Inversion method of initial in-situ stress based on correction of tunnel excavation disturbance

Abstract

The present invention discloses an inversion method for initial in-situ stress based on tunnel excavation disturbance correction, which includes the following steps: Step 1) Conduct in-situ stress tests on long tunnels to obtain the measured in-situ stress values; Step 2) Calculate the inclination angle value of the relationship between the force distribution of the in-situ stress at the measuring point and the tunnel alignment; Step 3) Construct a spatial rectangular coordinate system OXYZ, and convert the relationship between the force distribution of the in-situ stress at the measuring point and the tunnel alignment into the form of in-situ stress tensor in the spatial rectangular coordinate system OXYZ; Step 4) Set multiple principal stresses in sequence. Set the second principal stress Sz as generated by self-weight and invert the unit weight γ of the surrounding rock. Correct the first principal stress SH and the third principal stress Sh. Introduce correction coefficients k and λ for the first and second principal stresses respectively, and calculate the initial in-situ stress value; Step 5) Compare the initial in-situ stress value with the measured in-situ stress value to invert the result of the final initial in-situ stress. The beneficial effects of the present invention: Through the original principal stresses, invert the unit weight γ and introduce correction coefficients k and λ to calculate the initial in-situ stress value.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction, and particularly to an inversion method for initial in-situ stress based on the correction of tunnel excavation disturbance. Background Art

[0002] Due to the limitations of objective factors such as in-situ stress measurement technology and economy, in-situ stress inversion has become the mainstream method for clarifying the initial in-situ stress state in the tunnel site area and preventing geological disasters. At present, the most common in-situ stress inversion methods at home and abroad are divided into two categories: one is to perform back-analysis on the initial stress of the site according to the deformation of the tunnel during the excavation disturbance process; the other is to establish a calculation model by using the analytical method or numerical method based on the measured results of local in-situ stress in the site, and combine multivariate analysis methods such as linear regression and neural network for in-situ stress fitting.

[0003] For example, according to the local measured in-situ stress data of the Lanjiayan extra-deep highway tunnel site, boundary conditions with different forces and displacements are applied to simulate the tectonic movement of the site, and combined with ANSYS numerical simulation and multiple linear regression analysis, the back-analysis of the in-situ stress distribution law around the tunnel site and fault zone is carried out, and the relative error can be controlled within 13%; there is also to combine FLAC and RBF neural network to perform multivariate non-linear analysis on the in-situ stress field characteristics of the river valley slopes and main tunnel projects along the Sangri-Jiucha Canyon section. The maximum error of the principal stress is 25%, and the fitting is good, while the shear stress fitting is poor. And according to the stress distribution, the possible engineering problems during the tunnel construction process are proposed; there is also to use the displacement discontinuity numerical method to simulate the fault in the case of no measured in-situ stress, and thus propose an initial in-situ stress DDM regression inversion method for the fracture structure disturbance area based on the fault strike and throw. The application results show that the maximum error of this method is only 8.4%, and the results have a certain reliability.

[0004] To sum up, scholars at home and abroad have made certain research on the inversion of the initial in-situ stress field in the tunnel site area and achieved good applications, but there are still certain limitations. For example, most of them need to perform in-situ stress measurement before tunnel excavation disturbance. For extra-long tunnels with large depth and buried depth, the in-situ stress boreholes are far from the tunnel body area, and the inversion results may have certain differences from the actual situation. At the same time, if due to objective reasons, the in-situ stress test can only be carried out after the tunnel or auxiliary adit excavation disturbance in the actual project, the obtained results may be the excavation disturbance stress. For the above problems, at present, the measured in-situ stress is obtained after the tunnel excavation disturbance in the tunnels along the Lhasa-Nyingchi section of the Sichuan-Tibet Railway, and an inversion method for the initial in-situ stress based on the numerical simulation of tunnel construction excavation and the measured in-situ stress value needs to be studied according to the in-situ stress situation. However, from the above description, the inversion results of the initial in-situ stress obtained by the in-situ stress test after the excavation disturbance of extra-deep and long tunnels cannot be achieved. Summary of the Invention

[0005] The technical problem to be solved by the present invention is the technical problem that the inversion result of the initial in-situ stress in the tunnel site area cannot be measured after the excavation disturbance of an extremely large and deeply buried long tunnel. The purpose of the present invention is to provide an inversion method for the initial in-situ stress corrected based on tunnel excavation disturbance, and the present invention can measure the inversion result of the initial in-situ stress in the tunnel site area after the excavation disturbance of an extremely large and deeply buried long tunnel.

