Method for normal pressure cutter changing of shield in water-rich sandy cobble stratum

Abstract

The application discloses a method for changing a cutter of a shield under normal pressure in a water-rich sand and gravel stratum, and aims to solve the technical problem of high safety risk of an existing cutter changing method in a water-rich sand and gravel stratum environment. The method mainly comprises the following steps: (1) mud preparation; (2) measurement and lofting; (3) drilling of plain concrete pile; (4) pouring of plain concrete pile; (5) construction of each plain concrete pile in front of and on both sides of a cutter head; (6) drilling of a manhole; (7)-(9) cutter changing; (10) manhole plugging. The method has the advantages of high safety, low risk, stable tunnel face, and high cutter changing efficiency under normal pressure.

Description

Technical Field

[0001] This application relates to the field of shield tunneling technology, specifically to a method for shield cutterhead replacement under normal pressure in water-rich sandy and gravelly strata. Background Technology

[0002] A slurry shield tunneling machine (TBM) is a type of mechanical equipment used for underground tunnel construction. It employs the shield tunneling method and typically consists of a cutterhead, propulsion system, and slurry circulation system. The TBM excavates the tunnel through the soil using cutters on its cutterhead. During excavation, large hydraulic cylinders propel the cutterhead and tunnel lining, while slurry serves as a support medium to prevent tunnel instability and collapse. Simultaneously, the excavated soil is transported to the surface for processing via the slurry circulation system. Slurry shield tunneling machines are adaptable to various geological conditions and tunnel cross-sectional shapes, and are widely used in urban rail transit, water conservancy projects, and highway tunnels.

[0003] When using slurry shield tunneling machines to traverse water-rich sandy and gravelly strata, significant construction difficulties arise. Firstly, due to the large size of the gravels, the cutterhead is highly susceptible to collisions with the gravels during excavation and soil cutting. Furthermore, the high hardness of the gravels, especially when crushing large-diameter pebbles, causes severe wear on the cutterhead. Secondly, the sandy and gravelly strata have a high permeability coefficient. During tunneling, slurry shield tunneling machines rely primarily on the formation of a mud film at the tunnel face to stabilize it. However, the high permeability of sandy and gravelly strata makes mud film formation difficult, resulting in poor tunnel face stability.

[0004] When the cutterhead wears out, it needs to be replaced promptly. However, when replacing cutters in water-rich sandy and gravelly formations:

[0005] On the one hand, slurry shield tunneling machines use slurry to form a mud film on the tunnel face to stabilize the face, and adjust the pressure in the earth chamber by adjusting the pressure of the slurry liquid level with the high-pressure air in the air cushion chamber to balance the pressure with the stratum pressure. However, the poor sealing and high permeability of water-rich sandy gravel strata make it difficult to form a mud film and cause the liquid level in the air cushion chamber to be unstable. When the liquid level in the air cushion chamber is too low, high-pressure air enters the stratum, disturbing the stratum and making the water-rich sandy gravel stratum even looser, which can easily cause the cutterhead to jam.

[0006] On the other hand, the stratum is rich in groundwater, which can enter the working face through pores, easily causing instability of the working face and posing a danger to personnel changing tools.

[0007] On the other hand, when using conventional cutter replacement methods such as pressurized or atmospheric pressure cutter replacement, it is necessary to reinforce the working face with advanced grouting. However, in actual construction in water-rich sandy gravel strata, the strata have strong convergence, making advanced drilling difficult. Moreover, the strata are rich in groundwater, and water is constantly flowing through the advanced grouting holes during the drilling process, making drilling time-consuming, labor-intensive, and with poor reinforcement effect.

[0008] The information disclosed in this background section is intended only to enhance the understanding of the background technology of this disclosure and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0009] In view of at least one of the above technical problems, this disclosure provides a method for replacing shield cutterheads under normal pressure in water-rich sandy and gravelly strata, aiming to solve the technical problem of high safety risks when replacing shield cutterheads in water-rich sandy and gravelly strata.

