WO2018218378A1

WO2018218378A1 - Distension techniques for protecting future underground works exposed to rock explosions

Info

Publication number: WO2018218378A1
Application number: PCT/CL2017/000015
Authority: WO
Inventors: Guillermo Enrique BASUALTO LIRA
Original assignee: Basualto Lira Guillermo Enrique
Priority date: 2017-05-30
Filing date: 2017-05-30
Publication date: 2018-12-06

Abstract

The invention relates to distension techniques for neutralising the rock explosions that often occur during the construction of underground works located in environments exposed to high stress fields, such as caverns, main tunnels or branches, degrading the rock in the surroundings thereof, applying tension-reducing techniques that involve fracturing by blasting long holes. The distension procedure is executed before the start of construction. In caverns, for example, from two or more horizontal drilling shafts that are parallel and perpendicular to σ1, two sets of long holes are drilled, each set being made up of two rows forming an envelope around same. Then, the long holes are loaded with explosives and detonated. The intensely fractured area of rock that will surround the excavations forms a shield that will prevent the occurrence of rock explosions.

Description

DISTENSION TECHNIQUES TO PROTECT FUTURE UNDERGROUND WORKS EXPOSED TO ROCK EXPLOSIONS

SCOPE

As mining progresses to greater depths, many of the underground works are being developed in environments of high stress fields, therefore, they are exposed to the occurrence of severe rock explosions.

PREVIOUS TECHNIQUE

De-tensioning.- "The distensioning was conceived as a fracturing technique with explosives to relieve stress in areas with potential rock explosion. It was initially developed and widely used in the exploitation of gold guides in Witwatersrand in South Africa in the 1950s ( Roux, et al., 1957.) The concept of distension resulted from the observation that the area of highly fractured rock immediately around deep underground openings seemed to offer some protection to both: the occurrence of and damage by the explosion of rocks, then it was postulated that if this naturally fractured area could be extended by split fracture in front of the forehead, both: the occurrence and effects of the rock explosion could be reduced "(Blake W.).

Development dissemination.- "The most successful and widely accepted application of relaxation has been with respect to linear excavations: tunnels, chimneys and pikes. In areas of high stress and brittle rock the excavation of these openings is commonly accompanied by sudden mini detachments of Rock plates (popping) and the separation of thin layers of rock from the rock mass (spalling), occasionally noises and small bursts and usually excessive rock shedding.The problem is the high concentration of stress resulting from the sharp geometric vertices in the front of the excavation. The drilling and blasting of long shots, in front of the forehead almost always control this problem. " (Blake W.)

Stretching of pillars.- The veins with strong manteo are exploited by enhancement in horizontal slices and filling, which results in the creation of pillars prone to rock explosion. In the 1970s, the distensioning of pillars in veins was successfully developed, using the explosive fracturing technique.

Pre - conditioning.- "The distensioning in advance of the exploitation or the pre - conditioning, in the exploitation of sub-vertical tabular bodies by ascending or descending advance (" Stope "), is the last development (1979) with respect to distension. The concept is to pre-fracture or pre-condition a Stope or zone of solid rock prior to its exploitation so that the high stresses that usually result from exploitation are relieved by the elasticity of the pre-conditioned zone. " (Blake W.)

In 2001, Codelco started a pioneer program in the sinking of primary rock blocks at the Rio Blanco mine, pre-conditioning the blocks in situ, to degrade them with the long throw blasting technique, with the purpose of increasing their fragmentation and sinking.

Fortification.- "The design of support systems is one of the most difficult problems in rock engineering. The difficulties are centered on the inability to quantify the loading conditions, even in the most elementary cases. In addition, the rock structural support system is often statically undetermined. In the case of the rock explosion, the problem is aggravated by the dynamic forces that must be accommodated by the support structure. "(Wagner, H.).

El Teniente New Mine Level.- In 2015, in one of the access tunnels to the future Production Level, a violent rock-burst was recorded. International experts concluded that the tunnel is near a creek, so that the vertical load generates a horizontal component there, which induces an unbalanced inclined load, which the initial model did not detect. This has forced Codelco to reformulate the project to better respond to the geo-mechanical conditions it faces. The project is already four years late.

