GB1572556A - Process for protecting underground cavities against water inrush - Google Patents

Description

(54) A PROCESS FOR PROTECTING UNDERGROUND CAVITIES AGAINST WATER INRUSH (71) We, BANYASZATI KUTATO INTEZET of Budapest III., Mikoviny utca 2-4, Hungary, TATABANYAI SZENBANYAK, TATABANYA, of Vertanuk tere 1, Hungary, ALUMINIUM IPARI TERVEZO VALLALAT of Budapest XIII., Pozsonyi ut 56, Hungary, all bodies corporate organized under the laws of Hungary, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention concerns a process for the protection of underground cavities against inrush of water.

Pits, shafts, mines or other underground cavities are often subject to water inrush.

The safety of human life and goods requires prevention against undesired inflow or inrush of water, or at least a subsequent limitation of their damaging consequences.

According to the method of intervention used, there are basically two kinds of pro tection: preventive protection and subse quent, i.e. post-inflow defence.

The defensive methods are restricted to the removal of the damaging consequences of a water inrush occurring inside of an already developed underground cavity, i.e.

the removal of the water that has penetrated into the cavity and to the limitation or elimination of such a recurrence by a subsequent sealing-off of the sources of water.

Post-inrush defence often necessitates a temporary evacuation of the cavity to salvage life and goods.

Post-inrush defensive measures have inherent drawbacks that are now discussed here in further detail.

Methods of preventive protection aim at the exclusion in advance, of the possibility of a water inrush in the area of the cavity yet to be developed by changing the hydrogeological conditions in the surroundings of the cavity to be protected.

Known methods of preventive protection include construction of dams and lowering of the level of the water table.

A protective water dam can be achieved by: - a protective sealing-off or reinforce- ment of the strata between the cavity to be protected and water-bearing rock; - by walling (sheet-pile, slab-plug, sinkwall) erected before the development of the cavity, and safety pillars built from rocks suitable for construction of water dams.

Preventive protection methods are, in general, characterised in that no water movement follows the rock movements involved.

In contrast, by preventively lowering the water table level advantageous water movements are induced in the reservoirs or waterbearing rock that endangers the planned cavity; in other words, the process of natural water movements is enhanced by a preventive tapping of the water reservoir. It is also characteristic of preventive water level lowering that the movements of water and the changes in the conditions of movements are induced before the development of the cavity (i.e. before the rock movements) by a cavity system separated from the cavity to be protected, wherein the tapping elements of this cavity system are formed directly into the water-bearing rock itself, and more particularly in its zones that have (yood water conducting capacity thus allowing the accumulation of the required quantity of water with the minimum possible number of tapping elements.

The methods of preventive protection are undoubtedlv more advanced than the methods of post-inflow defence. In some cases preventive protection is comoulsorily prescribed by the authorities, for safety reasons.

The known methods of preventive pro tection have several serious drawbacks, however. Some methods of preventive water damming (preventive sealing-off or reinforcement of rocks, sink-walls, sheet-piling) can only be applied to smaller cavities and cavity systems (pits, adits) in view of the costs involved. For the erection of suitable safety pillars favourable natural conditions are required and thus their applicability is also limited.

The most widely used water controlling method is the preventive lowering of the water level. Although this is more expensive than post-inflow defence, it is, in view of the technology involved and of safety, substantially better than the latter, A particular drawback of this method, however, is that it often has grave, unforeseeable direct and indirect damaging effects on the environment. Such environmental damage includes e.g. the drying-out of wells and springs or a reduction of their abundance of water; in some cases, subsidence, damage to agriculture, pollution of natural waters, allowing the infiltration of contaminated pit water etc.

In certain cases damage to the environment can be made good. The dried-out wells and springs may for instance be replaced by water supply systems. There are, however, medicinal waters or spas of irreplaceable value, the drying-out of which is equivalent to an elemental disaster.

For instance, in Hungary, due to preventive water level lowering employed in the region of bauxite mines in the hilly country of Southern Transdanubia several important wells have dried out completely and even the water abundance of the world-famous hot springs is He'viz has decreased. In the northern region of the Transdanubia Downs, learning the lessons from this experience, methods of post-inrush defence are used in the main in order to prevent jeopardising the world-famous hot springs of Budapest.

