Surrounding rock control method for large-section soft rock roadway

Abstract

The invention relates to the field of roadway engineering, in particular to a surrounding rock control method for a large-section soft rock roadway, which comprises the following steps of: acquiring actual geological conditions of a mine to obtain geological data; establishing a numerical model by the numerical simulation software, substituting the geological data into the numerical model, and performing excavation simulation to obtain a mine pressure appearing rule; and determining a supporting scheme according to the mine pressure display rule.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel engineering, in particular to a surrounding rock control method for a large-section soft rock tunnel. Background Art

[0002] With the increase in the depth and scale of coal mining, the engineering challenges faced by large-section soft rock tunnels are becoming increasingly severe, and the requirements for safe mining are also increasing. The engineering difficulty of coal mine tunnels is gradually increasing, especially for large-section soft rock tunnels under deep soft rock geological conditions. In coal mining, the deformation and damage of large-section soft rock tunnels are mainly due to the low strength and weak bearing capacity of soft rock, which causes the surrounding rock to enter the elastic-plastic transition stage or even the post-peak plastic damage stage under high stress environment. With the increase in mining depth, the vertical stress borne by the tunnel surrounding rock will also increase. Under complex stress conditions, the internal stress of the surrounding rock is concentrated, the plastic zone expands, and the anchor cable is prone to breakage, resulting in deformation and damage of the surrounding rock; the superposition of original rock stress, tectonic stress and mining disturbance stress makes it difficult to implement shallow coal seam excavation, mining and tunnel support technology under deep complex conditions. The low cohesion and friction between rock blocks of soft rock are not enough to maintain stability, and it softens when exposed to water, further accelerating the destruction of the surrounding rock. The surrounding rock of deep soft rock tunnels usually exhibits obvious soft plasticity, creep, and layer cracking characteristics, which causes the tunnel surrounding rock to be in a stress adjustment stage for a long time after excavation, and is prone to large deformation, plastic flow and even creep. This deformation will not only cause deformation and shrinkage of the tunnel, but may also cause the yield and failure of the surrounding rock support system, seriously threatening the service life and construction safety of the tunnel.

[0003] In recent years, with the increase in the depth of coal mining, the tunnel surrounding rock support technology has experienced a development from single type to combined type. In the early days, coal mines mainly used wood support, and later with the advancement of materials, concrete and reinforced concrete were gradually introduced.

[0004] At present, the soft rock tunnel support technology mainly includes four support methods: anchor support, anchor mesh spray support, anchor column support and anchor mesh spray support. The support effect of anchor rods depends on the strength and anchoring force of the rock mass. However, in soft rock, due to the low strength of the rock mass, the anchoring effect of anchor rods is poor, and they are prone to pull out and break under stress. The anchor rods of anchor mesh spray support are combined with metal mesh and sprayed concrete, which can not only suspend support, but also close cracks to improve the support effect. However, it is suitable for medium soft rock and has poor support effect for surrounding rock that is extremely easy to break or has strong rheology. Although anchor support has a good supporting effect on soft rock tunnels, the construction cost is high, and the applicability of grouting slurry is limited by engineering conditions; anchor mesh spray support can well control rheological deformation and improve support strength, but the construction is too complicated and the cost is high, so it is more suitable for deep soft rock tunnels or those that are greatly affected by water; traditional support technology has good effects under small-section or medium-hardness rock conditions, but in soft rock large-section tunnels, insufficient support strength often leads to surrounding rock instability and failure of the support system. Summary of the invention

[0005] Due to the low strength and weak bearing capacity of soft rock tunnels, traditional support technologies and support materials are often difficult to provide sufficient support when facing large sections of soft rock, resulting in large deformation, collapse, poor stability, high economic costs and other problems of tunnel surrounding rock. In order to further improve the surrounding rock deformation control of large-section soft rock tunnels, the present invention proposes a large-section soft rock tunnel surrounding rock control method.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A surrounding rock control method for a large-section soft rock tunnel comprises the following steps:

[0008] Collect the actual geological conditions of the mine and obtain geological data;

[0009] Numerical simulation software builds a numerical model, substitutes geological data into the numerical model, performs excavation simulation, and obtains the law of mine pressure manifestation;

[0010] The support plan is determined based on the law of mine pressure manifestation.

