CN111324968B - Laying method of microseismic monitoring sensors for inclined stratum tunnel engineering - Google Patents

Abstract

The invention provides a method for arranging microseismic monitoring sensors for inclined strata tunnel engineering, and belongs to the technical field of underground engineering safety monitoring. This method firstly determines the main incidence direction of P waves of microseismic events in the monitoring area; then establishes the regional construction coordinate system and the inclined layered stratigraphic model that conforms to the geological characteristics of the monitoring area. Ignore the influence of interference waves such as reflected waves and refracted waves, and further establish the ray path equation of the P wave; then substitute the ray parameters, formation parameters, and wave velocity parameters into the ray equation in turn to obtain the optimal position of the sensor layout in the inclined formation medium; finally Solving the sensor positions corresponding to the other main incidence directions of P waves of each seismic source in the monitoring area is the optimal layout position of the sensors in the three-dimensional monitoring area. The method is simple in calculation and accurate in results, and can be applied to the optimal position design of microseismic monitoring sensors in underground projects with inclined layered media such as highway tunnels, hydropower tunnels, and underground mines.

Description

A method for deploying microseismic monitoring sensors for tunnel engineering in inclined strata

Technical Field

The invention relates to the technical field of underground engineering safety monitoring, and in particular to a method for arranging microseismic monitoring sensors for inclined stratum tunnel engineering.

Background Art

Sedimentary rocks with layered structures in nature account for about 2/3 of the land area, and my country accounts for 77.3%, and many metamorphic rocks also have significant layered structural characteristics. my country has become the world's fastest-growing underground engineering construction market, especially in the special landforms dominated by mountains in the western region. A large number of inclined layered rock stability problems will be encountered in underground engineering construction, which puts forward new requirements and challenges for builders. Microseismic monitoring technology has been widely used in the field of underground engineering safety monitoring due to its advantages such as continuity, regionality and real-time monitoring, such as the construction monitoring of Letuan Tunnel of Binlai Expressway, TBM construction monitoring of No. 3 diversion tunnel of Jinping Hydropower Station, safety monitoring of dam slope of Ertan Hydropower Station, and safety monitoring of tailwater connection pipe on the left bank of Baihetan Hydropower Station. The spatial layout research of microseismic monitoring sensor network is the primary task of microseismic monitoring technology research: the advantages and disadvantages of sensor layout location seriously restrict the operation stability, data reliability, and microseismic positioning accuracy and interpretation accuracy of microseismic monitoring system. These in turn determine the rationality of the safety assessment of underground projects, such as the development trend of potential cracks that may cause landslides or tunnel collapses.

Few scholars at home and abroad have conducted systematic research on the optimization design method of microseismic monitoring network for underground engineering in inclined strata. Most of the engineering sites refer to the relevant theories or methods of underground microseismic monitoring network or network layout in the field of earthquake monitoring in coal mines. For example, the microseismic system of the Yuanyanghui Tunnel in Shanxi adopts the "in-field", "near-field" and "far-field" sensor layout methods in the field of coal mines; the design method of the Guangshan No. 1 Tunnel in Yunnan adopts the overall monitoring of the whole area and the key monitoring of the face; the left bank slope of Jinping I Hydropower Station is based on the D value optimization theory, combined with the microseismic event source positioning accuracy, monitoring system sensitivity requirements, engineering conditions and monitoring purposes. The selection of microseismic sensors and the optimization design of the monitoring system network are carried out; when arranging the sensors of the microseismic monitoring system for ground pressure disasters in the residual mining area of Xianglushan Tungsten Mine, the first consideration is to have a small positioning error in the key monitoring area and a high sensitivity to small magnitude events, while taking into account the limitations of the on-site layout conditions; the optimal monitoring system configuration scheme for the microseismic monitoring requirements of the first mining area of Dongguashan Copper Mine is obtained through the D value theory, and the optimization problem of the network layout of the microseismic monitoring system for large-scale deep well mining is studied and determined to meet the requirements.

