Constitutive Model Of Steel-soil Contact Interface And Its Application In The Bearing Behavior Study Of Rock-socketed Filling Pile With Steel Tube

As construction of the three gorges reservoir area ports, rock-socketed filling pile with steel tube was widely used. However, the contact surface of rock-socketed filling pile with steel tube was different from traditional concrete piles. The contact surface of rock-socketed filling pile with steel tube was steel-soil contact, which was different from pile-soil contact and pile-rock contact. Sandtone and Mudstone were widely distributed of the upper region of Yangtze river and the backfilling area of rock-socketed filling pile with steel tube often overburdened by the mixture of sandstone and mudstone. Which mechanical properties were different from traditional sandy soil and cohesive soil. Due to large variation of water level of ports of upper region Yangtze river, the overburden soil was in the process of the cycle saturated and unsaturated all the year round which made the study of the mechanical properties of steel-soil contact surface with the degree of saturation was particularly important.Based on the shear test of steel-soil contact interface, improving the interface direct shear apparatus, the mechanical properties of steel-soil contact interface were researched.According to the test results, the relationships between the grain size distribution, mixture ratio, moisture content, dry density and steel-soil contact interface were analyzed.Meanwhile, the constitutive model which in line with the stress-strain relationship of the contact surface was put forward and the corresponding numerical simulation method was further proposed to study the bearing behavior of rock-socketed filling pile with steel tube.The main work and achievements were obtained as follows:(1)Through the direct shear test of steel-soil contact interface, the mechanical properties of steel-soil contact interface under the different grading, mixture ratio, moisture content and dry density were studied. According to test results, analyzed the relationship between various influencing factors and the interface shear strength index.(2)According to the obtained strain-stress relationship, combining with current research, the amended hyperbolic constitutive model of the contact surface was brought forward, and then the derivation process of the model parameters were also provided. With the analysis of test data, the effects of various factors on the model parameters were discussed.(3) The direct shear test finite element model was established and the implementmethod of contact surface model in numerical simulation was proposed. Through the comparative analysis of the units with thickness, no thickness and different thickness the numerical simulation method of contact elements was determined. Then the numerical simulation and experimental results were compared to verify the correctness of the model and simulation methods.(4) The finite element model of rock-socketed filling pile with steel tube was established and the simulation method of contact surface was applicated in the study of bearing behavior of rock-socketed filling pile with steel tube. Moreover, the effect of rock-socketed depth on the bearing behavior of rock-socketed filling pile with steel tube was researched. Finally, the ultimate bearing capacity results of theoretical calculation and numerical simulation were analyzed to verify the validity of the model calculation. Then,the problems of ultimate bearing capacity calculation in the existing specification were pointed out and the foundation for subsequent theoretical research was lay.