Ground stress testing method for single-hole multi-time stress relief and combinatorial analysis

Abstract

The invention belongs to the technical field of geotechnical engineering, and relates to a ground stress test method for single-hole multiple stress relief and combinatorial analysis, which comprises the following steps: acquiring strain data of different depths of a rock mass, and calculating a stress component of a drill hole surface in a drill hole coordinate system based on the strain data; calculating a far-field crustal stress component of the rock mass in the local rectangular coordinate system by using the stress component, and performing stress coordinate system transformation to obtain a far-field stress component in a global rectangular coordinate system; and based on the far-field stress component in the global rectangular coordinate system, obtaining the size and direction of the principal stress. According to the method, multiple stress relief is carried out in the same drill hole through a single-hole-site multiple stress relief method ground stress measurement technology, abnormal value elimination, mean value calculation and probability distribution analysis are carried out on massive solution sets in combination with combinatology and a Monte Carlo statistical analysis technology, and finally, the size and direction of principal stress are obtained, so that the requirement for repeated drilling is reduced, and the working efficiency is improved. And the data scientificity and the measurement efficiency are improved.

Description

Technical Field

[0001] The present invention relates to the field of geotechnical engineering technology, and in particular to a ground stress testing method for single-hole multiple stress relief and combined analysis. Background Art

[0002] In-situ stress refers to the three-dimensional stress state experienced by rock masses in their natural state. It is the fundamental cause of deformation, failure, and stability changes in underground projects. Accurately measuring in-situ in-situ stress states is a crucial foundation for underground project design, construction safety assessment, and rock mechanics research. Therefore, conducting in-situ in-situ in-situ stress measurements has significant theoretical and engineering value.

[0003] Currently, commonly used methods for measuring in-situ stress in engineering practice include ultrasonic wave, hydraulic fracturing, and stress relief. The stress relief method is widely used due to its suitability for hard rock and its ability to quantitatively invert three-dimensional stress components. Stress relief measurement techniques, such as the hollow inclusion method, typically rely on installing strain gauges at a single borehole location, removing stress by drilling or cutting a core, and then inverting the in-situ rock stress using elasticity theory.

[0004] However, existing stress relief methods face the following major problems in practical applications:

[0005] (1) Insufficient data sample size and poor statistical representativeness: Theoretically, six independent strain readings are sufficient to invert the three-dimensional stress components. However, considering the influence of field conditions and the discreteness of strain data, conventional methods only use single measurement results and cannot perform reliable statistical analysis, which can easily lead to unstable ground stress results and large errors.

[0006] (2) Repeated drilling is costly and inefficient: To obtain multiple measurement data to enhance statistical robustness, traditional methods usually require the deployment of multiple boreholes in the same survey area, resulting in a large amount of repeated construction. Especially in deep engineering or hard rock environments, construction costs increase significantly and efficiency is difficult to guarantee.

[0007] (3) Weak ability to identify abnormal data and difficult to control accuracy: The measurement process is affected by factors such as rock mass heterogeneity, construction disturbance, and strain gauge bonding quality. The measured strain data may contain abnormal values that deviate from the main trend. Existing methods lack a systematic mechanism to eliminate abnormal values and often rely on manual judgment, which is highly subjective and affects the accuracy of the solution.

[0008] (4) The solution method is limited and the principal stress direction is unstable: Most methods use a single solution or a small number of combinations for stress inversion, ignoring the non-uniqueness of the solution and the periodicity of the direction statistics. As a result, the principal stress direction calculation is easily affected by individual values and lacks reliability.

[0009] In summary, there is an urgent need for a geostress measurement technology that combines high precision, high efficiency and strong statistical robustness, which can realize multiple strain acquisition and batch solution under single-hole conditions, thereby improving the scientific nature and engineering applicability of geostress inversion. Summary of the Invention

[0010] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a ground stress testing method of single-hole multiple stress release and combined analysis. Through the ground stress measurement technology of single-hole multiple stress release method, multiple stress releases are performed in the same borehole. Combined with combinatorics and Monte Carlo statistical analysis technology, outliers are eliminated, mean calculation and probability distribution analysis are performed on the massive solution set, and finally the magnitude and direction of the principal stress are obtained, thereby reducing the need for repeated drilling, improving data scientificity and measurement efficiency, and being suitable for high-precision determination of in-situ rock stress in underground engineering.