[0006] The present invention is realized through the following technical solutions:

[0007] An inversion method for the initial in-situ stress corrected based on tunnel excavation disturbance includes the following steps:

[0008] Step 1) Use the hollow inclusion method to test the in-situ stress after the excavation disturbance in the tunnel site area of the long tunnel, and obtain the measured in-situ stress values of the measuring points in the buried tunnel site area;

[0009] Step 2) Use the measured in-situ stress values to calculate the dip angle value of the relationship between the force distribution of the in-situ stress of the measuring points in the tunnel site area and the tunnel alignment;

[0010] Step 3) Construct a spatial rectangular coordinate system OXYZ, and use the spatial rectangular coordinate system OXYZ as the spatial rectangular coordinate system OXYZ for constructing the analysis of the measured in-situ stress. Convert the relationship between the force distribution of the in-situ stress of the measuring points in the tunnel site area and the tunnel alignment into the form of in-situ stress tensor in the spatial rectangular coordinate system OXYZ. Among them, assume that the force distribution of the in-situ stress of the measuring points is multiple principal stresses, and set the angle between each principal stress and the coordinate axis as the dip angle;

[0011] Step 4) Sequentially set the first principal stress as S H , the second principal stress as S Z and the third principal stress as S h . Set that the second principal stress S Z is generated by the self-weight of the surrounding rock. Through the second principal stress S Z , the unit weight γ of the surrounding rock is inversely calculated. The first principal stress S H and the third principal stress S h are corrected and the correction coefficients k and λ are introduced respectively. Combining with the measured in-situ stress values, when k and λ are determined, the initial in-situ stress value of the surrounding rock is calculated;

[0012] Step 5) Compare the initial in-situ stress value of the surrounding rock with the measured in-situ stress values. Within the allowable error range after comparison (the value of the allowable error does not exceed 5%), the final result of the initial in-situ stress is obtained.

[0013] In step 1), when testing the in-situ stress after the excavation disturbance in the tunnel site area of the long tunnel, set the test part or measuring points at the arch waist of the tunnel chamber, and conduct the test at a distance of 2 times the tunnel diameter from the tunnel wall.

[0014] In step 2), when analyzing the inclination angle value of the relationship between the force distribution of the ground stress at the measuring point in the tunnel site and the tunnel direction, the number of inclination angles is set to a plurality of inclination angles.

[0015] In step 3), each principal stress corresponds to its own inclination angle, and the spatial rectangular coordinate system OXYZ is set, with the tunnel direction as the Y axis, the vertical direction as the Z axis, the X axis and the Y axis in the same plane, and the X axis and the Z axis perpendicular.

[0016] In step 4), the first principal stress S H and the third principal stress S h Distributed along the horizontal direction, the second principal stress S Z Distributed along the vertical direction, the first principal stress S H To the third principal stress S h After the inclination angle transformation f in the spatial rectangular coordinate system OXYZ, the transformation process of the ground stress tensor form is as follows:

[0017]

[0018] The specific steps for converting the geostress tensor form in the spatial rectangular coordinate system OXYZ are as follows:

[0019] Step S1) setting the second principal stress S Z Distributed along the deadweight direction or vertical direction, the first principal stress S H , the third principal stress S h Located in the horizontal plane and the two directions are perpendicular to each other;

[0020] Step S2) setting the surrounding rock in the tunnel as a continuous medium model, which is isotropic;

[0021] Step S3) Set the second principal stress S Z Mainly generated by the deadweight of the surrounding rock, through the second principal stress S Z Inversely calculate the gravity γ of the surrounding rock;

[0022] Step S4) The first principal stress S H , the third principal stress S h Correction is made. The formula (1) is a linear transformation process, so the first principal stress S H and the third principal stress S h Equivalent to S xx and S yy Correction, S xx and S yy Introducing the correction coefficients k and λ respectively, the distribution component S' of the initial ground stress is xx 、S' yyWith the distribution component S of the in-situ stress tested xx and S yy Calculate through the relationship of the following formulas (2) and (3):

[0023] S' xx = kS xx (2)

[0024] S' yy = λS yy (3)

[0025] When the correction factors k and λ are determined, the initial in-situ stress value of the surrounding rock can be determined.

