Research on support technology of karst fracture and water-rich large fault roadway

In the mine construction and production process, the well and road engineering will inevitably pass through the unfavorable geological sections such as fault fracture zone. When the tunnel engineering crosses the fault fracture zone, if the roadway support is not paid attention to during the excavation process, it may cause water inrush and roof collapse. Safety accidents such as collapse, mudslides, etc. [1-2].
At present, for the problem of large fault fracture zone in the roadway excavation process, domestic and foreign scholars have carried out a lot of research work and achieved great results. However, the geological conditions of each mine are different, and the support situation cannot be generalized. There are still many problems to be solved. .
Hydrogeological conditions Makeng iron ore is extremely complex, often need to pass through karst underground construction broken water-rich big fault, support the process, not simply the choice of the most commonly used mine I-beam, U-shaped steel frame shed or bolt , anchor cable joint support [3-5]. According to its own hydrogeological conditions, it is necessary to choose the appropriate support method. Based on years of field practice and experience, the Makeng Iron Mine has proposed reasonable support technology for the roadway over the karst water-rich large fault fracture zone. The Ma Hang Iron Mine has been successfully used.
1 Deposit geological and hydrogeological conditions
The Makeng Iron Ore Mine is located in the Huaxia fold belt of the Caledonian fold system in South China, and the east side of the Yongmei Upper Depression Belt. The Indosinian movement in the region, especially the Yanshan movement, is very strong. The fractures, folds and magmatism in the area where the mining area is located are very strong and complex, reflecting the results of the multi-stage tectonic movement in the long history of the area. The ore body is mainly buried in the lowest erosion datum of the area below the elevation of 420m, and the main ore body is found in the middle Carboniferous meridian group (C2j). The Chongqing Formation (C3c-Plq) carbonate rock salt (hereinafter referred to as limestone) of the Chuanshan Formation with large thickness, karst development and water-richness is its top plate. The mining area is surrounded by faults, forming a natural boundary and the outside is rich in water. Poor fractured rock layers, lateral recharge, and karst water-filled, are semi-concealed karst hydrogeological deposits of medium and complex hydrogeological conditions.
During the development of the mine, some sections of the slope and inclined wells will pass through the F11 and F3 fault fracture zone, the fracture development zone, the karst development zone and the Tongziyan Formation, the Wenbishan Formation mudstone, and the sandy mudstone. Due to the fracture of the rock, the compressive strength is low, the stability is poor, and the dome, the carcass collapse, and collapse may occur. Inclined wells, stage roadways, slipways and other projects may have collapsed and collapsed wells in areas with poor engineering properties such as fracture development zones and karst development zones. Near the west ore section, the lower part of the ore body is the F2' large fault. The lithology is the interbedded layer of mudstone and siltstone , and the fault breccia is filled, and the overall stability is extremely poor. According to the disclosure of the construction, the rock is relatively broken, and the roadway has crack development, water, and the work surface is yellowish brown. The transportation of the veined roadway in the stage requires multiple crossings of the F2' large fault, and the roadway driving support is very difficult.
2 problems
Due to the strong and complex fractures, folds and magmatism in the area where the Mikeng iron ore is located, the joints and fissures of the faults are relatively developed, the rocks are relatively broken, the stability is poor, and the rock permeability and water-richness are strong. Excavation of roadway in this type of rock mass has great safety hazards, which greatly increases the difficulty of roadway driving and roadway maintenance. The difficulties are mainly reflected in:
(1) When the rock mass is broken, it is difficult to form a large section space easily, and it is difficult for the shaft to pass through the rock mass.
(2) The karst fracture large fault rock mass is rich in water, the water source is sufficient, the structure is fully communicated, and the existence of quicksand filling in karst water and karst cave leads to safety hazard of large debris flow.

(3) Permanent roadway maintenance is difficult, costly, and has high safety risks. The underground mining development system mainly includes slopes, inclined shafts, and stage transportation lanes. It has large section specifications, long service time and high safety level requirements. When the main body development project is arranged in the dissolution fractured rock mass, the roadway is Permanent support methods, support materials, support parameters,
Construction techniques and other requirements are bound to raise higher requirements than conventional projects. At the same time, proper construction and maintenance costs of wells must be controlled to ensure the overall economic benefits of the mines.

