Correction method for solving hole drilling eccentricity error in hollow inclusion crustal stress measurement

Abstract

The invention discloses a correction method for solving a drilling hole eccentric error in hollow inclusion crustal stress measurement. The correction method comprises the following steps: establishing a geometric simplified model of an eccentric drilling hole based on various parameters required in a confining pressure calibration test; on the basis, a stress calculation graph under bipolar coordinates is established, and hole wall circumferential strain is obtained based on an eccentric rock core hole wall circumferential stress calculation formula and a physical equation; by combining the obtained hole wall strain with the arrangement angle of a strain rosette of the hollow inclusion meter and a confining pressure calibration formula, a correction method for the elastic modulus of the rock before and after eccentricity is provided, the elastic modulus E1 of the rock measured by the confining pressure calibration during eccentricity is corrected, and a rock elastic modulus correction value E0 is obtained; substituting the corrected elastic modulus value into a correction coefficient calculation formula to obtain each corrected ki coefficient value; and finally, the E0 and the corrected ki are substituted into a conventional principal stress calculation process, so that six corrected crustal stress components and three corrected principal stress sizes and directions are obtained.

Description

Technical Field

[0001] The invention relates to the technical field of rock mechanics, and in particular to a correction method for solving drilling eccentricity error in hollow inclusion ground stress measurement. Background Art

[0002] Geostress is the natural stress state of natural rock before it is disturbed by excavation. Understanding the distribution characteristics of geostress in the construction area is of great significance in geotechnical engineering investigation and design, underground mining engineering, surrounding rock stability analysis, tunnel engineering construction and many other aspects.

[0003] The casing stress relief method is the most widely used measurement method in various types of ground stress measurements. This method requires that the casing core drill hole and the measuring hole have strict coaxiality. However, in actual work, the eccentricity of the casing core drill hole and the measuring hole cannot be avoided due to construction errors. From a theoretical analysis, although the eccentricity of the drill hole has no effect on the strain value during the stress relief process, the stress distribution state and size inside the casing core after the casing core is released will be different from that when it is concentric, which will eventually lead to a large error in the rock elastic modulus value measured by the confining pressure calibration test.

[0004] In addition, although existing literature has analyzed the borehole eccentricity problem in the aperture deformation method and the magnetostriction method through theoretical and field test methods, no scholar has analyzed the borehole eccentricity error in the hollow inclusion ground stress measurement. The hollow inclusion stress relief method is currently the most widely used ground stress test method. When a large eccentricity occurs during construction, the ground stress measurement data is corrected, which can not only improve the accuracy of ground stress measurement, but also has great significance for the safety and stability of mining and underground engineering construction.

[0005] Therefore, the present invention proposes a correction method for solving the borehole eccentricity error in the ground stress measurement of hollow inclusions, which can provide practical guidance for the correction of ground stress measurement data under the condition of borehole eccentricity in actual coal mines, gold mines and other mining and tunnel engineering. Summary of the invention

[0006] In order to solve the problems existing in the above-mentioned prior art, a method for correcting the drilling eccentricity error in the measurement of hollow inclusion ground stress is provided. The specific operation of the present invention is as follows:

[0007] A method for correcting borehole eccentricity error in hollow inclusion ground stress measurement, the method comprising the following steps:

[0008] Step 1: Establish a simplified geometric model of the eccentric borehole based on various parameters required in the confining pressure calibration test;

[0009] Step 2: Establish a compression eccentric circular stress calculation model under bipolar coordinates, and obtain the hole wall annular strain based on the calculation formula of the annular stress of the eccentric core hole wall and the physical equation;

[0010] Step 3: Based on the obtained hole wall annular strain, combined with the layout angle of the hollow inclusion gauge strain rosette and the confining pressure determination formula, a correction method for the rock elastic modulus before and after eccentricity is proposed, and the rock elastic modulus E measured by the confining pressure determination at eccentricity is corrected. 1 Correction is made to obtain the rock elastic modulus correction value E 0 ;

[0011] Step 4: Correct the rock elastic modulus E 0 Substitute into the correction coefficient calculation formula to obtain the corrected k i coefficient value;

[0012] Step 5: Finally, E 0 and the corrected k i Substituting them into the conventional principal stress calculation process, the six corrected ground stress components and the three corrected principal stress magnitudes and directions are obtained in turn.

