A giant span cavern support structure for fractured rock mass and its construction method

Abstract

The present invention discloses a giant-span cavern support structure of a fractured rock mass and a construction method thereof, wherein the support structure comprises: a cavern surface flexible support structure, arranged on the arch and side walls of the excavation surface, comprising steel fiber concrete and steel mesh; a rock mass self-bearing arch structure, arranged on the arch and side walls of the cavern, comprising ordinary mortar anchor rods, expansion shell prestressed grouting anchor rods and rock mass; a locking foot prestressed anchor cable, arranged at the cavern arch foot; a block reinforcement prestressed anchor cable, arranged within the range of unstable blocks in the cavern; and a resin anchor rod, arranged in the deformation mutation area after excavation. The support structure of the present invention has rich means, comprehensive range, distinct functions, strong bearing capacity and good economy, simple construction method and process, convenient construction organization, smooth step sequence connection and high safety, can mobilize the self-bearing capacity of the rock mass at multiple levels, and reinforces the unstable blocks so that the giant-span cavern can reach a stable state.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel and underground engineering design and construction, and in particular to a giant-span cavern support structure of a fractured rock mass and a construction method thereof. Background Art

[0002] For underground caverns, generally speaking, excavation spans of 5 to 8.5 meters are small spans, 8.5 to 12 meters are medium spans, 12 to 14 meters are large spans, 14 to 16 meters are extra-large spans, and when the excavation span is greater than 16 meters, it is an extra-large span. At present, the spans of extra-large span caverns are mainly concentrated below 30 meters, and there are only a handful of caverns with spans of 30 to 40 meters at home and abroad. Underground caverns with a span of more than 40 meters can be called giant span underground caverns. The increase in span also brings huge risks. At present, there is no theoretical construction system for giant span underground structures, and there are few engineering examples. The construction of giant span underground caverns is risky and can easily cause landslide accidents. It has the following characteristics:

[0003] 1) The increase in span leads to a larger range of loose rock mass in the upper part, which can easily cause arch collapse and block falling;

[0004] 2) If the span is huge, the cavern will inevitably encounter cracks, joints, etc., and the risk of adverse geology is high;

[0005] 3) The rock mass above the cavern will form blocks after being cut by cracks. For giant span caverns, the stability of the blocks is the main factor determining the stability of the cavern;

[0006] 4) The loose load generated after the excavation of a giant span cavern is huge. It is unrealistic to rely solely on the support structure to bear the upper loose load. The self-bearing capacity of the rock mass must be considered.

[0007] In view of the above characteristics, the existing large-span cavern support structure has the following shortcomings:

[0008] 1) The existing large-span cavern support structure does not consider the support of unstable blocks and cannot guarantee the safety of unstable blocks;

[0009] 2) The existing surface support structure of super-large span caverns generally adopts the form of grid steel frame. However, for giant span caverns, grid steel frame is difficult to erect, the nodes are weak, and the force is limited, which cannot meet the construction and safety requirements of giant span underground caverns;

[0010] 3) The existing large-span cavern support structure adopts a single anchor rod form, which cannot fully mobilize the self-bearing capacity of the rock mass;

[0011] 4) The existing construction and support of super-large span caverns mostly adopts the method of partial excavation and erection of temporary supports. This type of support has complex force transformation, weak support at the nodes, and difficult operation, which is not suitable for the construction of giant span caverns;

[0012] (5) The existing secondary lining of super-large span caverns bears a certain amount of rock load. For giant span caverns, if the lining bears the load, the thickness will be huge, which will bring problems such as difficulty in pouring and high cost.

[0013] For giant-span underground caverns, conventional super-large-span support structures and concepts are not feasible and uneconomical. Therefore, the support structure of giant-span caverns needs to use various means to mobilize the self-bearing capacity of the rock mass, and should strengthen the support of unstable blocks to achieve stability during the construction and operation periods of the cavern. Summary of the invention

[0014] The purpose of the present invention is to provide a giant-span cavern support structure for a fractured rock mass and a construction method thereof. The support structure has rich means, comprehensive range, distinct functions, strong bearing capacity and good economy, simple construction method and process, convenient construction organization, smooth step connection and high safety, and can mobilize the self-bearing capacity of the rock mass at multiple levels, and reinforce unstable blocks to enable the giant-span cavern to reach a stable state.

