A construction method for tunneling in the contact zone of expansive broken skarn

Abstract

The present invention belongs to the technical field of tunnel excavation, and proposes a construction method for tunneling in the contact zone of expansive broken skarn, which includes drilling according to the designed size of the roadway section and the size of the footage section. When drilling, first drill around the roadway to obtain water injection holes, and inject water into the heading face through the water injection holes; after the water injection is completed and waiting for 24 hours, adopt the pilot drift method for tunneling construction. After excavating a pilot drift smaller than the designed size of the roadway section, gradually expand and brush the roadway to the designed size of the section; after the roadway is expanded and brushed to the designed size of the section, immediately carry out primary spraying support treatment and install passive support structures at the same time; after the installation of the passive support structure is completed, carry out active support; repeat the construction. For each footage section, repeat the above steps until the entire roadway tunneling is completed. Through water injection treatment, the present invention improves the friction force between skarn rock masses, reduces the risk of roof fall, and reduces costs and improves construction efficiency.

Description

Technical Field

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

[0002] Skarn is a metamorphic rock formed during the contact metasomatism 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 are prone to swelling and sludging when exposed to water. At the same time, the surface of skarn is usually relatively smooth, which results in a low frictional force between rocks and increases the difficulty of tunneling construction. During the construction of underground roadways, when the construction passes through a strongly expansive and fractured skarn contact zone, due to the small frictional force of the rock mass, roof falls often occur in the roadway, seriously affecting the construction safety and progress. Therefore, in current mine construction, for the tunneling of roadways in expansive and fractured rocks, methods such as advanced support or advanced pre-grouting are often adopted.

[0003] The patent application with the patent publication number CN119288546A discloses a construction method for controlling the large deformation of soft rock in a mine tunnel. This method changes the properties and structure of the surrounding rock by over-excavating the roadway and backfilling with lightweight foam soil, blocking the transmission of high ground stress, and thus effectively controlling the deformation of soft rock masses. However, when facing a skarn contact zone with developed fractures and soft fragmentation, the over-excavation method is prone to cause the falling of roof rocks, increasing the construction risk and making it difficult to advance the subsequent construction. Therefore, it has certain limitations. The patent application with the patent publication number CN118933905A discloses a method for repairing advanced grouting of a large-deformation soft rock roadway. By evaluating the roadway deformation and performing hierarchical advanced pre-grouting, the loose surrounding rock is reinforced to form a reinforced arch with higher strength. However, the applicability of this method to the fractured skarn contact zone is poor. In addition, after grouting, due to the easy diffusion of the grout, the consumption of materials is large, the cost is high, and the grouting pressure is difficult to reach the expected value, resulting in poor final reinforcement effect and certain deficiencies. In order to overcome the above problems, it is urgent to develop a new method that can effectively solve the problem of rapid tunneling construction in a strongly expansive and fractured skarn contact zone. Summary of the Invention

[0004] In order to solve the problems of low tunneling efficiency, poor stability, high construction risk and high cost existing in the current tunneling construction of strongly expansive and fractured skarn contact zones, the invention proposes a construction method for tunneling through an expansive and fractured skarn contact zone.

[0005] The invention provides a construction method for tunneling through an expansive and fractured skarn contact zone, including the following steps:

[0006] S1. After designing a drilling plan according to the roadway section design dimensions and the advance section dimensions, drill holes. When drilling, drill holes at the periphery and the center of the roadway to obtain water injection holes, and inject water into the heading face through the water injection holes;

[0007] S2. After the water injection is completed and waiting for at least 24 hours, use the pilot tunnel method for tunneling construction. After excavating a pilot tunnel smaller than the roadway section design dimensions, gradually expand and brush the roadway to the section design dimensions;

[0008] S3. After the roadway is expanded and brushed to the section design dimensions, immediately carry out primary shotcrete support treatment and install passive support structures at the same time;

[0009] S4. After the installation of the passive support structure is completed, carry out active support;

[0010] S5. Repeat the construction. For each advance section, repeat steps S1 to S4 until the entire roadway tunneling is completed.

