A construction method for filling green mine underground structure with pumped low-carbon filling material

Abstract

This invention relates to the field of underground structure construction technology, specifically to a construction method for filling green mine underground structures with pumped low-carbon filling material. The method includes: pre-construction preparation, setting up grouting pipelines through 3D scanning and fluid simulation; preparing low-carbon filling material; implanting anchor bolts and fixing grid mesh in the inner wall of the roadway connecting to the goaf, constructing a retaining wall to seal the area to be filled; high-pressure atomized spraying of a strong alkaline activator solution onto the surface of the surrounding rock in the goaf to generate an active transition layer; injecting the filling material into the sealed cavity using a pumping system, and optimizing the transport flow through spiral guide vanes; and pressure stabilization and curing. This invention improves the fluidity of the low-carbon filling material through the spiral structure of the transport pipeline. Combined with the synergistic effect of physical anchoring of the roadway and chemical activation of the surrounding rock, it ensures dense filling while significantly enhancing the bonding strength between the filling body and the surrounding rock interface, effectively solving the problems of easy delamination, sliding, and interface cracking of the filling body during long-term service.

Description

Technical Field

[0001] This invention relates to the field of mine backfilling construction technology, specifically to a construction method for filling green mine underground structures with pumped low-carbon backfilling materials. Background Technology

[0002] As mining development models shift towards green and low-carbon practices, resource-based remediation of underground goaf areas has become a key technological approach to ensure mine safety and ecological restoration. Low-carbon backfill materials prepared using mine tailings and industrial slag have significant carbon reduction benefits and resource utilization value, making them an important choice for underground structure backfilling in green mines.

[0003] Traditional underground filling pumping construction involves setting up retaining walls in the roadways to enclose the goaf in the mine into a closed cavity. Then, using methods such as gravity casting or centrifugal pumping, fluid filling materials are directly injected into the area to be filled, including the goaf and connecting roadways. The slurry flows and forms, filling the cavity of the goaf up to the retaining wall of the roadway, thereby filling the voids in the underground structure and providing support and reinforcement after hardening.

[0004] For low-carbon backfill slurries prepared from mine tailings and industrial slag, in order to minimize the carbon footprint, the proportion of cement in the backfill material is greatly reduced and replaced by high-volume recycled powder and fine mineral powder. Due to the extremely high specific surface area and complex surface charge characteristics of fine powder, the backfill slurry is prone to forming a dense flocculated structure, and tends to exhibit extremely high yield stress and apparent viscosity.

[0005] Traditional construction techniques, characterized by open, pressureless, and passive filling methods, struggle to effectively disrupt the flocculated structure within the grout. This results in the grout failing to spread and flow fully after entering the goaf, easily creating dead zones within the complex goaf structure and tunnel spaces, leading to internal cavities. Furthermore, existing construction methods rely solely on the natural flow of the grout to bond the filling material to the original structural surfaces (i.e., the original surrounding rock) in the goaf and tunnels. Since the surface of the original rock strata is typically covered with mining dust, there is a significant difference in wettability between the dust and the filling grout. Consequently, the natural bonding between the grout and the original rock strata fails to form a strong interface. Under the long-term effects of groundwater pressure, differential settlement of rock strata, and the weight of the filling material itself, the filling material is prone to developing through cracks and cavities. In severe cases, this can directly lead to instability or sliding of the underground filling system, causing significant hidden dangers such as uneven structural load-bearing.

[0006] In summary, existing technologies struggle to address the high viscosity of low-carbon backfill materials and ensure the strength of the interface between the backfill material and the underground structure in green mine underground filling projects. Therefore, there is an urgent need in this field for a new pumping construction method for low-carbon backfill materials used in green mine underground structures to solve these problems. Summary of the Invention

