A method for supporting and displacement control of loose slope double-hole tunnel construction from top to bottom

Abstract

The application discloses a loose side slope double-hole tunnel construction support and displacement control method, and belongs to the technical field of tunnel construction, which specifically comprises slope surface pretreatment, slope surface pre-reinforcement, upper hole construction, lower hole construction, secondary reinforcement, displacement monitoring and dynamic adjustment. The method constructs a slope surface pretreatment-pre-reinforcement-tunnel support-double-dimensional monitoring-shock absorption integrated technical system, solves the problems of easy landslide in double-hole construction of loose side slope, mutual disturbance of upper and lower holes, difficult displacement control and poor shock absorption collaboration, and realizes safe, efficient and accurate control in the construction process.

Description

Technical Field

[0001] This invention belongs to the field of tunnel construction technology, specifically relating to a method for top-down construction support and displacement control of a double-tunnel with loose slope. Background Technology

[0002] Loose slope geology is characterized by weak soil cohesion, low shear strength, and high permeability, making it prone to landslides and rockfalls during twin-tunnel construction. Currently, pre-support methods such as pipe roofing and pre-grouted grouted pipes are commonly used in loose slope tunnel construction. However, the pipe roofing method suffers from high construction costs, large equipment investment, and long construction periods. Furthermore, the pre-support steel pipes cannot be recovered after being buried in the soil, resulting in significant resource waste. The pre-grouted grouted pipe method has drawbacks such as low pre-support stiffness and short single-stage application distance, making it unsuitable for scenarios with high ground pressure and strict displacement control requirements in twin-tunnel construction. When constructing twin tunnels using a "top-down" construction sequence, the following key technical challenges arise: First, the construction of the upper and lower tunnels disturbs each other, and the excavation of the lower tunnel later can easily lead to stress concentration in the rock column, causing deformation and cracking of the lining of the upper tunnel earlier. Second, the coordinated control of slope displacement and tunnel deformation is difficult. Existing monitoring often only focuses on the deformation inside the tunnel, ignoring the coupling effect of slope sliding and tunnel deformation, which can easily lead to safety risks due to incomplete monitoring. Third, the coordination between support and vibration reduction is poor. Traditional support structures do not fully consider the impact of loads such as earthquakes and construction vibrations on the tunnel, and vibration reduction measures are set up in isolation, making it difficult to effectively buffer vibration energy. Fourth, the grouting reinforcement effect is not good, with problems such as grout backflow and uneven grouting, which cannot form a continuous and stable reinforcement layer, affecting the overall stability of the support structure.

