Supporting structure and supporting method for excavation of III2 type surrounding rock cavern bifurcated opening

Abstract

The invention discloses a III2 type surrounding rock cavern bifurcated opening excavation supporting structure which is arranged at the crossed part of a main cavern and a bifurcated cavern and comprises a system anchor rod I anchored in a rock mass of a rock cavern wall at the crossed part and steel supports I arranged at intervals along the trend of the main cavern, and the steel supports I are anchored on the rock cavern wall through feet-lock bolts I; a reinforcing mesh I is laid and connected to the outer side of the steel support I, and the outer side of the reinforcing mesh I is covered with a sprayed concrete top surface; system anchor rods I are arranged in the rock mass of the tunnel wall at the crossed part; the same supporting structure is arranged in the area corresponding to the excavation outline of the subsequent forked tunnel, and the part of the supporting structure is configured to be a detachable structure. The invention further discloses a supporting method for excavation of the branch hole of the III2 type surrounding rock cavern, and by means of the supporting structure and method, the construction progress and safety of the branch hole are guaranteed while the construction progress and safety of the main hole are guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of water conservancy and hydropower construction technology, specifically relating to the excavation and support structure of the tunnel entrance of Class III2 surrounding rock, and also relating to the excavation and support method of the tunnel entrance of Class III2 surrounding rock. Background Technology

[0002] In the field of water conservancy and hydropower engineering, traditional methods for excavation and support of tunnel entrances with poor surrounding rock stability typically employ a comprehensive support system combining pipe roofs, steel supports, anchor bolts, steel mesh, and shotcrete. While this method can reinforce the rock mass and maintain the stability of the excavation face to a certain extent, it still has significant limitations in practical applications, especially under conditions of relatively fractured rock such as Class III-2. On the one hand, the structural stress at the intersection of the main tunnel and the branch tunnel is complex, and traditional support procedures are cumbersome and have long construction cycles, often requiring frequent stops during the main tunnel excavation to reinforce the branch tunnel entrance, severely slowing down the overall excavation speed of the main tunnel. On the other hand, the fractured surrounding rock has poor self-stabilizing ability, and stress concentration at the intersection is prominent. If the support is not timely or its strength is insufficient, it can easily lead to local collapses, rockfalls, and other safety hazards, threatening the safety of construction personnel and equipment.

[0003] Therefore, how to design a method that can efficiently coordinate the excavation sequence of the main tunnel and the branch tunnel, ensure the smooth transition of the crossroads support structure, and precisely control the excavation process of the branch tunnel entrance, so as to simultaneously ensure the construction progress of the main tunnel, the construction safety of the branch tunnel, and the overall stability of the surrounding rock under the condition of fractured surrounding rock, has become an urgent technical problem to be solved. Summary of the Invention

[0004] The first objective of this invention is to provide an excavation support structure for branch tunnel entrances in Class III2 surrounding rock caverns. This structure ensures both the construction progress and safety of the main tunnel and the construction progress and safety of the branch tunnels.

[0005] The second objective of this invention is to provide a method for excavation and support of the entrance to a branch tunnel in Class III2 surrounding rock.

[0006] The first technical solution adopted in this invention is: a support structure for the excavation of a branch tunnel in Class III2 surrounding rock, set at the intersection of the main tunnel and the branch tunnel, including: a system anchor rod I anchored inside the rock mass of the tunnel wall at the intersection; steel supports I spaced along the direction of the main tunnel; the steel supports I are anchored to the rock wall by locking anchor rods I; a steel mesh I is laid and connected to the outside of the steel supports I; and the outside of the steel mesh I is covered with a shotcrete top surface; the system anchor rod I is arranged in the rock mass of the tunnel wall at the intersection. Within the area corresponding to the excavation outline of the subsequent branch tunnel, the same support structure is provided, and this part of the support structure is configured to be removable.

[0007] The first technical solution adopted in this invention is further characterized by: Furthermore, the support structure within the excavation outline of the branch tunnel includes steel support II, steel mesh II, system anchors II, and a concrete layer I covering them.