[0007] To address the problem that existing pumping methods for filling materials cannot guarantee the absence of cracks and voids within the filling body, which can easily lead to instability and slippage during long-term service, this invention provides a construction method for pumping low-carbon filling materials to fill underground structures in green mines, comprising the following steps: Step S1, pre-construction preparation: Perform three-dimensional laser scanning on the cavity inside the goaf to obtain the distribution pattern of the original surrounding rock on its inner wall and perform full-phase modeling; After modeling, use fluid dynamics software to simulate a high-pressure spraying scheme that can cover the inner wall of the goaf, determine the high-pressure spraying method and spraying points, and according to the scheme, pre-set grouting holes and lay grouting pipelines at the corresponding positions in the goaf; At the same time, open at least one exhaust overflow port with an openable and closable valve at the top of the goaf, and install high-pressure clamps and pressure sensors at the ends of the grouting pipelines; Step S2, preparation of low-carbon backfill material: According to the volume measurement of the backfill body, prepare the raw materials of low-carbon backfill material including mine tailings powder, aggregate, strong alkaline activator solution, water reducing agent and water, and add composite expansion agent and fiber components to it, and then stir at high speed to form a fluid slurry for later use; and prepare a certain amount of strong alkaline activator solution for later use. The strong alkaline activator solution is prepared by mixing liquid sodium silicate and sodium hydroxide solution. Step S3: Construction of the roadway anchoring system and sealing of the retaining wall; Several anchor rods are implanted on the inner wall surface of each roadway connected to the goaf, with the other end of the anchor rod protruding from the inner wall surface of the roadway, and a grid mesh is fixed at this end. The grid mesh is made of metal or composite material, and after fixing, a gap of 20mm to 50mm is maintained between it and the inner wall surface; Finally, a retaining wall is constructed at the exit of each roadway and water-stopping construction is carried out. Diagonal bracing is set outside the retaining wall to enclose the area to be filled into a closed cavity. Step S4, activation treatment of the inner wall of the goaf; a high-pressure spraying device is inserted into the grouting pipeline. The high-pressure spraying device includes a nozzle with high-pressure atomization function. The nozzle enters the inner cavity of the goaf and faces the surface of the surrounding rock. An external pipeline is connected to the goaf. The pipeline is used to transport the strong alkaline activator solution prepared in step S2. Then the spraying is started. The strong alkaline activator solution is atomized under high pressure and sprayed evenly on the surface of the surrounding rock of the goaf. Step S5, formal pumping and filling; remove the high-pressure spraying device, connect the grouting pipeline to the pumping system's delivery pipeline, and inject the prepared low-carbon filling material into the area to be filled through the pumping system's delivery pipeline within 0.5 to 2 hours after spraying with the strong alkaline activator solution; the delivery pipeline is a composite steel pipe lined with high-chromium wear-resistant alloy, and the inner wall of the delivery pipeline is integrally formed with spiral guide vanes; Step S6, pressure stabilization and curing: When the pressure information collected by the pressure sensor rises rapidly, and the filling slurry with uniform consistency and no air bubbles flows out of the exhaust overflow port, immediately close the valve on the exhaust overflow port, and adjust and reduce the pumping flow rate of the pumping system in real time to maintain the current pumping pressure of the pumping system within a preset threshold, and maintain the pumping pressure for 30-60 minutes. After that, shut down the pumping system, use the high-pressure clamps on the grouting pipeline to cut off and seal the grouting pipeline, and enter the curing stage of the filling material.

[0008] Furthermore, in step S1, the grouting pipeline pre-embedded in the grouting hole is a steel pipe with a water-swellable sealing strip wrapped around its outer wall. The length of the end of the steel pipe extending into the cavity of the goaf is not less than 150 mm. Then, fast-hardening cement grout is used to seal the annular gap between the grouting hole and the steel pipe.

[0009] Furthermore, the exhaust overflow port is located at the highest point of the goaf roof, and a diversion pipe is connected to the exhaust overflow port. The end of the diversion pipe extends to the liquid collection tank outside the goaf. The total cross-sectional area of ​​the exhaust overflow port is set to 1 / 2 to 1 / 3 of the total cross-sectional area of ​​the grouting pipeline.

[0010] Furthermore, in step S2, the mine tailings powder undergoes ultrafine grinding to control its specific surface area to the range of 400 to 500 m² / kg, wherein the content of particles smaller than 45 μm is not less than 85%; the aggregate uses porous lightweight aggregate including shale ceramsite and expanded perlite, and is pre-wetted before preparation to reach a water-saturated state. The added composite expanding agent is composed of calcium sulfoaluminate expanding components and lightly calcined magnesium oxide components, with a dosage of 5% to 8% of the tailings powder mass; the fiber component is polypropylene fiber, with its dosage set at 0.8 kg / m³ to 1.0 kg / m³ of the filling volume, and the polypropylene fiber is soaked in the strongly alkaline activator solution and drained before being added.

[0011] Furthermore, the strongly alkaline activator solution is prepared by mixing liquid sodium silicate with a modulus controlled in the range of 1.2 to 1.8 and sodium hydroxide solution with a mass percentage concentration of 25% to 35% in a mass ratio of 3:1, and the pH value is maintained above 13.

[0012] Furthermore, in step S3, the anchor bolt is implanted into a stable rock layer on the inner wall of the tunnel for no less than 1m. After the anchor bolt is implanted, the lattice mesh is welded and fixed to the end of the anchor bolt that protrudes from the inner wall surface of the tunnel.

[0013] Furthermore, before the spraying operation in step S4, a high-pressure blower is inserted into the grouting pipeline to blow away the surface of the surrounding rock in the goaf, removing weathered debris and dust from the surface; after the spraying operation is completed, a high-pressure blower is inserted again to blow away excess activator droplets that have accumulated on the surface of the surrounding rock due to gravity.

[0014] Furthermore, in step S5, a pulse generator is provided at one end of the delivery pipeline near the grouting pipeline. During the formal pumping and filling, the pulse generator is turned on to continuously generate high-frequency pressure pulse waves to the delivery pipeline, thereby disrupting the flocculation structure of the slurry inside the pipeline.

[0015] Furthermore, in step S6, the preset threshold is set to 80% of the structural safety bearing limit of the surrounding rock or retaining wall, taking the minimum value between the two.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention utilizes anchor bolts and a grid mesh installed on the inner wall of the roadway. The anchor bolts penetrate deep into stable rock strata, and the grid mesh forms a reinforced concrete structure with the filling material, providing reliable physical anchoring and constraint to the ends of the filling material. Simultaneously, by pre-spraying a strongly alkaline activator solution onto the surface of the surrounding rock in the goaf, chemical depolymerization and condensation reactions occur on the surface of the silica-alumina mineral-rich surrounding rock, generating a highly reactive aluminosilicate transition layer in situ. This transition layer undergoes deep ion exchange and chemical bonding with the low-carbon filling material, transforming the physical contact interface into a continuous chemically bonded interface. Through the synergistic effect of these two methods, the bonding strength between the filling material and the roadway and goaf surrounding rock is significantly enhanced, solving the problem of easy slippage and voiding of the filling material during long-term service. The chemical bonding method is particularly suitable for filling construction scenarios in surrounding rock rich in aluminosilicate components.

