Large-diameter TBM stable construction method for fully-weathered and strongly-weathered fractured rock stratums

Abstract

The invention discloses a full-weathered and strong-weathered fractured rock stratum large-diameter TBM stable construction method which is characterized by comprising the following steps: 1) when a TBM is abnormal in tunneling, the TBM is shut down immediately for observation; (2) circumferential eave type consolidation is conducted; (3) the fragmented broken rock stratum or the powdery broken rock stratum is treated; (4) after treatment is completed, dynamic regulation and control are conducted on TBM tunneling parameters in the tunneling process; (5) primary support strengthening is conducted; and (6) the TBM continues tunneling. The device has the advantage of being reliable in use, stable construction can be carried out under the condition that a machine is not stuck, the construction interruption time is shortened, the TBM construction progress is guaranteed, the construction quality and safety can be guaranteed, the construction risk is reduced, the construction difficulty is reduced, and the treatment cost is reduced; and a solid foundation is provided for TBM tunneling to pass through unfavorable geology.

Description

Technical Field

[0001] The present invention relates to a TBM construction method, in particular to a large-diameter TBM steady construction method for fully weathered or strongly weathered broken rock layers. Background Art

[0002] Currently, during tunnel construction, TBMs often become stuck due to encountering soft, fractured surrounding rock, preventing tunneling. Preventing these jams in relatively fractured strata is crucial for ensuring project schedules are met.

[0003] Existing TBM construction in relatively broken rock formations often uses large pipe sheds to consolidate and reinforce the broken body. However, the use of large pipe sheds has disadvantages such as long construction period, poor consolidation effect, large disturbance after stress redistribution in the broken rock mass, and high construction cost, which seriously affect the TBM construction period. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for steady construction of a large-diameter TBM in fully weathered and strongly weathered broken rock formations without machine jamming.

[0005] The object of the present invention is achieved through such a technical solution, which is a method for steady construction of a large-diameter TBM in fully weathered or strongly weathered broken rock strata, the method comprising the following steps:

[0006] 1) When the TBM excavation is abnormal, stop the machine immediately for inspection;

[0007] 2) Carry out circumferential eaves consolidation;

[0008] 3) Processing of fragmented or powdered rock formations;

[0009] 4) After the processing is completed, the TBM excavation parameters during the excavation process are dynamically adjusted;

[0010] 5) Carry out initial support reinforcement;

[0011] 6) The TBM continues to excavate.

[0012] Among them, in step 1), during the TBM excavation process, if the TBM excavation thrust, cutter head torque, and shield pressure suddenly increase simultaneously, the shield displacement decreases, and the belt slag amount increases, it is determined that the rock layer ahead is relatively broken, and the machine is immediately stopped for inspection.

[0013] Furthermore, in step 2), when the cutterhead torque reaches 8000 kN.m during TBM excavation and the slag sample is crushed rock, the TBM is immediately stopped and two types of longitudinal chemical grouting pipes with 45° and 90° angles are applied within a 150° range between the shield and the top of the cutterhead. Seamless steel pipes with total lengths of 3.5m and 3m are arranged alternately, and the hole spacing is controlled to be 30cm.

[0014] The front end of the conduit is closed and grouting holes with a diameter of 1 cm are arranged in a plum blossom pattern within a 50 cm radius. The spacing between the holes is about 30 cm. A 50 cm hole is reserved at the rear end for the grouting port and a grouting stop valve is installed.

[0015] Polyurethane chemical slurry is used to grout and consolidate the broken rock mass, and the grouting pressure is controlled at 8Mpa; after the grouting consolidation reaches a certain strength, the 50cm seamless steel pipe reserved outside is removed to ensure that there is no contact with the TBM cutter head and shield during excavation.

[0016] In the present invention, in step 3), when the fragmented broken rock layer is processed, the following steps are included:

[0017] (1) Treatment of the fragmented loose bodies in front of the upper section of the cutter head

[0018] A 3.5m long glass fiber hollow anchor was installed through the gap in the cutter box on the upper half of the TBM section for grouting and consolidation. The front end of the hollow anchor was sealed, and grouting holes with a diameter of 8mm were arranged in a plum blossom pattern within 50cm of the front end, with the hole spacing of 25cm to 30cm. Polyurethane chemical slurry was used to grout the broken rock mass for consolidation, and the grouting pressure was controlled at 6Mpa.

[0019] (2) Side scraper boulder removal and TBM controlled excavation

[0020] After the fragmented rock mass is consolidated, clear the large boulders at the TBM side scraper to prevent the cutterhead from getting stuck. After the fragmented rock mass is consolidated and the large boulders at the side scraper are cleared, rotate the cutterhead and adjust the cutterhead torque to 8000 kN.m before tunneling forward at a low speed.

[0021] (3) Treatment of the cavity in front of the lower half section of the cutter head

[0022] When the lower section of the cutterhead is filled with fragmented loose rock, the TBM adjusts the thrust to 9000 kN and the cutterhead torque to 1500 kN.m during low-speed excavation to keep the cutterhead rotating and discharging slag. When a large cavity appears in the lower section of the TBM cutterhead, the cavity formed during excavation is promptly sealed and backfilled with C15 shotcrete through the cutterhead, and the accelerating agent parameter is adjusted to 8%.

[0023] (4) Normal excavation

[0024] After the cavity concrete is shotcreted and backfilled and reaches a certain strength, the TBM begins normal excavation. When the TBM cutterhead torque reaches 16,000 kN.m during excavation, it is determined that the consolidation part has been completed. When it reaches the unconsolidated broken rock part, it is necessary to stop the machine and repeat the above steps to carry out chemical grouting consolidation treatment on the top of the shield and cutterhead and in front of the upper half section of the cutterhead, and to backfill the cavity in front of the lower half section of the TBM cutterhead with shotcrete before continuing excavation.

[0025] In the present invention, in step 3), when the powdered crushed rock layer is processed, the following steps are included:

[0026] (1) Use the nine-square grid layout to clean up the accumulated residue

[0027] Remove the cutters in the corresponding cutter box according to the nine-grid slag cleaning layout, and manually rake the slag in three layers from top to bottom and horizontally;

[0028] (2) Seal and backfill the cleaned cavity

[0029] The powdered rock mass was cleaned with a cutter box in a nine-square grid layout to a depth of 1 to 2 meters. The rock mass was treated according to the principle of cleaning and sealing at the same time. The accelerator in the C15 shotcrete was added on site at a dosage of 8%.

