A wet shotcrete support system for underground mines

Abstract

This utility model provides a wet-sprayed concrete support system for underground mines, belonging to the field of underground mine roadway support technology. It solves the problem of poor stability in traditional concrete support. The system includes surrounding rock with anchor bolt holes, and a support pipe. The support pipe is a steel pipe with a circular upper cross-section, and four steel claws are evenly distributed on its outer side. A metal mesh is provided below the steel claws. An anchor bolt tray is located at the upper end of the steel pipe, and the lower end of the steel pipe is positioned above the surrounding rock. Anchor bolts are installed inside the support pipe, passing through the anchor bolt holes and the anchor bolt tray. The anchor bolts can be long or short. Wet-sprayed concrete is applied between the lower part of the anchor bolt tray and the upper part of the surrounding rock. This utility model has significant advantages such as high construction efficiency and good support effect.

Description

Technical Field

[0001] This utility model belongs to the field of underground mine roadway support technology, specifically relating to an underground mine wet shotcrete support system. Background Technology

[0002] In the current tunnel support practice in a mining area in Northwest China, taking the Jinchuan mining area as an example, the existing 2.25m long anchor bolts have significant defects. Through multi-dimensional research and demonstration, including empirical analysis, studies on the stress condition of the anchor bolt trays underground, actual observation of tunnel deformation, stress analysis of repaired anchor bolts, and loosening zone testing, it was found that anchor bolts of this length are difficult to anchor to stable bedrock, resulting in poor restraint on surrounding rock deformation and failing to fully exert their anchoring function. At the same time, the traditional shotcrete-anchor-mesh construction sequence also revealed many problems. During construction, the anchor bolt trays cannot effectively restrain the shotcrete and steel mesh, especially in the construction of double-layer shotcrete-anchor-mesh, where weak support areas easily form at the trays, severely weakening the overall support effect. Furthermore, the traditional dry shotcrete support method long used in the Jinchuan mine has obvious drawbacks. Its strength grade is only about C15-C20, which not only has poor density but also poor strength uniformity. This directly leads to difficulty in ensuring tunnel stability, a high repair rate, and poses a great threat to mine production safety, while also severely restricting production efficiency. In comparison, wet-sprayed concrete has significant advantages, with strength grades typically reaching C25-C30, or even C50, resulting in high support strength and good performance. Utility Model Content

[0003] The purpose of this invention is to provide a wet shotcrete support system for underground mines to solve the problem of poor stability in traditional concrete support systems.

[0004] The technical solution of this utility model is: a wet shotcrete support system for underground mines, including surrounding rock, with anchor bolt holes opened in the surrounding rock, and a support pipe. The support pipe is a steel pipe with a circular upper cross section. Four steel claws are evenly distributed on the outside of the steel pipe. A metal mesh is provided at the lower part of the steel claws. An anchor bolt tray is provided at the upper end of the steel pipe. The lower end of the steel pipe is located on the upper part of the surrounding rock. An anchor bolt is provided inside the support pipe. The anchor bolt passes through the anchor bolt hole and the anchor bolt tray. The anchor bolt includes a long anchor bolt or a short anchor bolt. Wet shotcrete is provided between the lower part of the anchor bolt tray and the upper part of the surrounding rock.

[0005] As a further improvement of this utility model, an anchor nut is provided between the anchor tray and the anchor rod.

[0006] As a further improvement of this utility model, the inner diameter of the steel pipe is 1.2-1.6 times that of the anchor rod, the wall thickness is 2-3mm, the height is consistent with the thickness of the wet sprayed concrete, and the total length of the steel claw is greater than the diagonal length of the metal mesh.

[0007] As a further improvement of this utility model, the metal mesh is made of φ6.5 round steel by spot welding.

[0008] As a further improvement of this utility model, the anchor bolts are mortar-bonded anchor bolts, and both short and long anchor bolts are made of φ22mm threaded steel.