[0017] 2. To address the issues of high yield stress and high apparent viscosity in low-carbon filler materials caused by high content of fine powder, this invention incorporates spiral guide vanes on the inner wall of the pumping pipeline. This causes the slurry to rotate during transport, utilizing centrifugal force to moderately deflect coarse aggregate particles towards the pipe wall, forming a low-viscosity slurry enrichment zone in the center of the pipe. This effectively prevents aggregate deposition and pipe blockage, significantly improves slurry fluidity, and ensures that the slurry can flow fully within the area to be filled, penetrating into all cracks and dead corners, thus enhancing the compaction effect of the filling.

[0018] 3. The filling material of this invention uses solid waste such as mine tailings powder and industrial slag as the main raw materials, reducing the use of cement and thus significantly reducing the carbon emissions per cubic meter of filling material. Furthermore, the improved bonding effect between the filling body and the surrounding rock through the construction method of this invention effectively extends the service life of the filling structure and reduces carbon emissions from later maintenance and secondary treatment. The entire life cycle, from material preparation to construction and service, embodies the green concept of low-carbon and resource-based utilization. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall construction process of a method for filling green mine underground structures with pumped low-carbon filling material according to the present invention. Figure 2 This is a schematic diagram of a construction scenario for a method of filling green mine underground structures with pumped low-carbon filling material according to the present invention.

[0020] In the attached diagram: 1. Goaf; 2. Roadway; 3. Grid mesh; 4. Retaining wall; 5. Grouting pipeline; 51. High-pressure clamp; 6. Exhaust overflow port; 7. Pumping system; 71. Conveying pipeline. Detailed Implementation

[0021] The technical solution of the present invention will now be described with reference to the accompanying drawings. However, the described embodiments are only some embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] It should be noted that in the description of this invention, the terms "upper," "lower," "inner," "outer," etc., which indicate the direction or positional relationship, are based on the direction or positional relationship shown in the drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0023] Reference Figure 1-2 As shown, one embodiment of the present invention is a treatment project for a goaf area 1 in a mine, which requires pressure filling of irregular and complex cavities to compensate for the bearing capacity of the foundation. In this embodiment, the original underground structure of goaf area 1 is naturally formed by the surrounding rock. The area to be filled includes the cavity of goaf area 1 and the connecting roadway 2 around it. Low-carbon filling materials prepared from mine tailings and industrial slag are to be used to reinforce and fill the area to be filled. The pumping construction method used specifically includes the following steps: Step S1, Pre-construction preparation; Before the filling operation, a three-dimensional laser scan is performed on the cavity inside the goaf 1 to obtain the distribution pattern of the original surrounding rock of its roof and sidewalls and to perform full-phase modeling. After modeling, the high-pressure spraying arrangement scheme that can cover the inner wall of the goaf 1 is simulated using fluid dynamics software to determine the high-pressure spraying method and spraying points. According to the spraying points, grouting holes are preset at the corresponding positions in the goaf 1 and grouting pipelines 5 are laid out. At the same time, at least one exhaust overflow port 6 with an openable and closable valve is opened at the top of the goaf 1, and a pressure sensor is installed at the end of the grouting pipeline 5 to monitor the pressure information of the subsequent grouting process. Specifically, in this embodiment, an industrial-grade high-precision 3D laser scanning device is first installed at the entrance of goaf 1 to acquire 3D point cloud data of the roof and sidewall rock surfaces of goaf 1. The geometric model of the underground structure of goaf 1 is then reconstructed in modeling software. Considering that subsequent steps require high-pressure spraying of an activator before pumping the filling material, a virtual spraying model is established in a computational fluid dynamics environment based on this model to simulate the dynamic distribution trajectory of the strong alkaline activator solution on the rock surface under different nozzle arrangement schemes. Through iterative calculations using software simulation, the optimal nozzle selection and arrangement scheme that can achieve large-area coverage of the strong alkaline activator solution on the roof and sidewalls is selected. Alternatively, the optimal nozzle selection and arrangement scheme is determined by simulating and identifying areas in goaf 1 that are prone to detachment from the rock surface due to long-term settlement of the filling material. The optimal nozzle selection and arrangement scheme is then determined based on whether the strong alkaline activator solution can cover these areas after spraying. After marking the preset positions of the grouting holes at the corresponding locations in goaf 1 according to the scheme, grouting holes are drilled outside goaf 1 using a pneumatic down-the-hole hammer.

