# Bridging Macro-Microscopic Parameters: Correspondence and Calibration Approaches
However, certain parameters, like tangential stiffness and normal stiffness, cannot be directly acquired through experiments due to their less intuitive connection with macroscopic parameters [19]. These parameters, which lack intuitive determination methods, often exhibit significant uncertainty in their values, thereby leading to a reduction in the accuracy of simulation results. Therefore, there is an urgent need for a method to effectively determine the values of these parameters (such as normal stiffness and tangential stiffness), which cannot be efficiently obtained from experiments, in order to effectively calibrate the microscopic parameters required for numerical simulation. Currently, global research on the correspondence and calibration methods of macro-micro parameters of sand materials is predominantly focused on rock materials [20], clay materials, and mineral materials [21; 22]. Some studies rely on empirical values [23], which to some extent undermine the reliability of simulations. Generally, research on material parameter calibration can be classified into several types. First, methods like those of [PERSON] et al. (2021) rely on triaxial tests and employ trial-and-error approaches for material parameter calibration [24]. Although this method is relatively straightforward and demonstrates good correlation between simulation and experiment, it often necessitates a large number of simulation tests [18; 25], resulting in lengthy and somewhat illogical simulations. Second, approaches similar to that of [PERSON] (2007) are based on uniaxial compression tests for material parameter calibration, optimizing the calibration process through methods such as screening test designs and central composite designs [14]. However, their generality for specific material parameter calibration is limited. Third, methods like those of [PERSON] et al. (2019) are based on the cellular automata method for material parameter calibration and propose a calibration process for the microscopic parameters of rocks [26]. This type of method often exhibits clear logic and good repeatability [27]. The aforementioned three types of research primarily concentrate on rock materials, thus leaving a gap in the systematic study of small particle media such as sandy soil, as well as in the development of reasonable and effective calibration methods. However, the calibration of microscopic parameters often has a significant impact on the reliability of simulations. Therefore, there is an urgent need to propose a method that can reasonably and effectively calibrate the microscopic parameters of sand-like materials. This paper focuses on studying the correspondence and calibration methods of macroscopic and microscopic parameters of sandy soil. Through four types of experiments, namely interparticle friction tests, friction angle tests, uniaxial compression tests, and direct shear tests, as well as three types of simulations including numerical simulations of uniaxial compression tests, numerical simulations of direct shear tests, and numerical simulations of pile-up tests, the correspondence between macroscopic and microscopic parameters of sandy soil is analyzed. Furthermore, empirical formulas and calibration methods for sandy soil parameters are proposed.