[0009] As a further improvement of this utility model, the wet sprayed concrete is 100mm thick C50 wet sprayed concrete.

[0010] As a further improvement of this utility model, the wet sprayed concrete uses Jinchuan wet spraying aggregate, and is prepared according to a water-cement ratio of 0.41, with cement, water, dry river sand, green pebbles and admixtures in a mass ratio of 600:208:969:646:1.8.

[0011] As a further improvement of this utility model, the admixture is RWXJ-002 high-strength concrete plasticizer and slump retainer.

[0012] The beneficial effects of this utility model are as follows:

[0013] 1. Improved Support Strength and Stability: Traditional dry-mixed shotcrete has a strength grade of only C15-C20, while this invention uses C50 high-strength wet-mixed shotcrete, significantly increasing its strength. Based on shear failure theory, increasing concrete strength can reduce the thickness of the shotcrete, thus reducing concrete cracking and roadway instability caused by low shear and flexural strength. In practical applications, this effectively enhances the long-term stability of the roadway, reduces the roadway repair rate, ensures safe mine production, reduces production interruptions caused by roadway instability, and improves mining efficiency.

[0014] 2. Optimizing Anchor Bolt Anchoring Effect: The existing 2.25m anchor bolts are too short, making it difficult to anchor them into stable bedrock and effectively restrain surrounding rock deformation. This invention adopts a combination of long and short anchor bolts, with short anchor bolts (2.25m) and long anchor bolts (3.0m) working together. The long anchor bolts can penetrate deep into stable rock mass, providing more reliable anchoring force; the short anchor bolts can reinforce shallow surrounding rock. The two work together to expand the anchoring range, enhance the anchoring effect on the surrounding rock, suppress tunnel deformation, and improve the overall reliability of the support.

[0015] 3. Improved Shotcrete-Rail-Mesh Construction Sequence: Traditional shotcrete-rail-mesh construction sequences have many problems, such as the anchor trays failing to effectively restrain the shotcrete and steel mesh, and weak support zones forming at the trays during double-layer shotcrete-rail-mesh construction. This invention optimizes the construction sequence by using support pipes. The support pipes position the anchor trays outside the shotcrete, effectively restraining the shotcrete and steel mesh, and enhancing the collaborative working ability of the shotcrete-rail-mesh combined support structure. In high-stress mines, it can fully utilize the support function of double-layer shotcrete-rail-mesh, avoid support failure caused by construction sequence problems, and improve the overall effectiveness of roadway support.

[0016] 4. Reduced Support Costs: Although the new support scheme increases the cost of some materials, its support effect is better in the long run. The new scheme uses C50 wet shotcrete, which reduces the amount of shotcrete used compared to traditional support. At the same time, it reduces repair costs by improving roadway stability. Calculations show that the new scheme achieves increased support strength with a limited increase in cost, demonstrating good economic benefits and making it suitable for widespread application in mining engineering. Attached Figure Description

[0017] Figure 1 This is a top view of the support tube structure in this utility model;

[0018] Figure 2 for Figure 1 Sectional view along the AA direction;

[0019] Figure 3 This is a schematic diagram of the structure of the system of this utility model;

[0020] Figure 4 This is a schematic diagram of the convergence method measurement principle in this utility model;

[0021] Figure 5 This is a diagram showing the anchor bolt arrangement in Embodiment 1 of this utility model.

[0022] In the diagram: 1-Anchor bolt; 2-Steel pipe; 3-Steel claw; 4-Anchor bolt tray; 5-Wet sprayed concrete; 6-Metal mesh; 7-Anchor bolt hole; 8-Surrounding rock; 9-Anchor bolt nut. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] like Figures 1-5 As shown, the system and method used in this embodiment include the following.

