Directional grouting method for drilling

Abstract

The application discloses a drilling directional grouting method and a small-section tunnel advanced grouting excavation method, and a small-section tunnel advanced supporting structure, and relates to the field of tunnel engineering, and solves the problem that an existing directional grouting scheme cannot effectively control the diffusion direction of slurry. The drilling directional grouting method is characterized in that: after drilling construction is completed, a supporting plate is inserted into the drilling, the supporting plate divides the drilling into a first grouting area and a second grouting area, then mortar is poured into the first grouting area, the pores and cracks of the rock-soil body on the grouting side are closed and controlled, finally, a small guide pipe is inserted into the second grouting area of the drilling and grouting is performed, since the cracks of the rock-soil body on the grouting side have been closed, most of the slurry can only diffuse to the rock-soil body on the directional grouting side, so that directional grouting is realized. The small-section tunnel advanced grouting excavation method adopts the drilling directional grouting method. The application is used for directional grouting of drilling and advanced grouting excavation of small-section tunnels.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering, specifically to a borehole directional grouting method, a method for advanced grouting excavation of small-section tunnels, and an advanced support structure for small-section tunnels. Background Technology

[0002] Currently, the excavation and construction of small-section tunnels in weak and fractured sections with groundwater mainly adopts the advanced small-pipe grouting method. By grouting through advanced small pipes, the rock and soil mass after advanced drainage is pre-consolidated, forming an arched shell above the excavation section, which enhances the ability to resist the load at the top of the tunnel.

[0003] Conventional pre-grouting with small guide pipes has shortcomings. In weak, fractured tunnel sections with groundwater, the soil and rock contain numerous pores. During small guide pipe grouting, the grout more easily penetrates into the soil and rock within the excavation area, consolidating and hardening it. However, the actual grouting volume outside the excavation area is insufficient, resulting in grout waste and increased excavation difficulty and construction risks. Furthermore, the borehole diameter of the small guide pipes is typically no more than 50mm, matching the outer diameter of the grouting pipe, leading to a large number of boreholes and slow construction speed. To save costs, the borehole spacing of the small guide pipes is generally controlled between 20 and 50cm. Larger spacing makes it difficult for the soil and rock between adjacent small guide pipes to effectively consolidate and harden, causing loose soil and rock to fall, posing safety hazards and even the risk of collapse.

[0004] Patent CN 112538850 A discloses a device and method for pre-grouting of underground utility tunnels to protect trees. This method solves the problem of protecting trees during the construction of underground utility tunnels through directional grouting. The device includes a directional grouting pipe with a grouting directional plate on it. The directional grouting plate is located on the longitudinal outer wall of one side of the grouting pipe. A grout outlet is located on the grouting pipe inside the directional grouting plate. The width of the directional grouting plate is greater than or equal to the diameter of the grouting pipe, and the length of the directional grouting plate is greater than or equal to the designed length that restricts the diffusion of grout from the outlet to the structure on one side of the grouting pipe. Directional grouting pipes use grouting directional plates to block the diffusion direction of grouting fluid. However, since there are unavoidable gaps between the borehole wall and the grouting directional plate, as well as gaps in the rock and soil of the borehole wall, and since grouting is completed in one go, the grouting directional plate has a very weak blocking effect on the diffusion of grouting fluid. It can only block the upward diffusion of grouting fluid when the grouting pressure is low enough, and cannot be used to block the downward diffusion of grouting fluid. Summary of the Invention

[0005] This invention first provides a borehole directional grouting method to solve the problem that existing directional grouting schemes cannot effectively control the direction of grout diffusion.

[0006] The technical solution adopted in this invention is: a borehole directional grouting method, comprising the following steps:

[0007] S1. After drilling is completed, insert the support plate into the borehole. The front end of the support plate is inserted to the bottom of the borehole or deeper than the bottom of the borehole. The two sides of the borehole are the control grouting side and the directional grouting side, respectively. The support plate has an M-shaped cross-section with a single groove on one side and a double groove on the other side. The support plate divides the borehole into a first grouting area on the control grouting side and a second grouting area on the directional grouting side. The first grouting area is the side corresponding to the double groove of the support plate, and the second grouting area is the side corresponding to the single groove of the support plate.

[0008] To facilitate the insertion of the support plate into the borehole, a further feature is provided: a triangular tip is provided at the front end of the support plate, and the front end of the support plate is inserted into the rock and soil at the bottom of the borehole.

