A protection device and method for controlling settlement of a sand layer of a subway tunnel

Abstract

The present application belongs to the field of tunnel and underground engineering operation and maintenance, and particularly relates to a protection device and method for controlling settlement of an existing subway tunnel in a sand layer. In view of the problems of large stratum disturbance, poor grouting targeting, and difficult control of settlement in the existing subway tunnel in a water-rich sand layer, the present application realizes adaptive targeted grouting reinforcement of the tunnel surrounding rock defects by means of synchronous grouting layer compensation grouting, back wall wrapping grouting, and foundation layered pipe wrapping grouting, in combination with the diffusion-solidification characteristics of the slurry in the water-rich sand layer and the automatic real-time monitoring data of the tunnel structure, until the tunnel settlement control target is achieved.

Description

Technical Field

[0001] This invention belongs to the field of tunnel and underground engineering operation and maintenance, specifically relating to a protective device and method for controlling settlement in existing subway tunnels in sandy layers. It is applicable to the control and treatment of settlement deformation diseases such as continuous settlement and differential settlement in operating subway shield tunnels in water-rich sandy layers. Background Technology

[0002] After a certain number of years of service, existing subway tunnels in water-rich sandy layers often experience abnormal settlement due to changes in the external environment. Existing cases show that without timely and proactive intervention, abnormal tunnel settlement will continue to develop, causing varying degrees of longitudinal deformation, accompanied by track bed delamination, increased water leakage, and other problems. In severe cases, it can even endanger the tunnel structure and operational safety. Due to the influence of surface structures and underground pipelines, sections of existing subway tunnels experiencing abnormal settlement often lack the conditions for surface artificial intervention (grouting), forcing on-site intervention (grouting) within the tunnel to control settlement in existing subway tunnels.

[0003] For existing subway tunnels in water-rich sandy layers, settlement control through grouting is currently mainly achieved by referencing the micro-disturbance grouting method used in soft soil strata. This involves creating a continuous and effective columnar support structure at the tunnel bottom through perforated grouting within the tunnel segments. However, due to the low porosity and poor groutability of water-rich sandy layers, micro-disturbance grouting cannot form a continuous and effective bottom support structure, making it difficult to achieve the expected goal of controlling tunnel settlement. Unlike soft soil strata, the settlement mechanism of existing subway tunnels in water-rich sandy layers is mainly due to damage to the synchronous grouting layer of the tunnel segments and the sand layer near it during service, resulting in a certain degree of non-compaction and weakening of the segment constraint, thus causing tunnel settlement. Micro-disturbance grouting has a good remediation effect on tunnel settlement caused by consolidation settlement of soft soil; however, it cannot achieve ideal remediation results for tunnel settlement caused by water-rich sandy layers and non-compaction of the synchronous grouting body. To address this problem, a protective device and method for controlling settlement in existing subway tunnels with sand layers are proposed. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of existing technical solutions, the present invention provides a protective device and method for controlling settlement in existing subway tunnels with sand layers.

[0005] This invention proposes a protective device and method for controlling settlement in existing subway tunnels with sandy layers, aiming to control and remediate settlement deformation problems such as continuous settlement and differential settlement in existing subway tunnels. Specifically, it applies to existing subway tunnels with water-rich sandy layers, including the tunnel's internal space, segment structure, synchronous grouting layer, and water-rich sandy layer.

[0006] This invention proposes a protective device for controlling settlement in existing subway tunnels with sand layers. The subway tunnel includes tunnel segments, pre-drilled grouting holes (which also serve as hoisting holes) for the segments, evacuation platforms, contact rails, steel rails, and track bed, etc.

[0007] When abnormal settlement occurs in the tunnel, the first step is to treat the leakage of the tunnel segments. Specifically, this involves grouting to stop the leakage at the joints, bolt holes, and grouting holes of the segments. For leakage above the track bed, grouting is used to stop the leakage, while for leakage below the track bed, grouting is used to seal the leakage.

[0008] Secondly, grouting is performed to compensate for voids and loose areas in the synchronous grouting layer through pre-reserved grouting holes in the tunnel segments. Specifically, the synchronous grouting layer is wrapped with a grouting strip, which is formed by compensating for the synchronous grouting layer and wrapping grouting behind the wall. By compensating for the synchronous grouting layer and wrapping grouting behind the wall, the loose synchronous grouting layer close to the tunnel segments is compacted, improving the stress environment of the tunnel segments and reducing water leakage.