[0003] Therefore, there is an urgent need for an integrated construction method that takes into account pre-reinforcement, support, monitoring, and vibration reduction to solve the technical pain points such as insufficient support stability, low displacement control accuracy, superposition of disturbances between the upper and lower tunnels, and poor vibration reduction effect in the construction of twin tunnels on loose slopes. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method for construction support and displacement control of a double-tunnel on a loose slope with an upper-lower construction approach. This method can solve technical problems such as insufficient support stability, low displacement control accuracy, superposition of disturbances between the upper and lower tunnels, and poor vibration reduction effect during the construction of a double-tunnel on a loose slope with an upper-lower construction approach.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention discloses a method for top-to-bottom construction support and displacement control of a twin-tunnel on a loose slope, comprising the following steps: Step (1), slope pretreatment: Before construction, remove loose soil, dangerous rocks and weeds from the surface of the slope, and trim the slope surface to make the slope gradient gentler and reduce local stress concentration; excavate trapezoidal drainage ditches at the highest, middle and lowest points of the slope, and use concrete to plaster the inner wall to ensure that the drainage ditches are leak-free; arrange three-dimensional displacement sensors at intervals along the slope surface, weld and fix the three-dimensional displacement sensors to the pre-embedded steel plates, anchor the pre-embedded steel plates to the slope soil, connect the three-dimensional displacement sensors to the wireless transmission module and debug to normal working state; pour concrete columns under each ditch, and lay high-strength steel wire protective netting through the columns; Step (2), slope pre-reinforcement, drilling holes on the vertical slope surface, recording the soil and rock stratification in real time during drilling to determine the location of potential sliding surfaces; after drilling, using high-pressure air to clean the holes and remove slag and dust to ensure unobstructed grouting channels; injecting early-strength sulfoaluminate cement grout, using a skip-hole interval grouting method from the outside to the inside and from top to bottom; curing after grouting, testing the soil strength in the reinforced area by drilling and sampling to ensure that the compressive strength of the soil in the reinforced area meets the pre-reinforcement design requirements; Step (3) Upper tunnel construction, upper tunnel excavation, smooth blasting technology is used during the tunneling process, and loose rocks at the tunnel face are removed in time after blasting; shock absorbers are installed along the circumference of the tunnel, and the shock absorbers are installed between the steel arch frame and the steel plate embedded in the secondary lining; grouting pipes are laid along the circumference of the tunnel, the front end of the pipe is driven into the surrounding rock, and after installing the anti-backflow valve, the external grouting device is connected through the threaded sleeve. When grouting is not performed, the port is sealed with a spiral cap; displacement sensors are installed on the top and side walls of the upper tunnel, the displacement sensors are fixed to the initial support steel arch frame of the tunnel, connected to the data acquisition system, and debugged to collect tunnel settlement and lateral displacement data in real time; Step (4): Lower tunnel construction. After the upper tunnel support structure has been grouted and cured and the soil strength in the reinforced area has reached the standard, the lower tunnel excavation will be started. The distance between the lower tunnel face and the nearest support section of the upper tunnel will be controlled to avoid superimposed construction disturbances. The lower tunnel will be excavated using the same excavation method as the upper tunnel. The installation procedures of shock absorbers, inverted cone anchor bolt structures, grouting pipes and displacement sensors in the tunnel will be repeated during the construction of the upper tunnel. Step (5), secondary reinforcement: open the spiral cap of the grouting pipe, remove the sealing parts, connect the external grouting device through the threaded sleeve, and inject cement grout; during the grouting process, prevent grout backflow through the anti-backflow valve, monitor the grouting pressure changes in real time, stop grouting when the pressure reaches the design value and stabilizes, close the grouting device valve, and seal the grouting pipe port; after the secondary reinforcement is completed, carry out curing, test the grouting density, and ensure that the soil around the tunnel is reinforced evenly and without holes or cracks; Step (6), displacement monitoring and dynamic adjustment: throughout the construction process, three-dimensional displacement sensors collect slope displacement data, and displacement sensors inside the tunnel monitor tunnel deformation in real time; when the slope cross-sectional displacement is detected to be close to the threshold, grouting is supplemented through pressure grouting holes; when the lateral displacement of the tunnel is close to the threshold, the tunneling speed is reduced.

[0006] Furthermore, in step (3), after the shock absorber is installed, three excavation holes are opened in the surrounding rock of the tunnel. The three holes are connected in series through the central hole. The three holes are distributed in an irregular pentagonal shape. The threaded steel bars are driven into the holes from the surrounding rock in opposite directions at a certain inclination and elevation angle. The steel bars are exposed in the holes for a certain length. Concrete is injected into the three excavation holes and compacted with a vibrator. After curing, an inverted cone anchor structure is formed, which forms an integral anchoring system with the steel bars.

[0007] Furthermore, before the construction of the upper and lower tunnels, isolation columns are constructed. The isolation columns are located between the upper and lower tunnels and are made of concrete. Multiple strain gauges are evenly spaced along the axial direction on both sides of the isolation columns. The strain gauges are attached to the inside of the steel cage of the isolation columns and led out to the monitoring equipment through wires to monitor stress changes in real time.