[0013] Preferably, in step 1, the parameters required for the confining pressure calibration test are: core external pressure P 0 , core radius r 0 , small hole radius r 1 , the eccentricity error d of the core.

[0014] Preferably, the calculation formula for the hoop stress on the eccentric core hole wall under pressure in step 2 is:

[0015]

[0016] Among them, η is the bipolar coordinate parameter, ranging from 0 to 2π, which represents the angle around the hole wall in the bipolar coordinate system; ξ = ξ 1 The curve representing the core hole wall in bipolar coordinates;

[0017] The physical equation is:

[0018]

[0019] In the formula, is the annular strain of the core hole wall; is the radial strain of the core hole wall, and ν is the Poisson's ratio of rock, and E is the elastic modulus of rock.

[0020] Preferably, in step three:

[0021] The formula for determining the confining pressure rate considering the influence of the colloid deformation parameters of the hollow inclusion and the bonding gap is:

[0022]

[0023] Where E is the test value of rock elastic modulus; ε is the average hoop strain caused by confining pressure, K 1 is the correction factor;

[0024] The layout angle of the hollow package gauge strain rosette is as follows: 3 groups of strain rosettes A, B, and C are embedded in the middle layer of the cylinder along the same circumference at equal distances. Each group of strain rosettes consists of 4 strain gauges and are 120° apart from each other. There are 12 strain gauges in total, and each strain gauge is 45° apart from each other.

[0025] The correction method of rock elastic modulus is:

[0026]

[0027] In the formula, σ 0 is the average hoop stress of the hole wall under concentricity; σ' A ,σ' B ,σ' C is the hoop stress at points A, B, and C under concentricity; σ 1 is the average hoop stress of the hole wall under eccentricity; σ A , σ B , σ C is the hoop stress at points A, B, and C under eccentricity; Δ is the elastic modulus error; E 1 E is the rock elastic modulus measured by the formula for determining the confining pressure at eccentricity; 0 It is the elastic modulus measured by the concentric confining pressure determination formula, and is also the corrected value of the elastic modulus.

[0028] Preferably, in step 4, the correction coefficient calculation formula is:

[0029]

[0030] Where:

[0031]

[0032] n=G 1 / G 2 ; m = R 1 / r 1

[0033] D=(1+x 2 n)[x 1 +n+(1-n)(3m 2 -6m 4 +4m 6 )]+(x 1 -x 2 n)m 2 [(1-n)m 6 +(x1 +n)]

[0034] x 1 =3-4ν 1 ;x 2 =3-4ν

[0035] Among them, R 1 r is the inner radius of the hollow package; 1 is the radius of the small hole; G 1 G is the shear modulus of epoxy resin of hollow inclusion material; 2 is the shear modulus of rock; v 1 is the Poisson’s ratio of epoxy resin of hollow inclusion material; v is the Poisson’s ratio of rock; ρ is the radial distance of the resistance strain gauge embedded in the hollow inclusion.

[0036] Preferably, in step 5, the main contents of the conventional principal stress calculation process are: based on the in-situ stress calculation formula and the release strain values ​​of 12 strain gauges measured by the hollow inclusion stress gauge, a normal equation between strain and stress components is established, and the least squares method is used to solve the equation group to obtain the corrected 6 in-situ stress component values; the in-situ stress magnitude calculation formula is:

[0037]

[0038] Among them, ε ij is the release strain value measured by the jth strain gauge of the i-th strain rosette, θ i is the polar angle corresponding to the i-th strain rosette, is the angle corresponding to the jth strain gauge of the ith strain rosette, k i is the correction coefficient of the i-th strain gauge; σ x , σ y , σ z , τ xy , τ yz , τ zx are the six original rock stress components at the measuring point;

[0039] Using the least squares method principle of mathematical statistics, the normal equations for solving the optimal values ​​of stress components are obtained as follows:

[0040]

[0041] In the formula,

[0042]

[0043] ε k is the strain value of the 12 strain gauges inside the hollow package, where k = 4(i-1) + j, i = 1 to 3, j = 1 to 4;