[0011] For a tunneling construction method for an expansive fractured skarn contact zone according to some embodiments of the present application, in step S1, the water injection holes include peripheral roadway drill holes and central roadway drill holes; the peripheral roadway drill holes are arranged at the periphery of the roadway, the depth of the peripheral roadway drill holes is 3 meters, and the depth of the over-advance section is 1 meter, and the spacing between two adjacent peripheral roadway drill holes is 1 meter; the central roadway drill holes are arranged at the center of the roadway, the depth of the central roadway drill holes is 3 meters, and the number of the central roadway drill holes is 1 to 2.

[0012] For a tunneling construction method for an expansive fractured skarn contact zone according to some embodiments of the present application, in step S1, the water injection pressure is 0.3 MPa to 0.5 MPa, and the water injection volume is as shown in formula (1):

[0013] (1)

[0014] Wherein, represents the water injection volume, represents the total volume of skarn that needs to expand during the water injection treatment, represents an empirical coefficient used to adjust the expansibility of skarn, the value range of is 0.4 to 0.6, represents the porosity of skarn.

[0015] For a tunneling construction method for an expansive fractured skarn contact zone according to some embodiments of the present application, in step S2, the excavation of a pilot tunnel smaller than the roadway section design dimensions includes using the drill and blast method to excavate a pilot tunnel smaller than the roadway section design dimensions, and the drill and blast method adopts a small blasting method with multiple holes and less explosive during drilling and blasting.

[0016] A construction method for tunneling in the swelling and broken skarn contact zone according to some embodiments of the present application. In step S2, the step of gradually enlarging and brushing the roadway to the designed section size includes using a pneumatic pick to drop the remaining surrounding rock and gradually enlarging and brushing the roadway to the designed section size.

[0017] A construction method for tunneling in the swelling and broken skarn contact zone according to some embodiments of the present application. In step S3, the primary shotcrete support includes supporting the surrounding rock of the roadway by combining a wire mesh and shotcrete.

[0018] A construction method for tunneling in the swelling and broken skarn contact zone according to some embodiments of the present application. In step S3, the passive support structure includes a steel arch.

[0019] A construction method for tunneling in the swelling and broken skarn contact zone according to some embodiments of the present application. In step S4, the active support includes using bolts 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.

[0020] A construction method for tunneling in the swelling and broken skarn contact zone proposed by the present invention makes full use of the swelling and sludging characteristics of skarn after encountering water. By treating the surrounding rock with water injection, the friction between rock blocks is increased, the stability of the surrounding rock is enhanced, and the risk of roof fall caused by insufficient friction can be effectively reduced. Compared with the existing grouting process, this method significantly reduces the cost and improves the construction efficiency at the same time. In addition, this method uses the pilot tunnel method for tunneling construction, 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 a reasonable support method, especially the combination of bolt and shotcrete support, the stability of the surrounding rock of the roadway is further enhanced, ensuring safety and efficiency during the construction process. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic flow chart of a construction method for tunneling in the swelling and broken skarn contact zone of the present invention;

[0022] Figure 2 It is a schematic diagram of the arrangement of water injection holes in an embodiment of the present invention;

[0023] Figure 3 It is a schematic diagram of the construction of the pilot tunnel method in an embodiment of the present invention.

[0024] In the figure, 1, broken skarn contact zone; 2, water injection hole; 3, sludged skarn; 4, pilot tunnel; 5, remaining surrounding rock. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The following further describes in detail the embodiments of the present invention in conjunction with the accompanying drawings and embodiments. The following embodiments are used to illustrate the present invention, but cannot be used to limit the scope of the present invention.

[0026] Example 1. This example provides a construction method for tunneling in the contact zone of expansive fractured skarn, as Figure 1 shown, including the following steps:

[0027] S1. After designing a drilling plan according to the designed size of the roadway section and the size of the footage section, drill holes. When drilling, as Figure 2 shown, drill holes around the roadway perimeter and at the center to obtain water injection holes 2, and inject water into the heading face through the water injection holes 2; after water injection, the expansive slaking characteristics of the skarn will be activated, the skarn will expand in-situ, increasing the interaction between skarn rock masses, and promoting the slaking of the fracture surface, thereby increasing the friction between skarn rock masses, and further improving the stability of the roadway surrounding rock.

[0028] S2. After the water injection is completed and waiting for no less than 24 hours, use the pilot drift method for tunneling construction. As Figure 3 shown, excavate a pilot drift 4 smaller than the designed size of the roadway section and gradually expand and brush the roadway to the designed size of the section.

[0029] S3. After the roadway is expanded and brushed to the designed size of the section, immediately carry out primary shotcrete support treatment and install a passive support structure at the same time.

