CN114970234A - Initial ground stress field inversion method considering influence of sliding fracture activity - Google Patents
Initial ground stress field inversion method considering influence of sliding fracture activity Download PDFInfo
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Abstract
The invention discloses an initial ground stress field inversion method considering the influence of sliding fracture activity, which relates to the field of geological exploration and comprises the following steps: acquiring topographic and geological data and a ground stress measurement result of an area to be analyzed; establishing a three-dimensional finite element model simulating a fracture zone according to topographic and geological data; transforming the coordinate system of the ground stress measurement result; setting boundary conditions of the three-dimensional finite element model according to the ground stress measurement result after the coordinate system transformation; and carrying out regression analysis on the three-dimensional finite element model by a multivariate regression method, and checking the regression effect by significance checking calculation to obtain an initial ground stress field inversion result. The method is suitable for the engineering rock mass area containing the sliding fracture activity, the self weight and the geological structure effect of the rock mass on two sides of the fracture zone are fully considered, the geological structure effect is reflected by boundary displacement, and the rock mass ground stress inversion result is more practical.
Description
Technical Field
The invention relates to the field of geological exploration, in particular to an initial ground stress field inversion method considering the influence of sliding fracture activity.
Background
The initial ground stress of the rock mass is the natural stress which is not disturbed by engineering in the crust, and the size and the direction of the ground stress field of the rock mass are known so as to analyze the stress state of the rock mass engineering and provide basis for supporting and reinforcing the rock mass. Conventionally, the stress inversion analysis mainly considers a self-weight stress field and a structural stress field of a rock mass, and independently applies self-weight stress, unit structural stress in an X direction, unit structural stress in a Y direction and XOY plane shear structural stress on a model boundary respectively. However, the southwest area of china is strongly squeezed by the himalayan structure movement and undergoes surface denudation and erosion, so that a part of the area is broken and a fluctuated terrain is formed, and in this case, inversion is performed through the conventional boundary load, so that the real situation of the stress field in the research area is difficult to embody.
The conventional boundary construction load is not clear enough and can not be matched with the actual rock mass construction activity, and when a fault is considered, the rock mass parameters are usually considered only in a weakening mode and are still considered according to continuous media, so that the conventional boundary construction load is not consistent with the actual condition.
Disclosure of Invention
Aiming at the defects in the prior art, the initial ground stress field inversion method considering the influence of the sliding fracture activity solves the problem that the existing ground stress inversion method cannot accurately analyze the rock mass ground stress field influenced by the sliding fracture activity.
In order to achieve the purpose of the invention, the invention adopts the technical scheme that:
an initial earth stress field inversion method considering the influence of sliding fracture activity comprises the following steps:
s1, obtaining topographic and geological data and a ground stress measurement result of the area to be analyzed;
s2, establishing a three-dimensional finite element model simulating a fracture zone according to the topographic and geological data;
s3, transforming the coordinate system of the ground stress measurement result;
s4, setting boundary conditions of the three-dimensional finite element model according to the ground stress measurement result after the coordinate system transformation;
and S5, carrying out regression analysis on the three-dimensional finite element model through a multiple regression method, and checking the regression effect through significance test calculation to obtain an initial ground stress field inversion result.
Further, the topographic and geological data of the area to be analyzed in the step S1 includes: the method comprises the following steps of region topographic map, engineering site topographic map, region geological structure plane map, region geological structure longitudinal section map and region geological structure transverse section map.
Further, the step S2 includes the following sub-steps:
s21, performing fitting interpolation on the topographic and geological data to construct a complete three-dimensional curved surface topographic and geological model;
s22, importing the three-dimensional curved surface terrain geological model obtained in the step S21 into finite element solving software;
s23, meshing the three-dimensional curved surface topographic geological model in the finite element solving software, and increasing the mesh density in a fracture zone of the three-dimensional curved surface topographic geological model;
and S24, establishing a contact unit for simulating fault sliding of the fracture zone, and completing establishment of a three-dimensional finite element model.
