Construction and supporting method for upward slope above reconstructed and extended tunnel portal section

Abstract

The invention relates to the technical field of tunnel extension, in particular to a construction and support method for an upward slope above a reconstructed and extended tunnel portal section, which comprises the following steps of: S1, reconnaissance and construction measurement of rock masses of the upward slope and the portal section; s2, the upward slope is partitioned and reinforced; s2.1, an upward slope on the upper portion of the hole opening section is divided into three reinforcing areas, namely an advanced pipe shed grouting reinforcing area (1), an expanded excavation upper portion grouting reinforcing area (2) and a ground surface anchor rod grouting reinforcing area (3); s2.2, the construction reinforcement sequence is from the second area to the third area to the first area; s3, extension excavation and supporting of the tunnel at the portal section; and S3.1, adopting a cross mid-partition method for hidden holes at the openings of the first extension tunnel and the second extension tunnel. According to the method, the influence of construction disturbance on the overall stability of the existing tunnel and the upward slope can be reduced to the maximum extent through the upward slope partition reinforcing method, and the safety and stability in the construction process are ensured; meanwhile, through tunnel extension excavation and supporting of the portal section, the influence of tunnel construction on the existing tunnel and interlaid rocks is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel expansion, and particularly to a construction and support method for the upper slope of the entrance section of a reconstructed and expanded tunnel. Background Art

[0002] With the rapid development of the economy and the continuous increase in traffic flow, many existing tunnels are facing the urgent need for reconstruction and expansion due to long service time, serious deterioration of surrounding rocks, and the inability of the cross-sectional scale to meet the current transportation requirements. During the construction of tunnel reconstruction and expansion, the construction of the entrance section has become one of the key points and difficulties of the entire tunnel project.

[0003] The entrance section of a tunnel refers to the transition area from the tunnel portal to the area completely buried underground. This area is usually near the mountain surface, which is a key position where the tunnel intersects with the mountain slope. The overlying layer above it is thin, the weathering degree of rock and soil mass is high, the geological conditions are complex, and the stability is poor. Especially during the reconstruction and expansion process, it is necessary to excavate the upper slope above the existing tunnel to meet the requirements of the new tunnel cross-section, and the construction risk in this area increases significantly.

[0004] The upper slope of the entrance section is mostly composed of severely weathered rock masses or accumulations. During the construction of the existing tunnel, a large amount of concrete pouring is relied on to ensure its stability. The existing reconstruction and expansion construction process requires the removal of a large volume of concrete at the entrance of the existing tunnel and the excavation of the upper slope, which may not only cause rockfalls and surface cracks, but also cause serious damage to the existing tunnel, resulting in cracking, collapse, and even complete blockage of the tunnel entrance. Therefore, the stability of the upper slope above the entrance section of the reconstructed and expanded tunnel has become a key issue for construction safety, and scientific exploration, reasonable design, and effective support treatment are required before excavation.

[0005] However, the existing support design and construction process are mainly for newly built tunnels. When reconstructing and expanding on the basis of existing tunnels, especially when it comes to the excavation and re-support of the upper slope of the entrance section, the current existing construction methods are not perfect, and there is still a lack of mature and systematic reference cases and technical guidance. Therefore, in view of the difficulties and problems existing in the excavation and support process of the upper slope above the entrance section during the tunnel reconstruction and expansion project, the present invention proposes a construction and support method for the upper slope above the entrance section of a reconstructed and expanded tunnel, providing a reliable technical solution for this field. Summary of the Invention

[0006] The purpose of the present invention is to provide a construction and support method for the upper slope above the entrance section of a reconstructed and expanded tunnel to solve the problems existing in the above-mentioned prior art.

[0007] To achieve the above purpose, the present invention provides the following solution: A construction and support method for the upper slope above the entrance section of a reconstructed and expanded tunnel, comprising the following steps:

[0008] S1. Investigation and construction survey of the cutting slope and the rock mass at the tunnel entrance;

[0009] S2. Division and reinforcement of the cutting slope;

[0010] S2.1. Divide the cutting slope at the upper part of the tunnel entrance section into three reinforcement areas, namely the advanced pipe shed grouting reinforcement area ①, the upper excavation grouting reinforcement area ②, and the surface bolt grouting reinforcement area ③;

[0011] S2.2. The construction reinforcement sequence is: area ② → area ③ → area ①;

[0012] S3. Tunnel expansion excavation and support of the tunnel entrance section;

[0013] S3.1. The CRD method is adopted for the blind tunnels at the entrances of the expanded tunnel 1 and the expanded tunnel 2.