[0009] The next step is to use a drilling and grouting machine to perform forward-mounted pipe insertion grouting to form a grouting band wrapped around the insertion pipe. First, the plain concrete track bed at the location of the newly added vertical grouting holes is removed. A suitable location for removing the plain concrete is selected, at the 5 and 7 o'clock positions where the track bed connects to the tunnel segment, and the removal location is symmetrical on both sides of the track bed. Holes are drilled in the tunnel segment to install the orifice pipes. The specific process is: drilling - cleaning the hole - applying anchoring adhesive - installing the orifice pipes. After that, ball valves and blowout preventers are installed.

[0010] For the grouting holes at points 5 and 7 of the same ring segment, synchronous symmetrical pipe insertion and grouting are performed. First, grouting is repeatedly performed on the 0-50cm layer behind the synchronous grouting layer using a drilling and grouting machine until the grout volume significantly decreases or the grouting pressure significantly increases, forming the first grouting band. Then, grouting is repeatedly performed on the 50cm-100cm layer behind the synchronous grouting layer using a drilling and grouting machine until the grout volume significantly decreases or the grouting pressure significantly increases, forming the second grouting band. If the preset target for a single grouting session is not yet achieved, repeated pipe insertion and grouting can be performed on the less dense areas behind the synchronous grouting layer until the preset target for a single grouting session is reached.

[0011] The next step is to carry out grouting construction of different segments in sequence according to the pre-determined grouting sequence, the preset target for each grouting, and the final settlement control standard of the tunnel, until the settlement control of the segments reaches the final settlement control standard.

[0012] By repeatedly inserting and grouting sections into the tunnel lining segments, grouting is stopped once the segments reach the final settlement control standard, such as a 10mm rise in tunnel elevation. The grouting drill rods of the integrated drilling and grouting machine are then removed, the ball valves are closed, and the blowout preventer is dismantled. This repeated grouting process enhances the density of the sand layer at the bottom of the tunnel segments, improving the foundation's rigidity and bearing capacity.

[0013] In another embodiment of the present invention, the present invention provides a protection method for controlling settlement in existing subway tunnels with sand layers, which is used to implement the above-mentioned protection device.

[0014] The protection method includes the following steps: S1: Grouting is performed to stop water leakage at the joints of the pipe segments, bolt holes, and grouting holes. S2: Perform compensating grouting on the outer side of the synchronous grouting layer and wrapping grouting behind the synchronous grouting layer wall; S3: Layered insertion of the grouting strip behind the wall is performed to form a grouting strip wrapped with the insertion tube.

[0015] Prior to step S1, the procedure also includes: S01: Obtain design data, settlement deformation monitoring data, and detection data such as voids behind tunnel segments from existing subway tunnels in abnormal settlement sections.

[0016] S02: Based on the above detection data, a numerical simulation model is established to numerically invert the abnormal settlement of existing subway tunnels. Through numerical calculations, design and construction parameters such as grouting hole layout, grouting parameters, grouting sequence, preset targets for single grouting, and the final settlement control standards for the tunnel are determined. Specifically, the layout of transverse and longitudinal grouting holes in the existing subway tunnel in the settlement section is designed, and a numerical simulation module for grout diffusion and solidification within the tunnel is built to simulate, determine, and optimize grouting-related parameters.

[0017] Of course, these parameters can also be obtained through field tests.

[0018] Further, step S1 specifically includes: Grouting is used to stop water leakage at the joints, bolt holes, and grouting holes of the tunnel segments. Specifically, grouting is used to stop water leakage above the track bed, while grouting is used to seal water leakage below the track bed.

[0019] Furthermore, step S2 specifically includes the following steps: S21: Compensation grouting is performed using pre-reserved grouting holes on the tunnel lining segments. The grouting volume and pressure are determined based on the current status of the synchronous grouting layer near the grouting holes. The core objective is to fill the voids in the synchronous grouting layer, compact the pores of the grouting layer, and restore the constraint capacity of the synchronous grouting layer on the tunnel lining segments.

[0020] S22: Remove the plain concrete track bed at the location of the newly added vertical grouting holes. The newly added vertical grouting holes are located at the center of the segment circumference, at positions 5 and 7 where the track bed connects to the segment.