[0026] The correction factor k range of the first principal stress S on the X-axis H is 1.236 to 1.404, and the correction factor λ range of the third principal stress S on the Y-axis h is 0.846 to 1.069.

[0027] The method for determining the initial in-situ stress value includes the following steps:

[0028] Step a) Determine the unit weight γ of the surrounding rock according to the second principal stress S Z ;

[0029] Step b) Determine the physical property parameters of the surrounding strata and the parameters of the tunnel construction project according to the exploration and design data;

[0030] Step c) Set the correction factors k and λ;

[0031] Step d) Construct the field area of the initial in-situ stress;

[0032] Step e) Use numerical calculation software to simulate the tunnel construction, and extract the in-situ stress value or state of the measuring point;

[0033] Step f) Compare the in-situ stress value of the measuring point with the initial in-situ stress value of the initial in-situ stress field area. If the comparison value is within the allowable error value range, invert the final initial in-situ stress value or state, otherwise return to step c) and re-determine the final initial in-situ stress value or state.

[0034] In step 4), use the correction factors k and λ to construct the initial in-situ stress value of the surrounding rock, simulate the excavation disturbance using construction software, and calculate the maximum error between the values of the first principal stress S H and the third principal stress S h of the surrounding rock in the tunnel site area after excavation disturbance and the tested in-situ stress value.

[0035] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0036] 1. The present invention mainly aims at the inversion of the initial in-situ stress in the tunnel along a certain section of the Lhasa-Nyingchi section of the Sichuan-Tibet Railway, that is, a super-large and deeply buried long tunnel. It also proposes an inversion method for the initial in-situ stress of the excavation disturbance simulation and field in-situ stress test results of the super-large and deeply buried long tunnel. The present invention uses the original first principal stress S H 、the second principal stress S Z and the third principal stress S h . It is assumed that S Z is generated by the self-weight of the surrounding rock. Through S Z , the unit weight γ of the surrounding rock is inversely calculated. For S H and S h , corrections are made, that is, S H and S h respectively introduce correction coefficients k and λ. Combining the measured in-situ stress values, when k and λ are determined, the initial in-situ stress value of the surrounding rock is calculated. As long as the initial in-situ stress value is compared with the measured in-situ stress value, within the allowable error range after comparison, the final result value of the initial in-situ stress is inversely calculated.

[0037] 2. The present invention is applied in a typical tunnel of a certain plateau railway. The range of the correction coefficient k of the X-direction principal stress (the first principal stress is S H ) is 1.236 - 1.404, and the range of the correction coefficient λ of the Y-direction principal stress (the third principal stress is S h ) is 0.846 - 1.069. Considering that the X-direction principal stress has a greater impact on the tunnel and the in-situ stress test results after excavation disturbance are on the small side, the inversion of the initial in-situ stress is beneficial and necessary for the construction of the project.

[0038] 3. The present invention uses the correction coefficients k and λ to construct the initial in-situ stress field and conducts construction simulation of the excavation disturbance. After the tunnel excavation disturbance, the maximum error between the calculated values and the measured values of the X and Y direction principal stresses of the surrounding rock in the tunnel site area is 2.01% and less than 5%, indicating that the inversion method of the initial in-situ stress constructed by the present invention is reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following will briefly introduce the drawings required in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, so they should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings. In the drawings:

[0040] Figure 1 It is a relationship diagram of the principal stress azimuth angle of each tunnel, the tunnel alignment and the XY axes of the present invention;

[0041] Figure 2It is the initial in-situ stress inversion flow chart of the present invention;

[0042] Figure 3 It is the calculation model diagram of the tunnel analysis of the present invention;

[0043] Figure 4 It is the initial in-situ stress inversion result diagram of the present invention for Test Tunnel 1;

[0044] Figure 5 It is the initial in-situ stress inversion result diagram of the present invention for Test Tunnel 2;

[0045] Figure 6 It is the initial in-situ stress inversion result diagram of the present invention for Test Tunnel 3;

[0046] Figure 7 It is the initial in-situ stress inversion result diagram of the present invention for Test Tunnel 4;

[0047] Figure 8 It is the initial in-situ stress inversion result diagram of the present invention for Test Tunnel 5. Detailed implementation manners [[ID=2)8]]

[0048] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in combination with embodiments and the accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0049] Embodiment 1

[0050] The present invention is directed to the tunnels along the Lhasa-Nyingchi section of the Sichuan-Tibet Railway in a certain section. Specifically, a certain plate suture zone high-speed railway line is 433 km in total length, with a designed speed of 160 km / h. There are 46 tunnels along the line, with a total length of 206.984 km, accounting for 51.66% of the line length.

