Ground pre-reinforcement method for unfavorable geological tunnel section of TBM construction tunnel

Abstract

The invention discloses a TBM construction tunnel unfavorable geological tunnel section ground pre-reinforcement method which comprises the following steps: S1, a tunnel surrounding rock category map is compiled, and surrounding rock categories and stake numbers are marked on the map; s2, the surrounding rock confirmed to be in the V type is rechecked as a target reinforcing area; s3, directional grouting drill hole arrangement; s4, drilling design is conducted in combination with the tunnel excavation design drawing and the drilling task book; s5, drilling equipment is selected; s6, drilling equipment is installed; s7, designing and installing a grouting system; s8, drilling an orifice section; s9, drilling a vertical section; s10, drilling in a deflecting section; s11, horizontal grouting section drilling is carried out; s12, horizontal section bare hole grouting is conducted; s13, lowering a floral tube; s14, grouting the floral tube; s15, the grouting effect is checked; and S16, hole sealing is conducted. Advanced reinforcement grouting is conducted on the tunnel surrounding rock on the earth surface through drilling, the physical and mechanical parameters of the tunnel surrounding rock are improved, the risk of engineering geological problems during tunnel excavation is reduced, and the tunnel construction efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of TBM construction, and in particular to a method for pre-reinforcing the ground in a poor geological section of a TBM-constructed tunnel. Background Art

[0002] Due to restrictions on ventilation and other construction conditions, the length of single-headed tunnels (including branch tunnels) in drilling and blasting construction should not exceed 5km. Due to the depth and length of the tunnel, many deep-buried tunnels do not have the conditions for arranging branch tunnels, making it difficult to implement drilling and blasting entirely. Currently, many tunnels in China use a "TBM + drilling and blasting" excavation scheme. Drilling and blasting are used for tunnel sections that can accommodate branch tunnels. For tunnel sections in large fault zones that do not have the conditions for branch tunnels and are not suitable for TBM construction, bypass tunnels are set up and the main tunnel is excavated using drilling and blasting, with the TBM then advancing through them. For Class V surrounding rock in the TBM excavation section, advance reinforcement and enhanced initial support measures are implemented before TBM passage. Advanced geological prediction and advanced treatment are conducted for tunnel sections with unfavorable geology, and TBM equipment is required to have advanced geological prediction, advanced support, and advanced grouting capabilities.

[0003] Tunnel boring machines (TBMs) are widely used in tunnel construction for hydropower, roads, railways, and other applications due to their advantages, such as high excavation speed, high-quality tunneling, significant economic benefits, civilized construction environment, and high safety. However, TBM construction has poor adaptability to strata. During construction, adverse geological problems such as karst caves, water and mud inrush, fault fracture zones, high-stress soft rock deformation, and hard rock rockbursts often cause disasters such as water and mud inrush, landslides, machine jams, and rockbursts, seriously endangering construction safety and affecting project progress. Therefore, it is extremely important to identify adverse geological bodies and their water content in front of the tunnel face in advance and reinforce them.

[0004] TBMs have limited adaptability to changing geological conditions (faults, fracture zones, compression zones, water gushing, and hard rock). Currently, many TBMs are equipped with fast advance drilling rigs for geological surveys and reinforcement. However, when performing advance grouting reinforcement at the tunnel face, the TBM is suspended, impacting the project schedule. Furthermore, prolonged exposure to unfavorable tunnel sections poses significant safety risks.

[0005] A certain domestic tunnel faces major engineering geological and environmental geological problems such as karst groundwater, active faults, high ground stress, and large deformation of soft rock. It also faces world-class technical difficulties such as the difficulty of deep tunnel construction, groundwater treatment, crossing broken faults, coping with large deformation of soft rock, earthquake protection, rock burst hazard treatment, toxic and harmful gas prevention and control, comprehensive management of geothermal hazards, and TBM manufacturing process. Therefore, in response to this situation, in order to ensure the smooth progress of tunnel excavation projects, it is necessary to develop a construction method for reinforcing and improving the unfavorable geological sections, so as to achieve advanced pre-reinforcement of the TBM unfavorable geological sections and prevent the occurrence of machine jams. Summary of the Invention

[0006] Based on the above technical problems, the purpose of the present invention is to provide a ground pre-reinforcement method for poor geological sections of tunnels under TBM construction, which is a method of forming boreholes around the tunnel body on the surface through directional drilling technology, and injecting grouting into the holes to reinforce the tunnel surrounding rock, thereby ensuring stability, safety and efficiency during construction of deep-buried long tunnels and reducing construction costs. Before tunnel excavation, directional drilling technology is used to perform a certain number of drilling construction from the surface to the surrounding area of ​​the tunnel body by a directional drilling rig, and the tunnel surrounding rock is pre-reinforced and grouted on the surface through drilling holes, thereby improving the physical and mechanical parameters of the tunnel surrounding rock, reducing the risk of engineering geological problems during tunnel excavation, and improving the efficiency of tunnel construction, so as to achieve the purpose of non-interference between pre-grouting reinforcement and tunnel construction, avoiding pre-grouting in the tunnel occupying the linear construction period, and improving the working environment of workers during pre-grouting reinforcement work.