[0044] By solving this set of equations, the six stress components of the modified geostress state can be obtained;

[0045] From the elasticity theory we get:

[0046]

[0047] Among them, S is the principal stress, l, m, and n are the three direction cosines of the principal stress;

[0048] The necessary condition for this system of equations to have non-zero solutions is that the determinant of its coefficients is 0, then:

[0049]

[0050] in,

[0051]

[0052] J 2 =9I 3 -I 1 I 2

[0053] I 1 =σ x +σ y +σ z

[0054]

[0055] S 1 is the maximum principal stress, S 2 is the intermediate principal stress, S 3 is the minimum principal stress; J 1 is the first invariant of the stress tensor, J 2 is the second invariant of the stress tensor, J 3 is the third invariant of the stress tensor;

[0056] The principal stress directions are determined by:

[0057]

[0058] Solving the system of equations yields l i 、m i 、n i ;

[0059] The inclination and azimuth formulas of the principal stress are:

[0060]

[0061] The beneficial effects of the present invention are as follows: the present invention provides a correction method for solving the drilling eccentricity error in the ground stress measurement of hollow inclusions. The hollow inclusion stress relief method is currently the most widely used and most extensive ground stress testing method. When a large eccentricity occurs during construction, the ground stress measurement data is corrected, which can not only improve the accuracy of ground stress measurement, but also has great significance for the safety and stability of mining projects and underground engineering construction; it can provide practical guidance for the correction of ground stress measurement data under the condition of drilling eccentricity in actual coal mines, gold mines and other mining and tunnel projects.

[0062] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0064] Figure 1 A flow chart of a method for correcting drilling eccentricity error in hollow inclusion ground stress measurement provided in an embodiment of the present application;

[0065] Figure 2 A geometrically simplified model for determining the confining pressure of eccentric cores;

[0066] Figure 3 It is the stress calculation model of compressed eccentric annular ring in bipolar coordinates;

[0067] Figure 4 It is the measurement principle of the hollow body strain gauge;

[0068] Figure 5 Schematic diagram of elastic modulus error at different eccentricities when the core radius is 65 mm and the small hole radius is 18 mm. DETAILED DESCRIPTION

[0069] 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.

[0070] See also Figure 1-5As shown, the present invention provides a correction method for solving the drilling eccentricity error in the ground stress measurement of hollow inclusions, which effectively solves the ground stress error caused by the drilling eccentricity problem in the ground stress measurement work, and realizes the accurate correction of the ground stress data when eccentric, which can not only improve the accuracy of ground stress measurement, but also has great significance for the safety and stability of mining engineering and underground engineering construction.

[0071] A method for correcting the drilling eccentricity error in the measurement of hollow inclusion ground stress, the specific operation of the present invention is as follows:

[0072] Step 1: Establish a simplified geometric model of the eccentric borehole based on various parameters required in the confining pressure calibration test;

[0073] Step 2: Establish a compression eccentric circular stress calculation model under bipolar coordinates, and obtain the hole wall annular strain based on the calculation formula of the annular stress of the eccentric core hole wall and the physical equation;

[0074] Step 3: Based on the obtained hole wall annular strain, combined with the layout angle of the hollow inclusion gauge strain rosette and the confining pressure determination formula, a correction method for the rock elastic modulus before and after eccentricity is proposed, and the rock elastic modulus E measured by the confining pressure determination at eccentricity is corrected. 1 Correction is made to obtain the rock elastic modulus correction value E 0 .

[0075] Step 4: Correct the rock elastic modulus E 0 Substitute into the correction coefficient calculation formula to obtain the corrected k i coefficient value;

[0076] Step 5: Finally, E 0 and the corrected k i Substituting them into the conventional principal stress calculation process, the six corrected ground stress components and the three corrected principal stress magnitudes and directions are obtained in turn.

