End reinforcement construction method for excavation section of underground railway tunnel

Abstract

The invention relates to the technical field of underground railway tunnel construction, and discloses an underground railway tunnel excavation section end reinforcement construction method which comprises the following steps of reinforcement scheme selection, reinforcement range determination, high-pressure jet grouting pile construction, precipitation well arrangement, grooving quality control and construction pretreatment. A double-pipe high-pressure jet grouting pile is adopted to form a secant pile body, and layered pressure control is implemented; the manufacturing process of the guide wall sequentially comprises the steps of surveying and setting out, exploring trench excavation, guide wall trench excavation, trench bottom tamping, steel bar binding, formwork installation and concrete pouring. Differentiated reinforcing combinations are adopted for different geological conditions, a three-dimensional waterproof curtain is formed through a stepped built-in structure, and the method adapts to the permeability difference of complex stratums; the high-pressure jet grouting pile is precisely controlled, layered pressure control is combined with graphene modified cement grout, and the pile body meshing compactness is ensured; and therefore, the effects of efficient reinforcement and water stop of the shield end under the complex geological condition are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of subway tunnel construction, and specifically to a construction method for strengthening the end of an excavation section of a subway tunnel. Background Technique

[0002] In the construction of subway tunnel projects, the reinforcement of the end of the shield section is a core link to ensure construction safety and quality. In recent years, with the rapid development of urban rail transit, shield tunneling construction has been widely used because of its small impact on ground traffic and the surrounding environment. However, the problem of the stability of the end formation when the shield machine enters and exits the tunnel has always been a difficult point in construction. If the end formation is not effectively reinforced, it is easy to cause accidents such as water inrush, sand inrush, and even collapse when the shield machine enters and exits the tunnel, seriously affecting construction safety and progress.

[0003] Traditional single reinforcement methods (such as single-row jet grouting piles or ordinary diaphragm walls) are difficult to cope with complex geological conditions such as uneven soft and hard strata, highly permeable sand layers, or water-rich faults, and are prone to reinforcement blind spots or water-stop failure, resulting in a significant increase in the risk of leakage and collapse at the end during shield launching / receiving. At present, methods such as high-pressure jet grouting piles and diaphragm walls are generally used in the industry for end reinforcement, but the applicability and effectiveness of these technologies are greatly restricted by factors such as geological conditions and construction techniques. In addition, construction in the central urban area often faces complex environments such as dense underground pipelines and adjacent buildings, further increasing the technical difficulty of shield end reinforcement and water-stop. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a construction method for strengthening the end of an excavation section of a subway tunnel, which solves the problem that the traditional construction method has unsatisfactory shield end reinforcement and water-stop effects under complex geological conditions.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions: A construction method for strengthening the end of an excavation section of a subway tunnel includes the following steps: Reinforcement plan selection: Select the reinforcement combination method according to the end geological conditions. For the large mileage end, use high-pressure jet grouting piles with a diameter of 600 mm in combination with steel pipe dewatering wells with a diameter of 600 mm. For the small mileage end, use a C20 plain concrete diaphragm wall with a thickness of 800 mm in combination with high-pressure jet grouting piles and dewatering wells. For the end of the interval ventilation shaft, use double-layer high-pressure jet grouting piles in combination with dewatering wells; Determine the reinforcement scope: Longitudinally, it is the solid pile section from 3 m above the tunnel roof to 3 m below the tunnel bottom, and the empty pile section from the ground to 3 m above the tunnel roof. Transversely, it is 3 m on each side of the tunnel, extending longitudinally by 10 m. Vertically, a stepped anchorage structure is formed at the bottom of the diaphragm wall and the bottom of the high-pressure jet grouting pile, with a height difference ≥ 1 m; High-pressure jet grouting pile construction: Double-tube high-pressure jet grouting piles are used to form interlocking pile bodies, and layered pressure control is implemented, with the upper layer at 15MPa, the middle layer at 18MPa, and the lower layer at 20MPa. The lifting speed is controlled at 10 to 15cm per minute, and the rotation speed is controlled at 10 to 15 revolutions per minute. Dewatering well layout: Dewatering wells with a wall thickness of 5 mm are laid out within 10 m of the shield advancing direction. The well group adopts a combination of circular and radial layouts, and pre-dewatering is started 3 days before the shield arrives. Trench quality control: a dual system is used to monitor the verticality of the trench in real time, and nano-silica sol injection is used to ensure that the sediment thickness meets the standard; pre-construction treatment: the hardened part of the end is broken with concrete, and the surrounding environment is monitored simultaneously during construction.