[0051] This railway is located at the junction of the Indian plate and the Eurasian plate. Most of the tunnels along the line are located on the suture line of the south and north continental extrusion-collision in this area. The tunnel site area is characterized by high mountains and deep valleys, with complex rock formations and geological structures. The tectonic deformation is very strong, and the problems of high in-situ stress and tectonic stress are very prominent. Rock bursts and large deformations and other surrounding rock instability phenomena often occur during tunnel construction, which greatly affects the safety of tunnel construction.

[0052] Therefore, before the construction of a new tunnel, based on the test results of the in-situ stress of the existing tunnel, it is of great significance to deduce or invert the initial in-situ stress of the distribution of in-situ stress in this area for the construction risk prevention and control before the construction of the new tunnel.

[0053] To ensure the integrity and universality of the analysis results, five tunnels with different burial depths along a certain section of the Lhasa-Nyingchi section of the Sichuan-Tibet Railway were selected as typical cases for testing and analysis. The hollow inclusion method was used to test and analyze the in-situ stress after tunnel excavation. The test locations or points were at the arch waist of the tunnel chamber, and the measuring points were 2 times the tunnel diameter away from the tunnel wall. The burial depth of the measuring points and the in-situ stress test results are shown in Table 1. The relationship between the in-situ stress distribution in the tunnel site area and the tunnel alignment is as Figure 1 shown.

[0054] Table 1

[0055]

[0056] From the above table, it can be seen that when analyzing the dip angles of the in-situ stress components (principal stresses) of the measuring points in the area and the dip angle values of the relationship between the in-situ stress distribution (in-situ stress components of the measuring points) and the tunnel alignment in the tunnel site area, the number of dip angles is set to multiple dip angles, and each principal stress corresponds to its respective dip angle. In the space rectangular coordinate system OXYZ, the tunnel alignment is set as the Y-axis, the vertical direction is the Z-axis, the X-axis and the Y-axis are in the same plane, and the X-axis is perpendicular to the Z-axis. The average dip angle of the first principal stress is 3.96°, the average dip angle of the second principal stress is 77.3°, and the average dip angle of the third principal stress is 11.48°. Therefore, the first principal stress and the third principal stress in this area are approximately distributed horizontally, and the second principal stress is approximately distributed vertically. Let S H represent the first principal stress, S Z represent the second principal stress, S h represent the third principal stress, then S H 、S Z 、S h are perpendicular to each other pairwise.

[0057] In terms of magnitude, S H 、S Z 、S h are all positive values (compression is positive), and S H >S Z >S h . Therefore, the tectonic stress in the direction of S H in this area is relatively prominent. It should be noted that the above Table 1 and the test results of the in-situ stress components of the area measuring points represent the in-situ stress state after tunnel excavation. At the tunnel design stage, based on the in-situ stress state after tunnel excavation, it is necessary to clarify the initial in-situ stress state in this area, and invert the initial in-situ stress after tunnel excavation from the in-situ stress state after tunnel excavation.

[0058] From Figure 1As can be seen, (a) is Test Tunnel 1, (b) is Test Tunnel 2, (c) is Test Tunnel 3, (d) is Test Tunnel 4, and (e) is Test Tunnel 5. During analysis, the tunnel direction is taken as the Y-axis, and the vertical direction is taken as the Z-axis, that is Figure 1 the N-axis in Figure 1 is in the same plane as the X-axis and the Y-axis, the X-axis is perpendicular to the Z-axis, and a spatial rectangular coordinate system OXYZ for in-situ stress analysis is constructed.