Search for new solutions.- In the case of the New Mine Level, it has been concluded that this rock, being at the limit, would not support the excavation, so the high induced stress will have to be faced with a fortification other than the current one, whose application would be robotic, which will increase its cost and execution time. DISADVANTAGES OF THE STATE OF THE TECHNIQUE:

Fortification is the main technique used today to contain the rearrangement of efforts induced by underground excavations.

The fortification required, to try to neutralize the rock explosion, is exceptionally robust and very expensive. Its application is very slow because, due to its high density and robustness, the progress of the excavations progresses in small increments.

With the current state of the art, the larger the excavation section, the greater its instability and the slower its progress.

DISCLOSURE OF THE INVENTION

The scope of the explosive fracturing technique to relieve stress in areas of rock explosion has so far been applied exclusively to the interior of those bodies that are required to degrade, to provide some protection against the explosion of rocks {on floor pillars and veins) and on the immediate front that surrounds underground workings such as the development of linear excavations (galleries, chimneys and pikes) or increasing the subsidence as in the sinking methods by blocks or panels

The invention consists in extending the applicability of the explosive fracturing technique in new underground workings; creating - externally - to them and prior to their development a protective shield piercing in their surroundings a curtain of long shots and by means of the blasting of those long shots, preventing the occurrence of rock explosion to safeguard the integrity of these expensive and vital underground works and so that they remain unscathed, until they complete their useful life.

The explosive to be used in the blasting will be an emulsion of great power and high detonation speed (VOD), ideally, with water plugs in cartridges.

In each long shot, the detonation will start with electronic detonators and as the preconditioning experience suggests, they should be initiated with minimum delays of 100 millis seconds. BRIEF DESCRIPTION OF THE DRAWINGS

90 Caverns

Fig. 1 shows a hypothetical infrastructure 1 that is required to protect, for example, a cavern. On both sides are the Drilling Galleries 2 which, in this particular case will be: horizontal and parallel to each other, perpendicular to σ and also coplanar with the geometric center of the future cavern and with σ \. There are also sets of 95 long 3 shots drilled from each drilling gallery; Each set consists of two rows; the long throw sets frame the future cavern 1. The overlapping zones 4 of the long throw sets are also shown.

Fig. 2 shows the thickness (a) area fractured by the detonation of a row of long shots 3 (line of segments) and also shows the significant thickness (b) of the degraded area, just 100 in the direction of σ i. Even if a small, b will always be important.

Construction of vertical underground works.

Fig. 3 shows the fracturing technique with explosives applicable to: ore hoppers or pikes 5. In these cases, a vertical long throw curtain 8 arranged in two rows must be drilled from the Drilling Galleries 7. It is also appreciated, the hexagonal arrangement 105 of the Drilling Galleries, which will facilitate its excavation.

Tunnels

Subhorizontal Long Shot Curtain.- Fig. 4 shows, schematically, the plant of an excavating tunnel, its current front 9, affected by a high subhorizontal field of stresses σ sub-perpendicular to the tunnel. The proposed method to apply the fracturing technique with explosives, requires digging, from the vicinity of the forehead, the lunges

10, from which the new long shots 11 will be drilled, which will be parallel to the tunnel. Long shots 12 and 13 are also visualized, perforated from previous thrusts 14, which were already thundered. It also shows the future progression of the tunnel, represented by lunges 15 and forehead 16.

115 In the same Fig. 4, section A - A is a schematic side view of the tunnel and the current front 9. There are new 10, old 14 and future 15 lunges, as well as long shots: new 11; old 12 and 13 and the future front 16.

Umbrellas with long peripheral shots. - Fig. 5 shows, schematically, the plant of an excavation tunnel 17, located in a high subhorizontal or subvertical field of 120 efforts with σ ι sub-parallel to the axis of the tunnel. On the periphery of its current front, long shots 18 have been drilled to form a kind of umbrella, which once thundered will allow to continue advancing protected with that external protective shield. Also shown there are future fronts 19. A series of long shots corresponding to the umbrellas that made it possible to advance 20 are also displayed.