[0010] According to one aspect of this disclosure, a method for replacing cutterheads in a shield tunneling machine under normal pressure in water-rich sandy and gravelly strata is provided, comprising the following steps:

[0011] (1) Set up a mud tank including a sedimentation tank for slurry return and a mud storage tank, and use a mud mixer to make mud, the mud volume of which is at least 4 times the corresponding borehole volume;

[0012] (2) Set up the field measurement control network according to the measurement and layout benchmark and verify it. Use the verified measurement control network and total station to lay out the pile positions in the corresponding area outside the cutterhead and install the protective casing at the pile positions.

[0013] (3) The drilling rig is positioned at the corresponding location of the pile, and the verticality of the drill rod is adjusted so that its central axis is collinear with the center of the pile. Mud is injected as drilling progresses to ensure that the mud surface is kept more than 1m above the bottom of the casing. The drilling speed of the drilling rig is controlled. After drilling to a certain depth and the wall mud forming a wall mud skin, drilling at full speed is resumed.

[0014] (4) Concrete is continuously poured into the pile hole through a guide pipe, and the depth of the guide pipe embedded in the concrete is controlled to be 2 to 6 m;

[0015] (5) Repeat steps (2)-(4) and apply concrete piles to stabilize the face and block groundwater at the corresponding positions in front of and on both sides of the cutterhead.

[0016] (6) Repeat steps (2)-(3) to drill a manhole at a certain distance from the bottom of the cutter head. After the manhole is drilled, a manhole casing is placed in the hole, and a water pump is used to pump water to dewater the manhole. The liquid level in the manhole is monitored and the manhole is ventilated.

[0017] (7) After the construction personnel enter the manhole, they manually dig down to the cutterhead and gradually reduce the pressure of the shield machine air cushion chamber according to the depth of manual digging until the pressure of the air cushion chamber drops to 0 when digging down to the cutterhead.

[0018] (8) After the construction personnel leave the manhole and rotate the cutter head to bring the cutter to be replaced into the range of the manhole, the construction personnel re-enter the manhole to replace the cutter head cutter.

[0019] (9) Repeat step (8) to replace each worn tool;

[0020] (10) Weld a steel plate to seal the bottom of the manhole and backfill with sand, gravel and soil.

[0021] In some embodiments of this disclosure, in step (1), the total volume of the mud tank is at least 1.5 times the borehole volume.

[0022] In some embodiments of this disclosure, in step (1), the raw materials for preparing the mud include bentonite, barite powder, and carboxymethyl cellulose.

[0023] In some embodiments of this disclosure, in step (2), after the pile position is laid out, control piles are set on both sides of its longitudinal and transverse directions, and positioning control lines are connected between the opposite control piles. The projection of the intersection of the two positioning control lines at the pile position coincides with the pile center of the pile position.

[0024] In some embodiments of this disclosure, in step (3), the drill rod is provided with a mark at the position corresponding to the designed drilling depth to control the hole depth.

[0025] In some embodiments of this disclosure, in step (3), the pile frame or pile pipe of the pile location is provided with a scale for controlling the drilling depth.

[0026] In some embodiments of this disclosure, in step (3), a dewatering well is opened at a corresponding location around the pile hole.

[0027] In some embodiments of this disclosure, after the drilling rig reaches the designed depth, the drilling is stopped, and reverse circulation drilling is performed for more than 2 minutes, with the relative density of the drilling mud controlled between 1.1 and 1.25.

[0028] One or more technical solutions provided in the embodiments of this application have at least one of the following technical effects or advantages:

[0029] 1. By driving several plain concrete piles at corresponding positions in front of and on both sides of the cutterhead, the working face can be stabilized and groundwater can be blocked. This effectively solves the problem of high safety risks in existing cutter replacement methods, reduces the risk factors of working face instability and water inrush during cutter replacement, and facilitates quick and safe cutter replacement.