[0025] 1. System Composition

[0026] (1) Anchor bolt assembly: The system proposed in this utility model proposes that the anchor bolt 1 adopts a combination of long anchor bolts and short anchor bolts. The short anchor bolts (such as φ22mm×2.25m) and the long anchor bolts (such as φ22mm×3.00m) cooperate with each other and are arranged in a quincunx pattern with a spacing of 1m between rows. The length of the anchor bolt 1 is generally 1 / 2 of the width of the excavation section of the 8th roadway in the surrounding rock.

[0027] Taking the tunnels in the Jinchuan mining area as an example, the excavation width of the segmented tunnels is generally 5.0m, so the length of anchor bolt 1 should not be less than 2.5m. However, the actual length on site is 2.25m. Therefore, based on extensive experience, the length of anchor bolt 1 is too short. In light of the above analysis, the overall length of anchor bolt 1 in the Jinchuan mining area is relatively short, while the range of movement of unstable surrounding rock is greater than the length of anchor bolt 1 (2.2m). Therefore, the existing 2.25m anchor bolt 1 is insufficient to anchor one end of the anchor bolt to the stable surrounding rock mass 8, resulting in the anchor bolt 1 not providing maximum reinforcement for the surrounding rock 8. Therefore, it is necessary to lengthen the existing anchor bolt 1 and adopt an anchoring method combining long and short anchor bolts.

[0028] (2) Support pipe structure: The support pipe is used during roadway support construction to position the anchor plate 4 outside the sprayed wet concrete 5, thereby achieving effective constraint of the anchor 1 and the anchor plate 4 on the sprayed wet concrete 5. The support pipe in this utility model system consists of a steel pipe 2 and four steel claws 3 welded to one end. The steel pipe 2 is made of Q235 steel, the inner diameter of the steel pipe 2 is 1.2-1.6 times that of the anchor 1, the wall thickness of the steel pipe 2 is 2-3mm, and the height is consistent with the thickness of the sprayed wet concrete 5.

[0029] The steel claw 3 is used to hold down the metal mesh 6, making it adhere tightly to the rock surface of the surrounding rock 8. The height of the steel pipe 2 is equal to the thickness of the sprayed wet concrete 5, that is, the concrete thickness is 100mm. One of its functions is to indicate the thickness of the sprayed wet concrete 5. The second function is that, due to the spacing effect of the support pipe between the anchor plate 4 and the metal mesh 6, even if the construction sequence of hanging the metal mesh 6 first and then spraying is adopted, the anchor plate 4 can still press on the outer surface of the sprayed wet concrete 5. Through the anchor 1 and the anchor plate 4, the bearing capacity of the sprayed wet concrete 5 layer is maximized, and the stability of the roadway is improved through the combined support resistance formed by the shotcrete, anchor and mesh.

[0030] ① The steel pipe 2 of the support pipe is made of Q235 or equivalent strength material. Its inner diameter is required to be able to easily pass through the ф22mm anchor rod 1. The outer diameter of the support pipe must be greater than the inner diameter of the center hole of the anchor rod tray 4.

[0031] ② The total length of the steel claws 3 of the support tube should be greater than the diagonal length (212mm) of the mesh size (mesh size: 150mm×150mm) of the metal mesh 6, so as to press down the mesh.

[0032] ③ The steel claw 3 of the support pipe is made of ф6mm steel bars welded to the steel pipe 2.

[0033] (3) Concrete materials: Wet-sprayed concrete 5 can fully mix all components and strictly control the water-cement ratio. Therefore, the uniaxial compressive strength of wet-sprayed concrete 5 is generally around 25MPa. At the same time, wet-sprayed concrete 5 has good density and high concrete strength uniformity. Dry-sprayed concrete not only has low average strength and poor density, but also poor concrete strength uniformity. The stability of roadways supported by wet-sprayed concrete 5 is significantly better than that of roadways supported by dry-sprayed concrete. Using Jinchuan wet-sprayed aggregate and RWXJ-002 high-strength concrete plasticizer and slump retainer, wet-sprayed concrete 5 with a strength of C50 or higher was prepared. The test results of wet-sprayed concrete 5 prepared by RWXJ-002 high-strength concrete plasticizer and slump retainer are shown in Table 1 below.

