## 1 Introduction  
The mining of shallow coal seams severely disrupts groundwater equilibrium, adversely impacting the mining area's ecology and increasing mine water inflow [1, 2, 3, 4]. In China, coal resources and water resources exhibit an inverse spatial distribution. Due to policy-driven development, western regions have emerged as the primary coal-producing areas. As illustrated in Figure 1, the typical geological characteristics of shallow buried coal seam groups include multi-seam intervals, argillaceous soft rock layers, and sandy hard rock structures [5]. These regions face water scarcity and ecological fragility, exacerbated by high-intensity coal mining [6, 7]. In 2023, the five major western coal bases accounted for over 80% of national coal production. The expansion of large-scale mining operationsand soaring coal output have significantly increased goat areas. After a mining fracture destroys the aquifer, groundwater migrates to the goaf [8; 9; 10]. To prevent water irnush accidents, extensive groundwater drainage is implemented, leading to several critical issues (Figure 2): (a) Declining ecological water levels cause vegetation degradation [1,11]; (b) Over recent decades, large volumes of discharged mine water have primarily evaporated, leaving behind heavy metals and solutes that contaminate both water and soil [12]; (c) Current regulations prohibit mine water discharge due to water quality and balance concerns, while treatment costs remain prohibitively high [13; 14]; (d) Concealed water sources, when connected by mining-induced fractures, often trigger large-scale casualties [15]. Aquifers are particularly vulnerable to mining-induced fractures following shallow coal seam extraction [16; 17]. The seepage characteristics of compacted broken rock in goaf areas are crucial for evaluating the permeability of repeatedly mined overburden, which is essential for ensuring mining safety. Numerous compaction-seepage experiments on broken rock have significantly enhanced our understanding of nonlinear seepage behavior. By integrating mechanical testing systems with water pressure control systems, researchers can analyze the seepage characteristics of broken rock under various compaction conditions. The displacement control method proves effective for establishing theoretical models of broken rock compaction-seepage under different compaction levels, while the load control method is more suitable  
Figure 1: Distribution of the main coal seams and overlying strata structures in the Ordos coal-accumulating basin [5]. Figure 2: Water and environment problems caused by shallow coal seam group mining. for investigating compaction-seepage characteristics (CSCs) under specific engineering conditions [18]. Current research has examined CSCs related to lithology, particle size, and mixed-particle-size samples, with particular attention to complex phenomena such as particle migration, erosion of weakly cemented minerals, and water-rock mixed flow [19; 20; 21; 22]. However, in underground coal mining engineering, the roof--as a critical surrounding rock zone--typically consists of multiple lithological combinations. While studies have established CSCs for single lithology samples, research on the CSCs of combined lithologies in goat areas remains relatively limited. The hardness, lithology, and structural composition of roof strata are fundamentally linked to key strata control elements, including mine pressure manifestation, bolt support design, non-pillar mining techniques, and coal pillar width determination [23; 24; 25]. These geological parameters, along with roof structure characteristics and the thickness ratio between bedrock and overburden layers, serve as critical criteria for water resource protection zoning in mining areas [26]. Coal measure strata can be classified into three primary types based on mineral composition and mechanical properties, mudstone, sandstone, and coal seams, each exhibiting distinct functional behaviors during mining operations [27; 28].