[0015] To achieve the above-mentioned purpose, the specific technical scheme of a giant-span cavern support structure for a fractured rock mass and a construction method thereof of the present invention is as follows:

[0016] A giant span cavern support structure for a fractured rock mass, comprising:

[0017] The flexible support structure of the cave surface is set on the arch and side walls of the excavation surface, including steel fiber concrete and steel mesh;

[0018] The rock mass self-supporting arch structure is set in the arch and side wall of the cavern, including ordinary mortar anchor rods, expansion shell prestressed grouting anchor rods and rock mass;

[0019] The locking foot prestressed anchor cable is set at the arch foot of the cavern;

[0020] Block reinforcement prestressed anchor cables are set within the unstable blocks of the cavern; and

[0021] Resin anchor rods are set in the area where deformation suddenly changes after excavation.

[0022] A construction method for a giant span cavern support structure of a fractured rock mass, comprising:

[0023] Step 1: After the cavern is excavated, the surface broken and unstable blocks are removed, and steel fiber concrete is initially sprayed to level and seal the excavation surface;

[0024] Step 2: Install common mortar anchors and expansion shell prestressed grouting anchors, apply prestress after the slurry solidifies, and form a self-bearing arch structure with the rock mass; apply resin anchors in the deformation mutation area;

[0025] Step 3: symmetrically install three rows of prestressed anchor cables at the arch foot, and apply prestress after the slurry solidifies;

[0026] Step 4: Apply block reinforcement prestressed anchor cables within the range of the unstable blocks in the cavern. The free section of the anchor cables passes through the unstable blocks above the cavern, and suspends and reinforces them. Prestress is applied after the slurry solidifies.

[0027] Step five: lay the steel mesh and carry out the second steel fiber concrete spraying to form a flexible support structure for the giant span cavern.

[0028] The advantages of the giant-span cavern support structure for fractured rock mass and the construction method thereof of the present invention are:

[0029] 1) The support structure has the characteristics of rich means, comprehensive scope, clear functions, strong bearing capacity and good economy. The construction method is suitable for giant span underground caverns with a span greater than 40m. It has the characteristics of simple construction technology, convenient construction organization, smooth step sequence connection and high safety;

[0030] 2) The steel fiber concrete adopted in the present invention is easy to operate, can be used as a flexible support for giant caverns, and can maximize the self-bearing function of the surrounding rock; the combination of ordinary mortar anchor rods and shell-expanding prestressed grouting anchor rods can greatly improve the longitudinal and transverse squeezing and suspension effects of the anchor rods on the rock mass, and can ensure the formation of an effective self-bearing arch structure. The suspension effect of the shell-expanding prestressed grouting anchor rods on the self-bearing arch structure can enhance the bearing capacity of the self-bearing arch and ensure the overall stability of the cavern;

[0031] 3) The stability of the arch foot and the side wall is the foundation of the stability of the self-supporting arch structure and the cavern. The support structure of the present invention adopts a high-strength locking anchor cable to prevent the arch foot and the side wall from slipping, thereby ensuring the stability of the arch foot and the side wall;

[0032] 4) The block reinforcement anchor cable in the present invention has a strong supporting capacity, and can suspend and squeeze the unstable block, thereby ensuring the safety of the unstable block; the resin anchor rod can achieve rapid tensioning, timely support, and can provide buffer time for the application of subsequent support structures;

[0033] 5) In order to ensure the safety of the cavern during operation, conventional caverns need to be constructed with secondary lining. However, for giant span caverns, if the secondary lining load is taken into consideration, the lining thickness will be very large, which will lead to problems such as high cost and difficulty in pouring. The support structure of the present invention has distinct functions and strong operability. It can fully mobilize the self-bearing capacity of the surrounding rock and can mobilize the self-bearing capacity of the rock mass at multiple levels to reinforce unstable blocks, so that the giant span cavern can reach a stable state for a long time. Under the action of this system, the secondary lining does not bear the rock mass load and can be omitted under waterless conditions, thereby greatly reducing the cost and construction difficulty.

[0034] 6) The support structure of the present invention does not need to set up temporary supports, and the force system does not need to be transformed multiple times, which can better ensure the safety of the project. The construction process is simple, the construction sequence is interconnected, the steps are smooth, the construction organization is convenient, and a lot of time and cost are saved. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic diagram of a giant-span cavern support structure for a fractured rock mass provided by the present invention;

[0036] Figure 2 A schematic diagram of the construction process of the initial spraying of steel fiber concrete for the giant span cavern support structure of the fractured rock mass provided by the present invention;

[0037] Figure 3 A schematic diagram of the construction process of ordinary mortar anchor rods, expansion shell type prestressed grouting anchor rods and resin anchor rods for the giant span cavern support structure of fractured rock mass provided by the present invention;

[0038] Figure 4 A schematic diagram of the construction process of the locking foot prestressed anchor cable of the giant span cavern support structure of the fractured rock mass provided by the present invention;

[0039] Figure 5 A schematic diagram of the construction process of the prestressed anchor cable for the block reinforcement of the giant span cavern support structure of the fractured rock mass provided by the present invention;

[0040] Figure 6 A schematic diagram of the construction process of laying steel mesh and spraying steel fiber concrete for the giant span cave section self-bearing support structure provided by the present invention.

