Numerical simulation calculation and identification method for loose circle of tunnel surrounding rock

Abstract

The invention discloses a tunnel surrounding rock loosening circle numerical simulation calculation identification method. The method comprises the steps that firstly, a three-dimensional numerical calculation model is established according to the actual working condition of tunnel excavation, a plurality of measuring lines are arranged on the tunnel cross section of the model in different directions, and a plurality of monitoring points are arranged on each measuring line; secondly, simulating the tunnel excavation process through numerical simulation software, obtaining displacement data of each monitoring point after excavation, and then processing the displacement data of each monitoring point, including displacement decomposition and change rate calculation, and drawing a radial displacement curve and a change rate curve; and finally, determining the boundary of the loose circle according to the radial displacement change rate curve, determining the loose circle range of the whole tunnel cross section through the displacement rate slowdown points on the measuring lines, and completing the final recognition of the tunnel surrounding rock loose circle. The method does not depend on complex rock mechanical parameters and error influence of artificial subjective judgment, is simple and convenient to identify, and is convenient for direct application in engineering.

Description

Technical Field

[0001] The present invention belongs to the field of numerical simulation calculation, and particularly relates to a method for numerically simulating and identifying the loosening zone of tunnel surrounding rock. Background Art

[0002] With the gradual expansion of the scale of tunnel engineering construction, higher requirements are put forward for tunnel construction, making the geological conditions faced during tunnel construction increasingly complex. Tunnel construction shows a trend of "deep, long, and large", and a series of engineering problems such as excessive deformation and cracking of the support structure, and tunnel collapse will be faced during construction, seriously threatening personal and property safety.

[0003] The loosening zone can accurately describe the range of the relaxation and fracture zone generated in the tunnel surrounding rock and the elastoplastic state of the surrounding rock. After years of theoretical development and engineering practice, the theory of the surrounding rock loosening zone has played a huge guiding role in the design of tunnel support structures. Accurately, quickly, and economically determining the range of the surrounding rock loosening zone to guide tunnel construction has important practical engineering value and significance.

[0004] Regarding the determination of the loosening zone of tunnel surrounding rock, there are currently three common methods: on-site measurement, numerical simulation, and theoretical calculation. Among them, numerical simulation is superior to the other two methods in terms of economy, efficiency, flexibility, visualization, and intuitiveness. However, when processing the simulation calculation results, how to scientifically and accurately identify the range of the loosening zone has always been a difficult problem. Currently, when using numerical simulation to calculate the loosening zone, the methods for judging the range of the loosening zone are mainly the following categories:

[0005] (1) It is considered that the plastic zone obtained by numerical simulation can be called the plastic loosening zone, that is, the range of the plastic loosening zone is regarded as the range of the surrounding rock loosening zone.

[0006] (2) The maximum tensile strain criterion is used to explain the loosening failure of the surrounding rock. That is, when the tensile strain value of the surrounding rock in the numerical simulation calculation results exceeds the ultimate tensile strain value of the rock, the surrounding rock enters the loosening state, and the range of the unit body in this loosening state in the surrounding rock is the range of the surrounding rock loosening zone.

[0007] (3) The plastic loosening zone, volumetric strain nephogram, and shear strain nephogram obtained by numerical calculation are comprehensively used to judge the range of the loosening zone. This method believes that within the loosening zone, the volumetric strain is positive, and the unit has obvious yielding. In addition, near the boundary of the loosening zone, there should be an obvious mutation in the shear deformation of the unit. Considering these three factors comprehensively, the overlapping range is the range of the surrounding rock loosening zone.

[0008] Currently, quite a number of scholars have used one of the above three discrimination criteria and adopted numerical simulation methods to determine the range of the loosening zone. The above three methods have different limitations:

[0009] The first method is simple and easy to implement, with obvious simulation results and is easy to judge the range of the loosening zone. It is also the most widely used method for determining the range of the loosening zone when using simulation. However, its disadvantage is that the judgment basis is somewhat single and cannot reflect the volume change of the surrounding rock.

[0010] The second method has the disadvantage that it is very difficult to obtain the uniaxial tensile strength of the rock in the engineering field, especially under the conditions of high in-situ stress and soft rock. It is extremely difficult to prepare rock specimens. Even if the specimen preparation is successful, it is restricted by experimental conditions and experimental methods, and the effect may not be ideal. If the recommended values in relevant specifications or relevant literature are referred to, due to the complex and changeable engineering geological conditions, it is difficult to match the actual engineering geological situation. From the research done by predecessors, when using this method for judgment, the error range is also the largest among these three methods.