[0021] S23: Drill holes in the tunnel lining segments and install the orifice pipes. The specific process includes drilling, cleaning the holes, applying anchoring adhesive, and installing the orifice pipes, followed by installing ball valves and blowout preventers. The blowout preventer used in this project is a mature existing technology. Its core function is to prevent grout from splashing out of the grouting holes during the grouting process, avoiding grout waste and construction safety hazards, while also facilitating the control of grouting pressure.

[0022] S24: Drill through the remaining tunnel segments and synchronous grouting layer. Use a water drill to drill small holes. Select a small, portable water drill and control the drilling speed during the drilling process to avoid disturbing the tunnel segment structure and the surrounding water-rich sand layer. After drilling through, immediately pull out the drill rod and quickly close the ball valve to prevent water and sand in the water-rich sand layer from rushing into the tunnel and affecting construction safety and the working environment.

[0023] S25: Perform synchronous symmetrical backwall grouting at the grouting holes at points 5 and 7 of the same segment.

[0024] Furthermore, step S3, which involves wrapping the grouting strip behind the wall and performing layered insertion to form the insertion tube wrapped with the grouting strip, specifically includes the following steps: S31: Based on the single grouting preset target determined in step S02, perform synchronous symmetrical pipe insertion and grouting at the grouting holes at points 5 and 7 of the segment.

[0025] S32: When it is determined that the segment lifting has reached the preset target for a single grouting, stop grouting, remove the grouting drill rod of the drilling and grouting machine, and close the ball valve; S33: Once the final grouting conditions are met, remove the ball valve and seal the vertical grouting hole.

[0026] Since controlling settlement in existing subway tunnels generally requires coordination of settlement control for different tunnel segments, grouting construction needs to be carried out for different tunnel segments. Therefore, the following steps are included after step S32: S321: Based on the grouting sequence, single grouting preset target and final settlement control standard determined in step S02, determine the next segment that needs grouting; S322: Perform synchronous symmetrical grouting by inserting pipes and wrapping the grouting holes at points 5 and 7 of the next segment until the segment reaches the preset target for a single grouting.

[0027] The specific conditions for achieving the final grouting in step S33 are as follows: all segments requiring grouting achieve the corresponding single grouting preset target, and the overall settlement control reaches the final settlement control standard.

[0028] Based on the above steps, permanent repairs will be carried out on newly emerging water leakage and track bed gaps, the track bed cut-off locations will be permanently restored, the track geometry will be measured, and alignment and slope adjustments will be made if necessary.

[0029] The beneficial effects of this invention are as follows: 1. It can target the settlement mechanism of tunnels in water-rich sandy layers and carry out targeted grouting to control and treat settlement and deformation diseases in tunnels, "medicating" from the essential defect level and truly achieving "curing the disease with medicine".

[0030] 2. Based on the diffusion characteristics of static pressure grouting in water-rich sand layers, the protective device proposed in this invention has higher construction reliability and implementation degree.

[0031] 3. Compared with the bottom support reinforcement formed by micro-disturbance grouting reinforcement, the grouting band that confines the entire circumference of the tunnel proposed in this invention has higher reliability and is more conducive to improving the long-term service performance of tunnels in water-rich sandy layers.

[0032] 4. By adopting the protection device and method proposed in this invention, design and construction parameters such as grouting hole layout, grouting parameters, and grouting sequence can be provided for specific settlement and deformation diseases. This avoids poor quality of the grouting strip due to insufficient grouting or waste of resources due to excessive grouting. At the same time, it reduces the number of on-site trial grouting, shortens the grouting construction cycle, reduces operation and maintenance costs, and solves the pain point of traditional grouting relying entirely on experience and having unpredictable effects. Attached Figure Description

[0033] Figure 1 This is a plan view of a protective device for controlling settlement in existing subway tunnels with sand layers, as shown in an embodiment of the present invention. Figure 2 This is a cross-sectional view of a protective device for controlling settlement in existing subway tunnels with sand layers, as shown in an embodiment of the present invention. Explanation of reference numerals in the attached drawings: 11—segment; 12—segment pre-reserved grouting hole; 13—evacuation platform; 14—contact rail; 15—rail; 16—track bed; 161—location of plain concrete removal from track bed; 21—synchronous grouting layer; 22—void; 23—uncompacted area; 31—vertical grouting hole; 32—grouting strip wrapped behind the wall; 33—grouting strip wrapped after the first insertion of pipe; 34—grouting strip wrapped after the second insertion of pipe. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention belong to the present invention.

