Expansive broken skarn contact zone tunneling construction method

Abstract

The invention belongs to the technical field of tunnel excavation, and provides an expansive broken skarn contact zone tunneling construction method which comprises the following steps: drilling after designing a drilling scheme according to a roadway section design size and a footage section size, during drilling, firstly drilling in the periphery of a roadway to obtain water injection holes, and injecting water into a tunnel face through the water injection holes; after water injection is completed and 24 hours are waited, a pilot tunnel method is adopted for tunneling construction, and after a pilot tunnel smaller than the designed size of the section of the roadway is excavated, the roadway is gradually expanded and brushed to the designed size of the section; after the roadway is expanded to the section design size, primary spraying supporting treatment is conducted immediately, and meanwhile a passive supporting structure is installed; after the passive supporting structure is installed, active supporting is conducted; construction is repeated, and for each footage section, the steps are repeated till tunneling of the whole roadway is completed. Through water injection treatment, the friction force between skarn bodies is improved, the roof fall risk is reduced, the cost is reduced, and the construction efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel excavation, and specifically discloses a construction method for excavating a contact zone of expansive broken skarn. Background Art

[0002] Skarn is a metamorphic rock formed during the contact and replacement process between magma and carbonate rock. Its mineral composition is complex. When the metamorphism is weak, it often contains clay minerals such as chlorite and montmorillonite, which easily swell and become muddy when in contact with water. At the same time, the surface of skarn is usually relatively smooth, which makes the friction between the rocks lower and increases the difficulty of excavation construction. During the construction of underground tunnels, when the construction passes through the contact zone of strongly expansive broken skarn, the roof of the tunnel often collapses due to the low friction of the rock mass, which seriously affects the safety and progress of the construction. Therefore, in the current mine construction, for tunnel excavation of expansive broken rocks, methods such as advance support or advance pre-grouting are often used.

[0003] The patent application with the patent publication number CN119288546A discloses a construction method for controlling large deformation of soft rock in mining tunnels. This method changes the properties and structure of the surrounding rock and blocks the transmission of high ground stress by over-excavating the tunnel and backfilling with foamed lightweight soil, thereby effectively controlling the deformation of the soft rock mass. However, when facing a skarn contact zone with developed fissures and weak and broken rock, the over-excavation method is likely to cause the top rock to fall, increase the construction risk, and make it difficult to promote subsequent construction, so it has certain limitations. The patent application with the patent publication number CN118933905A discloses a pre-grouting repair method for a large-deformation soft rock tunnel. By evaluating the deformation of the tunnel and performing graded pre-grouting, the loose surrounding rock is reinforced and a high-strength reinforcement arch is formed. However, this method has poor applicability to the broken skarn contact zone. In addition, after grouting, the slurry is easy to diffuse, resulting in a large amount of consumables, high cost, and the grouting pressure is difficult to reach the expected level, resulting in poor reinforcement effect, and there are certain shortcomings. In order to overcome the above problems, it is urgent to develop a new method that can effectively solve the difficulty of rapid excavation construction in the contact zone of highly expansive broken skarn. Summary of the invention

[0004] The present invention proposes a digging construction method for a digging zone of a strongly expansive and broken skarn contact zone in order to solve the problems of low tunnel excavation efficiency, poor stability, high construction risk and high cost in the existing digging construction of a strongly expansive and broken skarn contact zone.

[0005] The present invention provides a construction method for expansive broken skarn contact zone excavation, comprising the following steps: S1. Drilling is performed after designing a drilling plan according to the design dimensions of the tunnel section and the dimensions of the footage section. During drilling, water injection holes are obtained by drilling holes around the tunnel and in the center, and water is injected into the tunnel face through the water injection holes; S2. After the water injection is completed and the waiting time is no less than 24 hours, the tunneling construction is carried out by using the pilot tunnel method. A pilot tunnel smaller than the design cross-sectional dimensions of the tunnel is excavated and then the tunnel is gradually expanded to the design cross-sectional dimensions; S3. After the tunnel is expanded to the designed cross-sectional dimensions, the initial spraying support treatment is immediately carried out and the passive support structure is installed at the same time; S4. After the passive support structure is installed, active support is carried out; S5. Repeat the construction. For each advancement section, repeat steps S1 to S4 until the entire tunnel excavation is completed.

