CN118094998A - Stability evaluation method for tunnel surrounding rock under dynamic and static combined stress - Google Patents
Stability evaluation method for tunnel surrounding rock under dynamic and static combined stress Download PDFInfo
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Abstract
The invention discloses a stability evaluation method of tunnel surrounding rock under dynamic and static combined stress, which comprises the following steps: adopting a finite element pretreatment module to establish a two-dimensional numerical model of a rock mass part of the tunnel surrounding rock, and entering a grid division module to carry out structural grid division; importing a statics calculation module, inputting engineering geological material numerical model parameters, carrying out statics loading on the statics calculation module, setting boundary conditions, and carrying out statics calculation; the static calculation data is imported into a dynamics calculation module, dynamics numerical simulation analysis is carried out by using a difference method, and a dynamic stress concentration coefficient in the surrounding rock of the tunnel and a dynamic stress intensity factor curve of the crack tip of the surrounding rock are calculated; and comprehensively evaluating the dynamic stability of the surrounding rock of the fracture tunnel. The invention is beneficial to developing the research of the problems of dynamic stress distribution rule and dynamic crushing behavior prediction of the surrounding rock of the deep tunnel under the action of dynamic and static combination, and provides scientific basis for the safety design and construction of deep underground engineering.
Description
Technical Field
The invention relates to a stability evaluation method of tunnel surrounding rock under dynamic and static combined stress, and belongs to the technical field of rock mechanics.
Background
The deep mineral resource exploitation usually adopts a drilling and blasting method to carry out dynamic crushing excavation in tunnel surrounding rock, and the drilling and blasting method has the advantages of flexible construction, good maneuverability and the like, is suitable for mineral resource exploitation under more geological environment conditions, and is a main mode of deep mineral resource exploitation. In this engineering background, the deep surrounding rock mass is subjected to static load such as ground stress, and also various dynamic loads induced during excavation and tunneling, and the dynamic loads mainly propagate in the surrounding rock mass in different forms of waves. For this reason, deep underground rock crushing excavation and mineral resource exploitation activities are dynamic processes of combined action of original rock stress and dynamic disturbance load, for example, sunk-positive mining and tun mine exploitation, fu-hong-transparent mountain copper mine exploitation and the like, and these deep mine tunnel projects all involve rock safety evaluation problems of combined action of different ground stress levels and dynamic disturbance load. Therefore, whether the tunnel surrounding rock has different ground stress conditions, dynamic load coupling action mechanisms and dynamic stress concentration coefficients can be well characterized is a key of the safe exploitation of deep underground mineral resources, and the development rule of dynamic stress distribution rules and dynamic destructive behaviors of the tunnel surrounding rock under the action of dynamic and static combination is the most important problem in the research of dynamic and static coupling action mechanisms.
Because of the complex characteristics of the surrounding rock of the deep tunnel, the full-size physical model test of the tunnel model is very difficult, the full-size numerical simulation becomes an important means for realizing the full-scale model test of the surrounding rock of the deep tunnel, most of the numerical simulation is now taking unilateral statics or dynamics numerical simulation into consideration, the numerical simulation research of the surrounding rock of the tunnel crack under the action of dynamic and static combined load is relatively less in calculation of dynamic stress concentration coefficients, and a certain limitation exists in the partial dynamic and static combined numerical simulation, so that the stress state of joints or cracks in the surrounding rock of the tunnel cannot be well represented, and an effective dynamic and static combined numerical simulation method is established to describe the dynamic concentration coefficients and dynamic fracture toughness of the surrounding rock of the tunnel crack, so that the method has strong engineering significance.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide a stability evaluation method for tunnel surrounding rock under dynamic and static combined stress.
