RU2568452C1 - Method to seal anti-filtration screen under water reservoir after pit depletion - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: into a lower part of the already created antifiltration screen containing doleritic rocks, they pump cement mortar on the basis of sulphate-resistant or aluminous cement with 2% additive of calcium chloride under pressure of 0.7-0.8 MPa exceeding hydrostatic pressure, via wells drilled from underground mines. Maintain until hardened. After hardening the created rock-cement layer of the antifiltration screen and the upper part of the ore block are additionally plugged with local injections of gelling compositions GALKA® under pressure of 0.5-0.6 MPa, which is below fracture pressure of the ore safety block thickness left under the antifiltration screen. The gelling composition GALKA® has the following ratio of components, wt %: aluminium salt 5-15; carbamide 20-35; urotropine 3-10; water - balance.

EFFECT: increased strength and reinforcement of antifiltration properties of a screen when filling a pit for safe performance of underground mining works.

4 cl, 3 dwg, 1 tbl

Description

 The invention relates to methods for eliminating the influx of groundwater into mine workings during the completion of deposits by the underground method, for example, for the permafrost zone of Western Yakutia.

A known method of protecting underground operations from water penetration, including creating an anti-filter screen between underground mining operations and a body of water on a day surface, a bed of a body of water is created by a recess of rocks, and a bottom is formed in a zone of permafrost, a coating of cemented cemented clay mixture is applied to the bottom. As a clay mixture, the washing tailings of the processing plant with a density higher than the density of groundwater are used. Then the reservoir is filled with water from aquifers located above the created cover (AS USSR No. 1633125, E21C 41/00, application No. 4474377 from 08.15.88, publ. 07.03.91., Bull. No. 9).

The disadvantage of this method is the impossibility of creating an anti-filter screen at the bottom of the quarry due to the elimination of transport berms and roads. The absence of permafrost in the required intervals of the section for isolation of underground mine workings, the presence of a constant influx of aggressive drainage brines into the quarry also prevents the creation of a freezing clay stratum.

Known methods of constructing an underground impenetrable curtain and to reduce underground flow outside the curtain, including sinking a vertical shaft, drilling horizontal wells from it, injecting fixing and hardening solutions through them. In the zone of the necessary intersection of the aquifer or near the underground technological process, vertical shafts are additionally constructed, connected with each other by rows of horizontal wells, which are placed in a vertical plane one above the other, then injecting a hardening solution into them, form an underground impenetrable curtain that overlaps the aquifer from upper to lower confining or distribution zone of an underground technological process (RF Patent No. 2375580 C1, E21F 17/00, application No. 2008131979 of 08.08.2008, published on 10.12.2009, B Jul. No. 4).

The disadvantage of this method is the low efficiency of a continuous grouting curtain in a pressure aquifer. A similar event at the field was already carried out with the creation of an cement-cement grouting curtain while drilling 300 wells around the quarry and pumping cementitious mixtures into a water-saturated layer with design volumes of 3000 m ^{3 of} solution for each well, which proved to be ineffective. In addition, in the case of the implementation of the method, the cost of the sinking and construction of vertical shafts, the location of which requires the mandatory freezing of the water-saturated mass before opening, with the subsequent drilling of horizontal wells, providing complete overlap of the aquifer required for the mudding of the underground, is quite high.

The closest in technical essence and the achieved result is a method of stabilization of underground formations, including the introduction of a stabilizing composition into the underground formation, for example, pumping through the cracks and pores present in the formation and holding the stabilizing composition until it cures, in which the formation is stabilized. The stabilizing composition includes a non-shrinkable polyester resin, a catalyst, various additives and fillers (RF Patent No. 2109922 C1, E21B 33/13, application No. 95109919 from 06/17/93, publ. 04/27/98, bull. No. 12).

The disadvantage of this method is the low strength characteristics of the constructed screen, the inability to create a rigid technogenic stratum that can withstand the required increased geomechanical loads due to increased geostatic pressure when the drainage of the dry preservation system stops, followed by filling the quarry with overburden and drainage water from the aquifer. In an aggressive environment and at low temperatures, these compositions do not create the necessary strength and antifiltration characteristics of the crack filler, because the material formed by mixing the components with foaming acquires hygroscopic properties.