[0077] As an embodiment of the present invention, in step 1, the parameters required in the confining pressure calibration test are: the core external pressure P 0 , core radius r 0 , small hole radius r 1 , the eccentricity error d of the core can be obtained by measuring the difference between the maximum wall thickness and the minimum wall thickness of the core; the geometric simplification of the confining pressure determination of the eccentric core is as follows Figure 2 As shown;

[0078] As an embodiment of the present invention, in step 2,

[0079] The calculation model of eccentric circle stress under bipolar coordinates is as follows: Figure 3 As shown, where ξ=ξ 0 Represents the radius r 0 =acschξ0 The outer circle of 1 Represents the radius r 1 =acschξ 1 The inner circle of , a is a constant;

[0080] The calculation formula for the hoop stress on the wall of the eccentric core hole under pressure is:

[0081]

[0082] In formula (1), P 0 is the external pressure of the core; r 0 is the core radius; r 1 is the radius of the small hole; d is the eccentricity error; η is the bipolar coordinate parameter, ranging from 0 to 2π, which represents the angle around the hole wall in the bipolar coordinate system;

[0083] When d=0 (concentric circles), the above equation is adjusted to the following equation (2), which is consistent with the derivation result of elasticity theory.

[0084]

[0085] The physical equation is:

[0086]

[0087] In formula (3), is the annular strain of the core hole wall; is the radial strain of the core hole wall, and ν is the Poisson's ratio of rock, and E is the elastic modulus of rock.

[0088] As an implementation mode of the present invention, in step 3, the method for correcting the rock elastic modulus specifically includes:

[0089] 1. Considering the influence of the colloid deformation parameters of the hollow inclusion and the confining pressure rate formula of the bonding gap, the formula is:

[0090]

[0091] In formula (4), E is the test value of rock elastic modulus; r 0 is the core radius; r 1 is the radius of the small hole; ε is the average hoop strain caused by the confining pressure, K 1 is the correction factor;

[0092] 2. Figure 4The main body of the hollow core body strain gauge is a hollow cylinder made of epoxy resin. Three groups of strain rosettes are embedded in the middle layer of the cylinder along the same circumference at equal distances. Each group of strain rosettes consists of 4 strain gauges and is 120° apart from each other. There are 12 strain gauges in total. Each strain gauge is 45° apart from each other. Each group of strain gauges is numbered in turn.

[0093] 3. When the confining pressure rate is set, the average value of the 1st, 5th and 9th strain gauges is generally taken as the calibration curve of the elastic modulus. According to the elastic theory, the circumferential stress and strain of each point on the hole wall are the same when concentric, that is,

[0094]

[0095] In formula (5), 0 is the average hoop stress of the hole wall under concentricity; σ' A ,σ' B ,σ' C is the hoop stress at points A, B, and C when they are concentric;

[0096] 4. Combining the stress distribution of the small hole wall with formula (1), we can know that due to Figure 4 The angles of the three groups of strain rosettes A, B, and C are always kept at 120°. When the eccentricity remains unchanged, no matter how θ (the direction angle corresponding to the strain rosette) changes, the sum of the stresses at points A, B, and C remains a constant, that is:

[0097]

[0098] Where σ 1 is the average hole wall stress under eccentricity; σ A , σ B , σ C is the hoop stress at points A, B, and C when eccentric;

[0099] This means that we only need to know the core radius r 0 、R 1 And the eccentricity error d can be used to obtain the error of the elastic modulus.

[0100] 5. According to formulas (3) to (6), the elastic modulus correction error can be obtained as:

[0101]

[0102] In the formula, E 1 E is the rock elastic modulus measured by the formula for determining the confining pressure at eccentricity; 0 It is the elastic modulus measured by the concentric confining pressure determination formula, and is also the corrected value of the elastic modulus.

[0103] The radius of the small hole r 1 , core radius r 0Substitute the eccentricity error d into equation (1) and combine it with equation (6) to obtain σ 1 and σ 0 , substitute into formula (7) to obtain the specific elastic modulus error, according to E 0 =E 1 / (1+Δ) Finally, the corrected elastic modulus E is obtained 0 ;

[0104] As an implementation mode of the present invention, in step 4, the correction coefficient calculation formula given by Duncan Farmer and Pender is:

[0105]

[0106] In formula (8):

[0107]

[0108] n=G 1 / G 2 ; m = R 1 / r 1

[0109] D=(1+x 2 n)[x 1 +n+(1-n)(3m 2 -6m 4 +4m 6 )]+(x 1 -x 2 n)m 2 [(1-n)m 6 +(x 1 +n)]

