The Force Performance And Nonlinear Damage Creep Model Of Soft-cut Pile Head Concrete Were Studied

When pouring the pile top on the concrete perfusion pile,it is possible to drain the pile top mud by way of over-filling,to ensure that the top quality of the pile will not be affected by the mud,and the super-filling pile head is broken by labor or machinery in the subsequent construction process,it is difficult to ensure the quality of the pile head,which can easily affect the construction progress.The new soft-cut pile head construction method,based on the principle of water ejaculation,can avoid the technical defects of traditional pile-breaking head,but the effect of this technique on the strength of pile head concrete needs to be scientifically verified.Among them,the creep characteristics of pile concrete and the evolution of the properties of the force when creeping have an important impact on the safety of the use of building structures.Based on the test comparison of core patterns under different forming environments of soft-cut pile head concrete,this paper explores the trend of creep under different loads,and builds a new nonlinear creep damage model on this basis,and systematically studies the creep characteristics of soft-cut pile head concrete.The main research contents and achievements of the thesis are as follows:(1)Comparing the soft-cut pile head coagulated pile head concrete sampled on site with the laboratory maintenance concrete,the performance of the three-axis compression test in the simulated pile head service conditions was compared.The evolution trend of damage in concrete under different stresses is discussed in the partial stress-strain curve of the test part.Through the three-axis compression test under different pressure,the effect of pressure on concrete pressure strength is discussed.Comparing the parameter size and discreteness of the extreme pressure strength and elasticity model of each group of concrete,the feasibility of the soft cutting pile head method is illustrated.(2)Based on the average pressure strength of each group of test pieces in the three-axis compression test,the graded loading creep test is designed,the first stage load is 60% of the average pressure strength and the load rung is 10% of the average pressure strength.Through the creep test under load at all levels,the creep rate curve and transient strain curve are obtained,and the creep evolution law of each group of concrete under load at all levels is analyzed.Among them,the creep evolution trend of the pile top height and the cumulative creep variable of the laboratory maintenance concrete are close.(3)Starting from the classical creep-based equation of fluid dynamics,a nonlinear viscous element based on fractional equations and damaged forces is introduced,and the creep equation is constructed in stages for the characteristics of concrete creep curves,which is combined with the principle of overlay to obtain a nonlinear one-dimensional-based model that can describe the whole process of creep.According to the definition of elastic force pair,the force state of the test piece is represented in the form of stress and strain,and the one-dimensional creep model is extended to the three-dimensional form.(4)Comparing the experimental data with the model in this study shows that the model can better reflect the creep development trend of soft-cut pile head concrete,and on this basis,the general applicability of the model is verified by other research data.Based on the construction characteristics of the corresponding segments and the parameters in the model with creep test data,the creep data and model curves under loads at all levels are compared,and it is proved that the model can have a good reflection on the full-process creep characteristics of concrete under three-axis stress,which can provide reference for the quality identification and safety evaluation of the coagulation structure.