[0008] Furthermore, in step (3), the shock absorber includes an upper base, a lower base, a spring, and a limiting structure. The upper base is slidably disposed in the inner hole of the lower base. The upper base and the lower base are connected by a spring, which is disposed on the inner side of the upper base and the lower base. The limiting structure is fixed on the outer side of the lower end of the upper base. The upper base and the lower base of the same set of shock absorbers are respectively connected to the steel arch frame and the steel plate embedded in the secondary lining.

[0009] Furthermore, in step (6), a displacement control threshold is set: when the single displacement of the slope is ≥5mm, the tunnel settlement is ≥3mm, or the stress of the partition column is ≥1.5MPa, construction is immediately stopped and emergency response measures are initiated; when the displacement of a certain section of the slope is monitored to reach 4.8mm, grouting is supplemented through the pressure grouting hole, the grouting pressure is 1.5MPa, and the supplementary grouting volume is 0.5m³ / hole. After 3 days, the displacement stabilizes within 1.2mm, and normal construction is resumed; when the lateral displacement of the tunnel approaches the threshold, the tunnel excavation speed is adjusted from 1.5m / d to 1.0m / d.

[0010] The beneficial effects of this invention are as follows: This invention discloses a method for construction support and displacement control of a double-tunnel on a loose slope, which involves constructing a three-dimensional slope protection system using drainage ditches, protective nets, and pressure grouting holes. The inverted cone anchor bolt structure and the grouting pipe form a composite anchor for the tunnel, and the isolation columns isolate disturbances between the upper and lower tunnels. This achieves coordinated stability between the loose slope and the double-tunnel, effectively avoiding safety risks such as slope landslides and tunnel collapses. Attached Figure Description

[0011] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following figures are provided for illustration: Figure 1 This is a schematic diagram of the slope protection structure and displacement monitoring of the present invention; Figure 2 This is a schematic diagram showing the location of the partition column and the tunnel in this invention; Figure 3 This is a schematic diagram of the tunnel support system of the present invention; Figure 4 This is a schematic diagram of the grouting conduit of the present invention; Figure 5 This is a schematic diagram of the shock absorber structure of the present invention; The following are labeled in the attached diagram: 1. Drainage ditch; 2. Three-dimensional displacement sensor; 3. Concrete column; 4. Surface soft soil; 5. Lower unstable rock and soil mass; 6. Pressure grouting hole; 7. Upper tunnel; 8. Isolation column; 9. Strain gauge; 10. Lower tunnel; 11. Shock absorber; 12. Reinforcing bar; 13. Three-chamber excavation hole; 14. Grouting pipe; 15. Rock mass; 16. Anti-backflow valve; 17. Threaded sleeve; 18. Grouting pipe cover; 19. External grouting device; 20. Upper base; 21. Spring; 22. Limiting structure; 23. Lower base; 24. Displacement sensor inside the tunnel. Detailed Implementation

[0012] like Figures 1-5 As shown, the present invention discloses a method for top-down construction support and displacement control of a twin-tunnel on a loose slope, comprising the following steps: Step (1), slope pretreatment: Before construction, remove the surface soil, loose rocks and weeds of the slope, and trim the slope surface to make the slope gradient gentler and reduce local stress concentration; excavate trapezoidal drainage ditch 1 at the highest, middle and lowest points of the slope, and use concrete to plaster the inner wall to ensure that the drainage ditch 1 is leak-free; the cross section of the drainage ditch 1 is trapezoidal, with a width of 50cm and a depth of 30cm on the upper side of the trapezoid, and the inner wall is plastered with C15 concrete. A rounded transition is set at the corner to prevent water flow from eroding the slope soil, quickly drain the surface water, reduce the soil moisture content and reduce the risk of landslide.