[0011] To achieve the above object, the present invention provides the following solutions:

[0012] A method for geostress testing with multiple stress relief and combined analysis of a single hole, comprising:

[0013] Acquiring strain data at different depths of the rock mass, and calculating stress components on the borehole surface in a borehole coordinate system based on the strain data;

[0014] The far-field stress components of the rock mass in the local rectangular coordinate system are calculated using the stress components, and the stress coordinate system is transformed to obtain the far-field stress components in the global rectangular coordinate system; based on the far-field stress components in the global rectangular coordinate system, the magnitude and direction of the principal stress are obtained. Optionally, calculating the stress components of the borehole surface in the borehole coordinate system based on the strain data includes: calculating the stress components of the borehole surface in the borehole coordinate system based on the strain data, and in the process of calculating the stress components, eliminating strain data for which the least squares fitting error of the in-situ rock stress inversion of the single release data is less than a target value; the expression for calculating the stress components of the borehole surface in the borehole coordinate system based on the strain data is: Among them, E and ν are the elastic modulus and Poisson's ratio of the rock, σ θ is the tangential normal stress, σ x is the axial normal stress, τ θx is the tangential and axial shear stress, ε θ is the tangential strain, ε x is the axial strain, ε 45 is the strain in the 45° direction. Optionally, the far-field stress component of the rock mass in the local rectangular coordinate system calculated using the stress component includes: {σ} θx =[A]{σ0} xyz Where, {σ} θx =[σ θ,θ=0 , σx,θ=0 , τ θx,θ=0 , σ θ,θ=90 , σ x,θ=90 , τ θx,θ=90 , σ θ,θ=225 , σ x,θ=225 , τ θx,θ=225 ] T , {σ0} xyz =[σ 0x , σ 0y , σ 0z , τ 0yz , τ 0zx , τ 0xy ] T ; where {σ} θx is the stress component of the borehole surface in the borehole coordinate system, [A] is a 9×6 coefficient matrix, {σ0} xyz is the far-field stress component of the rock mass in the local rectangular coordinate system, σ θ,θ=0 , σ x,θ=0 , τ θx,θ=0 is the stress component at the 0° position on the drilling surface in the drilling coordinate system, σ θ,θ=90 , σ x,θ=90 , τ θx,θ=90 is the stress component at 90° on the borehole surface in the borehole coordinate system, σ θ,θ=225 , σ x,θ=225 , τ θx,θ=225 is the stress component at the 225° position on the borehole surface in the borehole coordinate system, σ 0x , σ 0y , σ 0z , τ 0yz , τ 0zx , τ 0xy is the far-field stress component of the rock mass in the local rectangular coordinate system, and T is the transposed matrix symbol.

[0015] Optionally, obtaining the far-field stress component in the global rectangular coordinate system includes:

[0016] {σ} XYZ =[R] T {σ0} xyz [R]

[0017] Among them, {σ} XYZ is the far-field stress component of the rock mass in the global rectangular coordinate system, [R] is the transformation matrix, {σ0} xyz is the far-field stress component in the local rectangular coordinate system.

[0018] Optionally, the transformation matrix is expressed as:

[0019]

[0020] In the formula, l1=-cosγsinα, m1=-cosβcosα, n1=-sinβ, l2=cosα, m2=-sinα, n2=0, l3=-sinβsinα, m3=-sinβcosα, n3=cosβ;

[0021] Among them, l1, l2, l3, m1, m2, m3, n1, n2, and n3 are the direction cosines of the coordinate axes of the local coordinate system in the global coordinate system, α is the strike direction of the drilling direction, and β is the inclination angle of the drilling direction.

[0022] Optionally, obtaining the magnitude and direction of the principal stress includes:

[0023] Obtaining the magnitude of the principal stress based on the far-field stress component in the global rectangular coordinate system;

[0024] In the process of obtaining the magnitude of the principal stress, the far-field stress component is substituted into a calculation model to obtain multiple available calculation models, a target number of available calculation models are randomly selected to obtain multiple principal stress solutions, the mean and standard deviation of all principal stress magnitudes are calculated, and extreme solutions whose deviation from the mean exceeds a target multiple of the standard deviation are discarded;

[0025] The discarded principal stress magnitudes are averaged twice to obtain the final principal stress magnitudes, and the directions of the principal stresses are obtained through the direction cosines of the final principal stress magnitudes in the global rectangular coordinate system.

[0026] Optionally, obtaining the magnitude of the principal stress includes:

[0027] σ 3 -J1σ 2 -J2σ-J3=0

[0028] Where J1 is the first constant, J2 is the second constant, J3 is the third constant, and σ is the unknown principal stress to be solved.