The objective of the invention is to increase the strength and strengthen the anti-filter properties of the screen when filling (preserving) the quarry for the safe conduct of underground mining.

This goal is achieved by the fact that in the method of sealing the antifiltration screen under a pond after working out the quarry, which includes pumping the filling materials and holding them before curing, cement mortar is pumped into the lower part of the antifiltration screen containing dolerite rocks under a pressure exceeding hydrostatic, through wells drilled from underground workings, and after hardening, the created rock-cement layer of the antifiltration screen and to the top a part of the ore safety pillar left under the anti-filter screen is additionally tamped with local injections of the GALKA ^® -NTM gel-forming composition based on the aluminum salt – carbamide – urotropin – water system under a pressure lower than the burst pressure of the ore safety pillar.

Moreover, the cement mortar is pumped under a pressure of 0.7-0.8 MPa, and the injection of the GALKA ^® -NTM gel-forming composition is carried out under a pressure of 0.5-0.6 MPa.

The cement mortar for injection is prepared on the basis of sulfate-resistant or aluminous cements with a 2% addition of calcium chloride.

And the gel-forming composition GALKA ^® -NTM is pumped in the following ratio of components, wt. %:

aluminum salt  5-15 urea  20-35 urotropin  3-10 water  rest

The injection of cement mortar into the lower part of the safety screen containing dolerite rocks allows you to create a rigid monolithic slab capable of withstanding the geostatic pressure that will arise when filling the quarry with drainage water and overburden. The pressure at which the cement slurry is pumped is determined based on the hydrostatic pressure created by the height of the brine column above the safety screen, and is calculated on forecast models. When setting cement mortar, a cement stone is formed, which forms the rigidity of the technogenic thickness. The power of the additional geomechanical screen in the form of a rock-cement slab, according to the calculations, should be about 10 m.

Additional grouting of the created rock-cement layer with gel-forming solutions allows eliminating the remaining pore-crack voids with the creation of a continuous waterproof screen. The pressure at which the thickness is injected is determined taking into account the hydrostatic pressure in the created screen (0.5 MPa) and the strength characteristics of the kimberlites of the ore safety pillar. When injecting gel-forming solutions under a pressure of 0.5-0.6 MPa, the local voidness of the array is filled and the injected solutions solidify with the creation of a waterproof screen.

Injection by gel-forming solutions of the upper part of the ore safety pillar creates additional filtration resistance in the rock mass and allows to reduce or completely remove groundwater breakthroughs in the mine workings.

In FIG. Figure 1 shows a section of the Mir pipe deposit with an existing anti-filtration screen created during dry conservation of a quarry.

In FIG. 2 shows the stages of sealing the antifiltration screen under a dangerous water body above underground mine workings - a) cementing of dolerite rock (dumping); b) additional injection plugging with gel-forming solutions in the already created rock-cement layer of the remaining water-conducting zones, as well as the upper part of the ore safety pillar.

In FIG. Figure 3 shows the dependences of the liquid filtration coefficient and pressure gradient with the initial gas permeability in μm ² : a - 14.165; b - 11.852 (after the injection of a cement-sand mortar based on sulfate-resistant or alumina cement with 2% calcium chloride addition at a temperature of 2 ° C into a disintegrated kimberlite rock corresponding to the lower part of the antifiltration screen) from the injection volumes of the solutions of gelling compositions,

where 1 - meteher-icher aquifer;

2 - ore body with the remaining reserves of diamonds;

3 - dolerite filling;

4 - loamy soils on which a welded polyethylene screen from a film 2 mm thick is laid;

5 - adit for collecting water from the surface of the screen;

6 - ore safety pillar;

7 - underground mining;

8 - wells for injection of cement-sand mortar;

9 - wells for injection of the gel-forming composition GALKA ^® .

Example.