The technical scheme provided by the invention for solving the technical problems is as follows: a stability evaluation method of tunnel surrounding rock under dynamic and static combined stress comprises the following steps:
S1, establishing a two-dimensional numerical model of a rock mass part of a tunnel surrounding rock by adopting a finite element preprocessing module, and entering a grid dividing module to divide a structural grid;
S2, importing a statics calculation module, inputting engineering geological material numerical model parameters, carrying out statics loading on the statics calculation module, setting boundary conditions, and carrying out statics calculation;
S3, importing static calculation data into a dynamics calculation module, performing dynamics numerical simulation analysis by using a difference method, and analyzing according to a theoretical model to obtain a stress field of units around the tunnel surrounding rock and a maximum main stress time path curve of crack tips of the tunnel surrounding rock after static load is applied to the tunnel surrounding rock;
s4, calculating a dynamic stress concentration coefficient based on a stress field of units around the tunnel surrounding rock after static load is applied to the tunnel surrounding rock;
s5, calculating a stress intensity factor curve of the crack tip based on a maximum principal stress time curve of the crack tip of the tunnel surrounding rock;
S6, determining the dynamic fracture toughness of the crack tip according to the dynamic fracture moment, and comprehensively evaluating the dynamic stability of the crack tunnel surrounding rock according to the dynamic stress concentration coefficient and the dynamic fracture toughness of the crack tip.
The further technical scheme is that the specific steps of the step S1 are as follows:
S11, a preprocessing software ICEM CFD module establishes a two-dimensional geometric model according to actual tunnel engineering, performs structural grid division, and stretches grids along a normal direction to form a three-dimensional grid model;
s12, importing a two-dimensional geometric numerical model file into a geometric module, and stretching the model along a normal direction to form a three-dimensional geometric model;
s13, opening the three-dimensional grid model, and importing the calculation grid.
Further technical scheme is that the engineering geological material numerical model parameters comprise density, elastic modulus, poisson ratio, tensile strength and compressive strength.
The further technical scheme is that the specific steps of the step S4 are as follows:
S41, determining horizontal stress, vertical stress and shear stress of units around the tunnel surrounding rock according to the stress field of the units around the tunnel surrounding rock after static load is applied to the tunnel surrounding rock;
S42, calculating radial stress and hoop stress of the surrounding units of the tunnel surrounding rock according to the horizontal stress and the vertical stress of the surrounding units of the tunnel surrounding rock and the shear stress;
s43, calculating the dynamic stress concentration coefficient of the surrounding units of the tunnel surrounding rock according to the radial stress and the hoop stress of the surrounding units of the tunnel surrounding rock.
The further technical scheme is that the calculation formula of step S42 is as follows:
σθθ＝σxcos2θ+σysin2θ-2τxysinθcosθ
σrr＝σxcos2θ+σysin2θ+2τxysinθcosθ
Wherein: σ θθ is the hoop stress of the tunnel surrounding rock in polar coordinates; σ rr represents the radial stress at the polar coordinates of the tunnel surrounding rock; σ x、σy and τ xy are the horizontal stress, the vertical stress and the shear stress of the monitoring unit in the planar coordinate system, respectively.
The further technical scheme is that the calculation formula in the step S43 is as follows:
DSCF＝σθθ/σ
wherein: σ θθ is the hoop stress of the tunnel surrounding rock in polar coordinates; sigma is the input initial stress; DSCF is the dynamic stress concentration factor.
The further technical scheme is that the specific steps of the step S5 are as follows:
S51, obtaining a crack tip opening displacement time-course curve based on a maximum main stress time-course curve of the crack tip of the tunnel surrounding rock;
s52, substituting the crack tip opening displacement time course curve into a theoretical model to calculate the stress intensity factor of the crack tip, and obtaining a stress intensity factor curve of the real-time crack tip.
The further technical scheme is that the theoretical model in the step S52 is as follows:
wherein: q I and Q R are the real and imaginary parts of the constant Q 0, respectively; r k and I k are the real and imaginary parts, respectively, of the imaginary number C k; y I and Y II are dimensionless stress intensity factors of K I and K II, respectively.
The further technical scheme is that in the step S6, the fracture of the tunnel surrounding rock is closely related to the distribution of the circumferential tensile stress, and the distribution condition of the circumferential tensile stress around the tunnel under the action of stress waves in different directions is focused, namely, the dynamic stress concentration coefficient around the tunnel is researched, wherein the positive value of the dynamic stress concentration coefficient represents the compression stress concentration, and the negative value represents the tensile stress concentration; when tensile stress is concentrated, the smaller the value of DSCF, the greater the degree of tensile stress concentration.
