## 3 Evaluation Indicators
### Geological Disasters  
There are various types of geological hazards; however, the selection of geological hazards for evaluation should be based on the specific characteristics of the study area (Figure 2).  
(1) Corrosion of groundwater;  
Groundwater in runoff discharge areas is highly corrosive, making it unsuitable for the development of UUS. This corrosive groundwater typically forms in limestone regions, mountainous and hilly terrains, humid climates, and areas associated with sulfur-containing mining activities. Additionally, groundwater in regions with saline soil also exhibits high corrosivity. Such groundwater can significantly corrode construction materials, including concrete and steel reinforcements in underground structures. To assess the corrosion potential of groundwater, sample collection and testing should be conducted. Qualitative evaluations can be performed based on the rating standards outlined in the \"Engineering Geology Handbook\" [96].  
(2) Land subsidence;  
Land subsidence refers to the vertical lowering of the ground or soil surface due to various factors, including groundwater extraction, soil compaction, and geological structural changes. This phenomenon alters the stress on buildings and underground structures, potentially leading to instability and structural damage. Geological exploration, benchmark fixed on different stratum, leveling, InSAR, and other methods can be employed to determine the cumulative settlement amount and settlement rate. Subsequently, classification and risk assessment can be conducted in accordance with relevant specifications [97].  
(3) Seismic saturated sand;  
Earthquake-saturated sand refers to a condition in which saturated sand loses its bearing capacity due to liquefaction triggered by an earthquake. During an earthquake, the water pressure within the soil increases sharply, weakening the contact between soil particles and causing the sand to display liquid-like characteristics under dynamic loading. This phenomenon adversely affects the stability of buildings, foundations, and underground structures. The liquefaction potential can be assessed through geological exploration, standard penetration tests (SPT), static cone penetration tests (CPT), and other methodologies.  
(4) Soft soil;  
Various types of soil, including soft soil and expanded clay, are susceptible to deformation, which complicates the maintenance of stability in underground structures. Soft soils [70] typically form in lacustrine and marine environments. To assess the grade of soft soil, it is necessary to collect samples and calculate the sensitivity of these soil samples.  
(5) Saline soil;  
Saline soils typically develop in arid and semi-arid regions, particularly in inland areas or low-lying zones adjacent to the ocean. These saline soils often corrode concrete, steel reinforcement bars, and other materials used in underground structures. To assess the corrosion potential of saline soil, sample collection and testing should be conducted. Evaluations can be performed using qualitative calculations based on the rating standards outlined in the \"Engineering Geology Handbook\" [96].  
(6) Cave, solitary stone, freeze-thaw;  
Karst caves, boulders, and freeze-thaw processes are all geological hazards characterized by significant regional variations. Karst caves predominantly form in the Custer landform area, while boulders develop in diluvial regions surrounding bedrock mountains. Additionally, freeze-thaw phenomena are primarily observed in high-latitude areas. This article will not address investigation and evaluation methods.