The following is the relevant content brought to you by Zhongda Consulting on ground drilling and grouting to seal water-conducting tunnels for your reference.
After the middle ventilation tunnel of Wudong Coal Mine in Huaibei City, Anhui Province was built, the support collapsed due to roof collapse and deformation of the tunnel, and the amount of water conducted through the cracks increased, bringing the topsoil mud and sand into the tunnel, causing the ground surface to sink, forming a deep The collapse pit is 2m in diameter and 6m in diameter, and has a tendency to gradually expand, forcing the well to be flooded. Ground drilling was used to fill aggregates and grouting, and three drilling holes were constructed. It took one month to seal the ventilation tunnel, with a water blocking rate of 100%, and the mine production was resumed smoothly.
1. Basic situation
The Quaternary alluvial layer in Wudong Mine is 35m thick and is mainly composed of sand, sandy clay and a clay layer with poor water barrier properties at the bottom. The weathered bedrock has a vertical depth of 55m and is mainly composed of sandstone and mudstone with soft lithology. During the construction of the well, it was revealed that the mixed water inflow volume of the alluvium and weathered rock layers was 330m3/h.
The mine has two shafts, a lifting shaft and an air shaft, with depths of 90m and 47m respectively. The vertical depth of the first horizontal transport tunnel 90m, the middle tunnel is a 45° semi-coal inclined tunnel, 66m long, connected with the first transportation lane, and another downhill connection lane is dug at a depth of 65m to connect with the transportation lane. During the excavation process, part of the coal was mined in this ventilation tunnel, and excessive coal slipping and falling occurred, which affected the fissure zone upwards. The fissures communicated, and the upper layer water was introduced into the tunnel (water inflow 250m3/h), and the topsoil mud and sand were brought into the tunnel, causing The ground sank, forming a 2m deep and 6m diameter collapse pit, which gradually expanded and the amount of water inflow increased. The underground water tank was silted up and could not operate normally, forcing the well to flood.
2. Water control plan
The bedrock weathered zone is 20m thick and highly water-rich. The upper section of the ventilation tunnel is located in weakly weathered rock. The rock is loose and cracks are developed. In addition, the upper layer water is introduced into the tunnel, causing the rock mass to be destroyed and lose stability. The water in the topsoil layer and the bedrock weathering zone carries mud and sand into the tunnel in large quantities, and the water carries mud and sand. When scouring loose rock mass, the path is short, the flow rate is fast, and the tunnel has the conditions for pressure relief and sand storage. It is bound to expand the water channel and increase the amount of water inflow until the water storage in the upper strata is drained. However, this condition is not met. , only measures to block water inflow in the roadway can be taken.
Considering the large amount of water inflow in the tunnel, the surrounding rock in the upper section is unstable, part of the roof has already collapsed, and the supports have collapsed. If partial sealing is used, the effect of water on the top of the tunnel will not be eliminated, which will still threaten the safety of the mine. Therefore, it was decided to block all the ventilation tunnels that carry water. At present, grouting is often used for consolidation and sealing, which is more economical, reasonable, safe and reliable. Therefore, two construction options can be adopted: underground working surface grouting or ground drilling and grouting.
Option 1, namely grouting of underground working face. It is necessary to build a slurry-stop wall at the lower end of the ventilation tunnel and the upper end of the contact tunnel to seal the water inflow in the ventilation tunnel, and then pour cement slurry or cement mortar from bottom to top through the slurry-stop wall to fill the ventilation tunnel. This solution has simple technology and convenient construction; however, the ventilation tunnels are all coal-rock tunnels, and the roof and floor are made of loose rock. When constructing a grout-stop wall in a tunnel with loose surrounding rock, it is difficult to seal the water inflow in the tunnel, and there is a threat of well flooding, and pressure grouting cannot be performed.
Option 2 is to drill holes from the ground through the tunnel, then fill it with aggregate and grouting for consolidation. A slurry retaining wall needs to be built at the lower end of the ventilation tunnel and the upper end of the contact tunnel to prevent the injected slurry from flowing into the transportation tunnel under still water conditions after the well is flooded. This solution is safe to construct, pours gravel aggregate into the tunnel, saves cement, and is of reliable quality; however, it increases the amount of drilling work, making the construction difficult and demanding.
Considering construction safety and quality, we decided to choose option 2.
3. Grouting construction design
Grouting is used to seal the outlet section of the ventilation tunnel. Block both ends first, and then pressurize the outlet section to ensure dense grouting filling in the tunnel. , and can also seal the water passage in the rock cracks on the roof and floor of the tunnel.
The grouting construction design includes the following contents:
(1) Number of grouting holes. Three grouting holes are arranged along the center line of the tunnel, arranged from bottom to top, with hole spacing of 14m and 12m respectively.
(2) Depth of grouting holes. The No. 1 hole is 79m, the No. 2 hole is 65m, and the No. 3 hole is 53m.
(3) Amount of aggregate filling in the tunnel. The cross-section of the ventilation tunnel is trapezoidal, and its area S=(1.62.5)×1.6÷2=3.3m2. The inclined tunnel below hole 3 is filled with aggregate length L=58m. Then the amount of aggregate V=SL=3.3×58= 191.4m3.
(4) Grouting parameters.
①Grouting pressure: The grouting pressure can only be increased after the tunnel is filled with aggregate. The end pressure of the grouting holes at both ends must be greater than 1 times the hydrostatic pressure; the grout injected into the middle grouting hole needs to be pressed into the crack to block the water passage, and the corresponding grouting pressure must be high, 2 to 2.5 times the hydrostatic pressure.