[0007] The present invention provides a ground pre-reinforcement method for a tunnel section with poor geological conditions during TBM construction, which is characterized in that the reinforcement method, for a tunnel section not yet excavated by the TBM, uses "L"-shaped directional drilling on the ground to review the geological conditions of the tunnel section with Class V surrounding rock, further explores the geological characteristics of the tunnel section with poor geological conditions, identifies the distribution of tunnel sections with poor geological conditions at the tunnel elevation, and uses directional drilling to pre-grout the tunnel section with Class V surrounding rock geological conditions during the directional drilling exploration process, thereby reinforcing the top arch of the tunnel section excavated by the TBM and the top arch of the tunnel section with poor local surrounding rock conditions, thereby preventing the TBM from jamming during subsequent excavation; for a tunnel section with locally predicted strong water-rich strata, ground pre-grouting reinforcement is performed around the tunnel to achieve the purpose of controllable water gushing, thereby preventing the problem of mud and water gushing; the specific steps are as follows: S1: Based on the geological exploration data from the project proposal, feasibility study, and preliminary design phases, and in accordance with the design drawings, a tunnel surrounding rock classification diagram is prepared. The surrounding rock classification and pile number are marked on the diagram. The evaluation parameters include the uniaxial saturated compressive strength of the rock, rock mass integrity, structural surface development, and groundwater conditions. S2: Re-check and confirm that the surrounding rock of Class V is the target reinforcement area: Directional drilling and continuous coring using rope coring technology were used to obtain cores indicating that the surrounding rock of the TBM tunnel axis was estimated to be Class V. Digital imaging of the cores and the entire borehole wall, as well as acoustic verification, confirmed that the tunnel section with Class V surrounding rock was the target area for ground pre-reinforcement. The following steps are involved: S21. Select an appropriate drilling path based on the depth and length of the tunnel axis, which is estimated to be Class V surrounding rock. The borehole selection should be based on the surface topography, mountain, and Class V surrounding rock to ensure that the drilling path reaches the tunnel and passes through the pre-reinforcement target area along the tunnel axis. S22, using a single-open drill bit to drill an oblique section of the road surface in a downwardly inclined direction. During the drilling process, the single-open drill bit continuously breaks and removes the core along the rope coring mechanism configured inside the single-open drill bit, thereby completing the drilling and coring of the oblique section of the hole; S23. After the oblique section drilling is completed, the first drilling tool is removed, and then a casing is installed in the oblique drilled hole; S24: The secondary drilling tool is replaced. The pilot drill bit of the secondary drilling tool passes through the casing and continues drilling. During the drilling process, the pilot drill bit of the secondary drilling tool changes the drilling direction under the weight of the coring drill pipe to complete the drilling of the curved section. The rope coring mechanism configured inside the secondary drilling tool breaks and removes the core. S25. The three-hole drilling tool is replaced. The pilot drill bit of the three-hole drilling tool passes through the casing and continues drilling. During the drilling process, the pilot drill bit of the three-hole drilling tool changes the drilling direction under the weight of the coring drill pipe, completing the drilling of the horizontal section. The rope coring mechanism configured inside the three-hole drilling tool breaks and removes the core. S26: Complete the digital imaging of the entire hole wall and the drilling acoustic wave test; S27: Based on the core and full-hole wall digital imaging images and acoustic waves, the tunnel section with Class V surrounding rock was confirmed as the target area for ground pre-reinforcement; S3: Arrange directional grouting drilling holes according to the terrain, landform, traffic conditions and the location of the target reinforcement area. The parameters include grouting section range, grouting hole number, hole mouth section length, vertical section length, deflection section length, horizontal grouting section length and total drilling length. S4: Drilling design is carried out in combination with the tunnel excavation design drawing and the drilling task book. The drilling design includes drilling trajectory design and drilling structure design. The design steps are as follows: S41: Design the deflection point and deflection intensity according to the location of the drilling point and target point, and draw the hole profile trajectory; S42: Design the drilling structure based on the drilling trajectory design, site and engineering geological conditions, drilling equipment, drilling methods and processes, final hole diameter, deflection tool type and method, in-hole grouting, etc. S43: The drilling is divided into the first, second, and third sections from top to bottom. The first section includes the orifice section and the vertical section, the second section is the curved section, and the third section is the horizontal grouting section. The orifice section has a diameter of 311.1 mm; the vertical and curved sections have a diameter of 215.9 mm; and the horizontal grouting section has a diameter of 152.4 mm. S5: Drilling equipment selection: Directional drilling rigs should be selected with a wide speed range, appropriate torque, and engine power. The directional drilling rig's speed, torque, and maximum feed force performance parameters should meet drilling requirements. For wireline