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

Patent metadata

Field	Value
Publication number	US-11085279-B2
Application number	US-201716463358-A
Country	US
Kind code	B2
Filing date	Sep 30, 2017
Priority date	May 10, 2017
Publication date	Aug 10, 2021
Grant date	Aug 10, 2021

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

What is claimed is:

1. A stress-transfer method in a tunnel comprising:
drilling holes from the tunnel towards a targeted surrounding rock surrounding the tunnel, wherein a horizontal portion of an extending direction of each of the holes directs from the tunnel to a gob; and
fracturing the holes to create a fracturing ring;
wherein an inner boundary of the fracturing ring defines a protective circle and a radius of the protective circle keeps a certain width from an edge of a support body of the tunnel to reserve safety coal pillar barriers.

2. The stress-transfer method in the tunnel according to claim 1 , wherein to get a wide fracturing ring, the fracturing is performed throughout the holes; or to get a narrow fracturing ring defining a cutting and interruption circle, a pre-slotting is further performed followed by the fracturing conducted at bottoms of the holes.

3. The stress-transferethod in the tunnel according to claim 2 , wherein
a vertical position of the bottom of the hole is located in the targeted surrounding rock; the targeted surrounding rock comprises a roof, a floor, a sidewall or a combination thereof, and a width of the fracturing ring is adjusted by changing fracturing lengths of the holes.

4. The stress-transfer method in the tunnel according to claim 3 , wherein when one layer or multilayer of hard rock stratum exists in the roof, a pillar with a certain width exists between the tunnel and the gob,
the holes are drilled at an angle into the roof having the hard rock stratum from the tunnel, a location of an end part of the hole reaches to the pillar with certain distance in a horizontal direction, a location of the end part of the hole in a vertical direction is located at a center of the roof; and
the holes are pre-slotted to generate an initial slot and fractured to form fractures, wherein
the initial 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 end parts of the holes;
the 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 to cut off the roof having the hard rock stratum at a roof-breaking line; and
the roof-breaking line is positioned at a boundary line between a plastic zone and a crushing zone of the pillar.

5. The stress-transfer method in the tunnel according to claim 4 , wherein both long holes and short holes are drilled in rows along the axis of the tunnel into the roof having the hard rock stratum, vertical positions of ends of both the short holes and the long holes are located at the center of the roof having the hard rock stratum, wherein the long holes have a small angle of elevation and long length, and are closer to a side of the gob and more far away from the tunnel; the short holes have a large angle of elevation and short length, and are 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 long- short-long-short; the pre-slotting is performed firstly and the fracturing is conducted secondly in the holes, the pre-slotting and the fracturing create a long holes fracture arc in the main fracturing holes and a short holes fracturing arc in the assisting fracturing holes, the long holes fracture arc is used to cut off rock strata of the roof and the short holes fracture arc is utilized to prevent an impact energy caused by a break of the roof from influencing the tunnel.

6. The stress-transfer method in the tunnel according to claim 4 , wherein
when there are two or more layers of hard roofs, a group of holes is respectively constructed to fracture each layer of the hard roofs, a number of groups of the holes corresponds to a number of the layers of the hard roofs, the holes for each layer of the hard roofs are arranged in an identical manner, and ends of the holes in the vertical direction are at respective centers of respective hard roofs.

7. The stress-transfer method in the tunnel according to claim 2 , wherein the holes are sealed; and bottoms of the holes are pre-slotted and fractured to form a narrow fracture zone or the cutting and interruption circle to prevent the high-stress from transmitting towards the tunnel to achieve the stress-transfer, wherein the pre-slotting and fracturing is conducted at an early stage of forming the tunnel, before an influence of a front abutment pressure on the tunnel or in the tunnel influenced by the tectonic high-stress.

8. The stress-transfer method in the tunnel according to claim 2 , wherein the holes are sealed and fractured to form the fracturing ring with some width, wherein the fracturing ring transmits a high stress to farther zones to form the protective circle, the tunnel and an integrated surrounding rock of the protective circle is in a low-stress zone to avoid the high-stress, and the drilling is conducted in the tunnel influenced by the high-stress of deep mines or tectonic zones.

9. The stress-transfer method in the tunnel according to claim 8 , wherein the holes on the sides of the tunnel are drilled to weaken zones within the fracturing ring in the whole tunnel, also, a sector drilling on a tunnel driving face is conducted in a heading direction to weaken front zones within the fracturing ring; and a protective pillar with a width of 3˜10 meters is reserved at a borehole section near the tunnel when fracturing.

10. The stress-transfer method in the tunnel according to claim 1 , wherein the fracturing includes hydraulic fracturing, gas fracturing, CO 2 phase-transition fracturing, electromagnetic pulse fracturing, capsule-expanding fracturing and bolts-expanding mechanical fracturing.

Assignees

• Univ China Mining
• Xuzhou Usure Mining Tech Co Ltd

Inventors

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

Classifications

• 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

• 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