In summary, these current methods have the following disadvantages: (1) Related deployment methods such as "inside-outside field", "far-near field", and "overall coverage-regional key monitoring" only plan the sensor deployment area from a macro qualitative perspective, and cannot provide specific coordinates that can be directly used for on-site installation; (2) The core of theoretical algorithms such as D value optimization and C value optimization are all solved in an ideal environment where the medium is uniform or the wave velocity is constant, without considering the impact of the inclined layered strata of the underground project, which is inconsistent with the actual project.

Summary of the invention

The technical problem to be solved by the present invention is to provide a method for laying out microseismic monitoring sensors for inclined stratum tunnel engineering. The main incident direction of the P wave of the microseismic event in the monitoring area is determined by the stress characteristics of the monitored object and the statistical laws of the focal mechanism characteristics in the monitoring area; a two-dimensional regional construction coordinate system and a layered stratum model that conforms to the geological characteristics of the monitoring area are established, and the ray path equation of the P wave is further established. The ray parameters, stratum parameters, wave velocity parameters, etc. are substituted into the ray equation in sequence, and finally the optimal position of the sensor layout in the inclined layered medium can be obtained; the sensor positions corresponding to the other main incident directions of the P wave of each source in the monitoring area are solved in sequence, which is the optimal layout position of the sensor in the three-dimensional monitoring area. This method is also applicable to the optimal position design of microseismic monitoring sensors for underground projects in horizontal layered media such as civil engineering and hydropower.

The method comprises the following steps:

(1) Determine the main incident direction of the P wave: Determine the main incident direction of the P wave of the microseismic event in the monitoring area based on the stress characteristics of the monitored object and the statistical laws of the focal mechanism characteristics in the monitoring area;

(2) Establishing a coordinate system and formation model: According to the main microseismic monitoring area and the sensor deployment area, establish a regional construction coordinate system and an inclined layered formation model, and obtain the wave velocity and layer thickness geological parameters of each layer in the formation model based on field survey data or wave velocity testers;

(3) Geological conversion of dip angle and layer thickness of inclined strata: The inclined strata model needs to consider the influence of dip and dip angle on the propagation direction of P waves. The section where the P-wave ray propagation trajectory is located may not be parallel to the strata dip. Therefore, the true dip angle must be converted into the apparent dip angle in advance during the calculation process. In addition, the vertical distance between the top and bottom boundaries of each rock layer is no longer the true thickness of the strata, but the apparent thickness. Since the vertical thickness of the strata is constant, the apparent thickness can be calculated by the vertical thickness and the apparent dip angle. The inclined strata model needs to consider the influence of dip and dip angle on the propagation direction of P waves. In the calculation process, the true dip angle must be converted into the apparent dip angle in advance, and the vertical thickness of the strata must be converted into the apparent thickness;

(4) Establishing the ray path equation of the P wave: The energy of reflected waves, refracted waves, etc. in the mine microseismic monitoring signal accounts for a relatively small proportion. Only the transmitted waves received by the sensor are considered, and the influence of interference waves is ignored. Based on the main incident direction of the P wave determined in step (1), combined with Snell's law, the ray path equation of the P wave in this direction in the coordinate system and the formation model in step (2) is established;

(5) Solving the optimal position of the sensor: Substituting the layer thickness parameters, wave velocity parameters, etc. in step (2) and the apparent dip angle, apparent thickness, etc. in step (3) into the ray path equation in step (4) in sequence, and obtaining the optimal position of the sensor in the inclined layered stratum medium in step (2);

(6) Determining the sensor positions in the three-dimensional monitoring area of underground engineering: According to steps (2) to (5), the sensor positions corresponding to the main incident directions of the P waves of each earthquake source in the monitoring area are solved in sequence, which are the optimal deployment positions of the sensors in the three-dimensional monitoring area.