②Grouting volume: The slurry that fills the gravel gaps, collapse spaces and cracks in the surrounding rock of the tunnel will inevitably flow into the upper loose strata because it is close to the topsoil in the weathered zone. The estimated slurry injection volume is:
Q=A (nSL0.5mLHd)/βS (66-L)
In the formula: A is the slurry diffusion consumption coefficient, which is 1.5; S is Cross-sectional area of ??the tunnel, S=3.3m2; L is the length of the filled tunnel, L=58m; H is the average height affected by caving, H=4m; d is the width of the bottom edge affected by caving, d=1.6m; n is the gravel void rate, n=40%; m is the porosity of the loose zone affected by caving, m=20%; β is the slurry stone rate, β=85%. After calculation, it is concluded that the amount of slurry to be injected is about 227m3, which is equivalent to 193t of cement.
4. Grouting construction
Project the center line of the ventilation tunnel to the ground and determine the location of the main water outlet. After re-measurement, the position of the drilling hole will be determined when the error does not exceed 10cm, respectively. Install the drill to drill holes.
4.1 Grouting hole drilling
(1) Drilling structure. Use a φ168mm drill bit to open a hole, drill 3m into the complete bedrock, run a φ146mm casing, and consolidate the whole pipe with 0.75:1 cement slurry. The lower part has a φ108mm aperture for aggregate filling and grouting.
(2) Grouting hole requirements. According to the engineering drilling specifications, the drilling deflection rate is less than 8‰, but the hole depth does not exceed 100m, and the slope distance does not exceed 0.8m. Normal operation can achieve the purpose of tunnel penetration.
(3) Drilling tool assembly. Use a φ108mm core pipe to connect a cylindrical core drill bit, a φ73mm 8m long weighted drill pipe, and use a φ50mm drill pipe to drive the core drill into the grouting hole section.
4.2 Aggregate filling
Choose clean gravel as aggregate, with a particle size not exceeding 15mm and a porosity of 40%. Before adding slag, lower the φ50mm drill pipe to the bottom of the hole. , ascertain the depth of the hole bottom, and start pumping clean water to remove the mud, sand and other materials accumulated at the bottom of the hole. A chute is installed at the entrance of the hole, and the gravel is manually fed into the chute, and clean water is used to flush the gravel in the chute into the borehole. The water-to-slag ratio is maintained at 10:1 to 4:1, allowing normal filling for a long time. When the aggregate is blocked, start the drilling rig to rotate or move the drill pipe up and down. At the same time, connect a slightly curved short pipe to the bottom of the drill pipe. When rotating, the gravel will be scattered around. When the gravel filling height exceeds 0.5m from the top of the tunnel, slag filling will be stopped and grouting will begin.
4.3 Grouting operation
(1) Grouting sequence. Grout No. 1 and No. 3 first, seal both ends of the ventilation tunnel, and keep the water outlet tunnel in a closed state to facilitate the extrusion grouting of No. 2 hole constructed later in the middle to improve the compactness of the consolidated body.
(2) Grouting construction. First lower the drill pipe into the hole, insert it into the tunnel gravel and close to the bottom plate. Install a hole sealing device so that the seal between the casing and drill pipe can withstand the grouting pressure. Connect the orifice device and the slurry conveying pipeline, and use a pump to pump the mixed concentrated slurry to the bottom of the tunnel (because the cement slurry has a large proportion and good permeability, the water in the gaps between the gravel can be replaced, so that the slurry level gradually rises ), then lift the drill pipe, and when the lower end of the drill pipe is 0.5m away from the top of the tunnel, inject 1:1 cement slurry. When the tunnel is open and the grout passage is open, quantitative grouting is used, and then the holes are scanned and re-injected multiple times until the grout passage is blocked and the grouting pressure increases. The pressure in hole No. 1 reaches 1MPa and the pressure in hole No. 3 reaches 0.7MPa ( are greater than 1 times the hydrostatic pressure), reaching the grouting completion standard. The No. 2 hole constructed later is the focus of grouting. It not only fills the gaps left by the gravel in the tunnel tightly, but also seals the water passage of the surrounding rock. The drill hole is extended to 3m below the tunnel floor, and grouting pipes are used to separately grout the tunnel floor. , the middle part, and the roof were repeatedly grouted, and the slurry concentration gradually became thinner in sequence. Finally, a slurry with a water-cement ratio of 1.5:1 was injected until the pressure reached 1.5MPa.
The grouting construction lasted one month. There are 183m3 of aggregate and 225t of cement. After drainage, other tunnels are basically intact. The water blocking rate of the ventilation tunnel reaches 100%, and production has been resumed smoothly.
5. Conclusion
(1) The upper section of the ventilation tunnel of Wudong Mine is in weakly weathered rock formations with loose lithology, close to the Quaternary aquifer, large water volume, and unstable The protection of the water-proof layer threatens the safety of the mine. It is feasible to adopt ventilation tunnels that block water to ensure the safe production of the mine.
(2) The three-hole ground grouting construction plan is adopted to provide safe and convenient construction conditions. As the technical measures were feasible, all three boreholes were drilled into the tunnel and a large amount of gravel was poured in for filling. This not only saved cement, but also improved the consolidation quality of the blocked tunnel. It only took 1 month to block 100% of the water inflow in the tunnel. , after the mine is drained, other tunnels are basically intact, eliminating the threat of mine water damage.
(3) The construction equipment is simple, the process is simple, and the grouting water blocking effect is good. This method can be used for grouting under dynamic water conditions in similar projects.
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