I-patterned filling method for initial stage of coal mining based on roof fracture feature characteritics

An I-patterned filling method for an initial stage of coal mining based on roof fracture characteristics, comprising:

• (1) determining a relationship between an overburden load borne by a main roof and an overhang size of the main roof based on principle of virtual work and a surgery theory when an overhang distance of the main roof reaches an initial weighting interval of the main roof to enter a plastic limit state with an advance of a working face, and calculating the initial weighting interval of the main roof through the following equation:
• b
• =
• 4
• ⁢
• h
• ⁢
• σ
• s
• ⁢
• 3
• ⁢
• a
• 2
• ⁢
• q
• -
• 4
• ⁢
• 2
• ⁢
• q
• ⁢
• σ
• s
• ⁢
• a
• ⁢
• h
• 3
• ⁢
• 2
• ⁢
• a
• ⁢
• q
• ⁢
• σ
• s
• -
• 8
• ⁢
• h
• ⁢
• σ
• s
• ⁢
• q
• ;
• wherein b is the initial weighting interval of the main roof, h is a thickness of the main roof, σs is a tensile strength of the main roof, a is a width of the working face, and q is the overburden load borne by the main roof;
• (2) determining a relationship between an overburden load borne by an immediate roof and an overhang size of the immediate roof based on the principle of virtual work and the surgery theory when an overhang distance of the immediate roof reaches an initial fracturing interval of the immediate roof to enter a plastic limit state with the advance of the working face, and calculating the initial fracturing interval of the immediate roof through the following equation:
• L
• 0
• =
• 4
• ⁢
• h
• 0
• σ
• s
• ⁢
• 0
• ⁢
• 3
• ⁢
• a
• 2
• ⁢
• q
• 0
• -
• 4
• ⁢
• 2
• ⁢
• q
• 0
• ⁢
• σ
• s
• ⁢
• 0
• ⁢
• a
• ⁢
• h
• 0
• 3
• ⁢
• 2
• ⁢
• a
• ⁢
• q
• 0
• ⁢
• σ
• s
• ⁢
• 0
• -
• 8
• ⁢
• h
• 0
• ⁢
• σ
• s
• ⁢
• 0
• ⁢
• q
• 0
• ;
• wherein L0 is the initial fracturing interval of the immediate roof, h0 is a thickness of the immediate roof, σs0 is a tensile strength of the immediate roof, a is the width of the working face, and q0 is the overburden load borne by the immediate roof;
• and
• (3) according to a subsidence law of the main roof in an inverted hip roof form, performing filling at a key position around an internal plastic hinge line through I-patterned three-strip filling;
• wherein a first end strip is parallel to a haulage roadway, a second end strip is parallel to an air-return roadway, and a length of each of the first end strip and the second end strip is equal to the initial weighting interval b of the main roof;
• a width of the first end strip extending from a first end point of a central plastic hinge line towards the haulage roadway and a width of the second end strip extending from a second end point of the central plastic hinge line towards the air-return roadway are both L1, and 0<L1<t;
• wherein t is a distance from the first end point of the central plastic hinge line to the haulage roadway or a distance from the second end point of the central plastic hinge line to the air-return roadway, and is calculated through the following equation:
• t
• =
• 2
• ⁢
• q
• ⁢
• σ
• s
• ⁢
• h
• q
• ;
• a middle strip is perpendicular to the haulage roadway and the air-return roadway, and has the same length as the central plastic hinge line;
• the middle strip is located directly below the central plastic hinge line;
• the central plastic hinge line corresponds to a central position of the middle strip;
• and a width L2 of the middle strip is determined by the initial weighting interval b of the main roof and the initial fracturing interval of the immediate roof, and satisfies L2>b−2L0, such that no fracture occurs in both the immediate roof and the main roof.