[0013] Three-dimensional displacement sensors 2 are arranged at intervals along the slope surface, with a spacing of 5m. The sensors are fixed to the slope soil by pre-embedded steel plates, with the steel plates embedded in the soil to a depth of not less than 30cm to ensure monitoring stability. The sensor range is ±50mm, and the monitoring accuracy is ±0.1mm. The slope sliding displacement data is collected in real time through a wireless transmission module to capture the relative sliding trend between rock layers. The three-dimensional displacement sensors 2 are welded and fixed to the pre-embedded steel plates, which are anchored to the slope soil. The three-dimensional displacement sensors 2 are connected to the wireless transmission module and debugged to normal working condition. Concrete columns 3 are poured under each ditch, and high-strength steel wire mesh is laid through the concrete columns 3. Three sets of concrete columns 3 are evenly arranged along the slope direction, with a cross-sectional size of 0.3m×0.3m, and are buried in the slope soil to a depth of 1.5-2m. The columns are made of C30 concrete and are internally reinforced with four 16mm diameter HRB400 threaded steel bars 12 as main reinforcement. Concrete columns 3 were poured beneath each ditch. After the 12 cages of reinforcing steel for the columns were tied, they were placed in the foundation pit, and C30 concrete was poured and vibrated to ensure compaction. After curing for 7 days, connectors were installed on the top of the columns. The protective netting used high-strength steel wire mesh with a mesh size of 5cm×5cm was fixed to the connectors on the top of the concrete columns 3 with clips, forming a double-layer protective barrier to prevent falling rocks from impacting the tunnel structure.

[0014] Step (2) Slope pre-reinforcement: Drill holes vertically on the slope surface, record the soil and rock stratification in real time during drilling, and determine the location of potential sliding surfaces; use pressure grouting holes 6 to be laid vertically on the slope surface, with a hole spacing of 2-3m, a hole diameter of 80-100mm, and a hole depth of 6-10m, penetrating from the surface soft soil 4 to the lower unstable soil and rock 5, to ensure that the grouting reinforcement depth covers the potential sliding surface. The grouting holes are dry drilled with a drilling rig. After drilling, the holes are cleaned with high-pressure air to remove the slag and debris in the holes to avoid blocking the grouting channels; inject early-strength sulfoaluminate cement grout with a grout ratio of 0.8:1, and control the grouting pressure at 1.2MPa. Use a skip-hole grouting method from the outside to the inside and from top to bottom, with an interval of no less than 4 hours between adjacent grouting holes to avoid grout cross-hole. The grouting method is adopted from the outside to the inside and from top to bottom with staggered holes. After grouting, curing is carried out, and soil strength is tested by drilling to ensure that the compressive strength of the soil in the reinforced area meets the pre-reinforcement design requirements. After grouting, curing is carried out for 8 days, and soil strength is tested by drilling to ensure that the compressive strength of the soil in the reinforced area is ≥0.8MPa, which meets the pre-reinforcement design requirements.

[0015] Step (3) Construction of Upper Tunnel 7: Upper Tunnel 7 is excavated, and the advance of each excavation is controlled at 3-5m. Smooth blasting technology is used during the excavation process to reduce the disturbance to the surrounding rock. After blasting, the loose rocks on the tunnel face are removed in time. Shock absorbers 11 are installed along the circumference of the tunnel. The shock absorbers 11 are installed between the steel arch frame and the steel plate embedded in the secondary lining. Grouting pipes 14 are laid along the circumference of the tunnel. The front end of the pipe is driven into the surrounding rock. After installing the anti-backflow valve 16, it is connected to the external grouting device 19 through the threaded sleeve 17. When grouting is not performed, the port is sealed with a spiral cap. Displacement sensors 24 are installed on the top and side walls of Upper Tunnel 7. The displacement sensors are fixed to the initial support steel arch frame of the tunnel and connected to the data acquisition system. The system is adjusted to collect tunnel settlement and lateral displacement data in real time. Displacement sensors 24 are installed on the top and side walls of the upper tunnel 7 and the lower tunnel 10, with three sensors deployed in each tunnel section: one on the top and one on each side wall. The sensors are fiber optic displacement gauges with a range of 0~50mm and a monitoring accuracy of ±0.05mm. They monitor tunnel settlement and lateral displacement in real time, forming a two-dimensional monitoring network with the slope three-dimensional displacement sensors 2.

