# Research Progress in Methods for the Analysis of the Internal Stability of Landslide Dam Soils
## 2 Qualitative Identification of Internal Stability Based on Physical Properties of Soils
### Identification Based on Characteristic Particle Size  
Among these identification methods, representative ones include those proposed by [PERSON], [PERSON], [PERSON] and [PERSON], and [PERSON], as shown in Table 1. The Istomina Identification method considers the coefficient of uniformity \(C_{u}\) as a control variable to determine the internal stability of soils [30]. For soils with \(d_{10}>0.5\) mm or \(d_{60}>10\) mm, most soils with \(C_{u}<10\) are stable, while those with \(C_{u}>20\) are unstable. However, for soil with \(d_{10}<0.5\) mm and \(d_{60}<10\) mm, some unstable soils are mistakenly identified as  
Figure 1: Global distribution of landslide dams.  
stable [31]. Therefore, the Istomina Identification method exhibits large error in predicting the internal stability of soils.  
When analyzing the internal stability of the soils in a landslide dam, the [PERSON] method can only be used as a preliminary assessment method.  
Analogous to the Kezdi criterion, the Kenney and Lau method is also specifically designed for non-cohesive soils. [PERSON] and [PERSON] found that the internal stability of soils depends on the geometric shape of the gradation curve [22]. Particles with a diameter of \(d\) will be obstructed by particles with diameters between \(d\) and \(4d\); if there are not enough particles in this range, particles smaller than \(d\) will be lost [34]. Accordingly, [PERSON] and [PERSON] proposed using the \((H/F)_{\text{min}}\) curve to evaluate the internal stability of soils, where \(H/F\) is the ratio of the mass percentage difference \(H\) of particles with diameters between \(d\) and \(4d\) to the mass percentage \(F\) of particles smaller than \(d\)[35]. For broadly graded soils, when the fine particle content is less than \(15\%\), the Kenney and Lau method has high accuracy [33]; when the fine particle content is greater than \(15\%\), the Kenney and Lau method tends to conservatively classify stable soils as unstable [36]. Some scholars [37] have shown through experiments that the Kenney and Lau method is relatively conservative in assessing the internal stability of broadly graded coarse soils. Therefore, whether this method is suitable for assessing the stability of dam soils requires further experimental verification.  
Based on internal stability tests of gravelly soils, [PERSON] [23] proposed a method to analyze the internal stability of broadly graded gravelly soils using the indices \(h^{\prime}=d_{90}/d_{60}\) and \(h^{\prime\prime}=d_{90}/d_{15}\) (where \(d_{90}\), \(d_{60}\), and \(d_{15}\) are the particle sizes corresponding to \(90\%\), \(60\%\), and \(15\%\) of the total mass, respectively, on the gradation curve). The values of \(h^{\prime}\) and \(h^{\prime\prime}\) reflect the slopes of the gradation curve in two different intervals. The higher these values, the broader the particle size distribution of the soil [25]. If \(h^{\prime}\) and \(h^{\prime\prime}\) meet the corresponding geometric conditions in Table 1, the soil is internally stable [26]. Although the Burenkova method can be used to determine whether broadly graded soils have internal stability, it cannot accurately distinguish the boundary between stability and instability [34]. Thus, [PERSON] and [PERSON] [38] suggested replacing the original \(d_{90}/d_{15}\) with \(d_{20}/d_{5}\), believing that the modified Burenkova method improves applicability and effectively predicts the internal stability of broadly graded soils.