[0035] This invention proposes a protective device and method for controlling settlement in existing subway tunnels with sandy layers, aiming to control and treat settlement deformation problems such as continuous settlement and differential settlement in existing subway tunnels. Specifically, it applies to existing subway tunnels with water-rich sandy layers, involving the tunnel's internal space, segment structure, synchronous grouting layer, and water-rich sandy layer.

[0036] In one embodiment of the present invention, a protective device for controlling settlement in existing subway tunnels with sand layers is proposed. For example... Figure 1-2 As shown, the subway tunnel includes segments 11, pre-reserved grouting holes 12, evacuation platforms 13, contact rails 14, rails 15, and track bed 16, etc.

[0037] When abnormal settlement occurs in the tunnel, the first step is to treat the leakage of the segment 11 structure. Specifically, grouting is used to stop the leakage at the joints, bolt holes, and grouting holes of segment 11. The leakage above the track bed 16 is grouted to stop the leakage, while the leakage below the track bed is sealed with grout.

[0038] Secondly, grouting is performed to compensate for voids 22 and loose areas 23 in the synchronous grouting layer 21 through the pre-reserved grouting holes 12 in the tunnel segment. Specifically, a grouting strip is wrapped around the synchronous grouting layer 21, which is formed by compensating for the synchronous grouting layer 21 and wrapping grouting behind the wall. The compensating grouting and the wrapping grouting strip 32 behind the wall are used to fill and compact the loose synchronous grouting layer 21 that is close to the tunnel segment 11, thereby improving the stress environment of the tunnel segment 11 and reducing water leakage of the tunnel segment 11.

[0039] The next step is to use a drilling and grouting machine to perform forward-mounted pipe insertion grouting to form a grouting band wrapped around the insertion pipe. First, the plain concrete track bed at the location of the newly added vertical grouting hole 31 is removed. A suitable plain concrete removal location 161 is selected, which is located at the 5 and 7 o'clock positions where the track bed connects to the segment 11. The plain concrete removal location 161 is located symmetrically on both sides of the track bed. First, holes are drilled in the segment 11 to install the orifice pipe. The specific process is: drilling - cleaning the hole - applying anchoring adhesive - installing the orifice pipe. Then, the ball valve and blowout preventer are installed.

[0040] Synchronous symmetrical grouting with inserted pipes is performed on the grouting holes at points 5 and 7 of the same ring segment 11. First, grouting is repeatedly performed on the 0-50cm area behind the synchronous grouting layer 21 of segment 11 using a drilling and grouting machine until the grouting volume significantly decreases or the grouting pressure significantly increases, forming the first grouting band 33. Then, grouting is repeatedly performed on the 50cm-100cm area behind the synchronous grouting layer 21 of segment 11 using a drilling and grouting machine until the grouting volume significantly decreases or the grouting pressure significantly increases, forming the second grouting band 34. If the preset target for a single grouting session is not yet achieved, repeated grouting with inserted pipes can be performed on the less dense areas behind the synchronous grouting layer 21 of segment 11 until the preset target for a single grouting session is achieved.

[0041] The next step is to carry out grouting construction of different segments 11 in sequence according to the pre-determined grouting sequence, the preset target for single grouting, and the final settlement control standard of the tunnel, until the tunnel settlement control reaches the final settlement control standard.

[0042] By repeatedly inserting and wrapping grouting sections, grouting is stopped once the tunnel reaches the final settlement control standard, such as a 10mm rise. The grouting drill rods of the integrated drilling and grouting machine are then removed, the ball valves are closed, and the blowout preventer is dismantled. This repeated grouting process enhances the density of the sand layer at the bottom of segment 11, improving the foundation's rigidity and bearing capacity.

[0043] In another embodiment of the present invention, the present invention provides a protection method for controlling settlement in existing subway tunnels with sand layers, which is used to implement the above-mentioned protection device.

[0044] The protection method includes the following steps: S1: Grouting is performed to stop water leakage at the joints of the pipe segments, bolt holes, and grouting holes. S2: Perform compensating grouting on the outer side of the synchronous grouting layer and wrapping grouting behind the synchronous grouting layer wall; S3: Layered insertion of the grouting strip behind the wall is performed to form a grouting strip wrapped with the insertion tube.

