Composite reinforcing mesh structure for tunnel overexcavation treatment and construction method

Abstract

The invention relates to the technical field of tunnel supporting, in particular to a composite reinforcing mesh structure for tunnel over-excavation treatment and a construction method.The composite reinforcing mesh structure for tunnel over-excavation treatment comprises a separation net, the separation net is used for covering an over-excavation area, and a plurality of connectors are arranged on the separation net; the connector comprises a fixing device and a clamping part, the fixing device is used for being connected with the reinforcing mesh, the clamping part is fixed to the separation net in a clamping mode, and the fixing device is connected with the clamping part through a connecting piece, so that the separation net is fixed to the reinforcing mesh. By the adoption of the composite steel bar mesh structure, primary support of a tunnel can be normally carried out, after primary support is completed, grouting treatment can be carried out on an over-excavation area through the reserved grouting holes, grouting of the over-excavation area does not need to adopt concrete of the same level, and cost reduction and efficiency improvement of tunnel construction are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel support, and in particular to a composite steel mesh structure for tunnel over-excavation treatment and a construction method. Background Art

[0002] Over-excavation is a common problem in tunnel construction using the drill and blast method. The part outside the tunnel design excavation contour line is the over-excavation part. The main reasons for over-excavation include poor control of the drilling and blasting holes and local block loss of surrounding rock: Drill and blast excavation mainly includes blasting hole construction, blasting slag removal, excavation measurement and quality inspection. During blasting hole construction, the position, inclination angle and depth of the surrounding blasting holes are very important. Poor control will cause over-excavation; block loss of the surrounding rock with disturbed joints will also cause over-excavation.

[0003] Over-excavation treatment has the following significance:

[0004] Safety: Stress is concentrated in the over-excavation area of ​​the tunnel, and the stress concentration factor increases with the increase of the ratio of over-excavation depth to over-excavation width (h / L);

[0005] Cost: The over-excavation volume is large and the disposal cost is high (over-excavation 15cm + 12m span + 3km length + C25 concrete unit price 420 yuan / m 3 +0.2 spray rebound condition material cost = 0.15 × 3.14 × 12 × 42 × 3 × 1.2 = 8.546 million yuan, if C10 concrete (unit price 377 yuan / m 3 ) can save 875,000 yuan in material costs;

[0006] In terms of construction period: over-excavation is handled by filling the space between the rough hole and the initial support with wet spraying or grouting. When the over-excavation is thick, the wet spraying construction is mainly manifested as the total time for concrete to solidify between multi-layer construction; grouting is a formwork construction, which is different from the front and rear rough hole formation and initial support process. The construction time of a single process is fixed, and if properly arranged, it does not occupy the key line of drilling and blasting construction.

[0007] In addition, the overspray volume of wet shotcrete rebound will also increase the cost, and the backfill grouting template materials and processes also affect cost control. Therefore, the process and timing control of over-excavation disposal are very important.

[0008] At present, in actual construction, concrete injection or backfilling with crushed stone soil or no treatment is usually used. If the same grade of concrete is used, it will cause engineering waste. If crushed stone soil is used for backfilling, the side walls and arches will be difficult to fill, which will cause great safety hazards. Summary of the invention

[0009] The purpose of the present invention is to address the defects of the prior art and provide a composite steel mesh structure and construction method for tunnel over-excavation treatment. The initial support of the tunnel can be carried out normally. After the initial support is completed, the over-excavation area can be grouting treated through the reserved grouting holes, thereby reducing costs and increasing efficiency of tunnel construction.

[0010] In order to solve the above technical problems, in a first aspect, the present invention provides a composite steel mesh structure for tunnel over-excavation treatment, including an isolation net, wherein the isolation net is used to cover the over-excavation area, and a plurality of connectors are arranged on the isolation net, wherein the connectors include a fixer and a clamping portion, wherein the fixer is used to connect to the steel mesh, and the clamping portion is fixed to the isolation net by clamping, and the fixer is connected to the clamping portion by a connecting piece, so that the isolation net is fixed on the steel mesh.