[0016] Grouting conduits 14 are laid out along the circumference of the tunnel, with a circumferential spacing of 0.8–1.1 m, a length of 6–7 m, and an outer diameter of 36–50 mm. They are welded steel pipes with a wall thickness of 1–2 mm. From 1 m at the rear end to the front end, a grout outlet hole with a diameter of 8–10 mm is set every 15–20 cm, arranged in a quincunx pattern. An anti-backflow valve 16 is installed inside the grouting conduit 14, with a working pressure of 0.3–1.0 MPa, to prevent grout backflow during the grouting process and ensure grouting quality. The anti-backflow valve 16 is a backward-inclined steel plate installed inside the grouting conduit 14; two sets of stacked steel plates constitute one set.

[0017] Step (4): Construction of Lower Tunnel 10. After the grouting and curing of the support structure of Upper Tunnel 7 and the soil strength of the reinforced area reach the standard, the excavation of Lower Tunnel 10 will be started. The distance between the face of Lower Tunnel 10 and the nearest support section of Upper Tunnel 7 will be controlled to avoid the superposition of construction disturbances. Lower Tunnel 10 will be excavated using the same excavation method as Upper Tunnel 7. The installation procedures of shock absorber 11, inverted cone anchor bolt structure, grouting pipe 14 and displacement sensor 24 in the tunnel will be repeated during the construction of Upper Tunnel 7. Specifically, after grouting and curing of the support structure of Upper Tunnel 7 for 28 days and the soil strength of the reinforced area reaches 1.0MPa, the excavation of Lower Tunnel 10 will be started. The distance between the face of Lower Tunnel 10 and the nearest support section of Upper Tunnel 7 will be controlled at 12m, which is greater than twice the tunnel excavation width of 6m, to avoid the superposition of construction disturbances.

[0018] The excavation speed of Upper Tunnel 7 was controlled at 2m / day, and the excavation speed of Lower Tunnel 10 was controlled at 1.5m / day. When the displacement of a certain section of the slope was monitored to reach 4.8mm, the excavation was stopped in time, and grouting was supplemented through pressure grouting hole 6. After 3 days, the displacement stabilized within 1.2mm, ensuring construction safety.

[0019] Step (5), secondary reinforcement: open the spiral cap of the grouting conduit 14, remove the sealing parts, connect the external grouting device 19 through the threaded sleeve 17, inject cement grout with a water-cement ratio of 1:1, control the grouting pressure at 0.6MPa, adopt the skip-hole interval grouting method, the grouting duration of each grouting hole is 25 minutes, and the grouting volume is 1.4m³; during the grouting process, the anti-backflow valve 16 is used to prevent mortar backflow, and the grouting pressure change is monitored in real time. When the pressure reaches the design value and stabilizes, stop the grouting, close the grouting device valve, and seal the port of the grouting conduit 14; after the secondary reinforcement is completed, perform curing, check the grouting density, and ensure that the soil around the tunnel is reinforced evenly without holes or cracks; Step (6), displacement monitoring and dynamic adjustment: throughout the construction process, the three-dimensional displacement sensor 2 collects slope displacement data, and the tunnel displacement sensor 24 monitors tunnel deformation in real time; when the slope cross-sectional displacement is detected to be close to the threshold, grouting is supplemented through the pressure grouting hole 6; when the tunnel lateral displacement is close to the threshold, the tunneling speed of the lower tunnel 10 is reduced.

[0020] In this embodiment, in step (3), after the shock absorber 11 is installed, a three-chamber excavation hole 13 is opened in the surrounding rock of the tunnel. The three chambers are connected in series through a central hole. The three holes are distributed in an irregular pentagonal shape. Threaded steel bars 12 are driven into the holes from the surrounding rock at a certain inclination and elevation angle, with a certain length of steel bar 12 exposed inside the hole. C35 early-strength concrete is injected into the three-chamber excavation hole 13 and compacted using a vibrator. After curing, an inverted cone anchor structure is formed, which forms an integral anchoring system with the steel bar 12. The diameter of the three-chamber excavation hole 13 is 18cm, the depth is 5.5m, and the three holes are distributed in an irregular pentagonal shape. Threaded steel bars 12 with a diameter of 3.5cm are driven into the holes at a 50° included angle and a 7° upward elevation angle, with a 10cm exposed length of steel bar 12.

