Drilling directional grouting method and advance grouting excavation method for small cross-section tunnels

Abstract

This invention discloses a borehole directional grouting method and a method for advanced grouting excavation of small-section tunnels, as well as an advanced support structure for small-section tunnels, relating to the field of tunnel engineering. It solves the problem that existing directional grouting schemes cannot effectively control the direction of grout diffusion. The technical solution adopted in this invention is as follows: In the borehole directional grouting method, after drilling is completed, a partition plate with a small guide tube fixed to its surface is inserted into the borehole. The partition plate divides the area between the outer wall of the small guide tube and the borehole wall into a first grouting zone and a second grouting zone. Mortar is injected into the first grouting zone of the borehole to seal and control the pores and fissures of the soil and rock mass on the grouting side. Grout is then injected into the second grouting zone through the small guide tube to achieve directional grouting. The method for advanced grouting excavation of small-section tunnels adopts the above-mentioned borehole directional grouting method. This invention is used for directional grouting of boreholes 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, a partition plate with a small guide tube fixed to its surface is inserted into the borehole. The front end of the partition plate is inserted to the bottom of the borehole or deeper than the bottom. The two sides of the borehole are the control grouting side and the directional grouting side, respectively. The partition plate divides the area between the outer wall of the small guide tube and the borehole wall into a first grouting zone on the control grouting side and a second grouting zone on the directional grouting side. Grouting holes are provided in the wall of the front section of the small guide tube, and the rear section is the grout-stopping section.

[0008] To facilitate the insertion of the small guide pipe and the diaphragm into the borehole, the diaphragm is further provided with a triangular tip at the front end, the small guide pipe is provided with a pointed cone at the front end, and the front end of the diaphragm is inserted into the rock and soil at the bottom of the borehole.

[0009] To prevent the first and second grouting zones from connecting, further measures are taken: the width of the partition is greater than or equal to the diameter of the borehole, and the outer diameter of the small guide tube is not greater than the radius of the borehole; or, the width of the partition is less than the diameter of the borehole, the small guide tube is fixed at the centerline of the partition, and on the cross-section of the small guide tube, the diameter of the circumscribed circle corresponding to the two ends of the partition and the point of the small guide tube farthest from the partition is consistent with the diameter of the borehole.

[0010] To further improve the stability between the small guide tube and the partition, the partition is made of a strip steel plate, and an arc groove is provided on one side of the partition. The diameter of the arc groove is adapted to the outer diameter of the small guide tube, and the small guide tube is welded and fixed in the arc groove of the partition.

[0011] To optimize the stress distribution between the small conduit and the septum, the length of the small conduit is greater than the length of the septum, and the rear end of the small conduit coincides with the rear end of the septum. For example, the small conduit is welded and fixed to the centerline of the septum, and the small conduit is 20cm longer than the septum.

[0012] The small guide pipe and the partition plate are generally installed as a whole by driving or jacking. To prevent damage to the rear end of the small guide pipe during construction and to facilitate grouting, a stiffening hoop is installed at the rear end of the small guide pipe. For example, the small guide pipe 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 hole spacing of 20cm, and are arranged in a quincunx pattern. The length of the grout-stopping section of the small guide pipe is not less than 30cm.

[0013] S2. Prepare the mortar and inject it into the first grouting zone of the borehole through the grouting pipe. After the mortar injection is completed, seal the borehole opening of the first grouting zone. To further accelerate the setting speed of the mortar, an accelerator is added when preparing the mortar.

[0014] S3. Prepare the grout and inject it into the second grouting zone through a small pipe.

[0015] To ensure the grouting quality of the second grouting zone, the following steps are taken: first, clean the inner cavity of the second grouting zone and the small guide pipe, and then perform grouting.

[0016] The beneficial effects of the borehole directional grouting method of the present invention are as follows: the partition divides the area between the outer wall of the small guide tube and the borehole wall 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 the small guide tube. 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.

[0017] 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:

[0018] A. Near the working face, first remove the loose slag at the bottom, install steel supports, and carry out the support construction of the steel supports.

[0019] B. 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 distance between adjacent holes should be 30-40 cm, and the elevation angle of each hole should not exceed 5°.