[0045] Prior to step S1, the procedure also includes: S01: Obtain design data, settlement deformation monitoring data, and detection data such as voids behind tunnel segments from existing subway tunnels in abnormal settlement sections.

[0046] S02: Based on the above detection data, a numerical simulation model is established to numerically invert the abnormal settlement of existing subway tunnels. Through numerical calculations, design and construction parameters such as grouting hole layout, grouting parameters, grouting sequence, preset targets for single grouting, and the final settlement control standards for the tunnel are determined. Specifically, the layout of transverse and longitudinal grouting holes in the existing subway tunnel in the settlement section is designed, and a numerical simulation module for grout diffusion-solidification within the tunnel is built to simulate, determine, and optimize grouting-related parameters.

[0047] In another embodiment, these parameters can also be obtained through field testing.

[0048] Further, step S1 specifically includes: Grouting should be used to stop leaks at joints and bolt holes. Leaks above the track bed should be stopped by grouting, while leaks below the track bed should be sealed by grouting. For joint leaks, first, drill a vertical hole across the joint where there is no visible water seepage around the leak, extending to the water-swellable sealing strip or elastic gasket. Create a grout blockage point within the hole using a cement-water glass double-liquid grout. Then, within the area enclosed by the grout blockage point, embed grouting nozzles across the joint using quick-setting polymer mortar, seal the joint with epoxy putty, and inject elastic epoxy resin grout. For bolt hole leaks, drill angled holes to the bolt holes, inject polyurethane grouting material to stop the leak, and then seal and tighten the bolts. To address water leakage below the track bed, drilling was carried out according to the grouting hole layout design. The hole depth was determined by drilling to the pipe surface. Early-strength cement was used to seal the holes and embed the pipe. After solidification, hydrophilic epoxy resin was applied according to the hole sequence. The grouting end pressure was 0.4 MPa. When the end pressure was reached, the pressure was stabilized for 5 minutes to end the grouting.

[0049] Furthermore, step S2 specifically includes the following steps: S21: Compensation grouting is performed using pre-reserved grouting holes on the tunnel lining segments. The grouting volume and pressure are determined based on the current status of the synchronous grouting layer near the grouting holes. The core objective is to fill the voids in the synchronous grouting layer, compact the pores of the grouting layer, and restore the constraint capacity of the synchronous grouting layer on the tunnel lining segments.

[0050] S22: Remove the plain concrete track bed at the location of the newly added vertical grouting holes. The newly added vertical grouting holes are located at the center of the segment circumference, at positions 5 and 7 where the track bed connects to the segment.

[0051] S23: Drill holes in the tunnel segments and install the orifice pipes. The specific process includes drilling, cleaning the holes, applying anchoring adhesive, and installing the orifice pipes, followed by installing ball valves and blowout preventers. The blowout preventer used in this project is a mature existing technology, and its core function is to prevent water and sand inrush, avoiding loss of external sand layers and water and sand inrush accidents.

[0052] S24: Drill through the remaining tunnel segments and simultaneously grout the layer. The specific construction process and requirements are as follows: Use a water drill to open the hole, control the drilling speed during the drilling process, and reduce disturbance to the tunnel segment structure and the surrounding water-rich sand layer; after drilling through, withdraw the drill rod to between the ball valve and the blowout preventer, immediately close the ball valve, then open the blowout preventer's pressure relief ball valve to release pressure, and finally pull out the drill rod to prevent water and sand inrush; this drilling operation should be carried out in a timely manner before grouting construction, and should not be carried out too early to avoid prolonged exposure of the borehole and loss of the surrounding sand layer.

[0053] S25: Perform synchronous and symmetrical backfill grouting at the grouting holes at points 5 and 7 of the same segment. After the drill rod is pulled out, connect the grouting pipeline in time, close the pressure relief ball valve of the blowout preventer, pressurize the blowout preventer to the design value (slightly higher than the external water and soil pressure) through the grouting pipeline, and then open the ball valve to perform backfill grouting. The above operations should be carried out synchronously at the grouting holes at points 5 and 7 of the same ring segment. Grouting pipelines branched off from the same grouting device should be used to ensure synchronous and symmetrical backfill grouting.