[0030] S4. After the installation of the passive support structure is completed, carry out active support.

[0031] S5. Repeat the construction. For each footage section, repeat steps S1 to S4 until the entire roadway tunneling is completed.

[0032] Example 2. This example provides a construction method for tunneling in the contact zone of expansive fractured skarn, including the following steps:

[0033] S1. After designing a drilling plan according to the designed size of the roadway section and the size of the footage section, drill holes. When drilling, as Figure 2 shown, drill holes around the roadway perimeter and at the center to obtain water injection holes 2, and inject water into the heading face through the water injection holes 2.

[0034] Traditional grouting techniques face many difficulties in practical applications. First of all, the diffusivity of the grout often causes the grout to fail to accurately fill the fissures. Especially in cases where the fissures are well-developed or the rock formation is fractured, the grout cannot spread to the areas it should reach, resulting in unstable reinforcement effects and affecting the entire construction process. Moreover, due to the permeation characteristics of the grout, relatively high pressure often needs to be applied to push the grout into the fissures. However, due to the looseness of the skarn rock mass, it is often difficult to control this grout-pushing pressure, and it is impossible to ensure that the grout spreads evenly to the expected areas. Therefore, there are many uncertainties during the construction process. More importantly, the cost of the grouting materials is relatively high. The composition of the grout 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. Through the permeation of water, the swelling minerals in the rock are activated, causing the rock mass to expand and increasing the friction between rock blocks, thereby enhancing the stability of the rock mass. In contrast, the grouting technique relies on the physical filling effect of the grout and its chemical reaction with the rock mass, so that the fissures in the rock mass are filled and the overall strength of the rock mass increases during the hardening process of the grout. The advantage of water injection is that it can effectively overcome the shortcomings of excessive grout diffusion and difficult precise control in grouting, and at the same time 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 high-pressure equipment is not needed 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 tunneling of the roadway in the swelling and fractured rock formation, water injection can significantly improve the stability of the rock mass and avoid safety hazards such as rock fall and roof caving, which are difficult to effectively solve by traditional grouting techniques. Therefore, water injection can not only reduce costs, but also improve construction efficiency and solve many problems in grouting. It is a more efficient and sustainable construction method.

[0035] As a preference of this embodiment, specifically, as Figure 2 shown, the water injection holes 2 include the peripheral holes of the roadway and the central holes of the roadway; the peripheral holes of the roadway are arranged around the roadway, the depth of the peripheral holes of the roadway is 3 meters, and the depth of the over-advance section is 1 meter, and the distance between the two peripheral holes of the roadway is 1 meter; the central holes of the roadway are arranged in the center of the roadway, the depth of the central holes of the roadway is 3 meters, the number of the central holes of the roadway is 1 to 2, and the central holes of the roadway can also be used as reinforcement holes. The setting of the reinforcement holes helps to enhance the stability of the heading face and prevent the surrounding rock of the heading face from collapsing during the construction process. In addition, the water injection holes 2 can also be used for subsequent blasting operations to reduce the construction cost. After water injection, the swelling and sludging characteristics of the skarn will be activated, the skarn will expand in-situ, increasing the interaction between the skarn rock masses, and promoting the sludging of the fissure surface, thereby increasing the friction between the skarn rock masses, and further improving the stability of the surrounding rock of the roadway.

[0036] 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 all have important impacts on the effect. Water injection pressure is a key factor affecting the water injection effect. Generally speaking, the water injection pressure should be controlled within a reasonable range. Excessive pressure is likely to cause the rock formation to rupture, while too low pressure may not be able to activate the swelling minerals in the rock mass. Usually, the water injection pressure will be adjusted according to the porosity and permeability of the rock mass. In this embodiment, the water injection pressure is controlled at 0.3 MPa to 0.5 MPa. By controlling the water injection pressure, it can be ensured that the water evenly penetrates into the interior of the skarn rock mass without causing local overstress on the rock mass. In terms of the water injection time, it usually needs to be set according to the water absorption of the rock mass and the reaction rate of the swelling minerals. Generally, after water injection, it is necessary to wait for 24 to 48 hours to ensure that the water can fully penetrate into the rock formation and activate the swelling minerals, resulting in the expansion of the rock mass and an increase in 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.

