WO1999030003A1

WO1999030003A1 - Method for excavating a vertical rock cavern having an elliptical or oval cross section and a rock cavern made by the method

Info

Publication number: WO1999030003A1
Application number: PCT/SE1998/002232
Authority: WO
Inventors: Per-Anders Daerga; Karl Ivar Sagefors
Original assignee: Daerga Per Anders; Karl Ivar Sagefors
Priority date: 1997-12-08
Filing date: 1998-12-07
Publication date: 1999-06-17
Also published as: SE9704572D0; SE508833C2; AU1895599A; SE9704572L

Abstract

The present invention refers to a method for excavating a vertical rock cavern having an elliptical or oval cross section, whereby access from ground level to the cavern takes place via a ramp or through a vertical shaft, and that the cavern is intended for the storage of bulk products, e.g. gas and/or fluids. Vertical rock caverns combine a good environment for storage with favourable rock stability in the surrounding rock, which is a pre-requisite for being able to construct caverns with large spans. However, the work of excavating a vertical rock cavern has not been carried through in a sufficiently efficient manner as the work has, among other things, taken place on far too many levels. The procedure according to the invention is distinguished in that a roof section (2) and a bottom section (3) are developed on at least two levels, and that the volume existing between them is bench drilled, blasted and removed.

Description

Method for excavating a vertical rock cavern having an elliptical or oval cross-section and a rock cavern made by the method

The present invention refers to a method for excavating a vertical rock cavern having an elliptical or oval cross-section, whereby the rock cavern is intended for the storage of bulk products, e.g. gas and/or fluids. The invention even refers to a rock cavern made by means of the method according to the invention.

Constructing a rock cavern is a problem of optimisation. Different demands, often opposing one another, must be conciliated into a uniform solution. The rock bed is crossed throughout by displacement slips, crushed zones and crack systems that have more or less an irregular orientation and distribution. The rock bed is also exposed to tensions caused by its own weight and by the slow drift of the continental plates and internal collisions. The cracks and tensions in the rock bed must be taken into consideration when planning tunnels and caverns. Cracks, both large and small, are potential planes of weakness and points of fracture. Tensions in the rock generate secondary tension around the area surrounding the cavern, and in cases of an unfavourable design, can produce high concentrations of tension, often combined with cracks, that can lead to serious problems of stability.

Vertical rock caverns combine a good environment for the stored product with favourable rock stability in the surrounding rock, which is a pre-requisite for being able to build caverns with large spans. Compared with horizontal (tunnel-shaped) caverns, vertical caverns induce fewer concentrations of tension, which improves the stability and, as pointed out above, permits wider spans. In addition, vertical caverns have a smaller roof area in proportion to the storage volume when compared with horizontal caverns. This means that less roof strengthening is needed. Furthermore, vertical caverns can, with regard to the tension in the rock and the occurrence of cracks, be flexibly grouped into larger operating units. Vertical caverns can now be built with efficient methods and at a very low cost in relation to horizontal (runnel-shaped) caverns of the same size. The working environment in vertical caverns is better and the safety is higher for the underground personnel when compared with horizontal caverns. As such, vertically oriented caverns are at present those that are best optimised from the points of view of operations (running and maintenance) and the mechanical and technological aspects of the rock.

From SE-C-504 669, a procedure is previously known for excavating a vertical cavern that, however, has an essentially cylindrical cross section. For this reason, ring-shaped tunnels are excavated at three different levels in a vertical direction. As the horizontal primary tensions in the rock bed usually differ in magnitude, a cavern with an elliptical or oval cross- section is preferable compared with a cylindrical. The drilling or blasting of the large volume of rock in the cavern in SE-C-504 669 takes place at different levels and in different sequences inwards and outwards in a radial manner.

The objective of the present invention is to show a procedure for excavating a vertical or inclined rock cavern with an elliptical or oval cross-section and a rock cavern made with the said procedure. The procedure according to the invention permits a small number of working cycles and a concentration of the work to preferably only the roof and the bottom sections of the cavern. With the characteristics according to the invention, the benefit of removing material on two different levels at the same time is achieved, which allows the significant rock volume that results from the bench mining to be very quickly removed from the space it occupies. A unique place of collection is obtained at the bottom of the cavern, which allows room for collecting possible particles that precipitate from the medium that is stored in the cavern. The vertical shaft between the upper and lower loading levels in the cavern has here a funnel-shape, whereby the particles precipitated from the stored medium are led down further to the permanent bottom level. To simplify drainage and to allow cleaning of the bottom section of the cavern, it can be considered to line certain wall sections with concrete and arrange a flushing system in the bottom tunnels of the cavern. During flushing, suitable materials such as sludge and waste are transported to a collection point arranged for this purpose.

