Stress-transfer method in tunnel with high ground pressure based on fracturing ring

Patent metadata

Field	Value
Publication number	US-2019316454-A1
Application number	US-201716463358-A
Country	US
Kind code	A1
Filing date	Sep 30, 2017
Priority date	May 10, 2017
Publication date	Oct 17, 2019
Grant date	—

Abstract

A stress-transfer method in tunnel with high ground pressure based on fracturing ring. According to the stress source of the tunnel, fracturing by drilling holes to form artificial weaken zones in surrounding rocks, that's named fracturing ring. The fracturing ring is the weaken zone with some width, whose inner boundary is the protective circle. The fracturing ring with small width is called the cutting and interruption circle and the cutting or interruption arc. The radius of the protective circle is determined by setting a certain width of safety coal pillar barriers at the edge of a support body. The radius of the fracturing ring is determined by the surrounding rock structure and the stress conditions as well as the construction technology. Usually, the higher the stress, the wider the radius of the fracturing ring. The cutting and interruption circle or arc could cut off all of the targeted rock which transmits the stress.

First claim

1 . A stress-transfer method in a tunnel with high ground pressure based on a fracturing ring, wherein firstly, according to stress conditions of the tunnel, a stress source which has caused or will cause the strong ground pressure in the tunnel is targeted; secondly, a hole targeting the stress source is drilled to implement fracturing to create a circle of artificial weaken zones in the surrounding rocks of the tunnel, which is “the fracturing ring”; a radius of the fracturing ring is determined by setting a certain width of safety coal pillar barriers at an edge of a support body; the width of the fracturing ring is determined by a structure of the surrounding rocks and in-situ stress conditions as well as construction technology, wherein the higher the in-situ stress is, the wider radius the fracturing ring.

2 . The stress-transfer method in tunnel with high ground pressure based on fracturing ring according to claim 1 , wherein to get a wide fracturing ring, the hole is drilled to perform the fracturing in the entire hole; to get a narrow fracturing ring, that is, “a cutting and interruption circle”, the hole is drilled and the pre-slotting and fracturing are conducted at a bottom of the hole.

3 . The stress-transfer method in tunnel with high ground pressure based on fracturing ring according to claim 2 , wherein the fracturing ring changes based on the engineering requirements:
when a transmission of concentrated high-stress or mining-induced stress towards the tunnel needs to be interrupted, the hole is drilled in targeted surrounding rocks where the stress is concentrated; a vertical position of the bottom of the hole is located in the targeted surrounding rocks; the targeted surrounding rocks could be a roof, a floor, a pillar a sidewall or combination thereof; the width of the fracturing ring is adjusted by changing a fracturing length of the hole; the fracturing ring with a smaller width is substantially close to a fracturing circle, which is a “cutting and interruption circle”; the cutting and interruption circle is used to proactively cut off the mining-induced stress and the high stress transmitted from tectonic zones and a far-field in deep mines, achieving a stress-interruption; when it needs to cut off a hard hanging roof, the formed fracturing ring has a smaller width and only a part of the fracturing ring is needed, which is called a “cutting and interruption arch”; the cutting and interruption arch is used to proactively cut off the hard overhanging roof to unload the tunnel.

4 . The stress-transfer method in tunnel with high ground pressure based on fracturing ring according to claim 3 , wherein when there is one layer or multilayer of hard rock stratum in the roof,
the hole is drilled at an angle into the hard roof in the tunnel, an end part of the hole reaches to the pillar with certain distance in the horizontal direction, and the pillar with a certain width is set between the tunnel and a gob, a location of the end part of the hole in the vertical direction is located at a center of the hard roof; the hole is pre-slotted and fractured; a preset slot is induced along a direction of a fracture initiation; the fractures propagate and extend along several directions to form a fracture plane consisting of one or multiple cracks whose center is at the end of the hole; rows of holes are set along an axis of the tunnel at a certain intervals to be drilled and fractured; the cracks created by fracturing connect with each other or neighbor with each other cut off the hard roof to remove the high-stress from a origin; for roofs in some mines which are particularly hard, wherein the roofs hang but not break, such roofs are fractured after recovering from the working surface; or, such roofs are fractured before recovering from the working surface according to the design to form the fracture plane so the fractured roofs collapse by themselves under an influence of gravity after recovering from the working surface, avoiding the hanging hard roof; the cutting and interruption circle or arc cuts off all targeted rocks which transmit the stress; the cutting and interruption arc is a section which is created by the fracturing which cut off the hard roof, it is called a roof-breaking line; an optimum position of the roof-breaking line is a boundary line between a plastic zone and a crushing zone of the coal pillar.