[0041] In the figure: 1. Steel fiber concrete; 2. Steel mesh; 3. Self-supporting arch structure; 4. Ordinary mortar anchor; 5. Expanding shell prestressed grouting anchor; 6. Locking foot prestressed anchor cable; 7. Block reinforcement prestressed anchor cable; 8. Block reinforcement prestressed anchor cable; 9. Resin anchor cable. DETAILED DESCRIPTION

[0042] In order to better understand the purpose, structure and function of the present invention, the following is a further detailed description of a giant-span cavern support structure for a fractured rock mass and a construction method thereof in conjunction with the accompanying drawings.

[0043] like Figures 1 to 6 As shown, it shows a fractured rock mass giant span cavern support structure and its construction method of the present invention, which is suitable for giant span underground caverns with a span greater than 40m. Figure 1 As shown, the support structure includes a flexible support structure on the surface of the cavern, a self-supporting arch structure 3 of the rock mass, a locking prestressed anchor cable 6, a block reinforcement prestressed anchor cable 8 and a resin anchor rod 9. Among them, the flexible support structure on the surface of the cavern is arranged on the arch and side wall of the excavation surface, including steel fiber concrete 1 and steel mesh 2; the self-supporting arch structure 3 of the rock mass is arranged on the arch and side wall of the cavern, including ordinary mortar anchor rods 4, expansion shell prestressed grouting anchor rods 5 and rock mass; the locking prestressed anchor cable 6 is arranged at the arch foot of the cavern; the block reinforcement prestressed anchor cable 8 is arranged within the range of the unstable block 7 of the cavern; the resin anchor rod is arranged in the deformation mutation area after excavation, which is an emergency reinforcement measure.

[0044] Furthermore, the flexible support structure on the cave surface includes three layers. After the cave is excavated, a layer of steel fiber concrete 1 is first sprayed, then a steel mesh 2 is laid, and finally a layer of steel fiber concrete 1 is sprayed again. The steel fiber concrete used in the present invention is easy to operate, can be used as a flexible support for giant caves, and maximizes the self-bearing function of the surrounding rock.

[0045] Furthermore, the steel fiber concrete 1 in the flexible support structure on the cave surface has a strength grade of not less than C35, a bending strength of not less than 4Mpa, and a thickness of generally 30cm. In addition, the diameter of the steel mesh 2 is 6 to 12mm, and the steel mesh spacing is 250x250mm or 200x200mm, which can be set as a single layer or double layer according to the geological conditions.

[0046] Further, the length of the common mortar anchor rod 4 in the rock mass self-supporting arch structure 3 is set according to the thickness of the self-supporting arch required for the stability of the cavern, and passes through the loose circle of the rock mass, and the length is generally 6 to 10 meters, the circumferential spacing is 1 to 1.5 meters, and the longitudinal spacing is 1 to 1.5 meters. The shell expansion type prestressed grouting anchor rod 5 assists in forming the rock mass self-supporting arch structure 3 and can be suspended and reinforced. The length is generally 1.2 to 1.8 times (preferably 1.5 times) the length of the common mortar anchor rod 4, the circumferential spacing is 2 to 3 meters, the longitudinal spacing is 2 to 3 meters, and the prestress is 120 to 180 KN (preferably 150 kN). The present invention adopts the combination of common mortar anchor rods and shell expansion type prestressed grouting anchor rods, which can greatly improve the longitudinal and transverse squeezing and suspension effect of the anchor rods on the rock mass, can ensure the formation of an effective self-supporting arch structure, and the suspending effect of the shell expansion type prestressed grouting anchor rods on the self-supporting arch structure can strengthen the bearing capacity of the self-supporting arch and ensure the overall stability of the cavern.

[0047] Furthermore, the locking foot prestressed anchor cable 6 is set to ensure the stability of the arch foot. The length of the locking foot prestressed anchor cable 6 is generally 3 / 1 to 2 / 1 of the span of the cavern. The arch foot is symmetrically arranged in three rows with a longitudinal spacing of 4 to 6m. The initial prestressing force of the locking foot prestressed anchor cable 6 is 1500kN, and additional tensioning is performed later. Since the stability of the arch foot and the side wall is the foundation of the stability of the self-supporting arch structure and the cavern, the support structure of the present invention adopts a high-strength locking foot anchor cable to prevent the arch foot and the side wall from slipping, thereby ensuring the stability of the arch foot and the side wall.