[0009] To prevent the first and second grouting zones from connecting with each other, the width of the support plate is greater than or equal to the diameter of the borehole.

[0010] S2. Prepare mortar and inject it into the first grouting zone of the borehole through the grouting pipe. After the mortar injection is completed, seal the opening of the first grouting zone.

[0011] To further accelerate the setting speed of mortar, an accelerator is added during mortar preparation.

[0012] S3. Insert a small guide pipe into the second grouting zone of the borehole, prepare grout, and grout through the small guide pipe; wherein, the pipe wall of the front section of the small guide pipe is provided with grouting holes, and the rear section of the small guide pipe is provided with a grout stopping section.

[0013] To facilitate the insertion of the small guide tube into the borehole, the tip of the small guide tube is further shaped into a pointed cone.

[0014] To prevent the small guide pipe from slipping out of the borehole during construction, the small guide pipe is further positioned in the groove on the side of the single groove of the support plate, and the rear end of the small guide pipe is fixed to the rock and soil at the borehole opening by anchors.

[0015] Small guide pipes are typically installed by driving or jacking them in. To prevent damage to the rear end of the guide pipe and to facilitate grouting, a stiffening hoop is installed at the rear end of the guide pipe.

[0016] To ensure the grouting quality of the second grouting zone, the following steps are taken: after inserting the small guide pipe, the hole in the second grouting zone is cleaned before grouting is performed.

[0017] Specifically: the small guide tube is made of hot-rolled seamless steel pipe with a wall thickness of 3.5mm and an outer diameter of 42mm. The diameter of the grouting hole is φ8mm. The spacing between the grouting holes is 20cm and they are arranged in a quincunx pattern. The length of the grout-stopping section of the small guide tube is not less than 30cm.

[0018] The beneficial effects of the directional grouting method of the present invention are as follows: the support plate divides the borehole into a first grouting zone and a second grouting zone. First, mortar is injected into the first grouting zone to seal the pores and fissures of the rock and soil on the grouting side. Then, grout is injected into the second grouting zone through a small guide pipe. Since the fissures and fissures of the rock and soil on the grouting side have been sealed, most of the grout can only diffuse into the rock and soil on the directional grouting side, thereby effectively realizing directional grouting.

[0019] This invention also provides a method for advanced grouting excavation of small-section tunnels, solving the problem that existing advanced small-diameter pipe grouting methods cause consolidation and hardening of the soil and rock within the excavation area, which wastes grout and increases excavation difficulty and construction risk. The technical solution adopted is: a method for advanced grouting excavation of small-section tunnels, including the following steps:

[0020] A. Draw the excavation outline on the tunnel face. Mark the drilling positions outside the arching line and along the direction of the arching line, and drill holes in an upward direction. For example, the spacing between adjacent holes should be 30-40 cm, and the elevation angle of each hole should not exceed 5°.

[0021] B. Following step S1 of the above-mentioned directional grouting method, insert a support plate into each borehole. The plane corresponding to the support plate is perpendicular to the radial direction of the arching line. The first grouting zone is located on the side of the tunnel that needs to be excavated, and the second grouting zone is located on the side of the tunnel that needs to be excavated.

[0022] C. Following step S2 of the above-mentioned directional grouting method for boreholes, mortar is injected into the first grouting zone of each borehole.

[0023] D. Following step S3 of the above-mentioned borehole directional grouting method, insert small guide pipes into the second grouting zone of each borehole and grout them separately to form an arched consolidation shell.

[0024] After inserting small guide pipes into each borehole, in order to prevent the small guide pipes from slipping out of the borehole, the following steps are taken: after the small guide pipes are inserted into the second grouting zone of the borehole, the rear ends of each small guide pipe are connected into a whole by connecting bars, and the connecting bars are fixed to the rock and soil mass using soil nails, and then grouting is performed separately.

[0025] E. Excavation, muck removal, and support of the tunnel.