[0021] The three-chamber excavation holes 13 of this invention are opened within the surrounding rock of the tunnel, with a diameter of 15-20 cm and a depth of 6-8 m. The three holes are irregularly distributed in a pentagonal shape, forming an inverted cone shape with the innermost hole being larger than the outermost. The reinforcing bars 12 are HRB400 threaded steel bars with a diameter of 3-4 cm. The driving angle is 40°-60° with the longitudinal vertical plane of the tunnel. Adjacent reinforcing bars 12 are arranged in opposite directions and have pointed ends to facilitate driving into the surrounding rock. C30 early-strength concrete is injected into the three-chamber excavation holes 13 to form a mechanically interlocking whole with the reinforcing bars 12, enhancing the anchorage force between the tunnel and the surrounding rock.

[0022] In this embodiment, before the construction of the upper tunnel 7 and the lower tunnel 10, a partition column 8 is constructed. The partition column 8 is located between the upper tunnel 7 and the lower tunnel 10. The partition column 8 is made of cast concrete. Multiple strain gauges 9 are evenly spaced along the axial direction on both sides of the partition column 8. The strain gauges 9 are attached to the inside of the steel reinforcement cage 12 of the partition column 8 and are led out to the monitoring equipment through wires to monitor stress changes in real time. One partition column 8 is arranged every 5m along the radial direction of the tunnel, penetrating the central rock column between the upper tunnel 7 and the lower tunnel 10. The cross-sectional dimensions are 1.0m × 1.2m. It is made of C35 concrete and has a double-layer steel reinforcement mesh inside. A strain gauge 9 is staggered every 1m along the height direction inside the partition column 8. The strain gauge 9 is model BX120-3AA and is used to monitor stress changes in the central rock column in real time and isolate the upper tunnel 7 and the lower tunnel 10 from construction disturbances.

[0023] In this embodiment, in step (3), the shock absorber 11 includes an upper base 20, a lower base 23, a spring 21, and a limiting structure 22. The upper base 20 is slidably disposed in the inner hole of the lower base 23. The upper base 20 and the lower base 23 are connected by the spring 21, which is disposed on the inner side of the upper base 20 and the lower base 23. The limiting structure 22 is fixed on the outer side of the lower end of the upper base 20. The upper base 20 and the lower base 23 of the same set of shock absorbers 11 are respectively connected to the steel arch frame and the steel plate embedded in the secondary lining. The shock absorbers 11 are evenly distributed along the circumference of the tunnel, with a spacing of 1.5 to 2 m. The upper base 20 is made of Q235 steel plate and is fixed to the initial support steel arch frame of the tunnel by welding. The lower base 23 is bolted to the steel plate embedded in the secondary lining of the tunnel. The spring 21 is a cylindrical helical compression spring 21 with a stiffness of 50 to 80 N / mm. The limiting structure 22 adopts a sleeve design, with a maximum extension and contraction of 50-80mm, to prevent the spring 21 from excessively deforming and failing, and to achieve buffering and absorption of earthquake and construction vibration loads.

[0024] In this embodiment, in step (6), a displacement control threshold is set: when the single displacement of the slope is ≥5mm, the tunnel settlement is ≥3mm, or the stress of the partition column 8 is ≥1.5MPa, construction is stopped immediately and emergency response measures are initiated; when the displacement of a certain section of the slope is monitored to reach 4.8mm, grouting is supplemented through the pressure grouting hole 6, the grouting pressure is 1.5MPa, and the supplementary grouting volume is 0.5m³ / hole. After 3 days, the displacement stabilizes within 1.2mm, and normal construction is resumed; when the lateral displacement of the tunnel approaches the threshold, the tunneling speed of the lower tunnel 10 is adjusted from 1.5m / d to 1.0m / d.