An aim of the invention is the elimination, or at least reduction, of the drawbacks of the methods of preventive protection de- scribed above.

The underlying task of the invention is to provide a process for preventive protection which is significantly simpler and cheaper than known processes and which causes no or very little damage to the environment.

The process of the invention is based on the perception that the abundance of water inrushes occurring spontaneously in underground cavities is smaller, generally considerably smaller, than the quantity of water that it is necessary to tap off in order to achieve an effective preventive lowering of the water level. If, therefore, a tapping element is constructed in close vicinity of the cavity to be protected, which tapping element is independent from the cavity but conforming thereto, the cavity can be protected by "cheating" nature. The quantity of water to be removed by this kind of tapping element is substantially smaller than would be the case for a possible preventive lowering of the water level; in other words, no aggressive disturbance of the hydrogeological conditions takes place.

Based on this recognition, the invention solves the problem by providing a process for the preventive protection of an underground cavity against water inrush from a waterbearing layer, wherein a water confining layer is located between the waterbearing layer and the cavity to be driven, and wherein the water confining layer can, due to rock movements occurring on driving of the cavity, become permeable to water, the process being such that before the driving of the cavity, one or more tapping element(s) are driven into the water confining layer adjacent to the location on which the cavity is to be driven, whereby the sort of rock movements are initiated between the tapping element(s) and the waterbearing layer as occur at the driving of the cavity, so that water permeating said water confining layer as a result of said rock movements is removed by the tapping element(s).

It is advantageous if in the vicinity of the cavity to be protected, a drift or a borehole constituting the tapping element is formed, the latter expediently by a drilling ng.

In a preferred mode of carrying out the process according to the invention, the waterreleasing tapping element is sealed off from its surrounding and, under a pressure greater than the pressure of the water to be drained, a self-hardening sealant is pressed into the tapping element. It also proved to be advantageous to press into the tapping element contiguous with the water-releasing tapping element a self-hardening sealant, and preferably in such a way that the self-hardening sealant is first pressed into the tapping element contiguous with the water-releasing tapping element, and thereafter into the water releasing tapping element itself, but only after the hardening of the first dispensed sealant.

In another preferred form of carrying out the invention, sealing-off of the waterreleasing tapping element is carried out by an injector pipe introduced into the tapping element and sealed by a packing piece. It is of advantage if the interior of the packing element is also filled in with a self-hardening element or several packing pieces are used and the annular space between the packing pieces is also filled with a selfhardening sealant.

In another embodiment, the sealing of the water-releasing tapping element from its surroundings is carried out by an injector pipe introduced into the tapping element sealed by a swelling hardening material. The vein of the water source is capped by a cover bell to withstand the water pressure of the water source and the injector pipe is connected to this cover bell. It is expedient to fill in also the space inside the tapping eiement between the outside of the bell and the injector pipe with sealant that hardens by swelling. It is advantageous if those tapping-elements that do not release water are sheet-piled.

The self-hardening material is prepared on the surface conveniently without binder and the binder is only added directly before bringing the material into the injector pipe.

In certain cases it might be of advantage at least partly to fill with a self-hardening material two previously formed tapping elements before forming a further tapping element to be disposed between the first two tapping elements. In other cases it may be advantageous to develop the tapping element at least partially by hydraulic mining.

The invention is further explained by reference to preferred embodiments illustrated in the accompanying drawings, wherein: Figure 1 is a schematic plan view of a longwall face; Figure 2 is a section taken along the plane II-II of the longwall face shown in Figure 1; Figure 3 is a schematic plan view of another longwall face; Figure 4 is a section taken along the plane IV-IV of the longwall face shown in Figure 3; Figure 5 is a vertical section of the surroundings of a planned tunnel; Figure 6 is a schematic plan view of yet another longwall face; Figure 7 is a section taken along the plane VII-VII of the longwall face shown in Figure 6; Figure 8 is a section taken along the plane VIII-VIII of the longwall face shown in Figure 6; Figure 9 is a schematic plan view of a longwall face with a tapping element;; Figure 9a is a vertical section of the longwall face shown in Figure 9 perpendicular to the development roads or headings; Figure 9b is a stepped vertical section of the longwall face shown in Figure 9 across a heading and a drainage road; Figure 10 shows the application of an injector pipe line secured by a packing piece in a water-releasing tapping-element; Figure 11 shows a schematic lay-out of the preparation and introduction of the sealant and sheet-piling materials; Figure 12a shows the first phase of the development of contiguous parallel tapping elements; Figure 12b shows the second phase of the development of the latter; Figure 13 shows the extension of the tapping elements by hydraulic mining; Figure 14 shows the use of an injector pipe provided with a cover bell at the location of a water inrush;; Figure 15 shows the use of a sealant that self-hardens by swelling for the injectorpipe; and Figure 16 shows the use of a sealant that self-hardens by swelling in the case of a multiple water inrush.