[0020] C. Following step S1 of the above-mentioned directional grouting method, insert a partition plate with a small guide tube fixed on its surface into each borehole. 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 away from it. The rear end of the small guide tube and / or partition plate is fixedly connected to the steel support.

[0021] D. Following step S2 of the above-mentioned borehole directional grouting method, mortar is injected into the first grouting zone of each borehole.

[0022] E. Following step S3 of the above-described borehole directional grouting method, grout is injected into the second grouting zone of each borehole to form an arched consolidation shell.

[0023] F. Excavation, muck removal, and support of the tunnel.

[0024] The present invention also provides a small-section tunnel advanced support structure, which is a structure obtained by construction according to steps A to E of the above-mentioned small-section tunnel advanced grouting excavation method. The pre-support structure for small-section tunnels includes steel supports installed near the tunnel face. Drill holes are spaced along the outer side of the tunnel's arching line, with the centerline of each hole pointing upwards. A baffle plate with a small guide tube fixed to its surface is inserted into each hole. The front end of the baffle plate is located at the bottom of the hole or deeper. The rear end of the small guide tube and / or the baffle plate is fixedly connected to the steel supports. Grouting holes are located in the front section of the small guide tube, and a grout-stopping section is located in the rear section. The baffle plate divides the area between the outer wall of the small guide tube and the borehole wall into a first grouting zone and a second grouting zone. The first grouting zone is located on the side of the tunnel that needs to be excavated and is filled with mortar. The second grouting zone is located on the side opposite the tunnel that needs to be excavated. The second grouting zone and the inner cavity of the small guide tube are filled with grout. The solidified and hardened mortar, grout, and surrounding soil and rock, along with the small guide tube and the baffle plate, together form an integral arched solidified shell.

[0025] To facilitate the insertion of the small guide pipe and the diaphragm into the borehole, the diaphragm is further provided with a triangular tip at the front end, the small guide pipe is provided with a pointed cone at the front end, and the front end of the diaphragm is located in the rock and soil at the bottom of the borehole.

[0026] To prevent the first and second grouting zones from connecting, further measures are taken: the width of the partition is greater than or equal to the diameter of the borehole, and the outer diameter of the small guide tube is not greater than the radius of the borehole; or, the width of the partition is less than the diameter of the borehole, the small guide tube is fixed at the centerline of the partition, and on the cross-section of the small guide tube, the diameter of the circumscribed circle corresponding to the two ends of the partition and the point of the small guide tube farthest from the partition is consistent with the diameter of the borehole.

[0027] To further improve the stability between the small guide tube and the partition, an arc-shaped groove is provided on one side of the partition, and the small guide tube is welded and fixed in the arc-shaped groove of the partition.

[0028] To optimize the stress distribution between the small conduit and the septum, the length of the small conduit is greater than the length of the septum, and the rear end of the small conduit coincides with the rear end of the septum. For example, the small conduit is welded and fixed to the centerline of the septum, and the small conduit is 20cm longer than the septum.

[0029] The small guide pipe and the partition plate are generally installed as a whole by driving or jacking. To prevent damage to the rear end of the small guide pipe during construction and to facilitate grouting, a stiffening hoop is installed at the rear end of the small guide pipe. For example, the small guide pipe 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 hole spacing of 20cm, and are arranged in a quincunx pattern. The length of the grout-stopping section of the small guide pipe is not less than 30cm.

[0030] Specifically: the spacing between adjacent boreholes is 30-40cm, and the borehole elevation angle is no more than 5°.

[0031] 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.

[0032] The consolidated and hardened mortar, grout, and surrounding soil and rock mass, along with the small guide pipes and partitions, together form an integral arched consolidated shell. The arched consolidated shell has high strength and can provide stable support to 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

[0033] Figure 1 This is a schematic diagram of the small-section tunnel advance support structure of the present invention.

[0034] Figure 2 yes Figure 1 A magnified view of the highest borehole in the center.

[0035] Attached reference numerals: 1. Drill hole; 2. Small guide pipe; 3. Baffle plate; 4. First grouting zone; 5. Second grouting zone; 6. Steel support. Detailed Implementation

[0036] The invention will now be further described with reference to the accompanying drawings.

[0037] 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.