[0025] This invention constructs an integrated technical system of slope pretreatment, pre-reinforcement, tunnel support, dual-dimensional monitoring, and shock absorption. It forms a three-dimensional slope protection through drainage ditch 1, protective net, and pressure grouting hole 6. The inverted cone anchor bolt structure and grouting pipe 14 form a composite tunnel anchorage. The isolation column 8 isolates the disturbance of the upper and lower tunnels 10, realizing the coordinated stability of loose slope and double tunnel, and effectively avoiding safety risks such as slope landslide and tunnel collapse.

[0026] This invention employs a dual-dimensional monitoring network consisting of 2 three-dimensional slope displacement sensors, 24 tunnel displacement sensors, 8 partition columns, and 9 strain gauges to capture real-time changes in slope sliding, tunnel deformation, and stress in the rock columns. The monitoring accuracy reaches ±0.05mm, enabling early warning and dynamic control of displacement risks. This solves the problems of traditional single-dimensional monitoring and delayed early warning.

[0027] By coordinating the design of the shock absorber 11 with the support structure, buffering vibration energy with the spring 21, and preventing excessive deformation with the limiting structure 22, the impact of earthquakes and construction vibrations on the tunnel structure is effectively reduced, and the seismic performance is improved by more than 40%, making it suitable for tunnel construction in areas with high intensity earthquakes.

[0028] The design of the threaded sleeve 17 connection, the spiral grouting pipe cover 18 and the anti-backflow valve 16 of the grouting component of this invention avoids grout leakage and backflow, and improves the uniformity of grouting by 35%; the inverted cone anchor bolt structure enhances the anchoring force through mechanical interlocking, and works with the grouting conduit 14 to form a reinforcement system, which improves the bearing capacity of the tunnel surrounding rock by more than 50%.

[0029] The construction method of this invention has a continuous process and clear parameters. It can be implemented using conventional construction equipment without the need for special equipment. It reduces construction costs by 28% and shortens the construction period by 32%, which has significant economic benefits and engineering practicality. It can be widely applied to the construction of twin tunnels on loose slopes.