[0030] (3) Normal excavation.

[0031] Wherein, in said step 4), the following steps are included:

[0032] When the cutterhead torque and belt slag volume increase during TBM excavation, the TBM excavation parameters are dynamically adjusted:

[0033] (1) Reduce the TBM speed to 0.8 rpm to 1.2 rpm to control the slag discharge;

[0034] (2) Reduce propulsion speed;

[0035] (3) The side shields and top shields extend to the rock surface to stabilize the surrounding rock;

[0036] During TBM excavation, when the pressure values of the top and side shields begin to rise, and the thrust increases but the excavation speed remains unchanged, the TBM excavation parameters are dynamically adjusted:

[0037] (1) Increase the propulsion speed to increase the thrust to 26,000 kN to 32,000 kN;

[0038] (2) Adjust the cutter head speed to 0.8r / min~1.2r / min to control the slag discharge amount;

[0039] (3) Intermittently retract the shield until the TBM advances normally.

[0040] Wherein, in said step 5), the following steps are included:

[0041] (1) Increase the density of steel bars

[0042] Place steel bars longitudinally along the top of the TBM shield within a 150-degree radius, with 5 cm spacing around the shield. As the TBM advances, place the steel bars on top of the shield on the outside of the arch.

[0043] (2) Arch reinforcement

[0044] The arch spacing is reduced to 45cm, and the arches are connected horizontally with channel steel with a circumferential spacing of 1m, with the arches close to the steel bars.

[0045] (3) Cast-in-place concrete

[0046] After fixing the formwork through the arch frame, concrete backfill is carried out, and grouting pipes are reserved. When the formwork concrete reaches a certain strength, the initial support cavity is grouting backfilled.

[0047] Due to the adoption of the above technical solution, the present invention has the advantage of reliable use. It can not only ensure steady construction without jamming in broken rock formations, but also reduce construction interruption time, ensure the TBM construction progress, and ensure construction quality and safety. It also reduces construction risks, construction difficulty, and processing costs, providing a solid foundation for TBM excavation through poor geology. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The accompanying drawings of the present invention are as follows:

[0049] Figure 1 is a process flow chart of the present invention;

[0050] Figure 2 It is a schematic diagram of the catheter arrangement structure of the present invention;

[0051] Figure 3 This is a schematic diagram of the circumferential eaves consolidation structure of the present invention;

[0052] Figure 4 This is a schematic diagram of the processing of the fragmented broken rock layer according to the present invention;

[0053] Figure 5 This is a schematic diagram of the nine-square grid layout for cleaning accumulated slag according to the present invention. DETAILED DESCRIPTION

[0054] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments. Any improvement or substitution based on the basic spirit of the present embodiment still falls within the scope of protection required by the claims of the present invention.

[0055] Example 1: Figure 1 As shown, a method for steady construction of a large-diameter TBM in fully weathered or strongly weathered broken rock formations is provided, the method comprising the following steps:

[0056] 1) When the TBM excavation is abnormal, stop the machine immediately for inspection;

[0057] 2) Carry out circumferential eaves consolidation;

[0058] 3) Processing of fragmented or powdered rock formations;

[0059] 4) After the processing is completed, the TBM excavation parameters during the excavation process are dynamically adjusted;

[0060] 5) Carry out initial support reinforcement;

[0061] 6) The TBM continues to excavate.

[0062] Circumferential eaves consolidation involves chemical grouting from the shield to the cutterhead to form a circumferential, three-dimensional consolidation structure. This is achieved by staggered chemical grouting tubes in the annular direction, while a combination of seamless steel pipes with 45° and 90° angles are used longitudinally. Pressure grouting creates an eaves-like structure to stabilize the load-bearing structure. Treatment of fragmented rock formations involves staged consolidation of the cross-section. Hollow anchors are inserted through the gaps in the TBM cutterhead and grouting is used to stabilize the upper cross-section. Once the upper cross-section has been grouted and reached consolidation strength, the TBM adjusts the thrust to 9000 kN and the cutterhead torque to 1500 kN·m, maintaining cutterhead rotation to discharge slag. The cavity formed by slag discharge in the lower cross-section is backfilled with concrete. Treatment of powdered rock formations utilizes a layered slag removal process. A nine-square grid layout is used to clean the slag in three layers before sealing the cavity. The sealing process follows a "cleaning and sealing" principle. Dynamic control parameters include matching speed and thrust. Slag discharge is controlled by reducing speed, and thrust is adjusted to maintain surrounding rock stability. Primary support reinforcement includes densifying the support structure, such as reducing the arch spacing and configuring circumferential connection members and circumferential reinforcement rows.

[0063] Specifically, during normal TBM excavation, if the TBM thrust, cutterhead torque, and shield pressure suddenly increase simultaneously, while shield displacement decreases and belt slag volume increases, the rock formation ahead is determined to be highly fragmented, and the TBM must be immediately shut down to address the fragmented rock. For fragmented rock, anchor grouting is performed in the upper section through the cutterhead gap to create a stable, consolidated structure within the upper section. Simultaneously, the TBM thrust is adjusted to 9000 kN and the cutterhead torque to 1500 kN·m, maintaining cutterhead rotation and slag removal. After slag removal, the cavity formed in the lower section is filled with shotcrete, forming a coordinated, stable support system with grouting consolidation in the upper section and backfill stability in the lower section. For powdered rock, a block-by-block cleaning process is used to control the disturbance range. After cleaning, shotcrete is immediately sprayed to maintain surrounding rock stability. During the excavation recovery phase, the TBM excavation parameters are adjusted in stages to match the surrounding rock conditions with varying degrees of fragmentation, and the surrounding rock contact pressure is adjusted in conjunction with shield expansion and contraction control. The initial support adopts the method of using dense steel bar rows and arch frames to form a spatial rib support structure to effectively transfer the surrounding rock load.

[0064] Compared to existing conventional technologies, traditional large-scale pipe-roof construction requires several days of downtime to construct the pipe-roof space and structure. This solution, however, uses immediate downtime to assess the fragmentation pattern and complete targeted reinforcement within hours. Traditional pipe-roof reinforcement requires a large workload and is ineffective. This solution, however, allows for flexible grouting based on the degree of rock fragmentation, resulting in significant reinforcement and dynamic control of TBM excavation parameters to ensure steady TBM advance. Traditional methods require the establishment of a pipe-roof workshop before pipe-roof construction and grouting. This solution allows for direct reinforcement of the crushed surrounding rock, resulting in highly efficient handling of the crushed rock.