[0026] The present invention also provides a small-section tunnel pre-support structure, which is a structure obtained by construction according to steps A to D of the above-mentioned small-section tunnel pre-grouting excavation method. The pre-support structure for small-section tunnels features boreholes spaced along the outer side of the tunnel's arching line. The centerline of each borehole points upwards at an angle, and a support plate is inserted within each borehole. The front end of the support plate is located at the bottom of the borehole or deeper than the bottom. The support plate has an M-shaped cross-section with a single groove on one side and a double groove on the other. The plane corresponding to the support plate is perpendicular to the radial direction of the arching line. The support plate divides the borehole into a first grouting zone and a second grouting zone. The first grouting zone is located on the side of the support plate corresponding to the double groove and is filled with mortar, closer to the tunnel and requiring excavation. The second grouting zone is located on the side away from the tunnel and requiring excavation. A small guide pipe is inserted into the second grouting zone. Grouting holes are set in the pipe wall at the front end of the small guide pipe, and a grout-stopping section is set at the rear end of the small guide pipe. The second grouting zone is located on the side of the support plate corresponding to the single groove and is filled with grout. The solidified and hardened mortar, grout, and the surrounding soil and rock mass, along with the support plate and small guide pipe, together form an integral arched solidified shell.

[0027] To facilitate the insertion of the tray into the borehole, a further feature is provided: a triangular tip is provided at the front end of the tray, and the front end of the tray is located in the rock and soil at the bottom of the borehole.

[0028] When injecting mortar into the first grouting zone, in order to reduce or avoid mortar from entering the second grouting zone from the first grouting zone, the width of the support plate is greater than or equal to the diameter of the borehole.

[0029] To facilitate the insertion of the small guide tube into the borehole, the tip of the small guide tube is tapered, and the small guide tube is located in the groove on the side of the single groove of the support plate.

[0030] To prevent the guide pipes from slipping out of the borehole during construction, the rear ends of the guide pipes are further secured to the soil and rock mass at the borehole opening using anchors. Specifically, the rear ends of each guide pipe are connected into a single unit by connecting bars, which are then secured to the soil and rock mass by at least one soil nail.

[0031] Small guide pipes are typically installed by driving or jacking them in. To prevent damage to the rear end of the guide pipe and to facilitate grouting, a stiffening hoop is installed at the rear end of the guide pipe.

[0032] To further optimize the stress distribution between the small catheter and the support plate, the front end of the small catheter and the front end of the support plate are aligned.

[0033] Specifically: the small guide tube is made of hot-rolled seamless steel pipe with a wall thickness of 3.5mm and an outer diameter of 42mm. The diameter of the grouting hole is φ8mm. The spacing between the grouting holes is 20cm and they are arranged in a quincunx pattern. The length of the grout-stopping section of the small guide tube is not less than 30cm.

[0034] Specifically: the spacing between adjacent boreholes is 30-40cm, and the borehole elevation angle is no greater than 5°.

[0035] The beneficial effects of the pre-grouting excavation method and pre-support structure for small-section tunnels of the present invention are as follows: by first injecting mortar into the first grouting zone to seal the borehole and control the pores and cracks of the rock and soil on the grouting side, the grout can be diffused as much as possible into the rock and soil outside the tunnel excavation range when grouting is performed through a small pipe. This not only saves the amount of grouting but also facilitates the excavation operation of the rock and soil.

[0036] The consolidated and hardened mortar, grout, and surrounding soil and rock mass, along with the support plate and small guide pipe, together form an integral arched consolidated shell. The arched consolidated shell has high strength and can provide stable support for the soil and rock mass above the tunnel during excavation, preventing collapse accidents during excavation and reducing safety risks during construction. The soil and rock mass below the arched consolidated shell has little or no grouting or mortar, which reduces the difficulty of excavation. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the small-section tunnel advance support structure of the present invention.

[0038] Figure 2 yes Figure 1 A magnified view of the highest borehole in the center.

[0039] Attached diagram labels: 1. Drill hole; 2. Support plate; 3. First grouting zone; 4. Second grouting zone; 5. Small guide pipe. Detailed Implementation

[0040] The invention will now be further described with reference to the accompanying drawings.

[0041] The first subject of this invention is a borehole directional grouting method. See also Figure 2 The borehole directional grouting method includes the following steps S1 to S3.