[0006] According to a construction method for expansive broken skarn contact zone excavation in some embodiments of the present application, in step S1, the water injection holes include tunnel periphery boreholes and tunnel center boreholes; the tunnel periphery boreholes are arranged at the tunnel periphery, the tunnel periphery boreholes have a depth of 3 meters, and the over-advancement section has a depth of 1 meter, and the spacing between two tunnel periphery boreholes is 1 meter; the tunnel center borehole is arranged at the tunnel center, the tunnel center borehole has a depth of 3 meters, and the number of tunnel center boreholes is 1 to 2.

[0007] According to a construction method for expansive broken skarn contact zone excavation in some embodiments of the present application, in step S1, the water injection pressure is 0.3 MPa-0.5 MPa, and the water injection volume is as shown in formula (1): (1) in, Indicates the amount of water injected. represents the total volume of skarn that needs to be expanded during the water injection process, represents the empirical coefficient used to adjust the expansion of skarn. The value range is 0.4~0.6, Indicates the porosity of skarn.

[0008] According to a construction method for expansive broken skarn contact zone excavation in some embodiments of the present application, in the step S2, the excavation of a pilot tunnel smaller than the design size of the tunnel section includes using a drilling and blasting method to excavate a pilot tunnel smaller than the design size of the tunnel section, and the drilling and blasting method adopts a small blasting method with multiple holes and less explosives when drilling and blasting.

[0009] According to a construction method for expansive broken skarn contact zone excavation in some embodiments of the present application, in step S2, gradually expanding the tunnel to the designed cross-sectional dimensions includes using a pneumatic pick to drop the remaining surrounding rock and gradually expanding the tunnel to the designed cross-sectional dimensions.

[0010] According to a construction method for expansive broken skarn contact zone excavation in some embodiments of the present application, in step S3, the initial shotcrete support includes supporting the surrounding rock of the tunnel by combining a mesh and shotcrete.

[0011] According to a method for expansive broken skarn contact zone excavation construction in some embodiments of the present application, in step S3, the passive support structure includes a steel arch.

[0012] According to a construction method for expansive broken skarn contact zone excavation in some embodiments of the present application, in step S4, the active support includes using anchor rods to support the primary shotcrete support and the passive support structure, and applying a pre-tightening force to the primary shotcrete support and the passive support structure.

[0013] The present invention proposes a construction method for tunneling in the contact zone of expansive and broken skarn, which makes full use of the swelling and muddying characteristics of skarn after it meets water, and treats the surrounding rock by injecting water, thereby increasing the friction between rock blocks, enhancing the stability of the surrounding rock, and effectively reducing the risk of roof collapse caused by insufficient friction. Compared with the existing grouting process, the method significantly reduces the cost and improves the construction efficiency. In addition, the method performs tunneling construction through the pilot tunnel method, which can make full use of the soft and broken characteristics of skarn, reduce the working time of construction personnel in dangerous areas, and ensure personal safety. Through reasonable support methods, especially the combination of anchor rods and shotcrete support, the stability of the tunnel surrounding rock is further enhanced, ensuring safety and efficiency during the construction process. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the process of a construction method for expansive broken skarn contact zone excavation according to the present invention; Figure 2 Schematic diagram of water injection hole arrangement in an embodiment of the present invention; Figure 3 It is a schematic diagram of the construction of the pilot tunnel method in an embodiment of the present invention.

[0015] In the figure, 1. broken skarn contact zone, 2. water injection hole, 3. muddied skarn, 4. pilot tunnel, 5. remaining surrounding rock. DETAILED DESCRIPTION

[0016] The following embodiments of the present invention are described in further detail in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0017] Example 1: This example provides a method for excavating a contact zone of expansive broken skarn. Figure 1 As shown, the following steps are included: S1. Design the drilling plan according to the tunnel section design dimensions and footage section dimensions and then drill the holes. Figure 2 As shown, water injection holes 2 are drilled around the periphery and center of the tunnel, and water is injected into the tunnel face through the water injection holes 2. After water injection, the expansion and mudification characteristics of the skarn are activated, the skarn expands in situ, the interaction between the skarn rock masses is increased, and the mudification of the fracture surface is promoted, thereby increasing the friction between the skarn rock masses, and then improving the stability of the tunnel surrounding rock.

