# Study on Filling Material Strength and Dam Failure Characteristics of Loess Dam
## 4 Discussion  
Studying the failure characteristics of loess dams and the mechanical properties of fillers is helpful for exploring the maintainability of water conservancy projects in loess areas and provides a theoretical basis for the maintenance of loess dams, which has important engineering significance. The results and limitations of the study are briefly discussed below:  
1. The failure forms of remolded loess are affected by confining pressure, moisture content, and dry density. Under the conditions of low confining pressure, low moisture content, and high dry density, there is significant shear plane and shear dilatancy. Under the conditions of high confining pressure, high moisture content, and low dry density, the samples exhibited swelling failure, volume reduction, and shear shrinkage. Figure 23: Cloud chart showing the displacement for the third instance of damage. Figure 24: Cloud chart showing the maximum shear strain increment for the third instance of damage. 2. Water content and dry density will change the shear performance of loess, especially the internal friction angle. At a low dry density, the increase in water content causes the internal friction angle to decrease. However, when the dry density is 1.7 g/cm\({}^{3}\), due to the small internal porosity, the movement of soil particles caused by external force will again make the soil particles tightly mesh. When the water content is 10% or 15%, the water film on the surface of the particles is thinner and does not play a significant role. When it is raised to 20%, the water film thickens and the lubricating effect is more significant. When the water content is 25%, the water film inside the sample dissolves a large amount of cemented material, no longer has a lubricating effect, and at the same time resists some external force, so the internal friction angle increases. 3. By conducting a horizontal orthogonal test of the remolded soil sample and a simulation of the progressive failure process of the loess dam, it was found that when the loess dam sheared, a shear failure surface formed. The shear failure surface gradually shifts to the water surface after the loess is washed, and finally, instability occurs. In the shear test, it is found that when the water content is low, it is also easy to form a shear failure surface similar to dam failure, which is in line with the law of the dam's gradual water absorption failure. 4. In this work, the shear characteristics of unsaturated remolded loess are studied. However, in the actual loess accumulation dam project, the shear failure surface of the dam is affected by water pressure and pore water pressure, and the parameters of the undisturbed soil samples of the loess dam may change under the infiltration of water. Therefore, the data obtained in the test may be different from the actual loess dam materials in the case of failure. Moreover, the flow scouring effect of seepage water in the process of dam failure is not considered. Therefore, the conclusion of the test can only be used as a qualitative analysis, which can provide reference for the design, construction and reinforcement of the loess dam. We have studied the improvement of local loess, and a small amount of attapulgite and nano-montmorillonite can greatly improve the shear strength of loess. We also conducted a corresponding study on saturated remolded loess, and monitored the damage process on site. We found that the dam experienced three significant instances of damage during the monitoring period (XU 2020) [23], which was due to the gradual formation of loess via water infiltration. According to the results of the test, we improved the local loess. Adding a small amount of attapulgite and nano-montmorillonite can greatly improve the shear strength of loess (Cao 2021) [24]. N.C.: Conceptualization, Methodology, Software, Investigation, Formal Analysis, Writing--Original Draft; Q.L. : Data Curation, Writing--Original Draft; W.W.: Investigation; D.Z. : Resources, Supervision; X.W. : Writing--Review and Editing; J.X.