[0011] In some embodiments, the clamping portion includes a clamping sub-portion and a clamping mother portion, and the clamping sub-portion and the clamping mother portion are respectively arranged on both sides of the isolation net, a sub-matching portion is arranged on the side of the clamping sub-portion close to the clamping mother portion, and a mother-matching portion is arranged on the side of the clamping mother portion close to the clamping sub-portion, and the sub-matching portion and the mother-matching portion can cooperate with each other to fix the isolation net.

[0012] In some embodiments, the sub-matching portion and the female matching portion are both tooth-shaped, and the sub-matching portion and the female matching portion are meshed with each other, thereby fixing the isolation net between the clamping sub-part and the clamping female part.

[0013] In some embodiments, the sub-matching portion is conical, the female matching portion includes a conical groove opened on the clamping female portion, and the sub-matching portion is inserted into the female matching portion to fix the isolation net between the clamping sub-portion and the clamping female portion.

[0014] In some embodiments, the connecting member includes a supporting screw, and the clamping portion and the fixer are both connected to the supporting screw via threads.

[0015] In some embodiments, the connecting member includes an anchor, the clamping portion and the fixer are both connected to the anchor via threads, and one end of the anchor is used to anchor into the surrounding rock.

[0016] In some embodiments, the fixer comprises a cross-shaped fixing rod, and the fixing rod is used to be connected to the steel mesh.

[0017] In a second aspect, the present invention provides a construction method for tunnel over-excavation treatment, comprising:

[0018] An isolation net is laid on the steel mesh of the initial support. The isolation net is laid at the corresponding position of the over-excavation area to completely cover the over-excavation area. The isolation net is fixed on the steel mesh through multiple connectors.

[0019] Reserve grouting holes within the over-excavation area and spray concrete to form a closed grouting shell;

[0020] The over-excavation area is grouted through the reserved grouting holes.

[0021] In some embodiments, the method for fixing the isolation net includes:

[0022] Use the fixing device to tie and fix it on the steel mesh, and use the clamping part to clamp it on the isolation net;

[0023] In the case of using arch concrete for initial support, the isolation mesh is fixed to the steel mesh by connecting the fixer and the clamping part using support screws;

[0024] In the case of using anchor spraying for initial support, the fixer and the clamping part are connected by using a support screw or an anchor. When using a support screw, one end of the support screw is fixedly connected to the anchor of the initial support, and when using an anchor, one end of the anchor is anchored into the surrounding rock.

[0025] In some embodiments, the method of fixing the isolation net to the steel mesh through multiple connectors includes:

[0026] When the equivalent side length of the over-excavation area is ≤1.0m, connectors are arranged at the four corners of the isolation net. When the equivalent side length of the over-excavation area is between 1.0 and 1.5m, an additional connector is added in the middle of the isolation net. When the equivalent side length of the over-excavation area is greater than 1.5m, the connectors are arranged in a plum blossom shape with equal spacing.

[0027] The beneficial effects of the present invention are:

[0028] 1. The present invention arranges the isolation net on the side of the steel mesh close to the surrounding rock. After the over-excavation area is covered with the isolation net, the isolation net can prevent concrete from being sprayed into the over-excavation area, so that the initial support of the tunnel can be carried out normally. After the initial support is completed, the over-excavation area can be grouted through the reserved grouting holes. The grouting of the over-excavation area does not need to use the same grade of concrete, thereby achieving cost reduction and efficiency improvement in tunnel construction.

[0029] 2. The fixer, clamping part and isolation net of the present invention can be prefabricated. During construction, the isolation net of suitable size can be directly cut according to the size of the over-excavation area, and then the isolation net can be directly fixed on the steel mesh through the fixer and clamping part, which has high installation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the connection structure of the isolation net and the connector of the present invention;

[0031] Figure 2 An exploded view of the isolation net and the connector of the present invention;

[0032] Figure 3 It is a side view of the isolation net and the connector when the connector of the present invention adopts a supporting screw;

[0033] Figure 4 It is a side view of the isolation net and the connection head when the connection piece of the present invention adopts a support screw and is connected to the anchor rod;

[0034] Figure 5 This is a schematic diagram of the over-excavation area of ​​the present invention;

[0035] Figure 6 This is a construction schematic diagram of the present invention when the initial support adopts arch concrete;

[0036] Figure 7 It is a schematic diagram of the arrangement of the isolation net and the connector of the present invention;

[0037] Figure 8 It is a process diagram when the composite steel mesh structure of the present invention is adopted.