coring, the speed should not be less than 300 r / min, the space-building torque should not be less than 3000 N·m, and the formation feed force should not be less than 60 kN. For non-coring drilling, a high-torque rig should be selected. For drilling holes with complex geological conditions and borehole structures, a rig with high drilling depth capability, high torque, high maximum feed force, and strong adaptability to drilling processes should be selected. S6: Drilling equipment installation: Including the installation of the drilling tower and the installation of the drilling rig, the steps are as follows: S61: Drilling tower installation: (1) The steel beams of the drilling rig chassis are firmly spliced ​​to ensure that the chassis is flat and stable as a whole; (2) The drilling tower bolts are complete and tightened; (3) According to the actual situation of the drilling site, set up a guy rope, set a rope tightener on the guy rope, and fix it with a ground anchor or anchor pile. The burial depth should be greater than 1.5m; (4) Install a lightning rod on the top of the drilling tower and do grounding work; S62: Drilling rig installation: (1) The drilling rig is installed on the chassis with bolts, and the bolts and gaskets are complete and tightened; (3) The drilling rig is installed horizontally, with the turntable center, the overhead crane center and the drilling center forming a vertical line and tightening the nuts; S7: Grouting system design and installation: The grouting system includes drilling equipment, grouting pumps, grouting pipelines, slurry preparation equipment, slurry stoppers and water pressure testing equipment, among which: Drilling equipment includes drilling rigs, drilling towers, mud pumps, mud purification equipment, drilling tools, downhole power drilling tools, directional drilling tools, inclinometers and directional instruments, and calipers; The grouting pump is a power device for conveying slurry; The grouting pipeline includes a high-pressure hose, an orifice device, a mixer, and a shut-off valve; The mixer is used for double-liquid grouting to fully mix the two slurries after they meet; Slurry preparation equipment is used to prepare qualified slurry for grouting. The corresponding preparation equipment is selected according to the grouting material, including clay cement slurry preparation equipment or single liquid cement slurry preparation equipment; Grout plugs are devices used to isolate the grouting section from the non-grouting section in the borehole during grouting, preventing the slurry from flowing to the non-grouting section or out of the hole. They include slip-type grout plugs, hydraulic expansion grout plugs, reducing grout plugs, and double-tube grout plugs. S8: Drilling of the hole section: The length of the borehole section is based on the standard of entering the weakly weathered rock layer. The borehole diameter is Φ311.1mm. A Φ244.5×8.94mm casing is inserted and cement slurry is used to fix the casing to the borehole. S9: Vertical drilling: Continue drilling a Φ215.9mm hole downward in the casing of the orifice section, the length of which is 20% of the distance from the orifice to the centerline of the main tunnel. The hole is a vertical hole. S10: Drilling in the deflection section: Continue drilling a Φ215.9mm hole in the casing at the orifice section, gradually increasing the hole inclination until the drilling trajectory is parallel to the main hole axis, drilling to the level of the main hole centerline, then insert a Φ177.8×8.05mm casing, and use cement slurry to fix the entire section of the casing to the orifice; A mud pulse wireless inclinometer is used for inclination measurement. The inclination, azimuth and tool face angle of the hole body are measured during drilling, providing hole body parameters in a timely manner for drilling. The wireless inclinometer while drilling consists of two parts: surface equipment and in-hole measuring instruments. The surface equipment includes pressure sensors, host computer, driller display, computer and related connecting cables; the in-hole measuring instrument consists of inclinometer probe, main control, mud pulse generator, battery and centralizer. S11: Drilling the horizontal grouting section: Continue drilling a Φ215.9mm hole in the orifice casing, gradually increasing the hole inclination until the drilling trajectory is parallel to the main hole axis. Drill to the level of the main hole centerline, then insert a Φ177.8×8.05mm casing and secure the entire section to the orifice with cement slurry. S12: horizontal section open hole grouting; S13: Lower the flower tube:; In S12 and S13, one section is drilled and grouting is carried out. When the grouting pressure and flow rate meet the technical requirements, the next section is drilled and grouting is started, realizing segmented forward open hole grouting until all grouting sections are completed. After the grouting construction of the open hole grouting section is completed, the flower pipe string is lowered by the pipe throwing method. After it is lowered into place, the annular space between the grouting casing and the borehole wall is filled with filling materials; The annular space filling material must meet the pumping requirements, with a water separation rate of less than 5%, an initial setting time of 30 minutes to 1 hour, a final setting time of 6 to 10 hours, and an initial strength controlled at 0.5-2.0 MPa; S14: Flower tube grouting: The area where the open hole grouting is completed is subjected to segmented high-pressure splitting and compaction grouting through the flower pipe, with the splitting pressure exceeding 3MPa; S15: Grouting effect inspection: For the borehole water pressure test, one grouting hole is selected at each drilling site as a water pressure test hole, and magnetotelluric detection is used. The water pressure test and magnetotelluric detection are carried out once before and after grouting. S16: Sealing: After the grouting effect is checked and qualified, cement slurry is used to seal the hole.