The longwall face shown in Figures 1 and 2 consists, as usual, of a front 1 and of two headings 2, 3 that run parallel to each other and perpendicularly to the front 1. Since the raw material deposit 4 on which the longwall face is supported is slanting (Figure 2), the heading 2 runs deeper than the heading 3. The immediate sill of the deposit 4 consists of a water-tight layer of clay 5 under which a water-bearing layer 6 is situated.

The thickness of the water-tight clay layer 5 is not sufficient to stop the water inrushes flowing out of the water-containing layer 6.

The preventive protection according to the invention is in this case applied in such a way that from the deeper heading 2 that runs ahead of the front 1, boreholes 8 serving as tapping elements are inserted which run approximately parallel with the sill surface 7 and also parallel with or at an angle to front 1 in the water-tight layer 5. Where the longwall face crosses a fault line 9 (the crossing point can be determined when the headings 2, 3 are advanced) bore-holes 8 are placed on both sides of the fault-line; at other places of the longwall face the number of bore-holes to be formed will depend on the expected abundance of water. Driving the tapping elements 8 causes rock movements similar to those caused by driving the headings and advancing the front 1 so that water permeating the layer 5 as a result of these movements is removed by the elements 8.

Thus, with the aid of the bore holes running ahead of the front 1 the cavity system of the longwall face is mapped out and a "trap" is set for the water inrushes. The water is drained away from the bore-holes 8 by the heading 2 and via a per se known and a non-illustrated water collecting- road system to a water-raising installation (e.g. a water pumping station).

In the case of a longwall face as shown in Figures 3 and 4 which also consists of a front 1 and two headings 2, 3 the tappmg elements 10 are-formed with the aid of drilling rigs in the deposit 4 itself. Pipe lines 11 are inserted into the water bearing tap ping elements 10, as distinct from the nonwater-bearing tapping elements which are filled in with granular sheet piling material 13 by a known pneumatically operated sheet piling device 12.

Figure 5 shows a cavity to be protected which is a tunnel 14 of large cross-section.

The planned cross-section of tunnel 14 is shown in broken lines and is set in a watertight layer 5 consisting of rendible marl to which a water-bearing layer 6 consisting of karst is tectonically connected, the layer 6 being bounded by an interchange surface 15. The tunnel 14 is exposed to water inrushes originating from layer 6 because the protective effect of the water-tight layer 5 is insufficient The preventive protection according to the invention is achieved here by advancing a drainage road 17 as the tap ping element along the immediate vicinity of the planned line of the tunnel 14, whereby the cavity to be protected is mapped out.

This will result in the same water and rock displacements as by constructing the planned tunnel 14.

A "trap" is therefore set for the water and the inrushing water is removed via the drainage road 17. In the cross-section of the planned tunnel 14 and parallel to the drainage road 17 a sill adit 18 is formed, the front of which is advanced in relation to the front of the drainage road 17 by a distance of 10 to 15 meters. The adit 18 lies higher than the drainage road 17 and is connected to it by rise entries 19 spaced at a distance of 50 to 150 meters. Adit level 18 forms, therefore, an escape roadway of the drainage road 17 and, at the same time, serves for ventilation. The tunnel 14 is advanced by any desired distance ahead of the front of the adit. The drainage road 17 can be permanently retained for water removal, mine ventilation and technical servicing.