[0008] Furthermore, if there is a void section in the top rock wall of the support structure, grouting is carried out to form a top arch backfill grouting section, and removable locking anchor rods II are anchored on the top rock wall.

[0009] The second technical solution adopted in this invention is: a method for excavation and support of the entrance to a branch tunnel in Class III2 surrounding rock, which involves constructing the support structure as described above, including the following steps: S1. Construct an initial support structure at the intersection of the main tunnel and the branch tunnel. The initial support structure includes steel support I, anchor bolt I, steel mesh I, and shotcrete top surface. S2. After the main tunnel excavation face has passed the planned opening position of the branch tunnel and advanced a preset distance, the excavation construction of the branch tunnel opening will be carried out. S3. Conduct a void inspection on the top arch at the intersection, and grout backfill the voided areas to form the top arch backfill grouting section. S4. Before excavating the tunnel entrance, partially dismantle the initial support structure located within the tunnel excavation outline, and strengthen the support system before and after dismantling. S5. Install anchor bolts at the junction entrance of the tunnel outside the outline of the tunnel entrance. S6. Excavate the entrance of the branch tunnel step by step in the predetermined sequence; S7. Provide timely support during and after the excavation of the branch tunnel entrance.

[0010] The second technical solution adopted in this invention is further characterized by: Furthermore, the preset distance in step S2 is 50 meters.

[0011] Furthermore, in step S1, the steel support I is made of I18 steel, with a spacing of 1.0m to 1.2m, and the steel supports are connected by connecting bars; the anchor rod I is made of 25mm diameter steel bar, with a length of 4m to 4.5m, and a spacing of 1.5m to 3.0m; the steel mesh I is made of 8mm diameter steel bar, with a mesh size of 150mm×150mm to 200mm×200mm, and is welded to the steel support I; the thickness of the shotcrete top surface is 23cm to 25cm. Step S1 also includes: after the top surface of the shotcrete reaches the design strength, installing system anchor rod I on the tunnel wall. System anchor rod I uses steel bars with a diameter of 28mm, a length of 6m, and a spacing of 1.5m×1.5m to 2.0m×2.0m.

[0012] Furthermore, in step S3, the grouting backfilling treatment uses cement mortar with a grade of M25 to M30.

[0013] Furthermore, step S4 specifically includes: S4.1 At the location of the steel support II to be demolished, reinforced anchor rods II shall be installed in advance. The reinforced anchor rods II shall be made of steel bars with a diameter of 28mm, a length of 5m to 6m, and a quantity of not less than two. S4.2 Remove the concrete layer I, steel support II, steel mesh II and system anchor II located within the excavation outline of the branch tunnel; S4.3 Remove or cut off the exposed portion of the system anchor bolt I that was exposed due to the demolition; S4.4. In areas where excavation needs to be expanded at intersections, additional system anchor bolts shall be installed.

[0014] Furthermore, in step S5, the anchor bolts at the fork opening are arranged along the outer side of the fork opening outline.

[0015] Furthermore, in step S6, the excavation sequence is as follows: first excavate the central guide tunnel, then excavate the left transition section on one side, then excavate the right transition section on the other side, and finally excavate the side arch expansion section. In step S7, during the excavation of the branch tunnel entrance, steel supports, steel mesh, anchor bolts and system anchor bolts are used in a timely manner to support the excavation face.

[0016] The beneficial effects of this invention are: This invention provides a support structure and method for excavating the entrance of a branch tunnel in Class III2 surrounding rock. It employs methods such as steel supports, system anchors, locking anchors, steel mesh, backfill grouting, and shotcrete to ensure the safe excavation of the entrance section of the branch tunnel while ensuring the construction progress and safety of the main tunnel. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the excavation support structure for the branch entrance of a Class III2 surrounding rock cavern according to the present invention; Figure 2 This is a side view of the excavation support structure for the branch entrance of a Class III2 surrounding rock cavern according to the present invention; Figure 3 This is a schematic diagram showing the locations of the main tunnel and the branch tunnels in this invention.