The stress characteristics of the monitored object in step (1) include collapse under the action of gravity and horizontal stress of the regional tectonic stress field, bottom drum and rock burst caused by stress redistribution caused by excavation unloading; the statistical law of the focal mechanism characteristics in the monitoring area refers to the azimuth and elevation distribution characteristics of the main compressive stress axis, the intermediate stress axis or the main stress axis in the stress release direction of the main microseismic events in the monitoring area, so as to determine the main incident direction of the P wave; the initial incident angle of the P wave of a certain main earthquake source o (x ₀ , z ₀ ) is represented by θ ₀ .

In step (2), the regional construction coordinate system is determined according to the measurement practice of underground engineering sites, including the geodetic coordinate system and the Gaussian plane rectangular coordinate system; the regional construction coordinate system is established to ensure that the microseismic main monitoring area and the sensor deployment area are located in the first quadrant of the coordinate system, and the origin of the coordinate system is recorded as O(0,0); the stratum model is recorded as Z ₁ , Z ₂ , …, _Zi , …, Z _n from bottom to top, where i is the number of layers, i=1,2,…,n; Zi _, Zi ₊₁ are the lower boundary and upper boundary of the i-th layer respectively; _vi , θ _i , h _i , H _i respectively represent the velocity, incident angle, true thickness and vertical thickness of the i-th layer in the intended monitoring area; the stratum where the main earthquake source of the area to be monitored is located is represented by the 0th layer, and the stratum at the top of the area where the sensors are to be deployed is represented by the nth layer; v ₀ , H ₀ respectively represent the velocity of the stratum where the main earthquake source to be monitored is located, the vertical thickness from the bottom of the coordinate system to the interface of the upper rock layer, θ ₀ is the initial incident angle of the main earthquake source in the monitoring area, and _Hn represents the vertical thickness from the top of the monitored area to the interface of the rock layer below it.

The conversion relationship between the true dip angle and the apparent dip angle of the inclined stratum in step (3) is:

tanβ _i =tanα _i ·cosω,i＝0,1,2,…,n

The apparent thickness is calculated by vertical thickness and apparent inclination angle, and the formula is:

_Hi = _hi / _cosαi ,

H_i分别为第i层的真实厚度、视厚度和铅直厚度；待监测区域主震源所在地层用第0层表示，拟布设传感器区域最上层的地层用第n层表示，H₀分别表示待监测区域坐标系底面到其上部岩层分界面的铅直厚度，H_n表示待监测区域顶部到其下部岩层分界面的铅直厚度。Among them, α _i is the true dip angle of the i-th layer, β _i is the apparent dip angle of the i-th layer, ω is the angle between the section where the ray is located and the dip, that is, the angle between the apparent dip and the true dip; h _i ,

_Hi represents the true thickness, apparent thickness and vertical thickness of the i-th layer respectively; the stratum where the main earthquake source of the monitored area is located is represented by the 0th layer, and the uppermost stratum in the area where the sensors are to be deployed is represented by the nth layer. _H0 represents the vertical thickness from the bottom of the coordinate system of the monitored area to the interface of its upper rock layer, and _Hn represents the vertical thickness from the top of the monitored area to the interface of its lower rock layer.

The ray path equation in step (4) is:

p＝sinθ _i /v _i ;

Where p is the ray parameter, i is the layer number, i = 0, 1, 2, …, n, the stratum where the main earthquake source is located in the area to be monitored is represented by the 0th layer, and the uppermost stratum in the area where the sensors are to be deployed is represented by the nth layer; _vi , _θi represent the velocity and incident angle of the i-th layer in the area to be monitored, respectively.