[0029] Optionally, the expressions of the first constant, the second constant and the third constant are:

[0030]

[0031] Among them, σ x , σ y , σ z , τ xy , τ yz , τ zx is the far-field stress component of the rock mass in the global rectangular coordinate system.

[0032] Optionally, calculate the mean and standard deviation of all principal stress magnitudes by:

[0033]

[0034] Where i = 1, 2, 3, is the mean, s i is the standard deviation, N is the number of principal stress solution sets, is the kth principal stress solution set.

[0035] Optionally, obtaining the direction of the principal stress includes:

[0036]

[0037] β=-sin -1 n

[0038] Among them, l, m, and n are the direction cosines of the principal stresses in the global rectangular coordinate system, that is, the eigenvectors.

[0039] The beneficial effects of the present invention are:

[0040] The present invention significantly improves the reliability of ground stress measurement data: by multiple stress releases (6-10 times) on a single hole, a cumulative total of 54 to 90 strain data are obtained, combined with combinatorics and Monte Carlo statistics (generating tens of thousands of solution sets), expanding the sample size and eliminating outliers (deviating from the mean by 2σ and R 2 <0.5), making the principal stress mean and probability distribution analysis more scientific and reducing data discreteness by more than 30%.

[0041] The present invention reduces the cost of repeated drilling construction: multiple stress relief operations are completed in the same borehole (with a depth interval of 2-3 meters), avoiding the disadvantage of multiple drilling required by traditional methods. The construction efficiency is increased by 40%, and the drilling workload is reduced by 50%. It is particularly suitable for complex engineering environments such as deep rock masses.

[0042] The present invention realizes high-precision in-situ rapid stress analysis: based on the Liemann-Kirsch joint solution (Formulas 1-3) and coordinate system transformation (matrix [R]), combined with the Monte Carlo direction cosine matrix averaging method, the principal stress eigenvalue calculation (σ1, σ2, σ3) and direction statistics (stereoscopic projection diagram) of massive solution sets can be quickly completed by computer, with the error standard deviation controlled within 10%, meeting the real-time decision-making needs of the engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0044] Figure 1A schematic diagram of a multiple stress relief method according to an embodiment of the present invention;

[0045] Figure 2 This is a schematic diagram of the arrangement of the hollow enclosed strain gauges according to an embodiment of the present invention;

[0046] Figure 3 A schematic diagram of the relationship between a borehole coordinate system and a geodetic coordinate system in a scenario according to an embodiment of the present invention;

[0047] Figure 4 The probability density histogram of the maximum principal stress, minimum principal stress, and vertical principal stress measured by the stress relief method according to an embodiment of the present invention;

[0048] Figure 5 The equal-area projection diagram of the lower hemisphere of the direction of the principal stress measured in the embodiment of the present invention;

[0049] Figure 6 The equal-area projection diagram of the hemisphere in the direction of all calculated principal stresses of the embodiment of the present invention;

[0050] Figure 7 This is a flow chart of a method for geostress testing with multiple stress releases and combined analysis of a single hole according to an embodiment of the present invention;

[0051] Among them, 1-first hollow inclusion, 2-second hollow inclusion, 3-third hollow inclusion, n-nth hollow inclusion, 5-hollow inclusion, 6-0° strain rosette, 7-90° strain rosette, 8-225° strain rosette. DETAILED DESCRIPTION

[0052] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0053] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0054] This embodiment discloses a single-hole multiple stress relief and combined analysis ground stress testing method, including: obtaining strain data at different depths, and calculating the stress components of the borehole surface in the borehole coordinate system based on the strain data; using the stress components to calculate the far-field stress components of the rock mass in the local rectangular coordinate system, and performing stress coordinate system transformation to obtain the far-field stress components in the global rectangular coordinate system; based on the far-field stress components in the global rectangular coordinate system, obtaining the magnitude and direction of the principal stress.

[0055] Specifically, this embodiment discloses a method for geostress testing with multiple stress releases and combined analysis in a single hole, including:

[0056] S1. Drill a large hole, a tapered hole, and a concentric small hole in the surrounding rock in sequence;

[0057] S2. Install a hollow enclosure containing three sets of right-angled strain gauge rosettes in the small hole. The rosettes are distributed along the circumference at θ = 0°, 90°, and 225°. Each set contains three strain gauges spaced 45° apart.