[0110] x 1 =3-4ν 1 ;x 2 =3-4ν

[0111] Among them, R 1 r is the inner radius of the hollow package; 1 is the radius of the small hole; G 1 G is the shear modulus of epoxy resin of hollow inclusion material; 2 is the shear modulus of rock; v 1 is the Poisson's ratio of epoxy resin of hollow inclusion material; v is the Poisson's ratio of rock; ρ is the radial distance of the resistance strain gauge embedded in the hollow inclusion;

[0112] As an implementation mode of the present invention, in step five, the main contents of the conventional principal stress calculation process are: based on the ground stress calculation formula and the release strain values ​​of 12 strain gauges measured by the hollow inclusion stress gauge, a normal equation between the strain and stress components is established, and the least squares principle is used to solve the equation group to obtain the corrected 6 ground stress component values.

[0113] Then the six corrected geostress component values ​​are converted into the geodetic coordinate system, and then based on the characteristic equation of the three-dimensional stress state, the static equilibrium equation and the geometric relationship that the principal stresses are perpendicular to each other, the values ​​and directions of the three principal stresses are finally obtained.

[0114] First, the calculation formula of ground stress is:

[0115]

[0116] In formula (9): ε ij ——Relief strain value measured by the jth strain gauge of the i-th strain rosette, i = 1 to 3, j = 1 to 4,

[0117] θ i ——polar angle corresponding to the ith strain rosette,

[0118] ——The angle corresponding to the jth strain gauge of the ith strain rosette,

[0119] k i ——Correction factor of strain gauge;

[0120] Secondly, using the least squares principle of mathematical statistics, the normal equations for solving the optimal values ​​of stress components are obtained as follows:

[0121]

[0122] By solving the above equation (10), the six stress components of the modified geostress state can be obtained;

[0123] Third, from the elasticity theory:

[0124]

[0125] In formula (11), S is the principal stress, l, m, and n are the three direction cosines of the principal stress;

[0126] The necessary condition for this system of equations to have non-zero solutions is that the determinant of its coefficients is 0, so:

[0127]

[0128] In formula (12):

[0129]

[0130] J 2 =9I 3 -I 1 I 2

[0131] I 1 =σ x +σ y +σ z

[0132]

[0133] S 1 , S 2 , S 3 are the maximum principal stress, the intermediate principal stress, and the minimum principal stress respectively; where J 1 , J 2 and J 3 are the first, second and third invariants of the stress tensor;

[0134] The principal stress directions are determined by:

[0135]

[0136] Solving equation (13) yields l i 、m i 、n i ;

[0137] The inclination and azimuth formulas of the principal stress are:

[0138]

[0139] Example

[0140] 1. In actual engineering, the core diameter Φ128~135mm and the small hole diameter Φ35~38mm are usually used as conventional release parameters for hollow package stress relief operations. Therefore, the average value is taken and the core radius r is used. 0 =65mm, small hole radius r 1 =18mm, while the eccentricity error of the core is d=20mm, the external pressure P 0 =80Mpa.

[0141] 2. The above parameters r 0 、r 1 ,d,P 0 Entering equations (1) and (6), keeping the A strain rosette vertically upward, by selecting different azimuth angles θ (in Figure 4The magnitude of each stress is shown in the following table. Obviously, the value of the average hole wall stress σ1 remains unchanged under eccentricity, which makes it possible to correct the elastic modulus under eccentricity.

[0142] The magnitude of stress at different azimuth angles when the eccentricity is 20 mm

[0143]

[0144] 3. Keep r 0 =65mm, r 1 =18mm, P 0 =80Mpa unchanged, substitute d=1~30mm into equation (1) and equation (6) in turn, and combine with equation (7), and the elastic modulus errors under different eccentricities are obtained as shown in the following table and Figure 5 :

[0145] Elastic modulus error under different eccentricity

[0146] Eccentricity / mm 5 10 15 20 25 30 <![CDATA[σ 1 / MPa]]> 173.66 174.84 177.02 -180.61 -186.46 -196.52 <![CDATA[σ 0 / MPa]]> 173.29 173.29 173.29 173.29 173.29 173.29 Elastic modulus deviation rate % 0.22 0.90 2.15 4.22 7.60 13.41