[0030] 2. Because a manhole is installed above the cutterhead and a manhole casing is installed inside the manhole, the risk of manhole collapse is avoided by the casing, ensuring the safety of construction personnel when replacing the casing inside the manhole.

[0031] 3. The plain concrete piles in front of and on both sides of the cutterhead can reduce the hydraulic connection between the cutterhead and the surrounding soil. At the same time, the water pump in the manhole can effectively reduce the risk of water inrush at the cutterhead replacement point and ensure the construction safety of the operators.

[0032] 4. By adding appropriate amounts of barite powder and carboxymethyl cellulose to the mud, the mud's specific gravity and viscosity can be increased, thereby increasing the mud pressure inside the borehole and its ability to form a mud cake.

[0033] 5. The mud preparation volume should be at least 4 times the borehole volume to solve the problem of severe mud escape in water-rich sandy and gravelly formations and ensure an appropriate mud supply. Attached Figure Description

[0034] Figure 1 This is a top view of the plain concrete pile layout in one embodiment of this application.

[0035] Figure 2 This is a front view structural diagram of the plain concrete pile in front of the cutterhead in one embodiment of this application.

[0036] Figure 3 This is a cross-sectional view of a manhole in one embodiment of this application.

[0037] In the above figures, 1 is the cutterhead, 2 is the plain concrete pile, 3 is the dewatering well, 4 is the ground, 5 is the manhole, and 51 is the manhole casing. Detailed Implementation

[0038] To better understand the technical solution of this application, the above technical solution will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] Section 2, Construction Zone 03 of Luoyang Metro Line 2 is located in Xigong District and Luolong District of Luoyang City, comprising two stations and two sections. The section between Jiudu West Road Station and Museum Station is designed as two single-bore tunnels, constructed using two air-cushioned slurry balance shield tunneling machines. The shield excavation diameter is 6.5m, and the inner diameter and outer diameter of the tunnel segments are 5.5m and 6.2m respectively. The shield tunnel section between Jiudu West Road Station and Museum Station has a left line length of 2031m and a right line length of 2017m. The section crosses the Luo River, with a maximum overburden thickness of 23m and a minimum overburden thickness of 9m. The longitudinal profile of the section is V-shaped, with a maximum longitudinal slope of 27.7‰. The terrain of this section belongs to the riverbed and floodplain landform area. The soil layer traversed by the section is a pebble layer. The overlying strata from top to bottom are miscellaneous fill, plain fill, loess-like silty clay, silty clay, and clayey silt. The groundwater type within the exploration depth range is pebble pore water, which is mainly found in the pebble layer. The depth of the groundwater pore water level in the site is 0 to 22.5m.

[0040] During the construction of the right line in the Bojiu section, up to ring 1231, crossing the Luo River to the north side of Wenxing Sunshine Waterfront, an increase in tunneling thrust, torque, and articulated tension was observed. At ring 1232, the thrust increased rapidly, the torque surged dramatically, and the speed decreased to 5 mm / min. Based on the cutter wear observed when the left-line tunnel boring machine exited the tunnel, it was determined that the right-line cutter wear was severe.

[0041] When using conventional cutterhead replacement methods, it is necessary to reinforce the tunnel face with pre-grouting. However, the geological features of this construction section are water-rich sandy gravel strata with strong convergence, making pre-drilling difficult. Furthermore, the high groundwater content in the strata after drilling makes pre-drilling time-consuming, labor-intensive, and ineffective. In addition, conventional atmospheric pressure cutterhead replacement methods have high requirements for geological conditions, requiring stable strata and low groundwater content. Due to the poor sealing of water-rich sandy gravel strata and the high groundwater content, the tunnel face is prone to instability, affecting the safety of the personnel performing cutterhead replacement.

