S curve and the influence of the normal stress on the interface shear strength.5.Mohr-Coulomb strength criterion is used to describe the steel-mortar interface shear strength,it is concluded that the variation rule and mechanism analysis of friction angle,cohesive force,coefficient of friction.6.Using hyperbolic model describing the constitutive relation of interface shear bond strength.It provides a theoretical basis of steel casing rock socketed pile interface performance.