125 The vertical section A - A shows, schematically, the same elements of the plan view and additionally the future umbrellas 21.

DETAILED DESCRIPTION OF THE INVENTION

It is necessary to develop new tactics and strategies, to build and protect the expensive and vital underground works, - caverns, tunnels and pikes - from the destructive effects of the 130 rock explosions, from the beginning of its construction until they complete their useful life and of no less importance, reduce the construction period. The novelty of this invention is the creation of an external protective shield, for those infrastructure excavations exposed to high stress fields.

The shield consists of creating, previously, around the future underground work a degraded zone 135, creating in its surroundings - with long shots -, a protective curtain through the application of the fracturing technique with explosives of the long shots, of such that the high efforts existing in the deep deposits are relieved by the flexibility of the pre-conditioned area.

"To be truly successful, the relief blast will not only fracture, sufficiently, the rock 140 in the area prone to potential rock explosion, to reduce the ability to transmit efforts from the area; but it must also transmit or shift the efforts to the adjacent solid rock so that it does not translate into the creation of a similar problem. "(Blake W.)

Depending on whether they are major tunnels or major excavations such as Caverns or vertical works (chimneys, pikes or others), the following solutions are proposed - and their variants - 145 to form the external shield:

1.- Tunnels.

1.1.- Side curtains with long shots.

It will be applied, when the predominant stress component is subhorizontal and sub perpendicular to the tunnel axis.

150 It will consist of the drilling and its subsequent blasting, of a vertical curtain of long shots, perforated from lunges excavated on both walls of the new tunnel and parallel to them.

The new drilling lunges will be placed, at most, about 10 m behind the forehead. The distance between the thrusts will be a function of the length and precision that long shots can reasonably reach.

155 The distance between each row of long shots and the wall of the main tunnel will be of the order of 10 m or less.

Long shots will be mostly subhorizontals; the curtains will be oriented in the direction of the advance and parallel - or slightly divergent - of the tunnel axis.

At least five (5) long shots will be drilled from each lunge. The appropriate amount, 160 will depend on the height of the tunnel.

The long shots will have a diameter of between 100 and 150 mm and their length will be about 40 m.

For reasons of precision, it is recommended that the length not exceeding 40 meters be drilled. For this reason, special attention should be paid to maintaining the linearity of the perforations, to prevent the buckling from falling very 165 below the floor of the tunnel or getting too close to the tunnel to be protected.

The minimum distance between the front of the tunnel and the bottom of the shots already detonated will be at least 5 meters. Moving forward, without detonating the next long-throw curtain, will carry the risk of instability. 170 1.2.- Umbrella with long shots.

This scheme can be applied in all circumstances and mainly when σ \ presents a course parallel to the axis of the tunnel (sub horizontal or sub vertical).

The protective shield will consist of the perforation of an umbrella set, which will progressively form successive shields of blast-fractured rock in front of the tunnel front.

175 Each umbrella is made up of several long shots, those that are arranged in the shape of a pyramid trunk around the tunnel and whose smaller base will be the perimeter of the tunnel front and its subsequent blast, will configure a degraded area immediately in front of the current front , which will reduce the ability to transmit efforts.

Long shots will have a minimum length of 10 m. The minimum diameter of the perforations 180 will be of the order of 75 mm. All shots of the umbrella will form a divergent angle between 20 ° and 30 ° with respect to the longitudinal axis of the tunnel

As in 1.1.- Side curtains with long shots., The minimum distance between the front of the tunnel and the bottom of the shots already detonated, will be at least 5 meters. Moving forward, without detonating the next long-throw umbrella, will carry the risk of instability.

185 1.3.- Variant: Curtains and umbrellas with long shots.

In extreme environments with very high stress, you can use a combination of the two previous methods, that is: Long throw curtains pierced from lunges and long throw umbrellas.

2.- Large caverns.