[0147] 4. Take the data of ground stress measurement in a coal mine in Shandong as an example. There are 3 measuring points in this measurement. The diameter of the core drill hole is Φ130mm and the diameter of the measuring hole is Φ36mm. An eccentricity error of 20mm occurs during the measurement. The ground stress measurement data is corrected based on this. It can be seen from the above table that the elastic modulus error is 4.22% at this time. After correcting the rock elastic modulus, the elastic modulus E1 and E0 before and after correction are substituted into formula (8) respectively. The elastic modulus, Poisson's ratio and k coefficient values ​​of each measuring point before and after correction are obtained as shown in the following table.

[0148] Elastic modulus E1, Poisson's ratio, and k coefficient values ​​of each measuring point before correction

[0149]

[0150] Corrected elastic modulus E0, Poisson's ratio, and k coefficient values ​​at each measuring point

[0151]

[0152] 5. Set the release strain value ε of the 12 strain gauges ij Substituting the elastic modulus E1 and E0 before and after correction, the rock Poisson's ratio, and the ki coefficient value before and after correction into equations (9) and (10), the calculation results of the ground stress components of each measuring point before and after correction are shown in the following table.

[0153] Ground stress components at each measuring point before correction

[0154]

[0155]

[0156] Corrected ground stress components at each measuring point

[0157] Measuring point <![CDATA[σ x ]]> <![CDATA[σ y ]]> <![CDATA[σ z ]]> <![CDATA[τ xy ]]> <![CDATA[τ yz ]]> <![CDATA[τ zx <!-- 11 -->]]> 1 6.09 5.15 17.97 0.35 1.47 -0.12 2 5.19 6.23 15.48 0.28 1.87 -0.44 3 5.62 5.94 12.32 -0.37 -0.55 0.09

[0158] Substituting the six ground stress components of each measuring point before and after correction into equations (12-14), the magnitude and direction of the principal stress at each measuring point before and after eccentricity are finally obtained as shown in the following table.

[0159] Calculation results of principal stress at each measuring point before correction

[0160]

[0161] Corrected calculation results of principal stress at each measuring point

[0162]

[0163]

[0164] The above contents are merely examples and explanations of the concept of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A correction method for solving the drilling eccentricity error in the measurement of hollow inclusion ground stress. It is characterized in that The method comprises the following steps: Step 1: Establish a simplified geometric model of the eccentric borehole based on various parameters required in the confining pressure calibration test; Step 2: Establish a compression eccentric circular stress calculation model under bipolar coordinates, and obtain the hole wall annular strain based on the calculation formula of the annular stress of the eccentric core hole wall and the physical equation; Step 3: Based on the obtained hole wall annular strain, combined with the layout angle of the hollow inclusion gauge strain rosette and the confining pressure determination formula, a correction method for the rock elastic modulus before and after eccentricity is proposed, and the rock elastic modulus E measured by the confining pressure determination at eccentricity is corrected. 1 Correction is made to obtain the rock elastic modulus correction value E 0 ; Step 4: Correct the rock elastic modulus E 0 Substitute into the correction coefficient calculation formula to obtain the corrected k i coefficient value; Step 5: Finally, E 0 and the corrected k i Substituting them into the conventional principal stress calculation process, the six corrected ground stress components and the three corrected principal stress magnitudes and directions are obtained in turn.

2. A method for correcting drilling eccentricity error in hollow inclusion ground stress measurement according to claim 1, It is characterized in that In step 1, the parameters required for the confining pressure calibration test are: core external pressure P 0 , core radius r 0 , small hole radius r 1 , the eccentricity error d of the core.

3. A method for correcting drilling eccentricity error in hollow inclusion ground stress measurement according to claim 2, It is characterized in that The calculation formula for the hoop stress on the eccentric core hole wall under pressure in step 2 is: Where η is the bipolar coordinate parameter, ranging from 0 to 2π, which represents the angle around the core hole wall in the bipolar coordinate system; ξ = ξ 1 The curve representing the core hole wall in bipolar coordinates; The physical equation is: in, is the annular strain of the core hole wall; is the radial strain of the core hole wall, and ν is the Poisson's ratio of rock, and E is the elastic modulus of rock.

