# Research on Risk Assessment Method for Land Subsidence in Tangshan Based on Vulnerability Zoning
## 3 Hazard Assessment Results for the Study Area
### Construction of Hazard Assessment Index System for Ground Subsidence
#### 3.1.3 Inducing Factors  
The engineering factors that predominantly influence the ground collapse hazard include rainfall, underground pipeline leakage, seismic soil liquefaction, and seismic peak ground acceleration. These factors collectively account for a significant proportion (41%) of the ground collapse incidents in Tangshan City, underscoring the importance of analyzing these inducing factors for the development of an effective ground collapse hazard assessment method. (1) Rainfall. The rainfall distribution in the study area is uneven throughout the year, with approximately 70% of the annual rainfall occurring in summer. Historical data on ground collapse incidents in the study area indicate that July is the month most prone to them, which is also the month in which the highest rainfall is recorded. To analyze the rainfall factor, the maximum monthly rainfall was considered. A spatial interpolation analysis was performed on the July rainfall data from meteorological stations using the inverse-distance weighting method. The rainfall was then classified into four levels, as detailed in Table 11, and the classified rainfall map is presented in Figure 19.  
(2) Underground Pipeline Leakage  
The underground pipelines in the study area, which include stormwater pipes, sewage pipes, gas pipes, heat pipes, communication pipes, and water supply pipes, form a dense network. Significant leakage issues on some major roads, coupled with this dense network, contribute to ground collapse accidents. Therefore, the distribution and classification of the underground pipelines in the study area are key indicators for assessing the ground collapse hazard. Investigation and analysis of the construction of the underground comprehensive pipeline corridor project reveal severe underground pipeline leakage issues on some critical road sections in the study area, as detailed in Table 12. \begin{table}
\begin{tabular}{c c} \hline \hline
**Rainfall (mm)** & **Value** \\ \hline \(<\)180 mm & 1 \\
180–210 mm & 2 \\
210–230 mm & 3 \\ \(>\)230 mm & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Values of rainfall in the study area. Figure 18: Goal area of study area. (**a**) Distribution of goat area. (**b**) Classification of goat area. These roads were buffered within ArcGIS using a 30 m radius and classified based on the type of underground pipelines and their leakage conditions, as shown in Figure 20.  
(3) Seismic Soil Liquefaction  
The catastrophic Tangshan earthquake of 1976 induced significant liquefaction hazards in various areas, including the Tangshan Plain and Qian'an Basin. Within the study area, two major liquefaction zones were identified: one is situated in the northeastern part, extending from north of Wandaoshan and east of Ligeguancun, along the banks of the Douhe River to Houdouhe Village, with a maximum liquefaction layer thickness of 4 m, and the other is located in the southeastern part of the city, south of Shengli Bridge, with a maximum liquefaction layer thickness of 8 m.  
During intense seismic events, sandy soil can lose its load-bearing capacity and self-weight support, leading to foundation subsidence and structural damage. The failure of the foundation due to soil liquefaction can readily trigger ground collapse. Consequently, seismic soil liquefaction was selected as a critical indicator for assessing the ground collapse hazard. The study area was partitioned into liquefaction and non-liquefaction zones and assigned values of 2 and 1, respectively, as depicted in Figure 21.