## 4 Discussion  
A series of physical model tests for rainfall-induced shallow slides have been carried out then and reported on in this paper. The soil samples were made according to the natural soil in the Min Jiang River basin in southwestern China. The different soil types have unique characteristics. Silty soils are usually well-aggregated, but the aggregates break down rapidly when wetted, allowing non-aggregated soil particles to be easily transported [42]. For sandy soil, there is a clear linkage between landslides and sediment yield [43]. Seismic activity will generate a large amount of gravel soils and make the region susceptible to geohazards [22]. Therefore, the impact of the typical soil constitution on the landslides and sediment yield is analyzed in this paper. The sediment yield of the landslides that resulted from tests with different rainfall intensities, rainfall patterns, slope gradients, and soil particle compositions is shown in Table 3. All of the soil that slid down came from within 10 cm of the surface layer of the original mass, so the mass of the soil  
Figure 8: Variation in measured data when slope gradients are different: (**a**) water content; (**b**) matrix suction; (**c**) pore water pressure; (**d**) total stress.  
that slid down by landslide, as a percentage of the total mass of the upper 10 cm layer of the original slope, was used to measure the severity of the landslide.  
Some research on rainfall-induced shallow landslides has been conducted. A comprehensive physics-based Integrated Hydrology Model was set up, which is appliable to different rainfall characteristics [44]. In this paper, more factors are studied in order to investigate the mechanisms of rainfall-induced shallow landslides. The impact of the water content and pore water pressure was analyzed by monitoring a natural slope [45]. However, the variables of that study are not complete because matrix suction and total stress are lacking. A distributed one-dimensional modeling approach for predicting shallow-rainfall-induced landslides was established [46], but the actual landslides are complex. In this paper, more factors have been considered. The influence of soil depth on the occurrence of shallow landslides has been previously investigated [43], but evidence of how the rainfall and soil condition affect a landslide's occurrence is lacking.  
The occurrence of landslides and their sediment yield is related to many factors. To investigate the effect of one factor and the following comparisons, the other factors were kept the same. Under a rainfall intensity of 120 mm/h (Test 3), the first landslide occurred at 39 min. Under a rainfall intensity of 160 mm/h (Test 4), the first landslide occurred at 47 min. This suggests that the higher the intensity of rainfall, the earlier the initial landslide occurs. The sediment yield of Test 4 was also larger than that of Test 3. When the rainfall intensity was 80 mm/h, there was no landslide. This indicates that the occurrence of landslides under the test conditions requires the rainfall intensity to exceed 80 mm/h. The rainfall pattern also affected the occurrence of landslides and the first landslide's time of occurrence. In the tests with rainfall patterns II, III, and IV (Test 6, 7, and 3), the first landslides were at 42 min, 45 min, and 47 min, respectively. In the test with rainfall pattern I, no landslide occurred. For the different soil types, the initial landslide occurrence times of the gravel soil and the mixed soil were 39 min and 47 min, and the sediment yields were 9.8% and 11.2%, respectively. No landslide occurred in the silty soil or the sandy soil. Soils composed of coarse grains were shown to be prone to landslides. The landslide on the 30\({}^{\circ}\) slope (Test 12) occurred earlier, at 33 min, than those which occurred during all of the tests on the 15\({}^{\circ}\) slope. The sediment yield was 24.2%, which was also higher than those on the 15\({}^{\circ}\) slope.