Claims

1. A method for supporting and displacement control of loose slope double-hole tunnel construction from top to bottom, characterized in that, Includes the following steps: Step (1), slope pretreatment: Before construction, remove loose soil, dangerous rocks and weeds from the surface of the slope, and trim the slope surface to make the slope gradient gentler and reduce local stress concentration; excavate trapezoidal drainage ditches at the highest, middle and lowest points of the slope, and use concrete to plaster the inner wall to ensure that the drainage ditches are leak-free; arrange three-dimensional displacement sensors at intervals along the slope surface, weld and fix the three-dimensional displacement sensors to the pre-embedded steel plates, anchor the pre-embedded steel plates to the slope soil, connect the three-dimensional displacement sensors to the wireless transmission module and debug to normal working state; pour concrete columns under each ditch, and lay high-strength steel wire protective netting through the columns; Step (2), slope pre-reinforcement, drilling holes on the vertical slope surface, recording the soil and rock layering in real time during drilling to determine the location of potential sliding surfaces; after drilling, using high-pressure air to clean the holes and remove slag and dust to ensure unobstructed grouting channels; injecting early-strength sulfoaluminate cement grout, using a skip-hole interval grouting method from the outside to the inside and from top to bottom; curing after grouting, and testing the soil strength by drilling samples to ensure that the compressive strength of the soil in the reinforced area meets the pre-reinforcement design requirements; Step (3) Upper tunnel construction, upper tunnel excavation, smooth blasting technology is used during the tunneling process, and loose rocks at the tunnel face are removed in time after blasting; shock absorbers are installed along the circumference of the tunnel, and the shock absorbers are installed between the steel arch frame and the steel plate embedded in the secondary lining; grouting pipes are laid along the circumference of the tunnel, the front end of the pipe is driven into the surrounding rock, and after installing the anti-backflow valve, the external grouting device is connected through the threaded sleeve. When grouting is not performed, the port is sealed with a spiral cap; displacement sensors are installed on the top and side walls of the upper tunnel, the displacement sensors are fixed to the initial support steel arch frame of the tunnel, connected to the data acquisition system, and debugged to collect tunnel settlement and lateral displacement data in real time; Step (4): Lower tunnel construction. After the upper tunnel support structure has been grouted and cured, and the soil strength in the reinforced area has reached the standard, the lower tunnel excavation will begin. The distance between the lower tunnel face and the nearest support section of the upper tunnel will be controlled to avoid superimposed construction disturbances. The lower tunnel will be excavated using the same excavation method as the upper tunnel. The installation procedures for shock absorbers, inverted cone anchor bolt structures, grouting pipes, and displacement sensors inside the tunnel will be repeated during the upper tunnel construction. Step (5), secondary reinforcement: open the spiral cap of the grouting pipe, remove the sealing parts, connect the external grouting device through the threaded sleeve, and inject cement grout; during the grouting process, prevent grout backflow through the anti-backflow valve, monitor the grouting pressure changes in real time, stop grouting when the pressure reaches the design value and stabilizes, close the grouting device valve, and seal the grouting pipe port; after the secondary reinforcement is completed, perform curing, check the grouting density, and ensure that the soil around the tunnel is reinforced evenly and without holes or cracks; Step (6), displacement monitoring and dynamic adjustment: throughout the construction process, three-dimensional displacement sensors collect slope displacement data, and displacement sensors inside the tunnel monitor tunnel deformation in real time; when the slope cross-sectional displacement is detected to be close to the threshold, grouting is supplemented through pressure grouting holes; when the lateral displacement of the tunnel is close to the threshold, the tunneling speed is reduced.

2. The method according to claim 1, characterized in that, In step (3), after the shock absorber is installed, three excavation holes are opened in the surrounding rock of the tunnel. The three holes are connected in series through the central hole. The three holes are distributed in an irregular pentagonal shape. The threaded steel bars are driven into the holes from the surrounding rock in opposite directions at a certain inclination and elevation angle. The steel bars are exposed in the holes for a certain length. Concrete is injected into the excavation holes of the three holes and compacted with a vibrator. After curing, an inverted cone anchor structure is formed, which forms an integral anchoring system with the steel bars.

3. The method according to claim 2, wherein, Before constructing the upper and lower tunnels, partition columns are constructed between them. The partition columns are made of concrete and multiple strain gauges are evenly spaced along the axial direction on both sides of the partition columns. The strain gauges are attached to the inside of the reinforcing cage of the partition columns and led out to the monitoring equipment through wires to monitor stress changes in real time.

4. The method according to claim 3, characterized in that, In step (3), the shock absorber includes an upper base, a lower base, a spring, and a limiting structure. The upper base is slidably installed in the inner hole of the lower base. The upper base and the lower base are connected by a spring, which is installed on the inner side of the upper base and the lower base. The limiting structure is fixed on the outer side of the lower end of the upper base. The upper base and the lower base of the same set of shock absorbers are respectively connected to the steel arch frame and the steel plate embedded in the secondary lining.

5. The method according to claim 4, wherein, In step (6), the displacement control threshold is set as follows: when the single displacement of the slope is ≥5mm, the tunnel settlement is ≥3mm, or the stress of the partition column is ≥1.5MPa, construction is stopped immediately and emergency measures are initiated; when the displacement of a certain section of the slope is monitored to reach 4.8mm, grouting is supplemented through the pressure grouting hole, the grouting pressure is 1.5MPa, and the supplementary grouting volume is 0.5m³ / hole. After 3 days, the displacement stabilizes within 1.2mm, and normal construction is resumed; when the lateral displacement of the tunnel approaches the threshold, the tunnel excavation speed is adjusted from 1.5m / d to 1.0m / d.

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