A method for identifying key blocks based on 3D laser point cloud

Abstract

The present invention relates to a method for identifying key blocks based on three-dimensional laser point clouds, which relates to the field of image processing and includes the following steps: arranging targets according to the scheme, obtaining ranging observation values, lateral scanning angle observation values, and longitudinal scanning angle observation values by using a three-dimensional laser scanner, calculating to obtain point cloud data and performing noise point elimination; creating a three-dimensional network for simulation, and determining the grid size and resolution. And according to the characteristics of the structural plane network, setting the initial fluid state and boundary conditions; mapping the point cloud data onto the three-dimensional grid, and performing fluid simulation on the grid by using the Lattice Boltzmann method; monitoring the dynamic evolution of the velocity or pressure of the fluid during the simulation process to identify key blocks. The present invention has the advantages of accurately predicting the future motion mode of the blocks by applying fluid parameters around the blocks and combining fluid mechanics to judge the motion mode of the blocks.

Description

Technical Field

[0001] The present invention relates to the technical field of image processing, and particularly to a method for identifying key blocks based on three-dimensional laser point cloud. Background Art

[0002] In hard and semi-hard rock formations, due to the existence of structural planes, the rock mass is cut into spatially interlocking blocks of different shapes. In the natural state, these blocks are in a state of static equilibrium. When artificial excavation of slopes and underground chambers is carried out, or a new load is applied to the rock mass, some of the blocks exposed on the free face lose their original static equilibrium state. Therefore, it is possible that these blocks first slide along the structural plane and become unstable, leading to the collapse of the entire rock mass system. These blocks that first become unstable are called "key blocks".

[0003] As the premise of block identification, the collection of structural plane information has been extensively studied by those skilled in the art in recent years, and methods such as artificial on-site contact measurement, drilling technology, and close-range photogrammetry have been proposed. Among them, the artificial on-site contact measurement has a large workload, low efficiency, and safety hazards such as cave-ins, landslides, and poisonous gases. Drilling technology has strict requirements for the hole-forming process and hole-forming quality, and the scale information of the structural plane cannot be obtained. The close-range photogrammetry has a high technical content, requires high-level technical personnel and expensive hardware equipment investment, and the image quality obtained in the tunnel is not necessarily qualified due to the influence of light.

[0004] Therefore, in view of the above deficiencies, a method for identifying key blocks based on three-dimensional laser point cloud needs to be provided. Summary of the Invention

[0005] (1) Technical Problems to be Solved

[0006] The technical problem to be solved by the present invention is to solve the problems that the existing rock mass measurement methods have many drawbacks and the accuracy of rock mass image processing is poor.

[0007] (2) Technical Solutions

[0008] To solve the above technical problems, the present invention provides a method for identifying key blocks based on three-dimensional laser point cloud, including the following steps:

[0009] Ⅰ. Arrange the targets according to the plan, use a three-dimensional laser scanner to obtain range measurement observations, horizontal scan angle observations, and vertical scan angle observations, calculate the point cloud data and perform noise elimination;

[0010] Ⅱ. Create a three-dimensional network for simulation, and determine the grid size and resolution. And according to the characteristics of the structural plane network, set the initial fluid state and boundary conditions;

[0011] Ⅲ. Map the point cloud data onto a three-dimensional grid and perform two fluid simulations on the grid using the Lattice Boltzmann method;

[0012] Ⅳ. Monitor the dynamic evolution of the velocity or pressure of the fluid during the simulation to identify key blocks.

[0013] As a further illustration of the present invention, preferably, set a velocity or pressure threshold for each grid cell, and mark the grid cell as a movable block when the threshold is exceeded.

[0014] As a further illustration of the present invention, preferably, perform a mechanical analysis or seepage rate analysis on the marked movable blocks to determine whether the blocks are in motion modes of detaching from the rock mass, single-sided sliding, and double-sided sliding to determine whether they are key blocks.