[0042] S1. After drilling hole 1 is completed, insert the support plate 2 into borehole 1, with the front end of the support plate 2 inserted to the bottom of the borehole or deeper than the bottom. The two sides of borehole 1 are the control grouting side and the directional grouting side, respectively. The control grouting side is the side of borehole 1 that requires no or only a small amount of grouting, while the directional grouting side is the side of borehole 1 that requires grouting. The central angle corresponding to the control grouting side is generally equal to, but may not be equal to, the sum of which is 360°. The support plate 2 has an M-shaped cross-section, meaning that one side of the support plate 2 has a single groove, and the other side has a double groove structure, such as... Figure 2As shown. In other words, the support plate 2 has a double-hump shape in its cross-section, with a groove between the humps. The support plate 2 preferably has rounded corners at the corresponding angles of the grooves. The support plate 2 is used to divide the borehole 1 along its depth direction, therefore it is strip-shaped. To ensure the strength of the support plate 2, it is made of metal, such as steel. The support plate 2 divides the borehole 1 into a first grouting zone 3 and a second grouting zone 4. The first grouting zone 3 is marked as the side corresponding to the double groove of the support plate 2, and the second grouting zone 4 is the side corresponding to the single groove of the support plate 2. The orientation of the support plate 2 is very important. It must ensure that the first grouting zone 3 corresponds to the control grouting side of the borehole, that is, the side of the borehole that does not require or only requires a small amount of grouting, and the second grouting zone 4 corresponds to the directional grouting side of the borehole.

[0043] The support plate 2 can be inserted into the borehole 1 by hammering or pressing. To facilitate insertion, a triangular tip is provided at the front end of the support plate 2. The insertion of the front end of the support plate 2 into the soil and rock mass at the bottom of the borehole 1 not only completely separates the first grouting zone 3 and the second grouting zone 4, but also secures the support plate 2, preventing it from slipping out of the borehole 1. To prevent the triangular tip of the support plate 2 from causing communication between the first grouting zone 3 and the second grouting zone 4, the front end of the support plate 2 is inserted into the soil and rock mass at the bottom of the borehole 1.

[0044] S2. Prepare the mortar and inject it into the first grouting zone 3 of borehole 1 through the grouting pipe. After the mortar is injected, seal the opening of the first grouting zone 3. The mortar is used to seal the side of borehole 1 that does not require or only requires a small amount of grouting; therefore, the mortar is a dense cement mortar. To accelerate the setting speed of the mortar, a quick-setting agent can be added when preparing the mortar. The grouting pipe should be inserted into the bottom of the hole first, and then slowly and evenly pulled out as the mortar is injected. The mortar should be thoroughly mixed and used immediately after mixing. The mortar mix ratio should conform to the design. The mortar in the first grouting zone 3 should be dense and full. After the mortar is injected, seal the opening of the first grouting zone 3 with a sealing material to prevent mortar leakage.

[0045] If the first grouting zone 3 and the second grouting zone 4 are interconnected, grout will enter the second grouting zone 4 during step S2, affecting the subsequent grouting in step S3 and even the insertion of the small guide pipe 5. To avoid interconnection between the first grouting zone 3 and the second grouting zone 4, and to minimize or avoid grout entering the second grouting zone 4 during grouting of the first grouting zone 3, the width of the support plate 2 is equal to or greater than the diameter of the borehole 1.

[0046] S3. Insert the small guide tube 5 into the second grouting zone 4 of borehole 1, prepare the grout, and grout through the small guide tube 5.

[0047] The front section of the small guide pipe 5 is provided with grouting holes, and the rear section of the small guide pipe 5 is provided with a grout-stopping section. For example, the small guide pipe 5 is made of hot-rolled seamless steel pipe with a wall thickness of 3.5mm and an outer diameter of 42mm. The diameter of the grouting holes is φ8mm, the spacing between the grouting holes is 20cm and they are arranged in a quincunx pattern, and the length of the grout-stopping section of the small guide pipe 5 is not less than 30cm.

[0048] The small guide pipe 5 is used for grouting, so its length only needs to be sufficient to allow insertion into the second grouting zone 4. To ensure the grouting quality of the second grouting zone 4, after inserting the small guide pipe 5, the second grouting zone 4 is first cleaned before grouting. For example, after inserting the small guide pipe 5, high-pressure air is used to blow away the sand and gravel in the second grouting zone 4, and the hole opening and surrounding cracks are sealed with plastic materials such as hemp fiber or anchoring agent.

[0049] To improve grouting quality, the front end of the small guide pipe 5 should preferably be inserted to the bottom of the borehole 1 or deeper than the bottom of the borehole, for example, the front end of the small guide pipe 5 should overlap with the front end of the support plate 2. To facilitate fixing the small guide pipe 5 and to improve the integrity of the small guide pipe 5 and the support plate 2, the rear end of the small guide pipe 5 is fixedly connected to the rear end of the support.