[0014] Preferably, through the step S1, determine the bright-dark boundary line between the open cut tunnel and the blind tunnel, and determine the center lines, the excavation elevation and the excavation side line ranges of the expanded tunnel 1 and the expanded tunnel 2. At the same time, compare the overlapping situation between the rock mass fragmentation area and the excavation ranges of the expanded tunnel 1 and the expanded tunnel 2 to evaluate the potential risks of the construction.

[0015] Preferably, the construction sequence of the area ② is: at the upper part of the tunnel entrance section at the bright-dark boundary line at the junction of the open cut tunnel and the blind tunnel, excavate grouting holes in the area ②, insert grouting pipes into the grouting holes and inject grout into the grouting pipes.

[0016] Preferably, the grout is injected in two stages. First, inject the coarse-grained grout. After the preliminary consolidation of the coarse-grained grout, inject the thixotropic grout.

[0017] Preferably, the construction sequence of the area ③ is: clean the loose stones and the collapsed surface soil on the cutting slope surface, excavate in layers, and carry out bolt grouting on the cutting slope surface.

[0018] Preferably, the construction sequence of the area ① is: after the reinforcement of the area ③ is completed, arrange a number of positioning steel frames along the longitudinal direction in the area ①. Concrete foundations are installed at the two ends of the positioning steel frames. A number of guide steel pipes are welded to the top of the positioning steel frames through fixed steel bars. Formwork for the guide wall is erected along the excavation contour line outside the tunnel entrance for the positioning steel frames and the guide steel pipes. A steel reinforcement cage is arranged in the guide wall, and a number of grouting steel pipes are arranged in the steel reinforcement cage.

[0019] Preferably, the excavation parts of the expanded tunnel 1 and the expanded tunnel 2 are respectively divided into: part 1, part 2, part 3 and part 4; the excavation sequence is: part 1 → part 2 → part 3 → part 4.

[0020] Preferably, the No. 1 unit is arranged above the existing tunnel 1 and the existing tunnel 2, the No. 2 unit is arranged below the existing tunnel 1 and the existing tunnel 2, the No. 3 unit is arranged at the upper part of the excavation side of the existing tunnel 1 and the existing tunnel 2, and the No. 4 unit is arranged at the lower part of the excavation side of the existing tunnel 1 and the existing tunnel 2.

[0021] Preferably, the cross-middle diaphragm method is as follows: first excavate any one of the expanded tunnel 1 or the expanded tunnel 2, and then excavate the unexcavated expanded tunnel 1 or the expanded tunnel 2.

[0022] Preferably, the tunnel faces of the expanded tunnel 1 and the expanded tunnel 2 are staggered by a distance equal to the excavation width of one tunnel.

[0023] The present invention discloses the following technical effects:

[0024] By means of the slope partition reinforcement method, the present invention can minimize the influence of construction disturbance on the overall stability of the existing tunnel and the slope, and ensure the safety and stability during the construction process; meanwhile, through the excavation and support of the tunnel expansion at the portal section, the present invention effectively reduces the influence of tunnel construction on the existing tunnel and the middle rock stratum.

[0025] The present invention can effectively ensure the construction safety of the portal section of the reconstructed and expanded tunnel, provide a good construction safety space for the subsequent processes, and ensure the safe and efficient progress of the reconstruction and expansion project. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0027] Figure 1 It is a schematic diagram of the tunnel expansion plan of the present invention;

[0028] Figure 2 It is a schematic diagram of the slope reinforcement partition of the present invention;

[0029] Figure 3 For the present invention Figure 2 The schematic cross-sectional structure along 1-1 of the present invention;

[0030] Figure 4 It is a schematic diagram of the pipe shed advanced grouting reinforcement of the present invention;

[0031] Figure 5 For the present invention Figure 3 The enlarged structural schematic diagram at A in the present invention;

[0032] Figure 6Front view schematic diagram of the steel reinforcement cage inside the pipe shed of the present invention;

[0033] Figure 7 Of the present invention Figure 4 Enlarged structural schematic diagram at location B in the present invention;

[0034] Figure 8 Excavation schematic diagram of the CRD method of the present invention;

[0035] Among them, 1, open cut tunnel; 2, blind tunnel; 3, boundary line between open cut and blind tunnel; 4, perforated steel pipe; 5, steel mesh; 6, shotcrete; 7, hollow grouting bolt; 8, positioning steel frame; 9, guide wall; 10, grouting steel pipe; 11, concrete foundation; 12, support for the extended tunnel; 13, guide steel pipe; 14, fixed steel bar; 151, steel bar; 152, steel ring; 16, center line of the first extended tunnel. Specific embodiments

[0036] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all 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.