[0058] S3. Perform multiple stress relief operations, obtaining strain data at different depths after each relief operation;

[0059] S4. Establish the stress component equations in the borehole coordinate system based on the Leaman elastic solution, that is, use the stress components to calculate the far-field stress components of the rock mass in the local rectangular coordinate system;

[0060] S5. Use the Kirsch solution to construct a matrix equation to calculate the far-field stress components in the local rectangular coordinate system from the stress components in the borehole coordinate system;

[0061] S6. Based on the far-field stress components in the global rectangular coordinate system, the magnitude and direction of the principal stress are obtained, and outliers are eliminated from the massive solution set through Monte Carlo statistics to calculate the mean and probability distribution of the principal stress.

[0062] like Figure 1-2 As shown, obtaining strain data at different depths includes:

[0063] Holes are drilled in the surrounding rock in sequence, including large holes, tapered holes, and concentric small holes. Hollow inclusions containing three sets of right-angle strain gauge rosettes are installed in the small holes, and multiple stress relief operations are performed, including:

[0064] Drilling large holes: When measuring tunnels or chambers underground, use a drilling rig to drill stress relief holes horizontally into the surrounding rock. The drilling depth shall be based on the range of the tunnel surrounding rock stress field, and the end hole point shall not be affected by the tunnel surrounding rock stress field.

[0065] Drill a tapered hole: Replace the tapered drill bit and drill a tapered hole at the bottom of the hole. Its function is to serve as a positioning and ensure that the small hole to be drilled later is concentric with the large hole.

[0066] Drilling a small hole: Use a small drill bit with a diameter of 36mm, drill the hole to the bottom, make a mark on the outside of the drill rod, and then drill a small hole. Stop when the drill reaches the predetermined length.

[0067] The hollow inclusions include: a first hollow inclusion 1, a second hollow inclusion 2, a third hollow inclusion 3, an nth hollow inclusion n, and a hollow inclusion 5;

[0068] The three sets of right-angle strain gauge rosettes include: 0° strain gauge rosette 6, 90° strain gauge rosette 7, and 225° strain gauge rosette 8.

[0069] Clean the small hole and install the package: After drilling the small hole, remove the residue or rock powder inside the hole to keep the hole clean and ensure that the strain gauge can be tightly attached to the rock.

[0070] Installation of strain gauge: By recording the length, use the push rod to push the strain gauge into the small hole, and apply pressure to push the positioning pin to make the glue flow out and fully fill the gap between the rock mass and the strain gauge.

[0071] Stress relief: After the package has been installed for 24 hours, epoxied and the strain gauge installed. When the reading stabilizes, the value is the initial value. When the strain gauge reading stabilizes, no more stress relief is performed. The core is broken and removed.

[0072] On the basis of the first geostress measurement, repeat the measurement steps S2 to S3 to perform geostress measurements multiple times in succession.

[0073] When drilling large holes, the drilling angle is 3° to 5° upward, the drilling diameter is 130mm, and the hole depth is 3 to 5 times the excavation diameter.

[0074] Drill a small hole with a diameter of 36mm and a depth of 300mm.

[0075] Three groups of right-angle strain rosettes are embedded on the surface of the hollow package and distributed along the same circumference at θ of 0°, 90° and 225°. Each group of strain rosettes consists of three strain gauges, which are spaced 45° apart.

[0076] The ground stress measurement was carried out continuously for 6 to 10 times, and the stress relief depth interval was 0.5 meters each time.

[0077] Furthermore, the stress components of the borehole surface in the borehole coordinate system are calculated based on the strain data, including:

[0078] The stress components of the borehole surface in the borehole coordinate system are calculated based on the strain data. In the process of calculating the stress components, the strain data whose least square fitting error of the in-situ rock stress inversion of the single release data is less than the target value are eliminated.

[0079] Specifically, according to the strain ε measured at three measurement positions (ie, θ = 0°, 90°, and 225°), x , εθ and ε 45 , calculate the stress component {σ}θ on the borehole surface in the borehole coordinate system x The calculation is done using the Leeman elastic solution formula, the specific formula is as follows:

[0080]

[0081] Where E and μ are the elastic modulus and Poisson's ratio of the rock, respectively.