[0011] As a further solution of the present invention: the geological data includes the geological conditions of the tunnel, the strength of the surrounding rock and the physical and mechanical properties of the surrounding rock, such as the elastic modulus and the internal friction angle.

[0012] As a further solution of the present invention: the numerical simulation software is FLAC3D numerical simulation software. This software has mature technology and good use effect. It adopts the Mohr-Coulomb constitutive model, fixes the horizontal displacement of the X-axis, the horizontal displacement of the Y-axis and the vertical displacement of the Z-axis, and then applies compensation loads and initial stresses, sets boundary conditions, and applies ground stress values ​​around the tunnel.

[0013] As a further solution of the present invention: the support scheme includes an initial support scheme, an anchor support scheme and a reinforced support scheme. The support scheme is applied to on-site construction, and large-elongation anti-impact anchors are arranged in large-section soft rock tunnels. By setting support parameters, the stability of broken rocks within the plastic zone can be maintained and the expansion of the plastic zone boundary can be curbed.

[0014] As a further solution of the present invention: the surrounding rock control method of large-section soft rock tunnel also includes the following steps: the cross-point distribution method is used to detect the effect of the reinforcement support scheme. The cross-point distribution method has high technical reliability, simple operation, and strong adaptability, and can reduce the difficulty of the measurement process and the occurrence rate of potential problems. The cross-point distribution method gradually advances the position of the observation point to obtain more accurate actual on-site data. The acquired data is recorded and analyzed to obtain the roof settlement, the two sides moving closer, and the surrounding rock deformation rate under the support scheme. Different changes occur with the deepening of the excavation progress. These data are compared with the original surrounding rock deformation state obtained by excavation simulation to verify the rationality of the support scheme.

[0015] As a further solution of the present invention: the law of mine pressure manifestation includes the law of mine pressure manifestation during bottom extraction tunnel excavation, the law of mine pressure manifestation during mining tunnel excavation and the law of mine pressure manifestation during working face mining.

[0016] As a further solution of the present invention: the excavation simulation includes bottom extraction tunneling simulation, upper drift tunneling simulation, lower drift tunneling simulation and working face mining simulation. The model is cut open during the simulation, and the surrounding rock stress distribution cloud map and plastic zone distribution cloud map of the soft rock tunnel in different periods are drawn according to the processing results. The mine pressure changes during tunnel excavation, especially the stress distribution of the roof, bottom plate and two sides, are analyzed, and the changes in the stress concentration area and the plastic zone are observed; the deformation area and deformation amount of the tunnel in different excavation processes are analyzed through the plastic zone cloud map, the degree and range of surrounding rock damage are determined, and the surrounding rock damage area and the "butterfly damage" area that may appear in the large-section soft rock tunnel are found.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention accurately simulates the influence of bottom extraction tunnel excavation in large-section soft rock tunnel on the stability of tunnel surrounding rock, the influence on the law of mine pressure manifestation in bottom extraction tunnel during excavation of working face mining tunnel, and the influence on the stress state of bottom extraction tunnel and the morphology of plastic zone during mining of working face by adopting numerical simulation method, and comprehensively analyzes the damage state of surrounding rock after being disturbed by mining; then, a support scheme is formulated and constructed on site according to the surrounding rock damage state appearing in the simulation results; the deformation state of surrounding rock under the support scheme is monitored in real time, and the data obtained by real-time monitoring is analyzed and compared with the original support results; the results show that the support scheme formulated after simulation effectively improves the support effect of large-section soft rock tunnel. Compared with traditional technology, the method of the present invention not only significantly reduces the risk of surrounding rock deformation and support failure, but also reduces maintenance costs, optimizes construction schemes, and extends the service life of tunnels. It has broad application prospects and improves the reliability and stability of support. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The present invention is a flowchart of a surrounding rock control method for a large-section soft rock tunnel according to an embodiment of the present invention. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Reference Figure 1 A surrounding rock control method for a large-section soft rock tunnel comprises the following steps:

[0021] 1) First, relying on the domestic Zhaogu No. 2 Mine as the engineering background, the tunnel is a large-section soft rock tunnel, which is greatly affected by mining stress; a detailed survey of the geological conditions in the tunnel area is carried out to obtain basic data such as the mechanical characteristics of the surrounding rock and the ground stress state, obtain the distribution and mechanical properties of the soft rock, determine parameters such as the elastic modulus and internal friction angle, and conduct experimental tests on the core samples taken on site, and determine the mechanical parameters of the surrounding rock based on the test results; providing a basis for the establishment of the subsequent three-dimensional numerical model;

[0022] 2) Based on the actual tunnel survey results on site and the results obtained from testing the core samples, use FLAC 3D(Fast Lagrangian Analysis of Continua) numerical simulation software was used for modeling. During modeling, the dimensions of the model, X, Y, and Z, were determined to be 500m, 500m, and 150m respectively; and the working face was arranged along the X direction and advanced in the Y direction. The entire model had a total of 2.5048 million units and 258.5920 nodes; the Mohr-Coulomb constitutive model was used to perform numerical simulation of each rock layer in the model, and the horizontal displacement of the X-axis boundary, the horizontal displacement of the Y-axis boundary, and the vertical displacement of the lower boundary of the Z-axis were fixed. A compensation load of 18.52MPa and an initial stress of szz=18.52MPa and sxx=syy=24.076MPa were applied to the upper boundary. The thickness of each rock layer near the roof and floor of the coal seam in the model was modeled according to the actual geological thickness of the mine, and then the basic top and basic bottom were added above and below the roof and floor to increase the model thickness and reduce the boundary effect. The above steps were all preparations before excavation simulation;

[0023] 3) After the model is established, the excavation simulation plan for the working face is formulated. During the simulation, the working face is excavated 160m along the X-axis to simulate the working face length, starting from 425m on the Y-axis, and excavated 25m each time, for a total of 350m; the collapse zone is simulated using the double yield model for equivalent simulation; the filling plan is: the first two excavations are not filled to simulate the initial pressure, and after the third excavation, filling is carried out at 10m behind the working face, and the filling body size is 160×25×12.6m, and then it enters the periodic pressure stage, and the filling is delayed by 25m after every 25m of excavation. The whole process is excavated 14 times and the goaf is filled 14 times;