Open-pit mining at the Mir pipe field was completed in 2001 with a pit depth of 525 m. In the course of mining, the meteoro-icer aquifer complex 1 with a water inflow of about 1200 m ³ / h was opened at full capacity. In order to extract the remaining reserves of diamonds 2 at the deposit, the Mir underground mine was commissioned in 2009. Underground mining of deposits is performed in a descending order. Treatment works are carried out using a layered mining system with mechanized (combine) ore breaking and full laying of the worked out space with hardening mixtures. As of the end of 2013, in the mark. -226 ... -230 m, a cutting layer No. 4 was formed from a hardening bookmark with a thickness of 5 m, and No. 5, located at -230 ... -235 m. Only two tapes 33 and 35 were not worked out and laid. -265 m cutting work is completed on the cutting layer No. 11.

To protect the underground mine workings from flooding in 2004, an anti-filtration screen was built in the lower part of the quarry - a system of “dry” conservation of the quarry, consisting of an embankment of coarse clastic rocks - dolerite dump 3, over which a layer of rolled loamy soils 4 was poured, on which a welded polyethylene screen from a film 2 mm thick is laid. Water from the surface of the screen through a special adit 5 goes to submersible pumps located in water-wells drilled from the upper berm of the quarry. The pumped-out water through a system of water conduits laid on the surface is fed into a storage pond, from which it is pumped and removed back through special wells to a sub-permafrost aquifer complex at the injection site.

Treatment works are carried out under the protection of the ore safety pillar 6, left in the mark. -190 ... -210 abs. m, whose power, according to the calculations, does not exceed 20 m. The horizontal sectional area of the ore safety pillar 6 is about 30 thousand m ² .

Recently, due to an increase in the water level in the quarry above design levels and the dissolution of halite filler in the ore safety pillar 6, brines from the quarry with an increase in water inflows (up to 80 m ³ / h) into underground mine workings 7 have been observed. Block No. 1 of the Mir mine is represented mainly by soluble halogen rocks. Cracks and pores of kimberlite are also filled with rock salt, when kimberlites are moistened with underground waters, their strength sharply decreases and ore blocks collapse from the roofing of the workings.

Before the start of the first stage of research, an analysis was made of all existing geological, hydrogeological and other materials for the deposit, a strategy and methodology for sealing the antifiltration screen and the ore safety pillar at the Mir mine were outlined. Various technology options and sealing locations for this part of the array were considered, while taking into account the need for full extraction of quarry reserves at the field. The solution of the problem that arises requires the implementation of the following main provisions: 1) to create a screen with such deformation indicators that can withstand geostatic loads corresponding to the full filling of the Mir pipe’s career space to natural levels and higher, taking into account atmospheric precipitation; 2) the created (reinforced) rock-cement screen and the upper part of the ore pillar must be repamped by the method of local injection, for example, GELKA ^® gel-forming compositions.

The presented concept for solving the problem, taking into account the complete extraction of kimberlite ore in block No. 1, is outlined as follows (Fig. 2). Creating a rigid technogenic screen that can withstand geostatic loads when filling the quarry with water (rock) is possible only in the thickness of a large-volume dolerite filling, which must be fixed with appropriate cement-sand mortars based on sulfate-resistant or alumina cement with 2% calcium chloride additive to create a cement-cement screen . Therefore, at the first stage of research, the power of a hard rock-cement foundation of a technogenic screen with the required strength properties is calculated based on the following considerations.

External geo-and hydrostatic loads are calculated provided that the quarry is filled to a static level (+215 abs. M). The calculation of the geo- and hydrostatic pressure that an additional rock-cement slab must withstand when filling the quarry with water (natural brines) is defined as follows:

P = N × ρ = (215 m + 190 m) × 1.08 = 437 m (water column) = 4.4 MPa,

where P is the hydrostatic pressure, MPa;

N - the height of the liquid column (brine) is the sum of the liquid column from the pit to the mark of the static level in the aquifer, m;

ρ is the density of the liquid (brine), g / dm ³ .