[0037] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0038] Embodiment 1

[0039] Referring to Figures 1 - 8 , the present invention provides a construction and support method for the upper slope of the entrance section of an extended and reconstructed tunnel, including the following steps:

[0040] S1. Investigation and construction survey of the upper slope and the rock mass at the tunnel entrance; The rock mass situation of the upper slope above the tunnel entrance section is investigated on site. First, the upper slopes of the entrance sections of the existing Tunnel 1 and existing Tunnel 2 are investigated on site, and in combination with the geological exploration report, the fractured rock strata areas are judged to provide a basis for the rock mass reinforcement plan before excavation.

[0041] The boundary line 3 between the open cut tunnel 1 and the blind tunnel 2 is determined, and the center lines, the excavation elevation and the excavation side line range of the first extended tunnel and the second extended tunnel are determined. At the same time, the overlapping situation between the fractured rock strata areas and the excavation ranges of the first extended tunnel and the second extended tunnel is compared to evaluate the potential risks of construction.

[0042] S2. Division and reinforcement of the upper slope;

[0043] S2.1. Divide the upper cut slope of the tunnel entrance section into three reinforcement areas, namely the advanced pipe-roof grouting reinforcement area ①, the upper excavation grouting reinforcement area ②, and the surface anchor grouting reinforcement area ③. There is a large area of fragmentation in the rock mass above the existing tunnel entrance section. Construction disturbance may lead to a reduction in stability and is extremely prone to collapse. The upper cut slope above the tunnel entrance section is divided into three reinforcement areas, and different construction methods are adopted according to the rock mass characteristics and support requirements to achieve progressive stability control of the fractured surrounding rock.

[0044] S2.2. The construction reinforcement sequence is: area ② → area ③ → area ①;

[0045] The construction sequence of the advanced pipe-roof grouting reinforcement area ② is as follows: Drill grouting holes in the upper area ② of the tunnel entrance section at the light-dark boundary line 3 at the junction of the open cut tunnel 1 and the hidden tunnel 2. The grouting holes are arranged in a plum blossom shape, with an inclination angle of 5° - 15° downward. Drill holes from the light-dark boundary line 3 at the junction of the open cut tunnel 1 and the hidden tunnel 2, and use the steel flower pipe 4 as the grouting pipe for grouting. The grouting is carried out in two stages. First, carry out coarse-grained grouting. The injected slurry is cement mortar. The coarse-grained slurry is injected at a low pressure through the grouting pipe. The initial grouting pressure is 0.5 - 1 Mpa, and it is gradually pressurized to 2 Mpa. After the initial consolidation of the coarse-grained slurry, use the thixotropic slurry for the second-stage grouting.

[0046] The grouting adopts the intermittent grouting method. The pressure of the thixotropic slurry grouting is slightly higher than that of the coarse-grained slurry, so that the slurry can penetrate into small cracks and micropores. The grouting pressure is 1.0 - 2.0 Mpa. After the grouting is completed, lay a steel mesh 5 on the surface of area ② and spray concrete 6 to fix the cut slope.

[0047] The slurry is injected in two stages. First, carry out coarse-grained slurry grouting. After the initial consolidation of the coarse-grained slurry, inject the thixotropic slurry.

[0048] Area ② is the key point of the cut slope reinforcement and is also the area to be reinforced first. The purpose is that it can not only prevent the negative impact of the disturbance during the cut slope excavation on the existing tunnel, but also slow down the impact on the upper surface of the ground during the subsequent removal of the support. Due to the serious fragmentation of the rock mass in area ②, the construction disturbance may significantly affect the stability of the surrounding rock. For this area, the present invention adopts a reinforcement method combining double gradients of coarse-grained grouting and thixotropic slurry.

[0049] In area ②, a grouting method combining double gradients of coarse-grained grouting and thixotropic grout is adopted. First, coarse-grained grouting is carried out to fill and seal large pores and strata with relatively wide fissures, forming a preliminary support framework. After the preliminary consolidation of the coarse-grained grout, thixotropic grout is used for the second-stage grouting to fill smaller fissures and microvoids; the coarse-grained grouting is mainly used to fill large fissures, enhance the overall strength of the surrounding rock, form a preliminary support, and prevent large-scale sliding or deformation of the surrounding rock; the thixotropic grouting has good fluidity and can penetrate into smaller fissures and microvoids to play a role in the refinement and reinforcement stage after the coarse-grained grouting. After the thixotropic grout consolidates, a uniform and dense structure is formed to further enhance the stability of the surrounding rock.

[0050] The construction sequence in area ③ is as follows: Clean the loose stones and collapsed surface soil on the surface of the inverted slope, and excavate in layers to ensure the smoothness of the slope surface. Subsequently, carry out anchor grouting on the surface of the inverted slope. First, drill grouting holes in area ③ on the surface, arrange them in a plum blossom shape, and the hole angle forms a 20° angle with the vertical surface direction. Then insert the anchor rods into the drilled holes to ensure that the anchor rods penetrate completely into the stable surrounding rock to ensure their anchoring effect. The anchor rods used are hollow grouting anchor rods 7. Grouting is carried out from bottom to top, and the grouting material is cement slurry with a water-cement ratio of 0.8:1 - 1:1, and the grouting pressure is 1 - 1.5 MPa. By gradually lifting the grouting pipe, the uniform distribution of the slurry is controlled to increase the bonding force between the anchor rod and the surrounding rock and form a stable support.