[0042] Therefore, this example discloses a method for replacing cutterheads in water-rich sandy and gravelly strata under normal pressure, which solves the problem of high safety risks associated with existing cutterhead replacement methods in such environments. By driving plain concrete piles at appropriate locations to stabilize the tunnel face and seal groundwater, the method aims to reduce the construction risk factor and achieve rapid and safe cutterhead replacement. Specifically, it includes the following steps:

[0043] (1) Set up a mud tank including a sedimentation tank for slurry return and a mud storage tank, and use a mud mixer to make mud, with the mud volume being at least 4 times the corresponding borehole volume.

[0044] During the installation of plain concrete piles, drilling mud is introduced into the pile hole to assist drilling and ensure pile stability, preventing pile wall collapse. In this embodiment, a pre-reserved pit is excavated inside the foundation pit, and a mud tank is placed in the pit. In this example, the mud tank is made of 10mm thick steel plate and consists of three tanks. Their total volume is 1.5 times the borehole volume, thus allowing for a margin to prevent the mud from becoming too small due to sedimentation at the bottom of the tank after mixing with slag in the pile hole, which would lead to mud overflow, waste, and pollution of the construction environment. In other embodiments, the total volume of the mud tank is more than 1.5 times the borehole volume.

[0045] Considering that drilling mud also plays a role in removing drill cuttings during pile hole drilling, and that the slag mixed in the mud will reduce the quality of the mud, the mud tank includes a sedimentation tank for mud return and a mud storage tank. The sedimentation tank for mud return is used to settle the returned mud. After sedimentation, the slag mixed in the mud settles to the bottom of the tank. In this example, a slag area is set up next to the sedimentation tank. The slag at the bottom of the sedimentation tank is cleaned up with a backhoe and placed in the slag area to ensure the circulation space and storage space of the mud in the mud tank.

[0046] In addition, the mud storage tank in the mud tank is used to store mud. Mud is produced using a mud mixer with bentonite as the main raw material and stored in the mud storage tank. Considering the severe mud escape phenomenon in water-rich sandy gravel strata, in this example, the mud required for each pile is four times the borehole volume. This ensures sufficient mud to meet usage requirements. In other embodiments, the mud production is more than four times the borehole volume to reliably ensure usage needs. In this embodiment, the mud raw materials include bentonite, barite powder, and carboxymethyl cellulose. The addition of barite powder and carboxymethyl cellulose increases the mud's specific gravity and viscosity, thereby increasing the borehole mud pressure and the ability to form a mud cake.

[0047] (2) Set up the field measurement control network according to the measurement and layout benchmark and verify it. Use the verified measurement control network and total station to lay out the pile positions in the corresponding area outside the cutterhead and install the protective casing at the pile positions.

[0048] To ensure accurate positioning of the plain concrete piles, avoid damage to the cutterhead, and effectively stabilize the working face and block groundwater, a field survey control network was first established based on the survey benchmarks provided by the client. This network was then verified to ensure its accuracy and reliability. Using the verified traverse points and leveling points, a total station was used to precisely determine the pile positions for layout. Control piles were then set up on both the longitudinal and transverse sides of the pile positions, and fixed positioning control lines were established between pairs of opposite control piles. The projection of the intersection of these two positioning control lines at the pile position was ensured to coincide with the pile center, facilitating subsequent work such as drilling rig positioning and reinforcement cage alignment. Furthermore, after the pile positions were laid out, casings were installed at the pile locations. To ensure accurate and unbiased pile positioning, the locations were verified again after casing installation.

[0049] (3) The drilling rig is positioned at the corresponding location of the pile, and the verticality of the drill rod is adjusted so that its central axis is collinear with the center of the pile. Mud is injected as drilling progresses, ensuring that the mud surface is kept more than 1m above the bottom of the casing. The drilling speed of the drilling rig is controlled, and full speed drilling is resumed after drilling to a certain depth and the wall mud forms a wall mud skin.