[0008] In step S3, the goal is to improve the rock integrity of the tunnel crown in the general tunnel section, and to form an effective water control curtain in the water-rich tunnel section to achieve the goal of controllable water inrush, thereby providing safety for TBM excavation in the unfavorable Class V tunnel section; the directional grouting drilling trajectory adopts an "L" shape or a "human" shape according to the topographical, geological and environmental conditions.

[0009] The present invention has the following advantages: (1) The present invention can effectively identify the geological conditions, spatial distribution, scale, material composition, engineering properties and other characteristics of the stratum, form a three-dimensional geological description, and accurately verify the surrounding rock type of the tunnel section; (2) The present invention performs advance reinforcement grouting on the tunnel surrounding rock on the surface by drilling holes, thereby improving the physical and mechanical parameters of the tunnel surrounding rock, reducing the risk of engineering geological problems during tunnel excavation, and improving the efficiency of tunnel construction, so as to achieve the purpose of non-interference between advance grouting reinforcement and tunnel construction, avoid the linear construction period occupied by advance grouting in the tunnel, and improve the working environment of workers during advance grouting reinforcement work; (3) The present invention uses directional drilling technology to ensure that the drilling trajectory of the grouting section is always in the target formation, and adopts high-pressure splitting grouting to greatly increase the effective diffusion area of ​​the slurry. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic diagram of the technical composition structure of the present invention.

[0011] Figure 2 It is a schematic diagram of the directional coring drilling structure according to an embodiment of the present invention.

[0012] Figure 3 It is a schematic diagram of the cross-sectional trajectory of directional grouting drilling in an embodiment of the present invention.

[0013] Figure 4 It is a schematic diagram of the plane trajectory of directional grouting drilling in an embodiment of the present invention.

[0014] Figure 5 It is a schematic diagram of the cross-sectional arrangement of directional grouting drilling according to an embodiment of the present invention.

[0015] Figure 6It is a schematic diagram of the directional grouting drilling structure of an embodiment of the present invention.

[0016] Among them, the surface is 1, the mountain is 2, the tunnel is 3, the hole mouth is 4, the inclined section is 5, the curved section is 6, the horizontal section is 7, the first section of the borehole is 8, the second section of the borehole is 9, the third section of the borehole is 10, the directional grouting borehole is 11, the TBM construction tunnel is 12, the hole circle diameter is 13, and the slurry diffusion radius is 14. DETAILED DESCRIPTION

[0017] Example 1: A method for pre-reinforcement of a tunnel section with poor geological conditions during TBM construction. For a tunnel section not yet excavated by the TBM, an "L"-shaped directional drill is used on the ground to review the geological conditions of the tunnel section with Class V surrounding rock, further explore the geological characteristics of the tunnel section with poor geological conditions, identify the distribution of tunnel sections with poor geological conditions at the tunnel elevation, and use directional drilling to pre-grout the tunnel section with Class V surrounding rock geological conditions during the directional drilling exploration process. The top arch of the tunnel section where the TBM is excavating and the top arch of the tunnel section with poor local surrounding rock conditions are reinforced to prevent the TBM from jamming during subsequent excavation. For a tunnel section with locally predicted strong water-rich strata, ground pre-grouting reinforcement is performed around the tunnel to achieve the purpose of controllable water gushing, thereby preventing the problem of mud and water gushing. The specific steps are as follows: S1: Prepare tunnel longitudinal profiles based on the geological exploration data from the project proposal, feasibility study, and preliminary design stages, and mark the surrounding rock types and pile numbers on the diagrams; S2: Review and confirm that the surrounding rock of Class V is the target reinforcement area and determine the grouting range; S3: Arrange directional grouting holes based on terrain, landform, traffic, and the location of the target reinforcement area, including parameters such as grouting section range, grouting hole number, hole mouth section length, vertical section length, deflection section length, horizontal grouting section length, and total borehole length; S4: Conduct drilling design based on tunnel excavation design drawings and drilling task orders; S5: Drilling equipment selection; S6: Drilling equipment installation; S7: Grouting system design and installation; S8: drilling of the hole section; S9: vertical section drilling; S10: drilling in the deflection section; S11: drilling of horizontal grouting section; S12: horizontal section open hole grouting; S13: lower the flower tube; S14: flower tube grouting; S15: Grouting effect inspection; S16: Seal the hole.