The calculation of the thickness of the additional screen (slab) erected from concrete under the conditions of its strength can be performed by the formula

Where; L _p - the thickness of the geomechanical screen erected from concrete, m;

λ _p - overload coefficient, taken equal to 1.1-1.2;

P - the perimeter of the kimberlite pipe, 220 m;

k _in - coefficient taking into account the shape of the body and equal to 3.4-3.7;

S is the area perceiving the generated pressure, 30,000 m ² ;

P is the maximum pressure of a liquid column, 4.4 MPa or 440 m water column at a density of 1 g / dm ³ ;

α is the angle of inclination of the side faces of the jumper, taken equal to 80 °;

R _b - the estimated concrete resistance to compression, 50 MPa (or 500 m water. Art.).

To create a rigid technogenic screen that can withstand geostatic loads when filling the quarry with water (rock) at the first stage (Fig. 2a) from underground mine workings 7 of the mine, injection wells 8 are drilled 25-30 m long into the lower part - dolerite dump 3 the previously created antifiltration screen during the “dry” conservation of the quarry. Next, cement-sand mortar based on sulfate-resistant or alumina cement with a water-cement ratio of 0.5 and setting accelerator CaCl ₂ (2%) is injected through wells 8. Solid waste tails are recommended as fine aggregate. The injection is carried out at a pressure exceeding the hydrostatic pressure (0.7-0.8 MPa). Volumetric indicators of the injected cement-sand mortar are calculated in accordance with the required capacity of the created rigid anti-filter screen (10 m). After filling with a cement-sand mortar the void space in the coarse block part of the anti-filter screen, the shutter speed (BSC) is made to harden the mortar for 72 hours.

To improve the antifiltration properties of the elements of the “dry” conservation of the Mir quarry, aimed at reducing water inflow into the underground mine workings, a second stage of sealing the antifiltration screen and the ore safety pillar above the underground mine workings under a dangerous water body is necessary. The next stage in the elimination of individual water manifestations (Fig. 2b) is carried out by the method of local injection of gel-forming compositions GALKA ^® .

GALKA ^® gel-forming compositions are low-viscosity aqueous solutions having low pour points, which makes it possible to use them for low-permeability rocks in winter conditions. The solid commodity form of the composition GALKA ^® (TU 2163-015-00205067-01) is soluble in water of any mineralization.

Due to the injection of the gel-forming solution into the wells, a gel screen forms, which creates an anti-filtration curtain, which hardens upon freezing and thawing. They are harmless to humans and environmentally friendly.

Physico-chemical properties of the solution of the gel-forming composition are shown in the table.

Studies of the structural and mechanical properties of soil samples filled with a gelling composition have been carried out. As structural and mechanical properties, the elastic modulus and plastic strength were used. The formation of gel in soil samples is accompanied by an improvement in the structural and mechanical properties of soils filled with a solution of a gel-forming composition. The values of the elastic modulus increase by at least 40%, a maximum of 5.4 times, the values of plastic strength - by a minimum of 10-40%, a maximum of 28 times.

Physical modeling of the filtration process of mineralized water of the Mir quarry and gel-forming compositions at a constant flow rate through a model filled with disintegrated kimberlite rock from the Mir quarry (fraction 0.16-0.59 mm) and saturated with mineralized water of the Mir quarry was carried out at temperatures minus 2 ° С and plus 2 ° С. Used solutions of the gel-forming composition GALKA ^® . The characteristics of the composition used in the experiments are shown in the table.

The initial gas permeability of the models was in the range from 11.852 μm ² (Fig. 3a) to 14.165 μm ² (Fig. 3b), the back pressure was 7.5 atm. The test time at the indicated temperatures is from 36 to 48 hours. The pressure gradient (grad P, atm / m), and the filtration coefficient (V, m / day) were calculated from the obtained data. The research results are shown in FIG. 3. As can be seen from FIG. 3, the injection of the gel-forming composition GALKA ^® leads to a sharp decrease in the filtration coefficient: from 2.2-2.72 to 0.001-0.02 m / day for the composition GALKA ^® . In this case, the pressure gradient increases from 0.75-1.5 atm / m to 190-240 atm / m. Thus, it is proposed to use the GALKA ^® composition for plugging the safety and ore pillars of the Mir quarry. For the injection of gelling solutions, the following parameters for grouting work were adopted: the average value of porosity is 5%, the well length is 40-50 m, the distribution radius of the composition is 2-3 m, the injection volume of the composition will be ~ 1 m ³ per 1 m of penetration (well length), then there is ~ 50 m ³ per well.