[0054] Furthermore, step S3, which involves layered grouting outside the synchronous grouting layer to form a grouting band wrapped with grouting tubes, specifically includes the following steps: S31: Based on the single-time grouting preset target determined in step S02, perform synchronous symmetrical pipe insertion and grouting at the grouting holes at points 5 and 7 of the segment to form a pipe-wrapped grouting band. The specific construction process and requirements are as follows: Perform synchronous symmetrical pipe insertion and grouting at the grouting holes at points 5 and 7 of the same ring segment. First, use a drilling and grouting machine to repeatedly insert pipes and grout at 0-50cm behind the synchronous grouting layer of the segment until the grouting volume significantly decreases or the grouting pressure significantly increases, forming the first pipe-wrapped grouting band. Then, use a drilling and grouting machine to repeatedly insert pipes and grout at 50cm-100cm behind the synchronous grouting layer of the segment until the grouting volume significantly decreases or the grouting pressure significantly increases, forming the second pipe-wrapped grouting band. If the single-time grouting preset target has not yet been achieved, perform repeated pipe insertion and grouting in multiple segments at the non-dense locations behind the synchronous grouting layer of the segment until the single-time grouting preset target is achieved. S32: When the segment rise is determined to have reached the preset target for a single grouting operation, grouting is stopped, the grouting drill rod of the integrated drilling and grouting machine is removed, and the ball valve is closed. The preset target for a single grouting operation is controlled by three indicators: grouting pressure, grouting volume, and segment rise. Once any one of these indicators reaches its control value, the preset target is achieved. The grouting pressure, grouting volume, and segment rise can be determined using numerical simulation.

[0055] S33: Once the final grouting conditions are met, remove the ball valve and seal the vertical grouting hole.

[0056] Since controlling settlement in existing subway tunnels typically requires the coordination of different tunnel segments, grouting is necessary for each segment. Therefore, the following steps are included after step S32: S321: Based on the grouting sequence, single grouting preset target and tunnel final settlement control standard determined in step S02, evaluate and determine the next segment that needs grouting. S322: Perform synchronous symmetrical grouting and wrapping at the grouting holes at points 5 and 7 of the next segment until the segment 11 reaches the preset target for a single grouting. Specifically, grouting construction of different segments is carried out sequentially. After each segment is grouted, the lifting of the grouting ring and surrounding segments needs to be monitored and analyzed. If the settlement control does not meet the design requirements, additional grouting is required; only if the design requirements are met can the grouting construction of the next segment be carried out.

[0057] The specific conditions for achieving the final grouting in step S33 are as follows: all segments requiring grouting achieve the corresponding single grouting preset target, and the overall settlement control reaches the final settlement control standard.

[0058] Based on the above steps, permanent repairs will be carried out on newly emerging water leakage and track bed gaps, the track bed cut-off locations will be permanently restored, the track geometry will be measured, and alignment and slope adjustments will be made if necessary.

[0059] The above figures are merely illustrative of the processes included in the method according to exemplary embodiments of this application and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal order of these processes. Furthermore, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0060] It should be understood that this application is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A protective device for controlling settlement in existing subway tunnels with sand layers, characterized in that: The subway tunnel includes segments (11), pre-reserved grouting holes (12) in the segments, evacuation platform (13), contact rail (14), steel rail (15) and track bed (16). The protective device for controlling settlement of existing subway tunnels in sandy layers includes: synchronous grouting layer wrapped grouting tape and pipe wrapped grouting tape, wherein the synchronous grouting layer wrapped grouting tape is composed of synchronous grouting layer compensation grouting and wall-mounted wrapped grouting tape (32).

2. The protective device for controlling settlement in existing subway tunnels with sand layers according to claim 1, characterized in that: The synchronous grouting layer compensation grouting is performed by filling the voids (22) and the loose areas (23) of the synchronous grouting layer (21) through the reserved grouting holes (12) of the pipe segment. The wall-mounted wrapping grouting strip (32) is formed by wrapping grouting through newly opened grouting holes.