After technical and economic comparison analysis of various roadway over-fracture fracture zone support methods, combined with the actual characteristics of the karst fracture and water-rich large fault of Mikeng Iron Mine, the joint support method is adopted, that is, the work surface pre-grout consolidation Combined support with the advanced pipe shed as a support scheme for the roadway of the karst fracture and water-rich fault in the Makeng Iron Mine.
3 Combined support technology for karst crushing large fault water-rich roadway

3.1 working surface advanced pre-grouting process
In order to adapt to the actual characteristics of the karst fracture and water-rich faults in Mikeng Iron Mine, the pre-pre-grouting of the working face is carried out in advance, and the fractured rock mass to be dug into the roadway is pre-consolidated to form a composite solid compact. In the process of preventing the excavation, the self-stabilization time of the surrounding rock is short due to the fracture of the rock mass. It is difficult to form a large section space easily with the excavation, and it is difficult to pass through the rock mass. At the same time, because the Makeng iron ore mine is a large water mine, the hydrogeological conditions are extremely complicated, and the large faults in the fracture zone are natural water guiding channels. Pre-grouting can effectively block the effluent fissures, strengthen the surrounding rock and prevent water inrush. Debris flow safety accident [6-9].
3.1.1 Construction of the retaining wall
The construction roadway is over the fault-breaking zone, and the working surface is constructed to stop the mortar wall, and 3 holes are pre-buried. Three grouting holes are arranged in the whole section. The final hole depth depends on the width of the fracture zone of the fault. The site is tentatively set at 20m. The mortar wall is combined with the brick wall (commonly known as 24 wall) as the retaining wall, the thickness is 1000mm, and the orifice tube is made of seamless steel tube of Φ108mm×4mm, with a length of 1.5m and an exposed 0.5m. See Figure 1 for details.

3.1.2 grouting construction
It is mainly composed of single-liquid cement slurry, and cement-water glass double-liquid slurry is used for sealing. If the slurry consumption is large, mortar grouting is adopted. The ordinary 42.5R Portland cement is used; the modulus M of the water glass is 2.8 to 3.1, and the Baume degree is 38 to 40 Be'. Single slurry water to cement ratio of 2:1, 1.5:1, 1:1, 0.8:1; double slurry: cement slurry to water glass volume ratio of 1:1, 1:0.8, 1: 0.5; the amount of triethanolamine added is 0.05%, the amount of salt added is 0.5%, and the ratio of mortar is water: cement: sand = 1: 1: 2. Grouting construction is a concealed project. In order to ensure the quality of grouting and the effect of water shutoff, the grouting of each hole section must meet the design requirements of final pressure, final quantity and injection quantity. After reaching the final pressure of the design, the flow rate of the pump is 30L/min, stable for 20~30min, the grouting of the hole section can be finished, and the grouting record is carefully done.

3.2 advanced pipe shed support technology

According to the work of the front working face construction grouting to strengthen the surrounding rock, after the grouting work is completed, according to the actual situation of the surrounding rock grouting of the roadway, the roadway excavation and the advanced pipe shed support are determined [10-11].
3.2.1 Shelf back construction
(1) The steel shed is made of 25U steel. The shed and the shed are connected by connecting rods made of 8# channel steel. Each two sheds are connected by 7 connecting rods, two straight walls and three arches. Each shed has 3 connectors, and each connector is connected by bolts with 1 U-shaped cable. The structure is shown in Figure 2.

(2) According to the middle waist line provided by the technical department, the root shed is firstly built. The root shed should be welded with the rock reinforcement. The front beam is provided with a shed beam, and the front beam is made of Φ108mm×3000mm seamless steel pipe, which is connected with the U-shaped steel through the steel bar hook. After the frame beam is corrected, the connector is fixed.
(3) Next to the shed leg. The length of the shed leg and the shed beam is 400mm. It is locked by two U-shaped cables, and the bolts of the cable should be tightened.

The U-shaped cable is produced as shown in Figure 3.

(4) Construction connecting rod. Made of 8# channel steel, the length is 900mm, and each connecting rod is fixed by 4 Φ16mm×250mm hook bolts. See Figure 4 for details.