[0018] In step S1, the longitudinal section of the tunnel includes at least information such as pile number, bottom plate elevation, and surrounding rock type; In step S2, based on geological condition analysis, the surrounding rock of the section from DLI23+740 to DLI25+560 of a certain engineering fault is estimated to be Class V. A directional drilling continuous coring method based on rope coring drilling technology is used to obtain rock cores that are estimated to be Class V surrounding rock along the axis of the TBM tunneling tunnel. Based on the rock cores, full-hole wall digital imaging images, and acoustic waves, the tunnel section with Class V surrounding rock is confirmed as the target area for ground pre-reinforcement. The following steps are included: S21. Select an appropriate drilling path based on the depth and length of the tunnel axis, which is estimated to be Class V surrounding rock. The selection of hole 4 should be based on the surface 2 topography, anchors, mountain 3, and estimated Class V surrounding rock. Geological scrutiny should be used to ensure that the drilling path can reach the tunnel and pass through the section from DLI 23+740 to DLI 25+560 along the tunnel axis. S22, using a single-opening drill bit to drill an oblique section borehole 5 in a downwardly inclined direction on the road surface. During the drilling process, a rope coring mechanism configured inside the single-opening drill bit continuously breaks and removes the cores, completing the drilling and coring of the oblique section borehole; S23, after the oblique section drilling 5 is completed, the drilling tool is removed and then the casing is installed in the oblique drilled hole; S24. The secondary drilling tool is replaced. The pilot drill bit of the secondary drilling tool continues drilling after passing through the casing. During the drilling process, the pilot drill bit of the secondary drilling tool continuously changes the drilling direction under the weight of the coring drill pipe to complete the drilling of the curved section borehole 6. The rope coring mechanism configured inside the secondary drilling tool continuously breaks and removes the core. S25. Replace the three-hole drilling tool. After the pilot drill bit of the three-hole drilling tool passes through the casing, drilling continues. During the drilling process, the pilot drill bit of the three-hole drilling tool continuously changes the drilling direction under the weight of the coring drill pipe to complete the drilling of the horizontal section borehole 7. The rope coring mechanism configured inside the three-hole drilling tool continuously breaks and removes the core. S26: Complete full-hole wall digital imaging, drilling sonic wave and other tests; S27: The tunnel section with Class V surrounding rock, as confirmed by core and full-hole wall digital imaging, acoustic waves, etc., is the target area for ground pre-reinforcement (SDK23+800 to SDK25+318), and the length of the horizontal grouting section is approximately 1518m.

[0019] In step S3, the goal of the general tunnel section is to improve the integrity of the rock mass at the top arch of the tunnel, and the goal of the water-rich tunnel section is to form an effective water control curtain to achieve the purpose of controllable water inrush, providing safety for TBM excavation in the poor V-class tunnel section. The directional grouting drilling trajectory adopts "L" shape or "human" shape according to the terrain, geological conditions and environmental conditions, such as Figure 3 and Figure 4 shown.

[0020] Directional grouting drilling arrangements are carried out according to the terrain, landform, traffic, and location of the target reinforcement area, including parameters such as drilling location, grouting section range, grouting hole number, hole mouth section length, vertical section length, deflection section length, horizontal grouting section length, and total drilling length. For details, see Table 1 and Figure 5 .

[0021] Table 1 Directional grouting hole arrangement .

[0022] In step S4, drilling design includes drilling trajectory design and drilling structure design: S41: According to the location of the hole opening point and the target point, design the deflection point and deflection strength, and draw the hole body profile trajectory, such as Figure 6 As shown; S42: Design the drilling structure based on the drilling trajectory design, site and engineering geological conditions, drilling equipment, drilling methods and processes, final hole diameter, deflection tool type and method, in-hole grouting, etc. Figure 6 As shown; S43: The borehole is divided from top to bottom into the first section (including the hole section and vertical section) 8, the second section (curved section) 10, and the third section (horizontal grouting section 12). The borehole structure is divided into three levels. The oil casing is run into the following: S431: Orifice section, with a diameter of Φ311.1 mm, and a Φ244.5×8.94 mm matching casing string 9 is inserted; S432: vertical section, curved section, hole diameter Φ215.9mm, inserted into Φ177.8×8.05mm matching casing string 11; S433: Horizontal grouting section, hole diameter Φ152.4mm, Φ146×7mm+Φ127×7mm matching casing string 13 is lowered to the bottom of the hole, the horizontal section is Φ127×7mm flower pipe string 14, Φ146×7mm is lowered to 30m above the bottom of the second opening casing.

[0023] In step S5 , the drilling rig is selected as a ZJ30 or ZJ40 oil drilling rig, the mud pump specification model is: 3NB-1000, the wireless while drilling inclinometer model is: SMWD, and the grouting pump model is: 3NB-260.