[0048] Furthermore, the block reinforcement prestressed anchor cable 8 is installed within the range of the fracture cutting surface to squeeze and suspend the unstable block 7 above the cavern. The free section of the block reinforcement prestressed anchor cable 8 passes through 3 to 5 meters above the unstable block 7 above the cavern. The anchoring section of the block reinforcement prestressed anchor cable 8 is fixed in the stable rock mass above the fracture cutting surface. The prestressing and layout spacing of the block reinforcement prestressed anchor cable 8 are set according to the weight of the unstable block 7, and a certain safety reserve is considered. Due to the large cross-section of the giant span cavern, it is inevitable to encounter fractures and broken surrounding rocks, and unstable blocks are easily formed above the cavern. Therefore, the stability of the block is the main factor determining the stability of the giant span cavern. The block reinforcement anchor cable of the present invention has a strong supporting capacity and can suspend and squeeze unstable blocks, thereby ensuring the safety of unstable blocks.

[0049] Furthermore, the resin anchor rod 9 is arranged within the range of the unstable block 7, and can quickly provide tension. The length is generally 6 to 10 meters, and the spacing is determined according to the deformation area on site. The longitudinal spacing of the ring is generally 1.5m. Since the support structures such as anchor cables and anchor rods need to wait for the slurry to solidify before tensioning, and cannot provide timely support for sudden deformation on site, the resin anchor rod in the support structure of the present invention can achieve rapid tensioning and timely support, which can provide buffer time for the application of subsequent support structures.

[0050] In summary, the support structure of the present invention has the characteristics of rich means, comprehensive range, clear functions, strong bearing capacity and good economy. The construction method is suitable for giant span underground caverns with a span greater than 40m, and has the characteristics of simple construction process, convenient construction organization, smooth step connection and high safety.

[0051] The working process of the construction method of a giant span cavern support structure for a fractured rock mass of the present invention is described below in conjunction with the accompanying drawings:

[0052] like Figures 2 to 6 As shown, the present invention discloses a construction method of a giant span cavern support structure of a fractured rock mass, comprising the following steps:

[0053] Step 1: After the cavern is excavated, the surface broken and unstable blocks are removed, and a layer of steel fiber concrete 1 is sprayed to level and seal the excavation surface.

[0054] Specifically, it is preferred to initially spray 8 to 12 cm (preferably 10 cm) of steel fiber concrete 1.

[0055] Step 2: According to the designed spacing and length, ordinary mortar anchor rods 4 and expansion shell prestressed grouting anchor rods 5 are installed in sequence. The grouting material is cement slurry. After the slurry solidifies, prestress is applied to form a self-supporting arch structure 3 with the rock mass; resin anchor rods 9 are applied in the deformation mutation area.

[0056] Step three, three rows of prestressed anchor cables 6 are symmetrically applied at the arch foot, the grouting material is cement slurry, and prestress is applied after the slurry solidifies.

[0057] Step four, apply block reinforcement prestressed anchor cable 8 within the range of unstable block 7 in the cavern. The free section of the anchor cable passes through the unstable block 7 above the cavern to suspend and reinforce it. It can also serve as a safety reserve for the entire support system. The grouting material is cement slurry, and prestress is applied after the slurry solidifies.

[0058] Step five: laying the steel mesh 2 and spraying the steel fiber concrete 1 for the second time, so as to form a flexible support structure for the giant span cavern.

[0059] A support structure for a giant-span cavern in a fissured rock mass and a construction method thereof of the present invention, the support structure has the characteristics of rich means, comprehensive scope, distinct functions, strong bearing capacity and good economy, and the construction method is suitable for giant-span underground caverns with a span greater than 40m, and has the characteristics of simple construction process, convenient construction organization, smooth step connection and high safety, etc.; the support structure of the present invention has distinct functions and strong operability, fully mobilizes the self-bearing capacity of the surrounding rock, can mobilize the self-bearing capacity of the rock mass at multiple levels, reinforces the unstable blocks, and enables the giant-span cavern to reach a stable state for a long time, and the secondary lining under the action of this system does not bear the rock mass load, and can be omitted under waterless conditions, thereby greatly reducing the cost and construction difficulty; the support structure of the present invention does not need to set up temporary supports, and the force system does not need to be transformed multiple times, which can better ensure the safety of the project. The construction process is simple, the construction sequence is connected with each other, and the step sequence is smooth, which is convenient for construction organization and saves a lot of time and cost.