[0038] S1. After drilling 1 is completed, a partition 3 with a small guide tube 2 fixed on its surface is inserted into drilling 1. The front end of the partition 3 is inserted to the bottom of the hole or deeper than the bottom of the hole. The partition 3 divides the area between the outer wall of the small guide tube 2 and the hole wall of drilling 1 into a first grouting zone 4 located on the control grouting side and a second grouting zone 5 located on the directional grouting side.

[0039] 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 does not require or only requires 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 the central angle corresponding to the directional grouting side, but they may also be unequal. The sum of the two is 360°.

[0040] The small guide pipe 2 and the partition plate 3 need to be fixed in advance before being inserted into the drill hole 1 as a whole. The small guide pipe 2 is used for grouting. The front section of the small guide pipe 2 has grouting holes, and the rear section is the grout-stopping section. For example, the small guide pipe 2 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 2 is not less than 30cm.

[0041] The partition 3 separates the area between the outer wall of the small guide tube 2 and the hole wall of the borehole 1. Considering that the partition 3 will eventually be embedded in the borehole 1, and for strength reasons, the partition 3 is preferably made of metal, generally a strip of steel plate. The small guide tube 2 and the partition 3 can be mechanically fixed or welded together. To prevent the structural impact of the relatively fixed small guide tube 2 and the partition 3 on the insertion of the small guide tube into the borehole 1, the small guide tube 2 is preferably welded to one surface of the partition 3. The surface of the partition 3 refers to the surface with the largest area of ​​the partition 3. The partition 3 can have a straight cross-section or an obtuse angle. The small guide tube 2 is fixed to the surface of the partition 3 or within the obtuse angle. The small guide tube 2 can be fixed at any position on one surface of the partition 3, preferably at the center line of the surface, in which case the axis of the small guide tube 2 is parallel to the length direction of the partition 3. In order to increase the contact area between the small guide tube 2 and the partition plate 3, and thus improve the stability of the small guide tube 2 after welding with the partition plate 3, an arc groove can also be provided on one side of the partition plate 3. The diameter of the arc groove is adapted to the outer diameter of the small guide tube 2, and the small guide tube 2 is welded and fixed in the arc groove of the partition plate 3.

[0042] The small guide pipe 2 and the partition plate 3 form a single structure, which can be inserted into the borehole 1 by hammering or pressing. To facilitate the insertion of the small guide pipe 2 and the partition plate 3 into the borehole 1, the front end of the partition plate 3 is provided with a triangular tip, and the front end of the small guide pipe 2 is provided with a pointed cone. The front end of the partition plate 3 is inserted into the rock and soil at the bottom of the borehole 1 to prevent the first grouting zone 4 and the second grouting zone 5 from connecting at the bottom of the borehole 1. The front end of the partition plate 3, inserted into the rock and soil at the bottom of the borehole 1, also serves to fix the partition plate 3 and prevent the partition plate 3 and the small guide pipe 2 from slipping out of the borehole 1.

[0043] When the small guide pipe 2 and the partition plate 3 are inserted into borehole 1 as a single structure, either the small guide pipe 2 or the partition plate 3 can be used as the main load-bearing structure. Considering the high strength of the small guide pipe 2, it is generally used directly as the main load-bearing structure. To prevent damage to the rear end of the small guide pipe 2 during construction and to facilitate grouting, a stiffening hoop is installed at the rear end of the small guide pipe 2, for example, a φ6.5mm stiffening hoop is welded to the rear end of the small guide pipe 2. When the partition plate 3 is the main load-bearing structure inserted into borehole 1, the front end of the small guide pipe 2 is shorter than the partition plate 3 or they are aligned. That is, the insertion depth of the small guide pipe 2 into borehole 1 can be slightly shallower than the insertion depth of the partition plate 3 into borehole 1, or the insertion depth of both can be the same. When the small guide tube 2 is the main load-bearing structure inserted into the borehole 1, the front end of the small guide tube 2 is longer than the front end of the partition plate 3, or the front end of the small guide tube 2 coincides with the front end of the partition plate 3. That is, the depth to which the small guide tube 2 is inserted into the borehole 1 is slightly deeper than the depth to which the partition plate 3 is inserted into the borehole 1, or the depths to which both are inserted into the borehole 1 are the same. For example, the length of the small guide tube 2 is greater than the length of the partition plate 3, the rear end of the small guide tube 2 coincides with the rear end of the partition plate 3, the small guide tube 2 is welded and fixed at the centerline position of the partition plate 3, and the small guide tube 2 is 20cm longer than the partition plate 3.