(5) After the U-shaped steel scaffolding is set up, the erection of the reinforced concrete backing plate is carried out. The back panel is 150mm × 600mm × 50mm, and the length direction is placed perpendicular to the U-shaped steel. It is necessary to close the back panel, that is, every two pieces should be placed next to each other. The empty area behind the back panel is filled with a wooden backboard or a backboard.
3.2.2 Shotcrete construction
(1) Check whether the U-shaped shed installation and the backing plate are in conformity with the design requirements, remove the dangerous stone on the working surface, and clean the rock face. Preventing the failure of dangerous rock or rock surface rinsing to reduce the adhesion between concrete and rock face, affecting the integrity of the support and surrounding rock, and even affecting the support effect of part or whole;
(2) Optimize the mix ratio of shotcrete to ensure that the shotcrete meets the construction requirements such as strength, rebound, dust and bonding effect (smooth feed). Sand and stone materials for shotcrete are relatively strict, and the particle size of sand and stone should be strictly controlled. The concrete mixing process strictly controls the proportion of the quick-setting agent;
(3) Construction shall be carried out in strict accordance with the regulations during the spraying process. Control the injection angle and distance, the thickness of the primary shotcrete, the time interval of the stratified injection, etc. [12];
(4) The cement and fine aggregate of shotcrete are relatively more, and at the same time, it is mixed with quick-setting agent, so its shrinkage deformation is more serious. Therefore, within 7 days after the concrete is sprayed, water spray curing is required to ensure the strength growth of the shotcrete, improve the deformation properties and improve the impermeability of the concrete.
4 industrial application effects
From the current construction situation, the use of joint support technology has achieved good results:
(1) The tunneling speed is greatly improved, and each footage can be maintained for about 1m, which solves the problems of difficult roadway formation, short self-stabilization of surrounding rock, flooding with tunneling, water in the roadway, and slow construction progress.
(2) The large fault pre-grout consolidation in the water-rich position effectively blocks the effluent fissures and strengthens the surrounding rock, and the self-supporting ability of the surrounding rock of the roadway is greatly improved. Combined with the advanced pipe shed joint support, the deformation of the roadway is significantly reduced, and the influx in the roadway is significantly reduced. The amount of water inflow from the original maximum water inflow of 80m3 / h to 2m3 / h, and even no water.
(3) After the pre-grouting of the working face, the composite stable solid body is re-formed between the broken rock masses, and there is no large-scale collapse during the excavation process. At the same time, the advanced pipe shed support is supported, and the short branch is shortly mined to make the joint support. The form is combined with the surrounding rock of the roadway to further improve the stability of the surrounding rock of the roadway. At present, there are many tunnels in the +100m stage that cross the F2' fault.
There is no large area collapse or severe deformation in the roadway.
(4) With the joint support scheme, more than 10 tunnels for tunneling have been constructed in the +100m phase of the West Mine Section, each of which successfully crosses the F2' large fault; the longest water-rich fault with the excavation and support is broken. , etc.: Research on karst fracture and water-rich large fault roadway support technology with a belt of about 80m. After joint support, the surrounding rock of the roadway is stable, and the roadway has only slight deformation at local locations.
5 Conclusion
In view of the roadway excavation and support in the karst water-rich large fault under the complex hydrogeological conditions of the Makeng Iron Mine, the fractured rock mass is grouted in advance by pouring the grouting wall to re-form the fractured rock mass. The composite stable solid body, at the same time effectively block the effluent fissure, combined with the advanced pipe shed support, effectively improving the stability of the surrounding rock of the roadway. The construction results show that for the karst fracture zone of loose rock, fracture, bedding, joints and fissures, it is easy to cause large-scale landslides, large water-rich faults, easy water inrush or mudslides, and effectively solved by joint support. A series of technical problems in the construction process, and successfully applied to the well and road engineering in different locations of the mine.
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Article source: Mining Technology; 2017.12(1)
Author: Heyuan Fu, Jiang Fan Jun, Zhang Youxuan, Lai Wei; Changsha Institute of Mining Research Co., Ltd., Changsha 410012, National Metal Mining Engineering Research Center, Changsha 410012;
Qiu Yuhua , Dong Junting ; Fujian Makeng Mining Co., Ltd., Longyan, Fujian 364021 , China;
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