[0006] By adopting the above technical solutions: through differentiated reinforcement solutions (high-pressure jet grouting piles + dewatering wells / underground continuous wall combination) to accurately match different geological conditions, a three-dimensional water-stopping curtain is formed through a stepped embedded structure to adapt to the permeability differences in complex strata and ensure the reinforcement effect; the layered pressure-controlled high-pressure jet grouting piles (15-20MPa grading) are combined with graphene-modified cement slurry to make the 28-day compressive strength of the pile body ≥8MPa; the underground continuous wall and the jet grouting piles form a stepped embedded structure (height difference ≥1m), which cooperates with the dewatering well system (pre-dewatering for 3 days) to effectively block the groundwater infiltration path, thereby achieving the effect of efficient reinforcement and water-stopping of the shield end under complex geological conditions.

[0007] Preferably, the plain concrete underground continuous wall construction includes: Pour C20 plain concrete in sections, with each section length controlled at 18 to 28m, and the interval between construction jumps should be no less than 0.5m; A composite slotting process using a hydraulic grab, impact hammer and slot milling machine is used. A hydraulic grab is used above the rock layer, and an impact hammer is switched below the rock layer. A slot milling machine is used for extremely hard rock layers. The mud system is configured with a new mud density of 1.05 to 1.10, the circulating mud sand content is less than 7%, and solid-liquid separation is performed when the pH value of the waste mud exceeds 14; During concrete pouring, distributed fiber optic sensors are implanted to monitor the temperature field and stress distribution in real time. The distance between the conduits is no more than 3m, the distance from the trench end is no more than 1.5m, the burial depth is controlled between 1.5 and 3m, the pouring speed is no less than 2m per hour, and the slump range is 18 to 22cm.

[0008] Preferably, the high-pressure jet grouting pile construction includes: The parameters determined by the on-site pile test are as follows: slurry volume 70L / min, cement dosage 93-124kg per meter, 30% cement content is used in the area 2m above the tunnel bottom, and the content is increased to 35% in the area below; Use graphene-modified cement slurry with an initial setting time of 4h and a 28-day compressive strength ≥8MPa; When grout is leaking, stop lifting and grouting to stop the leak, and the slurry cannot be recovered; The waste slurry is treated by a slurry separator with a processing capacity of 200m3 / h. 3 The separation particle size is 0.074mm. The waste pulp treatment system integrates an automatic pH adjustment module to maintain the pH value of 7±0.5 during the treatment process. After purification, the sand content of the mud is less than 2% and the recycling rate reaches more than 80%.

[0009] Preferably, the construction of the precipitation well includes: A 6mm thick steel plate is set at the bottom of the well to seal the bottom, and a 30cm thick 0.5-1mm gravel layer and a 20cm thick sodium bentonite ball layer are alternately backfilled around the well. The water filter pipe adopts spiral laser drilling technology with a hole diameter of 2mm and a hole spacing of 50mm; Equipped with a dual-circuit 200KVA power supply system and a water level dynamic monitoring device, and a frequency conversion control water pump system with flow fluctuation ≤5%; Dynamically adjust the number of pumping wells opened according to measured data; The well construction process is as follows: well location measurement and placement, upper concrete breaking, impact drilling, water filter pipe wrapping, well pipe lowering, gravel clay ball filling, well washing and test pumping.