[0051] The construction sequence in area ① is as follows: After the reinforcement of area ③ is completed, arrange several positioning steel frames 8 along the longitudinal direction in area ①. Concrete foundations 11 are installed at both ends of the positioning steel frame 8. Several guide steel pipes 13 are welded to the top of the positioning steel frame 8 through fixed steel bars 14. The expansion tunnel support 12 is carried out above the guide steel pipes 13. The positioning steel frame 8 and the guide steel pipes 13 are used for formwork erection of the guide wall 9 outside the opening excavation contour line. A steel reinforcement cage is arranged inside the guide wall 9, and several grouting steel pipes 10 are arranged inside the steel reinforcement cage.

[0052] Carry out the construction of the guide wall 9 for the expansion tunnel 1 and the expansion tunnel 2, and carry out advanced large-diameter pipe-shed grouting support for area ①. Area ① is the 120° range of the contour arch for the expansion tunnel 1 and the expansion tunnel 2. Arrange several positioning steel frames 8 along the longitudinal direction in area ① of the expansion tunnel. Above the positioning steel frame 8, that is, within the 120° range of the expansion tunnel arch crown, arrange multiple guide steel pipes 13 according to the designed external insertion angle of 1° - 3°. The guide steel pipes 13 are welded and connected to the positioning steel frame 8 through fixed steel bars 14 to form a stressed whole. Subsequently, carry out formwork erection and concrete pouring of the guide wall 9 outside the opening excavation contour line. Wait for the concrete to cure to the designed strength to obtain the guide wall 9 for the two expansion tunnels.

[0053] After the construction of the guiding wall 9 is completed, grouting steel pipes are arranged by first drilling holes and then inserting pipes. The drilling depth is 20m - 30m, and the grouting steel pipes used are perforated steel pipes 4. The grouting steel pipes are jacked in manually and assisted by machinery. After the grouting steel pipes are placed, steel reinforcement cages are placed inside them to increase the stiffness of the grouting steel pipes. After the steel reinforcement cages are placed, grouting is carried out into the grouting steel pipes. The grouting uses cement slurry with a water-cement ratio of 1:1. The initial pressure is 1 - 1.5MPa, and the final pressure is 2MPa. Grouting is carried out layer by layer from bottom to top in the order of the steel pipes. After grouting, the grouting steel pipes are filled with cement mortar.

[0054] S3. Tunnel expansion excavation and support at the portal section;

[0055] S3.1. For the hidden tunnels 2 at the portals of Tunnel Expansion One and Tunnel Expansion Two, the cross-middle diaphragm method, i.e., the CRD method, is used for excavation.

[0056] Through the slope partition reinforcement method, the present invention can minimize the impact of construction disturbance on the overall stability of the existing tunnel and the slope, ensuring safety and stability during the construction process; at the same time, through the tunnel expansion excavation and support at the portal section, the present invention effectively reduces the impact of tunnel construction on the existing tunnel and the middle rock stratum.

[0057] The present invention can effectively ensure the construction safety of the portal section of the reconstructed and expanded tunnel, provide a good construction safety space for the subsequent processes, and ensure the safe and efficient progress of the reconstruction and expansion project.

[0058] For further optimized solutions, the excavation parts of Tunnel Expansion One and Tunnel Expansion Two are respectively divided into: Part 1, Part 2, Part 3, and Part 4; the excavation sequence is: Part 1 → Part 2 → Part 3 → Part 4.

[0059] For further optimized solutions, Part 1 is set above Existing Tunnel One and Existing Tunnel Two, Part 2 is set below Existing Tunnel One and Existing Tunnel Two, Part 3 is set at the upper part of the excavation side of Existing Tunnel One and Existing Tunnel Two, and Part 4 is set at the lower part of the excavation side of Existing Tunnel One and Existing Tunnel Two.

[0060] For further optimized solutions, the cross-middle diaphragm method is: first excavate any one of Tunnel Expansion One or Tunnel Expansion Two, and then excavate the unexcavated Tunnel Expansion One or Tunnel Expansion Two.

[0061] For further optimized solutions, the tunnel faces of Tunnel Expansion One and Tunnel Expansion Two adjacent to the tunnel are staggered by a distance equal to the excavation width of one tunnel.