[0050] After the pile positions were marked out, the drilling rig entered the site to begin drilling operations. In this example, a rotary drilling rig was used. Since the control piles around the pile positions ensured the accuracy and stability of the pile location and prevented displacement or misalignment, the control piles were strictly protected during construction to avoid damage caused by external impacts. Furthermore, considering the accuracy of the pile hole drilling, the roadbed was leveled and compacted before the drilling rig was positioned. In this example, to control ground load, a 2cm thick steel plate was laid on the ground. The large contact area between the steel plate and the ground dispersed the lateral pressure exerted on the pile hole wall by the rotary drilling rig and crane, ensuring the accuracy of the pile hole and preventing displacement or settlement during drilling.

[0051] After the drilling rig is positioned next to the pile location, the rig body is adjusted to be stable and the drill rod is made vertical. In this example, the positioning deviation of the drilling rig is adjusted to be less than 10mm. In addition, in order to control the drilling depth, in this embodiment, a mark is set at the position of the drill rod corresponding to the designed drilling depth to control the hole depth. According to the position of the mark, it is confirmed whether the hole has been drilled to the specified depth. In some other embodiments, a scale is set on the pile frame or pile pipe at the pile location to control the drilling depth. The drilling depth is observed and recorded during construction using the scale to ensure the drilling depth requirement is met.

[0052] After the drilling rig is adjusted and the drill bit and drill rod are aligned with the center of the pile position, drilling begins. In the initial stage, to prevent the drilling speed from being too fast and causing hole displacement or collapse, the drilling speed of the rig needs to be controlled and reduced accordingly. Once a certain drilling depth has been reached, the borehole becomes directional, and a protective mud cake has been formed on the wall, then drilling at full speed can resume. This ensures the verticality and quality of the hole. In addition, during the drilling process, the verticality of the drilling is monitored by observing the instruments on the rotary drilling rig. If any deviation is detected, appropriate adjustments are made promptly.

[0053] While the drilling rig is drilling, drilling mud is introduced into the pile hole. The mud serves to cool and lubricate the drill bit, and its viscosity and density support the hole wall, preventing collapse. Furthermore, the circulating mud carries away drilling debris, preventing blockages. The condition of the circulated debris is checked against the geological report, thus ensuring construction safety. In this embodiment, a mud tank ensures a sufficient supply of mud to the pile hole, maintaining the mud level at least 1 meter above the bottom of the casing, thereby controlling the stability of the pile hole wall. After the drilling rig reaches the designed depth, the drilling stops, and reverse circulation drilling is performed for at least 2 minutes to remove debris from the bottom of the hole. The relative density of the mud is controlled at 1.2, and a continuous mud supply is maintained during cleaning to ensure a stable mud level. In other embodiments, the relative density of the mud is controlled between 1.1 and 1.25. In addition, to ensure the quality of pile construction, the construction time interval between adjacent batches of piles should be greater than 24 hours. During drilling, the soil at the borehole opening should be cleared at any time. If phenomena such as drill rod jumping, frame shaking, or no progress are found, drilling should be stopped and inspected in time.

[0054] (4) Concrete is continuously poured into the pile hole through the guide pipe, and the depth of the guide pipe embedded in the concrete is controlled to be 2 to 6 m.

[0055] After the pile hole is formed, concrete is injected into the pile hole through a guide pipe inserted into the bottom of the hole. After the first batch of concrete is poured normally, concrete is continuously poured until it reaches the top of the pile. In addition, during the grouting process, the rising height of the concrete surface is periodically detected using a measuring rope. When the concrete surface rises to a certain height, the guide pipe is lifted appropriately, and the guide pipe is disassembled step by step to keep the depth of the guide pipe embedded in the concrete controlled between 2 and 6 meters. The number of times the measuring rope is detected is greater than the number of times the guide pipe is lifted, and the grout return is observed to determine the concrete grouting status in the hole.

[0056] (5) Repeat steps (2)-(4) to apply concrete piles to stabilize the face and block groundwater at the corresponding positions in front of and on both sides of the cutterhead.