[0015] As a further illustration of the present invention, preferably, when the structural plane of the block is not parallel to the movement direction of the block, the normal reaction force on each structural plane is 0, and the movement direction of the block is consistent with the direction of the resultant active force, then the block is detaching from the rock mass.

[0016] As a further illustration of the present invention, preferably, when the movement direction of the block is parallel to a certain plane and does not detach from the plane, the structural planes other than this plane are detached from the rock mass, and there is

[0017]

[0018] where

[0019] is the projection of the resultant active force direction on this plane, and is the same as the movement direction of the block;

[0020] is the upward normal vector of this plane;

[0021] is the resultant active force direction, and there is is the normal vector of this plane;

[0022] then the block is single-sided sliding.

[0023] As a further illustration of the present invention, preferably, when

[0024]

[0025]

[0026] and

[0027]

[0028]

[0029] When this occurs, the block experiences double-sided sliding, where

[0030] is the resultant force projected onto planes i and j;

[0031] are the upward normal vectors of planes i and j.

[0032] As a further illustration of the present invention, preferably, the Mohr-Coulomb criterion is adopted to analyze the stability of the blocks in three sliding modes, and the stability coefficient is obtained to determine whether the key blocks are stable.

[0033] As a further illustration of the present invention, preferably, when the block is in a state of detaching from the rock mass, the stability coefficient F s = 0.

[0034] As a further illustration of the present invention, preferably, when the block is in a state of single-sided sliding, the stability coefficient F s is:

[0035]

[0036] where

[0037] N i is the component of the resultant active force in the normal direction on the sliding surface;

[0038] is the internal friction angle of the sliding surface;

[0039] C i is the cohesion of the sliding surface;

[0040] S i is the area of the sliding surface;

[0041] P i is the component of the resultant active force in the tangential direction on the sliding surface.

[0042] As a further illustration of the present invention, preferably, when the block is in a state of double-sided sliding, the stability coefficient F s is:

[0043]

[0044] where

[0045] N i 、N j are the resultant active forces Components in the normal direction on two sliding surfaces;

[0046] Are the internal friction angles of the two sliding surfaces respectively;

[0047] C i 、C j Are the cohesion forces of the two sliding surfaces respectively;

[0048] S i 、S i Are the areas of the two sliding surfaces respectively;

[0049] P ij Is the resultant force of the active forces Components in the tangential direction on two sliding surfaces.

[0050] (III) Advantageous Effects

[0051] The above technical solution of the present invention has the following advantages:

[0052] By applying the Lattice Boltzmann method to identify key blocks, different permeabilities are set for the structural planes. According to the flow behavior of the simulated fluid in the structural plane grid, the fluid state on the grid is updated through iterative calculation, and the movement mode of the block is judged, so as to accurately analyze the key blocks and provide accurate information for subsequent tunnel support. Description of the Drawings

[0053] Figure 1 Is the schematic diagram of the movement of the block detaching from the rock mass of the present invention;

[0054] Figure 2 Is the schematic diagram of the single-sided sliding of the block of the present invention;

[0055] Figure 3 Is the schematic diagram of the double-sided sliding of the block of the present invention;

[0056] Figure 4 Is the tunnel point cloud map of the present invention;

[0057] Figure 5 Is the comparison diagram between the actually exposed structural plane of the first block and the identified structural plane of the present invention;

[0058] Figure 6 Is the structural schematic diagram of the first block of the present invention;

[0059] Figure 7 Is the comparison diagram between the actually exposed structural plane of the second block and the identified structural plane of the present invention;

[0060] Figure 8 Is the structural schematic diagram of the second block of the present invention;

[0061] Figure 9 It is a comparison diagram of the actual exposed structural plane of the No. 3 block of the present invention and the identified structural plane;

[0062] Figure 10 It is a schematic diagram of the structure of the No. 3 block of the present invention. Specific embodiments