[0018] S2. After the water injection is completed and the waiting time is not less than 24 hours, the tunneling construction is carried out by using the pilot tunnel method. Figure 3 As shown, after excavating a pilot tunnel 4 which is smaller than the design size of the tunnel section, the tunnel is gradually expanded to the design size of the tunnel section.

[0019] S3. After the tunnel is expanded to the designed cross-sectional dimensions, the initial spraying support treatment shall be carried out immediately and the passive support structure shall be installed at the same time.

[0020] S4. After the passive support structure is installed, active support is carried out.

[0021] S5. Repeat the construction. For each advancement section, repeat steps S1 to S4 until the entire tunnel excavation is completed.

[0022] Embodiment 2: This embodiment provides a construction method for expansive broken skarn contact zone excavation, comprising the following steps: S1. Design the drilling plan according to the tunnel section design dimensions and footage section dimensions and then drill the holes. Figure 2 As shown, water injection holes 2 are drilled around the periphery and the center of the tunnel, and water is injected into the tunnel face through the water injection holes 2.

[0023] Traditional grouting technology faces many difficulties in practical application. First, the diffusivity of slurry often leads to the inability of slurry to accurately fill cracks, especially when cracks are developed or rock formations are broken. The slurry cannot diffuse to the area it should reach, resulting in unstable reinforcement effect, which in turn affects the entire construction process. And due to the permeability of slurry, it is often necessary to apply a higher pressure to push the slurry into the cracks, but due to the looseness of skarn rock mass, this slurry pushing pressure is often difficult to control, and it is impossible to ensure that the slurry diffuses evenly to the expected area. Therefore, there are many uncertainties in the construction process. More importantly, the cost of grouting materials is high. The composition of slurry usually includes cement, chemical additives and other materials, which greatly increases the overall construction cost, and these costs continue to rise as the construction process continues. Compared with grouting, the mechanism of water injection is fundamentally different. Water injection mainly relies on the chemical reaction between water and swelling minerals in the rock mass. The swelling minerals in the rock are activated through the penetration of water, causing the rock mass to expand and increase the friction between rock blocks, thereby enhancing the stability of the rock mass. In contrast, the grouting process relies on the physical filling effect of the slurry and its chemical reaction with the rock mass, so that the cracks in the rock mass are filled and the slurry increases the overall strength of the rock mass during the hardening process. The advantage of water injection is that it can effectively overcome the shortcomings of the slurry diffusion in grouting that is too fast and difficult to accurately control, and can significantly reduce costs, because the main material required for water injection is only water, unlike grouting, which requires a large amount of cement and chemical materials, and no high-pressure equipment is required during the water injection process, making the construction process simpler and more efficient. Through water injection, the problem of insufficient friction during construction can be reduced, especially in the tunnel excavation of expansive broken rock formations. Water injection can significantly improve the stability of the rock mass and avoid safety hazards such as rock falling and roof collapse, which are difficult to effectively solve with traditional grouting technology. Therefore, water injection can not only reduce costs, but also improve construction efficiency, solve many problems in grouting, and is a more efficient and sustainable construction method.

[0024] As a preferred embodiment of this embodiment, specifically, Figure 2 As shown, the water injection hole 2 includes a tunnel periphery borehole and a tunnel center borehole; the tunnel periphery borehole is set at the tunnel periphery, the tunnel periphery borehole depth is 3 meters, and the over-feed section depth is 1 meter, and the spacing between the two tunnel periphery boreholes is 1 meter; the tunnel center borehole is set at the tunnel center, the tunnel center borehole depth is 3 meters, the number of tunnel center boreholes is 1~2, and the tunnel center borehole can also be used as a reinforcement hole. The setting of the reinforcement hole helps to enhance the stability of the face and prevent the face surrounding rock from collapsing during construction. In addition, the water injection hole 2 can also be used for subsequent blasting operations to reduce construction costs. After water injection, the expansion and mudification characteristics of skarn will be activated, the skarn will expand in situ, increase the interaction between the skarn rock masses, and promote the mudification of the fracture surface, thereby increasing the friction between the skarn rock masses, and thus improving the stability of the tunnel surrounding rock.