[0018] In the diagram, 1. Rock cave wall, 2. Anchor bolt I, 3. Steel mesh I, 4. Steel support I, 5. Shotcrete top surface, 6. System anchor bolt I, 7. Backfill grouting section of the top arch, 8. Anchor bolt II, 9. Concrete layer I, 10. Steel support II, 11. Steel mesh II, 12. System anchor bolt II, 13. Anchor bolt at the fork in the tunnel, 14. Central guide tunnel, 15. Left transition section, 16. Right transition section, 17. Side arch widening section. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] This invention provides a support structure for the excavation of branch tunnels in Class III2 surrounding rock, located at the intersection of the main tunnel and the branch tunnel. It includes: a system of anchor bolts I6 anchored inside the rock mass of the cave wall 1 at the intersection; steel supports I4 spaced along the direction of the main tunnel; the steel supports I4 are anchored to the rock cave wall 1 by locking anchor bolts I2; a steel mesh I3 is laid and connected to the outside of the steel supports I4; and a shotcrete top surface 5 covers the outside of the steel mesh I3. The cave wall rock mass includes the intersection where the system of anchor bolts I6 are arranged. Within the area corresponding to the excavation outline of the subsequent branch tunnel, an identical support structure is installed. This support structure is configured to be removable. The lengths of the anchor bolts (system anchor bolts and locking anchor bolts) that need to be removed are measured in advance. The parts of the anchor bolts to be removed are connected to the permanent parts using straight threads. The steel mesh and steel supports are removed using a plasma cutter. This part of the support structure was initially designed to ensure the stability of the surrounding rock of the main tunnel and needs to be removed before the branch tunnel excavation.

[0021] The support structure within the area of ​​the tunnel excavation outline includes steel support II10, steel mesh II11, system anchor II12, and concrete layer I 9 covering it.

[0022] If there is a cavity section in the top rock wall of the support structure, grouting is required to treat the cavity section and form the top arch backfill grouting section 7. After the treatment is completed, anchor bolts II 8 are anchored on the top rock wall.

[0023] This invention also provides a method for excavation and support of the entrance to a branch tunnel in Class III2 surrounding rock, which is implemented according to the following steps: S1. Steel supports, anchor bolts, steel mesh, shotcrete, and system anchor bolts are installed at the intersection of the main tunnel and the branch tunnel for support. S2. When the main tunnel and the branch tunnel are staggered by 50m, the branch tunnel construction shall be carried out; S3. Conduct a void inspection on the arch at the intersection of the main tunnel and the branch tunnel, and grout the voided area. S4. Cut off the steel support at the fork in the tunnel, and install system anchor bolts at the part where the main tunnel and the fork in the tunnel need to be widened. At the same time, use long anchor bolts to install densified locking anchor bolts for the steel support that has not been cut off. S5. System anchor bolts are installed outside the opening of the branch tunnel; S6. When excavating the branch tunnel, the central pilot tunnel is excavated first, followed by the gradual transition sections on both sides, and finally the gradual transition sections on the left and right sides are excavated. S7. Provide support.

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0025] Example 1 The excavation support structure for the branch tunnel entrance of Class III2 surrounding rock cavern is set at the intersection of the main tunnel and the branch tunnel, including: a system of anchor bolts I6 anchored inside the rock mass of the cavern wall 1 at the intersection; steel supports I4 spaced along the direction of the main tunnel; steel supports I4 anchored to the rock cavern wall 1 by locking anchor bolts I2; steel mesh I3 laid and connected to the outside of steel supports I4; and shotcrete top surface 5 covering the outside of steel mesh I3; the cavern wall rock mass includes the system of anchor bolts I6 arranged at the intersection. Within the area corresponding to the excavation outline of the subsequent branch tunnel, the same support structure is provided, and this part of the support structure is configured to be removable.

[0026] Example 2 The excavation support structure for the branch tunnel entrance of Class III2 surrounding rock cavern is set at the intersection of the main tunnel and the branch tunnel, including: a system of anchor bolts I6 anchored inside the rock mass of the cavern wall 1 at the intersection; steel supports I4 spaced along the direction of the main tunnel; steel supports I4 anchored to the rock cavern wall 1 by locking anchor bolts I2; steel mesh I3 laid and connected to the outside of steel supports I4; and shotcrete top surface 5 covering the outside of steel mesh I3; the cavern wall rock mass includes the system of anchor bolts I6 arranged at the intersection. Within the area corresponding to the excavation outline of the subsequent branch tunnel, the same support structure is provided, and this part of the support structure is configured to be removable.

