Systematic Similarity Design Method For The Dynamic Model Test Of Multi-Medium Coupling And Preparation Of Similar Material For Contact Interaction

Dynamic model testing,as a crucial support for engineering seismic design,holds great significance in the design of various large-scale projects such as buildings,dams,sea-crossing bridges,and metro tunnels.These projects rely on the reference of physical model test results to ensure their seismic performance meets the required standards.With the development of China’s socio-economic landscape,the simulated objects in model testing are progressively becoming larger and more complex.Furthermore,the research subjects inherently involve intricate coupling effects among different mediums.However,the existing model test similar design methods based on dimensional analysis theory encounter several challenges when applied to dynamic model tests.These challenges include a significant disparity between the theoretical similarity ratio and the actual test conditions,the inability to adequately account for the engineering characteristics of each substance,and the difficulty in achieving a realistic simulation of contacting and coupling interactions between different mediums.To solve the above problems,it is necessary to innovate from the theoretical level of similar design.Based on the theory of separated dimensional analysis,the systematic similarity design method has been established,which is more suitable for dynamic model tests with multi-medium coupling effects.This method divides the entire prototype system into multiple secondary subsystems,which have a multi-medium coupling effect.Then,the similar design is carried out based on the characteristics of each secondary subsystem itself,and the contact coupling between mediums is considered as an individual subsystem.In order to verify whether the systematic similarity design method can improve the simulation accuracy of the model test,the shaking table model tests of soil-underground pipe gallery dynamic interaction were carried out.The following conclusions can be drawn from the above work:（1）When using the system similarity design method of dynamic model testing,the mediums of the overall system,the contact interaction between mediums,and the input ground motions can be used as criteria for dividing subsystems.The overall system of the soil-underground pipe gallery can be divided into the soil subsystem,pipe gallery subsystem,input ground motion subsystem,and soil-underground pipe gallery contact interaction subsystem.（2）The surface roughness of soil or underground pipe gallery structures has a fractal feature of self-similarity,which is independent of the observation scale.The contact of soil-underground pipe gallery is"the rigid body-elastic body contact model".In a similar design,the key parameters are the ratio R₁/E₁of the average radius to the elastic modulus of the slightly convex body on the soil surface,the soil confining pressure P,the fractal dimension D of the rigid body contact surface,and the observation scale Q.（3）The three-dimensional box-counting method is used to measure the fractal dimension of the structural surface.The surface roughness can be reflected by the gray values of each pixel in the micrograph of the structural surface extracted by MATLAB.Through measurement and calculation,the fractal dimension of the concrete surface on the underground structure surface is 2.0631.The proportioning test was carried out,using fractal dimension as the main index,selecting graded fine sand,cement,and water as similar materials.Finally,the ratio of similar materials on the contact surface is graded fine sand:cement:water=2.5:3.33:1.（4）In this study,two shaking table tests were designed.Through comparison,it can be seen that the system similar design method has no obvious advantages in simulating the acceleration response of underground pipe gallery structures.However,in terms of simulating the strain response of underground pipe gallery structures,the system similar design method has obvious advantages,which can more accurately reflect the true laws of the prototype.