The procedure according to the invention makes use of the most modern techniques in underground mining, especially regarding drilling and blasting, and combines this with well thought out layout solutions. With regard to the roof section, this means simple development work with efficient drilling and blasting of the large underlying spatial volumes. It also allows a permanent monitoring of roof stability and permits effective ventilation during both the construction and operational phases. In the bottom section, this means a branched arrangement of gallery headings on at least two levels that unites effective removal of rock during the construction phase with a protective access and flexible layout solutions for installation, inspection and service during the operational phase. In comparison with rock caverns with circular cross-sections, caverns with elliptical or oval cross-sections offer a significantly larger storage space for the spatial width, which is of great importance when storing bulk products. In an alternative embodiment of the invention, it can be considered to use the procedure for arranging buildings for storage or archiving or other type of purpose that requires plenty of space in those cases where the rock bed lies close to the surface, plus where the horizontal spread of the building and its vertical extension from the ground level and downwards are large.

The excavation of the rock volume for the proposed building can be carried out in the same way as when constructing a cavern, apart from the fact that there is no roof. The development of the bottom section takes place in an unchanged manner, i.e. it is performed with a temporary ridge and at least one loading level. Access to the bottom level is achieved with a ramp from ground level.

The objective of the present invention is realised by means of a procedure and a rock cavern that have the features stated in the claims that follow. Preferred working procedures and embodiments are defined in the non-independent claims.

The drawings show:

Fig. 1 a vertical longitudinal section in space through the roof and bottom sections of a rock cavern according to the present invention;

Fig. 2 a horizontal section through the roof section of a rock cavern according to the invention;

Fig. 3 a vertical cross-section in space through the roof and bottom sections of a rock cavern according to the invention;

Fig. 4 a vertical longitudinal section in space through the roof section of a rock cavern according to the invention when the development work has been completed;

Fig. 5 a horizontal section through the roof section according to Fig. 4, whereby the vertical partial cross-sections of the said roof sections are also shown in Fig. 5;

Fig. 6 a vertical section through the roof section showing the drilling of roof columns;

Fig. 7 a horizontal section through a roof section according to Fig. 6;

Fig. 8 a vertical longitudinal section in space through the bottom section of the cavern with two loading levels and a temporary ridge,

Fig. 9 a horizontal section through both loading levels according to Fig. 8;

Fig. 10 a vertical cross-section in space through the cavern according to Fig. 8;

Fig. 11 a vertical longitudinal section in space through the cavern with bench drilling of vertical long -holes; )

Fig. 12 a vertical cross-section in space through the cavern with bench drilling of vertical long-holes;

Fig. 13 a vertical longitudinal section in space through the cavern with the blasting sequences marked;

Fig. 14 a horizontal section through the cavern according to Fig. 13 with the blasting sequences numbered;

Fig. 15 a vertical cross-section through the cavern with the blasting sequences marked;

Fig. 16 a vertical longitudinal section through the cavern with the drilling of the temporary ridge shown schematically;

Fig. 17 a vertical cross-section through the cavern with the drilling of the temporary ridge shown schematically;

Fig. 18 a vertical longitudinal section in space through the cavern with the rock working completed;

Fig. 19 a horizontal section through the roof section of the cavern with the rock working completed;

Fig. 20 a horizontal section through the bottom section of the cavern with the rock working completed;

Fig. 21 a vertical cross-section in space through the cavern with the rock working completed;

Fig. 22 a vertical longitudinal and cross-section in space through the roof section of the cavern with the bolt strengthening shown schematically;

Fig. ,23 a horizontal section through the roof section of the cavern.

Fig. .24 vertical cross-sections in space through the roof section of the cavern with the bolt strengthening shown schematically in a number of partial sections taken at different lengths along the roof section as indicated in Fig. 23; Fig. 25 vertical cross-sections in space through the roof section of the cavern with the ventilation holes between the cavern and the multi-purpose gallery headings; Fig. 26 a horizontal section through the roof section of the cavern with the ventilation holes shown schematically in a number of partial sections through the roof section; Fig. 27 a vertical longitudinal and cross-section in space through the roof section with the ventilation holes shown schematically; Fig. 28- different sections through the cavern according to the invention when a hydraulic Fig. 31 cage is arranged around the cavern.