[0062] The excavation method of the CRD for the expansion tunnel at one portal section is as follows: First, backfill with gravelly soil to the waist position of the existing tunnel 1, demolish the upper part of the support structure of the existing tunnel 1, excavate the upper bench of the right pilot drift and construct the initial support for the upper bench on the right, the vertical upper temporary support and the right lateral temporary support; after the excavation and support of the upper bench on the right are completed, carry out the excavation and support of the lower bench on the right. After the excavation and support of the right pilot drift are completed, carry out the excavation of the left subsequent drift. Excavate the upper bench of the left drift and construct the initial support and the left lateral temporary support; after the excavation and support of the upper bench on the left are completed, excavate the lower bench on the left and construct the initial support; finally, successively demolish the lateral and vertical middle wall temporary supports, pour the inverted arch secondary lining, and pour the arch wall secondary lining. The initial support of the expansion tunnel includes system bolt grouting, steel mesh and shotcrete.

[0063] Refer to Figure 8 , taking the left tunnel as an example, according to the center line 16 of the expansion tunnel 1, the cross - middle - diaphragm method is used for sectional excavation, and the excavation construction sequence is part 1 (upper bench on the right) → part 2 (lower bench on the right) → part 3 (upper bench on the left) → part 4 (lower bench on the left). The specific implementation steps are as follows:

[0064] Part 1 (upper bench on the right): Backfill with gravelly soil to the waist position ① of the existing tunnel → Demolish the upper secondary lining and initial support of the existing tunnel ② → Excavate the upper bench of the right pilot drift ③ → Construct the initial support, the vertical upper temporary support and the right lateral temporary support ④.

[0065] Part 2 (lower bench on the right): Excavate the lower bench on the right, successively excavate the gravelly soil ①, demolish the lower secondary lining and initial support ⑤, excavate the lower bench of the drift ⑥ → Construct the initial support for the lower bench on the right and the vertical lower temporary support ⑦.

[0066] Part 3 (upper bench on the left): Excavate the upper bench on the left ⑧ → Construct the initial support for the upper bench on the left and the left lateral temporary support ⑨.

[0067] Part 4 (lower bench on the left): Excavate the lower bench on the left ⑩ → Construct the initial support for the lower bench on the left → Demolish the lateral and vertical middle wall temporary supports → Complete the construction of the secondary lining for the inverted arch and the arch wall

[0068] The present invention provides a systematic and zonal construction and support method. Aiming at the special geological conditions of the upper cut - slope above the portal section of the reconstructed and expanded tunnel, an orderly reinforcement and construction plan applicable to the junction of the open - cut tunnel and the hidden - cut tunnel is proposed, effectively solving the problems of broken surrounding rock and poor stability in the portal section of the tunnel.

[0069] 1. The present invention innovatively divides the back slope into three areas for reinforcement, and adopts a "zoning progressive" construction method, starting from area ② and gradually advancing to areas ③ and ①. This sequential reinforcement process can minimize the impact of construction disturbance on the overall stability of the existing tunnel and back slope, ensuring safety and stability during the construction process.

[0070] 2. In the grouting reinforcement of area ②, the dual-gradient grouting process combining coarse-grained grouting and thixotropic grouting is adopted, which can not only quickly fill large cracks to form preliminary support, but also refine and reinforce the micro-cracks of the rock mass, significantly improving the overall strength and stability of the rock mass. This dual-process combination method overcomes the shortcomings of the traditional single grouting method and further optimizes the support effect. Area ③ adopts a support method combining surface anchors and grouting. Through efficient anchoring and uniform grouting, it achieves stable control of the surface rock mass of the back slope and effectively prevents surface slip or collapse caused by construction disturbance. Area ① uses pipe-roof advance support technology, combined with precisely designed guide steel pipes and guide walls, to further reduce the impact of tunnel expansion disturbance on the surrounding rock, ensure the stability of the vault surrounding rock, and provide reliable guarantee for subsequent tunnel excavation and support.

[0071] 3. During the tunnel excavation process, the cross-middle partition wall method was adopted, supplemented by measures such as gravel soil backfill, which significantly reduced the impact of tunnel construction on the existing tunnel and the middle rock. At the same time, the small grouting pipe was used to focus on reinforcing the middle rock, further improving the safety of small clearance tunnel construction and support reliability.