[0011] The third method considers both the calculated plastic loosening range and combines the volume change nephogram, with good comprehensiveness. However, it may cause mutual interference, and generally speaking, the number of applications is small and the experience accumulation is slightly insufficient.

[0012] In addition, some scholars also judge the range of the loosening zone according to the change of the maximum principal stress difference of the surrounding rock during the iterative calculation process (Equation 1).

[0013]

[0014] In the formula: is the maximum principal stress, is the minimum principal stress, is the maximum principal stress difference, is the cohesion of the rock, is the internal friction angle of the rock.

[0015] It is considered that: the loosening zone of the surrounding rock includes the loosening and fractured zone (residual strength zone or plastic flow zone) and the plastic softening zone in the surrounding rock. The stress is lower than the initial stress, and all belong to the unloading zone. According to the M-C criterion, the maximum principal stress difference of the surrounding rock The area where it is greater than 0 is the plastic zone (including the loosening zone), as shown in Formula 1. The rock in this area loses its bearing capacity, and at this time is a constant positive value. Through actual verification, is not a constant positive value. According to its judgment curve, for the undisturbed area, the major and minor principal stresses are fixed values, so the principal stress difference should be a fixed value, which is contrary to the given judgment curve, and this method is also not applicable. Summary of the Invention

[0016] The present invention provides a numerical simulation calculation and identification method for the loosening zone of tunnel surrounding rock in view of the deficiencies of the prior art.

[0017] The present invention includes the following steps:

[0018] Model construction: According to the actual working conditions of tunnel excavation, a three-dimensional numerical calculation model is established, and the boundary conditions and initial stress field of the model are set according to the actual engineering conditions;

[0019] Measuring point layout: A plurality of measuring lines are arranged along different directions on the tunnel cross-section of the model, and a plurality of monitoring points are arranged on each measuring line for monitoring the displacement change of the surrounding rock. The measuring point layout is based on the three-dimensional numerical calculation model established in the model construction step;

[0020] Simulation calculation: The process of tunnel excavation is simulated through numerical simulation software to obtain the displacement data of each monitoring point after excavation. The simulation calculation is based on the three-dimensional numerical calculation model established in the model construction step and the monitoring points arranged in the measuring point layout step;

[0021] Displacement data processing: The displacement data of each monitoring point is processed, including displacement decomposition and change rate calculation, and the radial displacement curve and change rate curve are drawn. The displacement data processing is based on the displacement data obtained in the simulation calculation step;

[0022] Loose circle range identification: The boundary of the loose circle is determined according to the radial displacement change rate curve, and the loose circle range of the entire tunnel cross-section is determined through the displacement rate slowdown points on each measuring line, and the final identification of the loose circle of the tunnel surrounding rock is completed.

[0023] Advantages of the present invention: On the basis of comparative analysis of the existing simulation calculation methods for loose circle identification, the present invention proposes a method for loose circle identification based on the displacement of the surrounding rock. This method does not depend on complex rock mechanics parameters and the error influence of subjective judgment by people, and the identification is simple and convenient for direct application in engineering. Description of the drawings

[0024] Figure 1 It is a schematic diagram for the construction of the calculation model;

[0025] Figure 2 It is a layout diagram of the monitoring lines and monitoring points;

[0026] Figure 3 It is a radial displacement curve diagram of the monitoring points;

[0027] Figure 4 It is a radial displacement rate curve diagram of the monitoring points. Specific implementation manners

[0028] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work belong to the scope of protection of the present invention.

[0029] During the tunnel excavation process, the formation of the loosening zone will significantly affect the displacement distribution characteristics of the surrounding rock. The rock mass within the loosening zone is greatly affected by the disturbance, the rock mass is broken, and the displacement change rate increases. Along the radial direction from the tunnel wall to the deep part of the surrounding rock, the disturbance of the rock mass gradually decreases, and the displacement shows a decreasing trend. At the boundary of the loosening zone, the rock mass displacement shows an obvious mutation. Therefore, the range of the loosening zone can be determined by using the displacement change gradient of the surrounding rock at different depths. This discrimination method is consistent with the discrimination principle of the actual loosening zone range measured by the multi-point displacement meter, has the advantages of being scientific, simple, and accurate, does not rely on complex rock mechanics parameters as the definition basis, and does not require artificial determination, excluding subjective influence.

