RU2551585C1 - Method of sealing impervious screen under water reservoirs after open pit mining - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: into the lower part of the impervious man-made screen containing dolerite rocks, the cement grouting is pumped, based on sulphate resistant or calcium aluminate cement with hardener (2% CaCl₂) under pressure greater than hydrostatic, through the wells drilled from underground excavations. In the cement grouting the filler is used as mill tailings with a fraction of 0.1-0.25 mm, corresponding to fine sand. It is kept till hardening. After hardening the resulting rock-cement layer of the impervious screen is tamped with local injections of synthetic resins under pressure, less than the pressure of fracture of rock mass of mining protective pillar left under the screen. And the cement grouting is pumped under pressure of 0.7-0.8 MPa, and local injections of synthetic resin is carried out at a pressure of 0.5-0.6 MPa. The synthetic resin is used as hydro-active compositions based on LT-70 with the addition of a solvent - dimethylformamide in an amount of 20-25%.

EFFECT: increased strength and increased of impervious properties of the screen when filling the open pit.

6 cl, 2 dwg

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 work from water penetration, including creating a safety screen between underground mining operations and a body of water on the surface of the day, the bed of the body of water is created by excavation of rocks, and the bottom is formed in the permafrost zone, 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 / 1 /.

The disadvantage of this method is the impossibility of creating such 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 on the open pit 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 the underground technological process / 2 /.

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 clay-cement grouting curtain while drilling 300 wells around the quarry and pumping cement mixtures into a water-saturated layer with design volumes of 3 thousand 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 / 3 /.

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.

An object 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 material and holding until curing it, cement mortar is pumped into the lower part of the antifiltration screen containing dolerite rocks through a pressure exceeding hydrostatic through wells drilled from underground workings, and after hardening, the created rock-cement layer of the tampo anti-filter screen They are injected with local injections of synthetic resins under a pressure lower than the pressure of the rupture of the thickness of the ore safety pillar left under the antifiltration screen.

Moreover, the cement mortar for injection is prepared on the basis of sulfate-resistant or aluminous cements with 2% addition of calcium chloride (CaCl ₂ ) to accelerate setting and is pumped under a pressure of 0.7-0.8 MPa.

In the cement slurry, the tailings of the OB are introduced with a fraction of 0.1-0.25 mm corresponding to fine-grained sands.

And as a synthetic resin, hydroactive compositions based on LT-70 are used with the addition of a solvent - dimethylformamide in an amount of 20-25%, pumped under a pressure of 0.5-0.6 MPa.

The injection of cement mortar into the lower part of the anti-filtration screen containing dolerite rocks allows creating 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 injected is determined based on the hydrostatic pressure created by the height of the brine column above the anti-filter 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. The choice of the type of cement and other technological parameters relating to the injection process were refined experimentally. The data are given in the example of a specific implementation.

Additional grouting of the created rock-cement layer by local injection of synthetic resins allows eliminating the remaining pore-fissure voids with the creation of a waterproof screen. The pressure at which synthetic resin solutions are injected is determined taking into account the hydrostatic pressure in the created thickness (0.5 MPa) and the strength characteristics of the kimberlites of the ore safety pillar. When injecting with synthetic resins 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 antifiltration screen. In relation to the tasks of resin injection technology for the formation of a waterproofing curtain in the ore body at the Mir mine, a new hydroactive synthetic bonding composition based on polyurethane resins was developed. Such was the polyurethane prepolymer LT-70 [Forpolymer ..., 2012] manufactured by NPP URETANMASH in Perm. By the order of AK ALROSA (OJSC), 3 tons of a pilot batch of resin were produced at NPP URETANMASH.

The technology for preparing the polyurethane composition is based on diluting the LT-70 prepolymer with a special solvent - dimethylformamide (component A). Polyurethanes are polymers containing an NCO group in a molecule. Polyurethane polymers are characterized by high strength, elasticity to aggressive environments. In appearance, the LT-70 prepolymer is a viscous liquid without mechanical inclusions and clots from light yellow to yellow. The composition has a high penetrating ability, adjustable setting time and the ability to expand during polymerization. The hardener of this synthetic composition is the hydroxyl groups of natural waters and brines. Thus, when the resin interacts with water or brine, a solid polymer composition is formed. It has been experimentally established that the addition of component A is a very effective way to reduce viscosity even at low temperatures of use or temporary storage of the resin. When the content of component A is 20-25% by volume, the effect of temperatures in the range from -200 to 200 ° C on the viscosity of the composition is almost leveled. The viscosity achieved at positive temperatures with the diluted component A of the resin composition (polyurethane prepolymer) is in the range between the viscosity of glycerol (1.48 Pa · s) and water (0.001 Pa · s). The experiments allow us to reasonably offer the technical ability to control the dynamic viscosity of the developed composition to even lower values, up to the values of the dynamic viscosity of saturated brines. The proposed composition during polymerization have a 15-30% expansion due to the formation of microinclusions of carbon dioxide bubbles.

Figure 1 shows a section of the Mir pipe field with the existing anti-filter screen, created during the "dry" conservation of the quarry.