[0010] Preferably, the grooving verticality control includes: Measure the wire rope deviation every 2m, calculate the inclination rate through trigonometric function, and backfill with clay or concrete to correct the deviation when it exceeds the standard; Generate 3D correction scheme in real time based on BIM-construction linkage system; The special-shaped trench section adopts the "L"-shaped split-section direct excavation process, and the guide wall at the corner is extended 30cm to assist in trenching; The "grouting before excavation" process is adopted for the slot section of the soft stratum: pre-injection of ultra-fine cement slurry with a water-cement ratio of 0.8, grouting pressure of 0.3-0.5MPa, and stabilization time ≥2h; When dividing the slot sections, the length of a single slot in the soft stratum is shortened to 18m.

[0011] Preferably, the guide wall construction includes: It adopts an inverted L-shaped reinforced concrete structure with a flange width of 200mm and built-in temperature stress relief joints with a spacing of 6m; Before tying the steel bars, pre-cast 100mm thick C15 plain concrete wings, with a main reinforcement spacing deviation of ±10mm; A self-sensing intelligent formwork with built-in strain gauges is used to monitor the expansion pressure of concrete, using a 2×6m steel formwork and wooden support with a spacing of 1m; After the concrete reaches final setting, a photovoltaic-driven atomization system is used to maintain the curing humidity ≥ 90% and the temperature gradient ≤ 3°C / m for ≥ 7 days; after demolition, double-layer supports made of 100×100 mm square timbers are used, with a spacing of 1500 mm to prevent deformation; The construction process of the guide wall is in sequence of measuring and setting out, exploratory trench excavation, guide wall trench excavation, trench bottom ramming, steel bar binding, formwork installation, and concrete pouring.

[0012] Preferably, it also includes dynamic adjustment measures during the construction stage: Adjust the grouting pressure of the high-pressure jet grouting pile according to the real-time monitoring data, and control the fluctuation range within ±5%; Establish a coupling model for multi-parameter regulation triggered when the formation loss rate exceeds 0.5‰; Deploy a microseismic monitoring system with a sensor spacing of 5 m. When the vibration speed exceeds 2 mm / s, suspend construction and carry out grouting reinforcement; During the trench forming process, if a soft interlayer is encountered, immediately inject bentonite slurry to stabilize the trench wall; Embed a pressure balance pipe with a fluctuation value of the mud pressure at the shield cutting opening not exceeding 0.02 MPa; During concrete pouring, dynamically adjust the depth of the conduit to ensure continuous pouring without faults.

[0013] Preferably, the emergency treatment measures include: Establish a three-level settlement response mechanism. When the settlement rate of level I > 3 mm / d, start double-fluid grouting and the standby well group; when the settlement rate of level II is 2 - 3 mm / d, implement single-fluid grouting and adjust the dewatering plan; when the settlement rate of level III < 2 mm / d, perform local plugging and densify the monitoring; Immediately inject mud powder and increase the slurry supply when a hole collapse occurs; use quick-setting cement to backfill and plug the leakage of the diaphragm wall; start the backfill of the standby injection well when the settlement caused by dewatering exceeds the standard; Use an intelligent grouting robot with a positioning accuracy of ±5 cm to adaptively adjust the grouting pressure of 0.3 - 1.2 MPa; when the construction of the high-pressure jet grouting pile is interrupted for more than 30 minutes, it is necessary to re-drill and overlap by 1 m.

[0014] Preferably, the material control standards include: The slurry is mainly made of high-quality mud powder and supplemented with clay, adding 2% nano-silica, controlling the specific gravity of 1.05 - 1.15, viscosity of 18 - 25 s, pH value of 8 - 10, shear strength of 25 Pa·s and filtration loss of 8 mL / 30 min; Add a retarder to the concrete to make the initial setting time ≥ 6 h, incorporate 0.8% steel fiber, and the strength of adjacent wall panels ≥ 70% before skip construction can be carried out, with the crack resistance performance improved by 50%; The geopolymer-based grouting material achieves a 28-day strength of 15 MPa and a permeability coefficient < 1×10 -8 cm / s.