[0030] As Figure 1 shown, a numerical simulation calculation and identification method for the loosening zone of tunnel surrounding rock provided by an embodiment of the present application includes the following steps:

[0031] (1) Model construction

[0032] According to the actual working conditions of tunnel excavation, a three-dimensional numerical calculation model is established. The boundary conditions and initial stress field of the model are set according to the actual engineering conditions, providing a basic framework for subsequent numerical simulations. Specifically:

[0033] The calculation model takes 5 times the excavation span to the left, right, and downwards, and the upper part and longitudinal direction are determined according to the actual working conditions. Constraints in the XYZ directions are applied to the bottom surface, the free surface is taken for the upper boundary, displacement constraints in the X direction are applied to the side surfaces, and displacement constraints in the Y direction are applied to the tunnel excavation direction (Y direction). The initial stress field is calculated according to the self-weight stress.

[0034] Furthermore, the construction of the model can be determined according to the actual working conditions, and the size and constraints are mainly based on conforming to the actual situation.

[0035] (2) Measuring point layout

[0036] On the tunnel cross-section of the model, multiple measuring lines are arranged in different directions, and multiple monitoring points are arranged on each measuring line to monitor the displacement change of the surrounding rock. The measuring point layout is based on the three-dimensional numerical calculation model established in the model construction step, providing specific positions for subsequent displacement monitoring. Specifically:

[0037] After the surrounding rock is disturbed by excavation, displacements will occur in three-dimensional space. However, in actual engineering, the tests and the design of support parameters are all based on the cross-section. In addition, the deformation along the longitudinal direction of the tunnel is not the key consideration for support. Therefore, in the embodiments of the present application, the measuring lines and measuring points are all on the two-dimensional cross-section.

[0038] Further, starting from the right horizontal direction, a measuring line is arranged every 30°, and a monitoring point is arranged every 0.2 m on the measuring line. The arrangement of the measuring lines and measuring points is shown in Figure 2 the figure.

[0039] Further, the arrangement of the measuring line angle, the measuring line length, and the measuring point spacing determines the calculation accuracy and calculation speed, which can be freely determined by the user according to the actual situation. The denser the measuring lines and measuring points are, the higher the accuracy of the calculated loose circle range will be, and the corresponding calculation time will be longer.

[0040] (3)Simulation calculation

[0041] Simulate the tunnel excavation process through numerical simulation software to obtain the displacement data of each monitoring point after excavation. The simulation calculation is based on the model established in the model construction step and the monitoring points arranged in the measuring point layout step, providing the original data for subsequent displacement data processing; specifically:

[0042] Simulate the tunnel excavation and export the displacements of each monitoring point in the x and z directions and for the next calculation.

[0043] Further, the simulation calculation software can be determined according to needs. It is recommended to use FLAD3D, and the displacements of the measuring points can be quickly exported through FISH language.

[0044] Further, for the convenience of subsequent calculations, the measuring point information is described as follows:

[0045] Any monitoring point is represented by Here, represents the angle of the monitoring line where the monitoring point is located, ranging from 0 to 360 degrees, which is determined according to the number of measuring lines set in the early stage. n represents the number of the monitoring point. Starting from the point close to the tunnel excavation boundary, it is marked as point No. 1, and the subsequent monitoring points are numbered sequentially. For example represents the second monitoring point on the measuring line with an angle of 30°.

[0046] Before the simulated excavation, the coordinates of the monitoring point are , and after the excavation, the monitoring point displaces to a new position point, denoted as , where , .

[0047] The monitoring point moves from to , the displacement generated is as follows:

[0048]

[0049] (4)Displacement data processing

[0050] Process the displacement data of each monitoring point, including displacement decomposition and change rate calculation, and draw the radial displacement curve and change rate curve. The displacement data processing is based on the displacement data obtained in the simulation calculation step, providing an analysis basis for the subsequent identification of the loose circle range; specifically:

[0051] After obtaining the displacement value of the measuring point , and the coordinates after displacement of the measuring point , according to vector decomposition, decompose the displacement into along the measuring line and perpendicular to the measuring line. Here is the displacement value of the measuring point along the tunnel radius after tunnel excavation. Accordingly, the radial displacement of any monitoring point on any measuring line can be obtained, and the radial displacement of monitoring points at different depths is drawn Figure 3 as shown in Figure 4 . To more intuitively reflect the change rate of the radial displacement of each measuring point, the derivative of each measuring point is calculated and the change rate curve is drawn, as shown in

