Quasi-static Test Study On Seismic Behavior And P-y Curves Of Nuclear Island Pile Group

Considering the prospect of nuclear power development and the scarcity of high-quality bedrock site resources,nuclear power plants will be developed on non-bedrock sites.If the nuclear power facilities are damaged during the earthquake,it will have disastrous consequences,so the seismic resistance of non-bedrock nucl.ear power plants is one of the key problems in the construction of nuclear power plants.Reinforced concrete pile groups are the main foundation form used in the future nuclear island structure,and the existing design methods can ensure that the superstructure will not be destroyed in an earthquake.Therefore,ensuring the seismic performance of piles is the key to the seismic safety of nuclear power plants.Different from common civil building structures and bridge piles,the superstructure of nuclear island piles has the unique load characteristics of "large mass,large stiffness,and concentrated load distribution,which undoubtedly puts the piles in a working state of high axial compression ratio.In this study,the quasi-static test of a reinforced concrete pile group with a high axial compression ratio is carried out.The response behavior and failure mechanism of a reinforced concrete pile group with a high axial compression ratio under an earthquake are studied.Based on the measured soil pressure and deflection data of piles,the interaction law between piles and soil is analyzed.The main work of this paper includes the following four aspects:(1)The existing methods of pile-soil interaction analysis for single piles and pile groups are summarized and reviewed.The analysis of the literature shows that the quasi-static test can reasonably evaluate the seismic performance of a pile group and analyze the pile-soil interaction.The "p-multipliers" method of pile group analysis based on the single pile p-y curve method is the most widely used method to analyze the lateral load characteristics of pile groups.(2)The quasi-static test of a reinforced concrete pile group with a high axial compression ratio of a nuclear island structure in a soil foundation was designed and carried out.The test results show that the piles of the nuclear island will bend and fail within 5 times the pile diameter depth below the pile top under an earthquake.The horizontal load distribution ratio of each pile in a pile group is calculated by the distribution regularity of strain energy.The failure mechanism of the pile head is revealed by using the simplified model of structural mechanics.The residual strain of the pile body is used to calculate the variation law of pile axial force with the increase in load displacement amplitude.(3)It is verified that although the ductility of reinforced concrete pile groups is obviously decreased by the high axial compression ratio,the high axial compression ratio pile groups can still have certain ductility and seismic performance due to the pile-soil interaction.It provides data support for improving the bearing capacity of nuclear island structures by using reinforced concrete pile groups on non-bedrock sites and expands the scope of nuclear power construction sites.It provides a reference for the follow-up theoretical analysis of the reinforced concrete pile group of the nuclear island structure and the improvement of the national design code.(4)The influence of axial compression ratio on the pile group effect and p-y curves of reinforced concrete pile groups are analyzed.The results show that the influence of axial compression ratio on pile-soil interaction can be ignored.Based on the ideology that the plastic hinges of the pile head will reduce the constraints of the pile group loading system and change the law of reaction quantity,the load displacement amplitude corresponding to the yielding of each pile is determined.