[0027] The support structure within the area of ​​the tunnel excavation outline includes steel support II10, steel mesh II11, system anchor II12, and concrete layer I 9 covering it.

[0028] Example 3 The excavation support structure for the branch tunnel entrance of Class III2 surrounding rock cavern is set at the intersection of the main tunnel and the branch tunnel, including: a system of anchor bolts I6 anchored inside the rock mass of the cavern wall 1 at the intersection; steel supports I4 spaced along the direction of the main tunnel; steel supports I4 anchored to the rock cavern wall 1 by locking anchor bolts I2; steel mesh I3 laid and connected to the outside of steel supports I4; and shotcrete top surface 5 covering the outside of steel mesh I3; the cavern wall rock mass includes the system of anchor bolts I6 arranged at the intersection. Within the area corresponding to the excavation outline of the subsequent branch tunnel, the same support structure is provided, and this part of the support structure is configured to be removable.

[0029] The support structure within the area of ​​the tunnel excavation outline includes steel support II10, steel mesh II11, system anchor II12, and concrete layer I 9 covering it.

[0030] If there is a void in the top rock wall of the support structure, grouting is carried out to form a top arch backfill grouting section 7, and the top rock wall is anchored with a removable locking foot anchor rod II 8.

[0031] Example 4 The method for excavation and support of the branch entrance of a Class III2 surrounding rock cavern involves constructing the support structure as described above, including the following steps: S1. Construct an initial support structure at the intersection of the main tunnel and the branch tunnel. The initial support structure includes steel support I4, anchor bolt I2, steel mesh I3, and shotcrete top surface 5. Steel supports I4 are made of I18 steel, spaced 1.0m to 1.2m apart, and connected by reinforcing bars; anchor bolts I2 are made of 25mm diameter steel bars, 4m to 4.5m long, spaced 1.5m to 3.0m apart; steel mesh I3 is made of 8mm diameter steel bars, with a mesh size of 150mm×150mm to 200mm×200mm, and is welded to steel supports I4; the thickness of the shotcrete top surface 5 is 23cm to 25cm. Step S1 also includes: after the top surface 5 of the shotcrete reaches the design strength, installing system anchor rods I6 on the tunnel wall. The system anchor rods I6 are made of steel bars with a diameter of 28mm, a length of 6m, and a spacing of 1.5m×1.5m to 2.0m×2.0m. S2. After the main tunnel excavation face has passed the planned opening position of the branch tunnel and advanced a preset distance, the excavation construction of the branch tunnel opening will be carried out. S3. Conduct a void inspection on the top arch at the intersection, and grout backfill the voided areas to form the top arch backfill grouting section 7. The grouting and backfilling treatment uses cement mortar with a grade of M25 to M30; S4. Before excavating the tunnel entrance, partially dismantle the initial support structure located within the tunnel excavation outline, and strengthen the support system before and after dismantling. Specifically, it includes: S4.1 At the location of the steel support Ⅱ10 to be demolished, reinforced anchor rods Ⅱ8 shall be installed in advance. The reinforced anchor rods Ⅱ8 shall be made of steel bars with a diameter of 28mm, a length of 5m to 6m, and a quantity of not less than two. S4.2 Remove the concrete layer I 9, steel support II 10, steel mesh II 11 and system anchor II 12 located within the excavation outline of the branch tunnel; S4.3 Remove or cut off the exposed portion of the system anchor bolt I6 that was exposed due to the demolition; S4.4. In areas where excavation needs to be expanded at intersections, additional system anchor bolts shall be installed; S5. Install the branch tunnel opening anchor bolt 13 in the area outside the outline of the branch tunnel opening; The anchor bolt 13 at the fork opening is arranged along the outer side of the fork opening outline; S6. Excavate the entrance of the branch tunnel step by step in the predetermined sequence; The excavation sequence is as follows: first, excavate the central guide tunnel 14, then excavate the left transition section 15 on one side, then excavate the right transition section 16 on the other side, and finally excavate the side arch expansion section 17. S7. Provide timely support during and after the excavation of the tunnel entrance; During the excavation of the tunnel entrance, steel supports, steel mesh, anchor bolts, and system anchor bolts were used in a timely manner to support the excavation face.