Figures 6 to 8 show an example of a combined application of the preventive protection according to the invention and the known post-inrush defence. The direct sill layer of the longwall face consisting of the front 1 and the headings 2, 3, is a watertight layer 5 of clay. The thickness of watertight laver 5 varies considerably along the longwall face (Figure 8). To the left (according to Figures 6 and 8) the probability of a water inrush is slight The application of the process according to the invention is, therefore, not absolutely necessary. It is more convenient to drill subsequently boreholes 21 into a more deeply advanced drainate road 20 according to necessity and to remove the inrushing water with the aid of these bore-holes. In other words, here, a subseauent or post-inrush defence is emploved.

On the right-hand side in Figures 6 and 8 the thickness of the water barrier layer is, in contrast, smaller; the probability of a water inrush is, therefore, higher. The process according to the invention is thus used here in such a way that bore-holes 8 are advanced ahead of front 1 in the sill surface 7 of the raw material deposit 4, expediently from the drainage road 20, and from the tapping-elements.

If not only the front 1 but also the heading 2 is to be protected by the process of the invention, the front of the drainage road 20 has to be advanced by at least a few metres ahead of the front of the heading 2.

If the process of the invention should for unforeseeable reasons not afford 100% protection or if it seems more expedient to design for an efficiency of less than 100% it is naturally possible to build afterwards water drainage bore-holes 21 into the possible locations of water inrush, within the ambit of protection of the process of the invention.

The process according to the invention may favourably be used in hydrogeological conditions where the subsequently sponi taneously released volume of water in the cavity system to be protected is substantially smaller than volume of water to be tapped in order to achieve an effective protection by preventive lowering of the water level in this cavity system. The tappingelements required for carrying out the process of the invention may easily be mechanised (boring, drilling rig). As prevously pointed out, the process according to the invention may advantageously be combined with known methods of protection and enables that method of protection to be selected which is best suited to the prevailing local conditions.

Since it does not cause catastrophic damage to the environment, the process according to the invention makes it possible to provide preventive protection even in cases where only the post-inrush defence has hitherto been the only admissible procedure, e.g. in the coal and bauxite mines planned in the region of Budapest, only the process of the invention may be used, because any potential damage to the worldfamous hot springs of Budapest must at all costs be avoided.

Figures 9, 9a and 9b illustrate a further advantageous embodiment of the process according to the invention. The elements of the process already described have been allotted the same reference numbers.

The headings 2, 3 of the illustrated longwall face are connected by a main escape road 30. The deeper drainage roads 20 disposed on both sides are connected to a main drainage road 31. Starting from the two drainage roads 20 bore-holes 81, 82 are advanced. These serve as tapping-elements and are practically horizontal. The boreholes 81 release water because they are disposed in the vicinity of a water inrush 32.

Injector pipes 83 are introduced into the bore-holes 81 through which a self-hardening sealant or grouting material is pressed in. The bore-holes 82 which do not release water, are filled with a sheet-piling material.

In the course of advancing, the drainage roads 20 are always ahead of the headings 2, 3.

Figure 10 shows a concrete example of the use of water-releasing tapping elements (bore-holes) for injection. A guide pipe 85, which is introduced into bore-hole 84, has several parts 86, 87. At its front, it is fitted with spring-loaded rollers 88, while at its rear end it has a main slider 89 and an injector pipe coupling 90. After opening of the main slider 89 the guide pipe 85 can be pushed in by hydraulic feed or with the aid of a lead screw (not shown), even against inflowing water. The guide pipe 85 represents the end of a non-illustrated injector pipe line and is sealed by annual packings 91. The inner space of each packing piece 91 is connected to an injector or pipe 92 through which it is filled with a self-hardening sealant or grouting material for securing it in position.After the hardening of the sealant or grouting material inside the packings 91, the section of the annular space bounded by the packings 91 between the wall of the guide pipe 85 and the tappingelement (i.e. bore-hole 84) is filled in via another injector pipe 93 disposed inside the guide pipe 85 with a self-hardening sealant or grouting material, thus driving out the air through a ventilation pipe 94. After the sealant has fully hardened, the injector pipe line is connected to the injector pipe coupling 90 and the main slider 89 is gradually closed.