The calculation formula of the horizontal distance Δ (epicenter distance) between the earthquake source and the receiving point can be obtained by using geometric relationships:

可以化为相同的形式，带入射线参数p＝sinθ_k/v_k可得：Different seismic phases have their own ray path equations, which are defined by the equivalent layer thickness

It can be transformed into the same form, and the ray parameter p = sinθ _k /v _k is obtained:

Where _hi represents the true thickness of the i-th layer in the planned monitoring area, _H0 represents the vertical thickness from the bottom of the coordinate system of the monitored area to the interface of the upper rock layer, and _Hn represents the vertical thickness from the top of the monitored area to the interface of the lower rock layer.

In step (5), according to Snell's law, the ray parameter p is a constant:

Where _θ0 is the initial incident angle of the main earthquake source in the monitoring area, _v0 represents the velocity of the stratum where the main earthquake source to be monitored is located, i is the number of layers, i = 0, 1, 2, ..., n, the stratum where the main earthquake source in the monitoring area is located is represented by the 0th layer, the top layer of the area where the sensor is to be deployed is represented by the nth layer, and _vi and _θi represent the velocity and incident angle of the i-th layer in the monitoring area respectively;

Finally, the position of the ray’s exit point in the layered strata is determined, which is the optimal position for sensor deployment:

为等效层厚，x₀表示震源在区域坐标系中的横向坐标，z₀表示震源在区域坐标系中的竖向坐标，H₀表示坐标系底面到其上部岩层分界面的铅直厚度，h_i为第i层的真实厚度，H_n表示待监测区域顶部到其下部岩层分界面的铅直厚度，β_i为第i层的视倾角，β₀为主震源所在地层的视倾角，α_i为第i层的真倾角，β_n表示待监测区域最上层的视倾角。In the formula,

is the equivalent layer thickness, _x0 represents the lateral coordinate of the earthquake source in the regional coordinate system, _z0 represents the vertical coordinate of the earthquake source in the regional coordinate system, _H0 represents the vertical thickness from the bottom of the coordinate system to the interface of the upper rock layer, _hi represents the true thickness of the i-th layer, _Hn represents the vertical thickness from the top of the area to be monitored to the interface of the lower rock layer, _βi represents the apparent dip angle of the i-th layer, _β0 represents the apparent dip angle of the stratum where the main earthquake source is located, _αi represents the true dip angle of the i-th layer, and _βn represents the apparent dip angle of the uppermost layer in the area to be monitored.

The beneficial effects of the above technical solution of the present invention are as follows:

(1) In the field of coal mining, relevant deployment methods such as "inside-outside field", "far-near field", "overall coverage-regional key monitoring" only plan the sensor deployment area from a macro qualitative perspective, and cannot provide specific coordinates that can be directly used for on-site installation. The present invention can calculate the exact deployment coordinates to facilitate construction.

(2) The core of the previous theoretical algorithms such as D value optimization and C value optimization is to solve in an ideal environment where the wave velocity is constant in a uniform medium, without considering the influence of the inclined layered strata of the underground project, which is inconsistent with the actual project. The solution process of the present invention is based on the real geological model on site, taking into account the influence of the inclined layered strata of the underground project, which is more in line with the project site.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a process flow chart of a method for deploying microseismic monitoring sensors for tunnel engineering in inclined strata according to the present invention;

FIG2 is a schematic diagram showing the positional relationship between the apparent inclination angle and the true inclination angle in the inclined stratum of the method for deploying microseismic monitoring sensors for tunnel engineering in inclined stratum according to the present invention;

FIG3 is a schematic diagram of the positional relationship between the true thickness, apparent thickness and vertical thickness in the inclined stratum of the method for laying microseismic monitoring sensors for tunnel engineering in inclined stratum according to the present invention, wherein (a) is the positional relationship between the true thickness and the vertical thickness, and (b) is the relationship between the apparent thickness and the vertical thickness;

FIG4 is a schematic diagram of a two-dimensional model of a method for deploying microseismic monitoring sensors for tunnel engineering in inclined strata according to the present invention;

5 is a schematic diagram of sensor solution and layout in a three-dimensional monitoring area of a microseismic monitoring sensor deployment method for a tunnel engineering project in inclined strata according to the present invention.