[0032] Example 5 The method for excavation and support of the branch entrance of a Class III2 surrounding rock cavern according to the present invention is implemented according to the following steps: S1. At the intersection of the main tunnel and the branch tunnel, I18 steel supports I4 are installed at a spacing of 1.0m. The steel supports are connected with φ25 steel bars. At the same time, the steel supports are anchored to the rock wall with (L=4.5m, φ25) locking anchor rods I2. The locking anchor rods are spaced at 1.5m to ensure the stability of the steel supports. On the outside of the steel supports, φ8@150*150 steel mesh I3 is installed and effectively welded to the steel support I4. S2. Spray a 25cm thick layer of concrete. S3. After the shotcrete reaches its design strength, install φ28 system anchor bolts I6, each 6m long, with a spacing of 1.5m x 1.5m between rows on the tunnel wall; S4. Inspect the main tunnel arch to check for voids, and backfill the voided areas with M25 cement mortar. S5. After the main tunnel is excavated 50m away from the branch tunnel opening, the branch tunnel opening will be excavated. First, the steel support at the tunnel opening will be removed. Before removal, φ28 anchor rods II8 (2 rods, 6m long) will be installed at the location where the steel support is removed. S6. Remove the C25 shotcrete layer I 9, steel support II 10, φ8 steel mesh II 11, and φ25 system anchor II 12 previously installed at the opening. After excavation, cut off the exposed part of system anchor I 6. S7. For the excavation of the branch tunnel entrance section, the central guide tunnel 14 will be excavated first, followed by the left transition section 15 and the right transition section 16. Finally, the side arch expansion section 17 will be excavated. During the excavation, steel supports, steel mesh, anchor bolts, and system anchor bolts will be used for timely support.

[0033] Example 6 The method for excavation and support of the branch entrance of a Class III2 surrounding rock cavern according to the present invention is implemented according to the following steps: S1. At the intersection of the main tunnel and the branch tunnel, I18 steel supports I4 are installed at a spacing of 1.2m. The steel supports are connected with φ25 steel bars. At the same time, the steel supports are anchored to the rock wall with (L=4m, φ25) locking anchor rods I2. The locking anchor rods are spaced 3m apart to ensure the stability of the steel supports. On the outside of the steel supports, φ8@200*200 steel mesh I3 is installed and effectively welded to the steel support I4. S2. Spray a 23cm thick layer of concrete. S3. After the shotcrete reaches its design strength, install φ28 system anchor bolts I6, 6m long, spaced 2m x 2m apart, on the tunnel wall; S4. Inspect the main tunnel arch to check for voids, and backfill the voided areas with M30 cement mortar. S5. After the main tunnel is excavated 50m away from the branch tunnel entrance, the branch tunnel entrance will be excavated. First, the steel support at the entrance will be removed. Before removal, φ28 anchor rods II8 (2 rods, 5m long) will be installed at the location where the steel support is removed. S6. Remove the C25 shotcrete layer I 9, steel support II 10, φ8 steel mesh II 11, and φ25 system anchor II 12 previously installed at the opening. After excavation, cut off the exposed part of system anchor I 6. S7. For the excavation of the branch tunnel entrance section, the central guide tunnel 14 will be excavated first, followed by the left transition section 15 and the right transition section 16. Finally, the side arch expansion section 17 will be excavated. During the excavation, steel supports, steel mesh, anchor bolts, and system anchor bolts will be used for timely support.