Figs. 1-3 show an overview of the rock cavern according to the invention. The excavation procedure begins with the development of at least one, but in this case two multipurpose gallery headings 1 , roof section 2 and bottom section 3 in that order. The multi-purpose gallery headings 1 constitute the platform for cable bolting of the roof section 2 and accommodate the ventilation equipment during the construction phase. During the operational phase, they are used for inspection of the stability of the roof section 2 and for evacuating/supplying air when the cavern is filled/emptied.

The roof section 2 is the work site for the bench mining, which is the largest operation from a volume point of view. This site is the starting point for the vertical long-hole drilling down to the bottom section 3, as well as for the setting of charges and the blasting of the bench rock.

The bottom section 3 is used for removing the rock broken down by blasting during the building phase and for pumping in or out the products that are to be stored during the operational phase, as well as for collection of sedimented deposits from the products.

Access to the cavern from the surface level is achieved via a ramp or a vertical shaft. The choice between these two depends primarily on the depth to the location of the cavern. Normally, a ramp is the most advantageous alternative from a time and cost point of view for depths relatively close to the surface (down to about 300 metres), while the shaft alternative is preferable at greater depths. The choice between these two decides which means of transport is used to bring the rock masses up to the surface. As a consequence of the excavation procedure according to the invention, access to the cavern is only needed at two places; the roof section 2 and the bottom section 3. These two areas are the primary work sites.

The roof section 2 is reached from the ramp/shaft via two horizontal galleries 4, see Figs. 1 and 2, that connect to the short sides of the cavern at the height of the abutment level of the roof section 2.

Roof section 2 is also connected with the multi-purpose galleries 1 above the roof section 2, whereby the multi-purpose galleries 1 are among other things used for strengthening the roof, ventilation and monitoring stability, as has been pointed out earlier. All removal of material takes place from the bottom section 3 of cavern at two levels, 3a and 3b. The upper level 3b exists only during the construction phase. It thus has a temporary design with an essentially wedge-shaped ridge 5, see Figs. 1 and 3, in the centre of the cavern in a longitudinal direction. The ridge 5 extends from one short side of the cavern to the other. The ridge 5 is surrounded by the loading trench 6, see Fig. 3, that runs along the long sides of the cavern. Both levels 3a and 3b have loading galleries 7a and 7b respectively and communication galleries 8a and 8b respectively. The loading gallery 7a of the lower level 3a is displaced in the longitudinal direction of the cavern in relation to the loading gallery 7b of the upper level 3b. The communication galleries 8a and 8b run centrally in the longitudinal direction of the cavern and branch into 7a and 7b respectively that open into loading trenches 6 to form gaps for loading.

The temporary ridge 5 has two functions. Firstly, it guides the flow of broken rocks out towards the periphery of the cavern where the gaps for loading are located. Secondly, it provides protection for personnel and equipment during the removal of the mass of blasted rocks.

When the removal is completed, the temporary ridge 5 is blasted away in stages. This will be described in greater detail below.

The development of the roof section will now be described with reference to Figs. 4-5. Two peripheral galleries 9 are pushed forwards from the respective short side of the cavern towards the short central axis of the cavern where they meet equivalent peripheral galleries from the other short side. The shape of the roof of the peripheral galleries 9 is adapted to the curvature of the abutment. A roof gallery 10 that follows the curvature of the bow-shaped roof is additionally driven forward along the long centre axis of the cavern from each respective short side. As the galleries are driven forward simultaneously from both short sides, a total of 6 (4+2) headings are in progress.

When all galleries have met their counterpart at the short centre axis of the cavern, clefts 11 are blasted out at right angles from the centre roof gallery 10 to the respective peripheral gallery 9. The clefts follow the short centre axis. The roof section 2 is now freed along the wall periphery of the cavern and back along the long centre line of the bowed roof and four elongated roof columns 12 hold up the roof section, which at this stage is still not a finished construction. These roof columns 12 will later be blasted away in stages until the whole roof section 2, with the help of the roof strengthening, is self-supporting through the action of the arched vault. The roof columns 12 are then drilled from the clefts 11 and from the short sides of the cavern in a continuous working operation with essentially horizontal long bore holes 13, see Figs. 6 and 7. The roof columns 12 are then stooped in suitable salvo rounds towards the peripheral galleries 9 and the roof gallery 10 respectively and are then removed from these galleries. When the roof columns 12 have been taken away, the remaining rock shoulder 14 can possibly be lowered and levelled to facilitate the bench drilling that can then begin.