The invention has the following beneficial effects:
1. The calculation time is short. According to the invention, the numerical calculation of the static load can be performed by using a static general solver of ANSYS, the solving time is short, the efficiency of achieving the initial static load stress balance of the fractured rock mass is high, the accuracy of the calculation result is high, the error of the calculation result of the static stress can be controlled within 5%, and the numerical simulation analysis of the fractured rock mass under the dynamic and static combined stress can be well performed by combining a software module of a finite difference method.
2. And a large number of same-series numerical simulation tests are convenient to develop. In the whole operation flow, the system can keep operation records, and can replace different model structures, static loads and dynamic loads by adjusting part of parameter data, so that the time for establishing a model and changing calculation settings can be saved, and the model establishment and calculation of the same type of numerical simulation can be facilitated.
3. Complex model structures and loading conditions can be simulated. The method can act on a complex model structure, can rapidly calculate the stress field after static load is applied even if calculation grids are intensive, and can realize dynamic and static combined loading of the three-dimensional model by adjusting and setting boundary conditions.
4. And the dynamic load strain rate calculation range is wide. The dynamic solver AUTODYN software combined with the content of the invention can well simulate the cracking behavior of the cracked rock mass in the dynamic and static combined stress state in the low, medium and high strain rate (0-1000 s < -1 >) range, and well evaluate the stability of the deep tunnel according to the cracking behavior in the dynamic and static combined stress.
5. The dynamic stress concentration coefficient is accurate. The dynamic stress concentration coefficient of the tunnel surrounding rock can be calculated in real time, and the calculated unit stress can well reflect the time domain change of the dynamic stress concentration coefficient of the tunnel surrounding rock.
Drawings
FIG. 1 is a schematic view of local polar coordinates of a tunnel;
FIG. 2 is a schematic diagram of module associations of model building, meshing, static calculation, dynamic calculation, etc.;
FIG. 3 is a schematic diagram of the steps of the dynamic and static combination numerical simulation method;
FIG. 4 is a schematic diagram of a type I crack tunnel surrounding rock model;
FIG. 5 is a schematic diagram of a type I crack tunnel surrounding rock grid;
FIG. 6 is a graph of the maximum principal stress time course of a portion of the monitoring unit after a static load is applied to the surrounding rock of the type I crack tunnel;
FIG. 7 is a graph of the maximum principal stress time course of the crack tip of a type I crack tunnel surrounding rock;
FIG. 8 is a graph of dynamic stress concentration coefficients of surrounding rocks of an I-type crack tunnel under the action of different original rock stresses;
FIG. 9 is a graph of dynamic fracture toughness of type I cracks in tunnel surrounding rock under different primary rock stresses;
FIG. 10 is a schematic diagram of an I/II composite crack tunnel surrounding rock model;
FIG. 11 is a schematic diagram of an I/II composite crack tunnel surrounding rock grid;
fig. 12 is a graph of dynamic stress concentration coefficients of an I/II composite crack tunnel rock mass under the action of original rock stress=0 MPa;
fig. 13 is a graph of dynamic stress concentration coefficients of an I/II composite crack tunnel rock mass under the action of original rock stress=0.5 MPa;
Fig. 14 is a graph of dynamic stress concentration coefficients of an I/II composite crack tunnel rock mass under the action of original rock stress=1 MPa;
fig. 15 is a graph of dynamic stress concentration coefficients of an I/II composite crack tunnel rock mass under the action of original rock stress=1.5 MPa;
fig. 16 is a graph of dynamic stress concentration coefficients of an I/II composite crack tunnel rock mass under the action of original rock stress=2 MPa;
Fig. 17 is a graph of dynamic stress concentration coefficients of an I/II composite crack tunnel rock mass under the action of original rock stress=2.5 MPa;
Fig. 18 is a graph of dynamic stress concentration coefficients of an I/II composite crack tunnel rock mass under the action of original rock stress=3 MPa;
FIG. 19 is an equivalent dynamic fracture toughness of I/II composite cracks in tunnel surrounding rock under different original rock stresses.