[0024] Furthermore, the grouting pipe 5 pre-embedded in the grouting hole is made of steel pipe, and the outer wall of the steel pipe is wrapped with a water-swellable sealing strip. After being inserted into the grouting hole, the length of its end extending into the inner cavity of the goaf 1 is not less than 150mm, so as to avoid premature blockage of the grouting hole due to splashing of the filling grout in the early stage of grouting. Then, fast-hardening cement grout is used to seal the annular gap between the grouting hole and the grouting pipe 5 tightly. The part of the steel pipe outside the goaf 1 is equipped with a high-pressure clamp 51, which is used to cut the steel pipe after grouting and quickly seal the grouting pipe 5 to prevent grout backflow. The exhaust overflow port 6 is located in the goaf 1. At the highest point of the roof, an exhaust overflow port 6 is connected to a drainage pipe, the end of which extends to a liquid collection tank outside the goaf 1 for easy observation of the overflow status. Furthermore, the total cross-sectional area of ​​the exhaust overflow port 6 is set to 1 / 2 to 1 / 3 of the total cross-sectional area of ​​the grouting pipeline 5. The design adopts the area difference between the cross-sectional area of ​​the exhaust overflow port 6 and the cross-sectional area of ​​the grouting pipeline 5. In the later stage of grouting, the grout entry rate is greater than the gas discharge rate, which naturally forms a weak initial back pressure inside the closed cavity. This can further drive the air accumulated in the cavity to the exhaust overflow port 6 for discharge, significantly improving the overall density of the filling body.

[0025] Step S2, preparation of low-carbon filling material; According to the volume of the filling body to be constructed, the raw materials including mine tailings powder, aggregate, strong alkaline activator solution, composite expansion agent and water reducing agent are measured according to the preset ratio and then stirred at high speed to form a fluid slurry that can produce an expansion effect during the hardening stage. In addition, a number of strong alkaline activator solutions are prepared for use. For mine tailings powder, a strongly alkaline activator solution is added to stimulate the potential activity of the silicon and aluminum components in the tailings powder and promote the hydration reaction of the tailings powder. The strongly alkaline activator solution is prepared on-site by mixing liquid sodium silicate with a modulus controlled in the range of 1.2 to 1.8 and sodium hydroxide solution with a mass percentage concentration of 25% to 35% at a mass ratio of 3:1. The mixed solution exhibits extremely strong alkalinity, with the pH value maintained above 13.

[0026] Specifically, the mine tailings powder, as the main cementitious material component, undergoes ultrafine grinding, with its specific surface area controlled within the range of 400 to 500 m² / kg. The content of particles with a specific particle size (e.g., less than 45 μm) is no less than 85%. Ultrafine grinding gives the mine tailings powder higher reactivity, facilitating a full alkali-activated reaction. The high content of fine particles improves slurry suspension, reduces bleeding and segregation, and enhances the slurry's ability to fill micropores. The water-reducing agent is a high-performance polycarboxylate-based water-reducing agent. The agent enables the low-carbon backfill material to maintain a certain initial expansion, ensuring that it does not clog pipes during long-distance pumping. The aggregate used is a porous lightweight aggregate including shale ceramsite and expanded perlite, which is pre-wetted before preparation (generally 24 hours in advance) to reach a water-saturated state. During the curing process of the backfill, the porous lightweight aggregate can continuously release internal moisture to compensate for water consumption during hydration. The overall water-cement ratio of the material preparation is controlled between 0.38 and 0.45 to ensure that the prepared slurry has good fluidity and improves pumping performance. The carbon emissions per cubic meter of the prepared backfill material meet the low-carbon evaluation standards.

[0027] Furthermore, to ensure the low-carbon backfill material possesses certain expansion properties during the curing stage and improves filling density, the composite expansion agent added during material preparation is composed of a calcium sulfoaluminate expansion component and a light-burned magnesium oxide component, with a dosage of 5% to 8% of the tailings powder mass. The ratio of the calcium sulfoaluminate expansion component to the light-burned magnesium oxide component is approximately 6:4 to 7:3. In the early stage of hydration, the calcium sulfoaluminate component reacts with water to produce a large amount of ettringite crystals, providing initial expansion to offset the plastic shrinkage of the material. In the later stage of hydration, the light-burned magnesium oxide component undergoes a hydration reaction to generate magnesium hydroxide crystals, compensating for the long-term drying shrinkage of the material. Overall, the backfill material has a restricted expansion rate of 0.02% to 0.04%. To enhance the fracture resistance of the backfill, polypropylene fibers with a length of 12 mm to 19 mm are also uniformly incorporated into the low-carbon backfill material, with a dosage set at 0.8 kg / m³ to 1.0 kg / m³ of the backfill volume. The addition of polypropylene fibers can form a three-dimensional fiber network after the filling material hardens, effectively inhibiting the initiation and propagation of microcracks in the filling body. Before feeding, the polypropylene fibers are soaked in an activator solution and then drained. The strongly alkaline activator can generate polar oxygen-containing functional groups such as hydroxyl and carboxyl groups on the fiber surface. These functional groups can form chemical bonds with calcium, aluminum, and other ionic gels in the filling material, giving the fibers better interfacial adhesion to the filling slurry. Furthermore, polypropylene fibers are typically hydrophobic and easily agglomerate in the slurry. Soaking in an alkaline solution can improve the hydrophilicity of the fiber surface, enabling uniform dispersion in the slurry after high-speed stirring.

