Consequently, the response of vertical fluid reservoirs to earthquakes has been the subject of several studies on fluid-structure interaction [8], and the study of fluid reservoirs remains fundamental to earthquake engineering, e.g., [PERSON] [12], [PERSON] [13], and others. With the development of numerical methods and computer technology, the finite element method has been increasingly used in dynamic analysis [14; 15; 16; 17; 18]. Many experimental, analytical, and theoretical studies have been carried out to describe the phenomenon of water fluctuations [19]. The most practical algorithm for analyzing hot-filled tanks under seismic or harmonic excitation involves some masses and springs to simulate the excitation and vibration modes of the fluid. The mechanical idea proposed by [PERSON] showed promising results for simple methods [4]. [PERSON] extended this research to flexible tanks [20]. [PERSON] [21] studied the dynamic behavior of rectangular liquid tanks' soil/foundation. This simple and fast method represents the interaction of two Hounser masses for liquid and a cylindrical model for soil/foundation. The results show that decreasing soil hardness decreases displacement and soil shear forces. However, embedment, flexibility, and soil-structure interaction do not significantly affect displacement volatility [21]. An analytical method was presented for rectangular tanks to determine the hydrodynamic pressures by solving the classical equations of the streaming potential [22]. This software provides a complete and comprehensive study of the interaction of structure and fluid with a seismic analysis for irregular geometries of slopes and the application of seismic loading as an accelerometer and time history analysis [23]. In other research on the dynamic analysis of rectangular water storage tanks, [PERSON] et al. [24; 25] show a numerical solution method to obtain the dynamic responses of rectangular tanks under the influence of horizontal and vertical soil excitations. In addition, [PERSON] et al. [26; 27] have proposed an iterative solution method to calculate the hydrodynamic pressure on the walls of rectangular tanks, which can take into account the flexibility effect of the walls. [PERSON] and [PERSON] [28] used ANSYS modeling software to solve a three-dimensional problem of the interaction of water and structures with flexible walls using computational fluid dynamics (CFD) tools and finite element stress analysis. [PERSON] studied sloshing in flexible tanks induced by an earthquake using a one-way coupling of the finite element model (FEM) and CFD techniques. He found that the elasticity of the walls increased impulsive pressure [29]. [PERSON] and [PERSON] [30] studied the effects of soil-structure interaction on ground-level cylindrical tanks. [PERSON] and [PERSON] [31] studied elevated tanks and showed that soil-structure interaction is crucial in this tank type. Therefore, fluid-structure and structure-soil interaction studies with FEM interaction using 3D FEM are essential to evaluating rectangular tanks' seismic behavior considering fluid-soil interaction. In addition, liquid storage tanks are generally characterized by low fundamental periods. However, many of these critical structures are in coastal regions with soft soils. Therefore, the seismic behavior of the structure may be significantly different compared to hard soils [32]. Soils can be classified into two categories based on their moisture amount: saturated and unsaturated. The difference between these two types of soils is related to their interactions with water and their mechanical properties. The distinction between saturated and unsaturated soils is essential in various geotechnical and environmental engineering applications, as it impacts the behavior and response of soils under different conditions. Extensive research on the principles of unsaturated soil mechanics has been carried out by researchers in integrated analysis [33; 34; 35; 36; 37].