The development of the bottom section 3 will now be described with special reference to Figs. 8-10. The said development begins in the same way as for the roof section 2. Communication galleries 8a and 8b on levels 3a and 3b respectively are driven from both short sides of the cavern along the long centre axis of the cavern to the space inside the projected temporary ridge 5. Loading galleries 7a and 7b are then driven from communication galleries 8a and 8b respectively towards both sides to the theoretical line of the wall in the room. On the upper loading level 3b, the leading edges of loading galleries 7b are joined together so that a continuous loading trench 6 is achieved along the long wall sides of the cavern on either side of the temporary ridge 5. Finally, the vertical openings 14 are blasted down from the loading trench 6 to the loading galleries 7a of the lower loading level 3a. With this, the bottom section is completed.

The overwhelming part of the volume of the cavern is bench drilled with vertical long holes 15 from the roof section 2 and down to the upper loading level 3b of the bottom section, to the temporary ridge 5 and to the loading trench 6 of the tunnel roof, see Figs. 11-12.

The drilling work is carried out as a coherent operation. It neither affects nor is affected by other activities. As the whole of the volume of the cavern between the roof section 2 and the bottom section 3 is bench drilled with long holes, the choice of drilling equipment is extremely important. During recent years, drilling technology has improved considerably. Water-driven ITH (In-The-Hole) machinery is preferred for the bench drilling in question here. In comparison with pneumatic ITH machinery, water-driven ITH machinery reaches up to 2-3 times a greater drilling depth and has a lesser hole deviation. In comparison with water-driven top hammer machinery, water-driven ITH machinery achieves significantly lower drilling rod costs, more drilling power and a considerably lower reduction of power with increased hole length. The spatial geometry and the plane of the drilling permit the blasting of large salvos. New techniques for initiating detonation also make it possible to carry out the blasting in a gentler manner and with good downfall. Figs. 13-15 show schematically the blasting sequence for the bench. As is especially evident from Fig. 14, the blasting work begins with two opening shafts being taken up on either side of the as yet not formed temporary ridge 14. The opening shafts 16 are expanded in stages in towards the centre of the chamber until they are united in a common cleft. The bench blasting then continues over the whole width of the chamber with the bench fronts retreating towards their respective ends of the cavern. Fig. 14 shows an example of the blasting stages la, lb, 2a, 2b; 3a, 3b; 4a, 4b; 5a, 5b.

The size of the salvos is modified according to the prevailing rock conditions. Electronic so-called microblasting caps with programmable interval times permit precision blasting of large salvos. Documented benefits include more precise timing, better fragmentation, less vibration on the ground and more even rock contours.

Removal of the fragmented rock takes place in principle as in a sub-level mine. It is performed at two levels, preferably with electrically-driven LHD (Load-Haul-Dump) machinery according to the load and carry principle. The compact spatial orientation eliminates the need for trucks. Both loading levels 3a and 3b are used during bench blasting when high capacity is required, which wins large gains in time. The arrangement allows a very high removal capacity due to the many loading galleries 7a, 7b, see, for example, Fig. 13. The safety of the work is good since all personnel work in protection within the temporary ridge 5.

After the bench blasting according to Figs. 13-15 has been completed and the fragmented rock has been removed, drilling of the temporary ridge 5 takes place. The said drilling takes place from the upper communication gallery 8b, which gives the drilling hole configuration 17 for the temporary ridge 5 shown in Figs. 16-17. Removal of the blasted ridge 5 takes place partly with the load and carry principle from level 3b and partly by the fragmented rock masses being directed to the loading galleries 7a for the lower loading level 3a, from where they are removed. The actual rock working of the cavern according to the present invention is thus concluded and different sections of the completed vertical elliptical cavern are shown in Figs. 18- 21.

According to the embodiment example, there are two multi-purpose galleries 1 above the roof section 2 of the cavern that are used for several purposes. During the construction phase, the multi-purpose galleries 1 are used to stabilise the roof section with cabling bolts and as an exit for ventilated air. During the operational phase, they are used for monitoring the stability of the roof and for evacuating/supplying air during the filling/emptying of the cavern. Figs. 22-24 show an example of using bolts to strengthen the roof section 2 and the abutment. Systematic or selective roof strengthening with, for example, cable bolts 18, is carried out from the multi-purpose galleries 1. Systematic roof strengthening can be necessary, especially for large spans, i.e. over 50 metres. As the multi-purpose galleries 1 are separated from one another along the larger part of the length of the cavern, the cable bolts 18 can be spread over a larger roof area than would otherwise be possible. The cable bolts 18 are put in place before the roof section 2 is freed. Once the freeing of the roof section is complete, the possible injection of the boltholes can be performed if required. It is important that the strengthening with the cables is performed before the freeing of the roof section is begun, as this achieves the best stabilisation of the roof.