[0015] Preferably, green construction techniques include: Intercepting ditches and sedimentation tanks are set up around the construction site to construct a three-level waste slurry treatment system to generate recycled building materials; Low-noise equipment is used in noise-sensitive areas and noise barriers are set up. Adaptive active noise reduction technology is used to control the equivalent sound level at 30m to ≤55dB(A); Monitor the settlement of surrounding buildings daily, and immediately activate the emergency plan if the cumulative settlement exceeds the warning value; After construction, the backfill thickness shall be ≥1m and the vegetation coverage rate shall be ≥80% within 30 days.

[0016] The present invention provides a construction method for reinforcing the end of an excavation section of an underground railway tunnel. It has the following beneficial effects: 1. In the present invention, differentiated reinforcement combinations are adopted according to different geological conditions, and a three-dimensional water-stopping curtain is formed through a stepped embedded structure to adapt to the permeability differences of complex strata; high-pressure rotary jet piles are precisely controlled, and layered pressure control is combined with graphene-modified cement slurry to ensure the bite density of the pile body; the cement content below the tunnel bottom is increased to 35% to enhance the bottom anti-seepage performance; annular + radial well group dewatering is started 3 days before the arrival of the shield, and laser drilling of the filter pipe and backfilling of the sodium-based bentonite ball layer are used to effectively lower the groundwater level and reduce the risk of construction seepage; thereby achieving the effect of efficient reinforcement and water-stopping of the shield end under complex geological conditions.

[0017] 2. In the present invention, by deploying a microseismic monitoring system and a three-level settlement response mechanism, combined with an intelligent grouting robot to plug leakage in real time, the surface settlement is controlled to the maximum extent; at the same time, the soft strata adopt the "grouting before excavation" and L-shaped direct excavation technology, and the corner guide wall is extended by 30cm to assist in trenching, reducing the risk of instability of the trench wall. By replacing traditional cement slurry with geopolymer-based grouting materials, the risk of grouting pollution to groundwater is reduced; the sand content of the mud system is <7%, and the pH value of the waste mud can be controlled after solid-liquid separation, reducing the environmental burden; the effect of reducing the impact of reinforcement construction on surrounding pipelines and buildings is achieved.

[0018] 3. In the present invention, the plain concrete underground continuous wall adopts hydraulic grab bucket + impact hammer + slot milling machine to form slots, and the construction efficiency of extremely hard rock formations is improved by 40%; the special-shaped slot section generates a three-dimensional correction plan through BIM to reduce the rework rate; the mud separator has a processing capacity of 200m 3 / h, the recycling rate of the purified mud is >80%; the three-level waste slurry treatment system converts waste slurry into recycled building materials, reducing material consumption costs; by real-time adjustment of grouting pressure and guide tube burial depth, combined with the shield cut-out pressure balance pipe, it avoids shutdowns and repairs due to parameter errors, and the overall construction period is shortened by 15%-20%, achieving the effect of optimizing the construction process to shorten the construction period and reduce costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a flow chart of the construction method for strengthening the end of the excavation section of an underground railway tunnel in the present invention. Specific implementation manners

[0020] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the accompanying drawings of the specification. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0021] Embodiment 1: Differential reinforcement design and intelligent construction control 1.1 Process details 1.1.1 Three-dimensional geological radar scanning and reinforcement scheme selection A three-dimensional geological radar with a frequency of 100 MHz is used, with a detection depth of 30 m and a resolution of ±0.5 m. Different reinforcement areas are divided according to the generated dielectric constant distribution map: Large mileage end (sand and pebble stratum): Adopt the combination of high-pressure jet grouting piles (pile diameter 600 mm) + dewatering wells; Small mileage end (soft soil stratum): Adopt an 800-mm-thick C20 diaphragm wall + high-pressure jet grouting piles + dewatering wells; End of the interval air shaft (fractured rock stratum): Adopt double-layer high-pressure jet grouting piles (offset by 30 cm up and down) + dewatering wells.

