# A Review of the Impact of Spontaneous Combustion on Slope Stability in Coal Mine Waste Dumps
## 4 Monitoring and Mitigation Strategies Combating Spontaneous Combustion  
### Monitoring Techniques  
Temperature monitoring, both on the surface and within the dump, is one of the most direct and reliable indicators of the extent of spontaneous combustion. Continuous gas monitoring also provides valuable information, as the presence and intensity of combustion can be inferred from the distinctive odor of released gases, which is often associated with hydrocarbons. Over the past few decades, numerous studies worldwide have focused on various techniques for detecting and monitoring spontaneous combustion in mine waste dumps. One commonly used approach is **field surveying**, which includes a range of in situ observations such as waste material characteristics, ambient environmental conditions, the emission of gases with hydrocarbon-like odors, the appearance of brown discolorations on the dump surface, and signs of sulfur mineralization. However, despite its usefulness, field surveying is generally characterized by low efficiency, high costs, and significant time requirements, making it unsuitable for large-scale detection and the continuous monitoring of extensive waste dump areas [81; 126; 127; 128; 129]. The monitoring of spontaneous combustion in mine waste dumps is usually carried out through **borehole temperature and gas measurements** at different depths [3; 7; 43; 86; 130; 131; 132; 133; 134; 135; 136]. However, temperature and gas measurements over a large area are expensive and inefficient, and in some cases they are impossible due to a lack of access to places with a high intensity of spontaneous combustion due to numerous hazards (toxic gases, collapses and landslides after burning). Its reliability also often depends on the density of measuring points for the whole area under evaluation, leading to high costs and lengthy construction timelines. Figure 5: A cavity formed within a mine waste dump. Because of their high cost and time performance, field survey and borehole temperature and gas measurement techniques are commonly used to validate the results obtained from others methods [131; 136; 137; 138; 139; 140]. Temperature measurement has been used for monitoring the spontaneous combustion of mine waste dumps by applying advanced technologies such as small-scale unmanned aerial vehicles (UAVs), large-scale satellite remote sensing, infrared imaging remote sensing and multi-source data fusion monitoring [137; 138; 139; 24; 140; 150; 151; 152; 153]. These technologies offer several advantages, including a reduced need for direct contact with the objects observed and the elimination of the risk of exposing personnel to hazardous fire zones. Equipped with high-precision sensors, aerial platforms can remotely detect the position, status, and other relevant data of target objects with a high degree of accuracy. However, these approaches usually require knowledge of the intensity and range of the fires. Consequently, these methods are not well-suited to detecting the potential spontaneous combustion process in its initial stages when the spontaneous combustion has not occurred yet on the surface and/or shallow subsurface of the dump, i.e., the combustion cells are located deep within the dumps. In such cases, combustion cells may be located deep within the dump body, making early detection difficult with surface-based thermal imaging techniques. Another alternative approach is based on **monitoring vegetation changes**, which are considered to be signals of underground temperature rise. It is well-known that spontaneous combustion releases a constant heat, which creates a stress environment for vegetation growth. Under the influence of an abnormal surface/underground temperature, vegetation is likely to decrease [154; 155; 156; 157; 158]. A number of studies have carried out investigations on reclaimed coal waste dumps by using a UAV equipped with an aboveground biomass (AGB) camera [159; 160; 161; 162; 144].