190 To protect those major works, which demand a large volume excavated - caverns, for example -, we will proceed to surround the work with long throw curtains, drilled from Perforation Galleries parallel to each other, perpendicular to σ-ι and located in the outside the work, which will be thundered to form the protective shield of the future work.

In facilities, such as: workshops, warehouses, offices or a crushing room; The external shield 195 will be configured from two or four drilling galleries - depending on the size of the work - which will surround the future excavation. All of them will be parallel to each other and perpendicular to σι.

At least two galleries will always be coplanar with σ-ι and with the geometric center of the cave and will be located on opposite sides of the cave.

200 Two sets of long shots are drilled from each gallery, with two rows each; one set facing the top of the cave and the other set towards the bottom of it. Ideally, each set of long shots, from each gallery, should overlap 4 above and below the infrastructure to be protected, framing the future caveman.

Fig. 2 graphs the importance of both sets of long shots, of each 205 drilling gallery, forming the vertical angle φ with σ i. It is also observed there that between each pair of shots of a row, a rock mattress fragmented by blasting of thickness (a) and which, the smaller the angle φ, significantly increases the thickness (b) of that degraded area. This, just in the sense of the maximum stress component σ \, which will increase the protective capacity of both: the occurrence and damage that would cause the explosion of rocks in future works.

The diameter of the perforations will be of the order of 100 to 150 mm.

Once the degradation blast has been carried out, the thundered zone of the long throw assemblies will become an effective shield, reducing the capacity for transmitting efforts to the infrastructure.

215 3.- Sub vertical works

The greatest risk to which these works are exposed, is represented by the component of the maximum effort σ i, whatever its orientation.

In those vertical works (transfer pits, hoppers, etc.), the shield of protection will consist of drilling, around it, descending (or ascending) wells, from 220 Drilling Galleries arranged in the form of a hexagon or another geometric figure. The work to be protected is located in the center of the hexagon.

For reasons of precision in the drilling of long shots, it is recommended that its length does not exceed 40 meters.

ADVANTAGES

225 Unlike other stretching techniques - hydraulic fracturing, e.g. - the proposed techniques will allow to advance in the excavation of the aforementioned infrastructures, very quickly, with few interruptions and in a safe way.

An important advantage of this technique is that the protection shield will remain in force throughout the useful life of the facilities.

230 On the other hand, the containment of the field of efforts, only by means of a laborious, dense, robust, slow and expensive fortification, etc., always keeps latent the possibility of an explosion of rocks, which can be triggered by earthquakes or by rearrangement of the field of efforts that induces the same mining exploitation.

By taking due precautions, a large part of the main works of the future 235 infrastructure, such as the Crushing Plants, can be executed in parallel with the process of the fracturing technique by blasting. For example, to gain time, you can excavate, in parallel with the Drilling Galleries and the drilling of long shots, access to the different levels of the work, as well as the excavation of pilot galleries at different levels, within the ship.

240 245 REFERENCES AND BIBLIOGRAPHY

Blake W., 1982. "Destressing To Control Rock Bursting," Underground Mining Methods Handbook.

Blake W. 1984, "Rock Preconditioning as a Seismic Control Measure in Mines," Proceedings of the International Congress on Rock burst and Seismicity in Mines, Johannesburg.

250 Wagner H. 1984. "Support requirements for rock burst conditions." Proceedings of the International Congress on Rock bursts and Seismicity in Mines. Johannesburg

U. S. DEPARTMENT OF THE INTERIOR, 1947. Bulletin 95. "A glossary of the mining and mineral industry"

Claims

CLAIMS What is claimed is:

1. Neutralize the occurrence of rock explosions and reduce the construction period of those main underground infrastructures, such as: caverns, tunnels, chimneys and pikes; located in depth and subjected to high stress fields, by means of the fracturing technique through the blasting of long shots; consistent in that, prior to its excavation or before each advance, permanently degraded areas were created in its immediate environment; where, the protection thus provided to these works will enable its construction to proceed safely, without major interruptions and, consequently, faster.

