A construction method for combined solidification support in deep vertical shafts of fractured rock mass

Abstract

This invention relates to the field of deep shaft construction technology in water conservancy projects, specifically disclosing a combined solidification support construction method for deep shafts in fractured rock masses. This method is applicable to secondary excavation and solidification support after collapse of deep shafts in Class IV-V fractured rock masses with well-developed joints and fissures that are prone to disintegration upon contact with water. This method combines a cantilevered concrete core support structure with various combined support forms. Through the selection of support structure, layered construction, and coordinated reinforcement, it solves the technical problems of shaft wall instability and secondary collapse during the excavation of deep shafts in fractured rock masses, improving the stability and safety of the support structure. It is suitable for the construction needs of large-size rectangular deep shafts and can be widely applied to similar deep shaft construction scenarios in water conservancy projects involving fractured rock masses.

Description

Technical Field

[0001] This invention relates to the field of underground construction technology in water conservancy projects, specifically to a combined solidification support construction method for deep vertical shafts in fractured rock masses. Background Technology

[0002] In the construction of deep vertical shafts in water conservancy projects, it is common to encounter Class IV to V fractured rock masses, such as tuffaceous siltstone and carbonaceous siltstone. These rock masses have poor integrity, well-developed joints and fissures, and are relatively soft and easily disintegrate when exposed to water. During excavation, shaft wall collapse is highly likely, resulting in severe disturbance of the rock mass and extremely high safety risks for secondary excavation. Existing deep vertical shaft wall support technologies mostly employ single shotcrete and anchor support or steel bracing. For large-sized rectangular deep vertical shafts in fractured rock masses, single support methods suffer from insufficient support strength and poor adhesion to the rock mass, easily leading to shaft wall instability and secondary collapse. Furthermore, existing support technologies are not specifically selected based on the actual disturbance of the rock mass after collapse, resulting in poor adaptability and inability to meet the wall support requirements for secondary excavation after a collapse in deep vertical shafts in fractured rock masses. This severely restricts the construction progress, increases project investment, and raises safety risks. Summary of the Invention

[0003] The purpose of this invention is to provide a construction method for combined solidification support in deep vertical shafts in fractured rock masses.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A combined solidified wall support construction method for deep vertical shafts in fractured rock masses is applicable to rectangular deep vertical shafts with a length of 15.7m × width of 7.7m and a depth of 60m, where the surrounding rock is tuffaceous siltstone / carbonaceous siltstone of Class IV to V fractured rock masses. The method includes six steps: pre-construction investigation, support type selection, layered construction preparation, combined support construction, shotcrete curing, and acceptance testing.

[0005] In the pre-construction survey phase, the actual geological conditions of the rock mass after the collapse are accurately grasped, providing data support for the selection of support methods. In the support method selection phase, four suitable combined support methods are provided to achieve a targeted combination of "main support + auxiliary support" to adapt to rock mass areas with different degrees of disturbance. In the layered construction phase, a top-down construction principle is adopted to match the secondary excavation process of the shaft, avoiding secondary disturbance to the rock mass during construction. In the combined support construction and shotcrete curing phase, the support structure and the well wall rock mass form an integral solidified body, which greatly improves the stability and firmness of the support structure. In the acceptance and testing phase, the quality of each layer of support is ensured to avoid safety accidents caused by substandard support.

[0006] The beneficial effects of this invention are as follows: 1. This application provides four combined support forms for the special scenario of secondary excavation after the collapse of deep vertical shafts in Class IV to V fractured rock masses. The forms can be selected according to the actual disturbance of the rock mass, which is highly adaptable and solves the problem of single support forms and poor adaptability of existing technologies. 2. The collaborative reinforcement process of "cantilever steel beam main support + auxiliary support + wire mesh shotcrete" is adopted to form an integral solid body between the support structure and the well wall rock mass, which improves the support strength and stability of the well wall, effectively prevents well wall instability and secondary collapse, and reduces construction safety risks. 3. The construction process is synchronized with the secondary excavation of the shaft, with layered construction and acceptance from top to bottom. The standardized construction process can ensure the construction progress, avoid project delays due to support issues, and reduce the risk of increased project investment. 4. The process is simple to operate, and the required materials are conventional materials for water conservancy projects. They are easy to obtain and the cost is controllable. It can be widely used in the construction of large-size rectangular deep vertical shafts in similar Class IV to V fractured rock masses in water conservancy projects, and has good promotion and application value. Detailed Implementation

[0007] The specific embodiments of the present invention will be described in further detail below with reference to the examples. These examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0008] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field; unless otherwise specified, the reagents or materials described are all from commercial sources.

[0009] This embodiment applies to a rectangular deep shaft with a length of 15.7m, a width of 7.7m, and a depth of 60m in a reservoir diversion and discharge tunnel. The surrounding rock of the shaft is tuffaceous siltstone and carbonaceous siltstone, belonging to Class IV to V fractured rock mass. In June 2022, a bottom collapse occurred with a collapse height of about 35m. The rock mass exhibits fragmentation, foliation, and mudification, with well-developed joints and fissures, requiring secondary excavation and wall reinforcement support after the collapse.