[0022] 1.1.2 Jet grouting pile layered pressure control technology Based on the soil stress distribution model, the pressure of the jet grouting pile is optimized for layered control: Upper layer (0 - 5 m): 15 MPa (reduce surface uplift); Middle layer (5 - 10 m): 18 MPa (balance lateral pressure); Lower layer (10 - 15 m): 20 MPa (enhance pile tip bearing capacity), effectively avoiding the problem of excessive disturbance of shallow soil caused by the traditional single pressure (20 MPa).

[0023] 1.1.3 Intelligent monitoring system Monitoring of the groove wall verticality: Double-system calibration is carried out using an ultrasonic wall thickness gauge (accuracy ±0.1°) and an inclination sensor (accuracy ±0.05°); Temperature monitoring: A distributed optical fiber sensor (sampling frequency 1 kHz) is used to monitor the temperature gradient of the diaphragm wall in real time, and an alarm is triggered when the temperature difference exceeds 5°C.

[0024] 1.2 Verification of implementation effect Index This embodiment Traditional method (control group) Test standard Surface heave amount (mm) ≤3 8～12 JGJ120 - 2019 Pile body compressive strength (MPa) 8.5 (28 days) 6.2 JGJ79 - 2012 Verticality qualification rate (%) 98 85 GB50299 - 2018 Precisely match geological conditions: Based on the three-dimensional geological radar scanning data, targeted reinforcement combinations are adopted for the ends with different geological conditions, effectively improving the reinforcement effect and ensuring the stability of the strata and the safety of construction.

[0025] Improve the quality of reinforcement: Through the stratified pressure control technology of jet grouting piles, the construction pressure of jet grouting piles is optimized, reducing the disturbance of shallow soil layers, enhancing the bearing capacity of the pile bottom, and improving the overall strength and stability of the pile body.

[0026] Enhance the control of the construction process: With the help of the intelligent monitoring system, the real-time monitoring of the trench forming verticality and temperature gradient is realized, problems in construction are discovered and processed in a timely manner, and the construction accuracy and quality control level are improved.

[0027] Example 2: Coordinated control of trench forming and dewatering under complex geological conditions 2.1 Process details 2.1.1 Composite trench forming process Aiming at the problem of sudden change at the rock formation interface, a three-stage process of "grabbing - ramming - milling" is adopted: Hydraulic grab (for 0 - 15m soil layer, efficiency 8m 3 / h); Impact hammer (for 15 - 20m gravel layer, impact energy 35kJ); Milling machine (for rock layer below 20m, milling torque 120kN·m).

[0028] 2.1.2 Optimization design of dewatering wells Based on CFD simulation, the filter pipe is optimized to be a spiral laser - drilled hole (porosity 15%, permeability coefficient 5×10 -3 cm / s); The well perimeter is alternately backfilled with sodium - bentonite ball layers (swelling rate 400%) and gravel layers to prevent the loss of fine particles.

[0029] 2.1.3 BIM - construction linkage deviation correction Based on the BIM model, the deviation of the trench forming axis is compared in real - time. When the deviation > 1 / 300, the system automatically generates a deviation correction instruction, and the hydraulic grab adjusts the excavation angle (±2°).

[0030] 2.2 Verification of implementation effect Improve the trench forming efficiency and quality: The "grabbing - ramming - milling" composite trench forming process is adopted, effectively dealing with the problem of sudden change at the rock formation interface, improving the trench forming efficiency, and ensuring the quality and stability of trench forming.

[0031] Reducing the risk of precipitation well blockage: By optimizing the design of precipitation wells, the porosity and permeability coefficient of the filter pipes are increased, effectively preventing the loss of fine particles, reducing the risk of precipitation well blockage, and ensuring the continuity and reliability of the precipitation effect.

[0032] Enhancing the stability of the groove wall: Through the BIM-construction linkage deviation correction technology, the deviation of the groove forming axis is adjusted in a timely manner, ensuring the stability of the groove wall, reducing the risk of hole collapse, and improving the construction safety.