[0028] Step S3: Construction of the anchoring system for tunnel 2 and closure of retaining wall 4; Several anchor bolts are implanted into the inner wall surface of each roadway 2 connecting to the goaf 1. The other end of each anchor bolt protrudes from the inner wall surface of the roadway 2. A grid mesh 3 is fixed to the anchor bolt. The grid mesh 3 is made of metal or composite material and, after fixing, maintains a gap between itself and the inner wall surface of the roadway 2 that allows the flow of low-carbon filling material, such as a gap distance of 20mm to 50mm, to ensure that the filling grout, the grid mesh 3, and the inner wall of the roadway 2 are effectively integrated into a whole. Finally, a retaining wall 4 is constructed at the exit of each roadway 2 and water-stopping construction is carried out. Diagonal bracing is installed on the outside of the retaining wall 4 to enclose the area to be filled into a closed cavity.

[0029] Specifically, during the construction preparation phase, drainage and necessary temporary support are first implemented in the roadways 2 surrounding the goaf 1. Next, the original surrounding rock surface of the roadway 2's inner wall undergoes surface treatment, including removing surface laitance, oil, loose layers, and debris. After surface treatment, anchor bolt holes are marked on the roof and sides of roadway 2 using a quincunx pattern and a pre-set density, employing a laser total station or infrared rangefinder. Anchoring holes are then drilled using a rock drilling rig or anchor bolt drilling machine, penetrating the loosened surrounding rock zone and extending at least 1 meter into the stable rock layer. Prestressed anchor bolts are then implanted into the anchoring holes using chemical anchoring. After fixing the anchor bolts according to the above steps, pre-processed lattice mesh 3 is fixed to the ends of the anchor bolts protruding from the inner wall of roadway 2 using welding or other methods, ensuring the lattice mesh 3 completely covers the inner wall of roadway 2. The lattice mesh 3 used in this embodiment is made of 12mm threaded steel bars welded together. In other embodiments, it can also be made of composite materials with the same strength level as the steel bars.

[0030] The construction of the anchoring system can significantly improve the integration between the filling material and the internal space of the tunnel 2. The lattice mesh 3 forms a rigid connection with the stable rock layer of the tunnel 2 through the anchor bolts, so that the filling material can form a synergistic force system with the surrounding rock of the tunnel 2 after hardening. Especially when dealing with tensile stress caused by geological subsidence or temperature changes, it can coordinate the stress distribution of the filling material through its own deformation, thereby enhancing the ductility and stability of the overall structure.

[0031] Step S4: Activation treatment of the inner wall of goaf 1; A high-pressure spraying device is inserted into the grouting pipeline 5 laid in step S1. The cross-sectional diameter of the high-pressure spraying device is smaller than the inner diameter of the grouting pipeline 5 so that it can extend into the goaf 1. The high-pressure spraying device includes a nozzle with high-pressure atomization function. The nozzle extends into the inner cavity of the goaf 1 and is connected to an external pipeline. The pipeline is used to transport the strong alkaline activator solution prepared in step S2. Then the spraying is started, and the strong alkaline activator solution is atomized under high pressure and evenly sprayed onto the surface of the surrounding rock of the roof and side walls of the goaf 1.

[0032] Specifically, in this embodiment, a rotary atomizing nozzle is selected, with an adjustable spray angle. After entering the goaf 1, the spray angle is directed towards the surrounding rock surface, specifically towards the sidewalls and top (the bottom has almost no issue of the filling material being vacated due to settlement). By controlling the spray pressure to a high-pressure range of 0.5-1.5 MPa, a uniform circular atomization range can be formed on the surrounding rock surface, spraying the solution onto the surrounding rock surface. In this embodiment, the surrounding rock surface of goaf 1 in the filling project was determined to be mainly composed of silica and alumina. Under the strongly alkaline environment of the strongly alkaline activator solution, silica and alumina undergo a chemical depolymerization reaction. Their stable silicon-oxygen bonds and aluminum-oxygen bonds are broken and reacted by the hydroxide ions of the strongly alkaline activator solution, generating a large number of silicate ions, aluminate ions, and silanol groups. A silica-aluminate transition layer of a certain thickness (about 3-5 mm) with high chemical activity and high wettability is constructed on the surrounding rock surface. This transition layer is rich in active silica-alumina monomers, providing ample reaction sites for the subsequent chemical bonding of the slurry.

[0033] Furthermore, prior to the spraying operation, a pretreatment step is included for the surrounding rock surface. Specifically, a high-pressure blower is inserted into the goaf 1 through the grouting pipe 5 to simply blow away weathered debris and dust from the surface of the surrounding rock. After the spraying operation is completed, the high-pressure blower is inserted again to blow away excess activator droplets accumulated on the surrounding rock surface due to gravity, leaving only the activated transition layer that has been firmly bonded to the rock surface through chemical adsorption or reaction, ensuring effective contact between the transition layer and the hard substrate.