[0072] Embodiment 2

[0073] Reference Figure 1 and Figure 2 , when the minimum clear distance between the existing tunnel one and the existing tunnel two is 10-15m, according to the geological exploration results, the tunnel of Example 2 is a rock tunnel, the surrounding rock level of the portal section is V, and the rock mass is shallow, strongly weathered, broken, and has poor stability; due to the large-scale crushing of the rock mass above the portal section of the existing tunnel, construction disturbance may lead to reduced stability and collapse is very likely to occur. The upper slope of the portal section is divided into three reinforcement areas, namely, the advanced pipe-roof grouting reinforcement area ①, the expanded upper grouting reinforcement area ②, and the surface anchor grouting reinforcement area ③; and different construction methods are used according to the rock mass characteristics and support requirements to achieve progressive stability control of the broken surrounding rock. The specific construction steps include:

[0074] 1. Expand the upper area and reinforce the grouting area②

[0075] Area ② is the key point of the slope reinforcement and also the area to be reinforced first. The purpose is that it can not only prevent the negative impact on the existing tunnel during the excavation of the slope, but also slow down the impact on the upper surface during the subsequent removal of the support. Due to the serious fragmentation of the rock mass in Area ②, construction disturbance may significantly affect the stability of the surrounding rock. For this area, the present invention adopts a reinforcement method combining double gradients of coarse-grained grouting and thixotropic slurry.

[0076] Coarse-grained grouting is mainly used to fill large fissures, enhance the overall strength of the surrounding rock, form a preliminary support, and prevent large-scale sliding or deformation of the surrounding rock; thixotropic grouting has good fluidity and can penetrate into smaller fissures and microvoids, playing a role in the refinement reinforcement stage after coarse-grained grouting. After the thixotropic slurry solidifies, it forms a uniform and dense structure, further enhancing the stability of the surrounding rock.

[0077] Construction steps for Area ②: Drill grouting holes in the upper area ② of the portal section of the light-dark dividing line 3 between the open cut tunnel 1 and the hidden tunnel 2, arranged in a plum blossom shape. The plane spacing of the drill holes is 1.5m×1.5m, the drill hole depth is 4m - 8m, the hole inclination angle is inclined downward by 5° - 15°, and the steel flower pipe 4 is used as the grouting pipe. The size of the steel flower pipe 4 is φ50 - 70mm. Insert the grouting pipe into the grouting hole and inject slurry into the grouting pipe, injecting in two stages respectively. First, carry out coarse-grained grouting, and the injected slurry is cement mortar. The water-cement ratio of the cement mortar is 0.6:1 - 1:1. Inject the coarse-grained slurry at low pressure through the grouting pipe. The initial grouting pressure is 0.5 - 1Mpa, and gradually increase the pressure to 2MPa. During the grouting process, continuously monitor the pressure and flow rate to ensure that the slurry can fill the large fissures and there is no obvious leakage.

[0078] After the initial consolidation of the coarse-grained slurry, inject the thixotropic slurry. The thixotropic slurry is a composite slurry of bentonite and cement, and the formula of the thixotropic slurry is cement: bentonite: water = 1:0.05:0.8. Adopt the intermittent grouting method. The grouting pressure of the thixotropic slurry is slightly higher than that of the coarse-grained slurry, and the grouting pressure is 1.0 - 2.0MPa, so that the slurry can penetrate into the fine fissures and microvoids. After the grouting is completed, lay a 20cm×20cm steel mesh 5 with a diameter of 8mm on the surface of the area, and spray 10cm thick C25 concrete 6 to fix the slope.

[0079] 2. Grouting reinforcement for the surface anchor rods in Area ③

[0080] Area ③ is located on the surface of the slope. By using the dual effects of anchor rods and grouting materials, the role of reinforcing the slope is achieved, preventing surface sliding or collapse caused by construction disturbance.

[0081] Construction steps for area ③: After cleaning the floating stones and collapsed topsoil on the surface of the slope, dig in layers to ensure the smoothness of the slope. Then, anchor grouting is carried out on the surface of the slope to ensure that the anchor is completely penetrated into the stable surrounding rock to ensure its anchoring effect. The diameter of the borehole is 42mm-50mm, the depth of the borehole is 6-10m, the hole angle is 20° with the vertical surface direction, the plane spacing is 2m×2m, and the plum blossom shape is arranged. The anchor rod adopts hollow grouting anchor rod 7. The grouting material is cement slurry with a water-cement ratio of 0.8:1-1:1, the grouting pressure is 1-1.5MPa, and the grouting pipe is gradually pulled up to evenly distribute the slurry, increase the bonding force between the anchor rod and the surrounding rock, and form a stable support.

[0082] 3. Pipe shed advance grouting reinforcement area①

[0083] The guide wall 9 of the expansion tunnel 1 and the expansion tunnel 2 is constructed, and the area ① is supported by the advanced large pipe shed grouting to reduce the impact of excavation disturbance and blasting on the surrounding rock. Area ① is the 120° range of the contour arch designed for the expansion tunnel 1 and the expansion tunnel 2.

