# Motion Characteristics of Collapse Body during the Process of Expanding a Rescue Channel
## 3 Expansion Test Simulation Considering Geometry and Material Properties
### Analysis of the Expansion Process  
When the rescue channel is expanded in the collapse body at the same lifting speed, there is a deviation in the duration of the different expansion sizes. In addition, different expansion sizes and the properties of the collapse bodies also have a certain influence on the displacement range of the collapse body, but the displacement of the collapse body in the expansion process can still be divided into the same stages. Figure 6 shows the displacement changes of the collapse body in a different time when the size of the expanded channel and the coefficient of internal friction are taken as single variables. The first stage is the initial start-up stage. The collapse body is lifted during the start-up of the supporting device and is further compacted. At this time, except for the small displacement of the bottom collapse particles directly above the supporting device, the collapse bodies at other positions are in a static or micro-displacement state. With the further uplift of the supporting device, a funnel-shaped displacement region with a small lower part and a large upper part appears in the collapse body, and the displacement region gradually expands with the increase in the displacement, which is embodied in the decrease in the inclination angle of the inclined edge of the funnel-shaped displacement region and the increase in the funnel opening. Furthermore, due to the effect of the interlocking force between the particles of the collapse body, the structure of the particles in the collapse body is relatively stable in the initial start-up stage, and the resistance of the expansion device is relatively large. The first two displacement diagrams of the different expansion tests in Figure 6 show that the duration of this stage is roughly 2.5-3.7 s, corresponding to the expansion height of 0.25-0.37 m, and the expansion process enters the next stage. The second stage is the uplift stage; the size of the displacement area of the collapse body is basically determined, and the displacement value in the displacement area continues to increase under the lifting effect of the supporting device. As the collapse body rises, the structure of the collapsed accumulation body becomes loose, as shown by the red boundary in Figure 7b; at this time, the displacement region and the stable region are obviously dislocated along the boundary. As the funnel-shaped displacement region is distributed in a wide position at the top and a narrow position at the bottom, the collapse body is inclined to the displacement region by gravity after rising and is supported by the stable region after redistribution. In addition, the displacement area of the collapse body begins to show obvious direct and indirect displacement divisions at this stage. The duration of this stage is generally still 2.5-3 s; apart from the internal friction angle of 45\({}^{\circ}\), the lifting height of the other working conditions reaches 0.5-0.6 m.  
The third stage is the collapse stage. After the funnel-shaped displacement region of the collapse body reaches a certain height, the collapse body in the displacement region will dislocate while the volume increases and will collapse after gradually losing the support of the stable regions on both sides. As shown in the red boundary in Figure 7c, the destabilized collapse bodies begin to slide down to fill the cavities formed by the expanded collapse body. The collapse bodies on the inner side of the boundary still rise with the lifting of the expansion device as a whole, but the collapse bodies above the boundary and the collapse bodies at the bottom also have relative dislocations due to the increase in the upper volume. This stage lasts the longest, until the expansion device stops lifting, and the relative movement of the particles is also the most complex and frequent in this stage.