4. A method for correcting drilling eccentricity error in hollow inclusion ground stress measurement according to claim 2, It is characterized in that In the step three: The elastic modulus of the rock of the hollow inclusion is generally determined by considering the influence of the colloid deformation parameters of the hollow inclusion and the confining pressure rate of the bonding gap: Where E is the test value of rock elastic modulus; ε is the average annular strain of the core hole wall caused by external pressure, K 1 is the correction factor; The layout angle of the hollow package gauge strain rosette is as follows: 3 groups of strain rosettes A, B, and C are embedded in the middle layer of the cylinder along the same circumference at equal distances. Each group of strain rosettes consists of 4 strain gauges and are 120° apart from each other. There are 12 strain gauges in total, and each strain gauge is 45° apart from each other. The correction method of rock elastic modulus is: In the formula, σ 0 is the average hoop stress of the hole wall under concentricity; σ' A ,σ' B ,σ' C is the hoop stress at points A, B, and C under concentricity; σ 1 is the average hoop stress of the hole wall under eccentricity; σ A , σ B , σ C is the hoop stress at points A, B, and C under eccentricity; Δ is the elastic modulus error; E 1 E is the rock elastic modulus measured by the formula for determining the confining pressure at eccentricity; 0 It is the elastic modulus measured by the concentric confining pressure determination formula, and is also the corrected value of the elastic modulus.

5. A method for correcting drilling eccentricity error in hollow inclusion ground stress measurement according to claim 4, It is characterized in that In step 4, the correction coefficient calculation formula is: Where: n=G 1 / G 2 ;m=R 1 / r 1 D=(1+x 2 n)[x 1 +n+(1-n)(3m 2 -6m 4 +4m 6 )]+(x 1 -x 2 n)m 2 [(1-n)m 6 +(x 1 +n)] x 1 =3-4ν 1 ;x 2 =3-4ν Among them, R 1 G is the inner radius of the hollow package; 1 G is the shear modulus of epoxy resin of hollow inclusion material; 2 is the shear modulus of rock; v 1 is the Poisson’s ratio of epoxy resin of hollow inclusion material; v is the Poisson’s ratio of rock; ρ is the radial distance of the resistance strain gauge embedded in the hollow inclusion.

6. A method for correcting drilling eccentricity error in hollow inclusion ground stress measurement according to claim 4, It is characterized in that In step 5, the main contents of the conventional principal stress calculation process are: based on the in-situ stress calculation formula and the release strain values ​​of the 12 strain gauges measured by the hollow package stress gauge, a normal equation between the strain and stress components is established, and the least squares method is used to solve the equation group to obtain the corrected 6 in-situ stress component values; the in-situ stress magnitude calculation formula is: Among them, ε ij is the release strain value measured by the jth strain gauge of the i-th strain rosette, θ i is the polar angle corresponding to the i-th strain rosette, is the angle corresponding to the jth strain gauge of the ith strain rosette, k i is the correction coefficient of the i-th strain gauge; σ x , σ y , σ z , τ xy , τ yz , τ zx are the six original rock stress components at the measuring point; Using the least squares method principle of mathematical statistics, the normal equations for solving the optimal values ​​of stress components are obtained as follows: In the formula, ε k is the strain value of the 12 strain gauges inside the hollow package, where k = 4(i-1) + j, i = 1 to 3, j = 1 to 4; By solving this set of equations, the six stress components of the modified geostress state can be obtained; From the elasticity theory we get: Among them, S is the principal stress, l, m, and n are the three direction cosines of the principal stress; The necessary condition for this system of equations to have non-zero solutions is that the determinant of its coefficients is 0, then: in, J 2 =9I 3 -I 1 I 2 I 1 =s x +s y +s z S 1 is the maximum principal stress, S 2 is the intermediate principal stress, S 3 is the minimum principal stress; J 1 is the first invariant of the stress tensor, J 2 is the second invariant of the stress tensor, J 3 is the third invariant of the stress tensor; The principal stress directions are determined by: Solving the system of equations yields l i 、m i 、n i ; The inclination and azimuth formulas of the principal stress are:

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