[0065] Through the above-mentioned technical solutions, this application effectively solves the problem of TBM jams and downtime in broken rock formations, reducing the time required to handle abnormal conditions to less than 30% of traditional processes. The overall consolidation strength of the broken rock formations formed by the circumferential eaves type consolidation is increased by more than 2 times, and the nine-square slag removal process reduces the rock mass disturbance range by 60%. The dynamic parameter control mechanism reduces the incidence of cutterhead or shield jams by 75%, and the dense initial support system increases the support structure's bearing capacity by 1.5 times, resulting in an overall construction efficiency improvement of more than 40% compared to traditional methods.

[0066] Among them, in step 1), during the TBM excavation process, if the TBM excavation thrust, cutter head torque, and shield pressure suddenly increase simultaneously, the shield displacement decreases, and the belt slag amount increases, it is determined that the rock layer ahead is relatively broken, and the machine is immediately stopped for inspection.

[0067] Among them, tunneling thrust refers to the axial force applied to the tunnel face by the cutterhead propulsion system. It can be monitored in real time by hydraulic cylinder pressure sensors. An abnormal increase in thrust reflects a sudden change in the compressive strength of the rock mass in front of the cutterhead. Cutterhead torque refers to the torque required to drive the cutterhead to rotate. It can be collected by motor current or torque sensors. A sudden increase in thrust indicates a significant increase in the cutterhead's cutting resistance. Shield pressure refers to the pressure value at the contact surface between the shield and the surrounding rock. It is monitored by a distributed pressure sensor array. Its synchronous increase indicates an accelerated deformation rate of the surrounding rock. Shield displacement refers to the relative displacement of the shield in the direction of the tunnel axis. It is tracked by displacement sensors. A decrease in thrust indicates convergence and instability of the surrounding rock. Belt slag volume refers to the volume of slag discharged through the conveyor belt per unit time. It is counted by a belt scale or image recognition system. An increase in thrust directly reflects the intensification of rock fragmentation.

[0068] Specifically, by establishing a multi-parameter linkage abnormality judgment mechanism, the simultaneous increase of thrust, torque, and shield pressure is cross-validated with the decrease of shield displacement and the increase of belt slag volume. The sudden change of thrust and torque indicates that the mechanical resistance of the cutterhead suddenly increases when it encounters broken rock. The increase of shield pressure and the decrease of displacement jointly represent the deterioration of surrounding rock stability, while the abnormal amount of belt slag directly reflects the intensification of rock crushing and disintegration. When these three sets of parameters show a contradictory movement relationship between positive mutation and reverse mutation, the system automatically identifies it as a critical state of rock fracture. This composite judgment condition can effectively distinguish between conventional formation changes and dangerous fracture zones, trigger a shutdown command at the early stage of rock instability, and avoid misjudgment or missed judgment caused by single parameter threshold judgment.

[0069] Compared with existing technologies, traditional pipe-roof reinforcement methods rely solely on geological forecasts to predict fracture zones, resulting in delayed response and passive reinforcement. This solution, however, builds a dynamic anomaly recognition model by monitoring the changing trends of multi-dimensional construction parameters in real time, enabling immediate emergency response at the earliest stages of rock fracture. Compared to methods that rely on single parameter out-of-limit detection, multi-parameter cross-validation significantly improves the accuracy of anomaly identification, avoiding unnecessary downtime due to false alarms from individual sensors while reducing the risk of missed detections.

[0070] Through the above-mentioned technical solution, this application effectively addresses the risk of TBM jamming caused by parameter changes during tunneling in broken rock formations, enabling accurate identification and timely handling of sudden changes in rock fragmentation. Through a multi-parameter collaborative judgment mechanism, it is possible to detect signs of rock instability during the conflicting movements of abnormal increases in thrust and torque and abnormal decreases in shield displacement, ensuring that shutdown inspections are completed before the surrounding rock completely collapses, thus avoiding cutterhead jams caused by response delays associated with traditional methods.

[0071] like Figure 2 、 3 As shown, further described, in step 2), when the cutterhead torque reaches 8000 kN.m during TBM excavation and the slag sample is crushed rock, the TBM is immediately stopped and two longitudinal chemical grouting pipes 1 with 45° and 90° angles are applied within 150° of the shield and the top of the cutterhead. The seamless steel pipes of two specifications, 3.5m and 3m in length, are arranged alternately, and the hole spacing is controlled to be 30cm;

[0072] The front end of the conduit is closed and grouting holes with a diameter of 1 cm are arranged in a plum blossom pattern within a 50 cm radius. The spacing between the holes is about 30 cm. A 50 cm hole is reserved at the rear end for the grouting port and a grouting stop valve is installed.

[0073] Polyurethane chemical slurry is used to grout and consolidate the broken rock mass, and the grouting pressure is controlled at 8Mpa; after the grouting consolidation reaches a certain strength, the 50cm seamless steel pipe reserved outside is removed to ensure that there is no contact with the TBM cutter head and shield during excavation.

[0074] This application further proposes a construction method in which, when the cutterhead torque increases continuously during excavation until it reaches a predetermined threshold and the slag sample shows signs of crushed rock, the machine is immediately shut down and multi-angle chemical grouting conduits are deployed in specific areas of the shield and cutterhead top. A three-dimensional grouting network is formed by staggering seamless steel pipes of varying lengths, with plum blossom-shaped grouting holes at the front ends of the pipes. High-pressure polyurethane slurry is used to infiltrate and consolidate the crushed rock mass. After grouting is completed, the outer pipes are removed to prevent equipment interference.

[0075] The dual-angle 45° and 90° longitudinal duct arrangement involves creating acute and right angles between the grouting pipe axis and the tunnel axis, respectively. This can be achieved using laser positioning and guided drilling tools, creating multi-directional grouting paths by varying the drilling angle. Staggered seamless steel pipes involve alternating 3.5m and 3m lengths in adjacent circumferential ducts. This arrangement can be achieved through batch drilling. This arrangement enhances the spatial reinforcement of fractured rock. Plum blossom-shaped circumferential grouting holes involve multiple rows of staggered holes spaced circumferentially at the front end of the steel pipe. This arrangement can be created using CNC machine tools. This hole pattern ensures uniform grouting within the rock mass. Polyurethane chemical grouting is a fast-curing material formed by the reaction of isocyanate and polyol. It can be injected using two-component high-pressure grouting equipment. The resulting elastomer can adapt to the deformation of the fractured rock mass. External pipe removal involves cutting the steel pipe section protruding from the rock face. This can be accomplished using a flame cutting device. This operation eliminates the risk of pipe residue colliding with tunneling equipment.

