# A 3D Two-Phase Landslide Dynamical Model on GIS Platform
However, the actual movement of landslides is often more complicated. Therefore, [PERSON] unified previously employed single-phase models and introduced a versatile two-phase mass flow model. The solid phase stress was governed by the Mohr-Coulomb criterion, while the fluid phase stress was characterized using non-Newtonian viscous stresses. A novel generalized resistance term was defined to discern fluid phases as mixed or separated. This model was applicable to the movement of the majority of two-phase flows [26]. Building upon this, [PERSON] introduced a multiphase mass flow model comprising three distinct phases, described using viscoplastic rheology, in which fine debris can be regarded as the third phase [27]. The depth-averaged model assumes landslides as shallow mass flows; However, questions arise about its validity when abrupt changes occur in the terrain. When encounteringsteep terrain and strong nonlinearity, the most appropriate method is to minimize the simplification of the Navier-Stokes equation, which means that we need to solve the complete three-dimensional Navier-Stokes equation [29; 30]. Some people combine 3D models with depth-averaged models to study the 3D motion of landslides. For instance, [PERSON] employed a depth-averaged model to reduce computational costs in regions with smooth changes of flow variables, while a three-dimensional model was utilized in areas such as the initiation and deposition regions to preserve the fundamental physical characteristics of the fluid [31]. However, the majority of studies involve localized three-dimensional simulations of landslides while adopting a depth-averaging approach for overall solution strategies. Few studies have conducted three-dimensional simulations of the entire landslide motion process. With the continuous advancement of hardware and software, coupled with the rapid growth of numerical and scientific computing techniques, numerical simulations have become the primary method for analyzing landslide motion processes. In practical landslide simulations, which frequently involve extensive geographical regions and copious amounts of geospatial data, the complexity and intricacy of data handling and analysis are notable. GIS effectively addresses these challenges through its advantages in data processing and representation [32; 33]. Notably, the emergence of three-dimensional GIS technology has further amplified the prowess of GIS in data acquisition, processing, modeling, visual representation, and data sharing. This has allowed for improved depiction of surface movement processes within the framework of landslide dynamics models on GIS platforms. For flow-like models on GIS platforms, employing a grid network of Digital Elevation Models (DEMs) is deemed the most appropriate approach. GIS has become the mainstream system for engineering design and urban planning. Many scholars have integrated models related to landslide motion processes into GIS platforms. [PERSON] developed the landslide motion simulation program raavaflow on the GIS platform, which integrates a multiphase flow method based on the depth-averaged theory. The program is currently widely adopted globally [34]. Building upon previous research, [PERSON] developed a three-dimensional landslide surge height calculation extension module on the GIS platform, thereby extending existing two-dimensional models to three dimensions. However, the majority of studies have primarily engaged in two-dimensional simulations of landslide motion processes or confined their investigations to localized three-dimensional simulations on GIS platforms [35; 36]. There is limited research on conducting real three-dimensional simulations of landslide dynamics throughout the entire process based on DEM on GIS platforms. The challenge of constructing a three-dimensional landslide dynamic model based on DEM and visualizing the computational results on GIS platforms remains an unresolved issue.