[0024] Step S6 includes installation of the drilling tower and the drilling rig.

[0025] In step S7, the grouting system includes drilling equipment, a grouting pump, a grouting pipeline, a slurry preparation equipment, a slurry stopper, a water pressure test equipment, etc. The drilling equipment includes a drilling rig, a drilling tower, a mud pump, a mud purification equipment, drilling tools, downhole power drilling tools, special directional drilling tools, inclinometers, calipers, etc. The grouting pump is a power device for conveying slurry. The grouting pipeline includes a high-pressure hose, an orifice device, a mixer, a stop valve, etc. The mixer is a device used for double-liquid grouting to allow two slurries to meet and mix fully, thereby causing a physical and chemical reaction. The slurry preparation equipment is a device that prepares qualified slurry for grouting. Depending on the grouting material, there are clay cement slurry preparation equipment, single-liquid cement slurry preparation equipment, and other slurry preparation equipment. The grouting plug is a device that isolates the grouting section from the non-grouting section in the borehole during grouting to prevent the slurry from flowing to the non-grouting section or out of the hole. It mainly includes slip-type grouting plugs, hydraulic expansion grouting plugs, different-diameter grouting plugs, double-tube grouting plugs, etc.

[0026] In step S8, the length of the orifice section is based on the standard of entering the weakly weathered rock layer, the borehole diameter is Φ311.1 mm, a Φ244.5×8.94 mm casing is inserted, and cement slurry is used to fix the entire section of the casing to the orifice.

[0027] In step S9, a Φ215.9 mm hole is continuously drilled downward in the casing of the orifice section, the length of which is 20% of the distance from the orifice to the centerline of the main hole, and the drilled hole is still a vertical hole.

[0028] In step S10, a Φ215.9mm borehole is drilled downwards in the casing at the borehole mouth section, gradually increasing the borehole inclination until the drilling trajectory is parallel to the main hole axis. The borehole is then drilled to the level of the main hole's central axis. Then, a Φ177.8×8.05mm casing is lowered and cement slurry is used to secure the entire section to the borehole mouth. In step S10, a mud pulse wireless inclinometer is used to measure inclination. During drilling, the inclination, azimuth, and tool face angle of the borehole body are measured to provide timely borehole body parameters for drilling. The wireless inclinometer consists of two parts: surface equipment and in-hole measuring instruments. The surface equipment includes a pressure sensor, a host computer, a driller's display, a computer, and related connecting cables. The in-hole measuring instrument mainly consists of an inclinometer probe, a main control unit, a mud pulse generator, a battery, a centralizer, etc.

[0029] In step S11, continue to drill a Φ215.9mm hole in the casing of the orifice section, gradually increase the hole inclination until the drilling trajectory is parallel to the main hole axis, drill to the level of the main hole centerline, then insert a Φ177.8×8.05mm casing, and use cement slurry to fix the entire section of the pipe to the orifice.

[0030] In steps S11 and S12, one section is drilled and grouting is performed. When the grouting pressure and flow rate meet the technical requirements, the next section is drilled and grouting is performed to achieve segmented forward open hole grouting until all grouting sections are completed.

[0031] In step S13, after the open hole grouting section is completed, the pipe string is lowered using a pipe-swinging method. Once lowered into place, the annular space between the grouting casing and the borehole wall is filled with a filling material. The annular space filling material must meet pumping requirements, with a water separation rate below 5%, an initial setting time of 30 minutes to 1 hour, a final setting time of 6 to 10 hours, and an early strength controllable between 0.5 and 2.0 MPa.

[0032] In step S14, the area where the open hole grouting is completed is subjected to segmented high-pressure splitting and compaction grouting through the flower pipe.

[0033] In step S15, the inspection includes a borehole water pressure test, with one grouting hole selected from each drilling site as the water pressure test hole, as well as geophysical tests such as magnetotelluric testing. The water pressure test and magnetotelluric testing are performed once before and after grouting. The quality inspection of the borehole water pressure test for ground pre-grouting projects should be carried out in accordance with the "Test Method for Water Pressure Test of Ground Pre-grouting Effect in Vertical Shafts" (MT / T1057-2008).

[0034] In step S16, after the grouting effect is checked to be qualified, cement slurry is used to seal the hole.