[0038] Figure numerals: isolation net 1; connecting head 2; fixing device 21; clamping part 22; clamping plate 221; extension plate 222; engaging teeth 223; gasket 23; connecting piece 24; supporting screw 241; anchor 242; bolt 25; mechanical joint 26; steel mesh 3; arch frame 4; grouting hole 5; air outlet hole 6; over-excavation area 7. DETAILED DESCRIPTION

[0039] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0040] like Figure 1 As shown, the present invention provides a composite steel mesh structure for tunnel over-excavation treatment, including an isolation net 1, the isolation net 1 is used to cover the over-excavation area 7, a plurality of connectors 2 are arranged on the isolation net 1, the connectors 2 include a fixer 21 and a clamping portion 22, the fixer 21 is used to connect with the steel mesh 3, the clamping portion 22 is fixed to the isolation net 1 by clamping, the fixer 21 and the clamping portion 22 are connected by a connecting piece 24, so that the isolation net 1 is fixed on the steel mesh 3.

[0041] It is understandable that after the isolation net 1 is arranged on the side of the steel mesh 3 close to the surrounding rock and the over-excavation area 7 is covered with the isolation net 1, the isolation net 1 can prevent concrete from being sprayed into the over-excavation area 7, so that the initial support of the tunnel can be carried out normally. After the initial support is completed, the over-excavation area 7 can be grouting treated through the reserved grouting holes 5, thereby reducing the cost and increasing the efficiency of tunnel construction. In addition, the fixing device 21, the clamping part 22, and the isolation net 1 of the present invention can be prefabricated. During construction, the isolation net 1 of suitable size can be directly cut according to the size of the over-excavation area 7, and then the isolation net 1 can be directly fixed on the steel mesh 3 through the fixing device 21 and the clamping part 22, and the installation efficiency is high.

[0042] The isolation net 1 can adopt an 18-mesh grid net to ensure that there is no leakage during concrete spraying. The isolation net 1 can be made of polyethylene or PPT nano mesh or stainless steel wire mesh. The strength of various types of isolation nets 1 can be tested in advance to see if they meet the requirements of injection impact. The number of connectors 2 is determined according to the area of ​​the over-excavation area 7 to avoid displacement of the isolation net 1 during concrete spraying.

[0043] In some embodiments, the clamping portion 22 includes a clamping sub-portion and a clamping mother portion, and the clamping sub-portion and the clamping mother portion are respectively arranged on both sides of the isolation net 1. A sub-matching portion is arranged on the side of the clamping sub-portion close to the clamping mother portion, and a mother-matching portion is arranged on the side of the clamping mother portion close to the clamping sub-portion. The sub-matching portion and the mother-matching portion can cooperate with each other to fix the isolation net 1.

[0044] In some embodiments, both the sub-matching portion and the female matching portion are tooth-shaped, and the sub-matching portion and the female matching portion mesh with each other, thereby fixing the isolation net 1 between the clamping sub-part and the clamping female part.

[0045] The structures of the clamping sub-part and the clamping mother part are similar, and the structure of the clamping sub-part is taken as an example for explanation. Figure 2 As shown, the clamping sub-part includes a clamping plate 221, a through hole is provided in the middle of the clamping plate 221, and extension plates 222 are provided at the upper end, the lower end, the left end, and the right end of the clamping plate 221, so that the clamping sub-part is cross-shaped, and a plurality of bite teeth 223 are provided on one side of the extension plate 222, and the length directions of the bite teeth 223 on different extension plates 222 can be perpendicular to each other. Figure 2 The length direction of the engaging teeth 223 on the extension plates 222 at the upper and lower ends of the clamping plate 221 is perpendicular to the length direction of the engaging teeth 223 on the extension plates 222 at the left and right ends of the clamping plate 221, so that the isolation net 1 can be stably clamped without displacement. The clamping part 22 is made of plastic.