[0082] Using the Kirsch solution, the stress components {σ}θ on the borehole surface in the borehole coordinate system are x Calculate the far-field stress component {σ0} in the local rectangular coordinate system xyz The specific calculation formula is:

[0083] {σ} θx =[A]{σ0} xyz (2)

[0084] Where, {σ} θx =[σ θ,θ＝0 , σ x,θ＝0 , τ θx,θ＝0 , σ θ,θ＝90 , σ x,θ＝90 , τ θx,θ＝90 , σ θ,θ＝225 , σ x,θ＝225 , τ θx,θ＝225 ] T , {σ0} xyz =[σ 0x , σ 0y , σ 0z , τ 0yz , τ 0zx , τ 0xy ] T ;

[0085] Among them, {σ} θx is the stress component of the borehole surface in the borehole coordinate system, [A] is a 9×6 coefficient matrix, {σ0} xyz is the far-field stress component of the rock mass in the local rectangular coordinate system, σ θ,θ＝0 , σ x,θ＝0 , τ θx,θ＝0 is the stress component at the 0° position on the drilling surface in the drilling coordinate system, σ θ,θ＝90 , σ x,θ＝90 , τ θx,θ＝90 is the stress component at 90° on the borehole surface in the borehole coordinate system, σ θ,θ＝225 , σ x,θ＝225 , τ θx,θ＝225 is the stress component at the 225° position on the borehole surface in the borehole coordinate system, σ 0x , σ 0y , σ 0z , τ 0yz , τ 0zx , τ 0xy is the far-field stress component of the rock mass in the local rectangular coordinate system, and T is the transposed matrix symbol.

[0086] [A] is a 9×6 matrix, and its explicit expression is:

[0087]

[0088] It should be noted that formula (2) means that 9 equations are needed to solve 6 unknowns.

[0089] Then, the stress coordinate system transformation is performed to obtain the far-field stress component {σ} in the global rectangular coordinate system XYZ , the specific transformation matrix is:

[0090] {σ} XYZ =[R] T {σ0} xyz [R] (4)

[0091] Among them, {σ} XYZ is the far-field stress component of the rock mass in the global rectangular coordinate system, [R] is the transformation matrix, {σ0} xyz is the far-field stress component in the local rectangular coordinate system.

[0092] The transformation matrix [R] is:

[0093]

[0094] In the formula, l1=-cosβsinα, m1=-cosβcosα, n1=-sinβ, l2=cosα, m2=-sinα, n2=0, l3=-sinβsinα, m3=-sinβcosα, n3=cosβ;

[0095] Among them, l1, l2, l3, m1, m2, m3, n1, n2, and n3 are the direction cosines of the coordinate axes of the local coordinate system in the global coordinate system, α is the strike direction of the drilling direction, and β is the inclination angle of the drilling direction.

[0096] Furthermore, obtaining the magnitude and direction of the principal stress includes: obtaining the magnitude of the principal stress based on the far-field stress component in the global rectangular coordinate system; in the process of obtaining the magnitude of the principal stress, substituting the far-field stress component into the calculation model to obtain multiple available calculation models, randomly selecting a target number of available calculation models to obtain multiple principal stress solutions, calculating the mean and standard deviation of all principal stress magnitudes, and discarding extreme solutions that deviate from the mean by more than a target multiple of the standard deviation; performing secondary averaging on the discarded principal stress magnitudes to obtain the final principal stress magnitude, and obtaining the direction of the principal stress through the direction cosines of the final principal stress magnitude in the global rectangular coordinate system.

[0097] Furthermore, the stress tensor [σ] is then calculated XYZThe eigenvalues and corresponding eigenvectors of are used to determine the magnitude and direction of the three in-situ principal stress components. The specific calculation formula is:

[0098] σ 3 -J1σ 2 -J2σ-J3=0 (6)

[0099] Where J1 is the first constant, J2 is the second constant, J3 is the third constant, and σ is the unknown principal stress to be solved.

[0100] J1, J2, and J3 can be calculated using formula (7), where formula (7) is as follows:

[0101]

[0102] It should be noted that, in some embodiments, after J1, J2, and J3 are calculated using formula (7), J1, J2, and J3 can be substituted into formula (6) to solve formula (6) to obtain the three solutions, namely, the magnitudes of the principal stresses σ1, σ2, and σ3. The maximum value among the three solutions is the maximum principal stress σ1, the minimum value among the three solutions is the minimum principal stress σ3, and the remaining solution is the intermediate principal stress σ2.

[0103] Finally, the main direction is represented by the strike α and dip β obtained by transforming the eigenvectors.

[0104]

[0105] β=-sin -1 n (9)

[0106] Where l, m, and n are the direction cosines of the principal stresses in the global rectangular coordinate system, i.e., the eigenvectors. The above is the theoretical basis and calculation process for calculating in-situ stress using strain values measured by the stress relief method.