[0034] Table 1

[0035]

[0036] 5. Strength monitoring of wet sprayed concrete: Using a 70mm×70mm×70mm mold, the uniaxial compressive strength of wet sprayed concrete was measured every other day at 7d and 28d in the early stage of the test. After the strength stabilized, the sampling interval was gradually extended.

[0037] 2. Construction Method

[0038] Primary support: Short anchor bolts are used in the primary support. The short anchor bolts are made of φ22mm threaded steel and are 2.25m long. All short anchor bolts are arranged in a quincunx pattern with a spacing of 1.0m. The metal mesh 6 is made of φ6.5 round steel spot welded together with a mesh size of 150mm×150mm. The gaskets are 200mm×200mm×10mm in size. The short anchor bolts are installed using support pipes. That is, after the roughing is completed, the loose stones are pried off first, then the metal mesh 6 is hung, and after installing the short anchor bolts, support pipes and anchor bolt trays 4, 100mm of wet shotcrete 5 is sprayed. The wet shotcrete 5 has a strength of C50. The short anchor bolts are bonded with mortar.

[0039] Secondary support: Long anchor bolts are used in the primary support. The long anchor bolts are made of φ22mm threaded steel, 3.0m in length, and are arranged in a staggered pattern with a spacing of 1.0m. The metal mesh 6 is made of φ6.5 round steel spot-welded together, with a mesh size of 150mm×150mm. The gasket specifications are 200mm×200mm×10mm. The long anchor bolts are installed using support pipes. That is, after installing the long anchor bolts, hanging the metal mesh 6, support pipes, and anchor bolt trays 4, wet shotcrete 5 is sprayed. The required shotcrete thickness is 100mm, and the wet shotcrete 5 strength is C50. The long anchor bolts are bonded with mortar.

[0040] After the initial support is completed by removing the loose rocks, the anchor bolt holes 7 are drilled, the metal mesh 6 is hung, and the short anchor bolts are installed. Then, the support pipe, anchor bolt tray 4, and anchor bolt nuts 9 are installed, followed by shotcreting to ensure that the anchor bolt tray 4 is located outside the shotcrete 5 after shotcreting. Similarly, for the secondary support, the anchor bolt holes 7 are drilled, the metal mesh 6 is hung, and the long anchor bolts are installed. Then, the support pipe, anchor bolt tray 4, and anchor bolt nuts 9 are installed, followed by shotcreting to ensure that the anchor bolt tray 4 is located outside the shotcrete 5 after shotcreting.

[0041] Example 1

[0042] 1. The material preparation stage is shown in Table 2 below.

[0043] Table 2

[0044]

[0045] 2. On-site construction phase

[0046] The process involves: using a YT-28 rock drill to construct anchor bolt hole 7; inserting anchor bolt 1 into anchor bolt hole 7; hanging metal mesh 6; placing support pipe; installing anchor bolt tray 4; tightening anchor bolt nut 9; and spraying wet concrete 5.

[0047] The first support construction steps are as follows: After roughing out the surface, remove loose rocks and clean the tunnel surface. Using a YT-28 rock drill, construct anchor bolt holes 7 according to the designed spacing of 1.0m. Use a φ38mm drill bit, a 2.5m long drill rod, and a short anchor bolt with a hole depth of 2.25m. Install a 150mm×150mm metal mesh 6 made of φ6.5mm round steel spot-welded to the anchor bolts. Install short anchor bolts of φ22mm×2.25m, filling each anchor bolt hole with material according to design requirements. The short anchor bolts are bonded with mortar. Place the support pipe over the short anchor bolts, ensuring the steel claw 3 presses down on the metal mesh 6. The height of the steel pipe 2 should match the designed thickness of the wet-mixed shotcrete 5. Then install and tighten the 200mm×200mm×10mm anchor bolt tray 4 and anchor bolt nuts 9. C50 wet shotcrete 5 was used, with materials supplied by an on-site mixing plant. A 100mm thick layer of concrete was sprayed using a shotcrete equipment. The angle, distance, and spray volume were carefully controlled during the spraying process.