[0057] To stabilize the tunnel face and seal off groundwater, adjacent plain concrete piles were constructed in front of and to the sides of the cutterhead to enclose the space around the tunnel boring machine. See also [reference needed]. Figure 1Seventeen Φ600 plain concrete piles 2 were constructed in front of and on both sides of the tunnel boring machine cutterhead 1. The plain concrete pile 2 located in front of the cutterhead 1 was 500mm away from the cutterhead panel. This spacing prevented damage to the cutterhead during pile drilling. See also... Figure 2 The bottom of the plain concrete pile 2 is located at a certain distance below the bottom of the cutterhead 1. In this embodiment, the bottom of the pile is 1000mm away from the bottom of the cutterhead 1. Thus, by burying the pile at a relatively deep depth relative to the cutterhead, the effect of sealing the groundwater is ensured, thereby ensuring the stability of the tunnel face.

[0058] Furthermore, during the drilling of plain concrete piles, when the groundwater content in the strata is high and the infiltration pressure of groundwater on the borehole wall is significant, wellpoint dewatering measures are used to lower the groundwater level. (See [link to relevant documentation]). Figure 1 Several dewatering wells 3 are installed on both sides of the plain concrete pile bank. The bottom of each dewatering well 3 is much lower than the bottom surface of the cutterhead 1. In this embodiment, the bottom of the dewatering well 3 is 5000mm from the bottom of the cutterhead 1, which lowers the water level and prevents the borehole wall from collapsing due to excessive water pressure. In addition, due to the limitations of the complex geological environment, in order to ensure construction safety and quality, concrete is poured within 8 hours after the pile hole is opened to avoid the risk of structural changes or even collapse of the pile hole over time.

[0059] (6) Repeat steps (2)-(3) to drill a manhole at a certain distance from the cutter head. After the manhole is drilled, lower the manhole casing into the hole and use a water pump to pump water to dewater the manhole. Monitor the liquid level in the manhole and ventilate the manhole.

[0060] After the construction of plain concrete piles for reinforcing the tunnel face and sealing groundwater is completed, the same method is used to drill manholes for changing the cutterheads. See [link to relevant documentation]. Figure 3 Manhole 5 is located directly above the cutterhead to facilitate the replacement of damaged tools at the edge of the cutterhead. In this example, a Φ1.2m manhole is constructed to allow workers to enter. Since workers need to enter the manhole, a manhole casing 51 is lowered after manhole 5 is drilled to ensure their safety. In this example, the manhole casing is a high-strength steel casing, which supports the borehole wall and prevents it from collapsing. Furthermore, considering the abundant groundwater in the construction environment, although dewatering wells have been constructed, seepage cannot be completely avoided. Therefore, a water pump is installed in the manhole to assist in dewatering, and the liquid level inside the manhole is constantly monitored to prevent large-scale water inrush and provide timely warnings. Also, because the manhole diameter is relatively small and located below ground level 4, the oxygen content at the bottom of the well is low or hazardous gases may be present. Therefore, in this example, ventilation pipes are installed in the manhole to ventilate and ensure the safety of workers entering to perform tool replacement operations.

[0061] When construction workers enter the manhole to change cutting tools, the bottom of the hole should be in contact with the cutterhead. However, when drilling with a drilling rig, ensuring the accuracy of the drilling depth cannot guarantee that the drilling rig will not damage the cutterhead. Therefore, when drilling the manhole, the drilling rig will drill to a certain height from the cutterhead. In this embodiment, when the drilling rig stops, the drill bit will be 300mm from the cutterhead, thus leaving a certain safety margin to avoid deviation in drilling depth, which could lead to excessive drilling and damage to the cutterhead.

[0062] (7) After the construction personnel enter the manhole, they manually dig down to the cutterhead and gradually reduce the pressure of the shield machine air cushion chamber according to the depth of manual digging until the pressure of the air cushion chamber drops to 0 when digging down to the cutterhead.