[0025] The specific operation process of water injection involves a series of delicate operation steps to ensure that the rock mass can fully expand and enhance the stability of the surrounding rock. In actual operation, factors such as water injection pressure, water injection time, and water injection volume have an important impact on the effect. Water injection pressure is a key factor affecting the effect of water injection. Generally speaking, the water injection pressure should be controlled within a reasonable range. Too high pressure can easily cause rock formations to break, while too low pressure may not activate the swelling minerals in the rock mass. Usually, the water injection pressure is adjusted according to the porosity and permeability of the rock mass. In this embodiment, the water injection pressure of water injection is controlled at 0.3MPa~0.5MPa. By controlling the water injection pressure, it can be ensured that water can penetrate evenly into the rock mass of skarn without causing excessive stress on the rock mass. In terms of the time of water injection, it is usually necessary to set it according to the water absorption of the rock mass and the reaction speed of the swelling minerals. In general, it is necessary to wait for 24 to 48 hours after water injection to ensure that the water can fully penetrate into the rock formation and activate the swelling minerals, causing the rock mass to expand and increase friction. The water injection time should not be too short, otherwise the expected expansion effect cannot be achieved; too long water injection time may lead to water loss or other adverse changes in the rock mass.

[0026] The water injection volume is generally calculated based on the volume and porosity of the rock mass. In this embodiment, the water injection volume is as shown in formula (1): (1) in, Indicates the amount of water injected. represents the total volume of skarn that needs to be expanded during the water injection process, represents the empirical coefficient used to adjust the expansion of skarn. The value range is 0.4~0.6, Indicates the porosity of skarn.

[0027] During the water injection process, the degree of water injection also needs to be controlled according to the changes in the rock mass. Generally, water injection should ensure that the rock mass reaches a certain degree of expansion, so that the friction between the rock blocks is enhanced, thereby stabilizing the surrounding rock. During the water injection process, the degree of water injection can be controlled by monitoring the water injection pressure and time to ensure that the water is evenly infiltrated into each crack of the skarn rock formation. If it is found that the rock mass expansion is insufficient, the water injection amount can be appropriately increased or the water injection time can be extended until the rock mass reaches the expected expansion effect. In some special cases, if the permeability of the rock formation is poor, it may be necessary to adopt a staged water injection method, that is, to inject water in multiple times, wait for a period of time after each water injection, so that the water can be fully diffused in the rock formation, and then the next round of water injection can be carried out. This can ensure that the water injection process is more uniform, while avoiding excessive water injection causing instability of the rock structure. Through reasonable water injection operations, the expansion of the skarn rock mass can be effectively activated, the friction of the skarn rock mass can be enhanced, thereby improving the stability of the surrounding rock and avoiding some difficulties in traditional grouting methods.

[0028] S2. After the water injection is completed and wait for 24 hours, construction can be carried out after the water is fully diffused to activate the expansion of the skarn. The pilot tunnel method is used for excavation construction. A pilot tunnel 4 smaller than the design size of the tunnel section is excavated, and then the tunnel is gradually expanded to the design size of the section.

[0029] As a preferred embodiment of this embodiment, specifically, Figure 3 As shown, excavating a pilot tunnel 4 smaller than the design size of the tunnel section includes using the drilling and blasting method to excavate a pilot tunnel 4 smaller than the design size of the tunnel section. The drilling and blasting method adopts a small blasting method with multiple holes and less explosives when drilling and blasting. Large-scale blasting is strictly prohibited, and the blasting intensity is strictly controlled to reduce blasting disturbance and ensure the integrity of the rock mass and construction safety; gradually expanding the tunnel to the design size of the section includes using a pneumatic pick to drop the remaining surrounding rock 5 and gradually expanding the tunnel to the design size of the section.

[0030] S3. After the tunnel is expanded to the designed cross-sectional size, the initial spraying support treatment shall be carried out immediately to prevent the strength of the tunnel surrounding rock from decreasing after being exposed. At the same time, the passive support structure shall be installed to further improve the stability of the tunnel surrounding rock and prevent the sudden fall of skarn.

[0031] As a preferred embodiment of the present invention, specifically, the initial spraying support includes supporting the tunnel surrounding rock by combining mesh and sprayed concrete to ensure the short-term stability of the tunnel surrounding rock. The passive support structure includes a steel arch frame. The installation of the initial spraying support and the passive support structure must be carried out simultaneously, and the stability of the initial spraying support and the passive support structure must be checked in time.

[0032] S4. After the passive support structure is installed, active support is carried out.