Figure 2 shows the stages of sealing the impervious screen under a hazardous water body above underground mine workings:

a) cementing of dolerite filling;

b) injection plugging in the created rock-cement layer of the remaining water-conducting zones, where:

1 - meteher-icher aquifer complex;

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;

9 - wells for injection of synthetic resins.

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 2009, the Mir underground mine was commissioned to extract the remaining reserves of diamonds 2 at the deposit. 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.

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 rock rock-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, the power of which 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 . As of the end of 2012, in the mark. -226 ... -230 m, a cutting layer No. 4 was formed from a hardening bookmark, 5 m thick, 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.

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 have been increasing with increasing water inflows (up to 270 m ³ / h) to underground mine workings 7. The host rocks in 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 field, a strategy and methodology for sealing the safety screen at the Mir mine were outlined. Various technology options and places for sealing the anti-filter screen are considered, while taking into account the need for full extraction of quarry reserves at the field. Solving this problem requires the implementation of the following main points: 1) to create a screen that has such deformation indicators that can withstand geostatic loads corresponding to the full filling of the career space of the Mir pipe to natural levels and above, taking into account atmospheric precipitation; 2) the created (reinforced) rock-cement screen must be repamped by the method of local injection, for example, with synthetic resins or other poly- or (mono) component mixtures.

The presented concept for solving the problem, taking into account the complete extraction of kimberlite ore in block No. 1, is outlined as follows (figure 2). The creation of a rigid anti-filtration screen capable of withstanding 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 mortars with the creation of a rock-cement screen. Therefore, at the first stage of research, the power of a hard rock-cement base of the anti-filter 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 the additional rock-cement slab must withstand when filling the quarry with water (natural brines) is defined as follows:

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

where: P - hydrostatic pressure, MPa;

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

ρ is the density of the liquid (brine), kg / 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 - 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, 20 MPa (or 200 m water. Art.).

To create a rigid anti-filtration screen that can withstand geostatic loads when filling the quarry with water (rock) at the first stage (Fig. 2a), from the underground mine workings 7 of the mine, injection wells 8 are drilled 25-30 m long into the lower part - dolerite dump 3 is already the previously created anti-filter screen with the “dry” conservation of the quarry. Then, cement-sand mortar with a water-cement ratio of 0.5 and a setting accelerator CaCl ₂ (2%) is pumped through wells 8. The choice of brand of cement was carried out experimentally. The studies were carried out on clay-cement mortars, cement mortars from sulfate-resistant cement and alumina cement.

When performing work on the selection of compositions, the required quality indicators of injection solutions are determined in accordance with GOST 1581-96 “Portland cement grouting. Technical conditions. " It was determined that the studied injectable compositions are of type I (cement-free cement), to which the following technological parameters are presented: a) the specific surface of the cement is at least 270 m ² / kg; b) the water separation of the solution is not more than 8.7 ml; c) the spreadability of the cement paste is not less than 220 mm (for plasticized cement); d) the setting time of the cement paste: start no earlier than 45 minutes, end no later than 10 hours; e) strength characteristics of sample samples at an early (7 days) and design (28 days) age; f) corrosion resistance of injection solutions in mineralized underground brines at various temperature conditions.

Studies conducted on samples prepared in clay cement solutions showed the following. The tensile strength of the material during bending was higher than the compressive strength, which indicates a low design coefficient. The absolute strength values of clay cement mortars are very low, which can cause the destruction of the injection clay cement mortar under the action of hydrostatic pressure. The temperature of the medium has a significant negative effect on the hardening of the solution at a temperature of 0 ± 2 ° C in 1.48 (R _ex ) ... 2.5 times compared to normal temperatures. According to the research results, it can be concluded that the clay cement mortar does not meet the requirements of GOST 1581-96 for all tested indicators, with the exception of delamination.

Injection solutions based on alumina and sulfate-resistant cements have a high hardening rate, much higher than the values of the clay-cement mortar, and are more suitable for grouting operations:

- in a solution based on alumina cement, an intensive set of strength occurred at an early age (up to 7-10 days of hardening), in the following days, the rate of hydration and the formation of calcium hydrosilicates significantly decreases, therefore, the increase in strength also decreases. When assessing the influence of the temperature regime of hardening, a more intensive increase in the strength characteristics of samples of alumina cement hardening at a negative temperature was noted;

- Samples of a solution based on sulfate-resistant cement, hardening under normal conditions, had higher strength characteristics in comparison with samples hardening at low temperatures, and at the same time showed the highest strength compared with all the studied solutions;

- to test samples after 4 and 24 hours, it was possible to extract samples of the solution based on aluminous and sulfate-resistant cements from the molds, while samples that hardened for 4 hours were broken in the hands and it was impossible to determine their strength; after 24 hours, the specified strength (0.5 MPa) was ensured in samples of sulfate-resistant cement, hardening in a chamber of normal hardening (at t _in = 20 ± 2 ° C, W _in = 95%), and in samples of alumina cement, hardening in the refrigerator at a temperature t _in = 0 ± 2 ° C.