[0033] Example 3: Green construction and emergency response system 3.1 Process details 3.1.1 Waste slurry regeneration system Adopting a three-stage treatment process: Cyclone sand removal (removing particles with a particle size > 0.1 mm); Chemical flocculation (PAC dosage 0.3‰, pH = 7.5); Vacuum dewatering (pressure -0.08 MPa, moisture content < 25%), and the recycled building materials are used for the temporary road cushion layer (compressive strength ≥ 5 MPa).

[0034] 3.1.2 Ecological restoration technology After construction, backfill the planting soil (organic matter content ≥ 3%, thickness 1.2 m), and implant a mixture of tall fescue (seeding rate 30 g / m 2 ) and ryegrass (seeding rate 25 g / m 2 ). After 30 days, the unmanned aerial vehicle remote sensing monitoring shows that the vegetation coverage rate reaches 85%.

[0035] 3.1.3 Three-level settlement response mechanism Level I response: Double-fluid grouting (cement-sodium silicate, volume ratio 1:0.6), grouting pressure 0.8 MPa; Level II response: Single-fluid grouting (ultrafine cement, water-cement ratio 0.8), and synchronously adjust the operation quantity of precipitation wells; Level III response: Nano-silica sol infiltration grouting (viscosity 50 cP), and cooperate to increase the monitoring frequency to once per hour.

[0036] 3.2 Implementation effect verification Index This embodiment Traditional method (control group) Test standard Waste slurry recycling rate (%) 82 35 CECS375 - 2014 Noise equivalent sound level dB(A) 53 (at 30m) 68 GB12523 - 2011 Settlement recovery time (days) Grade I: 3, Grade II: 7 Grade I: 7, Grade II: 15 GB50911 - 2013 Resource recycling: Through the waste slurry regeneration system, the efficient treatment and recycling of waste slurry are realized, reducing waste emissions, reducing the impact on the environment, and at the same time improving the resource utilization rate.

[0037] Accelerating ecological restoration: By adopting ecological restoration technology, after construction, backfill the planting soil in a timely manner and implant a mixture of grass seeds, promoting the rapid growth and coverage of vegetation, effectively reducing soil erosion, and accelerating the ecological restoration process of the construction area.

[0038] Improve the emergency response ability: Establish a three-level settlement response mechanism, take corresponding emergency measures for different settlement situations, can quickly and effectively control the development of settlement, reduce the impact of construction on the surrounding environment, and improve the safety and reliability of construction.

[0039] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A construction method for reinforcing the end of an underground railway tunnel excavation section, characterized in that: The following steps are involved: Selection of reinforcement scheme: Select the reinforcement combination according to the geological conditions of the end. The long-distance end adopts 600mm diameter high-pressure rotary jet piles with 600mm diameter steel pipe dewatering wells. The short-distance end adopts 800mm thick C20 plain concrete underground continuous wall with high-pressure rotary jet piles and dewatering wells. The interval ventilation shaft end adopts double-layer high-pressure rotary jet piles with dewatering wells. Determine the scope of reinforcement: vertically, it is the solid pile section from 3m above the tunnel top to 3m below the tunnel bottom, and the empty pile section from the ground to 3m above the tunnel top; horizontally, it is 3m on each side of the tunnel, and extends 10m in the longitudinal direction; vertically, it is the stepped embedded structure formed by the bottom end of the underground continuous wall and the bottom end of the high-pressure rotary jet pile, with a height difference of ≥1m; High-pressure jet grouting pile construction: Double-tube high-pressure jet grouting piles are used to form interlocking pile bodies, and layered pressure control is implemented, with the upper layer at 15MPa, the middle layer at 18MPa, and the lower layer at 20MPa. The lifting speed is controlled at 10 to 15cm per minute, and the rotation speed is controlled at 10 to 15 revolutions per minute. Dewatering well layout: Dewatering wells with a wall thickness of 5 mm are laid out within 10 m of the shield advancing direction. The well group adopts a combination of circular and radial layouts, and pre-dewatering is started 3 days before the shield arrives. Grooving quality control: dual systems are used to monitor the verticality of the groove in real time, and nano-scale silica sol injection is used to ensure that the sediment thickness meets the standard; Pre-construction treatment: Break the concrete of the hardened part of the end and implement surrounding environmental monitoring simultaneously during construction.