[0034] Step S5: Formal pumping and filling; After spraying with the strong alkaline activator solution, the high-pressure spraying device is removed from the grouting pipeline 5, and the grouting pipeline 5 is connected to the delivery pipeline of the pumping system 7. The low-carbon filling material prepared in step S2 is injected into the area to be filled through the delivery pipeline 71 of the pumping system 7. In this example, the delivery pipeline 71 is a composite steel pipe lined with high-chromium wear-resistant alloy, with a material hardness of HRC55 or higher, and an inner diameter of 150mm to 200mm to meet the large flow rate delivery requirements of 60m³ / h to 120m³ / h in this embodiment. To further optimize the flow stability of long-distance transportation, the inner wall of the transportation pipeline 71 is integrally formed with a spiral guide vane. Specifically, in this embodiment, the guide vane is integrally formed inside the pipeline using a lost foam precision casting process, and the pipeline is manufactured in segments to reduce manufacturing difficulty. Each segment of the pipeline is connected by flanges and locating pins to ensure the phase continuity of the guide vane in each segment. Under pumping pressure, the guide vane can cause the filling slurry to rotate spirally inside the pipeline. The centrifugal force generated by the rotation causes the coarse aggregate particles in the slurry to shift moderately towards the pipe wall, forming a low-viscosity slurry enrichment zone in the center of the pipe. This transportation method effectively prevents the high-density components in the filling slurry from depositing at the bottom of the pipe under gravity, greatly reducing the frictional resistance and pipe blockage risk of long-distance pumping.

[0035] Furthermore, since the activated transition layer exhibits optimal activity within 0.5 to 2 hours after the activator spraying, and its activity significantly decreases after 2 hours, the pumping system 7 must be started within 0.5 to 2 hours after the strong alkaline activator solution is sprayed to begin the formal filling operation, so as to fully utilize the residual chemical activity of the transition layer. When the low-carbon filling material comes into contact with the activated transition layer formed in step S4, since the low-carbon filling material is an alkaline-activated system, a condensation reaction can occur at the interface when it comes into contact with the activated transition layer. The active sites of the activated transition layer form a continuous gel network with the calcium ions and silicon-aluminum monomers in the filling slurry, so that the filling body and the surrounding rock achieve chemical bonding. Since tunnel 2 serves as the working space for the construction of retaining wall 4 during actual construction, no additional grouting holes are provided. If a strong alkaline activator solution is sprayed first, followed by the construction of retaining wall 4, and then pumping and filling operations are carried out, the above-mentioned time requirements cannot be met, and the window period of chemical activity of the strong alkaline activator solution cannot be well utilized. Therefore, the spraying of the strong alkaline activator solution was not adopted. Instead, the anchoring system in step S4 above was used to form a stable bond between the filling material and the inner wall of the surrounding rock of tunnel 2 in a physical manner.

[0036] Furthermore, a pulse generator is provided at one end of the delivery pipeline 71 near the grouting pipeline 5. During formal pumping and filling, the pulse generator is turned on to continuously generate high-frequency pressure pulse waves of 10-50Hz into the delivery pipeline 71, with the pulse amplitude set to 10%-15% of the pumping pressure. Under the dynamic shear force of the pressure pulse wave, the flocculation structure of the slurry inside the pipeline can be effectively destroyed, allowing the high-concentration slurry to maintain high flow characteristics and be injected into the area to be filled.

[0037] Step S6: Voltage stabilization and maintenance; Observe the state of the slurry flowing out of the exhaust overflow port 6. The initial outflow may contain air bubbles and thin slurry. During this period, observe the pressure information collected by the pressure sensor. When the pressure information collected by the pressure sensor rises rapidly from a stable state, combined with the uniform consistency and air bubble-free filling slurry flowing out of the exhaust overflow port 6, it can be determined that the cavity is basically filled. At this time, immediately close the valve on the exhaust overflow port 6 and adjust and reduce the pumping flow rate of the pumping system 7 in real time. Under continuous low flow pumping, maintain the current pumping pressure of the pumping system 7 within a preset threshold and maintain this pumping pressure for 30-60 minutes. After that, close the pumping system 7, use the high-pressure clamp 51 on the grouting pipeline 5 to cut off and seal the grouting pipeline 5, and enter the curing stage of the filling material. For the low-carbon backfill material in this example, its curing process mainly utilizes the pre-wetted saturated porous lightweight aggregate added during the preparation of the low-carbon backfill material in step S2. During the curing process, the porous lightweight aggregate can continuously release internal moisture, compensate for water consumption during hydration, and thus improve the mechanical properties of the material. During the curing period, due to the rigid constraints of the original surrounding rock of the goaf 1, the grid mesh 3 of the roadway 2, and the retaining wall 4, as well as the expansion characteristics of the low-carbon backfill material in the confined space, the original outward free expansion force of the backfill material is transformed into active compressive stress pointing towards the surrounding rock, the grid mesh 3, and the retaining wall 4. This drives the backfill material to form a tighter interlocking and interface bonding between the backfill body and the surrounding rock, in conjunction with the anchoring system of the roadway 2 and the chemical bonding of the goaf 1, and various cracks and cavities in the backfill area.