[0046] The shapes of the sub-matching part and the female matching part are various, and it is only necessary to ensure sufficient friction to fix the isolation net 1. In some embodiments, the sub-matching part is conical (the cone can be a polygonal cone, a circular cone, etc.), and the female matching part includes a conical groove opened on the clamping mother part. The sub-matching part is inserted into the female matching part, thereby fixing the isolation net 1 between the clamping sub-part and the clamping mother part.

[0047] like Figure 3 As shown, in some embodiments, the connecting member 24 includes a supporting screw 241, and the clamping portion 22 and the fixer 21 are both connected to the supporting screw 241 through threads.

[0048] like Figure 3As shown, in the case of using the concrete of the arch frame 4 for initial support, a bolt 25 is arranged on the support screw 241, a nut is arranged at one end of the support screw 241, and the other end of the support screw 241 is threadedly connected with the clamping part 22 and the fixer 21 in sequence, and a gasket 23 is arranged between the nut and the clamping part 22 and between the bolt 25 and the clamping part 22. The distance between the isolation net 1 and the steel mesh 3 can be adjusted by rotating the support screw 241 as needed to ensure that the thickness of the protective layer of the steel mesh 3 meets the requirements.

[0049] like Figure 4 As shown, in the case of initial support by anchor spraying, a bolt 25 is arranged on the support screw 241, a nut is arranged at one end of the support screw 241, and the other end of the support screw 241 is threadedly connected with the fixer 21 and the clamping part 22 in sequence, and the other end of the support screw 241 passes through the clamping part 22 and is fixedly connected with the anchor rod of the initial support through a mechanical joint 26, and a gasket 23 is arranged between the mechanical joint 26 and the clamping part 22 and between the bolt 25 and the clamping part 22, and the mechanical joint 26 and the anchor rod and the support screw 241 can be connected by threads, and the distance between the isolation net 1 and the steel mesh 3 can be adjusted by rotating the support screw 241 as needed to ensure that the thickness of the protective layer of the steel mesh 3 meets the requirements.

[0050] In some embodiments, the connector 24 includes an anchor 242, and the clamping portion 22 and the fixture 21 are connected to the anchor 242 through threads, and one end of the anchor 242 is used to anchor into the surrounding rock. If the support screw 241 cannot be connected to the anchor rod, the connector 24 can use the anchor 242, similar to Figure 4 The support screw 241 in the embodiment is different in that the anchor 242 passes through one end of the clamping portion 22 and is anchored into the surrounding rock. Therefore, the anchor 242 is suitable for the case where the initial support is performed by the anchor spraying method.

[0051] like Figure 1 As shown, in some embodiments, the fixer 21 includes a cross-shaped fixing rod, which is used to connect with the steel mesh 3. Since the fixing rod is cross-shaped, it can be tied with the transverse steel bars and vertical steel bars of the steel mesh 3 to ensure the connection strength.

[0052] like Figure 8 As shown, the present invention provides a construction method for tunnel over-excavation treatment, comprising:

[0053] S1. Construction preparation

[0054] Equipment inspection: Factory production equipment is transported to the site by a transport vehicle; the equipment includes grouting machines and transport vehicles. Equipment inspection ensures that: the grouting machines and transport vehicles are in good condition, and the feed pipes, pressure pipes and other components are intact;

[0055] Material preparation: Preparation of filling and mixing materials in the factory to ensure that the quality meets the requirements; preparation of initial construction materials on site to ensure smooth construction;

[0056] Personnel training: The construction team is required to be proficient in grouting construction.

[0057] S2. Cleaning of over-excavation area

[0058] like Figure 7 As shown, the area outside the tunnel outline is the over-excavation area 7. Loose rocks, scum and debris in the over-excavation area 7 are removed to ensure that the grouting surface is clean and tidy;

[0059] Check the surrounding rock around the over-excavation area 7. If there are cracks or unstable parts, they should be treated first.