Among them: 1-true dip of rock formation; 2-true thickness; 3-vertical thickness; 4-apparent dip of rock formation; 5-apparent thickness; 6-angle between true dip and apparent dip; 7-monitoring area and sensor deployment area; 8-horizontal line of sensor deployment position; 9-stratum boundary line; 10-various rock formations; 11-seismic source; 12-initial incident angle of P wave; 13-incident angle; 14-ray path; 15-optimal position of sensor.

DETAILED DESCRIPTION

In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

The present invention aims to solve the problems that the existing macro-qualitative methods for deploying microseismic monitoring sensors such as "inside-outside field" in the coal mine field cannot provide accurate installation positions, and quantitative methods such as D value optimization theory do not consider the influence of the on-site inclined stratum medium and are not accurate enough. A method for deploying microseismic monitoring sensors for tunnel engineering in inclined strata is provided.

As shown in FIG1 , the method comprises the following steps:

(1) Determine the main incident direction of the P wave: Determine the main incident direction of the P wave of the microseismic event in the monitoring area based on the stress characteristics of the monitored object and the statistical laws of the focal mechanism characteristics in the monitoring area;

(2) Establishing a coordinate system and a formation model: Based on the main microseismic monitoring area and the sensor deployment area, establish a regional construction coordinate system and an inclined layered formation model, and obtain the wave velocity and layer thickness geological parameters of each layer in the formation model based on the field survey data or the wave velocity tester;

(3) Geological conversion of dip angle and layer thickness of inclined strata: The model of inclined strata needs to consider the influence of dip and dip angle on the propagation direction of P waves. In the calculation process, the true dip angle needs to be converted into the apparent dip angle and the vertical thickness of the strata needs to be converted into the apparent thickness.

(4) Establishing the ray path equation of the P wave: Only the transmitted wave received by the sensor is considered in the mine microseismic monitoring signal. Based on the main incident direction of the P wave determined in step (1), combined with Snell's law, the ray path equation of the P wave in this direction in the coordinate system and the formation model in step (2) is established;

(5) Solving the optimal position of the sensor: Substituting the layer thickness parameter and wave velocity parameter in step (2) and the apparent inclination angle and apparent thickness in step (3) into the ray path equation in step (4) in sequence, and obtaining the optimal position of the sensor in the inclined layered stratum medium in step (2);

(6) Determining the sensor positions in the three-dimensional monitoring area of underground engineering: According to steps (2) to (5), the sensor positions corresponding to the main incident directions of the P waves of each earthquake source in the monitoring area are solved in sequence, which are the optimal deployment positions of the sensors in the three-dimensional monitoring area.

The stratum model used in the calculation of the present invention is shown in FIG4 , and the internal calculation principle of the three-dimensional monitoring area is shown in FIG5 .

In the specific implementation, the main incident direction of the P wave of the earthquake source in the monitoring area is first determined, and then a two-dimensional coordinate system is established in the monitoring area and the sensor layout area 7, as shown in Figure 4. The top layer of the area is the sensor layout position horizontal line 8, and the various rock layers 10 are divided into stratigraphic boundary lines 9. According to the initial incident angle 12 of the P wave of the earthquake source 11, the corresponding incident angle 13 of the ray path 14 in each rock layer 10 can be calculated, and finally the optimal position 15 of the sensor can be calculated.

The positional relationship between the apparent dip and the true dip in the inclined strata is shown in Figure 2, and the positional relationship between the true thickness, apparent thickness and vertical thickness in the inclined strata is shown in Figure 3, wherein 1 represents the true dip of the rock strata, 2 represents the true thickness, 3 represents the vertical thickness, 4 represents the apparent dip of the rock strata, 5 represents the apparent thickness, and 6 is the angle between the true dip and the apparent dip.