[0052] (5)Discrimination of the loose circle range

[0053] Determine the boundary of the loose circle according to the radial displacement change rate curve, and determine the loose circle range of the entire tunnel cross-section through the displacement rate slowdown points on each measuring line, completing the final identification of the loose circle of the tunnel surrounding rock. Specifically:

[0054] Through Figure 4 it can be clearly seen that the displacement rate slowdown point is the boundary point of the loose circle range. Determine the boundary points of the loose circle of each measuring line in turn, and finally obtain the loose circle range of the entire tunnel cross-section.

[0055] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only the specific embodiments. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A numerical simulation calculation and identification method for the loosening zone of tunnel surrounding rock, characterized in that, It includes the following steps: Model construction: According to the actual working conditions of tunnel excavation, a three-dimensional numerical calculation model is established, and the boundary conditions and initial stress field of the model are set according to the actual engineering conditions; Measuring point layout: Multiple measuring lines are arranged along different directions on the tunnel cross-section of the model, and multiple monitoring points are arranged on each measuring line to monitor the displacement changes of the surrounding rock. The measuring point layout is based on the three-dimensional numerical calculation model established in the model construction step; Simulation calculation: The process of tunnel excavation is simulated through numerical simulation software to obtain the displacement data of each monitoring point after excavation. The simulation calculation is based on the three-dimensional numerical calculation model established in the model construction step and the monitoring points arranged in the measuring point layout step; Displacement data processing: The displacement data of each monitoring point is processed, including displacement decomposition and change rate calculation, and radial displacement curves and change rate curves are drawn. The displacement data processing is based on the displacement data obtained in the simulation calculation step; Loose circle range identification: The boundary of the loose circle is determined according to the radial displacement change rate curve, and the loose circle range of the entire tunnel cross-section is determined through the displacement rate slowdown points on each measuring line, and the final identification of the loose circle of the tunnel surrounding rock is completed.

2. The numerical simulation calculation and identification method for the loosening zone of tunnel surrounding rock according to claim 1, wherein In the model construction step, the calculation model takes 5 times the excavation span to the left, right, and down; constraints in the XYZ directions are applied to the bottom surface, displacement constraints in the X direction are applied to the side surfaces, and displacement constraints in the Y direction are applied to the tunnel excavation direction.

3. The numerical simulation calculation and identification method for the loosening zone of tunnel surrounding rock according to claim 1 or 2, characterized in that, The initial stress field is calculated according to the self-weight stress.

4. The numerical simulation calculation and identification method for the loosening zone of tunnel surrounding rock according to claim 1, characterized in that, In the measuring point layout step, the arrangement of the measuring line angle, measuring line length, and measuring point spacing is adjusted according to the actual engineering requirements to balance the calculation accuracy and calculation speed.

5. The numerical simulation calculation and identification method for the loosening zone of tunnel surrounding rock according to claim 4, characterized in that, In the measuring point layout step, starting from the right horizontal direction, a measuring line is arranged every 30°, and a monitoring point is arranged every 0.2 meters on the measuring line.

6. The numerical simulation calculation and identification method for the loosening zone of tunnel surrounding rock according to claim 1, characterized in that, In the simulation calculation step, the FLAD3D software is used for numerical simulation, and the displacement of the measuring points is quickly exported through the FISH language.

7. The numerical simulation calculation and identification method for the loose zone of tunnel surrounding rock according to claim 1, characterized in that In the displacement data processing step, the displacement of the monitoring point is decomposed into the radial displacement along the measuring line and the transverse displacement perpendicular to the measuring line.

8. The numerical simulation calculation and identification method for the loosening zone of tunnel surrounding rock according to claim 7, characterized in that Among them, the radial displacement is used to draw the radial displacement curve.

9. The numerical simulation calculation and identification method for the loosening zone of tunnel surrounding rock according to claim 8, characterized in that In the loose circle range identification step, by drawing the radial displacement rate curve, the displacement rate slowdown point is determined as the boundary of the loose circle.

10. The numerical simulation calculation and identification method for the loosening zone of tunnel surrounding rock according to claim 9, characterized in that, The loose circle boundary points of each measuring line are determined in turn, and finally the loose circle range of the entire tunnel cross-section is obtained.

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