[0010] 1. Pre-construction investigation: Ground-penetrating radar was used to conduct a comprehensive investigation of the rock mass of the shaft wall after the collapse. It was determined that the core area of ​​the collapse was located within 35m of the bottom of the shaft, where the rock mass was severely disturbed and the joints and fissures were highly interconnected. The upper 25m of the shaft was the surrounding disturbance zone, where the rock mass was slightly more intact but still had local fissures. 2. Support method selection: In the core area of ​​the collapse, a combination of "cantilever steel beam concrete + anchor pile" is selected. The cantilever steel beam concrete is the main support to improve the support strength of the core area, and the anchor pile is used to reinforce the rock mass. In the upper and middle disturbed areas of the shaft, a combination of "cantilever steel beam + anchor rod + wire mesh shotcrete" is selected to balance support strength and construction efficiency. 3. Layered construction preparation: Use manual labor and machinery to clear loose rock from the shaft wall to prevent it from falling; erect a steel construction operation platform along the shaft wall, with a bearing capacity of not less than 2.0 kPa; prepare materials such as HW300×300 cantilever steel beams, Φ28mm anchor piles, Φ22mm anchor rods, C30 shotcrete, and Φ50mm grouting pipes; 4. Combined Support Construction: Following the principle of top-down layered construction, the construction height of each layer is controlled at 2m. First, HW300×300 cantilever steel beams are installed at preset points on the well wall at 1.0m intervals. The steel beams are fixed by welding, and the welded joints are coated with anti-rust and anti-corrosion paint. In the core area of ​​the collapse, after the steel beams are installed, Φ28mm anchor piles are constructed. The anchor piles are driven into the rock mass to a depth of not less than 3m and are spaced at 1.5m. Φ22mm anchor rods are constructed in the upper part of the shaft. The anchor rods are driven into the rock mass to a depth of not less than 2m and are spaced at 1.2m. At the same time, grouting is applied to the cracks between the steel beams and the well wall through Φ50mm grouting pipes. The grouting material is a mixture of cement grout and quick-setting mortar at a mass ratio of 3:1. The grouting pressure is controlled at 0.8MPa to ensure that the cracks are filled densely. 5. Shotcrete curing: A Φ6mm@150×150 steel mesh is hung on the outside of the combined support structure. The steel mesh is welded and fixed to the steel beams and anchor piles / anchors. The wet spraying method is used for shotcrete construction. The shotcrete strength grade is C30 and the thickness of the shotcrete is 18cm. It is sprayed in three layers, each with a thickness of 6cm. Each layer is compacted to form an integral solidified body with the support structure and the well wall rock mass. 6. Acceptance and Inspection: The stability of the support structure is tested using an ultrasonic testing instrument. At the same time, the flatness of the shotcrete layer is checked manually. The absence of hollow areas, cracks, or peeling is considered as passing the inspection. After passing the inspection, the next level of shaft excavation construction will proceed. Steps 1-5 will be repeated until the entire 60m deep shaft wall support is completed.

[0011] In this embodiment, the secondary excavation and wall reinforcement of the collapsed vertical shaft of the diversion and discharge tunnel of Xibotu Reservoir was successfully completed using the above-mentioned combined solid wall support construction method. After 6 months of monitoring, the support structure showed no displacement, deformation, or collapse, and its stability was good, ensuring the safety and progress of the shaft construction.

[0012] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0013] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for constructing a combined wall support of a deep vertical shaft in a rock mass, characterized in that, This method is suitable for rectangular deep shafts measuring 15.7m in length, 7.7m in width, and 60m in depth, where the surrounding rock is composed of tuffaceous siltstone and carbonaceous siltstone, Class IV to V fractured rock masses. The steps include: S1. Pre-construction investigation: Conduct geological investigation on the fractured rock mass after the collapse to determine the extent of rock mass fragmentation, foliation, and mudification, as well as the development of joints and fissures, and delineate the branch protection stratification areas; S2. Support Form Selection: Based on the survey results, a suitable combination support form is selected from cantilever steel beam concrete, cantilever steel beam + anchor pile, cantilever steel beam + anchor rod + wire mesh shotcrete, and cantilever steel support + grouting pipe + wire mesh shotcrete. The core area of ​​the collapse adopts cantilever steel beam concrete as the main support, and the surrounding disturbance area is equipped with anchor pile, anchor rod, and steel support as auxiliary support. S3. Layered construction preparation: Clean the loose rock mass of the vertical shaft wall, set up the construction operation platform, and prepare the materials required for support, such as steel beams, anchor piles, anchor rods, shotcrete, and grouting pipes. S4. Combined support construction: Following the principle of layered construction from top to bottom, the main support structure of the cantilever steel beam is constructed first. After the steel beam is fixed, the auxiliary support structure is constructed according to the selection results. At the same time, the grouting pipe is grouted to fill the gap between the steel beam and the well wall. S5. Shotcrete curing: The outside of the combined support structure is treated with wire mesh, and the well wall is sprayed with shotcrete to form an integral solidified body with the steel beam, anchor piles / anchors and well wall rock mass. S6. Acceptance and inspection: Inspect the firmness and flatness of the support structure. After the inspection is qualified, proceed to the next level of shaft excavation and construction. Repeat steps S1-S5 until the entire shaft wall support is completed.

2. The construction method for combined solidification support in deep vertical shafts of fractured rock mass according to claim 1, characterized in that, In step S4, the installation spacing of the cantilever steel beams is 0.8-1.2m. The steel beams are fixed by welding, and the welded joints are treated with anti-rust and anti-corrosion measures.

3. The construction method for combined solidification support in deep vertical shafts of fractured rock mass according to claim 1, characterized in that, In step S4, the grouting material for the grouting conduit is a mixture of cement grout and quick-setting mortar. The grouting pressure is controlled at 0.5-1.0 MPa to ensure that the cracks are filled tightly.

4. The construction method for combined solidification support in deep vertical shafts of fractured rock mass according to claim 1, characterized in that, In step S5, the thickness of the sprayed concrete is 15-20cm, and the concrete strength grade is not lower than C30. During the spraying process, the concrete is sprayed in layers and compacted layer by layer.