[0024] 4) After the excavation simulation plan is formulated, excavation is carried out. First, the law of mine pressure manifestation during the excavation of the bottom extraction lane of the 14050 working face is studied. Because the bottom extraction lane of the 14050 working face serves the upper working face, it is arranged before the working face; when the upper working face is mined, the bottom extraction lane will be affected by the mining stress, and the surrounding rock stress environment determines the damage range of the lane surrounding rock; the numerical model is cut along the axis of the lane, and the vertical stress cloud map of the horizontal section of the lane (vertical to the plane and parallel to the plane) and the vertical stress cloud map of the vertical section are obtained; the stress cloud map is analyzed to know that during the excavation, the vertical stress of the top floor and the two sides of the bottom extraction lane is obviously Obvious changes: stress reduction zones are formed in the roof and floor plates, and gradually return to the original rock stress state; stress concentration occurs on the two sides, and the vertical stress increases first and then stabilizes away from the two sides; the shallow surrounding rock is in the destruction stage, and the bearing capacity of the deep surrounding rock gradually increases and returns to the original rock stress state; the maximum vertical stress on the two sides of the tunnel is 29.18MPa, and the impact range is 3.83m. As the distance from the two sides of the tunnel increases, the final stress stabilizes at 20.46MPa; the model is also cut open to obtain the corresponding plastic zone distribution cloud map of the horizontal section (vertical to the plane and parallel to the plane) of the tunnel and the plastic zone distribution cloud map of the vertical section. 3D In numerical simulation software, the stability of surrounding rock is mainly determined by the shape of plastic zone. From the distribution cloud diagram of plastic zone of the processed model, it can be analyzed that the plastic zone of 14050 bottom extraction tunnel is limited: the depth of the middle part of the roof is 1m, the depth of the bottom plate is 2-3m (the deepest in the middle is 3m), and the depth of the two sides is 1-2m (the shoulder angle of the roof is 2m). By comparing the rock column diagram, it is known that the depth of the plastic zone of the roof is shallow; the bottom plate is sandy mudstone with low strength. Under the influence of unloading, the plastic zone is deep, which may be in the transition yield or peak of elastic-plastic transition. Post-destruction stage; The two sides of the bottom extraction tunnel are mudstone, which has low strength and stress concentration, resulting in an increase in the depth of the plastic zone, which is mainly manifested as shear failure, and the compressive strength of the rock mass reaches the destruction limit; Based on the above analysis, the depth of the plastic zone of the surrounding rock caused by excavation of the 14050 bottom extraction tunnel is relatively shallow, indicating that the impact on the stability of the surrounding rock is relatively weak, but considering the impact of subsequent 14050 working face mining and excavation activities on the bottom extraction tunnel, the stress state and the depth of the plastic zone will further increase, so the support method of the bottom extraction tunnel is determined to be full-section anchor cable support;

[0025] 5) Secondly, the bottom extraction tunnel is arranged before the working face is mined, and the excavation of the 14050 lower drift will affect the surrounding rock stress and plastic zone distribution of the bottom extraction tunnel. Therefore, the numerical simulation model is dissected along the strike and dip directions of the working face to generate stress cloud maps respectively. At the same time, the vertical stress data in the dip direction of the working face are extracted, and relevant images are drawn to study the influence of the excavation of the 14050 working face on the law of the bottom extraction tunnel's mine pressure manifestation. Analysis shows that during the mining period, the vertical stress distribution of the top and bottom plates of the bottom extraction tunnel is stable, forming a stress reduction zone, which gradually recovers to the original rock stress state; stress concentration occurs on both sides of the lower drift and the bottom extraction tunnel, and the stress near the two sides decreases, and gradually increases and tends to be stable as it moves away; the shallow surrounding rock is in the post-peak failure stage, and the bearing capacity is reduced, but the bearing capacity of the deep surrounding rock increases, and finally recovers to the original rock stress state; comparative analysis: during the excavation of the bottom extraction tunnel and the excavation of the lower drift, the stress concentration is relatively stable, and the stress concentration is relatively stable. The stress distribution law between the two is similar, the peak stresses are 29.18MPa and 28.86MPa respectively, and the influence range is basically the same; in summary, the excavation of the 14050 working face mining tunnel has little effect on the surrounding rock stress of the bottom pumping tunnel, and its stress state is similar to that during the excavation of the bottom pumping tunnel; the same model processing method is used to analyze the distribution state of the plastic zone. The plastic zone range of the lower drift of the 14050 working face is limited, the depth of the plastic zone of the roof is 2m, the depth of the bottom plate is 3m, and the depth of the two sides is 2m; the roof is mudstone, and the strength is slightly higher than the sandy mudstone of the bottom plate, resulting in the depth of the plastic zone greater than the roof of the bottom pumping tunnel; the two sides of the lower drift are solid coal, with low strength and stress concentration, which will lead to the deepening of the plastic zone, mainly manifested as shear failure; during the mining of the 14050 working face, the morphology and depth of the plastic zone of the bottom pumping tunnel did not change, indicating that the excavation of the mining tunnel has little effect on the bottom pumping tunnel;