[0084] Construction steps for area ①: After the reinforcement of area ③ is completed, four positioning steel frames 8 are arranged in the longitudinal direction of the expanded tunnel area ①. The bottom of the positioning steel frames 8 falls on a solid foundation. If the foundation is loose, concrete should be poured on the loose foundation to form a new solid concrete foundation 11. The spacing between each positioning steel frame 8 is 50cm-60cm. Above the positioning steel frame 8, multiple guide steel pipes 13 are arranged within the range of 120° of the expanded tunnel vault according to the designed external insertion angle of 1°, with a circumferential spacing of 40cm. The guide steel pipes 13 are welded and connected to the positioning steel frame 8 through fixed steel bars 14 with a diameter of 16mm to form a force-bearing whole. Subsequently, the guide wall 9 is molded and C30 concrete is poured on the positioning steel frame 8 and the guide steel pipe 13 outside the excavation contour line of the tunnel entrance, and the guide walls 9 of the two expanded tunnels are obtained after curing to the designed strength. The longitudinal direction of the tunnel guide wall 9 is the tunnel excavation direction, the positioning steel frame 8 is an I20b I-beam, the guide steel pipe 13 is a hot-rolled seamless steel pipe with a wall thickness of 10 mm and a diameter of 152 mm, and the cross-sectional size of the guide wall 9 is 2 m×0.8 m.

[0085] After the guide wall 9 is constructed, the grouting steel pipe 10 is arranged by drilling first and then inserting the pipe. The drilling depth is 20m-30m. The grouting steel pipe 10 used is a steel flower pipe with a diameter of 108mm and a wall thickness of 6mm. The pipe mouth section 2.5m is not drilled. The grouting steel pipe 10 is inserted with manual and mechanical assistance. After the grouting steel pipe 10 is placed, a steel cage is placed inside it to increase the rigidity of the grouting steel pipe 10. The gap between the steel pipe and the hole wall is sealed with hemp silk and anchoring agent at the pipe mouth, and the grouting pipe and the three-way joint are connected.

[0086] Reference Figure 6, wherein the steel reinforcement cage is composed of three steel bars 151 and steel rings 152. The steel rings 152 are connected to the multiple steel bars 151 by welding. The steel rings 152 are arranged longitudinally at intervals along the steel bars 151. The distance between adjacent steel rings 152 is 95 - 100 cm. The diameter of the steel bars 151 used is 22 mm, and the steel rings 152 are steel pipes with a diameter of 42 mm and a wall thickness of 4 mm. After the steel reinforcement cage is placed, grout is injected into the grouting steel pipe 10. The grout used is cement slurry with a water-cement ratio of 1:1, the initial pressure is 1 - 1.5 MPa, the final pressure is 2 MPa, and grouting is carried out layer by layer from bottom to top in the order of the steel pipes. After grouting, the grouting steel pipe 10 is filled with M30 mortar.

[0087] S3. Tunnel expansion excavation and support for the portal section; Carry out according to the tunnel expansion excavation and support for the portal section in Embodiment 1.

[0088] It should be noted that before the excavation construction, the existing tunnel's arch waist position is pre-backfilled with gravel soil to control the surrounding rock deformation in the way of "reducing the span and height". The excavation sequence follows the principle of excavating one side of the tunnel first, and the tunnel face of the adjacent tunnel is staggered by a distance equal to the excavation width of one tunnel to reduce the mutual influence between the two tunnels. The existing tunnel structure is demolished by mechanical cutting and crushing, and the length of each demolition cycle is not more than 6 m; The excavation of the enlarged part adopts controlled blasting construction, and the construction working face is excavated according to the scheme of excavating from both ends of the tunnel entrance and exit towards the middle. The length of the upper and lower benches of the pilot tunnel is 5 m - 8 m, and the staggering distance between the left and right pilot tunnels is not more than 15 m; The excavation footage of each cycle of the 1st and 3rd parts of the upper pilot tunnel is controlled to be the spacing of two steel arch frames, and the excavation footage of each cycle of the 2nd and 4th parts of the lower pilot tunnel can be appropriately increased according to the geological conditions.

[0089] The initial support is carried out in the way of supporting while excavating. The removal of the temporary support is carried out after the initial support is closed in a loop and confirmed to be stable through monitoring and measurement, and the one-time removal length is 4 m - 6 m. The initial support of the enlarged tunnel includes system bolt grouting, steel mesh and shotcrete 6 reinforcement. The grade of the used shotcrete 6 is C25, and the spraying thickness is 30 cm; The used steel mesh consists of two layers of steel bars with a diameter of 8 mm and a transverse and longitudinal spacing of 20 cm; The system bolts are hollow grouting bolts 7 with a size of φ25 mm and a wall thickness of 5 mm, a length of 500 mm, a longitudinal spacing of 60 cm, and a circumferential spacing of 100 cm. Since in this embodiment, the tunnel spacing is only 10 - 15 m and the middle rock stratum is in a weak part, grouting small ducts are used for key reinforcement. The used small ducts are seamless steel pipes with a diameter of 50 mm and a wall thickness of 5 mm, a length of 500 mm, arranged on the side of the enlarged tunnel adjacent to the middle rock stratum, with a longitudinal spacing of 60 cm and a circumferential spacing of 100 cm.