[0033] As a preferred embodiment of this invention, specifically, active support includes using anchor rods to support the primary spraying support and the passive support structure, and applying pre-tightening force to the primary spraying support and the passive support structure, so that the anchor rods, shotcrete, steel arch frames and meshes form an integral support structure together, giving full play to the support effect and ensuring the long-term stability of the tunnel.

[0034] S5. Repeat the construction. For each footage section, repeat steps S1 to S4 until the entire tunnel excavation is completed, and ensure that each construction can achieve the expected tunnel stability and progress.

[0035] Example 3, this example provides a construction method for excavating a contact zone of expansive broken skarn. The construction site of this example is a main transport tunnel at the -720 level in a metal mine tunnel, which passes through the contact zone of skarn. The design shape of the tunnel is a three-center arch tunnel with a width of 3m and a height of 3m. The surrounding rock of the tunnel is a typical strongly expansive skarn, and the rock surface of the skarn is relatively smooth. After the tunnel is exposed during excavation, the face cannot stand upright and the roof falls seriously.

[0036] A construction method for expansive broken skarn contact zone excavation in this embodiment includes the following steps: T1. Drilling and water injection: First, according to the cross-sectional shape, design dimensions and footage size of the tunnel to be constructed, a reasonable water injection hole 2 is designed. The drilling plan is as follows: Figure 2 As shown in the figure, after drilling and water injection, muddy skarn 3 is obtained in the broken skarn contact zone 1. When drilling, first drill holes around the tunnel, with a depth of 3 meters and a spacing of 1 meter. The designed drilling spacing and depth can ensure that the injected water diffuses to the surrounding rock formations, thereby fully activating the expansion and muddy characteristics of the skarn. After the drilling is completed, water is injected into the tunnel face through the water injection hole 2. After the water injection, the skarn rock mass will gradually expand and muddy, resulting in an increase in the friction between the skarn rock masses, improving the stability of the tunnel surrounding rock, and forming a stable rock formation area after muddying, laying the foundation for subsequent construction.

[0037] T2. Tunneling construction: After water injection, it is necessary to wait for about 24 hours to ensure that the water is fully diffused into the skarn layer and activate the expansion of the skarn. During the waiting period, the surrounding rock expands and muddies, which increases the friction between the skarn rock mass and makes the surrounding rock more stable. Figure 3As shown, the tunnel excavation construction is carried out by the pilot tunnel method. In the specific implementation, a pilot tunnel 4 smaller than the design size is first excavated by the drilling and blasting method, and the width of the pilot tunnel 4 is 2m. When drilling and blasting, the method of multiple holes and less charges is used. Each blasting hole is loaded with 1 to 2 charge rolls, and small blasting is carried out. Large-scale blasting is strictly prohibited to reduce the disturbance of blasting to the tunnel surrounding rock. After blasting, the remaining surrounding rock 5 is dropped by a pneumatic pick, and the tunnel is gradually expanded to the cross-section design size to ensure the integrity of the tunnel surrounding rock and construction safety during the construction process.

[0038] T3. Initial spraying support and installation of passive support structure: When the tunnel is expanded to the designed cross-section size, the initial spraying support treatment is immediately carried out. The initial spraying support adopts a combination of mesh and shotcrete. The shotcrete uses C20 cement with a thickness of 150mm; the mesh diameter is 6mm and the mesh size is 100×100mm. This can enhance the short-term stability of the tunnel surrounding rock, prevent the exposed rock strength from decreasing, and avoid support failure. Shotcrete can be constructed by high-pressure spraying to ensure its adhesion and structural strength to improve the support effect.

[0039] After the initial spraying support is completed, the passive support structure is installed immediately. The steel arch frame is used as the passive support structure. The steel arch frame uses 26.05kg / m 11# I-beams, with a yield limit of about 350MPa, a tensile strength limit of about 520MPa, and an elongation of 18% to 20%. The I-beams are arranged at intervals of 0.5m. The steel arch frame has good support strength and stability, which can effectively prevent sudden rock falls in the tunnel during construction and ensure the safety of construction workers.