2. Neutralize the occurrence of rock explosions and in passing reduce the construction period of those main underground infrastructures, by means of the fracturing technique through the blasting of long throws, according to Claim 1, CHARACTERIZED because, around the Caverns will be excavated, at least, two horizontal Drilling Galleries; where the Drilling Galleries are strategically located on opposite sides of the future cavern to be protected; where, in the case of large caverns, four or more Drilling Galleries will be required around it, parallel to each other and perpendicular to σ1; where, a couple of Drilling Galleries and the geometric center of the cavern will be contained in the same plane as the; where, from each drilling tunnel, two divergent sets of long shots will be drilled hugging the cave; where, each set will consist of two parallel rows of long shots; where the shots of each row will be distanced from each other in about 4 m; where, the sets of long shots, of neighboring Drilling Galleries, must overlap and embrace the cavern as a wrapper; where, all long shots must be contained in parallel and vertical planes forming a horizontal angle of about 20 ° with the vertical planes containing the maximum component of the stress field σ1; where, the long shots will be around 100 to 150 mm in diameter and will be spaced apart from each other by about 4.0 m; where, in order to obtain high precision, its length should be a maximum of about 40 m; where, the rows of long throws, are detonated thus creating, prior to digging the cavern, an external degraded area of fractured rock, which, as a shield, will surround the cavern.

3. Neutralize the occurrence of rock explosions and reduce the construction period of those main underground infrastructures, by means of the fracturing technique through the blasting of long throws, according to Claim 1 CHARACTERIZED because, to protect tunnels when σ is near the horizontal sub and perpendicular to the future tunnel, it is necessary to protect the flanks of the tunnel with Long Shot Curtains; where, near the front of the tunnel, two small and short transverse lunges of 5 to 10 m in length are excavated, one on each wall and about 5 meters away from the front of the tunnel; where from each lunge a Curtain is drilled with several long shots of about 40 meters long in the direction in which the tunnel advances; where, the shots will be 100 to 50 mm in diameter, parallel to the tunnel and separated from the walls by about 5 to 10 meters; where, the long throw rows are detonated, creating an area of intensely fractured rock on both sides of the tunnel, protecting it from rock explosions which will allow you to move forward, safely, with the excavation of the tunnel for about 30 to 35 meters ; where then a new pair of lunges will be excavated about 5 meters away from the forehead and a new cycle of long-throw drilling and the blasting of new Curtains will begin, and so on.

4. Neutralize the occurrence of rock explosions and in passing reduce the construction period of those main underground infrastructures, by means of the fracturing technique through the blasting of long throws, according to Claim 1 CHARACTERIZED because, to protect tunnels when the orientation of σ1 is sub parallel to the axis of the tunnel or is sub vertical to the same axis, it is necessary to provide it with a protective umbrella-shaped shield, by means of a set of long peripheral shots, perforated forward of the tunnel face and executed previously at each advance of the forehead; where, on the perimeter of the tunnel front, the set of long shots will diverge forward and outward from the periphery of the tunnel, forming angles of around 20 ° with the sub horizontal axis of the tunnel; where the length of the shots would be, ideally, about 20 m in length and about 75 mm in diameter; where, long shots loaded with explosives are detonated, creating an area of intensely fractured rock in front of the tunnel's forehead, protecting it, like a shield, from rock explosions; where, to protect the tunnel walls, the length of the blocks that confine the explosive should be about 5 m in length; this will allow to advance, of safe form, with the excavation of the tunnel of 10 to 15 m; where, then a new umbrella will be pierced and detonated and so on.

5. Neutralize the occurrence of rock explosions and in passing reduce the construction period of those main underground infrastructures, by means of the fracturing technique through the blasting of long throws, according to Claim 1 CHARACTERIZED because to protect sub vertical works such as: Piques; ventilation chimneys; ore collection hoppers; etc., in whose environment the component of the stress field σι is presented in any position; consisting of applying the fracture blasting technique with long shots; where two parallel rows of long shots are drilled vertically, from horizontal Perforation Galleries arranged on one or more levels in the form of a quadrangle or rhomboid, around the future work; where the work to be protected is located in the center; where, before digging the work, the Long Shot rows are detonated, creating, around them, a degraded area of intensely fractured rock.