[0050] To facilitate the insertion of the small guide pipe 5 into the borehole 1, the front end of the small guide pipe 5 is tapered. The small guide pipe 5 is generally inserted into the borehole 1 by driving or pushing. In order to avoid damage to the rear end of the small guide pipe 5 and to facilitate grouting, a stiffening hoop is provided at the rear end of the small guide pipe 5, for example, a stiffening hoop of φ6.5mm is welded to the rear end of the small guide pipe 5.

[0051] The small guide pipe 5 is located in the second grouting zone 4 of the borehole, preferably within the groove on the side of the single groove of the support plate 2. This allows the outer diameter of the small guide pipe 5 to be as large as possible, and the squeezing action between the support plate 2 and the borehole wall also helps to fix the small guide pipe 5 in place. In addition, to prevent the small guide pipe 5 from slipping out of the borehole 1 during construction, the rear end of the small guide pipe 5 can also be fixed to the rock and soil at the borehole opening of the borehole 1 by anchors, such as soil nails.

[0052] The second subject of this invention is a method for pre-grouting excavation of small-section tunnels. See also... Figure 1 The method for pre-grouting excavation of small-section tunnels includes the following steps A to E.

[0053] A. Draw the excavation outline on the tunnel face. Mark the drilling positions outside the arching line and along its direction, and drill holes at an upward angle. Drilling positions can be in one or two layers. The elevation angles of each layer of boreholes 1 can be equal or unequal. Boreholes 1 are located outside the tunnel excavation area and extend longitudinally into the tunnel. For example, using a Φ150mm drill bit, the spacing between adjacent boreholes 1 is 30-40cm, and the elevation angle of borehole 1 is no greater than 5°. An elevation angle of borehole 1 no greater than 5° means the angle between borehole 1 and the horizontal plane is no greater than 5°. Borehole 1 should be drilled strictly according to the designated drilling position to ensure accuracy. During drilling, observe the drill rod direction and insertion angle regularly. Adjustments should be made if significant deviations are found.

[0054] B. Following step S1 of the above-described directional grouting method, insert a support plate 2 into each borehole 1. The plane corresponding to the support plate 2 is perpendicular to the radial direction of the arching line. The first grouting zone 3 is located on the side of the tunnel that needs to be excavated, and the second grouting zone 4 is located on the side opposite to the tunnel that needs to be excavated. The plane corresponding to the support plate 2 refers to the plane corresponding to the centerline of the two sides of the support plate 2 that are in direct contact with the tunnel.

[0055] C. Following step S2 of the above-described directional grouting method, mortar is injected into the first grouting zone 3 of each borehole 1. The mortar seeps into the soil and rock mass on the side of the borehole 1 closest to the tunnel that needs to be excavated, and the first grouting zone 3 is completely filled with mortar.

[0056] D. Following step S3 of the above-mentioned borehole directional grouting method, insert small guide tubes 5 into the second grouting zone 4 of each borehole 1 and grout them respectively to form an arched consolidation shell.

[0057] Grouting equipment with good performance and working pressure meeting grouting requirements should be selected, and on-site test runs should be conducted. The maximum pressure at the borehole orifice during grouting should be strictly controlled within the allowable range. Even if single-pipe grouting can diffuse into the soil and rock mass within a radius of 0.5–1.0 m around borehole 1, the grouting pressure is generally 0.5–1.0 MPa to avoid fracturing the excavation face. Care should be taken to control the grouting volume; grouting should stop when the specified injection volume is reached for each small guide pipe 5. Grouting should also be stopped if the borehole orifice pressure has reached the specified pressure value but the injection volume is still insufficient.

[0058] To prevent the small guide pipes 5 from slipping out of the borehole 1 during construction, after the small guide pipes 5 are inserted into the second grouting zone 4 of the borehole 1, the rear ends of each small guide pipe 5 are connected into a whole by connecting bars, and the connecting bars are fixed to the soil and rock mass using soil nails before grouting. For example, φ14mm steel bars are used as connecting bars, and soil nails are set in the middle of two adjacent small guide pipes 5.

[0059] E. Excavation, muck removal, and support of the tunnel.