[0048] Secondary support construction steps: Based on the primary support, the secondary support is arranged in a staggered, quincunx pattern, with anchor holes drilled at 1.0m intervals (7) to accommodate 3.0m long anchors. A metal mesh (6) of the same specifications as the primary support is installed. φ22mm×3.0m long anchors are installed, also using mortar bonding. Support pipes, anchor trays (4), and anchor nuts (9) are installed, following the same procedure as the primary support. A 100mm thick C50 wet-mixed concrete (5) is sprayed, ensuring spraying quality.

[0049] After the support is completed, this utility model mainly conducts on-site monitoring of the convergence deformation of the roadway under the new support scheme. Specifically, three monitoring points are designed on the roof and sides of the roadway to measure the distance between points A, B, and C, and the deformation of the roadway sides and roof is calculated based on this distance.

[0050] 1. Support effect monitoring stage

[0051] (1) Monitoring of roadway convergence deformation

[0052] ①For example Figure 4 As shown, the JSS30A digital display convergence meter was used for this convergence deformation monitoring. It was mainly used to monitor the convergence deformation of the supported roadway. A total of 3 monitoring points were designed on the roof and sidewalls of the roadway surrounding rock 8. Initially, monitoring was carried out at intervals of 3-4 days. The monitoring cycle was adjusted according to the monitored deformation values. The total monitoring cycle was no less than 5 months. According to the monitoring cross section of 5m, 6 convergence deformation monitoring cross sections were set up for roadways with different support methods. The distance between the three points A, B, and C was measured and the deformation of the roadway sidewalls and roof was calculated based on this distance.

[0053] ② Monitoring point setup

[0054] Based on a monitoring section of 5m, three monitoring sections are set up in the 20m test roadway (the monitoring sections need to be located in the middle section of the test section). Since two different support methods are used for roadway comparison, a total of six convergence deformation monitoring sections are designed.

[0055] (2) Anchor bolt stress gauge stress monitoring

[0056] ① Monitoring methods

[0057] Anchor bolt force gauges are commonly used instruments for measuring changes in anchor bolt stress. Based on the anchor bolt size and stress conditions, the GAD400 intrinsically safe tension sensor for mining was selected for this anchor bolt stress monitoring. Measuring points were set at the sidewalls and arch feet of the roadway, with two measuring points (a and b) arranged at each cross-section. Monitoring was only carried out on secondary support. Three monitoring cross-sections were set up for anchor bolt stress monitoring of different support methods, with one monitoring cross-section every 5m. The monitoring cycle was consistent with the roadway convergence deformation monitoring, and was extended as much as possible until the anchor bolt was damaged.

[0058] The main technical performance of the equipment is as follows: the operating environment is 0-40℃, relative humidity ≤95% (+25℃), and atmospheric pressure 80-106kPa.

[0059] Working Principle: The anchor bolt stress sensor uses a through-hole fixing installation with a through-hole diameter of 25mm, which is determined by the diameter of the anchor bolt or anchor cable. The sensor is installed between the anchor bolt tray 4 and the anchor bolt nut 9, with the sensor fitted over the anchor bolt tray 4 and the anchor bolt nut 9 screwed on. It employs strain measurement technology to measure the axial load stress of the anchor bolt / anchor cable, and uses a fully sealed structure. The load force acts on the hydraulic cylinder, generating a pressure change. The strain gauge converts the sensed load stress change into a voltage signal, which is then processed by the signal acquisition and processing circuit and finally displayed by the display circuit.