[0044] To prevent the first grouting zone 4 and the second grouting zone 5 from connecting, the width of the partition plate 3 is greater than or equal to the diameter of the borehole 1, and the outer diameter of the small guide pipe 2 is not greater than the radius of the borehole 1. When the width of the partition plate 3 is greater than the diameter of the borehole 1, the width of the partition plate 3 is slightly greater than the diameter of the borehole 1 to avoid the problem that the partition plate 3 cannot be inserted into the borehole 1. The two sides of the partition plate 3 are embedded in the rock and soil of the borehole 1 wall. Alternatively, the width of the partition plate 3 is less than the diameter of the borehole 1, and the small guide pipe 2 is fixed at the centerline position of the partition plate 3. On the cross-section of the small borehole 1 and the guide pipe 2, the diameter of the circumscribed circle corresponding to the two ends of the partition plate 3 and the point of the small guide pipe 2 farthest from the partition plate 3 is consistent with the diameter of the borehole 1.

[0045] S2. Prepare the mortar and inject it into the first grouting zone 4 of borehole 1 through the grouting pipe. After the mortar is injected, seal the opening of the first grouting zone 4. 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 4 should be dense and full. After the mortar is injected, seal the opening of the first grouting zone 4 with a sealing material to prevent mortar leakage.

[0046] S3. Prepare the grout and inject it into the second grouting zone 5 through the small guide pipe 2. To ensure the grouting quality of the second grouting zone 5, clean the cavities of the second grouting zone 5 and the small guide pipe 2 before grouting. For example, use high-pressure air to blow away the sand and gravel from the second grouting zone 5 and the cavity of the small guide pipe 2, and seal the openings and surrounding cracks with plastic materials such as hemp fiber or anchoring agent.

[0047] 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 F.

[0048] A. Near the working face, first remove the loose slag at the bottom, install steel support 6 and carry out the support construction of steel support 6, where steel support 6 is a steel arch frame.

[0049] B. 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. The direction of borehole 1 should be obliquely upward. There can be one or two layers of drilling positions. The elevation angles of each layer of borehole 1 can be equal or set to two different angles. Borehole 1 is located outside the excavation area of ​​the tunnel and extends longitudinally into the tunnel. For example, using a Φ150mm diameter 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 of no more than 5° means that the angle between borehole 1 and the horizontal plane is no greater than 5°. Borehole 1 should be drilled strictly according to the determined drilling position to ensure the accuracy of its location. During drilling, observe the direction and outward insertion angle of the drill rod in a timely manner. If significant deviations in direction or outward insertion angle are found, adjustments should be made.

[0050] C. Following step S1 of the above-described directional grouting method, insert a partition 3 with a small guide pipe 2 fixed to its surface into each borehole 1. The first grouting zone 4 is located on the side of the tunnel that needs to be excavated, and the second grouting zone 5 is located on the side opposite the tunnel that needs to be excavated. The rear ends of the small guide pipe 2 and / or the partition 3 are fixedly connected to the steel support 6. For example, the rear ends of the small guide pipe 2 are welded to the steel support 6.

[0051] D. Following step S2 of the above-described directional grouting method, mortar is injected into the first grouting zone 4 of each borehole 1. The mortar seeps into the rock and soil body on the side of borehole 1 closest to the tunnel, and the first grouting zone 4 is completely filled with mortar.

[0052] E. Following step S3 of the above-mentioned borehole directional grouting method, grouting is performed into the second grouting zone 5 of each borehole 1. The solidified and hardened mortar, grout, and the surrounding soil and rock mass of borehole 1, along with the small guide pipe 2 and the partition plate 3, together form an integral arched solidified shell.

[0053] Grouting equipment with good performance and working pressure meeting grouting requirements should be selected and field test runs should be conducted. During grouting, the maximum pressure at the borehole orifice should be strictly controlled within the allowable range to ensure that the grout from a single pipe 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 be stopped when the specified injection volume is reached for each small guide pipe 2. Grouting should also be stopped if the borehole orifice pressure has reached the specified pressure value but the injection volume is still insufficient.

[0054] F. Excavation, muck removal, and support of the tunnel.