Figs. 25-27 show schematically a ventilation arrangement for the rock cavern according to the invention. Blasting gases and other air pollution are ventilated with suction fans (not shown) placed in bore holes 19 between the roof section 2 and the multi-purpose galleries 1. Exhaust air travels from the multi-purpose galleries 1 to an enclosed system of ducts leading up to the surface where purification takes place. Alternatively, the purification facility can be located adjoining the multi-purpose galleries 1, whereby purification takes place there.

The ventilation/bore holes 19 are drilled from the multi-purpose galleries 1 and are angled towards the sides so that ventilation can occur during both the development of the roof section 2 and during the subsequent bench blasting. The diameter of the boreholes 19 is determined by the space required by the fans and the turnover of air required.

If the cavern according to the invention is to be used for applications that require lining, the roof section 2 and the cavern walls must be drained so that water pressure does not build up in cracks in the rock. Figs. 28-31 show an arrangement with a curtain 20 of bore holes from the multi-purpose galleries 1 down to the galleries 21 on the abutment level of the cavern and further downwards to equivalent galleries 22 level with the bottom section 3. The bore curtain forms a ring around the cavern about 10 metres or so behind the cavern wall. Due to this arrangement, a hydraulic cage that negates the ground water pressure in the rock between the cavern and the bore hole curtain 20 is obtained.

When the cavern is filled or emptied, the air inside must be evacuated or returned respectively. This applies irrespective of whether the cavern is lined or not. It can be advantageous to use the existing ventilation boreholes 18 for this purpose. The present invention is not limited to that described above and shown in the drawings but can be modified and changed in a number of ways within the scope of the concept of the invention stated in the following claims.

Claims

1. Procedure for excavating an essentially vertical rock cavern with an elliptical or oval cross-section, whereby access from the ground level to the cavern takes place via a ramp or through an essentially vertical shaft, and where the cavern is intended for storing bulk products such as gas and/or fluids characterised in that at least one of what is known as a multipurpose gallery (1) is driven, that a roof section (2), which is located below the multi-purpose gallery (1), is developed by peripheral galleries (9) being driven that define the cavern partly in a sideways direction and partly in height, that at least one roof gallery (10) between the peripheral galleries (9) is driven to define the arched vault of the roof between the peripheral galleries (9), whereby roof columns (12) formed by the said driving are removed by boring/blasting, that a bottom section (3) is developed by driving communication galleries (8a, 8b) on at least two levels (3a, 3b) along the long centre axis of the cavern, that loading galleries (7a, 7b) are driven from the said communication galleries (8a, 8b) on at least two said levels (3a, 3b) out to the theoretical line of the wall of the cavern, that the volume of the cavern between the roof section (2) and the bottom section (3) is bench drilled, blasted and removed via at least the lower level (3a) of the bottom section (3).

2. Procedure according to claim 1 characterised in that the drilling of the roof columns (12) takes place by means of essentially horizontal boreholes (13).

3. Procedure according to claims lor2characterised in that the outermost ends of the loading galleries (7b) on the upper loading level (3b) are joined so that a continuous loading trench (6) is achieved along the long sides of the walls of the cavern, and that vertical openings (14) are blasted from the loading trench (6) down to the loading galleries (7a) of the lower loading level (3a).

4. Procedure according to any of claims 1-3 characterised in that a temporary ridge (5) with an extension along the long axis of the cavern is left remaining after bench drilling and blasting of the volume of the cavern between the roof section (2) and the bottom section (3).

5. Procedure according to any of claims l-4characterised in that two multipurpose galleries (1) are driven above the roof section (2) and are joined with one another in the area that is vertically above the short sides of the cavern.

6. Procedure according to claim 5characterised in that strengthening of the roof section (2) takes place from the multi-purpose galleries (1).

7. Procedure according to claim ╧îcharacterised in that the strengthening is carried out in the form of systematic or selective strengthening by means of cable bolts.

8. Procedure according to claim 5 characterised in that a ventilation hole (19) is drilled from the multi-purpose galleries (1) to the roof section (2).

9. Rock cavern with a vertical extension and an elliptical or oval cross-section, whereby the cavern includes a roof section (2), a bottom section (3) and a storage space between the two for bulk products, for example gas and/or fluids, characterised in that at least one multi-purpose gallery (1) is arranged above the roof section (2), and that the bottom section (3) includes a communication gallery (8a, 8b) running along the long axis of the cavern from which loading galleries (7a, 7b) extend out in a radial direction.

10. Rock cavern according to claim 9 characterised in that roof strengthening (18) and ventilation holes (19) are arranged between the multi-purpose galleries (1) and the roof construction (2).