A layered and stepped optimization excavation method for a super-span underground cavern

Abstract

This invention discloses a layered and step-by-step optimized excavation method for domes in ultra-large span underground caverns, comprising: S1, dividing the underground cavern into at least three layers according to the excavation sequence, from top to bottom, including the first layer, the second layer, the third layer, and so on; S2, first expanding the span into an arch, dividing the middle of the first layer into upper and lower layers, with the lower middle layer being excavated first. After the lower layer is excavated, the upper middle layer is excavated upwards to form the central dome. The surrounding rock on both sides is divided into several areas, and symmetrical excavation is carried out from the middle to both sides to completely excavate and shape the first layer, forming a complete dome; S3, then lowering the height to form the second layer, the third layer, and so on downwards until the underground cavern is formed. This invention can precisely control the redistribution of surrounding rock stress during the excavation process, effectively suppress the expansion of the damaged area, and achieve precise temporal and spatial matching between support and excavation, thereby fundamentally ensuring construction safety, controlling surrounding rock deformation, and achieving excellent forming quality.

Description

Technical Field

[0001] This invention belongs to the field of large-scale underground engineering construction technology, and in particular relates to a method for optimizing the layered and step-by-step excavation of domes for ultra-large span underground caverns. Background Technology

[0002] As my country's clean energy development extends into the high mountain and canyon regions of southwest China, the scale of large and extra-large hydropower stations is increasing daily, leading to a significant increase in the size and span of underground caverns, gradually entering the category of "ultra-large spans." These cavern domes often exhibit significant characteristics such as large diameters, deep burial depths, and high levels of ground stress. Controlling the stability of the surrounding rock during excavation has become a highly challenging technical problem in the field of underground engineering.

[0003] For underground caverns with a dome height exceeding 20 meters and a span exceeding 40 meters, the "size effect" of traditional methods becomes prominent, further amplifying the cavern stability problem. This often leads to overdevelopment of the excavation damage zone, penetration of the plastic zone, and difficulty in deformation control. Furthermore, the support structure is difficult to implement in a timely manner following the excavation face, leaving potential safety hazards.

[0004] Furthermore, under high-stress environments, the failure mode of surrounding rock exhibits a dynamic transformation characteristic: in the early stages of excavation, the risk of brittle failure due to stress concentration is dominant, while in the middle and later stages, it transforms into the risk of collapse-type failure caused by deformation accumulation and relaxation. This requires that excavation support schemes not only optimize stress paths but also closely coordinate with monitoring, early warning, and support timing. Although existing layered and segmented excavation technologies consider spatial division to some extent, they lack systematic structural engineering methods and supporting structural designs in areas such as how to coordinate with the main direction of the geostress field, how to achieve "damage control" rather than "stress release," and how to ensure that the support system can play a timely and effective role in each excavation step. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned technical problems existing in the prior art and to provide a layered and step-by-step optimized excavation method for the dome of ultra-large span underground caverns. This method can precisely control the redistribution of surrounding rock stress during the excavation process, effectively suppress the expansion of the damaged area, and achieve precise temporal and spatial matching between support and excavation. This fundamentally ensures construction safety, controls surrounding rock deformation, and achieves excellent forming quality.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for optimized, layered, and step-by-step excavation of domes for ultra-large span underground caverns, characterized by the following steps: S1. Divide the underground cavern into at least three levels according to the excavation sequence, in descending order of height, including the first level, the second level, the third level, and so on... S2. First, expand the span to form an arch, divide the middle of the first layer into upper and lower layers, excavate the lower middle layer first, and after the lower layer is excavated, excavate towards the upper middle layer to form the central dome. Divide the surrounding rock on both sides into several areas, and excavate symmetrically from the middle to the areas on both sides to completely excavate and shape the first layer, forming a complete dome. S3, then lower and shape the structure, excavating the second, third, and so on downwards until an underground cavern is formed.

[0007] Furthermore, in step S1, the height of each layer is 5~10m.

[0008] Furthermore, in step S2, the width of the central region is 10-15m.

[0009] Furthermore, in step S2, the width of the two sides is 5-10m.

[0010] Furthermore, in step S3, the detailed steps for excavating each layer are as follows: first, excavate downwards along the middle; after the middle excavation is completed, gradually excavate to both sides until the entire layer is excavated.

[0011] Furthermore, each excavation area is divided into three zones: Zone I, Zone II, and Zone III. Zone II is the central zone, and Zone III is the outer zone of Zone II. Zone I extends directly from the outer zone to the central zone. Zone I is excavated from the outer zone to the center, with a width of 5-10m. Then, the central zone II is excavated, with a width of 10-15m. Finally, the outer zone III is excavated, with a width of 5-10m.