The injection is firstly carried out into the tapping elements (bore-holes) close to the water inrush and the injection is effected directly into the water releasing tapping element only after hardening of the injected sealant. The process of injection is continued until a rapid increase of the injection pressure indicates the beginning of the hardening of the injected materials and the filling in of the bigger cavities and the penetration of the material into the smaller veins feeding these cavities.

The injection may be carried out with e.g. Kipk6sludge (clay-based cement with a water-glass binder) or with a sludge consisting of an ash-cement mixture with stabiliser additives (bentonite, clay, CMG, etc.).

Figure 11 shows an advantageous mode of preparing and supplying of the sealant.

The grouting sludge material 97 (e.g. ash, cinder) stockpiled on the surface is agitated in water and dispersed in a disaggregating machine 96 but contains, at this stage, no binder. It is then transported to the work site (drainage road 102) via a gravity pipe line 98 where it is mixed with a binder (e.g.

cement) in another disaggregating machine 99, the binder being conveyed there inde pendently by an aerial ropeway. The sealant or grouting thus obtained is pressed into the bore-hole 104 in a coal deposit 105 by an injector pump 101 via the injector pipe line 103. A separate transport of the binder is necessary because the mixing is carried out on the surface and if in the course of mixing a stoppage occurs, this would cause solidification of the grouting material inside the supply pipe line.

The material for sheet-piling the nonwaterbearing bore-holes is also prepared on the surface and is transported to the work site via a sealant-conveying pipe line during intervals in the sealing-off process (injection).

In some cases (e.g. for a longwall face) the tapping-elements for mapping out the underground cavity must be arranged relatively densely to each other. The coal-ribs between the tapping elements break after a certain time. Although this is advantageous from the point of view of triggering off the required rock movements, it could, however, have a disadvantageous effect on a subsequent injection at the debouching point of the tapping elements. In such cases only every second tapping element (bore hole 106) is advanced (Fig. 12/a) in the first place (Fig. 12/a) and their debouching point is filled in with grouting material 108 (Fig. 12/b). For the purpose of an injection to be carried out subsequently, an injector 109 is inserted into the grouting 108. The tapping elements (bores 110) lying therebetween are drilled only after the hardening of grouting 108 is completed.

If the operational field of the system to be protected cannot be mapped out even by densely arranged tapping-elements (boreholes), it may be useful to extend the tapping elements by hydraulic mining (Fig. 13).

Here from one of the drainage roads 102 driven into the coal deposit 105 bore-holes 104 of large diameter are advanced by means of a drilling machine 111. A hydraulic mining machine 113 provided with vanes that open in pincer-like manner is placed in these bore-holes by means of a rod mechanism 112. When opening, the vanes carve out room for themselves.

Thereafter, they are retraced by the rodmechanism 112 at the same rate as the hydraulic mining. The extension of the boreholes before their mouth (debouching point) is necessary to enable sealing 114 (or sheet-piling) to be carried out later.

Figures 14 to 16 show a further embodiment of locking the water-releasing tapping elements by injection (sealing).

In the case of Figures 14 to 16 there is concentrated water inrush 121 within a tapping element 120. A cover bell 122 is placed over the mouth of this concentrated water inrush. The bell is pressed into the rock that surrounds the mouth by a hydraulic or by a mechanical (e.g. lead-screw) pressure equipment (low resistance) is connected to the cover bell 122 and is fitted with a main slider 125 as well as an injector pipe coupling 126.

Then, the interior of the tapping element 120 around the cover bell 122 and the injector pipe 124 receives by blowing-in a swelling-hardening material produced by a foam-generator (not shown) e.g. a coldfoaming polyurethane (Figure 15). After hardening of this material 127, the main slider 125 is gradually closed and the injector pipe 124 is connected to the injector pipe line. The injection is then carried out as described above. After completion of the hardening of the injected hardening material the dam mode of swelling hardening material and the injecting means may be removed.

After hardening of material 127, the main slider 125 is gradually closed according to the procedure described above, and the injection is carried out. If the water inrush is close to the front, the front itself constitutes the first dam.

