故宫城墙在1406-1420年间随着紫禁城的建立而修建,现已成为重要的文物建筑[图1(a)]。根据近期施工勘查资料,发现该城墙部分土层存在局部下沉现象[图1(b)]。通过选取土体下沉明显位置进行探井勘查,发现城墙土分层多达6种,且在不同深度范围内具有大小不一的孔洞,见图2所示。根据勘查分析结果,推测城墙土产 Forbidden City Wall was built with the establishment of the Forbidden City between 1406 and 1420 and has now become an important heritage building [Fig. 1 (a)]. According to the recent construction survey data, it is found that there is a partial subsidence phenomenon in some soil layers of the wall (Figure 1 (b)). By selecting obvious subsidence of the soil body for exploratory well exploration, it is found that as many as 6 kinds of wall soil layers and holes of different sizes in different depth ranges are shown in FIG. 2. According to the survey results, speculated that the city wall indigenous