Test And Numerical Simulation Of Seismic-Soil-Pile-Nuclear Island-Interaction

The construction site selection of nuclear power plant has gradually developed from coastal bedrock site to non-bedrock site.The seismic performance of foundation is one of the key problems to ensure the seismic safety of nuclear power plant.Aiming at the earthquake resistance problem of nuclear power station foundation in non-bedrock site,the national major scientific and technological special project "Research on multi-module high-temperature-reactor pile foundation and impact resistance of large aircraft" has set up a special research topic "Test and analysis of pile foundation of multi-module high-temperature-reactor nuclear island plant in non-bedrock site".Under the support of this topic,relevant research with large-scale seismic simulation shaking table test equipment has carried out.In view of the characteristics of high quality and stiffness of nuclear island containment structure,a series of tests and numerical simulation of dynamic interaction of "soil-pile-nuclear island containment" model system in medium soft soil,medium hard soil and hard soil sites in the sense of nuclear power engineering are carried out.The dynamic response law,seismic failure mode and mechanism of nuclear island pile foundation under different site conditions are studied.At the same time,the influence of superstructure foundamental frequency on the seismic response characteristics of "soil-pile-superstructure" system especially on pile internal force is studied by shaking table test.The main work and research results of this paper are as follows:1)The shaking table test scheme of "soil-pile-nuclear island" is studied and determined.The nuclear island containment model,three superstructure models of single degree of freedom with different foundamental frequencies,pile group model and three foundation soil models with different shear wave velocities are designed and manufactured.The static and dynamic parameters of the foundation soil are tested.The dynamic characteristics of nuclear island containment and other test models are measured by shaking table test.The test results show that the test model can meet the design requirements of the test scheme.2)Shaking table tests of "soil-pile group" system and "soil-pile group-nuclear island" system were carried out in three foundation soil models.Kinematic interaction law and inertia interaction law are compared combined with the test data.Test results show that for superstructure with large mass and stiffness such as nuclear island,the inertial interaction between piles and soil plays a dominant role,and the softer the foundation soil,the greater the influence of inertial interaction.In order to deeply study the inertial interaction characteristics of superstructure with different foundamental frequencies,shaking table tests of "medium hard soil-pile group-superstructure" system is carried out with three superstructure models of different foundamental frequencies.Test results show that when the foundamental frequency of superstructure is close to the foundamental frequency of the "soil-pile group" system,the inertial interaction between soil and piles increases and the internal force at the pile top increases.When the foundamental frequency of superstructure is far away from the foundamental frequency of the "soil-pile group" system,the inertial interaction between soil and piles decreases and the internal force at the pile top decreases,and this trend becomes more obvious with the increase of ground motion amplitude.3)The macroscopic test phenomena of shaking table test in three foundation soil models show that the dynamic response and failure phenomena of nuclear island pile foundation model are closely related to the dynamic characteristics of soil around the pile.Under the action of ground motion with amplitude of 0.4 g,the pile foundation was seriously damaged after the test in medium soft soil condition,and only slight to medium damage was found after the test in medium hard soil condition.Under the condition of hard soil condition,when the input acceleration amplitude rose to 0.6 g,the pile foundation was still not damaged after the test.After the test,the pile foundation is excavated for inspection.It is found that the main failure position of the pile foundation is at the connection between the pile top and the pilecap,and the failure forms are mainly shear bending cracks and concrete crushing.In addition,in the test condition of medium soft soil,the outer side pile body breaks at the depth of 5-7 times the pile diameter from the pile top.Combined with the analysis and comparison of test data,it shows that increasing the hardness of foundation soil can effectively improve the seismic performance of nuclear island pile foundation.In the meantime seismic reinforcement should be focused on pile top and the pile body within 5-7 times the depth from the pile top in soft soil foundation.4)The numerical analysis model of "medium soft soil-pile foundation-nuclear island" model of shaking table test is established by using the finite element method,and the corresponding numerical calculation is carried out.The numerical calculation results are basically consistent with the test results which verify the rationality of numerical calculation modeling and calculation.It shows that the finite element numerical simulation method can be used to simulate the seismic response analysis of multi-condition "soil-pile foundation-nuclear island" system,so as to provide a theoretical basis for the seismic design of nuclear island pile foundation.