# Long-Term Creep Mechanical and Acoustic Emission Characteristics of Water-Immersed Coal Pillar Dam
## 1 Introduction  
Coal dominates energy production and consumption in China. However, coal mining leads to groundwater contamination and depletion, with approximately 60% of mine water remaining underutilized annually [1]. This contradiction is particularly pronounced in western China's major coal-producing regions in north-western China, which contribute 70% of the nation's coal output yet possess only 6.7% of the country's water resources [2]. To address the strategic needs of Western economic development and national priorities, Academician [PERSON] pioneered a key technological framework centered around the principle of \"diversion, storage, and utilization\", which encompasses the design, construction, operation, and safety monitoring of coal mine underground reservoirs (CMURs) [2]. The technology utilizes goals as storage spaces and constructs underground reservoirsby connecting artificial dams with coal pillar dams. Implemented for the first time in the Shendong Mining Area, 35 CMURs have been established [3], ensuring the synergistic utilization of coal resources and mine water in western China. CMURs consist of two main structural components as the main water barriers: coal pillar dams and artificial dams. Coal pillar dams serve as the primary water-retaining structures. These dams undergo stress loading-unloading adjustments during mining disturbances and are subjected to coupled influences from multiple factors during long-term operation. These factors include in situ geological conditions, ground stress, mine pressure, and dynamic disturbances such as earthquakes or mining tremors. Consequently, the stability of coal pillar dams and surrounding coal-rock masses has become a critical determinant for the long-term safety of CMURs. Existing research has extensively investigated the hydro-mechanical coupling behavior of coal pillar dams and coal-rock masses in CMURs. Studies have examined their mechanical responses, failure characteristics, and fracturing patterns under conditions of different moisture contents [4; 5], water immersion pressures [6], and dry-wet cycles [7]. Further research has explored the deformation behavior of coal pillar dams under long-term water immersion [7] and established failure criteria for coal-rock masses accounting for moisture content effects [4]. Concurrently, by numerical modeling [8], physical simulation with similar materials [9], and theoretical modeling, scholars have investigated how mining-induced disturbances affect coal pillar mechanics and failure mechanisms. For example, [PERSON] et al. [10] integrated the pressure arch theory with traditional safety factor design principles based on the mechanical properties of yielded coal pillars, thereby proposing a design method for room and pillar water-preserved mining pillars. As the primary load-bearing structure of CMURs, coal pillar dams may experience disasters such as reservoir leakage and support failure under prolonged high in situ stress conditions. Furthermore, the mechanical properties of coal and rock masses undergo further degradation due to long-term immersion in reservoir water. Conducting long-term creep tests under single-stage loading is essential for understanding the long-term mechanical behavior of coal pillar dams and analyzing their stability characteristics. Existing research has systematically investigated the long-term creep behavior of rocks under single-stage loading. For example, [PERSON] and [PERSON] [11] conducted a decade-long field creep test on granite and gabbro, revealing the significant influence of temperature fluctuations on long-term deformation. [PERSON] et al. [12] performed a 650-day creep test on halite, documenting an extremely slow creep rate of 7 \(\times\) 10\({}^{-13}\). [PERSON] et al. [13] executed a 12-year creep experiment on water-saturated tuff, establishing relationships between creep strain, strain rate, and time. [PERSON] et al. [14] carried out an 875-day salt rock creep test, uncovering differential initial creep characteristics under varying stress levels.