[0037] Regarding the water injection volume, it generally needs to be calculated according to the volume and pore conditions of the rock mass. In this embodiment, the water injection volume of water injection is shown in formula (1):

[0038] (1)

[0039] Where, represents the water injection volume, represents the total volume of skarn that needs to expand during the water injection treatment, represents the empirical coefficient used to adjust the expansibility of skarn, The value range of is 0.4 to 0.6, represents the porosity of skarn.

[0040] 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 swelling, so as to enhance the friction between rock blocks and thus stabilize 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 permeated into each crack of the skarn rock stratum. If it is found that the swelling degree of the rock mass is insufficient, the water injection volume can be appropriately increased or the water injection time can be extended until the rock mass reaches the expected swelling effect. In some special cases, if the permeability of the rock stratum is poor, it may be necessary to adopt the method of staged water injection, that is, inject water in multiple times, wait for a period of time after each water injection to allow the water to fully diffuse in the rock stratum, and then carry out the next round of water injection. This can ensure that the water injection process is more uniform and avoid the instability of the rock mass structure caused by excessive water injection. Through reasonable water injection operations, the expansibility 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 problems in traditional grouting methods.

[0041] S2. After the water injection is completed and after waiting for 24 hours, after the water has fully diffused to activate the expansibility of the skarn, construction is carried out. The adit method is used for tunneling construction. An adit 4 smaller than the designed size of the roadway section is excavated and then the roadway is gradually enlarged and brushed to the designed size of the section.

[0042] As an optimization of this embodiment, specifically, as Figure 3 shown, excavating an adit 4 smaller than the designed size of the roadway section includes using the drill and blast method to excavate an adit 4 smaller than the designed size of the roadway section. When drilling and blasting in the drill and blast method, a small blasting method with multiple holes and less explosive is adopted. Large-area blasting is strictly prohibited, and the blasting force is strictly controlled to reduce blasting disturbance and ensure the integrity of the rock mass and construction safety; gradually enlarging and brushing the roadway to the designed size of the section includes using a pneumatic pick to drop the remaining surrounding rock 5 and gradually enlarging and brushing the roadway to the designed size of the section.

[0043] S3. After the roadway is enlarged and brushed to the designed size of the section, primary shotcrete support treatment is immediately carried out to prevent the strength of the roadway surrounding rock from decreasing after exposure, and at the same time, a passive support structure is installed to further improve the stability of the roadway surrounding rock and prevent sudden skarn falling.

[0044] As an optimization of this embodiment, specifically, the primary shotcrete support includes using a combination of mesh and shotcrete to support the roadway surrounding rock to ensure the short-term stability of the roadway surrounding rock. The passive support structure includes a steel arch. The installation of the primary shotcrete support and the passive support structure needs to be carried out synchronously, and the stability of the primary shotcrete support and the passive support structure needs to be checked in time.

[0045] S4. After the installation of the passive support structure is completed, active support is carried out.

[0046] Preferably, in this embodiment, specifically, the active support includes using bolts 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, so that the bolts, shotcrete, steel arch and mesh jointly form an integral support structure, giving full play to the support effect and ensuring the long-term stability of the roadway.

[0047] S5. Repeat the construction. For each footage section, repeat steps S1 - S4 until the entire roadway driving is completed, and ensure that the expected roadway stability and progress can be achieved for each construction.

[0048] Embodiment 3. This embodiment provides a construction method for driving through the contact zone of expansive crushed skarn. The construction site of this embodiment is the -720 - level main haulage roadway in the underground of a metal mine passing through the skarn contact zone. The designed shape of the roadway is a three - centered arch roadway, with a width of 3 m and a height of 3 m. The surrounding rock of the roadway is typical strongly expansive skarn, and the rock surface of the skarn is relatively smooth. After the roadway driving is exposed, the face cannot stand upright and the roof caving is serious.

[0049] A construction method for driving through the contact zone of expansive crushed skarn in this embodiment includes the following steps:

[0050] T1. Drilling and water injection:

[0051] First, according to the cross - sectional shape, design dimensions and footage section dimensions of the roadway to be constructed, a reasonable water injection hole 2 is designed, and the drilling scheme is as Figure 2 shown. After drilling and water injection, the slaked skarn 3 is obtained in the expansive crushed skarn contact zone 1. When drilling, first drill holes around the roadway. The depth of the drill holes is 3 m and the spacing is 1 m. The designed drilling spacing and depth can ensure that the injected water diffuses to the surrounding rock strata, thus fully activating the expansive slaking characteristics of the skarn. After the drilling is completed, water is injected into the face through the water injection hole 2. The skarn rock mass after water injection will gradually expand and slake, resulting in an increase in the friction force between the skarn rock masses, improving the stability of the surrounding rock of the roadway, forming a stable area of the slaked rock stratum, and laying a foundation for subsequent construction.