Corrosion resistance was evaluated according to GOST 27677-88 “Protection against corrosion in construction. Concrete General requirements for testing. " As of November 1, 2012, the first test results of beam samples based on cement mortars aged for one month in fresh and mineralized water were obtained. To determine the corrosion resistance of the studied injection solutions in a temperature regime similar to the conditions of the Mir mine (ambient temperature from 2 to -5 ° C), a special cooling chamber was equipped to create temperature conditions close to the operating ones, 0 ± 2 ° C . From the data obtained it follows that the greatest resistance was shown by samples of alumina cement. Sufficient resistance (without loss of strength) possess samples of sulfate-resistant cement mortar.

As a fine aggregate, tailings of solid waste of OB with a fraction of 0.1-0.25 mm corresponding to fine-grained sands are used. The injection is carried out at a pressure exceeding the hydrostatic pressure (0.7-0.8 MPa). Volumetric indicators of the injected cement mortar are calculated in accordance with the required capacity of the created rigid anti-filter screen (10 m). After filling the void space with the cement mortar in the coarse part of the screen, an exposure (OZC) is performed to harden the mortar within 72 hours.

The next step in the elimination of individual existing permeable cracks (figb) is using the local injection method, for example, synthetic resins or other poly - (mono) component mixtures.

To inject synthetic resin into the created rock-cement stratum through an ore safety pillar from wells, underground wells 9 are drilled with a length of 22-23 m taking into account the cemented screen at a depth of 2-3 m. Next, the resin is injected, which fills the smallest remaining cracks in the rock - cement thicker and ore safety pillar. The pressure of the supplied synthetic resins should not exceed the burst pressure of the thickness of the ore safety pillar and correspond within 0.5-0.6 MPa. Grouting the solution into the well. The grouting work for each well was performed in the following sequence:

1. Television inspection of the well to identify cracks in the array, caverns, areas of high water cut. After the operation, the equipment is dismantled.

2. A flange is mounted to the gate valve. To tightly fit the flange to the valve, as well as to exclude brine leakage from the well and the injected composition, a rubber gasket was installed. The flange is a round metal plate with holes drilled around the edges for bolts and a centrally welded nut with a diameter of d = 32 mm, designed to screw a high-pressure hose of the KARTI type d = 25 mm reinforced with double metal thread. To pump the polyurethane composition into the wells, the NSh-10 gear pump was used, connected to an explosion-proof electric motor 4 BP 100 S4 U2.

A high-pressure hose was connected to the discharge port of the NSh-10 pump through a connection sleeve. The other end of the hose is connected to the connector on the flange. The supply pressure of the mixture was controlled by a pressure gauge with the expectation that the maximum pressure during injection of the polyurethane composition should not exceed 0.5-0.6 MPa. During the well grouting by visual observations, it was found that the maximum pressure during injection did not exceed 0.5-0.6 MPA. A sharp increase in pressure during the supply of the mixture indicated that the well was completely filled with resin. The grouting was stopped, the pump was turned off. The polymerization rate of the mixture with the formation of the hardest polymer substance extends within 3-4 hours, the final formation of the solid polymer occurs within 6-8 hours after entering into reaction with brine.

The sealed antifiltration screen is controlled by permeability data obtained using a set of developed control methods (georadar, strain gauge, geophysical, etc.), as well as by control wells drilled into the technogenic stratum, which are subsequently plugged, and by actual observations in underground mining workings.

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 the processing of kimberlite ore.

Information sources

1. A.S. USSR No. 1633125, E21C 41/00, application No. 4474377 from 08.15.88, publ. 03/07/91. Bull. No. 9.

2. RF patent No. 2375580 C1, E21F 17/00, application No. 2008131979 from 08/01/2008, publ. 12/10/2009. Bull. Number 4

3. RF patent No. 2109922 C1, E21B 33/13, application No. 95109919 from 06.17.93, publ. 04/27/98. Bull. No. 12.

Claims (6)

1. A method of sealing an antifiltration screen under a pond after working out a quarry, including pumping filling materials and holding them until their hardening, characterized in that cement mortar is pumped into the lower part of the screen containing dolerite rocks through a well with a pressure exceeding hydrostatic through wells drilled from underground workings, and after hardening, the created rock-cement layer of the screen is plugged with local injection of synthetic resins under pressure, less column fracture pressure them ore protective pillar, left under the impervious screen. 2. The method according to claim 1, characterized in that the cement mortar is pumped under a pressure of 0.7-0.8 MPa. 3. The method according to claim 1 and / or 2, characterized in that the cement mortar for injection is prepared on the basis of sulfate-resistant or aluminous cements with 2% addition of calcium chloride (CaCl ₂ ) to accelerate setting. 4. The method according to claim 1 and / or 3, characterized in that in the cement mortar as the filler enter the tailings OF with a fraction of 0.1-0.25 mm, corresponding to fine-grained sands. 5. The method according to claim 1, characterized in that the local injection of synthetic resins is carried out under a pressure of 0.5-0.6 MPa. 6. The method according to claim 1, characterized in that the synthetic resin used is a hydroactive composition based on LT-70 with the addition of a solvent of dimethylformamide in an amount of 20-25%.

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