## 2 Engineering Overview  
Fushun West Open Pit Coal Mine is located in Fushun City, Liaoning Province, China. It is located between the two central districts of Xinfu and Wanghua in Fushun City, a narrow plain between the Hun River in the north and the foot of the Chitai Mountain in the south. The ground elevation of the northern flank of the Qiantai Mountain ranges from 102.9 m to 204.9 m, with a relative height difference of 102 m and natural slopes ranging from 20\({}^{\circ}\) to 30\({}^{\circ}\). The north side of the mine is gently sloping and steeply sloping, with Fushun city to the north. The Fushun coalfield consists of inland sedimentary strata from the Paleogene of the Cenozoic era. The coal-bearing stratigraphic system includes the Archean Anshan Group, the Lower Cretaceous Longfengkang Formation, the Paleogene Fushun Group, and the Quaternary, as shown in Figure 1. The sedimentary strata are mainly composed of mudstone and shale, both of which are classified as soft rocks. These soft rock layers overlie granitic gneiss and volcanic rocks. The geological structure of the Fushun coalfield was formed within the Hunhe Fault Zone, which is a northern extension of the Tan-Lu Fault Zone. The structural characteristics of this area are mainly influenced by the horizontal compressive forces and strike-slip traction generated by the activity of the Hunhe Fault after the coal-forming period, resulting in a series of unique structural features. The West Open-Pit Mine is located in the western part of the Fushun coalfield, where the seam thickness ranges from 35 m to 178 m. The coal seams are embedded within the Early Tertiary rock sequence, consisting of Eocene basalts and tuffs, as well as Eocene coal, oil shale, and mudstone. The strata form a plunging syncline with an axial direction of N80\({}^{\circ}\) E. The north limb dips in the opposite direction, while the south limb is overturned. Compared to the north limb, which has a dip angle of approximately 48-55\({}^{\circ}\), the south limb is gentler, with dip angles ranging from about 20-40\({}^{\circ}\). The fold plunges slowly to the east, and the northern limb is partly cut by the F1 thrust fault. The main faults within the coalfield are represented by the Hunhe Fault, a group of NE-ENE striking thrust faults that are almost parallel to each other, represented by the F1 and F1A faults. Fault F1 strikes NE80\({}^{\circ}\) with dip angles of 47-52\({}^{\circ}\), while fault F1A strikes NE80-NE85\({}^{\circ}\) with dip angles of 70-75\({}^{\circ}\). There are also associated nearly SN-trending faults and NW-trending faults, such as the F6 fault located at the eastern end of the pit slope, which dips NW85\({}^{\circ}\) at an angle of 35\({}^{\circ}\). The groundwater in the Fushun West Open-Pit Mine area is primarily recharged by atmospheric precipitation as well as lateral inflow from the Hun River and Guchengzi River. The main discharge mechanisms include evaporation and lateral underground runoff. A hydrogeological unit is defined as a groundwater analysis region with certain boundaries and uniform conditions of recharge, flow, and discharge. It includes all aquifers involved in groundwater flow and storage, as well as aquicludes that constrain groundwater movement, together with boundary conditions such as groundwater recharge and discharge. The extent of an independent hydrogeological unit is determined by hydrogeological boundaries, which may consist of surface or subsurface watershed divides, aquicludes or impermeable rock bodies, surface water bodies, pumping wells, drainage tunnels, and other features. The large deep open-pit coal mine measures approximately 6.6 km in length from east to west, 2.2 km in width from north to south, and has a depth of about 424 m. The overall slope angles of the southern slope range between 19\({}^{\circ}\) and 27\({}^{\circ}\), while the northern slope angle is approximately 30\({}^{\circ}\).