## 3 Results  
A total of six observation points were observed in the test. The A3 and B3 observation points, which demonstrated superior results, were analyzed as exemplars. As illustrated in Figure 2, the samples exhibit a mixture of flocculated and plate-like structures. The interfacial joints are connected by broken flocculated structures, and the main fractures and pores of the observed samples are distributed at the junction of the two. Among these, a  
Figure 1: Test instruments ((a) collecting instrument; (b) scanning electron microscopy; (c) CT scanner; (d) CT scanning principle). small proportion are fractures resulting from the deterioration of the plate-like structure, while the majority are fractures and pores caused by the separation of the flocculated structure from the plate-like structure, as well as the detachment of the flocculated structure itself (Huang et al. [24]). The process of change is shown in Figure 2 below. In its natural state, the structure of the red-bed soft rock is characterized by two distinct types of structures: broken blocky structures and complete plate-like structures. The broken structure surrounds the plate-like structure, and the plate-like part is more complete. There are a few fractures distributed at the boundaries, while the internal structure has fewer fractures. The surrounding fragmented area is jagged and uneven in size and distribution, with clearly visible borders. Following a seven-day saturation period, the specimens exhibited a predominantly fragmented structure, with complete plate-like structures present in the surrounding area. However, the tiny fractures in the plate-like structure began to gradually extend to the surrounding area, and the originally smooth surface gradually became rough, with tiny pores sporadically distributed. Concurrently, some of the blocks were observed to be shedding in layers. The fractures around the block extended and opened up, resulting in an increase in the depth and area of the surrounding pores and the shedding of broken particles from the pore walls. The original tiny particles were partially detached from the rock mass, and the larger particles had become more fragmented, with the boundaries gradually blurring, resulting in the surrounding fragmented mass beginning to change towards a flocculent shape. After a period of one month during which the specimens were saturated with water, the lamellar shedding phenomenon on the surface of the originally intact block structure gradually intensified, resulting in the gradual disintegration of the entire piece. Pores of 3 \(\upmu\)m-5 \(\upmu\)m appeared in the middle of the specimen, dividing the intact rock mass. The peripheral fracture structure had essentially detached from the parent rock, and the boundary was blurred, essentially completely transformed into flocculent material. The form of contact also began to gradually transition from the original face-to-face contact to face-to-edge and edge-to-corner contact. As a result, the tiny particles on the surface began to fall off in large areas. Following a period of 30 days during which the specimens were once again saturated with water, the interfacial connection between the particles began to break away from the rock mass and dissolve with the water as it entered the interior of the soft rock. The original small pores began to expand around them, and the larger pores began to gradually connect to form fractures. The original intact portion of the large area was peeled off in layers, and the tiny particles were almost completely transformed into flocculent material. The  
Figure 2: Microstructural changes in red-bed soft rock. original intact rock mass began to soften and become loose. Overall, the micro-morphology changed significantly from the natural state, and the previous shape was almost eliminated. The deterioration of the red-bed soft rock at the microscopic level is primarily manifested by the softening effect of water on the filler between the particles.