2. The method for reinforcing the end of an underground railway tunnel excavation section according to claim 1 is characterized in that: Plain concrete underground continuous wall construction includes: Pour C20 plain concrete in sections, with each section length controlled at 18 to 28m, and the interval between construction jumps should be no less than 0.5m; A composite slotting process using a hydraulic grab, impact hammer and slot milling machine is used. A hydraulic grab is used above the rock layer, and an impact hammer is switched below the rock layer. A slot milling machine is used for extremely hard rock layers. The mud system is configured with a new mud density of 1.05 to 1.10, the circulating mud sand content is less than 7%, and solid-liquid separation is performed when the pH value of the waste mud exceeds 14; During concrete pouring, distributed fiber optic sensors are implanted to monitor the temperature field and stress distribution in real time. The distance between the conduits is no more than 3m, the distance from the trench end is no more than 1.5m, the burial depth is controlled between 1.5 and 3m, the pouring speed is no less than 2m per hour, and the slump range is 18 to 22cm.

3. The method for reinforcing the end of an underground railway tunnel excavation section according to claim 1 is characterized in that: High-pressure jet grouting pile construction includes: The parameters determined by the on-site pile test are as follows: slurry volume 70L / min, cement dosage 93-124kg per meter, 30% cement content is used in the area 2m above the tunnel bottom, and the content is increased to 35% in the area below; Use graphene-modified cement slurry with an initial setting time of 4h and a 28-day compressive strength ≥8MPa; When grout is leaking, stop lifting and grouting to stop the leak, and the slurry cannot be recovered; The waste slurry is treated by a mud separator with a processing capacity of 200m³ per hour and a separation particle size of 0.074mm. The waste slurry treatment system is integrated with an automatic pH adjustment module to maintain the pH value of 7±0.5 during the treatment process. After purification, the sand content of the mud is less than 2%, and the recycling rate reaches more than 80%.

4. The method for reinforcing the end of an underground railway tunnel excavation section according to claim 1, characterized in that: The construction of a dewatering well includes: A 6mm thick steel plate is set at the bottom of the well to seal the bottom, and a 30cm thick 0.5-1mm gravel layer and a 20cm thick sodium bentonite ball layer are alternately backfilled around the well. The water filter pipe adopts spiral laser drilling technology with a hole diameter of 2mm and a hole spacing of 50mm; Equipped with a dual-circuit 200KVA power supply system and a water level dynamic monitoring device, and a frequency conversion control water pump system with flow fluctuation ≤5%; Dynamically adjust the number of pumping wells opened according to measured data; The well construction process is as follows: well location measurement and placement, upper concrete breaking, impact drilling, water filter pipe wrapping, well pipe lowering, gravel clay ball filling, well washing and test pumping.

5. The method for reinforcing the end of an underground railway tunnel excavation section according to claim 1, characterized in that: Grooving verticality control includes: Measure the wire rope deviation every 2m, calculate the inclination rate through trigonometric function, and backfill with clay or concrete to correct the deviation when it exceeds the standard; Generate 3D correction scheme in real time based on BIM-construction linkage system; The special-shaped trench section adopts the "L"-shaped split-section direct excavation technology, and the guide wall at the corner is extended 30cm to assist in trenching; The "grouting before excavation" process is adopted for the slot section of the soft stratum: pre-injection of ultra-fine cement slurry with a water-cement ratio of 0.8, grouting pressure of 0.3-0.5MPa, and stabilization time ≥2h; When dividing the slot sections, the length of a single slot in the soft stratum is shortened to 18m.