Detailed Description
The following description of the embodiments of the present invention will be made apparent and fully in view of the accompanying drawings, in which some, but not all embodiments of the invention are shown. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention discloses a stability evaluation method of tunnel surrounding rock under dynamic and static combined stress, which comprises the following steps:
1. Establishing a two-dimensional model according to actual tunnel engineering in an ICEM CFD module of preprocessing software, dividing structural grids, and stretching the grids along a normal direction to form a three-dimensional grid model;
2. The association of modules such as model establishment, static calculation, power calculation and the like is realized by means of an ANSYS Workbench joint simulation platform, as shown in fig. 2;
3. Importing a two-dimensional geometric numerical model file into a geometric module, and stretching the model along a normal direction to form a three-dimensional numerical model;
4. The simultaneous ICEM CFD software opens a three-dimensional grid model and introduces a calculation grid;
5. The method comprises the steps of importing a model into a statics calculation module, setting relevant mechanical parameters of a model material in the module, setting static load conditions and relevant boundary conditions for the model, and carrying out static calculation;
6. the simultaneous dynamics calculation module is used for setting the same stress and displacement boundary conditions and carrying out explicit dynamics calculation;
7. Simultaneously displaying dynamic finite difference method AUTODYN software, establishing models of other parts, setting related material parameters, setting dynamic loads to related boundary conditions, realizing dynamic and static combined loading, performing AUTODYN software parallel calculation and calling by using Python language, and then realizing explicit finite difference method dynamics calculation;
8. according to the theoretical model analysis, a dynamic stress field distribution rule of the tunnel surrounding rock under dynamic and static combined loading and a maximum main stress time-course curve of the tunnel surrounding rock crack tip are obtained;
9. Obtaining the unit stress of each unit monitoring point around the surrounding rock of the fracture tunnel based on a dynamic stress field distribution rule, then calculating the sigma θθ circumferential stress and sigma rr radial stress of the surrounding rock under the condition of polar coordinates by using theoretical formulas (1) and (2), and calculating a dynamic stress concentration coefficient DSCF according to the circumferential stress sigma θθ and the radial stress sigma rr;
Taking the center of a tunnel section (simultaneously the tunnel center) as a coordinate starting point, establishing a local polar coordinate system as shown in fig. 1, increasing the polar coordinate theta along the clockwise direction, taking theta=0-90 degrees as the original direction of the prefabricated crack of the crack tunnel, and calculating the radial stress sigma rr and the hoop stress sigma θθ at any position of the surrounding rock of the tunnel through the following theoretical model formula:
σθθ＝σx cos2θ+σy sin2θ-2τxy sinθcosθ (1)
σrr＝σx cos2θ+σy sin2θ+2τxy sinθcosθ (2)
DSCF＝σθθ/σ (3)
Wherein: σ θθ is the hoop stress of the tunnel surrounding rock in polar coordinates; σ rr represents the radial stress at the polar coordinates of the tunnel surrounding rock; sigma x、σy and tau xy are respectively the horizontal stress, the vertical stress and the shear stress of the monitoring unit under the plane coordinate system; sigma is the input initial stress; DSCF is dynamic stress concentration factor;
the hoop tensile stress concentration coefficient is defined as the hoop stress divided by the amplitude of the incident stress wave at the same location without the tunnel, and a negative value of the dynamic stress concentration coefficient represents the tensile stress concentration, and when the tensile stress is concentrated, the smaller the value of the dynamic stress concentration coefficient, the greater the degree of the tensile stress concentration.
10. Obtaining a time domain curve of opening displacement of the crack tip of the tunnel surrounding rock based on the maximum principal stress time course curve of the crack tip of the tunnel surrounding rock, and then calculating a dynamic stress intensity factor curve of the crack tip in the tunnel surrounding rock by utilizing theoretical formulas (9) and (10);
Then continuously calculating the change rule of the dynamic fracture initiation toughness of the crack tip along with the stress condition based on the theoretical model of the stress intensity factor of the crack tip in the proposed crack tunnel surrounding rock;
First, according to the relation between the stress intensity factors and the stress function phi (z), the stress intensity factors K I and K II of the tunnel radial crack tip are
The stress function Φ (z) is the following expression:
substituting (5) into the above formula (6),
The stress intensity factors K I and K II are dimensionless, and then,
Wherein: And σ=max { σ h,σv }. Thus, Y I and Y II are dimensionless stress intensity factors of K I and K II, respectively, C k and Q 0 are plural, such that
Ck＝Rk+iIk, Q0＝QR+iQI (8)
Wherein: r k and I k are the real and imaginary parts, respectively, of the imaginary number C k; q I and Q R are the real and imaginary parts of the constant Q 0, respectively.