According to the statistical law of the main incident direction of P waves from other sources in the monitoring area, the sensor positions in different deployment directions can be obtained by solving again according to steps (2), (3) and (4). Since the P wave transmission directions of different sources are different, the positions of sensors will be distributed in the three-dimensional space of the monitoring area.

This will be described below with reference to specific embodiments.

Example 1

(1) An underground project under inclined geological conditions in the southwest region is in danger of collapse. To ensure the stability of the underground project, a microseismic monitoring system is planned to be introduced to monitor the area. The first batch of four sensors are planned to be installed on the boundary of the cube area _{A1B1C1D1 - ABCD} with a side length of 100m. Now it is necessary to optimize the design of the positions of the four _sensors .

(2) According to the stress characteristics of the monitored object and the statistical law of the focal mechanism characteristics in the monitored area, the main incident direction of the P wave of each source in the monitored area is preliminarily determined as shown in Figure 5. The incident point is located at the center of the bottom surface of the monitored area, which can be represented by J, and the incident angle θ _J = 10°. The incident direction belongs to the plane A ₁ C ₁ CA in the vertical direction and to the plane ABCD in the horizontal direction, that is, ω _J = 45°.

根据计算可知J点的施工坐标为X_J0＝(50,50,0)，J点距离上部岩层的铅直距离为d₀＝H₀/3，待监测区域顶部到其下部岩层分界面(第三层地质底面)的铅直厚度H₃＝32.57m。(3) The construction coordinate system of this area takes A as the origin, and the coordinate axes xyz are shown in Figure 4. The stratum consists of three layers, and the true inclination of each layer is equal to α = 30°. The relevant parameters of the four layers from bottom to top are as follows: v ₀ = 1995m/s, H ₁ = 22m, v ₁ = 2126m/s, H ₂ = 53m, v ₂ = 2320m/s, v ₃ = 2272m/s. The vertical thickness from the bottom of the coordinate system of the monitored area to the interface of the upper rock layer

According to calculation, the construction coordinates of point J are X _J0 = (50,50,0), the vertical distance between point J and the upper rock layer is d ₀ = H ₀ /3, and the vertical thickness from the top of the monitored area to the interface of the lower rock layer (the third geological bottom) is H ₃ = 32.57m.

(4) According to the conversion relationship between the true dip angle and the apparent dip angle of the inclined stratum in step (3), the apparent dip angle β _J = 22.21° can be obtained.

(5) According to the calculation formula for the optimal position of sensor deployment in step (5), the thickness of each layer, wave velocity, initial source position, initial incident angle, apparent dip angle and other parameters in steps (3) and (4) are substituted in sequence, and the coordinates of the optimal sensor deployment position in this direction are finally solved as follows: X _J0 = (96.68, 96.68, 100).

(5) Since four sensors are to be deployed, the other three main incident directions of the P waves of each source in the monitoring area are obtained according to the stress characteristics of the monitored object and the statistical law of the focal mechanism characteristics in the monitoring area, as shown in Figure 5. The incident points can be represented by three points D, M, and N, respectively, and the incident angles are: θ _D = 15°, θ _M = 20°, and θ _N = 25°. In the vertical direction, they belong to the planes D ₁ B ₁ BD, N ₁ E ₁ EN, and A ₁ B ₁ BA, respectively, and in the horizontal direction, they belong to the plane ABCD, that is, the angle distribution between the apparent dip and the true dip is ω _D = -45°, ω _M = 0°, and ω _N = 0°.

According to calculation, the construction coordinates of the three earthquake source points D, M, and N are X _D0 = (0,100,0), X _M0 = (0,50,0), and X _D0 = (0,50,0). The vertical distances between points D and N and the upper rock layer are d ₀ = h ₀ , and the vertical distance between point M and the upper rock layer is d ₀ = H ₀ /3, as shown in FIG3 .

According to the conversion relationship between the true dip angle and the apparent dip angle of the inclined stratum in step (3), the apparent dip angles β _D = 22.21°, β _M = 30°, and β _N = 30° can be obtained, as shown in FIG. 2 .