[0038] Specifically, during the formal pumping and filling process in step S5 and the pressure stabilization process in step S6, the delivery pressure of the pumping system 7 in this embodiment meets the following standards: In step S5, the main purpose is to basically fill the cavity to ensure the flow of slurry, prevent pipe blockage, and avoid generating impact force. Therefore, the pumping pressure is 0.2 to 0.4 MPa to achieve stable slurry filling and sufficient venting, and to avoid excessive pressure causing premature closure of the cavity and failure of gas to escape. After closing the exhaust overflow port 6 in step S6, the pumping pressure of the pumping system 7 is maintained at a preset threshold to establish micro-expansion pre-pressure of the filling body by compacting the filling material. Since the grouting pipeline 5 is located at the top of the goaf 1, after the filling material enters the filling area, it will fill the pores inside the filling area under its own gravity and expansion effect. Therefore, the preset threshold of the pressure stabilization stage should ensure that the process occurs effectively and prevent excessive pressure from the filling material squeezing the original surrounding rock and retaining wall 4, thus damaging the structural stress. Therefore, the preset threshold is set to 80% of the safety bearing limit of the surrounding rock or retaining wall 4 (taking the minimum of the two; under normal circumstances, the safety bearing limit of the retaining wall 4 structure will be lower than that of the surrounding rock). The safety bearing limit of the retaining wall 4 structure is determined by on-site survey or retaining wall 4 structural design before the filling operation. During the pressure stabilization process of 30-60 minutes, the pressure sensor will continuously monitor the pressure changes in the pipeline. If abnormal pressure fluctuations or drops occur, the operator should immediately check for leaks or blockages so as to take timely measures to ensure the effectiveness of the pressure stabilization process. Under the aforementioned pressure stabilization process at the preset threshold, the composite expanding agent inside the filling material continuously undergoes a hydration reaction. The calcium sulfoaluminate component reacts with water to form ettringite crystals, which continuously fill the tiny pores inside the slurry. The lightly calcined magnesium oxide component gradually generates magnesium hydroxide crystals in the later stages of hydration, further compensating for the shrinkage of the material. The active compressive stress generated by the filling body under the rigid constraints of the surrounding rock and retaining wall 4 structure allows the slurry to fill the cracks and uneven surfaces of the goaf 1 more tightly, forming a strong chemical bond and mechanical interlock with the activated surrounding rock surface.

[0039] In summary, this invention firstly uses mine tailings as backfill material, which aligns with the concepts of low-carbon and green mining. Secondly, the invention employs an anchoring system consisting of anchor bolts and grid mesh 3 within the roadway 2, and pre-sprays a strong alkaline activator solution onto the inner wall of the goaf 1 to create an active transition layer. The former ensures the bonding strength between the backfill material and the surrounding rock surface of the roadway 2 through physical means, while the latter enables deep chemical bonding between the backfill and the surrounding rock through chemical means. Together, these improvements enhance the backfill density and the effective mechanical connection between the backfill and the existing underground structure of the green mine, allowing the backfill to synergistically bear force with the original structure. Furthermore, the use of pulse wave intervention during pumping further ensures that the low-carbon backfill material possesses high fluidity to fill the internal space of the goaf 1 and the roadway 2. The above multiple mechanisms significantly enhance the mechanical strength and bonding strength required for the service life of the filling material, avoid the generation of cracks and pores, and ensure that the filling material can achieve high quality and long service life in various complex underground mine filling projects. This also further enhances the practical effect of the widespread use of low-carbon filling materials and further promotes the concept of green mining.

[0040] It should be noted that, in the actual construction process, this embodiment also strictly instructs the on-site construction teams on the following operating procedures to ensure filling quality and construction safety: 1. Before installing anchor bolts and grid mesh, and before spraying strong alkaline activator solution, the installation plan and spraying plan must be reported and approved by the safety authorities. Safety briefings must be given to construction personnel, and they can only start work after they have passed the training. 2. During the preparation and mixing of low-carbon filling materials, it is strictly forbidden to add water without authorization. The fluidity must be controlled by adjusting the amount of water-reducing agent. 3. After the grouting pipeline is cut off, due to the low strength of porous lightweight aggregate and insufficient early compressive strength of the filling body, heavy machinery operations or large disturbance loads are strictly prohibited above the filling area before the filling body is cured to the preset strength.

[0041] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A construction method for pumping low-carbon filling material to fill underground structures in green mines, characterized in that, Includes the following steps: Step S1, pre-construction preparation: Perform 3D laser scanning on the inside of the goaf to obtain the distribution pattern of the surrounding rock on its inner wall and perform full-phase modeling; After modeling, use fluid dynamics software to simulate a high-pressure spraying scheme that can cover the inner wall of the goaf, and determine the high-pressure spraying method and spraying points; According to the scheme, pre-set grouting holes and lay grouting pipelines at the corresponding positions in the goaf; At the same time, open at least one exhaust overflow port with an openable and closable valve at the top of the goaf, and install high-pressure clamps and pressure sensors at the ends of the grouting pipelines; Step S2, preparation of low-carbon backfill material; according to the volume measurement of the backfill body, prepare the raw materials of low-carbon backfill material including mine tailings powder, aggregate, strong alkaline activator solution, water reducing agent and water, and add composite expansion agent and fiber components to it, and then stir at high speed to form a fluid slurry for later use; additionally prepare a certain amount of strong alkaline activator solution for later use, the strong alkaline activator solution is made by mixing liquid sodium silicate and sodium hydroxide solution; Step S3: Construction of the roadway anchoring system and sealing of the retaining wall; Several anchor rods are implanted on the inner wall surface of each roadway connected to the goaf, with the other end of the anchor rod protruding from the inner wall surface of the roadway, and a grid mesh is fixed at this end. The grid mesh is made of metal or composite material, and after fixing, a gap of 20mm to 50mm is maintained between it and the inner wall surface; Finally, a retaining wall is constructed at the exit of each roadway and water-stopping construction is carried out. Diagonal bracing is set outside the retaining wall to enclose the area to be filled into a closed cavity. Step S4, activation treatment of the inner wall of the goaf; a high-pressure spraying device is inserted into the grouting pipeline. The high-pressure spraying device includes a nozzle with high-pressure atomization function. The nozzle enters the inner cavity of the goaf and faces the surface of the surrounding rock. An external pipeline is connected to the goaf. The pipeline is used to transport the strong alkaline activator solution prepared in step S2. Then the spraying is started. The strong alkaline activator solution is atomized under high pressure and sprayed evenly on the surface of the surrounding rock of the goaf. Step S5: Formal pumping and filling; Remove the high-pressure spraying device and connect the grouting pipeline to the delivery pipeline of the pumping system. Within 0.5 to 2 hours after spraying with the strong alkaline activator solution, inject the prepared low-carbon filling material into the area to be filled through the pumping system. The delivery pipeline is a composite steel pipe lined with high-chromium wear-resistant alloy, and the inner wall of the delivery pipeline is integrally formed with spiral guide vanes. Step S6, pressure stabilization and curing: When the pressure information collected by the pressure sensor rises rapidly and the filling slurry with uniform consistency and no air bubbles flows out of the exhaust overflow port, immediately close the valve on the exhaust overflow port and adjust and reduce the pumping flow rate of the pumping system in real time to maintain the current pumping pressure of the pumping system within a preset threshold; after maintaining this pumping pressure for 30-60 minutes, shut down the pumping system, use the high-pressure clamps on the grouting pipeline to cut off and seal the grouting pipeline, and enter the curing stage of the filling material.