[0026] 6) Finally, the stress distribution law and the distribution morphology of the plastic zone during the mining of the working face were studied; the numerical simulation model was dissected along the dip direction, and stress cloud maps and plastic cloud maps were generated when the working face advanced 25m, and the stress distribution and plastic distribution of the working face when it advanced to 50m, 100m, 150m, 250m and 350m (simulation mining completed) were analyzed; according to the stress distribution diagram under different excavation lengths, it was known that the goaf of the 14050 working face formed a vertical stress reduction zone due to collapse, and the overall stress was lower than the initial ground stress, and a stress increase zone appeared on the outside of the mining tunnel; stress reduction zones also appeared in the surrounding rock of the bottom pumping tunnel, but the amplitude was smaller; with the advancement of the working face, the unloading range of the top and bottom plate rock layers expanded, and the stress concentration on both sides of the mining tunnel increased; after the working face was mined, although the goaf was filled, it could not be restored to the original rock stress state; on the whole, the working face The influence of face advancement on the stress state of the surrounding rock of the bottom pumping tunnel is limited; and by comparing the plastic distribution diagram, it can be analyzed that the depth of the plastic zone of the tunnel roof and floor is relatively small when not affected by mining, but with the mining advancement of the 14050 working face, the depth and range of the plastic zone change significantly; when the working face advances 25m, the plastic zone of the bottom pumping tunnel expands in the left shoulder corner, right wall and floor, but the change is not significant; as the working face advances to 50m, the limestone layer on the roof begins to show leaping phenomenon, the depth of the plastic zone increases to 3m, and the plastic zone on the left wall expands to 6m; when it advances to 100m, the plastic zones of the floor and left wall expand to 4m and 7m respectively, and the plastic zone of the roof is connected with the upper rock layer; at 150m, the plastic zone begins to appear on the roof of the limestone layer, and the overall change tends to be stable; finally, the plastic zone of the tunnel roof and left wall presents a large damage range, and the shape of the plastic zone changes to a rotating "butterfly" damage shape;

[0027] 7) Through multi-angle numerical simulation profile analysis, the law of mine pressure manifestation of large-section soft rock tunnels under different profiles is revealed, which provides an important reference for subsequent support design and mine pressure control; for this reason, a comprehensive support plan is formulated for the deep large-section soft rock tunnel of the 14050 working face. The plan includes the use of a new type of large-elongation impact-resistant anchor cable, which can adapt to the large deformation of the surrounding rock, does not break and fail during the deformation process, maintains the stability of the broken rock within the plastic zone, and effectively curbs the vicious expansion of the plastic zone boundary; and has the following performance advantages: large elongation, impact resistance, simple construction and economic savings; the specific support form includes the initial spraying of a 50mm thick reinforced concrete layer on the tunnel to seal the surrounding rock surface; the use of anchor cables, steel mesh, and 100mm shotcrete for support to reinforce the surrounding rock; grouting after initial support can enhance the stability of the surrounding rock; finally, the use of reinforced anchor cables to further enhance the strength of the support, ensure the safety and stability of the tunnel, and form a comprehensive support system; the specific support parameters are shown in Table 1;

[0028] Table 1 Specific support parameters

[0029]

[0030]

[0031] As can be seen from Table 1, the support scheme includes anchor cables, metal mesh, shotcrete and grouting anchoring of different specifications to ensure the safety and stability of the tunnel. The specifications of the top and side anchor cables are φ22.2×4100mm, the spacing is 800×1000mm, and the anchoring length is not less than 2000mm; this type of anchor cable has a large elongation of more than 10%, and the impact resistance is more than 10 joules; the specifications of the bottom plate anchor cable are φ22×6250mm, the spacing is 1300×2000mm, and the grouting process is used for anchoring.