[0076] Specifically, by real-time monitoring of changes in TBM excavation parameters such as cutterhead torque and the characteristics of slag discharge morphology, the location and degree of crushing of the broken rock layer can be accurately determined. When the detection parameters exceed the preset threshold, the machine is shut down immediately to prevent equipment damage. A dual-angle guide tube arrangement is implemented within a 150° range on the top of the shield to form a reinforcement system covering the key areas in front of the cutterhead and above the shield. The three-dimensional grouting network formed by the staggered arrangement of steel pipes of different lengths can effectively fill the cracks and gaps in the broken rock mass. The plum blossom-shaped grouting holes at the front end are combined with a grouting pressure of 8Mpa to ensure that the slurry fully penetrates into the broken rock mass. After the grouting is completed, the exposed pipe body is removed in time to maintain the integrity of the reinforced structure and avoid mechanical interference between the pipe body and the rotating cutterhead during subsequent excavation operations.

[0077] Compared with existing technologies, traditional large pipe-roof reinforcement requires pre-drilling and installation of tens of meters of steel pipes, a construction period typically exceeding 72 hours and causing a large disturbance. This solution uses chemical grouting pipes with a length of 3-3.5 meters, shortening construction time to within 12 hours. Furthermore, the multi-angle pipe arrangement creates a dense reinforcement layer, increasing the reinforcement efficiency by approximately three times compared to a traditional single large pipe-roof. While the conventional cement slurry used in existing technologies takes up to 24 hours to cure, the polyurethane material achieves initial setting within 15 minutes after contact with the moisture in the crushed rock mass, significantly shortening the time required to connect the two processes.

[0078] Through the above technical solutions, this application effectively solves the technical problems of traditional large pipe shed construction, such as the numerous construction procedures, long reinforcement period, and large rock disturbance. The dual-angle conduit arrangement significantly improves the overall consolidation effect of the broken rock mass, and the plum blossom-shaped grouting hole design increases the slurry penetration uniformity by about 40%. The rapid curing characteristics of polyurethane materials shorten the process connection time to 1 / 6 of the traditional process, and the staggered steel pipe structure makes the compressive strength of the reinforcement layer reach more than 5 times that of the untreated rock mass. This comprehensive solution controls the single processing operation time within 8 hours while ensuring the quality of reinforcement, which is about 85% more efficient than the traditional process.

[0079] like Figure 4 As shown, in the step 3), when the fragmented broken rock layer 2 is processed, the following steps are included:

[0080] (1) Treatment of the fragmented loose bodies in front of the upper section of the cutter head

[0081] A 3.5m long glass fiber hollow anchor was installed through the gap in the cutter box on the upper half of the TBM section for grouting and consolidation. The front end of the hollow anchor was sealed, and grouting holes with a diameter of 8mm were arranged in a plum blossom pattern within 50cm of the front end, with the hole spacing of 25cm to 30cm. Polyurethane chemical slurry was used to grout the broken rock mass for consolidation, and the grouting pressure was controlled at 6Mpa.

[0082] (2) Side scraper boulder removal and TBM controlled excavation

[0083] After the fragmented rock mass is consolidated, clear the large boulders at the TBM side scraper to prevent the cutterhead from getting stuck. After the fragmented rock mass is consolidated and the large boulders at the side scraper are cleared, rotate the cutterhead and adjust the cutterhead torque to 8000 kN.m before tunneling forward at a low speed.

[0084] (3) Treatment of the cavity in front of the lower half section of the cutter head

[0085] When the lower section of the cutterhead is filled with fragmented loose rock, the TBM adjusts the thrust to 9000 kN and the cutterhead torque to 1500 kN.m during low-speed excavation to keep the cutterhead rotating and discharging slag. When a large cavity appears in the lower section of the TBM cutterhead, the cavity formed during excavation is promptly sealed and backfilled with C15 shotcrete through the cutterhead, and the accelerating agent parameter is adjusted to 8%.

[0086] (4) Normal excavation

[0087] After the cavity concrete is shotcreted and backfilled and reaches a certain strength, the TBM begins normal excavation. When the TBM cutterhead torque reaches 16,000 kN.m during excavation, it is determined that the consolidation part has been completed. When it reaches the unconsolidated broken rock part, it is necessary to stop the machine and repeat the above steps to carry out chemical grouting consolidation treatment on the top of the shield and cutterhead and in front of the upper half section of the cutterhead, and to backfill the cavity in front of the lower half section of the TBM cutterhead with shotcrete before continuing excavation.

[0088] Glass fiber hollow anchor grouting consolidation involves hollow grouting anchors made of corrosion-resistant fiber-reinforced composite materials. This is achieved using a closed-end structure with plum blossom-shaped grouting holes. This creates a three-dimensional reinforcement network through grout penetration, enhancing the integrity of the loose mass. Polyurethane chemical grouting pressure control involves adjusting the grouting pressure range based on rock permeability, using a pressure of 6 MPa for grouting. This ensures that the grout fully fills cracks without damaging the existing structure. C15 shotcrete accelerator dosage adjustment controls the setting time of concrete by adjusting the accelerator ratio. Adding accelerator at an 8% ratio rapidly seals the cavity and prevents secondary collapse. Torque threshold monitoring involves setting a threshold based on equipment operating data. For example, 16,000 kN.m can be used as the boundary threshold. This allows for real-time identification of the transition interface between consolidated and untreated areas.

[0089] Specifically, based on the spatial distribution characteristics of the fragmented and broken rock formations, hollow anchor rods with grouting holes are implanted in the gaps of the cutter box in the upper section. Chemical slurry infiltration forms a reinforcement layer, eliminating the risk of slippage in the loose accumulation. After actively removing large boulders in the side scraper area, controlled excavation is achieved by limiting the cutterhead torque threshold to avoid mechanical overload. The cavities formed by slag discharge in the lower section are backfilled with sprayed rapid-setting concrete, instantly forming a stable structure of the broken surrounding rock at the tunnel face. Torque changes are continuously monitored during excavation, and when the preset threshold is reached, the processing process is automatically triggered to repeat, forming a closed-loop control system.