[0012] Furthermore, in steps S2 and S3, the "excavate and support simultaneously" principle of surrounding rock control is adopted. The support operation closely follows the excavation face, and anchoring and shotcreting are completed before the rock mass undergoes significant deformation and damage. The support for the outer contour of the underground cavern is permanent support, while the support in the remaining steps is temporary support. Temporary support uses glass fiber anchors or basalt anchors that are easy to excavate and remove later, while permanent support uses traditional steel anchors in conjunction with long anchor cables.

[0013] The present invention, by adopting the above-described technical solution, has the following beneficial effects: This invention, through its core principle of "expanding the span first, then lowering the height," completely avoids the occurrence of temporary, high-risk structures such as "15-meter-high sidewalls" found in traditional methods. The maximum sidewall deformation during excavation is significantly reduced from 18.2mm to approximately 10mm, with a more uniform deformation distribution. This fundamentally eliminates the risk of sidewall spalling and collapse caused by sidewall loosening and deformation. The invention's small-block division provides a safe and convenient working platform for support operations. Construction personnel and equipment can closely follow the excavation face, completing anchoring and shotcreting before significant deformation and damage to the rock mass occurs. This allows the support system to function most effectively, sharing the load with the surrounding rock and ensuring the long-term stability of the dome and excellent excavation quality. Attached Figure Description

[0014] The present invention will be further described below with reference to the accompanying drawings: Figure 1 This is a schematic diagram illustrating the excavation sequence of the present invention: first expanding the span to form an arch, then lowering the height to shape the arch. Figure 2 This is a schematic diagram illustrating the excavation sequence for each layer of the present invention; Figure 3 This is a typical longitudinal section displacement cloud diagram after the excavation of the tunnel in this invention is completed; Figure 4 This is a typical cross-sectional displacement cloud diagram after the excavation of the tunnel in this invention is completed; Figure 5 This is a typical longitudinal section stress cloud diagram after the excavation of the tunnel in this invention is completed; Figure 6 This is a typical cross-sectional stress cloud diagram after the excavation of the tunnel in this invention is completed; Figure 7 This is a multi-point displacement gauge monitoring curve at a typical location after the excavation of the tunnel in this invention. Detailed Implementation

[0015] like Figure 1 As shown, a layered and step-by-step optimized excavation method for the dome of an ultra-large span underground cavern includes the following steps: S1. Divide the underground cavern into at least three levels according to the excavation sequence, in descending order of height, including the first level, the second level, the third level, and so on... S2. First, expand the span to form an arch, divide the middle of the first layer into upper and lower layers, excavate the lower middle layer first, and after the lower layer is excavated, excavate towards the upper middle layer to form the central dome. Divide the surrounding rock on both sides into several areas, and excavate symmetrically from the middle to the areas on both sides to completely excavate and shape the first layer, forming a complete dome. S3, then lower and shape the structure, excavating the second, third, and so on downwards until an underground cavern is formed.

[0016] This invention optimizes the excavation sequence of key steps, establishing a new construction principle of "first expanding the span to form an arch, then lowering the height to form the final shape." By prioritizing lateral expansion to form a stable load-bearing arch, the stress adjustment of the surrounding rock during excavation is transformed from a drastic, concentrated abrupt change to a smooth, gradual transition. This stable stress release process, combined with a refined "layered and segmented, zone-by-zone advancement" strategy, creates a crucial prerequisite for the timely intervention of support measures. This ensures that the support system can effectively exert its restraining and reinforcing effects before significant deformation or irreversible damage to the surrounding rock occurs, ultimately guaranteeing that the giant dome structure remains in a safe, controllable, and stable state.

[0017] In step S1, the height of each floor is 5~10m.

[0018] In step S2, the width of the central region is 10-15m.

[0019] In step S2, the width of the two sides is 5-10m.

[0020] like Figure 2 As shown, in step S3, the detailed steps for excavating each layer are as follows: first, excavate downwards along the middle; after the middle excavation is completed, excavate gradually to both sides until the entire layer is excavated. Each excavation area is divided into three zones: Zone I, Zone II, and Zone III. Zone II includes Zones II1 and II2, and Zone III includes Zones III1 and III2. Zone II is the central zone, and Zone III is the outer perimeter of Zone II. Zone I extends directly from the outer perimeter to the central zone. First, excavate Zone I from the outer perimeter to the center, with a width of 5-10m. Then, excavate the central zone II, with a width of 10-15m. Finally, excavate the outer perimeter zone III, with a width of 5-10m.