[0060] S3, spray concrete for the first time on the excavation surface, install the steel mesh 3, lay out the isolation net 1 on the steel mesh 3 of the initial support, the isolation net 1 is laid out at the corresponding position of the over-excavation area 7, and the over-excavation area 7 is completely covered. The isolation net 1 is fixed to the steel mesh 3 through a plurality of connectors 2; the thickness of the protective layer of the steel mesh 3 is ensured between the isolation net 1 and the steel mesh 3; Figure 6 As shown, it illustrates the situation of using arch frame 4 concrete for initial support;

[0061] In some embodiments, the method for fixing the isolation net 1 includes:

[0062] The fixing device 21 is used to bind and fix the fixing device on the steel mesh 3, and the clamping device 22 is used to clamp the fixing device on the isolation mesh 1;

[0063] In the case of using the arch frame 4 concrete for initial support, the fixing device 21 and the clamping part 22 are connected by the support screw 241, so that the isolation net 1 is fixed on the steel mesh 3;

[0064] In the case of using anchor spraying for initial support, the fixer 21 and the clamping part 22 are connected by using a support screw 241 or an anchor 242. When using the support screw 241, one end of the support screw 241 is fixedly connected to the anchor of the initial support, and when using the anchor 242, one end of the anchor 242 is anchored in the surrounding rock.

[0065] In some embodiments, the method of fixing the isolation net 1 on the steel mesh 3 through multiple connectors 2 includes:

[0066] like Figure 7 As shown, when the equivalent side length of the over-excavation area 7 is ≤1.0m, connectors 2 are arranged at the four corners of the isolation net 1; when the equivalent side length of the over-excavation area 7 is between 1.0 and 1.5m, an additional connector 2 is provided in the middle of the isolation net 1; when the equivalent side length of the over-excavation area 7 is greater than 1.5m, the connectors 2 are arranged in a plum blossom shape with equal intervals.

[0067] S4. Reserve grouting holes 5 within the over-excavation area 7, and spray concrete to form a closed grouting shell; the grouting holes 5 are reserved in the following manner: before spraying concrete, fix the grouting pipe (PVC pipe) on the steel mesh 3 and pass it through the isolation net 1, and before spraying concrete, use a rubber plug to seal the pipe mouth of the PVC pipe to avoid pipe mouth blockage; the spacing between the grouting holes 5: 1.0m in the circumferential direction and 0.5m in the longitudinal direction. Figure 6 Only one grouting hole 5 and one air outlet hole 6 are shown.

[0068] S5. Grouting is performed on the over-excavation area 7 through the reserved grouting holes 5.

[0069] The grouting method includes: when the strength of the primary concrete reaches 70%, grouting is performed through the grouting pipe, and the grouting pressure is 0.2-0.5MPa. The grouting sequence is from low to high, and when the slurry flows out from the air outlet 6, the grouting is stopped; the grouting hole 5 is closed, and pressure grouting is performed to the air outlet 6 until the air outlet 6 stops absorbing slurry for 10 minutes.

[0070] Within 30 minutes after the grouting is completed, use cement slurry with the same strength as the initial support to seal the hole: slowly inject the sealing material into the grouting hole 5 until the slurry overflows from the hole mouth; plug the hole mouth with a wooden plug, and after the sealing material solidifies, check to ensure the sealing quality.

[0071] Quality inspection and processing at a later stage:

[0072] (1) Appearance inspection

[0073] After the grouting is completed, conduct an appearance inspection on the primary support surface: observe whether there are defects such as leakage, cracks, etc. If any, they should be dealt with in time; check whether the sealing part is flat, dense, and has no obvious defects.

[0074] (2) Drilling and coring inspection

[0075] Select a certain number of grouting areas for core drilling inspection and strength testing. Core sampling inspection: observe the filling of grout in the core sample, the strength of the stone body and the bonding with the lining concrete; Strength testing: perform compressive strength test to test compliance.

[0076] The present invention is based on the existing primary support process and designs a composite steel mesh structure suitable for arch frame 4 concrete or anchor spraying primary support to replace the original steel mesh 3; after the primary support is finally set, backfill grouting is carried out with the help of a drilling and blasting trolley before the next drilling and blasting hole is formed, thereby completing the over-excavation treatment.

[0077] The present invention has high construction efficiency and reduces construction costs while ensuring the quality of over-excavation and backfilling.

[0078] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A composite steel mesh structure for tunnel over-excavation treatment, characterized in that: The invention comprises an isolation net (1), wherein the isolation net (1) is used to cover an over-excavation area (7), wherein a plurality of connectors (2) are arranged on the isolation net (1), wherein the connectors (2) comprise a fixer (21) and a clamping portion (22), wherein the fixer (21) is used to connect to a steel mesh sheet (3), wherein the clamping portion (22) is fixed to the isolation net (1) by clamping, and wherein the fixer (21) and the clamping portion (22) are connected by a connecting piece (24), so that the isolation net (1) is fixed to the steel mesh sheet (3).

