Effect of upward angle on the drawing mechanism in longwall top-coal caving mining

• Gravity is the dominant factor while the upward angle has little influence on the drawing body's shape in LTCC.
• The top-coal recovery ratio first decreases and then increases with the increasing of upward angle.
• The drawing sequence of the top-coal along the coal seam's vertical direction is top→low→middle in ULTCC.
• The top part of top-coal has a lower recovery ratio than the low and middle parts in ULTCC.