[0060] ② Monitoring point setup

[0061] In one cross-section, two measuring points, a and b, are arranged, located at the sidewall and arch foot of the roadway, respectively. Due to the dense arrangement of pipes in the roadway roof, it is impossible to install anchor bolt stress gauges on the roof; therefore, measuring points are not considered for the roof. Furthermore, considering that after installing anchor bolt stress gauges on the primary support, secondary shotcreting would inject the gauges into the concrete, making further on-site monitoring impossible, this study only monitors anchor bolt stress on the secondary support.

[0062] Based on a monitoring cross-section of 5m, three monitoring cross-sections will be set up in a 20m test roadway (the monitoring cross-sections need to be located in the middle section of the test cross-section). For anchor bolt stress monitoring of two different support methods, a total of three monitoring cross-sections are planned. The monitoring cycle, as described in the convergence monitoring, will be extended as much as possible until failure occurs.

[0063] Field measurements at the Jinchuan mine have shown that traditional dry-mixed shotcrete has a strength grade of approximately C15-C20, while wet-mixed shotcrete typically reaches C25-C30. The effectiveness of wet-mixed shotcrete in replacing dry-mixed shotcrete in roadway support at Jinchuan in recent years clearly demonstrates that roadways supported by wet-mixed shotcrete exhibit significantly better stability than those supported by dry-mixed shotcrete. The application of C50 wet-mixed shotcrete in roadway support at the Jinchuan mine provides a new support method for solving the support challenges of deep roadways in Jinchuan.

[0064] The solutions described in the embodiments are not intended to limit the scope of patent protection of this utility model. All equivalent implementations or modifications that do not depart from the scope of this utility model are included in the patent scope of this case.

Claims

1. A wet-shot concrete support system for underground mines, comprising surrounding rock, characterized in that: Anchor bolt holes (7) are provided in the surrounding rock (8), and a support pipe is also included. The support pipe is a steel pipe (2) with a circular upper cross section. Four steel claws (3) are evenly distributed on the outside of the steel pipe (2). A metal mesh (6) is provided at the lower part of the steel claws (3). Anchor bolt tray (4) is provided at the upper end of the steel pipe (2). The lower end of the steel pipe (2) is located at the upper part of the surrounding rock (8). Anchor bolts (1) are provided inside the support pipe. Anchor bolts (1) pass through the anchor bolt holes (7) and the anchor bolt tray (4). Anchor bolts (1) include long anchor bolts or short anchor bolts. Wet sprayed concrete (5) is provided between the lower part of the anchor bolt tray (4) and the upper part of the surrounding rock (8).

2. The wet shotcrete support system for underground mines according to claim 1, characterized in that: An anchor nut (9) is provided between the anchor tray (4) and the anchor (1).

3. A wet-shot concrete support system for underground mines according to claim 1 or 2, characterized in that: The inner diameter of the steel pipe (2) is 1.2-1.6 times that of the anchor rod (1), the wall thickness is 2-3mm, the height is consistent with the thickness of the wet sprayed concrete (5), and the total length of the steel claw (3) is greater than the diagonal length of the metal mesh (6) hole.

4. The wet shotcrete support system for underground mines according to claim 3, characterized in that: The metal mesh (6) is made of φ6.5 round steel by spot welding.

5. The wet shotcrete support system for underground mines according to claim 4, characterized in that: The anchor rod (1) is a mortar-bonded anchor rod, and both the short anchor rod and the long anchor rod are made of φ22mm threaded steel.

6. The wet shotcrete support system for underground mines according to claim 5, characterized in that: The wet sprayed concrete (5) is 100mm thick C50 wet sprayed concrete.

7. The wet shotcrete support system for underground mines according to claim 1, characterized in that: The wet sprayed concrete (5) uses Jinchuan wet sprayed aggregate, and is prepared according to a water-cement ratio of 0.41, and cement, water, dry river sand, green pebbles and admixtures are in a mass ratio of 600:208:969:646:1.

8.

8. The wet shotcrete support system for underground mines according to claim 7, characterized in that: The admixture is RWXJ-002 high-strength concrete plasticizer and slump retainer.

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