# A Stability Analysis of the Ancient Site of Liye Based on the Strength Reduction Method
## 2 Overview of Soil Sites in the Ancient City of Liye  
The Liye City is located on the West Bank of Youshui river in the southwest of Longshan County, which is situated within the Xiangxi Tujia and Miao Autonomous Prefecture in the Hunan Province. As an important part of the ancient city's ruins, the moat of Liye is in the central area of the town. The moat, as shown in Figure 2, was built during the Warring States period. According to preliminary archaeological exploration, the existing site measures 210 m from north to south and about 105 m from east to west; thus, the total area is about 22,000 square meters.  
The remaining moat is divided into two areas. An \"L-shaped\" moat in the south retains its original shape, while damage from a collapse is found on the west side of the \"L-shaped\" moat in the north. The bottom anchor bolt heads that were buried in the early stages of construction to strengthen the slope are exposed, and a gravel slope that was also intended to provide protection is loose and partially collapsed. Additionally, the slope protection below the long-term storage surface in the west and the area east of the western and southern sections of the moat lacks aquatic plants, and the backfill is seriously damaged.  
According to an inspection and evaluation, we concluded that the primary factors contributing to the deterioration of the moat in Liye included a perennial presence of water in the moat, the humid local environment, raw soil material defects, serious water erosion of the slope protection below the water level, and a large-scale collapse of the slope protection above the water level. At present, these factors have endangered the body of the inner moat, which urgently needs to be protected and reinforced. Specific results of our investigation into the current state of the moat include:  
1. In the western section of the north city wall, a lack of aquatic vegetation coverage has resulted in decreased slope protection below the water surface of the trench. There is serious water erosion of the backfill. The water erosion depth is 120-300 mm and most of the anchor heads of the bottom anchor bolts are exposed. A combination of water and soil loss and the effect of rain erosion on the wall foundation have caused a collapse of the outer skin of the earth wall. This affects the rammed earth of the wall around the collapsed portion. Figure 3a shows peeling and shedding of the outer layer of a wall that has been damaged by rain and snow. Likewise, the top of the remaining wall has suffered rain erosion, thus decreasing the wall height. Many large vertical cracks and gullies are found in the internal corners, which reduce the constraints of the external wall. These areas threaten the stability of the trench.  
Figure 2: Present situation of the ruins.  
2. There is serious water erosion of the backfilled rammed earth platform under the gravel revetment in the western section of the south city wall. As shown in Figure 3b, the water erosion depth on the inner side of the platform is 120-180 mm and that on the outer side is 250-300 mm. The gravel masonry slope protection in the middle of the south slope is loose and locally collapsed. At the bottom of the trench lie collapsed stones, dead branches, rotten leaves, and sporadic sundries. Figure 3c shows that the wall is longitudinally cracked, the surface soil has completely lost the texture characteristics of the original compacted soil layer, and there is a wide range of flake crusts and powdery material being shed.
3. The remaining parts of the trench are well preserved, as shown in Figure 3d. Some areas of the outer layer remain intact, but there are many cracks in the wall. During the repair process, efforts should be made to distinguish between wall cracks and protective layer cracks.