[0021] In steps S2 and S3, the "excavate and support simultaneously" principle of surrounding rock control is adopted. The support operation closely follows the excavation face, and anchoring and shotcreting are completed before the rock mass undergoes significant deformation and damage. The support for the outer contour of the underground cavern is permanent support, while the support in the remaining steps is temporary support. Temporary support uses glass fiber anchors or basalt anchors that are easy to excavate and remove later, while permanent support uses traditional steel anchors in conjunction with long anchor cables.

[0022] like Figures 3 to 7 As shown, using the excavation method of this invention, it can be seen that the numerical calculation results of deformation and stress of underground giant caverns with spans exceeding 40 meters and heights exceeding 100 meters, as well as the monitoring results of multi-point displacement gauges of the surrounding rock, converged very quickly after the excavation was completed. The maximum deformation value was also less than the requirements of relevant standards and specifications, indicating that the underground cavern was stable and safe.

[0023] This invention, through its core principle of "expanding the span first, then lowering the height," completely avoids the occurrence of temporary, high-risk structures such as "15-meter-high sidewalls" found in traditional methods. The maximum sidewall deformation during excavation is significantly reduced from 18.2mm to approximately 10mm, with a more uniform deformation distribution. This fundamentally eliminates the risk of sidewall spalling and collapse caused by sidewall loosening and deformation. The invention's small-block division provides a safe and convenient working platform for support operations. Construction personnel and equipment can closely follow the excavation face, completing anchoring and shotcreting before significant deformation and damage to the rock mass occurs. This allows the support system to function most effectively, sharing the load with the surrounding rock and ensuring the long-term stability of the dome and excellent excavation quality.

[0024] The above are merely specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications made based on the present invention to solve essentially the same technical problems and achieve essentially the same technical effects are all covered within the protection scope of the present invention.

Claims

1. A method for optimized, layered, and step-by-step excavation of domes for ultra-large span underground caverns, characterized in that, Includes the following steps: S1. Divide the underground cavern into at least three levels according to the excavation sequence, in descending order of height, including the first level, the second level, the third level, and so on... S2. First, expand the span to form an arch, divide the middle of the first layer into upper and lower layers, excavate the lower middle layer first, and after the lower layer is excavated, excavate towards the upper middle layer to form the central dome. Divide the surrounding rock on both sides into several areas, and excavate symmetrically from the middle to the areas on both sides to completely excavate and shape the first layer, forming a complete dome. S3, then lower and shape the structure, excavating the second, third, and so on downwards until an underground cavern is formed.

2. The method for optimized excavation of dome in a layered and step-by-step manner for ultra-large span underground caverns according to claim 1, characterized in that: In step S1, the height of each floor is 5~10m.

3. The method for optimized excavation of domes in a layered and step-by-step manner for ultra-large span underground caverns according to claim 1, characterized in that: In step S2, the width of the central region is 10-15m.

4. The method for optimized excavation of dome layers and steps for ultra-large span underground caverns according to claim 1, characterized in that: In step S2, the width of the two sides is 5-10m.

5. The method for optimized excavation of dome in a layered and step-by-step manner for ultra-large span underground caverns according to claim 1, characterized in that: In step S3, the detailed steps for excavating each layer are as follows: first, excavate downwards along the middle; after the middle excavation is completed, gradually excavate to both sides until the entire layer is excavated.

6. The method for optimized excavation of dome in a layered and step-by-step manner for ultra-large span underground caverns according to claim 5, characterized in that: Each excavation area is divided into three zones: Zone I, Zone II, and Zone III. Zone II is the central zone, and Zone III is the outer zone of Zone II. Zone I extends directly from the outer zone to the central zone. Zone I is excavated from the outer zone to the center, with a width of 5-10m. Then, the central zone II is excavated, with a width of 10-15m. Finally, the outer zone III is excavated, with a width of 5-10m.

7. The method for optimized excavation of dome in a layered and step-by-step manner for ultra-large span underground caverns according to claim 1, characterized in that: In steps S2 and S3, the "excavate and support simultaneously" principle is adopted for surrounding rock control. The support operation closely follows the excavation face, and anchoring and shotcreting are completed before significant deformation and damage occur in the rock mass. The support for the outer contour of the underground cavern is permanent support, while the support in the remaining steps is temporary support. Temporary support uses fiberglass anchors or basalt anchors that are easy to excavate and remove later, while permanent support uses traditional steel anchors in conjunction with long anchor cables.

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