Thus, the theoretical expression for the stress intensity factor for the tunnel radial crack tip is:
Finally, according to the theoretical model of dimensionless stress intensity factors Y I and Y II of crack tips in the tunnel surrounding rock, the dynamic fracture initiation toughness K IC and the equivalent fracture initiation toughness K eff of the crack tips in the crack surrounding rock under the action of the dynamic disturbance load can be calculated;
11. And determining the dynamic fracture toughness of the crack tip according to the dynamic fracture moment, and then comprehensively evaluating the dynamic stability of the fracture tunnel surrounding rock according to the dynamic stress concentration coefficient and the dynamic fracture toughness of the crack tip.
The dynamic stress concentration coefficient calculation method for the tunnel surrounding rock under dynamic and static combined stress provided by the invention mainly utilizes a calculation module of a static calculation module and an explicit dynamic module, and utilizes the finite difference method software which is used for leading the static calculation result and the initial boundary condition into the dynamic and static combined stress, so that the problem of coupling loading of initial static stress and dynamic disturbance load can be directly, efficiently and quickly solved on a three-dimensional level, a large amount of systematic numerical simulation research of the same type test is facilitated, and then the calculation of the dynamic stress concentration coefficient and dynamic fracture toughness in the tunnel surrounding rock is performed by utilizing a theoretical model, thereby being beneficial to developing the research of the problems of dynamic stress distribution rule and dynamic fracture behavior prediction of the deep tunnel surrounding rock under dynamic and static combined effect, and providing scientific basis for the safety design and construction of deep underground engineering.
Example 1
The implementation steps of the embodiment of the I-type crack deep buried tunnel surrounding rock are as follows, as shown in fig. 3:
Firstly, considering a section structure of an underground tunnel and a crack defect in a rock mass, establishing a two-dimensional numerical model in ICEM CFD software, and deriving a geometric file;
Selecting a test piece model with the size of 350mm multiplied by 300mm multiplied by 30mm, simultaneously taking the influence of 5 times radius range of surrounding rock of a tunnel into consideration, opening a horseshoe-shaped tunnel with the size of 60mm multiplied by 50mm multiplied by 30mm at the center position of the model test piece, and arranging an I-shaped penetrating crack with the length of 50mm above the tunnel arch part, wherein the crack width is 1mm, as shown in figure 4;
And a second step of: in ICEM CFD software, a BLOCK method is adopted to carry out grid division on a tunnel model, and the grid size is 1mm, as shown in FIG. 5; stretching the grids along a normal plane for 2mm to form a three-dimensional grid, wherein only one layer of grid is used for calculation, displacement constraint is applied to the thickness direction of the tunnel model, the grid thickness does not influence the stress calculation result of the tunnel model, so that the stress state of the model is consistent with the plane strain state and accords with the actual stress condition of underground tunnel engineering, therefore, the dimension similar to the dimension of the plane grid is used as the grid thickness, the phenomenon that the calculation time is long due to overlarge grid difference is avoided, a three-dimensional grid file is derived, and the model is stored; then, denser data monitoring points are arranged around the surrounding rock so as to better monitor x-direction stress sigma x, y-direction stress sigma y and shear stress tau xy around the surrounding rock;
And a third step of: opening an ANSYS Workbench platform, introducing a geometric module, setting a unit to be mm, introducing a two-dimensional geometric model into the module, and stretching along a normal plane to form a three-dimensional geometric model;
fourth step: the simultaneous ICEM CFD software sets the unit as mm, opens the model file established in the first step to import the calculation grid, and sets the unit as m;
Fifth step: and a simultaneous statics calculation module, wherein the density, dynamic elastic modulus and dynamic poisson ratio of the material are set at ENGINEERING DATA part, the module is stored and used, the setting unit is mm, defined material parameters are given to the model, normal displacement constraint is applied to the front plane and the rear plane of the model, vertical displacement constraint is applied to the upper plane and the lower plane of the model, stress condition is applied to the left plane and the right plane of the model, and the stress condition is basically consistent with the stress boundary condition applied in the horizontal direction and the vertical direction simultaneously. The calculation time is set to be 1s, and since the left end and the right end of the model are free from displacement constraint, WEAK SPRINGS options are required to be opened during calculation, so that the phenomenon of error reporting is avoided.