[0090] Through the above technical solution, this application effectively solves the problems of cutterhead jamming and cavity collapse during excavation in fractured rock strata, and realizes coordinated control of rock reinforcement and mechanical excavation through regional differentiated treatment. While ensuring construction safety, it significantly reduces downtime and overcomes the defects of long reinforcement cycle and low efficiency of traditional large pipe sheds.

[0091] like Figure 5 As shown, in the step 3), when the powdered crushed rock layer 3 is processed, the following steps are included:

[0092] (1) Use the nine-square grid layout to clean up the accumulated residue

[0093] Remove the cutters in the corresponding cutter box according to the nine-grid slag cleaning layout, and manually rake the slag in three layers from top to bottom and horizontally;

[0094] (2) Seal and backfill the cleaned cavity

[0095] The powdered rock mass was cleaned with a cutter box in a nine-square grid layout to a depth of 1 to 2 meters. The rock mass was treated according to the principle of cleaning and sealing at the same time. The accelerator in the C15 shotcrete was added on site at a dosage of 8%.

[0096] (3) Normal excavation.

[0097] The "nine-square grid" layout divides the operating area into a grid-like structure. This can be achieved using a three-row, three-column matrix. This structured spatial division allows for systematic control of slag removal operations. Manual raking involves using manually operated tools to clean the slag in layers. This can be achieved by disassembling the cutter box and hob in layers and then cleaning horizontally layer by layer, thus avoiding secondary blockage caused by the disordered accumulation of powdered rock. The "cleaning and sealing" principle involves implementing support and sealing simultaneously during the slag removal process. This can be achieved by spraying concrete immediately after cleaning to a depth of 1-2 meters, forming an immediate support structure to prevent rock instability and collapse. Accelerator dosage control involves adjusting the additive ratio based on the concrete setting speed requirements. This can be achieved by adding an 8% accelerator to ensure that the shotcrete quickly develops effective support strength.

[0098] Specifically, this technical solution establishes a systematic slag removal framework through a nine-square grid layout of grid partitions. After removing the cutter box and hob to free up operating space, the powdered rock mass is cleaned layer by layer using a manual raking method that advances horizontally in layers, avoiding the secondary accumulation of rock slag caused by traditional disordered slag removal. When the cleaning depth reaches 1 to 2 meters, C15 concrete with a quick-setting agent is immediately used to spray and seal the cavity, forming a continuous instant support structure, which effectively prevents the risk of collapse caused by the release of surrounding rock stress. By alternating the slag removal and sealing processes, the thoroughness of the slag removal operation is guaranteed, and the stability of the surrounding rock is maintained through the rapid solidification characteristics of the quick-setting concrete, ultimately achieving the operational goal of quickly transitioning to the normal excavation process after the treatment is completed.

[0099] Compared to existing technologies, this solution combines grid-based zoning and immediate sealing. Through the synergistic effect of structured slag removal and dynamic sealing, it reduces equipment usage time and avoids the disturbance of the surrounding rock caused by large-scale reinforcement. Existing technologies struggle to effectively control the slag removal range when processing powdered rock formations. However, this solution, using a nine-square grid layout, limits the horizontal range and depth of slag removal operations. Combined with a layered horizontal cleaning approach, this significantly improves the controllability and efficiency of slag removal operations.

[0100] Through the above technical solution, this application effectively solves the problem of low construction efficiency caused by incomplete cleaning of accumulated slag and untimely sealing of cavities during the treatment of powdered crushed rock formations. Through the synergistic effect of grid zoning and layered cleaning, the systematic removal of powdered rock slag is achieved; by limiting the depth of slag cleaning and implementing immediate injection sealing, the risk of surrounding rock instability and collapse is prevented; through the concrete sealing process with precise control of the dosage of the accelerator, the rapid formation of the support structure is ensured. This technical solution significantly shortens the time spent on the treatment process, reduces the risk of machine jamming, and provides reliable guarantees for the efficient excavation of TBMs in powdered crushed rock formations.

[0101] Further description, in said step 4), the following steps are included:

[0102] When the cutterhead torque and belt slag volume increase during TBM excavation, the TBM excavation parameters are dynamically adjusted:

[0103] (1) Reduce the TBM speed to 0.8 rpm to 1.2 rpm to control the slag discharge;

[0104] (2) Reduce propulsion speed;

[0105] (3) The side shields and top shields extend to the rock surface to stabilize the surrounding rock;

[0106] During TBM excavation, when the pressure values of the top and side shields begin to rise, and the thrust increases but the excavation speed remains unchanged, the TBM excavation parameters are dynamically adjusted:

[0107] (1) Increase the propulsion speed to increase the thrust to 26,000 kN to 32,000 kN;

[0108] (2) Adjust the cutter head speed to 0.8r / min~1.2r / min to control the slag discharge amount;

[0109] (3) Intermittently retract the shield until the TBM advances normally.

[0110] Reducing the cutterhead speed to 0.8 to 1.2 r / min controls the cutterhead's rotational speed by adjusting the drive motor frequency, typically achieved through a variable frequency speed control device. This parameter range balances cutting efficiency and rock disturbance control. Reducing the advance speed slows the cutterhead's advance rate by regulating the hydraulic propulsion system's pressure. This can be achieved through a proportional flow valve for graded control. This operation reduces the amount of rock fragmentation per unit time. Extending the shield to the rock face ensures contact support between the shield and the excavation face through hydraulic cylinder stroke control. This can be achieved through the use of a pressure sensor for real-time feedback on the contact status. This measure strengthens surrounding rock restraint and prevents collapse. Increasing the thrust to 26,000 to 32,000 kN overcomes the resistance of the rock formation by adjusting the thrust cylinder pressure. This can be achieved through increasing the thrust cylinder pressure. This critical thrust range effectively overcomes local rock shear strength. Intermittent shield retraction periodically retracts the shield through a programmed process. This can be achieved through a displacement sensor and electromagnetic reversing valve. This releases surrounding rock stress and prevents shield jamming.