[0059] Example 2

[0060] Based on Example 1, this example designs an inversion method for initial in-situ stress corrected by tunnel excavation disturbance, including the following steps:

[0061] Step 1) Use the hollow inclusion method to measure the in-situ stress after excavation disturbance in the tunnel site area of a long tunnel, and obtain the measured in-situ stress values of the measuring points in the buried tunnel site area;

[0062] Step 2) Use the measured in-situ stress values to calculate the dip angle values of the relationship between the in-situ stress force distribution of the measuring points in the tunnel site area and the tunnel direction;

[0063] Step 3) Construct a spatial rectangular coordinate system OXYZ, and use the spatial rectangular coordinate system OXYZ as the spatial rectangular coordinate system OXYZ for constructing in-situ stress analysis. Convert the relationship between the in-situ stress force distribution of the measuring points in the tunnel site area and the tunnel direction into the form of in-situ stress tensor in the spatial rectangular coordinate system OXYZ. Among them, the in-situ stress force distribution of the measuring points is set as multiple principal stresses, and the angle between each principal stress and the coordinate axis is set as the dip angle;

[0064] Step 4) Successively set the first principal stress as S H the second principal stress as S Z and the third principal stress as S h . Set the second principal stress S Z to be generated by the self-weight of the surrounding rock. Through the second principal stress S Z invert the unit weight γ of the surrounding rock, correct the first principal stress S H and the third principal stress S h . Introduce correction coefficients k and λ for the first principal stress S H and the third principal stress S h respectively. Combine the measured in-situ stress values. When k and λ are determined, calculate the initial in-situ stress value of the surrounding rock;

[0065] Step 5) Compare the initial in-situ stress value of the surrounding rock with the measured in-situ stress value, and within the allowable error range after comparison, obtain the result of the final initial in-situ stress.

[0066] The first principal stress S Hand the third principal stress S h is distributed horizontally, and for the second principal stress S Z is distributed vertically. After the angle transformation f of the inclination angle for the first principal stress S H to the third principal stress S h in the spatial rectangular coordinate system OXYZ, the conversion process of the in-situ stress tensor form is as follows in Equation (1):

[0067]

[0068] Combined with the in-situ stress distribution law measured at each tunnel measurement point, for the sake of simplifying the research, the following assumptions are made:

[0069] The specific conversion steps of the in-situ stress tensor form in the spatial rectangular coordinate system OXYZ are as follows:

[0070] Step S1) Assume that the second principal stress S Z is distributed along the self-weight direction or vertically, and the first principal stress S H , the third principal stress S h are located in the horizontal plane and their directions are perpendicular to each other;

[0071] Step S2) Assume that the surrounding rock in the tunnel is a continuous medium model and is isotropic;

[0072] Step S3) Assume that the second principal stress S Z is mainly generated by the self-weight of the surrounding rock, and the unit weight γ of the surrounding rock is inversely calculated through the second principal stress S Z ;

[0073] Step S4) Correct the first principal stress S H , the third principal stress S h . Equation (1) is a linear transformation process, so the first principal stress S H and the third principal stress S h are equivalent to the correction of S xx and S yy . Correction coefficients k and λ are introduced for S xx and S yy respectively. Then the distribution components S' xx , S' yy of the initial in-situ stress and the distribution components S xx , S yy of the measured in-situ stress are calculated through the relationships in the following Equations (2) and (3):

[0074] S' xx = kS xx (2)

[0075] S' yy = λS yy (3)

[0076] When the correction coefficients k and λ are determined, the initial in-situ stress value or state of the surrounding rock can be determined.

[0077] The first principal stress S on the X-axis H has a correction coefficient k range of 1.236 to 1.404, and the third principal stress S on the Y-axis h has a correction coefficient λ range of 0.846 to 1.069.

[0078] The analysis method and process of the initial in-situ stress value or state are as follows. That is, the method for determining the initial in-situ stress value or state includes the following steps:

[0079] Let the initial stress state of the measuring point be S', and the stress state of the measuring point after excavation disturbance be S. The main purpose of this invention is to deduce S' from S. When S' is determined, the specific gravity γ of the surrounding rock and the coefficient of lateral pressure in each direction can be determined. From this, the stress field state of the strata in the tunnel site area can be constructed. The analysis method and process are as Figure 2 shown.