Further, the contact unit in step S24 performs friction and force calculation of the broken belt by the following formula:
wherein σ 1 Is the maximum principal stress, σ 3 For minimum principal stress, p 0 Mu is the coefficient of friction of the fractured zone for pore pressure.
Further, the method for setting the boundary condition in step S4 includes:
(a) aiming at the self-weight stress of a rock mass, the following steps are adopted:
a1, applying 9.8 m.s in Z-axis direction -2 Acceleration of gravity of;
a2, setting normal displacement constraints on the side surface and the bottom surface of the three-dimensional finite element model;
a3, judging the condition of the rock mass self-gravity field of the area to be analyzed, and if the rock mass bottom wall self-gravity field needs to be considered in the three-dimensional finite element model, setting the density of the rock mass top wall model to be 0; if the self-gravity field of the upper rock mass tray needs to be considered in the three-dimensional finite element model, setting the density of the lower rock mass tray model to be 0;
(b) aiming at the extrusion structural stress of the rock lower wall:
applying the displacement of the rock mass bottom wall in the X-axis negative direction and the Y-axis negative direction, and limiting the normal displacement of the synthetic rock along the extrusion displacement of the fracture direction;
(c) aiming at the compressive structural stress of the upper plate of the rock mass:
applying displacements of the upper wall of the rock body in the X-axis negative direction and the Y-axis negative direction, and limiting the normal displacement of the synthetic rock along the extrusion displacement of the fracture direction;
(d) aiming at the structural stress of the rock mass sliding:
displacements are applied to the X-axis positive and negative directions and the Y-axis positive and negative directions of the rock lower plate, and sliding displacement along the trend of the fracture zone is synthesized.
The invention has the beneficial effects that:
1) the method is suitable for the engineering rock mass area containing the sliding fracture activity, the self weight and the geological structure effect of the rock mass on two sides of the fracture zone are fully considered, the geological structure effect is reflected by boundary displacement, and the rock mass ground stress inversion result is more practical.
2) In the setting of the boundary conditions of the three-dimensional finite element model, the self-weight stress of the rock mass, the extrusion tectonic stress of the lower wall of the rock mass, the extrusion tectonic stress of the upper wall of the rock mass and the sliding tectonic stress of the rock mass are fully considered; the compressive tectonic effect of the rock body lower wall sliding along the fracture zone, the compressive tectonic effect of the rock body upper wall sliding along the fracture zone and tectonic stress generated by the sliding movement of the fracture zone are simulated pertinently.
Drawings
FIG. 1 is a flowchart of an initial ground stress field inversion method considering the effect of the step-and-slip fracture activity according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a three-dimensional finite element model according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of setting boundary conditions of a three-dimensional finite element model according to an embodiment of the present invention, wherein: (a) self weight 1 (inlet direction); (b) self weight 2 (exit direction); (c) a lower disc extrusion structure; (d) the upper disc is of an extrusion structure; (e) a left-handed sliding configuration.
Detailed Description
The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined in the appended claims, and all matters produced by the invention using the inventive concept are protected.
In one embodiment of the present invention, as shown in FIG. 1, a method for initial ground stress field inversion that accounts for the effects of skid steer fracture activity comprises the steps of:
and S1, acquiring the topographic and geological data and the geostress measurement result of the area to be analyzed.
Wherein the topographic and geological data of the area to be analyzed comprises: the method comprises the following steps of region topographic map, engineering site topographic map, region geological structure plane map, region geological structure longitudinal section map and region geological structure transverse section map.
The range included by the regional topographic map can provide reliable basis for the finite element mechanical analysis calculation range and the determination of boundary constraint conditions. The proportion of a topographic map of the location of the project is generally small, so that the unit division is facilitated, the distribution, the trend and the trend of various rock strata and faults provided by a geological structure map, the geometrical position of project setting, typical stratum structures, particularly the spreading of discontinuous surfaces such as faults, joints and the like are facilitated. The engineering geological survey file includes the description of the distribution of the stratum and the fault, the fault activity degree and the threat to the engineering, and the like, and in addition, the physical and mechanical parameter indexes of the rock mass must be provided to be the basis of quantitative analysis.