In the preparation of the gel-forming composition GALKA ^® , the solid commodity form GALKA ^{® is used} , containing 30% wt. hydroxychloride aluminum and 70% wt. carbamide (TU 2163-015-00205067-01). To prepare 50 m ^{3 of} GALKA ^® gel-forming composition, the following reagents are required:

Solid commodity form of the composition GALKA ^®  16.7 t Technical urotropin (hexamethylenetetramine)  2.5 t Water (mineralized water of the Mir mine or fresh water)  30.8 t

The preparation of a solution of the GALKA ^® gelling composition under field conditions can be carried out using either mineralized water from the Mir mine and fresh water (method 1), or only mineralized water from the mine Mir (method 2). Two solutions are preliminarily prepared.

According to method 1, a solution is prepared by adding, to stirring, to 1 m ^{3 of} mineralized water from the Mir mine 1 ton of solid commercial form of the GALKA ^® composition, after dissolution we obtain ~ 2 tons of solution. To obtain a second solution, we add 150 kg of urotropine to 0.85 m ^{3 of} fresh water with stirring, after dissolution we obtain ~ 1 m ^{3 of} solution. Then, when mixing ~ 2 t of one solution and ~ 1 t of the second solution, we obtain ~ 3 t of the injected solution after mixing.

According to method 2, two solutions were prepared. To 0.5 m ^{3 of the} mineralized water of the Mir mine, we add 1 ton of the solid commercial form of the GALKA ^® composition with stirring, after dissolution we get ~ 1.5 m ^{3 of} solution 1. To prepare a second solution in 1.35 m ^{3 of} mineralized water of the Mir mine, add 150 kg of urotropine , after mixing, we obtain ~ 1.5 m ^{3 of} solution 2. Then we mix two solutions and obtain after mixing ~ 3 t of the injected solution.

The sealed antifiltration screen and the upper part of the ore safety pillar were monitored using permeability data obtained using a set of developed control methods (georadar, tensometric, geophysical, etc.), as well as data from control wells drilled into the technogenic stratum, which were subsequently plugged, and according to actual observations in underground mines.

In the process of further underground mining operations at the mine, it is possible to further enhance the shielding properties of the created geomechanical screen by storing dump rocks in the quarry mined out and their subsequent fine-graining clay tailings of concentration plant No. 3. This will reduce the area occupied by dump overburden near urban buildings and solve the problem of storage of liquid pulp-like waste after kimberlite ore dressing.

Thus, the proposed method allows you to completely seal an additional anti-filter screen under a pond after mining the quarry at the Mir pipe field.

Claims (4)

1. A method of sealing an antifiltration screen at the bottom of a pit under a pond after working out the pit, comprising pumping filling materials and holding them until their cure, characterized in that cement-sand mortar is pumped into the lower part of the antifiltration screen containing dolerite rocks sulfate-resistant or alumina cement with a 2% addition of calcium chloride under a pressure exceeding hydrostatic through wells drilled from underground workings, and after hardening, the created rock-cement layer of the antifiltration screen and the upper part of the ore safety pillar left under the antifiltration screen are additionally tamped with local injections of GALKA ^® gel-forming compounds based on the system "aluminum hydroxychloride - carbamide - urotropin - water" under a pressure lower than the pressure of the rupture of the thickness of the ore safety target . 2. The method according to p. 1, characterized in that the sand-cement mortar is pumped under a pressure of 0.7-0.8 MPa. 3. The method according to p. 1, characterized in that the local injection of gel-forming compositions is carried out under a pressure of 0.5-0.6 MPa. 4. The method according to p. 1, characterized in that the composition GALKA ^{® is} pumped at a ratio of components, wt.%:
aluminum hydroxyl chloride 5-15 urea 20-35 urotropin 3-10 water rest

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