5 . The stress-transfer method in tunnel with high ground pressure based on fracturing ring according to claim 4 , wherein both long holes and short holes are drilled in rows along the axis of the tunnel into the hard hanging roof, vertical positions of ends of both the short holes and the long holes are located at the center of the hard roof, wherein the long holes have a small angle of elevation, long length, is closer to a side of gob, and is more far away from the tunnel; the short holes have a large angle of elevation, short length, more far away from side of the gob, and closer to the tunnel; the ends of the long holes, arranged linearly, are main fracturing holes; the ends of the short holes, arranged linearly, are assisting fracturing holes; the holes are continuously staggered set with some space along the tunnel in an order of the long-the short-the long-the short; the pre-slotting is performed firstly and the fracturing is conducted secondly in the holes, the slotting and the fracturing could create a fracture arc which is called ‘the long holes fracture arc’ in the main fracturing holes and ‘the short holes fracturing arc’ in the assisting fracturing holes, the long holes fracture arc is used to cut off the rock strata of the hard roof and the short holes fracture arc is utilized to prevent the impact energy caused by the break of the roof from influencing the tunnel.

6 . The stress-transfer method in tunnel with high ground pressure based on fracturing ring according to claim 4 , wherein
when there are two layers or multilayer of hard roof, a group of holes is respectively constructed to fracture each layer of them, a number of layers of the holes corresponds to a number of layers of the hard roof, the arrangement of same group of hole is the same for the same layer of hard roof, the vertical direction of the ends of the holes is at the center of the hard roof, such slicing fracturing for the multilayer of hard roof make the entire hard roof form layered failure.

7 . The stress-transfer method in tunnel with high ground pressure based on fracturing ring according to claim 2 , wherein the holes are drilled into the targeted rocks which transmit the stress or the entire surrounding rocks from the roof, the floor and the sides of the tunnel, then seal the holes, pre-slot and fracture the bottom of the hole to form the narrow fracture zone or the fracture plane, namely, the cutting and interruption circle, the cutting and interruption circle to prevent the high-stress from transmitting towards the tunnel to achieve the stress-transfer, which is conducted at the early stage of the tunnel born, before the influence of the front abutment pressure on the tunnel or in the tunnel influenced by the tectonic high-stress.

8 . The stress-transfer method in tunnel with high ground pressure based on fracturing ring according to claim 2 , wherein the holes are drilled into the targeted rocks which transmit the stress or the entire surrounding rocks from the roof, the floor and the sides of the tunnel, then, the seal the hole and fracture the whole hole to form the fracture ring with some width, the fracture ring transmits the high stress to farther zones to form a protective circle, the tunnel and the integrated surrounding rocks of the protective circle are in the low-stress zone to avoid the high-stress, the job could be conducted in the tunnel which influenced

Assignees

• Univ China Mining
• Xuzhou Usure Mining Tech Co Ltd

Inventors

• Huang Bingxiang
• Liu Jiangwei
• Zhao Xinglong
• Chen Shuliang

Classifications

• E21C41/18 Primary

  for brown or hard coal · CPC title

• E21D9/00

  Tunnels or galleries, with or without linings; Methods or apparatus for making thereof (E02D29/045, E02D29/063 take precedence; linings per se E21D11/00); Layout of tunnels or galleries · CPC title

• E21B43/26 Primary

  by forming crevices or fractures · CPC title

• E21F17/00

  Methods or devices for use in mines or tunnels, not covered elsewhere (mine lighting F21, H05B) · CPC title