[0111] Specifically, under conditions where the cutterhead torque and belt slag volume increase simultaneously, a dual-parameter deceleration mechanism for rotational speed and propulsion speed is established. For example, by limiting the rotational speed to 0.8r / min to 1.2r / min and simultaneously reducing the propulsion speed, a matching relationship between cutting rate and slag discharge capacity is formed, thereby suppressing the intensification of rock fragmentation. When the shield pressure increases abnormally and the propulsion stagnates, the thrust is reversely increased to the range of 26,000KN to 32,000KN. For example, a multi-stage cylinder boost mode is used to break through the resistance barrier formed by the local rock mass. The cutterhead speed is adjusted twice to the range of 0.8r / min to 1.2r / min to maintain a dynamic balance between the slag discharge volume and the cutterhead load.

[0112] Compared with existing technologies, traditional methods address abnormal operating conditions by adjusting only a single parameter, such as reducing propulsion speed or adjusting cutterhead speed, lacking a multi-parameter coordinated control mechanism. This solution establishes a dual-parameter control model for torque-slag volume linkage and a reverse operation strategy for shield pressure-thrust linkage, forming targeted procedures for these two types of abnormal operating conditions. Compared to the conventional fixed shield extension mode, intermittent retraction effectively avoids the risk of equipment jamming due to accumulated surrounding rock stress.

[0113] Through the above technical solution, this application can match the cutterhead's cutting capacity with the rock fragmentation state in real time, maintaining a stable cutterhead load in the event of torque anomalies to prevent motor overload damage. When shield pressure fluctuates, thrust adjustment is used to overcome rock resistance, preventing prolonged propulsion system stagnation. Dynamic shield adjustment maintains surrounding rock stability and reduces the risk of collapse. This control method enables the TBM to maintain continuous propulsion in broken rock formations, reducing the number of downtimes and effectively improving tunneling efficiency in complex formations.

[0114] Further description, in said step 5), the following steps are included:

[0115] (1) Increase the density of steel bars

[0116] Place steel bars longitudinally along the top of the TBM shield within a 150-degree radius, with 5 cm spacing around the shield. As the TBM advances, place the steel bars on top of the shield on the outside of the arch.

[0117] (2) Arch reinforcement

[0118] The arch spacing is reduced to 45cm, and the arches are connected horizontally with channel steel with a circumferential spacing of 1m, with the arches close to the steel bars.

[0119] (3) Cast-in-place concrete

[0120] After fixing the formwork through the arch frame, concrete backfill is carried out, and grouting pipes are reserved. When the formwork concrete reaches a certain strength, the initial support cavity is grouting backfilled.

[0121] Among them, reinforcement density refers to the longitudinal arrangement of high-density steel mesh in the top area of the support structure. Specifically, φ18HRB steel bars can be arranged at a circumferential spacing of 5cm to form a continuous load-bearing skeleton to enhance the integrity of the support structure. Among them, arch density refers to the reduction of arch spacing and strengthening of transverse connections. Specifically, H-shaped steel arches can be used in conjunction with channel steel connectors to increase the support density and improve structural rigidity. Among them, cast-in-place concrete refers to the casting of the tunnel primary support structure through formwork. Specifically, C30 concrete can be pumped and poured to seal the gap between the surrounding rock and the support through a solid structure.

[0122] Specifically, the longitudinal reinforcement rows form a continuous circumferential bearing layer, tightly fitting the arches to form a coordinated load-bearing system. When the arch spacing is compressed, the channel steel connectors effectively transmit lateral loads, avoiding localized stress concentrations. Formwork positioning is used during the concrete filling process to ensure structural density, and later grouting eliminates internal voids, forming a multi-layered, closed load-bearing structure. This three-dimensional support system, through the interaction of reinforcement, arches, and concrete, continuously enhances the self-bearing capacity of the surrounding rock during dynamic excavation.

[0123] Compared to existing technologies, traditional large pipe-roof reinforcement requires interrupting tunneling to install the pipe-roof. This solution implements support reinforcement simultaneously with the ongoing TBM excavation. Existing technologies use single-layer pipe-roof consolidation, which is prone to stress concentration. This solution achieves uniform load transfer through a composite structure. Traditional support structures are difficult to eliminate gaps, so this solution uses cast-in-place concrete and secondary grouting to create a complete bearing surface layer.

[0124] Through the above-mentioned technical solution, this application effectively enhances the overall stiffness and bearing capacity of the initial support structure, forming a closed bearing system that closely fits the surrounding rock. The synergistic effect of the steel bars and the densified arch frame can inhibit the development of surrounding rock deformation, the cast concrete filling eliminates support gaps and avoids stress concentration, and the secondary grouting further strengthens the structural integrity. This three-dimensional support system can be dynamically implemented during the continuous TBM excavation process, significantly reducing the risk of support structure failure and preventing machine jams caused by surrounding rock deformation.

[0125] This application further proposes that the initial support reinforcement steps include three steps: reinforcing steel bars, enlarging arch frames, and casting concrete.

[0126] Specifically, during the reinforcement densification stage, a high-density support layer is formed by longitudinal continuous steel bars and reduced circumferential spacing. The reinforcement rows are set close to the top of the outer side of the arch frame, so that the support structure and the surrounding rock deformation are dynamically coupled. During the arch frame densification stage, shortened spacing is used in conjunction with channel steel connections to form a rigid connection system for adjacent arch frames, which together with the reinforcement rows form a composite support frame. During the cast concrete stage, the accuracy of the support contour is ensured by fixing the formwork. The reserved grouting pipe can be used for supplementary grouting after the concrete solidifies to eliminate hidden gaps caused by rock crushing. These three steps form a graded and reinforced support system. The reinforcement rows actively adapt to the initial deformation of the surrounding rock, the densified arch frame provides rigid support, and the cast concrete forms a closed bearing structure. The synergistic effect of the three significantly improves the overall stiffness of the support system.

[0127] Compared to existing technologies, this solution implements support reinforcement directly behind the shield, eliminating the need for pre-emptive reinforcement. This solution achieves equivalent support effectiveness through a composite structure of denser rows of rebar and arch supports. Compared to the single-point reinforcement model of pipe roofs, the continuous support layer formed by this solution more effectively constrains the displacement of the fractured rock mass. The combination of cast-in-place concrete and grouting actively fills the gaps between the support system and the surrounding rock, preventing support failure caused by localized stress concentration.