[0107] Calculating the mean and standard deviation of all principal stress solutions involves:

[0108]

[0109] Where i = 1, 2, 3, is the mean, s i is the standard deviation, N is the number of principal stress solution sets, is the kth principal stress solution set.

[0110] Specifically, as mentioned above, a single measurement can obtain 9 strain readings, and 6 stress components need to be solved from the 9 available equations (Equation 2). From a mathematical point of view, we have For multiple measurements of strain values at different depths at the same borehole, combinatorics can be used to solve tens of thousands of ground stress values, expanding the number of samples. Monte Carlo statistical analysis is performed on a large number of independent solutions to obtain the mean, deviation, and probability distribution of the three principal stresses.

[0111] Monte Carlo statistical analysis process:

[0112] For the strain data of each measurement section, first calculate the stress component in the drilling coordinate system

[0113] Outlier elimination: For stress data in a single analysis result, the stress data whose least squares fitting error of the in-situ stress inversion of the single release data is less than the target value is eliminated, that is, the mean and standard deviation of the solution set are calculated, and the solution that deviates from the mean by more than 3 times the standard deviation is eliminated; if the single inversion fitting error R 2 <0.5, the data were considered invalid.

[0114] Construct equation: Stress relief N times, stress components Substituting into formula (2), we will get 9N available equations.

[0115] Permutations and combinations of equations: Select 6 from the 9N available equations to get principal stress solutions.

[0116] Solution set data simplification: Calculate the mean and standard deviation of all solutions, discard extreme solutions that deviate from the mean by more than 2 times the standard deviation, and avoid outliers interfering with the statistical results.

[0117] Stress solution set: Perform quadratic averaging on the retained principal stress solution set to obtain the final principal stress magnitude. The direction of the principal stress is obtained through the direction cosine of the final principal stress magnitude in the global rectangular coordinate system.

[0118] Statistical calculation: For the stress solution set, calculate the following statistics:

[0119] ① Mean:

[0120] The mean is the measured principal stress.

[0121] ②Standard deviation:

[0122] Directional statistics: The mean of the principal stress directions (strike α and dip angle β) is calculated using the direction cosine matrix averaging method to avoid the periodicity problem of direct angle averaging.

[0123] Draw probability distribution: divide the principal stress into intervals, count the number of solutions in each interval, and generate a probability density curve (such as Figure 4 ).

[0124] Draw a stereographic projection: Display the distribution of principal stress directions ( Figure 5 ).

[0125] Draw a scatter plot: The principal stress directions of all solutions are projected onto the lower hemisphere ( Figure 6 ), which directly reflects the degree of data concentration.

[0126] like Figure 7 As shown, this embodiment discloses a specific implementation step of a single-hole multiple stress relief and combined analysis ground stress testing method, including:

[0127] Preparation for drilling construction: Select the measurement area: In underground engineering tunnels or chambers, select sections with good surrounding rock integrity and no obvious cracks as measurement points.

[0128] Equipment configuration: A three-axis directional drilling rig equipped with a 130 mm large-hole drill bit, a tapered repair drill bit, and a 36 mm small-hole drill bit; a hollow-enclosed strain gauge (including three sets of right-angle strain rosettes with strain gauges spaced 45° apart); a data acquisition instrument and a data processing terminal with a built-in Monte Carlo analysis module, as shown in Table 1.

[0129] Drilling construction and strain gauge installation:

[0130] Table 1 Drilling parameters for ground stress measurement

[0131] category Drilling name Report No. Drilling direction Drilling azimuth-inclination Overburden thickness Details Ch.1856 DYL001 94° 6° 725m

[0132] Step S1: Drilling a large hole: Using a 130 mm drill bit, drill a large hole in a horizontal direction (or upward at an inclination angle of 3° to 5° according to the design) to a depth of 8 meters.

[0133] Step S2: Trimming the tapered hole: Replace the tapered drill bit and machine a tapered hole (depth 50 mm) at the bottom of the hole for subsequent small hole positioning and concentricity assurance.

[0134] Step S3: Drilling a small hole: Use a 36mm small hole drill bit, continue drilling to a predetermined depth of 300mm, and mark the footage position on the outer wall of the drill pipe.

[0135] Step S4: Cleaning and Enclosure Installation: Use a high-pressure air gun to remove rock dust from the small hole, ensuring the hole wall is clean. A hollow enclosure strain gauge (the difference between the epoxy resin elastic modulus and the surrounding rock modulus is ≤15%) is pushed to the bottom of the small hole using a push rod. Pressure is applied to break the dowel pin, and the gap between the enclosure and the hole wall is filled with adhesive. The gauge is then left to cure for 24 hours.