[0034] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A support structure for the excavation of a branch opening of a Class III, Group 2 surrounding rock cavern, characterized in that, The support structure is arranged at the intersection part of the main hole and the branch hole, and comprises: a system anchor rod I (6) anchored in the rock wall (1) of the intersection part, a steel support I (4) arranged along the direction of the main hole, and a steel mesh I (3) arranged outside the steel support I (4) and connected to the steel support I (4); and a shotcrete top surface (5) arranged outside the steel mesh I (3); the rock wall contains the system anchor rod I (6) arranged at the intersection part; In the area corresponding to the subsequent branch hole excavation contour, the same support structure is arranged, and the part of the support structure is configured as a removable structure.

2. The support structure of claim 1, wherein, The support structure in the area of the branch hole excavation contour comprises a steel support II (10), a steel mesh II (11), a system anchor rod II (12), and a concrete I layer (9) arranged on the support structure.

3. The support structure of claim 1, wherein, If the top wall of the support structure has a void section, a grouting treatment is performed to form a top arch backfill grouting section (7), and a removable lock foot anchor rod II (8) is anchored on the top wall.

4. The method for excavating and supporting a branch hole of a class III2 surrounding rock cavern, characterized in that, The support structure is constructed according to any one of claims 1-3, comprising the following steps: S1, performing initial support construction at the intersection part of the main hole and the branch hole, wherein the initial support construction comprises a steel support I (4), a lock foot anchor rod I (2), a steel mesh I (3), and a shotcrete top surface (5); S2, after the main hole excavation working face passes the branch hole opening position and advances by a preset distance, performing excavation construction of the branch hole opening; S3, checking the top arch of the intersection part for voids, and performing grouting backfill treatment on the found voids to form a top arch backfill grouting section (7); S4, before the branch hole opening is excavated, partially removing part of the initial support structure located in the branch hole excavation contour, and strengthening the support system before and after the removal; S5, performing branch hole opening lock anchor rod (13) construction on the area outside the branch hole opening contour line; S6, performing step-by-step excavation of the branch hole opening in a predetermined order; S7, timely performing support construction during and after the branch hole opening excavation.

5. The method of supporting of claim 4, wherein, The preset distance in step S2 is 50 meters.

6. The method of supporting of claim 4, wherein, In step S1, the steel support I (4) is I18 steel, the interval is 1.0m to 1.2m, and the connecting rods are used to connect the steel supports; the lock foot anchor rod I (2) is a steel rod with a diameter of 25mm and a length of 4m to 4.5m, and the interval is 1.5m to 3.0m; the steel mesh I (3) is a steel rod with a diameter of 8mm, and the grid size is 150mm×150mm to 200mm×200mm, and the steel mesh I (3) is welded with the steel support I (4); The thickness of the shotcrete top surface (5) is 23cm to 25cm; Step S1 further comprises: after the shotcrete top surface (5) reaches the design strength, the system anchor rod I (6) is arranged on the wall, and the system anchor rod I (6) is a steel rod with a diameter of 28mm and a length of 6m, and the interval is 1.5m×1.5m to 2.0m×2.0m.

7. The method of supporting of claim 4, wherein, In step S3, the grouting backfill treatment uses cement mortar with a mark of M25 to M30.

8. The method of supporting of claim 4, wherein, Step S4 specifically comprises: S4.1, at the part of the planned demolition of steel support II (10), pre-constructed reinforced lock foot anchor II (8), the reinforced lock foot anchor II (8) uses steel bars with a diameter of 28 mm, a length of 5 m to 6 m, and a quantity of not less than two; S4.2, demolish the concrete I layer (9), steel support II (10), steel mesh II (11) and system anchor II (12) located within the excavation contour of the branch hole; S4.3, the exposed part of the system anchor I (6) is removed or cut off due to the demolition; S4.4, in the area where the intersection part needs to be expanded, additional system anchor is added.

9. The method of supporting of claim 4, wherein, In step S5, the branch hole mouth lock anchor (13) is arranged outside the branch hole contour line.

10. The method of supporting of claim 4, wherein, In step S6, the sequence of step-by-step excavation is: first excavate the middle pilot hole (14), then excavate the left gradual transition section (15) on one side, then excavate the right gradual transition section (16) on the other side, and finally excavate the edge top arch expansion part (17); In step S7, during the excavation of the branch hole mouth, steel support, steel mesh, lock foot anchor and system anchor are used in time to support the excavation surface.

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