[0052] T2. Driving construction by pilot - tunnel method:

[0053] After water injection, it is necessary to wait for about 24 hours to ensure that the water fully diffuses into the skarn rock strata and activates the expansibility of the skarn. During the waiting period, the process of expansion and slaking of the surrounding rock makes the friction force between the skarn rock masses increase and the surrounding rock becomes more stable. Subsequently, as Figure 3As shown in the figure, the drift method is used for roadway tunneling construction. In the specific implementation, first, a drift 4 smaller than the design size is excavated by the drill and blast method. The width of the drift 4 is 2m. When drilling and blasting, the method of using multiple holes with less explosive is adopted. Each blast hole is loaded with 1 to 2 cartridges, and small blasting is carried out. Large-area blasting is strictly prohibited to reduce the disturbance of the roadway surrounding rock by blasting. After blasting, the remaining surrounding rock 5 is removed by a pneumatic pick, and the roadway is gradually enlarged and brushed to the section design size to ensure the integrity of the roadway surrounding rock and construction safety during the construction process.

[0054] T3. Initial shotcrete support and installation of passive support structure:

[0055] After the roadway is enlarged and brushed to the section design size, initial shotcrete support treatment is immediately carried out. The initial shotcrete support adopts the combination of wire mesh and shotcrete. The shotcrete uses C20 cement with a thickness of 150mm; the wire mesh is made of steel bars with a diameter of 6mm and a mesh size of 100×100mm. This can enhance the short-term stability of the roadway surrounding rock, prevent the strength reduction of the exposed rock, and avoid support failure. The shotcrete can be constructed by high-pressure spraying to ensure its adhesion and structural strength to improve the support effect.

[0056] After the initial shotcrete support is completed, the passive support structure is immediately installed. The steel arch is used as the passive support structure. The steel arch is made of 11# I-beam with a weight of 26.05kg / m, a yield limit of about 350MPa, a tensile strength limit of about 520MPa, and an elongation rate of 18% - 20%. The I-beams are arranged at intervals of 0.5m. The steel arch has good support strength and stability, and can effectively prevent sudden rock falls in the roadway during construction, ensuring the safety of construction personnel.

[0057] T4. Installation of active support structure:

[0058] After the initial shotcrete support and the installation of the passive support are completed, the active support stage is entered. At this time, the bolt support method is adopted. The initial shotcrete support and the passive support structure are supported by bolts, and a pre-tightening force is applied to the initial shotcrete support and the passive support structure. Bolts with a length of 2.5m are selected, the bolt spacing and row spacing are 1.0m×1.0m, and the bolt diameter is 18mm. The main mechanical indexes are: density 7.8t / m3, elastic modulus 214GPa, yield force 92KN, average breaking force 138KN, and elongation rate 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 bolts, shotcrete, steel arch and wire mesh form an integral support structure to ensure the stability and safety of the roadway during long-term operation.

[0059] T5. Repeated construction:

[0060] For each footage section, repeat steps T1 - T4 to ensure that the expected roadway stability and progress can be achieved for each construction. After each footage section is completed, adjust the support design in a timely manner according to the actual on - site situation to ensure the safety and stability of the entire roadway.

[0061] The embodiments of the present invention are given for purposes of illustration and description, and are not exhaustive or limit the invention to the disclosed form. Many modifications and variations are obvious to those of ordinary skill in the art. The embodiments are chosen and described in order to better explain the principles of the invention and its practical application, and to enable those of ordinary skill in the art to understand the invention and design various embodiments with various modifications suitable for specific purposes.

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 footage section, repeat steps S1 to S4 until the entire tunnel excavation is completed; 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.

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 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.

4. 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.

5. 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.

6. A construction method for excavating a contact zone of expansive broken skarn according to claim 5, characterized in that: In step S3, the passive support structure includes a steel arch.

7. A construction method for excavating a contact zone of expansive broken skarn according to claim 6, 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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