[0080] Step a): Determine the specific gravity γ of the surrounding rock according to the second principal stress S Z ;

[0081] Step b): Determine the physical property parameters of the strata around the tunnel and the parameters of the tunnel construction project according to the exploration and design data;

[0082] Step c): Set the correction coefficients k and λ;

[0083] Step d): Construct the field area of the initial in-situ stress;

[0084] Step e): Use numerical calculation software to simulate the tunnel construction, and extract the in-situ stress value or state of the measuring point;

[0085] Step f): Compare the in-situ stress value of the measuring point with the initial in-situ stress value in the initial in-situ stress field area. If the comparison value is within the allowable error range, invert the final initial in-situ stress value or state; otherwise, return to step c) and re-determine the final initial in-situ stress value or state.

[0086] In step 4), the correction coefficients k and λ are used to construct the initial in-situ stress value of the surrounding rock, and the construction software is used to simulate the excavation disturbance. After the excavation disturbance, calculate the maximum error between the first principal stress S H and the third principal stress S h of the surrounding rock in the tunnel site area and the measured in-situ stress value. The allowable maximum error is taken as 5%.

[0087] According to engineering experience, the allowable error is taken as 5%. In actual analysis, the relationship between the measured in-situ stress value and the correction coefficients k and λ can also be explored through multiple groups of correction coefficients k and λ. Subsequently, a relatively reasonable set of k and λ can be determined by means of linear interpolation. Finally, k and λ are verified through numerical simulation and field measurement, so as to achieve the purpose of reducing the calculation amount.

[0088] Combined with finite difference software, an inverse analysis is carried out on the initial in-situ stress state of different measuring points of a certain plateau railway tunnel. The numerical simulation scheme is as follows.

[0089] Analysis conditions: Through trial calculation and analysis, for Test Tunnel 1, Test Tunnel 2 and Test Tunnel 5, k takes 1.2, 1.3, 1.4, and λ takes 0.9, 1.0, 1.1, 1.2; for Test Tunnel 3, the k value takes 1.1, 1.2, 1.3, and λ takes 0.9, 1.0, 1.1, 1.2; for Test Tunnel 4, the k value takes 1.3, 1.4, 1.5, and λ takes 0.7, 0.8, 0.9, 1.0, with a total of 60 conditions.

[0090] Overview of the calculation model for the tunnel construction simulation of the present invention: Considering the boundary effect, the left and right boundaries of the model are taken as 40m, the lower boundary is greater than 40m, both are greater than 5 times the tunnel span. Horizontal displacement constraints are applied to the left and right boundaries of the model, vertical displacement constraints are applied to the bottom, the buried depth of the upper part is taken as 50m, and the stress caused by the self-weight of the upper surrounding rock is applied to the upper surface. To simulate the influence of tunnel disturbance, the disturbance advance per step is 2m, and the total advance is 60m (not excavated through). The monitoring section and the corresponding principal stress extraction points are taken at 30m away from the tunnel entrance. The numerical model is as Figure 3 shown.

[0091] The physical and mechanical parameters of the materials used: The surrounding rock adopts an elastoplastic model under the Mohr-Coulomb criterion, the primary support is a liner structural unit, and the parameters of the surrounding rock and the primary support are shown in the numerical simulation calculation parameters in Table 2.

[0092] Table 2

[0093]

[0094] Example 3

[0095] The analysis results of the initial in-situ stress (inverse analysis of initial in-situ stress) in a typical tunnel area are as follows:

[0096] Under different correction coefficients k and λ, considering the tunnel excavation disturbance, the calculated results of the in-situ stress components S xx 、S yy of a certain typical tunnel in the tunnel site area of a plateau railway are as Figures 4 - 8 shown. As Figure 4As shown in the figure, the in-situ stress after excavation disturbance has a basically linear relationship with k and λ. The calculation results of the initial in-situ stress correction coefficients k and λ obtained by linear interpolation for typical tunnel measurement points are shown in Table 3, and Table 3 shows the calculated values of k and λ for each tunnel measurement point.

[0097] Table 3

[0098]

[0099] As shown in Table 3, due to excavation disturbance, part of the surrounding in-situ stress is released, resulting in the measured in-situ stress being smaller than the initial in-situ stress. Except for the Y-direction principal stress of the initial test tunnel 4, the other in-situ stress correction coefficients are all greater than 1. For the X-direction principal stress, the correction coefficient ranges from 1.236 to 1.404, and for the Y-direction principal stress, the correction coefficient ranges from 0.846 to 1.069. Among them, the X-direction stress has a greater influence on the tunnel stress. Generally speaking, excavation disturbance usually leads to the measured result of the in-situ stress value at the measurement point being smaller than the initial in-situ stress value. If the measured in-situ stress is used to characterize the initial in-situ stress state and further guide tunnel design and construction, it may bring certain construction risks.