[0040] T4. Install active support structure: After the initial spraying support and passive support installation are completed, the active support stage begins. At this time, the anchor support method is adopted, and the initial spraying support and passive support structures are supported by anchor rods, and pre-tightening force is applied to the initial spraying support and passive support structures. The anchor rods are 2.5m long, the spacing between anchor rods is 1.0m×1.0m, the anchor rod diameter is 18mm, and the main mechanical indicators are: density 7.8t / m3, elastic modulus 214GPa, yield force 92KN, average breaking force 138KN, and elongation 21.3%. The anchoring depth and the applied pre-tightening force are adjusted according to the geological conditions. By applying a certain pre-tightening force, the anchor rods, shotcrete, steel arch frames and mesh form an integral support structure to ensure the stability and safety of the tunnel in long-term operation.

[0041] T5. Repeated construction: Repeat steps T1 to T4 for each footage section to ensure that each construction can achieve the expected tunnel stability and progress. After each footage section is completed, adjust the support design in a timely manner according to the actual situation on site to ensure the safety and stability of the entire tunnel.

[0042] The embodiments of the present invention are given for the purpose of illustration and description, and are not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention and to enable those of ordinary skill in the art to understand the present invention and thereby design various embodiments with various modifications suitable for specific uses.

Claims

1. A construction method for excavating a contact zone of expansive broken skarn, characterized in that: The steps include: S1. Drilling is performed after designing a drilling plan according to the design dimensions of the tunnel section and the dimensions of the footage section. During drilling, water injection holes are obtained by drilling holes around the tunnel and in the center, and water is injected into the tunnel face through the water injection holes; S2. After the water injection is completed and the waiting time is no less than 24 hours, the tunneling construction is carried out by using the pilot tunnel method. A pilot tunnel smaller than the design cross-sectional dimensions of the tunnel is excavated and then the tunnel is gradually expanded to the design cross-sectional dimensions; S3. After the tunnel is expanded to the designed cross-sectional dimensions, the initial spraying support treatment is immediately carried out and the passive support structure is installed at the same time; S4. After the passive support structure is installed, active support is performed; S5. Repeat the construction. For each advancement section, repeat steps S1 to S4 until the entire tunnel excavation is completed.

2. The method for excavating a contact zone of expansive broken skarn according to claim 1, characterized in that: In step S1, the water injection holes include tunnel periphery boreholes and tunnel center boreholes; the tunnel periphery boreholes are arranged at the tunnel periphery, the tunnel periphery boreholes have a depth of 3 meters, and the over-feed section has a depth of 1 meter, and the spacing between two tunnel periphery boreholes is 1 meter; the tunnel center boreholes are arranged at the tunnel center, the tunnel center boreholes have a depth of 3 meters, and the number of tunnel center boreholes is 1 to 2.

3. The method for excavating a contact zone of expansive broken skarn according to claim 2, characterized in that: In step S1, the water injection pressure is 0.3MPa-0.5MPa, and the water injection volume is as shown in formula (1): （1） in, Indicates the amount of water injected. represents the total volume of skarn that needs to be expanded during the water injection process, represents the empirical coefficient used to adjust the expansion of skarn. The value range is 0.4~0.6, Represents the porosity of skarn.

4. The method for excavating a contact zone of expansive broken skarn according to claim 1, characterized in that: In the step S2, the excavation of a pilot tunnel smaller than the designed cross-sectional size of the tunnel includes excavating a pilot tunnel smaller than the designed cross-sectional size of the tunnel using a drilling and blasting method, wherein the drilling and blasting method uses a small blasting method with multiple holes and less explosives when drilling and blasting.

5. The method for excavating a contact zone of expansive broken skarn according to claim 1, characterized in that: In the step S2, the step of gradually expanding the tunnel to the designed cross-sectional dimensions includes using a pneumatic pick to drop the remaining surrounding rock and gradually expanding the tunnel to the designed cross-sectional dimensions.

6. The method for excavating a contact zone of expansive broken skarn according to claim 1, characterized in that: In step S3, the initial shotcrete support includes supporting the surrounding rock of the tunnel by combining a mesh with shotcrete.

7. A construction method for excavating a contact zone of expansive broken skarn according to claim 6, characterized in that: In step S3, the passive support structure includes a steel arch.

8. The method for excavating the contact zone of expansive broken skarn according to claim 7, characterized in that: In step S4, the active support includes using anchor rods to support the primary spraying support and the passive support structure, and applying a pre-tightening force to the primary spraying support and the passive support structure.

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