Claims

1. A method for pre-reinforcement of the ground in a poor geological section of a TBM tunnel, characterized in that This reinforcement method targets the tunnel sections where the TBM has not yet excavated. Using ground "L"-shaped directional drilling, the geological conditions of the tunnel sections with Class V surrounding rock are reviewed to further explore the geological characteristics of the tunnel sections with poor geological conditions. The distribution of tunnel sections with poor geological conditions at the tunnel elevation is identified. Directional drilling is then used to pre-grout the tunnel sections with Class V surrounding rock identified during the directional drilling exploration process. This reinforces the top arch of the tunnel sections where the TBM has been excavated, as well as the top arch of the tunnel sections with locally poor surrounding rock conditions, to prevent the TBM from jamming during subsequent excavation. For tunnel sections with locally predicted strong water-rich strata, ground pre-grouting is performed around the tunnel to achieve controllable water inrush and prevent mud and water inrush. The specific steps are as follows: S1: Based on the geological exploration data from the project proposal, feasibility study, and preliminary design phases, and in accordance with the design drawings, a tunnel surrounding rock classification diagram is prepared. The surrounding rock classification and pile number are marked on the diagram. The evaluation parameters include the uniaxial saturated compressive strength of the rock, rock mass integrity, structural surface development, and groundwater conditions. S2: Re-check and confirm that the surrounding rock of Class V is the target reinforcement area: Directional drilling and continuous coring using rope coring technology were used to obtain cores indicating that the surrounding rock of the TBM tunnel axis was estimated to be Class V. Digital imaging of the cores and the entire borehole wall, as well as acoustic verification, confirmed that the tunnel section with Class V surrounding rock was the target area for ground pre-reinforcement. The following steps are involved: S21. Select an appropriate drilling path based on the depth and length of the tunnel axis, which is estimated to be Class V surrounding rock. The borehole selection should be based on the surface topography, mountain, and Class V surrounding rock to ensure that the drilling path reaches the tunnel and passes through the target reinforcement area along the tunnel axis. S22, using a single-open drill bit to drill an oblique section of the road surface in a downwardly inclined direction. During the drilling process, the single-open drill bit continuously breaks and removes the core along the rope coring mechanism configured inside the single-open drill bit, thereby completing the drilling and coring of the oblique section of the hole; S23. After the oblique section drilling is completed, the first drilling tool is removed, and then a casing is installed in the oblique drilled hole; S24: The secondary drilling tool is replaced. The pilot drill bit of the secondary drilling tool passes through the casing and continues drilling. During the drilling process, the pilot drill bit of the secondary drilling tool changes the drilling direction under the weight of the coring drill pipe to complete the drilling of the curved section. The rope coring mechanism configured inside the secondary drilling tool breaks and removes the core. S25. The three-hole drilling tool is replaced. The pilot drill bit of the three-hole drilling tool passes through the casing and continues drilling. During the drilling process, the pilot drill bit of the three-hole drilling tool changes the drilling direction under the weight of the coring drill pipe, completing the drilling of the horizontal section. The rope coring mechanism configured inside the three-hole drilling tool breaks and removes the core. S26: Complete the digital imaging of the entire hole wall and the drilling acoustic wave test; S27: Based on the core and full-hole wall digital imaging images and acoustic waves, the tunnel section with Class V surrounding rock was confirmed as the target area for ground pre-reinforcement; S3: Arrange directional grouting drilling holes according to the terrain, landform, traffic conditions and the location of the target reinforcement area. The parameters include grouting section range, grouting hole number, hole mouth section length, vertical section length, deflection section length, horizontal grouting section length and total drilling length. S4: Drilling design is carried out in combination with the tunnel excavation design drawing and the drilling task book. The drilling design includes drilling trajectory design and drilling structure design. The design steps are as follows: S41: Design the deflection point and deflection intensity according to the location of the drilling point and target point, and draw the hole profile trajectory; S42: Design the drilling structure based on the drilling trajectory design, site and engineering geological conditions, drilling equipment, drilling methods and processes, final hole diameter, deflection tool type and method, in-hole grouting, etc. S43: The drilling process is divided into the first, second, and third sections from top to bottom. The first section includes the orifice section and the vertical section, the second section is the curved section, and the third section is the horizontal grouting section. The orifice section has a diameter of Φ311.1mm; the vertical section and curved section have a diameter of Φ215.9mm; the horizontal grouting section has a diameter of Φ152.4mm; S5: Drilling equipment selection: Directional drilling rigs should be selected with a wide speed range, appropriate torque, and engine power. The directional drilling rig's speed, torque, and maximum feed force performance parameters should meet drilling requirements. For wireline coring, the speed should not be less than 300 r / min, the space-building torque should not be less than 3000 N·m, and the formation feed force should not be less than 60 kN. For non-coring drilling, a high-torque rig should be selected. For drilling holes with complex geological conditions and borehole structures, a rig with high drilling depth capability, high