The ground stress measurement result is the basic original data of the regression analysis of the regional ground stress field, and the reliability of the data directly influences the accuracy of the regression analysis result. In order to improve the quality of the geostress measurement data, in addition to entrusting an experienced exploration team test, when considering the arrangement of the geostress test points, the following principles are also considered:
1) the device is arranged in a single lithologic stratum which is simple in structure and slight in weathering as much as possible. In order to avoid the interference of external factors such as artificial excavation and the like, the measuring points should be selected in the deep rock mass as much as possible.
2) The measuring points should be distributed properly within the measuring area, so that the measured ground stress value has better representativeness.
3) The key area of the measuring point arrangement is beneficial to providing services for research and demonstration of main engineering problems in the near term.
4) The measured data should be recorded in time, and instructions are added for reference during analysis.
And S2, establishing a three-dimensional finite element model simulating the fracture zone according to the topographic and geological data.
In the present embodiment, the parameters of the three-dimensional finite element model include: the deformation modulus, Poisson's ratio, volume weight and fracture zone friction coefficient of the rock mass.
Step S2 includes the following substeps:
and S21, performing fitting interpolation on the topographic and geological data to construct a complete three-dimensional curved surface topographic and geological model.
And S22, importing the three-dimensional curved surface terrain geological model obtained in the step S21 into finite element solving software.
S23, carrying out mesh division on the three-dimensional curved surface topographic and geological model in the finite element solving software, and increasing mesh density in a fracture zone of the three-dimensional curved surface topographic and geological model.
And S24, establishing a contact unit for simulating fault sliding of the fracture zone, and completing establishment of a three-dimensional finite element model.
In the embodiment, the SURFER software is used for fitting and interpolating into a three-dimensional curved surface, and the model is imported into ANSYS. When the three-dimensional finite element model is established, according to a field topographic map and a right-hand rule in ANSYS, in order to ensure the calculation precision and facilitate the division of units, the discretization of the three-dimensional model all adopts 10-node tetrahedron isoparametric units (Solid92), and the grids are properly encrypted near a fault fracture zone. Contact Pair is adopted to establish a Contact unit to simulate fault sliding.
The model established in this example is shown in fig. 2.
The rock mass calculation parameters are selected on the basis of comprehensive reference geological test data and field tests.
According to the Coulomb friction sliding rule, when the shear stress tau on the fracture surface is more than or equal to c + mu sigma n When the sliding occurs, the fracture surface slips. It is generally assumed that the fracture surface cohesion is 0, and the stress on the sliding fracture surface at this time can be expressed as τ ═ μ σ n Where τ is the shear stress on the fracture surface, σ n The normal stress on the fracture surface, mu is the sliding friction coefficient of the fracture surface. Introducing a relation of the friction coefficient at the time of the sliding of the fracture zone with the effective maximum principal stress and the minimum principal stress as a key calculation of the contact unit in step S24:
wherein σ 1 Is the maximum principal stress, σ 3 For minimum principal stress, p 0 Is the pore pressure.
According to the Anderson fault theory, the stress state of the fault is closely related to the spatial distribution of the fault, and the middle main stress of the fault is coplanar with the fault fracture surface. When the normal fault structure is active, sigma in the above formula 1 ＝σ v 、σ 3 ＝σ h When the reverse fault structure is moving σ 1 ＝σ H 、σ 3 ＝σ h When the walking and sliding structure is moving, sigma 1 ＝σ H 、σ 3 ＝σ h Where σ is H 、σ h 、σ v Maximum horizontal stress, minimum horizontal stress and vertical stress, respectively.
And S3, transforming the coordinate system of the ground stress measurement result.