[0055] 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.

[0056] The third subject of this invention is a pre-support structure for small-section tunnels, which is a structure constructed according to steps A to E of the pre-grouting excavation method for small-section tunnels described in the second subject above. For example... Figure 1 As shown, the small-section tunnel advanced support structure has steel supports 6 installed near the tunnel face, and the steel supports 6 are steel arch frames.

[0057] Drill holes 1 are spaced apart along the outer side of the tunnel's arching line. The side of drill hole 1 closest to the tunnel that needs to be excavated is the control grouting side, and the side of drill hole 1 opposite to the tunnel that needs to be excavated is the directional grouting side. The spacing between adjacent drill holes 1 is determined based on actual conditions, and is generally 30–40 cm. The centerline of drill hole 1 is angled upwards, and the elevation angle of drill hole 1 is generally no greater than 5°.

[0058] A partition 3, with a small guide pipe 2 fixed to its surface, is inserted into borehole 1. The partition 3 divides the area between the outer wall of the small guide pipe 2 and the borehole wall of borehole 1 into a first grouting zone 4 and a second grouting zone 5. The first grouting zone 4 is located on the side closer to the tunnel that needs to be excavated, and the second grouting zone 5 is located on the side opposite to the tunnel that needs to be excavated. The front end of the partition 3 is located at the bottom of borehole 1 or deeper than the bottom of borehole 1, ensuring that the first grouting zone 4 and the second grouting zone 5 are not connected. The first grouting zone 4 is filled with mortar, and the second grouting zone 5 and the inner cavity of the small guide pipe 2 are filled with grout. The solidified and hardened mortar, grout, and the surrounding soil and rock mass of borehole 1, as well as the small guide pipe 2 and the partition 3, together form an integral arched solidified shell.

[0059] The small guide pipe 2 is mainly used for grouting. Grouting holes are provided in the front section of the pipe wall, and a grout-stopping section is provided in the rear section. For example, the small guide pipe 2 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 hole spacing of 20cm, and are arranged in a staggered pattern. The length of the grout-stopping section of the small guide pipe 2 is not less than 30cm. The rear end of the small guide pipe 2 and / or the partition plate 3 is fixedly connected to the steel support 6, for example, by welding the rear end of the small guide pipe 2 to the steel support 6.

[0060] The small guide pipe 2 and the partition plate 3 are constructed as a single unit, typically by driving or jacking. To facilitate the insertion of the small guide pipe 2 and the partition plate 3 into borehole 1, the front end of the partition plate 3 is equipped with a triangular tip, and the front end of the small guide pipe 2 is equipped with a pointed cone. The front end of the partition plate 3 is located within the rock and soil at the bottom of borehole 1, preventing the first grouting zone 4 and the second grouting zone 5 from connecting at the bottom of borehole 1. To prevent damage to the rear end of the small guide pipe 2 during construction and to facilitate grouting, a stiffening hoop is installed at the rear end of the small guide pipe 2. For example, a φ6.5mm stiffening hoop is welded to the rear end of the small guide pipe 2. To improve the stability between the small guide pipe 2 and the partition plate 3 and prevent them from detaching during construction, an arc-shaped groove is provided on one surface of the partition plate 3, and the small guide pipe 2 is welded and fixed within the arc-shaped groove of the partition plate 3.

[0061] For the relationship between borehole 1, small guide tube 2 and diaphragm 3, please refer to the description of step S1 of the first topic of the borehole directional grouting method above.

[0062] To prevent the first grouting zone 4 and the second grouting zone 5 from connecting, the width of the partition 3 is greater than or equal to the diameter of the borehole 1, and the outer diameter of the small guide pipe 2 is not greater than the radius of the borehole 1. When the width of the partition 3 is greater than the diameter of the borehole 1, the partition 3 should have sufficient strength, serving as the main load-bearing structure, and bending during construction should be avoided. When the width of the partition 3 is less than the diameter of the borehole 1, the diameter of the circumscribed circle corresponding to the two ends of the partition 3 and the point of the small guide pipe 2 furthest from the partition 3 on the cross-section of the partition 3 is consistent with the diameter of the borehole 1. In this case, the small guide pipe 2 serves as the main load-bearing structure. The small guide pipe 2 is generally fixed at the centerline of the partition 3. To optimize the stress distribution between the small guide pipe 2 and the partition 3, the length of the small guide pipe 2 is greater than the length of the partition 3, and the rear end of the small guide pipe 2 coincides with the rear end of the partition 3. For example, the small guide pipe 2 is welded and fixed at the centerline of the partition 3, and the small guide pipe 2 is 20cm longer than the partition 3.