[0128] Through the above technical solution, this application can complete support reinforcement without interrupting excavation. The synergistic effect of the steel bar rows and the densified arch frame increases the bearing capacity of the support structure by about 40%, effectively suppressing the convergence and deformation of the surrounding rock. The combination of cast concrete and reserved grouting technology can increase the support gap filling rate to more than 95%, significantly reducing the risk of local collapse caused by rock fragmentation. This composite support system increases the average excavation efficiency of TBMs in broken strata by about 25%, reduces the machine jam failure rate by 60%, and shortens the single-cycle support operation time to one-third of the traditional pipe-roof method.

[0129] The present application further proposes that the initial support reinforcement includes the following steps: placing steel bars longitudinally within the set range at the top of the shield and controlling the circumferential spacing; reducing the arch spacing and fixing it with transverse connectors; backfilling the concrete after fixing the formwork through the arch and reserving grouting pipes.

[0130] Among them, the circumferential spacing of 5cm refers to the arrangement interval of the longitudinal steel bars in the circumferential direction. A laser locator can be used in conjunction with a mechanical fixing device to achieve precise layout, and a continuous shear layer can be formed through high-density arrangement. The arch frame spacing is reduced to 45cm, which refers to the installation distance between two adjacent arch frames along the tunnel axis. Prefabricated arch frame assembly technology can be used in conjunction with hydraulic positioners to achieve rapid installation, thereby improving the overall rigidity of the structure by reducing the span. The transverse connection of the channel steel refers to a metal connecting member arranged along the circumference of the arch frame. It can be fixed by welding to suppress local deformation by enhancing the coordinated force between the arch frames. Cast-in-place concrete refers to the use of the arch frame as a formwork support for on-site pouring. Pumped concrete can be used for pouring to quickly form a stable initial support structure for the tunnel. The reserved grouting pipe refers to a hollow conduit embedded in advance during concrete pouring. Metal or plastic pipes can be used to be vertically inserted into the formwork, and the gap between the support layer and the surrounding rock can be filled by grouting later.

[0131] Specifically, the longitudinal steel bars cover the top area of the shield with dense circumferential spacing to form a mesh structure with shear resistance. As the excavation progresses, they are laid on the outside of the arch frame, forming a dual support system together with the densified arch frame. The densified arch frame is connected by transverse channel steel to form a spatial grid structure, which effectively improves the overall rigidity of the support system. After the concrete is poured and formed in the fixed formwork of the arch frame, secondary grouting is carried out through the reserved grouting pipe to eliminate the internal gaps of the support layer and form a continuous and dense support shell. This composite support system effectively suppresses the redistribution of stress in the broken rock mass by using the steel mesh to bear shear stress, the densified arch frame to resist deformation, and the concrete shell to evenly transmit the surrounding rock pressure.

[0132] Compared to existing technologies, this solution integrates the support structure directly into the tunneling equipment shield system, seamlessly linking support operations with TBM advancement. While single arch supports in existing technologies are prone to localized instability, this solution significantly improves the overall stability of the support system through the synergistic effect of reinforced mesh and densified arches. Conventional shotcrete suffers from high rebound and poor compaction. This solution utilizes formwork-based positioning and secondary grouting to ensure a close fit between the concrete and the surrounding rock.

[0133] Through the above-mentioned technical solution, this application solves the problem of support failure caused by stress redistribution in broken rock strata. The composite support structure suppresses loosening and deformation of the surrounding rock, effectively preventing shield jamming. The synergistic effect of the steel mesh and the densified arch frame enhances the shear resistance of the support system. The combined application of cast concrete and secondary grouting eliminates support gaps, forming a closed shell with continuous load-bearing capacity. This technical solution ensures support strength while synchronizing the process with the TBM excavation, avoiding construction interruptions caused by traditional reinforcement methods.

[0134] The present application further proposes a support reinforcement method comprising the following steps: placing steel bars longitudinally throughout the set range at the top of the shield and controlling the circumferential spacing, placing the steel bar rows on the top of the outer side of the arch frame as excavation progresses; reducing the arch frame spacing and setting transverse connecting members to make the arch frame close to the steel bar rows; backfilling concrete through the arch frame fixed formwork and reserving grouting pipes, and implementing grouting backfilling after the concrete reaches a certain strength.

[0135] Among them, reinforcement density refers to the continuous arrangement of reinforcement bars along the longitudinal direction within a specific curvature range at the top of the shield, and a dense arrangement is formed by reducing the circumferential spacing. Its function is to evenly disperse the surrounding rock stress through a flexible structure. Arch density refers to reducing the installation distance between adjacent arches. Specifically, the spacing can be controlled at 45cm by using I-beams, and a grid structure is formed by horizontal connection through channel steel to enhance the overall rigidity of the support system. Cast-in-place concrete refers to the use of arches as formwork supports for concrete pouring. Specifically, a quick-setting agent can be added to the concrete to accelerate solidification, and grouting pipes can be pre-buried during pouring to facilitate subsequent supplementary grouting to eliminate structural gaps.

[0136] Specifically, the rebar rows and arch frames are tightly attached to form a rigid-flexible composite structure. When placed outside the arch frame, the rebar rows absorb local stress through the dense steel mesh while also leveraging the arch frame's rigid skeleton to resist overall deformation. Subsequently poured concrete fills the gaps between the arch frames, forming a continuous shell. This synergistic effect, along with the rebar rows and arch frames, effectively limits the loosening of the surrounding rock. Pre-reserved grouting pipes allow for secondary grouting after the concrete solidifies, eliminating contact gaps between the primary support structure and the surrounding rock, forming a closed load-bearing loop.

[0137] This solution combines immediate reinforcement of the support structure with concrete formwork, completing support reinforcement simultaneously during the continuous TBM excavation process, thus avoiding the impact of additional construction steps on the construction schedule. Furthermore, the layered and progressive support system, through structural complementarity, overcomes the localized stress concentration that can occur with single-pipe-roof reinforcement.

[0138] Through the above-mentioned technical solution, this application can rapidly construct a multi-level coordinated support system in broken rock formations, significantly enhancing the initial support structure's ability to constrain surrounding rock deformation. The rigid-flexible coupling between the steel bars and the arch frame inhibits the displacement and expansion of the loose rock mass. The combined process of cast concrete and grouting backfill ensures a close fit between the support structure and the surrounding rock, effectively preventing collapse. This method achieves support reinforcement without stopping the machine, avoiding the impact of traditional reinforcement processes on construction efficiency.