3. The protective device for controlling settlement in existing subway tunnels with sand layers according to claim 1, characterized in that: The grouting band is formed by synchronously and symmetrically inserting pipes to wrap the grouting holes at points 5 and 7 of the same ring segment. First, the grouting band behind the synchronous grouting layer of the segment is repeatedly inserted and grouted using a drilling and grouting machine from 0 to 50 cm until the grouting volume is significantly reduced or the grouting pressure is significantly increased, forming the first grouting band (33). Then, the grouting band behind the synchronous grouting layer of the segment is repeatedly inserted and grouted using a drilling and grouting machine from 50 cm to 100 cm until the grouting volume is significantly reduced or the grouting pressure is significantly increased, forming the second grouting band (34). If the preset target for a single grouting has not been achieved, multiple insertion and grouting operations are performed on the non-dense areas behind the synchronous grouting layer of the segment until the preset target for a single grouting is achieved.

4. The protective device for controlling settlement in existing subway tunnels with sand layers according to claim 3, characterized in that: Grouting construction of different tunnel segments is carried out in sequence according to the pre-determined grouting sequence, the preset target for each grouting, and the final settlement control standard of the tunnel, until the settlement control of the tunnel reaches the final settlement control standard.

5. The protective device for controlling settlement in existing subway tunnels with sand layers according to claim 4, characterized in that: The pre-determined grouting sequence, single grouting target, and final settlement control standard of the tunnel are obtained through numerical inversion or field tests based on existing subway tunnel design data, settlement deformation, and void monitoring data behind the tunnel segments in the abnormal settlement section.

6. A method for controlling settlement in existing subway tunnels with sand layers, characterized in that: The protection method is applied to the protection device for controlling settlement in existing subway tunnels with sand layers as described in any one of claims 1-5, and the protection method includes the following steps: S1: Grouting is performed to stop water leakage at the joints of the pipe segments and bolt holes; S2: Perform compensating grouting on the outer side of the synchronous grouting layer and wrapping grouting behind the synchronous grouting layer wall; S3: Layered grouting is performed on the outside of the synchronous grouting layer to form a grouting band wrapped by the grouting tube.

7. The protection method for controlling settlement in existing subway tunnels with sand layers according to claim 6, characterized in that: Before step S1, the following is also included: S01: Obtain design data, settlement deformation monitoring data, and cavities behind tunnel segments in the abnormal settlement section of the existing subway tunnel. S02: Based on the above monitoring data, establish a numerical simulation model to perform numerical inversion on the abnormal settlement of existing subway tunnels. Through numerical calculation, determine the grouting hole layout, grouting parameters, grouting sequence, preset target for single grouting, and the final settlement control standard design and construction parameters of the tunnel.

8. The protection method for controlling settlement in existing subway tunnels with sand layers according to claim 6, characterized in that: Step S2 specifically includes the following steps: S21: Compensation grouting is performed using the pre-reserved grouting holes on the tunnel segments; S22: Remove the plain concrete track bed at the location of the newly added vertical grouting holes; S23: Drill holes in the tunnel lining segments and install the borehole pipes; S24: Drill through the remaining segments and simultaneously inject grouting layer; S25: Perform synchronous symmetrical backwall grouting at the grouting holes at points 5 and 7 of the same segment.

9. The protection method for controlling settlement in existing subway tunnels with sand layers according to claim 7, characterized in that: Step S3, which involves wrapping the grouting strip behind the wall and performing layered insertion to form the insertion tube wrapped with the grouting strip, specifically includes the following steps: S31: Based on the single grouting preset target determined in step S02, perform synchronous symmetrical pipe insertion and grouting at the grouting holes at points 5 and 7 of the segment. S32: When it is determined that the segment lifting has reached the preset target for a single grouting, stop grouting, remove the grouting drill rod of the drilling and grouting machine, and close the ball valve; S33: Once the final grouting conditions are met, remove the ball valve and seal the vertical grouting hole.

10. The protection method for controlling settlement in existing subway tunnels with sand layers according to claim 9, characterized in that: The following steps are included after step S32: S321: Based on the grouting sequence, single grouting preset target and final settlement control standard design construction parameters determined in step S02, determine the next segment that needs grouting; S322: Perform synchronous symmetrical grouting by inserting pipes and wrapping the grouting holes at points 5 and 7 of the next segment until the segment reaches the preset target for a single grouting. The specific conditions for achieving the final grouting in step S33 are as follows: all segments requiring grouting achieve the corresponding single grouting preset target, and the overall settlement control reaches the final settlement control standard.

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