[0063] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0064] A method for identifying key blocks based on three-dimensional laser point cloud, comprising the following steps:

[0065] Ⅰ. Conduct a survey of the environment, determine the scanning range and site conditions, comprehensively consider the scanning range and the length, width and height of the tunnel, and select a scanning position to design a target layout plan. After arranging the targets according to the plan, set up a three-dimensional laser scanner, use the three-dimensional laser scanner to obtain ranging observation values, lateral scanning angle observation values and longitudinal scanning angle observation values, calculate the point cloud data and perform noise elimination through Gaussian filtering, median filtering or average filtering, etc.

[0066] Ⅱ. Create a three-dimensional network for simulation, and determine the grid size and resolution to retain the details of the key blocks. And according to the characteristics of the structural plane network, set the initial fluid state and boundary conditions.

[0067] Ⅲ. Map the point cloud data onto the three-dimensional grid, use the Lattice Boltzmann method to simulate the flow behavior of the fluid in the structural plane network, and update the fluid state on the grid through iterative calculation; based on the fluid simulation results, extract the position and characteristics of the structural plane network, and then perform visualization and analysis to study the distribution and properties of the structural planes.

[0068] After that, further use the Lattice Boltzmann method for further fluid simulation; generally, gas is selected as the fluid, and combined with Darcy's law, there is:

[0069]

[0070] Q is the flow rate of the fluid flowing through the structural plane (grid contact surface) A;

[0071] K is the permeability;

[0072] μ is the fluid viscosity;

[0073] is the pressure gradient. For gas permeability measurement, there is

[0074]

[0075] where, P i and P0 are the inlet and outlet pressures, and L is the grid length.

[0076] Ⅳ. Monitor the dynamic evolution of the fluid velocity or pressure during the simulation. The fluid velocity can also be calculated by Darcy's formula. Set a velocity or pressure threshold for each grid cell. When the threshold is exceeded, it indicates that there are pores between the grid cells and there is a certain risk of slip. Then mark the grid cell as a movable block.

[0077] Ⅴ. Conduct a mechanical analysis on the marked movable blocks to determine whether the blocks are in the motion modes of detaching from the rock mass, single-sided sliding, and double-sided sliding to determine whether they are key blocks.

[0078] Specifically:

[0079] As Figure 1 shown, when neither the structural plane of the block nor the motion direction of the block is parallel, and the normal reaction force on each structural plane is 0, and the motion direction of the block is consistent with the direction of the resultant active force, at this time, it is determined that the block is detaching from the rock mass.

[0080] As Figure 2 shown, when the motion direction of the block is parallel to a certain plane and does not detach from the plane, the structural planes other than this plane are detached from the rock mass, and there is

[0081]

[0082] where

[0083] is the projection of the resultant active force direction on this plane, and is the same as the motion direction of the block;

[0084] is the upward normal vector of this plane;

[0085] is the resultant active force direction, and there is is the normal vector of this plane;

[0086] Then the block is single-sided sliding.

[0087] As Figure 3 shown, when the following conditions are met

[0088]

[0089]

[0090] And

[0091]

[0092]

[0093] When it is, the block body is in double-sided sliding, where

[0094] is the resultant force The projections on planes i and j;

[0095] is the upward normal vector of planes i and j.

[0096] Ⅵ. After identifying the motion modes of the key block bodies, the Mohr-Coulomb criterion is adopted to conduct a stability analysis on the block bodies with three sliding modes, and the stability coefficient is obtained to judge whether the key block bodies are stable.

[0097] Specifically:

[0098] 1. When the block body is in a state of detaching from the rock mass, the stability coefficient F s = 0.

[0099] 2. When the block body is in a state of single-sided sliding, the stability coefficient F s is:

[0100]

[0101] Where

[0102] N i is the component of the resultant active force along the normal direction on the sliding surface;

[0103] is the internal friction angle of the sliding surface;

[0104] C i is the cohesion of the sliding surface;

[0105] S i is the area of the sliding surface;

[0106] P i is the component of the resultant active force along the tangent direction on the sliding surface.