Claims

1. A borehole directional grouting method, characterized in that: Includes the following steps: S1. After the drilling (1) is completed, a partition (3) with a small guide tube (2) fixed on its surface is inserted into the drilling (1). The front end of the partition (3) 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 partition (3) divides the area between the outer wall of the small guide tube (2) and the hole wall of the drilling (1) into the first grouting area (4) located on the control grouting side and the second grouting area (5) located on the directional grouting side. Among them, the pipe wall of the front section of the small guide tube (2) is provided with grouting holes, the rear section of the small guide tube (2) is a grout-stopping section, the width of the partition plate (3) is greater than or equal to the diameter of the borehole (1), and the outer diameter of the small guide tube (2) is not greater than the radius of the borehole (1); or, the width of the partition plate (3) is less than the diameter of the borehole (1), the small guide tube (2) is fixed at the center line position of the partition plate (3), and on the cross section of the small guide tube (2), the diameter of the circumscribed circle corresponding to the two ends of the partition plate (3) and the point of the small guide tube (2) farthest from the partition plate (3) is consistent with the diameter of the borehole (1); S2. Prepare mortar and inject mortar into the first grouting area (4) of the borehole (1) through the grouting pipe to seal the pores and gaps of the soil and rock on the grouting side. After the mortar is injected, seal the opening of the first grouting area (4). S3. Prepare grout, clean the inner cavity of the second grouting zone (5) and the small guide tube (2), and then grout the second grouting zone (5) through the small guide tube (2).

2. The borehole directional grouting method as described in claim 1, characterized in that: In step S1, a triangular tip is provided at the front end of the partition (3), a pointed cone is provided at the front end of the small guide tube (2), and the front end of the partition (3) 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 step S1, the length of the small catheter (2) is greater than the length of the septum (3), and the rear end of the small catheter (2) coincides with the rear end of the septum (3).

4. The borehole directional grouting method according to any one of claims 1 to 3, characterized in that: In step S1, a stiffening clamp is installed at the rear end of the small catheter (2).

5. The borehole directional grouting method as described in claim 4, characterized in that: In step S1, the small guide tube (2) is welded and fixed to the center line of the partition plate (3). The small guide tube (2) is 20cm longer than the partition plate (3). The small guide tube (2) 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 plum blossom pattern. The length of the grout-stopping section of the small guide tube (2) is not less than 30cm.

6. The borehole directional grouting method according to any one of claims 1 to 3, characterized in that: In step S2, an accelerator is added when preparing the mortar.

7. A method for pre-grouting excavation of small-section tunnels, characterized in that: Includes the following steps: A. At the location near the working face, first remove the floating slag at the bottom, install steel support (6) and carry out the support construction of steel support (6); B. Draw the excavation outline on the face of the tunnel, mark the drilling positions outside the arch line and along the direction of the arch line, and drill holes. The drilling direction (1) is obliquely upward. C. In step S1 of the borehole directional grouting method according to any one of claims 1 to 6, a partition (3) with a small guide pipe (2) fixed on its plate surface is inserted into each borehole (1), and the first grouting zone (4) is located on the side close to the tunnel that needs to be excavated, and the second grouting zone (5) is located on the side away from the tunnel that needs to be excavated, and the rear end of the small guide pipe (2) and / or the partition (3) is fixedly connected to the steel support (6). D. In step S2 of the borehole directional grouting method according to any one of claims 1 to 6, mortar is injected into the first grouting zone (4) of each borehole (1); E. In step S3 of the borehole directional grouting method according to any one of claims 1 to 6, grouting is performed in the second grouting zone (5) of each borehole (1) to form an arched consolidation shell; F. Excavation, muck removal, and support of the tunnel.

8. The method for advance grouting excavation of small-section tunnels as described in claim 7, characterized in that: In step B, the distance between adjacent boreholes (1) is 30-40cm, and the elevation angle of each borehole (1) is no greater than 5°.

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