[0032] 8) In order to observe the deformation characteristics of the surrounding rock during the excavation of the 14050 bottom extraction lane of Zhaogu No. 2 Mine and verify the rationality of the support parameters, the "cross point method" was used to collect the mine pressure data on site; the specific layout plan is: set the first measuring point at 528m of the lane excavation, and then arrange a measuring point every 10m, and continue to arrange points as the working face advances; after the measuring points are selected, use paint to mark and hang ropes, and the measuring points are arranged horizontally on the same section. Observations are carried out every two days to record the deformation of the roof and the two sides to reflect the surrounding rock deformation during the lane excavation process;

[0033] 9) The deformation and deformation rate of the top plate and the two sides of the surrounding rock of the 14050 working face bottom extraction tunnel obtained after the use of full-section anchor cable support measures as the excavation progresses are analyzed, and compared with the surrounding rock deformation state obtained under the original support scheme. For the deformation: under the original support scheme, the deformation of the tunnel surrounding rock is large, especially the movement of the two sides is large, the deformation of the top plate is also obvious, and the movement of the top and bottom plates is almost the same as the movement of the two sides; the tunnel surrounding rock continues to deform greatly, resulting in unsatisfactory support effect; under the support scheme of the present invention, the deformation of the top plate and the two sides of the surrounding rock is significantly reduced; the maximum and average deformations are much smaller than those of the original support scheme, indicating that the full-section support scheme effectively controls the deformation of the surrounding rock; for the deformation rate: under the original support scheme, the tunnel surrounding rock is After excavation, the deformation rate of the two sides is particularly high; the convergence rate of the two sides is higher than that of the top and bottom plates, and the deformation rate further accelerates with time; under the support scheme of the present invention, the deformation rate of the top plate and the two sides is significantly reduced; monitoring data show that the maximum and average values ​​of the deformation rate are much smaller than those under the original support scheme, and are within a controllable range, indicating that the deformation of the surrounding rock is well controlled; for the difference in deformation trends: under the original support scheme, the deformation amount and deformation rate continue to be high, the deformation trend of the surrounding rock is difficult to control, the support effect of the tunnel is not ideal, and the top plate and the two sides continue to deform; under the support scheme of the present invention, the deformation trend gradually tends to be stable, especially the deformation of the top plate and the two sides tends to be gentle after a certain period of time, indicating that the support scheme of the present invention can effectively limit the long-term deformation of the surrounding rock.

[0034] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A surrounding rock control method for a large-section soft rock tunnel, characterized in that: The following steps are involved: Collect the actual geological conditions of the mine and obtain geological data; Numerical simulation software builds a numerical model, substitutes geological data into the numerical model, performs excavation simulation, and obtains the law of mine pressure manifestation; The support plan is determined based on the law of mine pressure manifestation.

2. The surrounding rock control method of a large-section soft rock tunnel according to claim 1, characterized in that: Geological data include tunnel geological conditions, surrounding rock strength and surrounding rock physical and mechanical properties.

3. The surrounding rock control method of a large-section soft rock tunnel according to claim 1 or 2, characterized in that: The support scheme includes initial support scheme, anchor support scheme and enhanced support scheme.

4. The surrounding rock control method of a large-section soft rock tunnel according to claim 1, characterized in that: The numerical simulation software is FLAC3D numerical simulation software.

5. The surrounding rock control method of large-section soft rock tunnel according to claim 1, characterized in that: The mine pressure manifestation law includes the mine pressure manifestation law during bottom extraction tunnel excavation, the mine pressure manifestation law during mining tunnel excavation and the mine pressure manifestation law during working face mining.

6. The surrounding rock control method of large-section soft rock tunnel according to claim 1, characterized in that: The following steps are also included: The cross-point method is used to test the effectiveness of the reinforcement support scheme.

7. The surrounding rock control method for a large-section soft rock tunnel according to claim 1 or 5, characterized in that: Excavation simulation includes bottom extraction tunnel excavation simulation, upper drift excavation simulation, lower drift excavation simulation and working face mining simulation.

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