[0107] 3. When the block body is in a state of double-sided sliding, the stability coefficient F s is:

[0108]

[0109] Among them

[0110] N i 、N j are the components of the resultant driving force along the normal direction on the two sliding surfaces;

[0111] are the internal friction angles of the two sliding surfaces respectively;

[0112] C i 、C j are the cohesion forces of the two sliding surfaces respectively;

[0113] S i 、S j are the areas of the two sliding surfaces respectively;

[0114] P ij is the component of the resultant driving force along the tangential direction on the two sliding surfaces.

[0115] Through the above method, not only can the movable blocks be effectively identified, but also the motion modes of the movable blocks can be analyzed to determine whether they belong to key blocks. In addition, based on the Lattice Boltzmann method, the flow behavior of fluids in the fracture network can be simulated to generate a simulated network with a similar fracture distribution. Then, the block data composed of the fitted fractures is integrated, and physical values such as seepage rate and pressure are assigned based on the block data for further fluidity analysis, and then it can be determined whether it is a key block. The blocks analyzed based on this method can be closer to the actual situation of the rock mass in the tunnel. Combining with the stability analysis method of the blocks, more accurate information can be provided for the subsequent support and even the stability of the tunnel structure. In addition, according to the water content of the rock mass, the simulated fluid can be replaced with liquid to judge the influence on the stability of the rock mass at a certain water content, so as to improve the support safety.

[0116] To verify the feasibility, the present invention provides an example analysis of the No. 7 tunnel of Xulong Hydropower Station, as follows:

[0117] At the beginning of the measurement, the target is set, mainly using more than three common targets as the landmark points for station splicing. Then, the data collected is manually denoised by Poly-works, and the obvious peripheral scattered points are removed. Then, the data is thinned to obtain the Figure 4 point cloud data diagram as shown.

[0118] The obtained point cloud diagram is analyzed by the above method to obtain the Figure 4 ​​Three movable blocks are marked. Among them, block #1 is located on the left side wall of the upstream of the tunnel, block #2 is located on the right side wall of the downstream of the tunnel, and block #3 is located on the right side wall of the upstream. Combining Figure 5 、 Figure 7 and Figure 9 , the comparison diagram of the structural plane of the identified block and the actual photo can be obtained. It can be seen from the comparison diagram that the method proposed by the present invention can accurately identify the surrounding rock blocks of the tunnel.

[0119] According to the block stability analysis method proposed by the present invention, as Figure 6 shown, the specific shape and sliding mode of the block can be intuitively seen. According to the vertex coordinates of the four planes in the point cloud data, the sliding surface area and volume of block #1 are calculated. The calculation results are shown in Table 1,

[0120] Table 1 Parameter information of key block #1

[0121]

[0122] According to the above formula, the stability coefficient of the block can be calculated as 0.8, which is less than the temporary tunnel stability coefficient of 1.5. Therefore, it can be determined that block #1 is a key block, with a low stability coefficient, poor stability, and large weight, and it needs to be supported during the tunnel construction process.

[0123] As Figure 8 shown, it can be seen that block #2 slides unidirectionally along the bottom structural plane. According to the steps of calculating block #1, the stability coefficient of block #2 is calculated as 0.94, which is less than the temporary tunnel stability coefficient of 1.5. Therefore, it can be determined that block #2 is a key block. The calculation results of key block 2 are shown in Table 2. However, due to factors such as excavation vibration, block #2 has fallen and will not pose a threat to the tunnel construction.

[0124] Table 2 Parameter information of key block #2

[0125]

[0126] As Figure 10 shown, according to the steps of calculating block #1, the stability coefficient of block #3 is calculated as 0.11, which is less than the temporary tunnel stability coefficient of 1.5. Therefore, it can be determined that block #3 is a key block. The calculation results of key block #3 are shown in Table 3. Its stability coefficient is low, and its stability is poor. It needs to be supported during the tunnel construction process.