[0063] After the drilling rig reaches a certain distance from the cutterhead, construction workers enter the manhole and continue digging downwards manually. As the digging continues, the bottom of the manhole gets closer to the cutterhead. To stabilize the surrounding soil structure, the shield machine's air cushion chamber will have a certain pressure. In this example, the working face has been stabilized by pre-installing plain concrete piles. Therefore, as the workers approach the cutterhead, the air cushion chamber pressure needs to be gradually released to atmospheric pressure. In this embodiment, based on the progress of the manhole bottom clearing, i.e., the excavation depth, the air cushion chamber pressure is gradually and slowly reduced multiple times in coordination with the shield machine control personnel until the bottom of the manhole is cleared to the cutterhead position, at which point the air cushion chamber pressure is released to zero.

[0064] (8) After the construction personnel leave the manhole and rotate the cutter head so that the cutter to be replaced is within the range of the manhole, the construction personnel re-enter the manhole to replace the cutter head cutter.

[0065] Before replacing the cutterhead, ensure it is within the manhole area. Otherwise, evacuate personnel from the manhole and rotate the tunnel boring machine's cutterhead until the cutterhead is within the manhole's operating range. Once the cutterhead is positioned within the manhole, first clear away any surrounding soil to ensure sufficient working space. Second, replace severely worn cutters with the appropriate model. For detached cutters, considering their significant wear, the L-shaped pads used to secure them may be ineffective; determine whether to remove or replace them based on inspection. During cutter replacement, first remove the wedge bolt protection plate and cutterhead bolts, install the replaced L-shaped pads, and lower the cutterhead bolts and other structural accessories to the work position for fixation. Furthermore, due to the cutterhead's weight, use a truck crane to lift it to the switchable chain hoist position, switch the lifting points, and use the chain hoist to adjust accuracy for cutter installation. After the cutterhead bolts are secured, use a pneumatic wrench to retighten them. Finally, weld the cutterhead and tighten the bolt protection plate.

[0066] During the tool changing process, the water level at the working face is constantly monitored, and the water pump and slurry discharge pipeline are turned on to pump water to ensure that the water level in the manhole is below the working face and to avoid accidents.

[0067] (9) Repeat step (8). After the construction personnel withdraw from the manhole, rotate the shield machine cutterhead so that the next cutter to be replaced is rotated into the range of the manhole. Continue to replace the next cutter, thereby gradually realizing the replacement of each worn cutter.

[0068] (10) Weld a steel plate to seal the bottom of the manhole and backfill with sand, gravel and soil.

[0069] After the cutterhead was replaced, the manhole was promptly sealed. Since a steel casing was installed inside the manhole, a steel plate was welded to the bottom of the casing to seal the bottom of the hole. Sand, gravel, and soil were then backfilled inside the casing to ensure compaction and prevent slurry leakage during tunnel boring. Furthermore, as the tunnel boring machine passed the sealed manhole location, the pressure fluctuations in the slurry chamber were strictly controlled to avoid excessive disturbance to the riprap and surrounding soil, which could lead to insufficient gripping force and the riprap sinking into the excavation face.

[0070] This method was successfully applied to cutter replacement in the section between Museum Station and Jiudu West Road Station of Luoyang Metro Line 2. The plain concrete piles were constructed using mechanical equipment, resulting in fast pile formation and low labor intensity. During the preparation and operation of cutter replacement, the tunnel face remained stable, and the groundwater level was lower than that at the working face, effectively reducing the operational risks of cutter replacement. After the cutter replacement was completed, the tunnel boring machine's tunneling performance improved significantly. This method is not only applicable to water-rich sandy gravel strata but also to relatively loose strata with poor pre-grouting reinforcement, where it is difficult to maintain tunnel face stability, and is suitable for cutter replacement under normal pressure.