Sixth step: after the calculation is completed, the file of the ANASYWorkbench platform is saved, and the dat file of the result file of the statics calculation is found.
Seventh step: opening AUTODYN software, importing a three-dimensional grid model stored in the first step, setting the unit as mm, setting various related parameters of materials including but not limited to density, elastic modulus, poisson ratio, tensile strength and compressive strength, and describing the breaking behavior of the rock by adopting a maximum principal stress criterion and a maximum shearing stress criterion. Importing a result file of static force calculation in an initial boundary condition part, setting boundary conditions which are the same as those of the static force calculation in the boundary condition part, applying displacement boundary conditions to nodes, establishing a set of left end face and a set of right end face of a model in a stress condition, then calling parallel calculation of AUTODYN software, and calculating multiple cores and multiple threads of the digital model;
Eighth step: the result to be output is set, a period of calculation time is set for verifying whether a stable stress field is obtained, as shown in fig. 6, taking original rock stress of 1MPa as an example, units at a certain position are randomly selected in the model range for monitoring, the maximum principal stress time course curve of the randomly selected monitoring units is shown in the figure, each curve can be seen to vibrate, the variation amplitude is negligible compared with the average stress at the position, and the stable prestress field can be considered to be obtained.
Ninth step: and selecting a file which is not calculated yet, establishing a model related to dynamic load loading, and selecting a model for realizing dynamic loading of the drop hammer impact system. Models such as an incident rod, a transmission rod, an energy absorption rod and the like are built in AUTODYN software, displacement constraint is carried out on the normal direction of the whole model, dynamic impact stress waves obtained through early-stage tests are applied to the top surface of the incident rod model corresponding to the tests, meanwhile, the energy absorption rod is set to be a reflection-free boundary condition, a monitoring (Gauge) point and calculation time are set, and calculation is carried out after the adjustment of a result required to be output is completed.
Tenth step: and (3) replacing the static calculation result in AUTODYN by adjusting the stress of the original rock set in the fifth step and the seventh step, and adjusting the dynamic stress wave data in the ninth step to obtain the research on the destructive behavior of the surrounding rock of the deep I-shaped fracture tunnel under the coupling action of different static loads and dynamic loads. Deriving a maximum principal stress curve of the crack tip of the I-type fracture tunnel surrounding rock under different original rock stresses from the calculation result, as shown in fig. 7;
Eleventh step: carrying out calculation of sigma θθ radial stress and sigma rr hoop stress by taking monitoring point stress data sigma x、σy and tau xy around the tunnel surrounding rock into theoretical formulas (1) and (2), and then carrying out sigma θθ and sigma rr under different angles into a polar coordinate system according to the angle of the polar coordinate, so as to finally obtain a distribution coefficient of dynamic stress concentration in the tunnel surrounding rock under the polar coordinate condition, as shown in fig. 8;
Twelfth step: the stability of the tunnel surrounding rock is evaluated according to the dynamic stress concentration coefficient of the tunnel surrounding rock, and as can be seen from the figure, the dynamic stress concentration coefficient of the tunnel surrounding rock is in a butterfly shape, which indicates that the arch springing and the arch shoulder area of the tunnel surrounding rock are greatly influenced by dynamic disturbance load, the stability of the arch shoulders and the arch springing under the action of dynamic vibration load is worst, and the dynamic stress concentration coefficient of the tunnel arch springing is in a gradually increasing trend along with the increase of static side pressure;
Thirteenth step: the method comprises the steps of extracting crack tip opening displacement time course curves of crack tip displacement data u x、uy and u xy of tunnel surrounding rock, substituting theoretical models (9) and (10) to calculate I-type stress intensity factors of the crack tips in the surrounding rock, so as to obtain a stress intensity factor curve of the real-time crack tips, and then determining dynamic fracture toughness K IC of the surrounding rock according to the fracture starting time of the crack tips in the tunnel surrounding rock, wherein as shown in fig. 9, the dynamic fracture toughness is firstly reduced and then increased along with the increase of the ground stress, and then is reduced, and when the ground stress is 1.5MPa, the dynamic fracture toughness of the crack tips is the largest, which indicates that the stability of the tunnel surrounding rock crack tips under dynamic and static combined stress is the best.