[0136] Multiple stress relief and data collection:

[0137] Step S5: First stress relief: Use a thin-wall drill to extend the large hole and perform the first stress relief. The relief depth is 2-3 meters. The real-time strain data (ε) of three sets of strain rosettes (θ=0°, 90°, 225°) are recorded by the data acquisition instrument. x , ε θ , ε 45° ) until the core is completely separated from the surrounding rock and then broken off and taken out.

[0138] Step S6: Repeat the stress release operation: repeat steps S2-S5, re-trim the tapered hole and drill a new small hole before each stress release. A total of 8 stress releases were performed, with the adjacent release depths separated by 0.5 m. A total of 72 strain data were obtained, as shown in Table 2.

[0139] Table 2 Strain readings of borehole measurements for ground stress measurement

[0140]

[0141] Calculation and statistical analysis of geostress:

[0142] Step S7: Stress component calculation: According to the Leaman elastic solution (Formula 1), the strain data is converted into stress components {σ}θx in the drilling coordinate system.

[0143] Outlier elimination: For stress data in a single analysis result, the stress data whose least squares fitting error of the in-situ stress inversion of the single release data is less than the target value is eliminated, that is, the mean and standard deviation of the solution set are calculated, and the solution that deviates from the mean by more than 3 times the standard deviation is eliminated; if the single inversion fitting error R 2 <0.5, the data were considered invalid.

[0144] Step S8: Constructing a matrix equation: Based on the Kirsch solution (Formula 2), a 9×6 coefficient matrix [A] is established. The far-field stress {σ0}_xyz converted to the local coordinate system is:

[0145] The specific form of the matrix [A] is shown in formula (3) in the specification.

[0146] Step S9: Monte Carlo statistical analysis: Combinatorics solution set generation: Randomly select 6 from the 72 strain equations to generate C(72,6) solution sets.

[0147] like Figure 3 As shown, coordinate system transformation: {σ0}xyz is transformed to the global coordinate system {σ} through the matrix [R] (determined by the borehole strike α and inclination angle β) XYZ , and calculate the eigenvalues of the stress tensor to obtain the principal stresses σ1, σ2, σ3 and their direction cosines.

[0148] Statistical output: Calculate the mean and standard deviation of all solutions, discard extreme solutions that deviate from the mean by more than 2 times the standard deviation, and avoid outliers interfering with the statistical results. Perform a secondary mean on the retained principal stress solutions to obtain the final principal stress magnitude. The direction cosine of the final principal stress magnitude in the global rectangular coordinate system is used to obtain the direction of the principal stress and generate a stereographic projection ( Figure 5 ) and the probability density curve ( Figure 4 ).

[0149] The data is visualized using the data processing software MATLAB and the following chart is output:

[0150] Principal stress probability distribution histogram ( Figure 4 ): Displays the probability density distribution of σ1, σ2, and σ3 to verify the neutrality of the data set.

[0151] Directional hemispherical projection ( Figure 6 ): Displays the statistical distribution of principal stress directions and evaluates directional consistency.

[0152] Compare the standard deviation of multiple release results (usually required to be <10%). If it exceeds the limit, recalibrate the equipment or re-measure the data, as shown in Table 3.

[0153] Table 3 Ground stress measurement results

[0154] principal stresses average value Average Deviation Standard deviation Direction inclination <![CDATA[σ1]]> 16.31 2.37 2.9 100 50.4 <![CDATA[σ2]]> 8.52 1.87 2.36 251.6 36 <![CDATA[σ3]]> 2.34 1.69 2.2 352.2 14.2

[0155] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for geostress testing with multiple stress release and combined analysis of a single hole, characterized in that: include: Acquiring strain data at different depths of the rock mass, and calculating stress components on the borehole surface in a borehole coordinate system based on the strain data; Calculating the far-field stress components of the rock mass in a local rectangular coordinate system using the stress components, and performing stress coordinate system transformation to obtain the far-field stress components in a global rectangular coordinate system; Based on the far-field stress components in the global rectangular coordinate system, the magnitude and direction of the principal stress are obtained.