(6) A two-dimensional regional coordinate system is established in turn according to the vertical planes where the three main incident directions are located. Similarly, according to the optimal sensor layout calculation formula in step (3), the thickness of each layer, wave velocity, initial source position, initial incident angle, apparent dip angle and other parameters are substituted in turn, and the coordinates of the optimal sensor layout positions in these three directions are finally solved as follows: X _D0 = (56.49, 43.51, 100), X _M0 = (100, 0, 38.99), X _N0 = (100, 50, 63.97).

(7) Since the P-wave transmission directions of different earthquake sources are different, the locations of the sensors will be distributed in the three-dimensional space of the monitoring area. The locations of the four sensors are the black triangles of X _J1 , X _D1 , X _M1 , and X _N1 as shown in FIG5 .

The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims (6)

1. A method for laying microseismic monitoring sensors for tunnel engineering in inclined strata, characterized in that it comprises the following steps: S1: Determine the main incident direction of the P wave: According to the stress characteristics of the monitored object and the statistical law of the focal mechanism characteristics in the monitored area, determine the main incident direction of the P wave of the microseismic event in the monitored area; S2: Establishing coordinate system and formation model: According to the main microseismic monitoring area and sensor deployment area, establish the regional construction coordinate system and inclined layered formation model, and obtain the wave velocity and layer thickness geological parameters of each layer in the formation model according to the field survey data or wave velocity tester; S3: Geological conversion of dip angle and layer thickness of inclined strata: The inclined strata model needs to consider the influence of dip and dip angle on the propagation direction of P waves. In the calculation process, the true dip angle needs to be converted into the apparent dip angle and the vertical thickness of the strata needs to be converted into the apparent thickness. S4: Establishing the ray path equation of the P wave: Only the transmitted wave received by the sensor is considered in the mine microseismic monitoring signal. Based on the main incident direction of the P wave determined in step S1 and combined with Snell's law, the ray path equation of the P wave in this direction in the coordinate system and the formation model in step S2 is established; S5: Solving the optimal position of the sensor: Substituting the layer thickness parameter and wave velocity parameter in step S2 and the apparent dip angle and apparent thickness in step S3 into the ray path equation in step S4 in sequence, and obtaining the optimal position of the sensor arrangement in the inclined layered stratum medium in step S2; S6: Solving the sensor positions in the three-dimensional monitoring area of underground engineering: According to steps S2 to S5, the sensor positions corresponding to the main incident directions of P waves of each earthquake source in the monitoring area are solved in sequence, which are the optimal layout positions of the sensors in the three-dimensional monitoring area. 2. The method for deploying microseismic monitoring sensors for inclined stratum tunnel engineering according to claim 1 is characterized in that: the stress characteristics of the monitored object in step S1 include collapse under the action of gravity and horizontal stress of the regional tectonic stress field, bottom drum and rock burst caused by stress redistribution caused by excavation unloading; the statistical law of the focal mechanism characteristics in the monitoring area refers to the azimuth and elevation distribution characteristics of the main compressive stress axis, the intermediate stress axis or the main stress axis in the stress release direction of the main microseismic events in the monitoring area, thereby determining the main incident direction of the P wave; the initial incident angle of the P wave of a certain main earthquake source o (x ₀ , z ₀ ) is represented by θ ₀ . 3. The method for laying out microseismic monitoring sensors for tunnel engineering in inclined strata according to claim 1 is characterized in that: the regional construction coordinate system in step S2 is determined according to the on-site measurement habits of underground engineering, including the geodetic coordinate system and the Gaussian plane rectangular coordinate system; the established regional construction coordinate system ensures that the microseismic main monitoring area and the sensor laying area are located in the first quadrant of the coordinate system, and the origin of the coordinate system is recorded as O(0,0); the stratum model is recorded as Z ₁ , Z ₂ , …, _Zi , …, Z _n from bottom to top, wherein i is the number of layers, i=1,2,…,n; _Zi , Zi ₊₁ are the lower boundary and upper boundary of the i-th layer respectively; v _i , θ _i , h _i , H _i respectively represent the velocity, incident angle, true thickness and vertical thickness of the i-th layer in the intended monitoring area; the stratum where the main earthquake source of the area to be monitored is located is represented by the 0th layer, and the stratum of the uppermost layer of the area where the sensor is to be laid is represented by the nth layer, v ₀ , H i ₀ represents the velocity of the stratum where the main earthquake source to be monitored is located, the vertical thickness from the bottom of the coordinate system to the interface of the upper rock strata, _θ0 is the initial incident angle of the main earthquake source in the monitoring area, and _Hn represents the vertical thickness from the top of the area to be monitored to the interface of the lower rock strata. 4. The method for laying microseismic monitoring sensors for inclined stratum tunnel engineering according to claim 1, characterized in that: the conversion relationship between the true inclination angle and the apparent inclination angle of the inclined stratum in step S3 is: tanβ _i =tanα _i ·cosω,i＝0,1,2,…,n The apparent thickness is calculated by vertical thickness and apparent inclination angle, and the formula is: _Hi = _hi / _cosαi ,

