# Forecasting Landslides via Three-Dimensional Discrete Element Modeling: Helong Landslide Case Study
## 5 Conclusions  
In this study, we aimed to forecast the failure potential of the Helong landslide, which was temporarily stable but has a high probability of failure. Remote sensing images from different periods show the process of deformation that has occurred in recent years. Based on a field investigation and laboratory tests, the slope stability was calculated via LEM, and the outcome showed that the slope was metastable and may fail under rainfall or earthquake conditions. Then, we used a 3D DEM to simulate a potential landslide and different conditions were discussed. The results showed a potential failure might affect the surrounding road and buildings. DEM simulated the behavior of landslides well.  
Figure 12: Dynamic process of the Helong landslide (friction coefficient = 0.25) with snapshots at different times: (**a**) T = 2 s, (**b**) T = 10 s, (**c**) T = 18 s, and (**d**) T = 25 s.  
Figure 13: Run-out behavior in different parts of the sliding mass: (**a**) position of the monitoring balls and corresponding traces, and (**b**) velocity of the monitoring balls in the whole sliding process.  
Although the findings can be used as an example of the forecasting of the failure potential of landslides, some aspects are worth further exploration and improvement. In the stability analysis under the rainfall condition, we used the natural shear strength for soil above the river table and the saturated shear strength for soil below the water table to calculate the FOS of the slope. The buoyant effect and saturated shear strength could also be considered and incorporated in the calculation of FOS, which is based on statics. However, the effect of rainfall on the slope stability is much more complicated [34; 35; 36; 37], especially for unsaturated soil. Dynamic processes, such as seepage and the variation in pore water pressure from rainfall, affect the slope stability. Determining how to scientifically consider all these factors from rainfall is important but difficult. DEM has some limitations in the simulation of landslides as not all complex landslide mechanisms [38], especially those involving water, such as pore water pressure problems or seepage problems, are considered in the model. Integrating the calculation of FOS and the dynamic post-failure simulation into a model remains an issue. Although DEM can be used to theoretically calculate the FOS of slopes via the strength reduction technique [12; 39], the micro-parameters corresponding to the macro-parameters \(c\) and \(\varphi\) are too difficult to be determined under different reduction situations. Therefore, future studies should focus on the relationship between micro-parameters and macro-parameters.  
Writing--original draft preparation, W.P.; Project administration, S.S.; Funding acquisition, S.S.; Investigation, C.Y. and J.S.; Resources, C.Y. and J.S.; data curation, C.Y.; Writing--review and editing, Y.H.; Software, Y.B.; Formal analysis, Y.B.  
This research was funded by the National Natural Science Foundation of China (grant no. 41702301), opening fund of the State Key Laboratory of Geohazard Prevention and Geoenvironment Protection (Chengdu University of Technology) (grant no. SKLGP2018K017), and the China Postdoctoral Science Foundation (grant no. 2017M611324).  
We very thank for all the editors and reviewers who have helped us improve and publish the paper.  
The authors declare no conflict of interest.