[0100] Verification of the inversion result: The calculated results of the interpolated correction coefficients are numerically simulated and analyzed, and compared with the in-situ stress components after coordinate transformation of the measured in-situ stress values. The results are shown in Table 4.

[0101] Table 4

[0102]

[0103] As can be seen from Table 4, the initial in-situ stress field is constructed using the correction coefficients k and λ values, and then the tunnel construction is simulated. After the tunnel excavation disturbance, the maximum error of the principal stress values in the X and Y directions is 2.01%, which is less than 5%, indicating that the in-situ stress inversion method constructed by the present invention is reliable.

[0104] Example 5

[0105] Based on the measured in-situ stress characteristics of a plateau tunnel, on the premise of considering the tunnel excavation disturbance, an inversion method for the initial in-situ stress applicable to this area is proposed, and it is applied to 5 typical tunnels of the plateau railway tunnel. The main conclusions are as follows:

[0106] (1) An inversion method for the initial in-situ stress considering tunnel excavation disturbance simulation and field in-situ stress test results is proposed.

[0107] (2) This method is applied to a typical tunnel of a plateau railway. The range of the correction coefficient k of the principal stress in the X direction is 1.236 - 1.404, and the range of the correction coefficient λ of the principal stress in the Y direction is 0.846 - 1.069. Considering that the principal stress in the X direction has a greater impact on the tunnel and the measured results of in-situ stress after excavation disturbance are on the small side, the inversion of the initial in-situ stress is beneficial and necessary for the construction of similar projects.

[0108] (3) The initial in-situ stress is constructed by using the correction coefficients k and λ to simulate the excavation disturbance. The maximum error between the calculated values and the measured values of the principal stresses in the X and Y directions of the surrounding rock in the tunnel site area after disturbance is 2.01%, indicating that the inversion method of the initial in-situ stress constructed by the present invention is reliable.

[0109] To ensure the feasibility of numerical calculation, several calculation settings are made in the research process. In subsequent research, it is necessary to continue to explore the method of calculating the initial in-situ stress with multi-factor correction including vertical principal stress and angle correction to improve the deflection of the principal stress caused by excavation disturbance.

[0110] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. The inversion method of initial ground stress based on tunnel excavation disturbance correction is characterized by: The steps include: Step 1) using a hollow inclusion method to test the in-situ stress of a long tunnel site after excavation disturbance, and obtaining the test in-situ stress value of a measuring point in the deep tunnel site; Step 2) using the measured ground stress value to calculate the inclination angle value of the relationship between the ground stress distribution at the measuring point in the tunnel site and the tunnel direction; Step 3) Constructing a spatial rectangular coordinate system OXYZ, using the spatial rectangular coordinate system OXYZ as the spatial rectangular coordinate system OXYZ for constructing the test ground stress analysis, converting the relationship between the force distribution of the ground stress at the measuring point in the tunnel site and the direction of the tunnel into a ground stress tensor form in the spatial rectangular coordinate system OXYZ, wherein the force distribution of the ground stress at the measuring point is set as multiple principal stresses, and the angle between each principal stress and the coordinate axis is set as an inclination angle; Step 4) Set the first principal stress as S for multiple principal stresses in turn H , the second principal stress is S Z and the third principal stress is S h , set the second principal stress S Z Produced by the deadweight of the surrounding rock, through the second principal stress S Z The inverse calculation of the surrounding rock mass γ is used to determine the first principal stress S H , the third principal stress S h Corrections are made and correction coefficients k and λ are introduced respectively. Combined with the measured ground stress values, multiple sets of correction coefficients k and λ are used to explore the relationship between the ground stress value at the measuring point and k and λ. Then, a relatively reasonable set of k and λ is determined by linear interpolation. Finally, k and λ are verified through numerical simulation and field measurement. Once k and λ are determined, the initial ground stress value of the surrounding rock is calculated. Step 5) Compare the initial in-situ stress value of the surrounding rock with the tested in-situ stress value, and obtain the final initial in-situ stress result within the allowable error range after comparison.