Among them, α _i is the true dip angle of the i-th layer, β _i is the apparent dip angle of the i-th layer, ω is the angle between the section where the ray is located and the dip, that is, the angle between the apparent dip and the true dip; h _i ,

_Hi represents the true thickness, apparent thickness and vertical thickness of the i-th layer respectively; the stratum where the main earthquake source of the monitored area is located is represented by the 0th layer, and the uppermost stratum in the area where the sensors are to be deployed is represented by the nth layer. _H0 represents the vertical thickness from the bottom of the coordinate system of the monitored area to the interface of its upper rock layer, and _Hn represents the vertical thickness from the top of the monitored area to the interface of its lower rock layer. 5. The method for deploying microseismic monitoring sensors for inclined stratum tunnel engineering according to claim 1, characterized in that: the ray path equation in step S4 is: p＝sinθ _i /v _i ; Where p is the ray parameter, i is the layer number, i = 0, 1, 2, …, n, the stratum where the main earthquake source is located in the area to be monitored is represented by the 0th layer, and the uppermost stratum in the area where the sensors are to be deployed is represented by the nth layer; _vi , _θi represent the velocity and incident angle of the i-th layer in the area to be monitored, respectively. 6. The method for laying microseismic monitoring sensors for inclined stratum tunnel engineering according to claim 1, characterized in that: in step S5, according to Snell's law, the ray parameter p is a constant:

Where _θ0 is the initial incident angle of the main earthquake source in the monitoring area, _v0 represents the velocity of the stratum where the main earthquake source to be monitored is located, i is the number of layers, i = 0, 1, 2, ..., n, the stratum where the main earthquake source in the monitoring area is located is represented by the 0th layer, the top layer of the area where the sensor is to be deployed is represented by the nth layer, and _vi and _θi represent the velocity and incident angle of the i-th layer in the monitoring area respectively; Finally, the position of the ray’s exit point in the layered strata is determined, which is the optimal position for sensor deployment:

In the formula,

is the equivalent layer thickness, _x0 represents the lateral coordinate of the earthquake source in the regional coordinate system, _z0 represents the vertical coordinate of the earthquake source in the regional coordinate system, _H0 represents the vertical thickness from the bottom of the coordinate system to the interface of the upper rock layer, _hi represents the true thickness of the i-th layer, _Hn represents the vertical thickness from the top of the area to be monitored to the interface of the lower rock layer, _βi represents the apparent dip angle of the i-th layer, _β0 represents the apparent dip angle of the stratum where the main earthquake source is located, _αi represents the true dip angle of the i-th layer, and _βn represents the apparent dip angle of the uppermost layer in the area to be monitored.

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