The ground stress value measured on site is given according to the main stress plane direction, and in the ground stress field regression analysis, the coordinate stress component in the calculation coordinate system XYZ is taken as the basic object, so the measured ground stress coordinate system needs to be transformed.
According to the theory of elastic mechanics, the original coordinate system is marked as x, y, z, the new coordinate system is marked as x ', y ', z ', and the direction cosine between the two coordinate systems is marked as l, m, n, as shown in table 1.
TABLE 1 Direction cosine table
| Coordinate system | X | Y | Z |
| X′ | l 1 | m 1 | n 1 |
| Y′ | l 2 | m 2 | n 2 |
| Z′ | l 3 | m 3 | n 3 |
The transformation from the original coordinate system to the new coordinate system can be performed according to the following formula:
and S4, setting boundary conditions of the three-dimensional finite element model according to the ground stress measurement result after the coordinate system transformation.
The boundary conditions set in step S4 regard the ground stress field in the calculated domain as the linear superposition of the self-weight stress field and the boundary tectonic stress field according to the actually measured ground stress result, and finally combine into a calculated ground stress field value by decomposing and simulating the self-weight stress field and the boundary load stress field, as shown in fig. 3.
The method comprises the following steps:
(a) aiming at the self-weight stress of a rock mass, the following steps are adopted:
a1, applying 9.8 m.s in Z-axis direction -2 Acceleration of gravity of;
a2, setting normal displacement constraints on the side surface and the bottom surface of the three-dimensional finite element model;
a3, judging the condition of the rock mass self-gravity field of the area to be analyzed, and if the rock mass bottom wall self-gravity field needs to be considered in the three-dimensional finite element model, setting the density of the rock mass top wall model to be 0; if the self-gravity field of the upper rock mass tray needs to be considered in the three-dimensional finite element model, setting the density of the lower rock mass tray model to be 0;
(b) aiming at the extrusion structural stress of the rock lower wall:
applying the displacement of the rock mass bottom wall in the X-axis negative direction and the Y-axis negative direction, and limiting the normal displacement of the synthetic rock along the extrusion displacement of the fracture direction;
(c) aiming at the compressive structural stress of the upper plate of the rock mass:
applying displacements of the upper wall of the rock body in the X-axis negative direction and the Y-axis negative direction, and limiting the normal displacement of the synthetic rock along the extrusion displacement of the fracture direction;
(d) aiming at the structural stress of the rock mass sliding:
displacements are applied to the X-axis positive and negative directions and the Y-axis positive and negative directions of the rock lower plate, and sliding displacement along the trend of the fracture zone is synthesized.
And S5, carrying out regression analysis on the three-dimensional finite element model by a multiple regression method, and checking the regression effect by significance checking calculation to obtain an initial ground stress field inversion result.
In the present embodiment, a mathematical calculation model is established from the viewpoint that geomechanical analysis, the main components of which are a self-weight stress field and a structural stress field. According to the principle of multiple regression method, the ground stress is regressed to calculate value
As dependent variable, stress calculation values of the dead weight stress field and the structural stress field obtained by finite element calculation corresponding to actual measurement points
As independent variables, the regression equation is then of the form:
in the formula: k is the serial number of the observation point;
regression scores for k first observation points; b 0 Is a free term, b i Is a multiple regression coefficient corresponding to the independent variable;
and
a single column matrix of calculated values for the corresponding stress components, n being the number of operating conditions.
The regression effect is checked by calculating the multiple correlation coefficient R, the significance test (F test) of the linear regression model and the significance test of the regression coefficient. And comparing the regression values with the stress components of the actual measuring points, and obtaining the inversion result when the error between the regression values and the actual measuring values of the measuring points is within 10 percent.
In conclusion, the invention has the following beneficial effects:
1) the method is suitable for the engineering rock mass area containing the sliding fracture activity, the self weight and the geological structure effect of the rock mass on two sides of the fracture zone are fully considered, the geological structure effect is reflected by boundary displacement, and the rock mass ground stress inversion result is more practical.
