(Pr) 4. Mine Design
The length of current longwall panels at Prince Colliery is about 2.74 km (9000 feet). This length has been found to be appropriate because it matches the rate of panel development and avoids costly delay time. At present, longwall panels are working at a depth of about 320 m (1049.9 feet). Typically, there are no more than two crosscuts or cundies per panel, each 1 ~ 1.5 km (0.6 ~ 0.9 mile) apart. The coal pillars left between the mains slopes and the panels are 60 m (200 feet). The barrier pillars between adjacent panels are also about 60 m (200 feet) wide.
Prince Colliery was initially developed as a room and pillar mining operation. After encountering difficult mining conditions that led to several roof falls, the mine was driven to depths where longwall mining could take place. Each longwall panel is accessed by a two-single-entry roadways (the headgate and tailgate). Entries are 4.5 m (14.8 feet) wide but these often become wider due to spalling of the coal ribs. There are five main entries (slopes) at the portal.
The longwall panels are typically about 198 m (650 feet) wide. About 2.3 m (7.6 feet) of the coal is usually mined with some roof coal left to stabilize the roof strata.
In the main access slopes, crosscuts meet adjacent entries at acute angle on many occasions. Within the panels, crosscuts also meet the entries at acute angles. This angle of intersection results in a maximum exposure of roof strata (7 to 8 meters) Figure Pr5.
There was no extended cut practiced.