2. The construction method for pumping low-carbon filling material to fill underground structures in green mines according to claim 1, characterized in that, In step S1, the grouting pipeline pre-embedded in the grouting hole is a steel pipe with a water-swellable sealing strip wrapped on the outer wall. The length of the end of the steel pipe extending into the inner cavity of the goaf is not less than 150mm. Then, the annular gap between the grouting hole and the steel pipe is sealed tightly with fast-hardening cement grout.

3. The construction method for pumping low-carbon filling material to fill underground structures in green mines according to claim 2, characterized in that, The exhaust overflow port is located at the highest point of the goaf roof. The exhaust overflow port is connected to a drainage pipe, and the end of the drainage pipe extends to a liquid collection tank outside the goaf. The total cross-sectional area of ​​the exhaust overflow port is set to 1 / 2 to 1 / 3 of the total cross-sectional area of ​​the grouting pipeline.

4. The construction method for pumping low-carbon filling material to fill underground structures in green mines according to claim 1, characterized in that, In step S2, the mine tailings powder is subjected to ultrafine grinding to control its specific surface area in the range of 400 to 500 m² / kg, wherein the content of particles smaller than 45 μm is not less than 85%; the aggregate is a porous lightweight aggregate including shale ceramsite and expanded perlite, and is pre-wetted before preparation to reach a water-saturated state.

5. The construction method for pumping low-carbon filling material to fill underground structures in green mines according to claim 4, characterized in that, In step S2, the added composite expanding agent is composed of calcium sulfoaluminate expanding component and lightly calcined magnesium oxide component, and the dosage is 5% to 8% of the tailings powder mass; the fiber component is polypropylene fiber, and its dosage is set to 0.8 kg / m³ to 1.0 kg / m³ of the filling volume. The polypropylene fiber is soaked in the strong alkaline activator solution and drained before being added.

6. A construction method for filling green mine underground structures with pumped low-carbon filling material according to any one of claims 1, 4, or 5, characterized in that, The strongly alkaline activator solution is prepared by mixing liquid sodium silicate with a modulus controlled in the range of 1.2 to 1.8 and sodium hydroxide solution with a mass percentage concentration of 25% to 35% in a mass ratio of 3:1, and maintaining the pH value above 13.

7. The construction method for pumping low-carbon filling material to fill underground structures in green mines according to claim 1, characterized in that, In step S3, the anchor bolt is implanted into a stable rock layer on the inner wall of the tunnel for a depth of not less than 1m. After the anchor bolt is implanted, the lattice mesh is welded and fixed to the end of the anchor bolt that protrudes from the inner wall of the tunnel.

8. The construction method for pumping low-carbon filling material to fill underground structures in green mines according to claim 7, characterized in that, Before the spraying operation in step S4, a high-pressure blower is inserted into the grouting pipeline to blow away the surface of the surrounding rock in the goaf, removing weathered debris and dust from the surface; after the spraying operation is completed, a high-pressure blower is inserted again to blow away excess activator droplets that have accumulated on the surface of the surrounding rock due to gravity.

9. The construction method for pumping low-carbon filling material to fill underground structures in green mines according to claim 1, characterized in that, In step S5, a pulse generator is provided at one end of the delivery pipeline near the grouting pipeline. During the formal pumping and filling, the pulse generator is turned on to continuously generate high-frequency pressure pulse waves to the delivery pipeline, thereby disrupting the flocculation structure of the slurry inside the pipeline.

10. The construction method for pumping low-carbon filling material to fill underground structures in green mines according to claim 1, characterized in that, In step S6, the preset threshold is set to 80% of the structural safety bearing limit of the surrounding rock or retaining wall, taking the minimum value between the two.

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