2) In the setting of the boundary conditions of the three-dimensional finite element model, the self-weight stress of the rock mass, the extrusion tectonic stress of the lower wall of the rock mass, the extrusion tectonic stress of the upper wall of the rock mass and the sliding tectonic stress of the rock mass are fully considered; the compressive tectonic effect of the rock body lower wall sliding along the fracture zone, the compressive tectonic effect of the rock body upper wall sliding along the fracture zone and tectonic stress generated by the sliding movement of the fracture zone are simulated pertinently.
The principle and the implementation mode of the invention are explained by applying specific embodiments in the invention, and the description of the embodiments is only used for helping to understand the method and the core idea of the invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.
It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.
Claims (5)
1. An initial earth stress field inversion method considering the influence of sliding fracture activity is characterized by comprising the following steps:
s1, obtaining the topographic and geological data and the ground stress measurement result of the area to be analyzed;
s2, establishing a three-dimensional finite element model simulating a fracture zone according to the topographic and geological data;
s3, transforming the coordinate system of the ground stress measurement result;
s4, setting boundary conditions of the three-dimensional finite element model according to the ground stress measurement result after the coordinate system transformation;
and S5, carrying out regression analysis on the three-dimensional finite element model through a multiple regression method, and checking the regression effect through significance test calculation to obtain an initial ground stress field inversion result.
2. The method of claim 1, wherein the topographic geological data of the region to be analyzed in step S1 includes: the method comprises the following steps of region topographic map, engineering site topographic map, region geological structure plane map, region geological structure longitudinal section map and region geological structure transverse section map.
3. The method of claim 1, wherein the step S2 includes the following sub-steps:
s21, performing fitting interpolation on the topographic and geological data to construct a complete three-dimensional curved surface topographic and geological model;
s22, importing the three-dimensional curved surface terrain geological model obtained in the step S21 into finite element solving software;
s23, carrying out mesh division on the three-dimensional curved surface topographic model in the finite element solving software, and increasing mesh density in a fracture zone of the three-dimensional curved surface topographic model;
and S24, establishing a contact unit for simulating fault sliding of the fracture zone, and completing establishment of a three-dimensional finite element model.
4. The method of claim 3, wherein the contact unit in step S24 performs friction and stress calculation of fracture zone by the following formula:
wherein σ 1 Is the maximum principal stress, σ 3 For minimum principal stress, p 0 Mu is the friction coefficient of the fractured zone for pore pressure.
5. The method of claim 4, wherein the method of setting boundary conditions in step S4 comprises:
(a) aiming at the self-weight stress of a rock mass, the following steps are adopted:
a1, applying 9.8 m.s in Z-axis direction -2 Acceleration of gravity of;
a2, setting normal displacement constraints on the side surface and the bottom surface of the three-dimensional finite element model;
a3, judging the condition of the self-gravity field of the rock mass in the area to be analyzed, and if the self-gravity field of the rock mass footwall needs to be considered in the three-dimensional finite element model, setting the density of the rock mass footwall model to be 0; if the self-gravity field of the upper rock mass tray needs to be considered in the three-dimensional finite element model, setting the density of the lower rock mass tray model to be 0;
(b) aiming at the extrusion structural stress of the rock lower wall:
applying the displacement of the rock mass bottom wall in the X-axis negative direction and the Y-axis negative direction, and limiting the normal displacement of the synthetic rock along the extrusion displacement of the fracture direction;
(c) aiming at the compressive structural stress of the upper plate of the rock mass:
applying displacements of the upper wall of the rock body in the X-axis negative direction and the Y-axis negative direction, and limiting the normal displacement of the synthetic rock along the extrusion displacement of the fracture direction;
(d) aiming at the structural stress of the rock mass sliding:
displacements are applied to the X-axis positive and negative directions and the Y-axis positive and negative directions of the rock lower plate, and sliding displacement along the trend of the fracture zone is synthesized.
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