[0071] Although some preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0072] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of the invention. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for replacing cutterheads in a shield tunneling machine under normal pressure in water-rich sandy and gravelly strata, characterized in that, Includes the following steps: (1) Set up a mud tank including a sedimentation tank for slurry return and a mud storage tank, and use a mud mixer to make mud, the mud volume of which is at least 4 times the corresponding borehole volume; (2) Set up the field measurement control network according to the measurement and layout benchmark and verify it. Use the verified measurement control network and total station to lay out the pile positions in the corresponding area outside the cutterhead and install the protective casing at the pile positions. (3) The drilling rig is positioned at the corresponding location of the pile, and the verticality of the drill rod is adjusted so that its central axis is collinear with the center of the pile. Mud is injected as drilling progresses to ensure that the mud surface is kept more than 1m above the bottom of the casing. The drilling speed of the drilling rig is controlled. After drilling to a certain depth and the wall mud forming a wall mud skin, drilling at full speed is resumed. (4) Concrete is continuously poured into the pile hole through a guide pipe, and the depth of the guide pipe embedded in the concrete is controlled to be 2 to 6 m; (5) Repeat steps (2)-(4) and apply concrete piles to stabilize the face and block groundwater at the corresponding positions in front of and on both sides of the cutterhead. (6) Repeat steps (2)-(3) to drill a manhole at a certain distance from the bottom of the cutter head. After the manhole is drilled, a manhole casing is placed in the hole, and a water pump is used to pump water to dewater the manhole. The liquid level in the manhole is monitored and the manhole is ventilated. (7) After the construction personnel enter the manhole, they manually dig down to the cutterhead and gradually reduce the pressure of the shield machine air cushion chamber according to the depth of manual digging until the pressure of the air cushion chamber drops to 0 when digging down to the cutterhead. (8) After the construction personnel leave the manhole and rotate the cutter head to bring the cutter to be replaced into the range of the manhole, the construction personnel re-enter the manhole to replace the cutter head cutter. (9) Repeat step (8) to replace each worn tool; (10) Weld a steel plate to seal the bottom of the manhole and backfill with sand, gravel and soil.

2. The shield tunneling cutterhead replacement method under normal pressure in water-rich sandy and gravelly strata according to claim 1, characterized in that, In step (1), the total volume of the mud box is at least 1.5 times the borehole volume.

3. The shield tunneling cutterhead replacement method under normal pressure in water-rich sandy and gravelly strata according to claim 1, characterized in that, In step (1), the raw materials for preparing the mud include bentonite, barite powder, and carboxymethyl cellulose.

4. The shield tunneling cutterhead replacement method under normal pressure in water-rich sandy and gravelly strata according to claim 1, characterized in that, In step (2), after the pile position is laid out, control piles are set on both sides of the longitudinal and transverse directions, and positioning control lines are connected between the opposite control piles. The projection of the intersection of the two positioning control lines at the pile position coincides with the pile center of the pile position.

5. The shield tunneling cutterhead replacement method under normal pressure in water-rich sandy and gravelly strata according to claim 1, characterized in that, In step (3), the drill rod is marked at the position corresponding to the designed drilling depth to control the hole depth.

6. The shield tunneling cutterhead replacement method under normal pressure in water-rich sandy and gravelly strata according to claim 1, characterized in that, In step (3), the pile frame or pile pipe at the pile location is equipped with a scale for controlling the drilling depth.

7. The shield tunneling cutterhead replacement method under normal pressure in water-rich sandy and gravelly strata according to claim 1, characterized in that, In step (3), a dewatering well is opened at the corresponding position around the pile hole.

8. The shield tunneling cutterhead replacement method under normal pressure in water-rich sandy and gravelly strata according to claim 1, characterized in that, In step (3), after the drilling rig reaches the designed depth, the drilling is stopped and the reverse circulation drilling is carried out for more than 2 minutes, and the relative density of the mud is controlled at 1.1 to 1.25.

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