2. The composite steel mesh structure for tunnel over-excavation treatment according to claim 1, characterized in that: The clamping portion (22) comprises a clamping sub-portion and a clamping mother portion, wherein the clamping sub-portion and the clamping mother portion are respectively arranged on both sides of the isolation net (1), a sub-matching portion is arranged on a side of the clamping sub-portion close to the clamping mother portion, and a mother-matching portion is arranged on a side of the clamping mother portion close to the clamping sub-portion, and the sub-matching portion and the mother-matching portion can cooperate with each other to fix the isolation net (1).

3. The composite steel mesh structure for tunnel over-excavation treatment according to claim 2, characterized in that: The sub-matching portion and the female matching portion are both tooth-shaped, and the sub-matching portion and the female matching portion mesh with each other, thereby fixing the isolation net (1) between the clamping sub-part and the clamping female part.

4. The composite steel mesh structure for tunnel over-excavation treatment according to claim 2, characterized in that: The sub-matching portion is conical, and the female matching portion includes a conical groove formed on the clamping female portion. The sub-matching portion is inserted into the female matching portion, thereby fixing the isolation net (1) between the clamping sub-part and the clamping female portion.

5. The composite steel mesh structure for tunnel over-excavation treatment according to any one of claims 1 to 4, characterized in that: The connecting member (24) comprises a supporting screw rod (241), and the clamping portion (22) and the fixer (21) are both connected to the supporting screw rod (241) via threads.

6. The composite steel mesh structure for tunnel over-excavation treatment according to any one of claims 1 to 4, characterized in that: The connecting member (24) comprises an anchor (242), the clamping portion (22) and the fixer (21) are both connected to the anchor (242) via threads, and one end of the anchor (242) is used for anchoring into the surrounding rock.

7. The composite steel mesh structure for tunnel over-excavation treatment according to any one of claims 1 to 4, characterized in that: The fixer (21) comprises a cross-shaped fixing rod, and the fixing rod is used to be connected to the steel mesh (3).

8. A construction method for tunnel over-excavation treatment, characterized in that: include: An isolation net (1) is arranged on the steel mesh (3) of the initial support, the isolation net (1) is arranged at a position corresponding to the over-excavation area (7) to completely cover the over-excavation area (7), and the isolation net (1) is fixed to the steel mesh (3) via a plurality of connectors (2); A grouting hole (5) is reserved within the over-excavation area (7), and concrete is sprayed to form a closed grouting shell; The over-excavation area (7) is grouted through the reserved grouting holes (5).

9. The construction method for tunnel over-excavation treatment according to claim 8, characterized in that: The fixing method of the isolation net (1) includes: The fixing device (21) is used to bind and fix the fixing device on the steel mesh (3), and the fixing device (22) is used to clamp the fixing device on the isolation mesh (1); In the case of using the arch frame (4) concrete for initial support, the fixing device (21) and the clamping part (22) are connected by a support screw (241), thereby fixing the isolation net (1) on the steel mesh (3); In the case of using anchor spraying for initial support, the fixer (21) and the clamping part (22) are connected by using a support screw (241) or an anchor (242). When the support screw (241) is used, one end of the support screw (241) is fixedly connected to the anchor of the initial support. When the anchor (242) is used, one end of the anchor (242) is anchored into the surrounding rock.

10. The construction method for tunnel over-excavation treatment according to claim 8, characterized in that: The method for fixing the isolation net (1) on the steel mesh (3) through a plurality of connectors (2) comprises: When the equivalent side length of the over-excavation area (7) is ≤1.0m, connectors (2) are arranged at the four corners of the isolation net (1); when the equivalent side length of the over-excavation area (7) is between 1.0 and 1.5m, an additional connector (2) is arranged in the middle of the isolation net (1); when the equivalent side length of the over-excavation area (7) is greater than 1.5m, the connectors (2) are arranged at equal intervals in a plum blossom shape.

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