[0060] After the grout has solidified and reached its predetermined strength, excavation of the soil and rock mass begins. Excavation should employ a "weak blasting, short advance" method, with mechanical excavation used when necessary. After excavation, muck removal is carried out. Following muck removal, anchor bolts are installed inside the tunnel, steel mesh is hung, and shotcrete is applied. The shotcrete thickness is generally 8-10 cm to form a protective layer. If, after multiple excavations, the reinforced area no longer meets the requirements for continued excavation, the above steps are repeated.

[0061] The third main component of this invention is a small-section tunnel pre-support structure, which is a structure constructed according to steps A to D of the small-section tunnel pre-grouting excavation method described in the second main component above. For example... Figure 1 and Figure 2 As shown, in the advanced support structure of the small-section tunnel, boreholes 1 are provided at intervals on the outer side of the tunnel's arching line and along the direction of the arching line. The centerline of borehole 1 is oriented obliquely upward. For example, the spacing between adjacent boreholes 1 is 30-40 cm, and the elevation angle of borehole 1 is no greater than 5°.

[0062] A support plate 2 is inserted into borehole 1. The support plate 2 has an M-shaped cross-section, with one side having a single groove and the other side having a double groove. The support plate 2 divides borehole 1 into a first grouting zone 3 and a second grouting zone 4. The first grouting zone 3 is located on the side of the support plate 2 corresponding to the double groove, closer to the tunnel and requiring excavation. The second grouting zone 4 is located on the side of the support plate 2 opposite to the tunnel and requiring excavation, corresponding to the side of the support plate 2 with the single groove. According to... Figure 2 As shown, the first grouting zone 3 is the lower side of borehole 1, and the second grouting zone 4 is the upper side of borehole 1.

[0063] The front end of the support plate 2 is located at the bottom of borehole 1 or deeper than the bottom of the borehole to prevent the first grouting zone 3 and the second grouting zone 4 at the bottom of borehole 1 from communicating with each other. The width of the support plate 2 is greater than or equal to the diameter of borehole 1 to ensure that the support plate 2 can completely isolate the first grouting zone 3 and the second grouting zone 4. To facilitate the insertion of the support plate 2 into borehole 1, the front end of the support plate 2 is provided with a triangular tip, and the front end of the support plate 2 is located in the rock and soil mass at the bottom of borehole 1. When the width of the support plate 2 is greater than the diameter of borehole 1, both sides of the support plate 2 are partially squeezed into the rock and soil mass of borehole 1.

[0064] like Figure 1 As shown, the plane corresponding to the support plate 2 is perpendicular to the radial direction of the arching line. The first grouting zone 3 is located on the side of the tunnel that needs to be excavated and is filled with mortar. The support plate 2 and the borehole wall of the borehole 1 surround the first grouting zone 3, and the borehole wall corresponding to the first grouting zone 3 is rock and soil filled with mortar. The second grouting zone 4 of the borehole 1 has a small guide pipe 5 inserted. The small guide pipe 5 and the space between the small guide pipe 5 and the borehole wall are filled with solidified grout. The solidified and hardened mortar, grout, and the rock and soil surrounding the borehole 1, as well as the support plate 2 and the small guide pipe 5, together form an integral arched solidified shell.

[0065] The front section of the small guide pipe 5 has grouting holes, and the rear section has a grout-stopping section. For example, the small guide pipe 5 is made of hot-rolled seamless steel pipe with a wall thickness of 3.5mm and an outer diameter of 42mm. The grouting holes have a diameter of φ8mm, a spacing of 20cm, and are arranged in a staggered pattern. The length of the grout-stopping section of the small guide pipe 5 is not less than 30cm. The small guide pipe 5 is preferably located in the groove on the side of the single groove of the support plate 2. Figure 2 and Figure 1 As shown. The small guide pipe 5 is typically installed by driving or jacking. To prevent damage to the rear end of the small guide pipe 5 and to facilitate grouting, a stiffening hoop is installed at the rear end of the small guide pipe 5, for example, a φ6.5mm stiffening hoop is welded to the rear end of the small guide pipe 5. To optimize the stress distribution between the small guide pipe 5 and the support plate 2, allowing them to share the load, the front end of the small guide pipe 5 coincides with the front end of the support plate 2. Ideally, the small guide pipe 5 and the support plate 2 should be of equal length, and the front and rear ends of the small guide pipe 5 should correspond to the front and rear ends of the support plate 2, respectively. The rear end of the small guide pipe 5 is fixed to the rear end of the support plate 2.