2. The method for testing ground stress by multiple stress relief and combined analysis of a single hole according to claim 1, characterized in that: Calculating the stress components of the borehole surface in the borehole coordinate system based on the strain data includes: Calculating stress components of the borehole surface in the borehole coordinate system based on the strain data, and in the process of calculating the stress components, eliminating strain data for which the least squares fitting error of the in-situ stress inversion of the single release data is less than a target value; The expression for calculating the stress component of the borehole surface in the borehole coordinate system based on the strain data is: Among them, E and ν are the elastic modulus and Poisson's ratio of the rock, σ θ is the tangential normal stress, σ x is the axial normal stress, τ θx is the tangential and axial shear stress, ε θ is the tangential strain, ε x is the axial strain, ε 45 is the strain in the 45° direction.

3. The method for testing ground stress by multiple stress release and combined analysis of a single hole according to claim 1, characterized in that: Calculating the far-field stress components of the rock mass in the local rectangular coordinate system using the stress components includes: {s} θx =[A]{σ0} xyz In the formula, {σ0} xyz = [σ 0x , σ 0y , σ 0z , τ 0yz , τ 0zx , τ 0xy T ;​ Among them, {σ} θx is the stress component of the borehole surface in the borehole coordinate system, [A] is a 9×6 coefficient matrix, {σ0} xyz is the far-field stress component of the rock mass in the local rectangular coordinate system, is the stress component at 0° on the drilling surface in the drilling coordinate system, is the stress component at 90° on the drilling surface in the drilling coordinate system, is the stress component at 90° of the borehole surface in the borehole coordinate system, σ0x, σ0y, σ0z, τ0yz, τ0zx, τ0xy are the far-field stress components of the rock mass in the local rectangular coordinate system, and T is the transposed matrix symbol.

4. The method for testing ground stress by multiple stress relief and combined analysis of a single hole according to claim 1, characterized in that: Obtaining the far-field stress components in the global rectangular coordinate system includes: {s} XYZ =[R] T {σ0} xyz [R] Among them, {σ} XYZ is the far-field stress component of the rock mass in the global rectangular coordinate system, [R] is the transformation matrix, {σ0} xyz is the far-field stress component in the local rectangular coordinate system.

5. The method for testing ground stress by multiple stress relief and combined analysis of a single hole according to claim 4, characterized in that: The expression of the transformation matrix is: In the formula, l1=-cosβsinα, m1=-cosβcosα, n1=-sinβ, l2=cosα, m2=-sinα, n2=0, l3=-sinβsinα, m3=-sinβcosα, n3=cosβ; Among them, l1, l2, l3, m1, m2, m3, n1, n2, and n3 are the direction cosines of the local coordinate axes in the global coordinate system, α is the strike direction of the drilling direction, and β is the inclination angle of the drilling direction.

6. The method for testing ground stress by multiple stress relief and combined analysis of a single hole according to claim 1, characterized in that: Obtaining the magnitude and direction of the principal stress includes: Obtaining the magnitude of the principal stress based on the far-field stress component in the global rectangular coordinate system; In the process of obtaining the magnitude of the principal stress, the far-field stress component is substituted into a calculation model to obtain multiple available calculation models, a target number of available calculation models are randomly selected to obtain multiple principal stress solutions, the mean and standard deviation of all principal stress magnitudes are calculated, and extreme solutions whose deviation from the mean exceeds a target multiple of the standard deviation are discarded; The discarded principal stress magnitudes are averaged twice to obtain the final principal stress magnitudes, and the directions of the principal stresses are obtained through the direction cosines of the final principal stress magnitudes in the global rectangular coordinate system.

7. The method for testing ground stress by multiple stress release and combined analysis of a single hole according to claim 6, characterized in that: Obtaining the magnitude of the principal stress includes: s 3 -J1σ 2 -J2σ-J3=0 Where J1 is the first constant, J2 is the second constant, J3 is the third constant, and σ is the unknown principal stress to be solved.

8. The method for testing ground stress by multiple stress release and combined analysis of a single hole according to claim 7, characterized in that: The expressions of the first constant, the second constant and the third constant are: Among them, σ x , σ y , σ z , τ xy , τ yz , τ zx is the far-field stress component of the rock mass in the global rectangular coordinate system.

9. The method for testing ground stress by multiple stress release and combined analysis of a single hole according to claim 6, characterized in that: Calculating the mean and standard deviation of all principal stress magnitudes involves: Where i = 1, 2, 3, is the mean, s i is the standard deviation, N is the number of principal stress solution sets, is the kth principal stress solution set.

10. The method for testing ground stress by multiple stress release and combined analysis of a single hole according to claim 1, characterized in that: Obtaining the direction of the principal stress includes: β=-sin -1 n Among them, l, m, and n are the direction cosines of the principal stresses in the global rectangular coordinate system, that is, the eigenvectors.

Images