WHAT WE CLAIM IS: 1. A process for the preventive protection of an underground cavity against water inrush from a waterbearing layer, wehrein a water confining layer is located between the waterbearing layer and the cavity to be driven, and wherein the water confining layer can, due to rock movements occurring on driving of the cavity, become permeable to water, the process being such that before the driving of the cavity, one or more tapping element(s) are driven into the water confining layer adjacent to the location on which the cavity is to be driven whereby the sort of rock movements are initiated between; the tapping element(s) and the waterbearing layer as occur at the driving of the cavity, so that water permeating said water confining layer as a result of said rock movements is removed by tapping element(s).

2. A process according to Claim 1, wherein the or each tapping element which releases water is sealed off from its surroundings and subsequently a self-hardening sealing material is injected into the tapping element at a pressure that is higher than the pressure of the water released.

3. A process according to Claim 1 or 2, wherein into the tapping element next to the releasing tapping element a sealing material is injected which is also self-hardening.

4. A process according to Claim 3, wherein the sealing material is firstly injected into the tapping element adjacent to the water releasing tapping element and after hardening of the sealing material is subsequently injected into the water releasing tapping element.

5. A process according to any one of Claims 1 to 4, wherein in order to seal off the water releasing tapping element from the surroundings an injection pipe line is introduced into it which is sealed off by an expanding and hardening sealing material.

6. A process according to any one of Claims 1 to 5, wherein the flow of water within the tapping element is stopped by a cover-hood, fastened against the pressure of water, and the injection pipe line is connected to the cover-hood, the space of the tapping element outside the cover-hood and the injection pipe being filled with an expanding and hardening material.

7. A process for the preventive protection of an underground cavity substantially as herein described with reference to and as shown in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. In the case of Figures 14 to 16 there is concentrated water inrush 121 within a tapping element 120. A cover bell 122 is placed over the mouth of this concentrated water inrush. The bell is pressed into the rock that surrounds the mouth by a hydraulic or by a mechanical (e.g. lead-screw) pressure equipment (low resistance) is connected to the cover bell 122 and is fitted with a main slider 125 as well as an injector pipe coupling 126. Then, the interior of the tapping element 120 around the cover bell 122 and the injector pipe 124 receives by blowing-in a swelling-hardening material produced by a foam-generator (not shown) e.g. a coldfoaming polyurethane (Figure 15). After hardening of this material 127, the main slider 125 is gradually closed and the injector pipe 124 is connected to the injector pipe line. The injection is then carried out as described above. After completion of the hardening of the injected hardening material the dam mode of swelling hardening material and the injecting means may be removed. After hardening of material 127, the main slider 125 is gradually closed according to the procedure described above, and the injection is carried out. If the water inrush is close to the front, the front itself constitutes the first dam. WHAT WE CLAIM IS:

1. A process for the preventive protection of an underground cavity against water inrush from a waterbearing layer, wehrein a water confining layer is located between the waterbearing layer and the cavity to be driven, and wherein the water confining layer can, due to rock movements occurring on driving of the cavity, become permeable to water, the process being such that before the driving of the cavity, one or more tapping element(s) are driven into the water confining layer adjacent to the location on which the cavity is to be driven whereby the sort of rock movements are initiated between; the tapping element(s) and the waterbearing layer as occur at the driving of the cavity, so that water permeating said water confining layer as a result of said rock movements is removed by tapping element(s).

2. A process according to Claim 1, wherein the or each tapping element which releases water is sealed off from its surroundings and subsequently a self-hardening sealing material is injected into the tapping element at a pressure that is higher than the pressure of the water released.

3. A process according to Claim 1 or 2, wherein into the tapping element next to the releasing tapping element a sealing material is injected which is also self-hardening.

4. A process according to Claim 3, wherein the sealing material is firstly injected into the tapping element adjacent to the water releasing tapping element and after hardening of the sealing material is subsequently injected into the water releasing tapping element.

5. A process according to any one of Claims 1 to 4, wherein in order to seal off the water releasing tapping element from the surroundings an injection pipe line is introduced into it which is sealed off by an expanding and hardening sealing material.

6. A process according to any one of Claims 1 to 5, wherein the flow of water within the tapping element is stopped by a cover-hood, fastened against the pressure of water, and the injection pipe line is connected to the cover-hood, the space of the tapping element outside the cover-hood and the injection pipe being filled with an expanding and hardening material.

7. A process for the preventive protection of an underground cavity substantially as herein described with reference to and as shown in the accompanying drawings.