Static crushing directional anchor withdrawal method at end of large-mining-height working face

A static crushing directional anchor withdrawal method at the end of a large-mining-height working face, comprising the following steps:

• step 1, designing parameters of boreholes for static crushing
• borehole position:
• wherein the boreholes are located in a triangle area of the roof end, arranged around an anchor cable, and provided along a gateway strike;
• borehole diameter:
• wherein the borehole diameter is from 48 mm to 65 mm;
• borehole angle:
• wherein the borehole is perpendicular to the roof;
• borehole depth:
• wherein the depth is consistent with the length of a roof anchor cable;
• analysis of a spacing between boreholes:
• according to the propagation range of wall rock cracks when a static crushing agent acts, determining a spacing between the boreholes, and calculating according to the following formula
• L
• =
• 2
• ⁢
• q
• 2
• (
• t
• )
• π
• ⁢
• K
• IC
• :
• wherein L is the spacing between the boreholes, mm;
• q(t) is an expansion pressure load varying with time, KN;
• KIC is rock fracture toughness,
• N
• /
• mm
• 3
• 2
• ;
• step 2:
• designing parameters of a static crushing agent grouting technology
• wherein a water-cement ratio of the static crushing agent is 1:3;
• the volume of the static crushing agent required for each borehole is calculated according to the following formula:
• Q
• =
• K
• ⁢
• πγ
• ⁡
• (
• Φ
• 2
• )
• 2
• ⁢
• (
• s
• -
• s
• 1
• )
• ,
• wherein K is a grouting coefficient 1.4-1.5;
• γ is the bulk density of the material, g/cm3;
• Φ is the borehole diameter, m;
• s is the borehole depth, m;
• s1 is borehole sealing length, m;
• and Q is the volume of the crushing agent for each borehole, m3;
• the static crushing agent is grouted by a pneumatic double-liquid grouting pump, with the use of a tee pipe;
• a borehole packer is selected from one having a diameter of 50 mm, the borehole sealing range of 55 mm to 100 mm, and a working pressure of 5 MPa to 7 MPa, or the one having a diameter of 38 mm, the borehole sealing range of 43 mm to 55 mm, and a working pressure of 5 MPa to 7 MPa;
• the static crushing agent is stirred with a stirring barrel, wherein the stirring barrel has the capacity of 80 L, a rated air pressure of 0.6 MPa, a blade torque of 150 N·m, length×width×height of 0.5 m×0.5 m×1.0 m, and a weight of 120 kg;
• step 3:
• carrying out the static crushing agent grouting technology, comprising the following steps:
• a:
• prior to drilling and grouting operation, tapping wall and sounding roof;
• checking whether the position of a conveyer is suitable, and migrating the conveyor if the position is unsuitable;
• and making the construction area unobstructed within 5 m;
• debugging construction equipment such as an air duct and the grouting pump to ensure that the air duct is free from air leakage and blockage, and that the lift and rotating speed of the pneumatic grouting pump are in the normal range;
• b. erecting a temporary support by means of piling column within 5 m distance from the roof to be treated, and after erecting the temporary support, drilling on the roof according to a design scheme;
• c. carrying out borehole sealing technology by using a borehole packer, with a borehole sealing depth of 0.5 m;
• placing a flexible plastic sleeve in the borehole, placing the borehole packer in the plastic sleeve, and completely inserting the borehole packer into the borehole, and connecting a grouting pipeline of the pneumatic grouting pump to an exposed joint of the borehole packer, and enabling a rubber hose of the borehole packer to expand to achieve borehole sealing;
• d. mixing water and the static crushing agent according to a weight ratio of 1:3, stirring the mixture of the water and the static crushing agent with the stirring barrel to form a uniform slurry with fluidity, and filling the borehole with the slurry within 10 min;
• and
• step 4, carrying out an anchor withdrawal operation, and withdrawing anchor rods and anchor cables in an arc triangle area of the roof at the end.