torque, high maximum feed force, and strong adaptability to drilling processes should be selected. S6: Drilling equipment installation: Including the installation of the drilling tower and the installation of the drilling rig, the steps are as follows: S61: Drilling tower installation: (1) The steel beams of the drilling rig chassis are firmly spliced ​​to ensure that the chassis is flat and stable as a whole; (2) The drilling tower bolts are complete and tightened; (3) According to the actual situation of the drilling site, set up a guy rope, set a rope tightener on the guy rope, and fix it with a ground anchor or anchor pile. The burial depth should be greater than 1.5m; (4) Install a lightning rod on the top of the drilling tower and do grounding work; S62: Drilling rig installation: (1) The drilling rig is installed on the chassis with bolts, and the bolts and gaskets are complete and tightened; (3) The drilling rig is installed horizontally, with the turntable center, the overhead crane center and the drilling center forming a vertical line and tightening the nuts; S7: Grouting system design and installation: The grouting system includes drilling equipment, grouting pumps, grouting pipelines, slurry preparation equipment, slurry stoppers and water pressure testing equipment, among which: Drilling equipment includes drilling rigs, drilling towers, mud pumps, mud purification equipment, drilling tools, downhole power drilling tools, directional drilling tools, inclinometers and directional instruments, and calipers; The grouting pump is a power device for conveying slurry; The grouting pipeline includes a high-pressure hose, an orifice device, a mixer, and a shut-off valve; The mixer is used for double-liquid grouting to fully mix the two slurries after they meet; Slurry preparation equipment is used to prepare qualified slurry for grouting. The corresponding preparation equipment is selected according to the grouting material, including clay cement slurry preparation equipment or single liquid cement slurry preparation equipment; Grout plugs are devices used to isolate the grouting section from the non-grouting section in the borehole during grouting, preventing the slurry from flowing to the non-grouting section or out of the hole. They include slip-type grout plugs, hydraulic expansion grout plugs, reducing grout plugs, and double-tube grout plugs. S8: Drilling of the hole section: The length of the borehole section is based on the standard of entering the weakly weathered rock layer. The borehole diameter is Φ311.1mm. A Φ244.5×8.94mm casing is inserted and cement slurry is used to fix the casing to the borehole. S9: Vertical drilling: Continue drilling a Φ215.9mm hole downward in the casing of the orifice section, the length of which is 20% of the distance from the orifice to the centerline of the main tunnel. The hole is a vertical hole. S10: Drilling in the deflection section: Continue drilling a Φ215.9mm hole in the casing at the orifice section, gradually increasing the hole inclination until the drilling trajectory is parallel to the main hole axis, drilling to the level of the main hole centerline, then insert a Φ177.8×8.05mm casing, and use cement slurry to fix the entire section of the casing to the orifice; A mud pulse wireless inclinometer is used for inclination measurement. The inclination, azimuth and tool face angle of the hole body are measured during drilling, providing hole body parameters in a timely manner for drilling. The wireless inclinometer while drilling consists of two parts: surface equipment and in-hole measuring instruments. The surface equipment includes pressure sensors, host computer, driller display, computer and related connecting cables; the in-hole measuring instrument consists of inclinometer probe, main control, mud pulse generator, battery and centralizer. S11: Drilling the horizontal grouting section: Continue drilling a Φ215.9mm hole in the orifice casing, gradually increasing the hole inclination until the drilling trajectory is parallel to the main hole axis. Drill to the level of the main hole centerline, then insert a Φ177.8×8.05mm casing and secure the entire section to the orifice with cement slurry. S12: horizontal section open hole grouting; S13: Lower the flower tube:; In S12 and S13, one section is drilled and grouting is carried out. When the grouting pressure and flow rate meet the technical requirements, the next section is drilled and grouting is started, realizing segmented forward open hole grouting until all grouting sections are completed. After the grouting construction of the open hole grouting section is completed, the flower pipe string is lowered by the pipe throwing method. After it is lowered into place, the annular space between the grouting casing and the borehole wall is filled with filling materials; The annular space filling material must meet the pumping requirements, with a water separation rate of less than 5%, an initial setting time of 30 minutes to 1 hour, a final setting time of 6 to 10 hours, and an initial strength controlled at 0.5-2.0 MPa; S14: Flower tube grouting: The area where the open hole grouting is completed is subjected to segmented high-pressure splitting and compaction grouting through the flower pipe, with the splitting pressure exceeding 3MPa; S15: Grouting effect inspection: For the borehole water pressure test, one grouting hole is selected at each drilling site as a water pressure test hole, and magnetotelluric detection is used. The water pressure test and magnetotelluric detection are carried out once before and after grouting. S16: Sealing: After the grouting effect is checked and qualified, cement slurry is used to seal the hole.

2. The method for pre-reinforcement of the ground in a poor geological section of a TBM tunnel as claimed in claim 1, characterized in that In step S3, the goal is to improve the rock integrity of the tunnel crown in general tunnel sections, and to form an effective water control curtain in water-rich tunnel sections to achieve controllable water inrush, thereby providing safety for TBM excavation in unfavorable Class V tunnel sections. The directional grouting drilling trajectory adopts an "L" shape or a "human" shape according to the topographical, geological, and environmental conditions.

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