[0090] By adopting the cross-middle diaphragm method for excavation and applying support inside the tunnel, the tunnel safety can be further guaranteed.

[0091] The construction method of the present invention can effectively ensure the construction safety of the portal section of the reconstructed and expanded tunnel, provide a good construction safety space for the subsequent processes, and ensure the safe and efficient progress of the reconstruction and expansion project.

[0092] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0093] The above-described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for constructing and supporting the slope above the tunnel portal section for renovation and expansion, characterized in that: The following steps are involved: S1. Investigation and construction measurement of the back slope and the rock mass at the cave entrance; S2. Slope zoning and reinforcement; S2.

1. Divide the upper slope of the tunnel entrance into three reinforcement areas, namely, the advanced pipe shed grouting reinforcement area ①, the upper part grouting reinforcement area ②, and the surface anchor grouting reinforcement area ③; S2.

2. The construction reinforcement sequence is: Area ②→Area ③→Area ①; S3. Excavation and support of tunnel expansion at the entrance section; S3.

1. The blind tunnels (2) at the entrances of the expansion tunnels 1 and 2 are constructed using the cross-middle partition wall method.

2. The method for constructing and supporting the upward slope above the tunnel portal section according to claim 1 is characterized in that: Through the step S1, the light-dark boundary line (3) between the open tunnel (1) and the dark tunnel (2) is determined, and the center line, tunnel excavation elevation and excavation boundary range of the expansion tunnel 1 and the expansion tunnel 2 are determined. At the same time, the overlap between the rock stratum fracture area and the excavation range of the expansion tunnel 1 and the expansion tunnel 2 is compared to evaluate the potential risks of the construction.

3. The method for constructing and supporting the slope above the tunnel portal section according to claim 2 is characterized in that: The construction sequence of the area ② is as follows: a grouting hole is excavated in the area ② above the opening section of the light-dark dividing line (3) at the junction of the open tunnel (1) and the dark tunnel (2), a grouting pipe is inserted into the grouting hole and slurry is injected into the grouting pipe.

4. The method for constructing and supporting the upward slope above the tunnel portal section according to claim 3 is characterized in that: The slurry is injected in two stages. First, the coarse-grained slurry is injected. After the coarse-grained slurry is initially solidified, the thixotropic slurry is injected.

5. The method for constructing and supporting the upward slope above the tunnel portal section according to claim 1 is characterized in that: The construction sequence of the area ③ is: clearing the pumice and collapsed topsoil on the surface of the back slope, excavating in layers, and grouting anchor rods on the surface of the back slope.

6. The method for constructing and supporting the upward slope above the tunnel portal section according to claim 1 is characterized in that: The construction sequence of the area ① is as follows: after the reinforcement of the area ③ is completed, a plurality of positioning steel frames (8) are arranged along the longitudinal direction of the area ①, the two end feet of the positioning steel frames (8) are installed with concrete foundations (11), the top of the positioning steel frames (8) is welded with a plurality of guide steel pipes (13) through fixed steel bars (14), and the positioning steel frames (8) and the guide steel pipes (13) are used to form a guide wall (9) outside the contour line of the opening excavation, and a steel cage is arranged inside the guide wall (9), and a plurality of grouting steel pipes (10) are arranged inside the steel cage.

7. The method for constructing and supporting the upward slope above the tunnel portal section according to claim 1 is characterized in that: The excavation sections of Expansion Tunnel 1 and Expansion Tunnel 2 are respectively divided into Section 1, Section 2, Section 3 and Section 4; the excavation order is Section 1→Section 2→Section 3→Section 4.

8. The method for constructing and supporting the upward slope above the tunnel portal section according to claim 7 is characterized in that: The first part is arranged above the existing tunnel one and the existing tunnel two, the second part is arranged below the existing tunnel one and the existing tunnel two, the third part is arranged at the upper part of the excavation side of the existing tunnel one and the existing tunnel two, and the fourth part is arranged at the lower part of the excavation side of the existing tunnel one and the existing tunnel two.

9. The method for constructing and supporting the upward slope above the tunnel portal section according to claim 1, characterized in that: The cross-middle partition wall method is: first excavate any one of the expansion tunnel 1 or the expansion tunnel 2, and then excavate the unexcavated expansion tunnel 1 or the expansion tunnel 2.

10. The method for constructing and supporting the upward slope above the tunnel portal section according to claim 7, characterized in that: The adjacent tunnel faces of expansion tunnel 1 and expansion tunnel 2 are staggered by a distance of tunnel excavation width.

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