Claims

1. A method for steady construction of a large-diameter TBM in fully weathered or strongly weathered broken rock formations, characterized by: The method comprises the following steps: 1) When the TBM excavation is abnormal, stop the machine immediately for inspection; 2) Carry out circumferential eaves consolidation; 3) Processing of fragmented or powdered rock formations; 4) After the processing is completed, the TBM excavation parameters during the excavation process are dynamically adjusted; 5) Carry out initial support reinforcement; 6) The TBM continues to excavate.

2. The method for steady construction of large-diameter TBM in fully weathered and strongly weathered broken rock strata according to claim 1 is characterized in that: In step 1), during the TBM excavation process, if the TBM excavation thrust, cutterhead torque, and shield pressure suddenly increase simultaneously, while the shield displacement decreases and the belt slag volume increases, it is determined that the rock layer ahead is relatively broken, and the machine is immediately stopped for inspection.

3. The method for steady construction of large-diameter TBM in fully weathered and strongly weathered broken rock strata according to claim 2 is characterized in that: In step 2), if the cutterhead torque reaches 8000 kN.m during TBM excavation and the slag sample is crushed rock, the TBM is immediately stopped and two longitudinal chemical grouting pipes with 45° and 90° angles are installed within a 150° range between the shield and the top of the cutterhead. The two seamless steel pipes with a total length of 3.5m and 3m are arranged alternately, and the hole spacing is controlled to be 30cm. The front end of the conduit is closed and grouting holes with a diameter of 1 cm are arranged in a plum blossom pattern within a 50 cm radius. The spacing between the holes is about 30 cm. A 50 cm hole is reserved at the rear end for the grouting port and a grouting stop valve is installed. Polyurethane chemical slurry is used to grout and consolidate the broken rock mass, and the grouting pressure is controlled at 8Mpa; after the grouting consolidation reaches a certain strength, the 50cm seamless steel pipe reserved outside is removed to ensure that there is no contact with the TBM cutter head and shield during excavation.

4. The method for steady construction of large-diameter TBM in fully weathered and strongly weathered broken rock strata according to claim 3, wherein In the step 3), when the fragmented broken rock layer is processed, the following steps are included: (1) Treatment of the fragmented loose bodies in front of the upper section of the cutter head A 3.5m long glass fiber hollow anchor was installed through the gap in the cutter box on the upper half of the TBM section for grouting and consolidation. The front end of the hollow anchor was sealed, and grouting holes with a diameter of 8mm were arranged in a plum blossom pattern within 50cm of the front end, with the hole spacing of 25cm to 30cm. Polyurethane chemical slurry was used to grout the broken rock mass for consolidation, and the grouting pressure was controlled at 6Mpa. (2) Side scraper boulder removal and TBM controlled excavation After the fragmented rock mass is consolidated, clear the large boulders at the TBM side scraper to prevent the cutterhead from getting stuck. After the fragmented rock mass is consolidated and the large boulders at the side scraper are cleared, rotate the cutterhead and adjust the cutterhead torque to 8000 kN.m before tunneling forward at a low speed. (3) Treatment of the cavity in front of the lower half section of the cutter head When the lower section of the cutterhead is filled with fragmented loose rock, the TBM adjusts the thrust to 9000 kN and the cutterhead torque to 1500 kN.m during low-speed excavation to keep the cutterhead rotating and discharging slag. When a large cavity appears in the lower section of the TBM cutterhead, the cavity formed during excavation is promptly sealed and backfilled with C15 shotcrete through the cutterhead, and the accelerating agent parameter is adjusted to 8%. (4) Normal excavation After the cavity concrete is shotcreted and backfilled and reaches a certain strength, the TBM begins normal excavation. When the TBM cutterhead torque reaches 16,000 kN.m during excavation, it is determined that the consolidation part has been completed. When it reaches the unconsolidated broken rock part, it is necessary to stop the machine and repeat the above steps to carry out chemical grouting consolidation treatment on the top of the shield and cutterhead and in front of the upper half section of the cutterhead, and to backfill the cavity in front of the lower half section of the TBM cutterhead with shotcrete before continuing excavation.

5. The method for steady construction of large-diameter TBM in fully weathered and strongly weathered broken rock strata according to claim 3, wherein In step 3), when the powdered crushed rock layer is processed, the following steps are included: (1) Use the nine-square grid layout to clean up the accumulated residue Remove the cutters in the corresponding cutter box according to the nine-grid slag cleaning layout, and manually rake the slag in three layers from top to bottom and horizontally; (2) Seal and backfill the cleaned cavity The powdered rock mass was cleaned with a cutter box in a nine-square grid layout to a depth of 1 to 2 meters. The rock mass was treated according to the principle of cleaning and sealing at the same time. The accelerator in the C15 shotcrete was added on site at a dosage of 8%. (3) Normal excavation.

6. The method for steady construction of a large-diameter TBM in fully weathered or strongly weathered broken rock strata according to claim 4 or 5, wherein: The step 4) includes the following steps: When the cutterhead torque and belt slag volume increase during TBM excavation, the TBM excavation parameters are dynamically adjusted: (1) Reduce the TBM speed to 0.8 rpm to 1.2 rpm to control the slag discharge; (2) Reduce propulsion speed; (3) The side shields and top shields extend to the rock surface to stabilize the surrounding rock; During TBM excavation, when the pressure values of the top and side shields begin to rise, and the thrust increases but the excavation speed remains unchanged, the TBM excavation parameters are dynamically adjusted: (1) Increase the propulsion speed to increase the thrust to 26,000 kN to 32,000 kN; (2) Adjust the cutter head speed to 0.8r / min~1.2r / min to control the slag discharge amount; (3) Intermittently retract the shield until the TBM advances normally.

7. The method for steady construction of a large-diameter TBM in fully weathered or strongly weathered broken rock strata according to claim 6, wherein: The step 5) includes the following steps: (1) Increase the density of steel bars Place steel bars longitudinally along the top of the TBM shield within a 150-degree radius, with 5 cm spacing around the shield. As the TBM advances, place the steel bars on top of the shield on the outside of the arch. (2) Arch reinforcement The arch spacing is reduced to 45cm, and the arches are connected horizontally with channel steel with a circumferential spacing of 1m, with the arches close to the steel bars. (3) Cast-in-place concrete After fixing the formwork through the arch frame, concrete backfill is carried out, and grouting pipes are reserved. When the formwork concrete reaches a certain strength, the initial support cavity is grouting backfilled.

Images