[0060] The present invention is further described above with the aid of specific embodiments. However, it should be understood that the specific description here should not be construed as limiting the essence and scope of the present invention. Various modifications made to the above embodiments by ordinary technicians in the field after reading this specification are all within the scope of protection of the present invention.

Claims

1. A giant span cavern support structure for fractured rock mass, characterized in that: include: The cavern surface flexible support structure is arranged on the arch and side wall of the excavation surface and includes steel fiber concrete (1) and a steel mesh (2); The rock mass self-supporting arch structure (3) is arranged on the arch part and the side wall of the cavern, and comprises ordinary mortar anchor rods (4), expansion shell type prestressed grouting anchor rods (5) and rock mass; The locking foot prestressed anchor cable (6) is arranged at the arch foot of the cavern; The block reinforcement prestressed anchor cable (8) is arranged within the range of the unstable block (7) in the cavern, and the free section of the block reinforcement prestressed anchor cable (8) passes through the unstable block (7) above the cavern; and Resin anchor rods (9) are arranged in the area where deformation suddenly occurs after excavation; The cave surface flexible support structure comprises three layers. After the cave is excavated, a layer of steel fiber concrete (1) is first sprayed, and then ordinary mortar anchor rods (4), expansion shell prestressed grouting anchor rods (5), resin anchor rods (9), locking foot prestressed anchor cables (6) and block reinforcement prestressed anchor cables (8) are arranged. Then, a steel mesh (2) is laid, and a second layer of steel fiber concrete (1) is sprayed. The common mortar anchor rod (4) in the rock mass self-supporting arch structure (3) is set through the loose circle of the rock mass; The shell expansion type prestressed grouting anchor rod (5) assists in forming the rock mass self-supporting arch structure (3) and suspends and reinforces it.

2. A giant span cavern support structure for fractured rock mass according to claim 1, characterized in that: The steel fiber concrete (1) in the flexible support structure on the cavern surface shall have a strength grade of not less than C35, a flexural strength of not less than 4 MPa, and a thickness of 30 cm.

3. A giant span cavern support structure for fractured rock mass according to claim 1, characterized in that: The diameter of the steel mesh (2) in the flexible support structure on the cave surface is 6-12 mm, the spacing between the steel mesh is 250x250 mm or 200x200 mm, and it is arranged in a single layer or double layer.

4. A giant span cavern support structure for fractured rock mass according to claim 1, characterized in that: The length of the common mortar anchor rods (4) in the rock mass self-supporting arch structure (3) is 6 to 10 m, the circumferential spacing is 1 to 1.5 m, and the longitudinal spacing is 1 to 1.5 m.

5. A giant span cavern support structure for fractured rock mass according to claim 1, characterized in that: The length of the expansion shell type prestressed grouting anchor rod (5) is 1.2 to 1.8 times the length of the ordinary mortar anchor rod (4), the circumferential spacing is 2 to 3 m, and the longitudinal spacing is 2 to 3 m.

6. A giant span cavern support structure for fractured rock mass according to claim 1, characterized in that: The length of the locking foot prestressed anchor cable (6) is 3 / 1 to 2 / 1 of the span of the cavern, and the arch foot is symmetrically arranged in three rows with a longitudinal spacing of 4 to 6 m.

7. A construction method for a giant span cavern support structure in a fractured rock mass as claimed in any one of claims 1 to 6, characterized in that: include: Step 1: After the excavation of the cavern, the surface broken and unstable blocks are removed, and steel fiber concrete (1) is initially sprayed to level and seal the excavation surface; Step 2: installing common mortar anchor rods (4) and expansion shell prestressed grouting anchor rods (5), applying prestress after the slurry solidifies, and forming a rock mass self-supporting arch structure (3) with the rock mass; applying resin anchor rods (9) in the deformation mutation area; Step 3: symmetrically apply three rows of locking prestressed anchor cables (6) at the arch foot, and apply prestress after the slurry solidifies; Step 4: applying a block reinforcement prestressed anchor cable (8) within the range of the unstable block (7) in the cavern, wherein the free section of the anchor cable passes through the unstable block (7) above the cavern, and is suspended and reinforced, and prestress is applied after the slurry solidifies; Step 5: laying a steel mesh (2) and spraying steel fiber concrete (1) for the second time to form a flexible support structure for the giant span cavern.

8. The construction method of a giant span cavern support structure for a fractured rock mass according to claim 7, characterized in that: In step 1, 8-12 cm of steel fiber concrete (1) is initially sprayed.

9. The construction method of a giant span cavern support structure for a fractured rock mass according to claim 7, characterized in that: In steps 2, 3 and 4, the grouting material is cement slurry.

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