6. The method for reinforcing the end of an underground railway tunnel excavation section according to claim 1, characterized in that: Guide wall construction includes: It adopts an inverted L-shaped reinforced concrete structure with a flange width of 200mm and built-in temperature stress relief joints with a spacing of 6m; Before tying the steel bars, pre-cast 100mm thick C15 plain concrete wings, with a main reinforcement spacing deviation of ±10mm; A self-sensing intelligent formwork with built-in strain gauges is used to monitor the expansion pressure of concrete, using a 2×6m steel formwork and wooden support with a spacing of 1m; After the concrete has finally set, a photovoltaic-driven atomization system is used to maintain the curing humidity ≥ 90% and the temperature gradient ≤ 3℃ / m for ≥ 7 days; After demolition, double-layer support with 100×100mm square wood is used with a spacing of 1500mm to prevent deformation; The guide wall production process is measurement and layout, trench excavation, guide wall trench excavation, trench bottom compaction, steel bar binding, formwork installation, and concrete pouring.

7. The method for reinforcing the end of an underground railway tunnel excavation section according to claim 1, characterized in that: It also includes dynamic adjustment measures during the construction phase: Adjust the grouting pressure of high-pressure jet grouting piles according to real-time monitoring data, and control the fluctuation range within ±5%; Establish a coupling model that triggers multi-parameter regulation when the formation loss rate exceeds 0.5‰; A microseismic monitoring system with a sensor spacing of 5m was deployed. When the vibration speed exceeded 2mm / s, construction was suspended and grouting reinforcement was carried out; If a weak interlayer is encountered during the trenching process, bentonite slurry is immediately injected to stabilize the trench wall; The shield cutting pre-buried mud water pressure fluctuation value does not exceed 0.02MPa pressure balance pipe; The buried depth of the conduit is dynamically adjusted during concrete pouring to ensure continuous pouring without faults.

8. The method for reinforcing the end of an underground railway tunnel excavation section according to claim 1, characterized in that: Emergency response measures include: Establish a three-level settlement response mechanism. When the settlement rate of level I is greater than 3mm / d, start double-liquid grouting and spare well groups. When the settlement rate of level II is 2-3mm / d, implement single-liquid grouting and dewatering plan adjustment. When the settlement rate of level III is less than 2mm / d, implement local plugging and monitor encryption. Immediately inject mud powder and increase the slurry supply when a hole collapses; use quick-setting cement to refill and seal underground continuous wall leakage; start the standby water injection well to refill when precipitation causes excessive settlement; An intelligent grouting robot with a positioning accuracy of ±5cm is used to adaptively adjust the grouting pressure of 0.3-1.2MPa. When the high-pressure rotary jet pile construction is interrupted for more than 30 minutes, it needs to be re-drilled with an overlap of 1m.

9. The method for reinforcing the end of an underground railway tunnel excavation section according to claim 1, characterized in that: Material control standards include: The mud is mainly made of high-quality mud powder and supplemented with clay, with 2% nano-silicon dioxide added, and the specific gravity is controlled at 1.05-1.15, the viscosity is 18-25s, the pH value is 8-10, the shear strength is 25Pa·s and the filtration loss is 8mL / 30min; Add retarder to concrete to make the initial setting time ≥6h, add 0.8% steel fiber, and the adjacent wall strength ≥70% before switching construction, and the crack resistance performance is improved by 50%; Geopolymer-based grouting materials achieve 28-day strength of 15MPa and permeability coefficient <1×10⁻ 8 cm / s.

10. The method for reinforcing the end of an underground railway tunnel excavation section according to claim 1, characterized in that: Green construction techniques include: Intercepting ditches and sedimentation tanks are set up around the construction site to construct a three-level waste slurry treatment system to generate recycled building materials; Low-noise equipment is used in noise-sensitive areas and noise barriers are set up. Adaptive active noise reduction technology is used to control the equivalent sound level at 30m to ≤55dB(A); Monitor the settlement of surrounding buildings daily, and immediately activate the emergency plan if the cumulative settlement exceeds the warning value; After construction, the backfill thickness should be ≥1m and the vegetation coverage rate should be ≥80% in 30 days.

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