2. The inversion method of initial ground stress based on tunnel excavation disturbance correction according to claim 1, characterized in that: In step 1), when testing the ground stress after excavation disturbance in the tunnel site of a long tunnel, the test site is set at the arch waist of the tunnel chamber, and the measuring point is set at a distance of 2 times the tunnel diameter from the arch waist wall for testing.

3. The inversion method of initial ground stress based on tunnel excavation disturbance correction according to claim 1, characterized in that: In the step 2), when analyzing the inclination value of the relationship between the force distribution of the ground stress at the measuring point in the tunnel site and the tunnel direction, the number of inclination angles is set to multiple inclination angles.

4. The inversion method of initial geostress based on tunnel excavation disturbance correction according to claim 3, characterized in that: In step 3), each principal stress corresponds to its own inclination angle. In the spatial rectangular coordinate system OXYZ, the tunnel direction is set as the Y axis, the vertical direction is set as the Z axis, the X axis and the Y axis are set on the same plane, and the X axis is perpendicular to the Z axis.

5. The inversion method of initial ground stress based on tunnel excavation disturbance correction according to claim 4 is characterized in that: In step 4), the first principal stress S H and the third principal stress S h Distributed along the horizontal direction, the second principal stress S Z Distributed along the vertical direction, the first principal stress S H To the third principal stress S h After the angle transformation f of the inclination angle is applied in the spatial rectangular coordinate system OXYZ, the transformation process of the ground stress tensor form is as follows:

6. The inversion method of initial ground stress based on tunnel excavation disturbance correction according to claim 4, wherein the first principal stress S on the X-axis is H The correction coefficient k ranges from 1.236 to 1.404, and the third principal stress S on the Y axis h The correction coefficient λ ranges from 0.846 to 1.

069.

7. The inversion method of initial geostress based on tunnel excavation disturbance correction according to claim 5, characterized in that: The specific steps of converting the in-situ stress tensor form in the spatial rectangular coordinate system OXYZ are as follows: Step S1) setting the second principal stress S Z Distributed along the deadweight direction or vertical direction, the first principal stress S H , the third principal stress S h Located in the horizontal plane and the two directions are perpendicular to each other; Step S2) setting the surrounding rock in the tunnel as a continuous medium model, which is isotropic; Step S3) Set the second principal stress S Z Mainly generated by the deadweight of the surrounding rock, through the second principal stress S Z Inversely calculate the gravity γ of the surrounding rock; Step S4) The first principal stress S H , the third principal stress S h Correction is made, and formula (1) is a linear transformation process, then the first principal stress S H and the third principal stress S h Equivalent to S xx and S yy Correction, S xx and S yy Introducing the correction coefficients k and λ respectively, the distribution component S' of the initial ground stress is xx 、S' yy The distribution component S of the test ground stress xx 、S yy Calculate by the relationship between the following formula (2) and formula (3): S' xx =kS xx (2) S' yy =λS yy (3)。 8. The inversion method of initial ground stress based on tunnel excavation disturbance correction according to claim 7, characterized in that: The method for determining the initial geostress value comprises the following steps: Step a) According to the second principal stress S Z Determine the gravity γ of the surrounding rock; Step b) determining the physical properties of the bottom layer surrounding the tunnel and the parameters of the tunnel construction project based on the survey and design data; Step c) setting correction coefficients k and λ; Step d) constructing a field area of initial geostress; Step e) simulating the tunnel construction using numerical calculation software to extract the ground stress value or state of the measuring point; In step f), the in-situ stress value at the measuring point is compared with the initial in-situ stress value of the initial in-situ stress field area. If the comparison value is within the allowable error range, the final initial in-situ stress value or state is inverted. Otherwise, the process returns to step c) and the final initial in-situ stress value or state is re-determined.

9. The inversion method of initial geostress based on tunnel excavation disturbance correction according to any one of claims 1 or 8, characterized in that: The value of the allowable error is less than or equal to 5%.

10. The inversion method of initial geostress based on tunnel excavation disturbance correction according to claim 1, characterized in that: In step 4), the correction coefficients k and λ are used to construct the initial ground stress value of the surrounding rock, and the excavation disturbance is simulated using construction software. After the excavation disturbance, the first principal stress of the surrounding rock in the tunnel site is calculated as S H , the third principal stress is S h The maximum error between the value of and the test ground stress value.

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