Claims

1. A borehole directional grouting method, characterized in that: Includes the following steps: S1. After the drilling (1) is completed, insert the support plate (2) into the drilling (1). The front end of the support plate (2) is inserted to the bottom of the drilling (1) or deeper than the bottom of the hole. The two sides of the drilling (1) are the control grouting side and the directional grouting side, respectively. The support plate (2) has an M-shaped cross-section with a single groove on one side and a double groove on the other side. The support plate (2) divides the drilling (1) into a first grouting area (3) located on the control grouting side and a second grouting area (4) located on the directional grouting side. The first grouting area (3) is the side corresponding to the double groove of the support plate (2), and the second grouting area (4) is the side corresponding to the single groove of the support plate (2). S2. Prepare mortar and inject it into the first grouting area (3) of the borehole (1) through the grouting pipe. After the mortar is injected, seal the opening of the first grouting area (3). S3. Insert a small guide tube (5) into the second grouting zone (4) of the borehole (1), prepare grout and grout through the small guide tube (5); wherein, the pipe wall of the front section of the small guide tube (5) is provided with grouting holes and the rear section of the small guide tube (5) is provided with grout stopping section.

2. The borehole directional grouting method as described in claim 1, characterized in that: In S1, the front end of the support plate (2) is provided with a triangular tip, and the front end of the support plate (2) is inserted into the rock and soil body at the bottom of the borehole (1).

3. The borehole directional grouting method as described in claim 1, characterized in that: In S2, a quick-setting agent is added when preparing the mortar.

4. The borehole directional grouting method as described in claim 1, characterized in that: In S3, the front end of the small guide tube (5) is conical. The small guide tube (5) is made of hot-rolled seamless steel pipe with a wall thickness of 3.5mm and an outer diameter of 42mm. The diameter of the grouting hole is φ8mm. The spacing between the grouting holes is 20cm and arranged in a plum blossom pattern. The length of the grout-stopping section of the small guide tube (5) is not less than 30cm.

5. The borehole directional grouting method according to any one of claims 1 to 4, characterized in that: In S3, the small guide tube (5) is located in the groove on the side of the single groove of the support plate (2), and the rear end of the small guide tube (5) is fixed to the rock and soil at the borehole opening (1) by the anchor.

6. The borehole directional grouting method according to any one of claims 1 to 4, characterized in that: In S3, a stiffening hoop is provided at the rear end of the small guide tube (5), and the width of the support plate (2) is greater than or equal to the diameter of the borehole (1).

7. The borehole directional grouting method according to any one of claims 1 to 4, characterized in that: In S3, after inserting the small guide tube (5), the second grouting zone (4) is first cleaned, and then grouting is performed.

8. A method for pre-grouting excavation of small-section tunnels, characterized in that: Includes the following steps: A. Draw the excavation outline on the tunnel face, mark the drilling positions outside the arching line and along the direction of the arching line, and drill holes in the direction of the drilling diagonally upward. B. In step S1 of the borehole directional grouting method according to any one of claims 1 to 7, a support plate (2) is inserted into each borehole (1), and the plane corresponding to the support plate (2) is perpendicular to the radial direction of the arching line. Furthermore, the first grouting zone (3) is located on the side close to the tunnel that needs to be excavated, and the second grouting zone (4) is located on the side away from the tunnel that needs to be excavated; C. In step S2 of the borehole directional grouting method according to any one of claims 1 to 7, mortar is injected into the first grouting zone (3) of each borehole (1); D. In step S3 of the borehole directional grouting method according to any one of claims 1 to 7, small guide tubes (5) are inserted into the second grouting zone (4) of each borehole (1) and grout is injected respectively to form an arched solidified shell; E. Excavation, muck removal, and support of the tunnel.

9. The method for advance grouting excavation of small-section tunnels as described in claim 8, characterized in that: In step A, the distance between adjacent boreholes (1) is 30-40cm, and the elevation angle of each borehole (1) is no greater than 5°.

10. The method for pre-grouting excavation of small-section tunnels as described in claim 8 or 9, characterized in that: In step D, after the small guide tube (5) is inserted into the second grouting zone (4) of the borehole (1), the rear ends of each small guide tube (5) are connected into a whole by connecting bars, and the connecting bars are fixed to the rock and soil body by soil nails, and then grouting is performed separately.

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