[0127] Table 3 Parameter information of key block #3

[0128]

[0129] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for identifying key blocks based on three-dimensional laser point cloud, characterized in that: Including the following steps, Ⅰ. Arrange the targets according to the plan, use a three-dimensional laser scanner to obtain ranging observation values, lateral scanning angle observation values, and longitudinal scanning angle observation values, calculate the point cloud data and perform noise point exclusion; Ⅱ. Create a three-dimensional network for simulation, determine the grid size and resolution, and set the initial fluid state and boundary conditions according to the characteristics of the structural plane network; Ⅲ. Map the point cloud data onto the three-dimensional grid, and perform two fluid simulations on the grid using the Lattice Boltzmann method; Simulate the flow behavior of the fluid in the structural plane network, update the fluid state on the grid through iterative calculation; based on the fluid simulation results, extract the position and characteristics of the structural plane network; Monitor the dynamic evolution of the velocity or pressure of the fluid during the simulation, where the velocity of the fluid is calculated by the Darcy formula; Ⅳ. Set velocity or pressure thresholds for each grid cell. When the threshold is exceeded, it indicates that there are pores between the grid cells and there is a risk of slip. Then mark the grid cell as a movable block. Monitor the dynamic evolution of the velocity or pressure of the fluid during the simulation, perform mechanical analysis or seepage rate analysis on the marked movable blocks, and judge whether the block is in the movement modes of detaching from the rock mass, single-sided sliding, and double-sided sliding to determine whether it is a key block; adopt the Mohr-Coulomb criterion to perform stability analysis on the blocks in the three sliding modes, obtain the stability coefficient to judge whether the key block is stable; Among them, When the block is in a double-sided sliding state, the stability coefficient F s is as follows: Among them N i , N j is the resultant of the driving forces component in the normal direction on two sliding surfaces; are the internal friction angles of the two sliding surfaces respectively; C i and C j are the cohesive forces of two sliding surfaces respectively; S i and S j are the areas of two sliding surfaces respectively; P ij is the resultant force of the driving forces and the component along the tangential direction on the two sliding surfaces.

2. The key block recognition method based on three-dimensional laser point cloud according to claim 1, wherein: When the structural plane of the block is not parallel to the movement direction of the block, the normal reaction force on each structural plane is 0, and the movement direction of the block is consistent with the direction of the resultant active force, then the block is detaching from the rock mass.

3. The key block recognition method based on 3D laser point cloud according to claim 2, characterized in that: When the movement direction of the block is parallel to a certain plane and does not detach from the plane, the structural planes other than this plane in the movement direction are detached from the rock mass, and there is Among them is the direction of the resultant force of the driving force is the projection on this plane, and is the same as the moving direction of the block is the upward normal vector of the plane; is the direction of the resultant of the driving forces, and there is is the normal vector of this plane; Then the block is single-sided sliding.

4. A key block recognition method based on three-dimensional laser point cloud according to claim 3, characterized in that: When meeting And At this time, the block is double-sided sliding, where For the resultant force Projections on planes i and j; are the upward normal vectors of planes i and j.

5. A key block recognition method based on three-dimensional laser point cloud according to claim 1, characterized in that: When the block is in a state of being separated from the rock mass, the stability coefficient F s = 0.

6. The key block recognition method based on three-dimensional laser point cloud according to claim 1, wherein: When the block is in the state of single-sided sliding, the stability coefficient F s is as follows: Among them N i is the resultant force of the driving forces component along the normal direction on the sliding surface; is the internal friction angle of the sliding surface; C i is the cohesion of the sliding surface; S i is the area of the sliding surface; P i is the resultant of the active forces and the component along the tangent direction on the sliding surface.

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