The negative time indicates that the stress wave is not transmitted to the upper edge of the rock test piece, the incident wave is not transmitted to the crack tip, the monitored unit is in a pressed state due to the original rock stress, and the maximum main stress is maintained stable at the stage. After that, along with the transmission of stress waves, the compressive stress born by the monitored unit is increased, then the horizontal component of the stress waves changes the stressed state of the crack tip, the compressive stress is gradually converted into tensile stress, when the incident stress waves exceed the dynamic tensile strength of the rock, the crack tip unit is damaged and completely fails, the capability of bearing the tensile stress is not possessed any more, the maximum principal stress curve of the monitored unit is reduced to 0MPa, and the crack is cracked and expanded along with the maximum principal stress curve, for example, when the stress of the original rock is 0-0.5 MPa; when the incident stress wave cannot cause the crack tip to crack, the crack tip can crack and expand under the reflection effect of the stress wave, for example, when the stress of the original rock is 1-3 MPa. The numerical model is also indicated to be feasible for simulating the breaking behavior of the surrounding rock of the tunnel with the I-shaped fissure under the stress state of the original rock, and can provide important theoretical and practical values in the aspects of optimizing the supporting structure of the tunnel and controlling the deformation of the surrounding rock.
Example two
The implementation steps of the surrounding rock implementation case of the I/II composite crack deep buried tunnel are as follows:
The first step: changing the rotation angle of the prefabricated crack on the basis of the tunnel model containing the I-shaped crack, keeping the whole size of a test piece, the crack length and the tunnel arrangement unchanged, forming different tunnel models containing the I/II composite crack by changing the included angle alpha between the prefabricated crack and a vertical plane, and establishing a two-dimensional numerical model in ICEM CFD software as shown in figure 10;
And a second step of: in ICEM CFD, MESH division is carried out by adopting a MESH method, the MESH size is 1mm, the MESH is divided into triangular units on a plane, MESH encryption is carried out on the whole to-be-expanded area of a crack, the MESH side length of an encryption area is 1mm, the MESH side length of a non-encryption area is 2-3 mm, a tunnel model MESH is stretched along the normal direction to form a three-dimensional MESH, the MESH thickness is 2mm, the MESH is more accurate when a crack expansion path is simulated, a three-dimensional MESH file is derived, and the model is stored, as shown in figure 11;
And a third step of: opening an ANSYS Workbench platform, introducing a geometric module, setting a unit to be mm, introducing a two-dimensional geometric model into the module, and stretching along a normal plane to form a three-dimensional geometric model;
fourth step: the simultaneous ICEM CFD software sets the unit as mm, opens the model file established in the first step to import the calculation grid, and sets the unit as m;
Fifth step: and a simultaneous statics calculation module, wherein the density, dynamic elastic modulus and dynamic poisson ratio of the material are set at ENGINEERING DATA part, the module is stored and used, the setting unit is mm, defined material parameters are given to the model, normal displacement constraint is applied to the front plane and the rear plane of the model, vertical displacement constraint is applied to the upper plane and the lower plane of the model, stress condition is applied to the left plane and the right plane of the model, and the stress condition is basically consistent with the stress boundary condition applied in the horizontal direction and the vertical direction simultaneously. The calculation time is set to be 1s, and since the left end and the right end of the model are free from displacement constraint, WEAKEN SPRING options are required to be opened during calculation, so that the phenomenon of error reporting is avoided;
sixth step: after the calculation is completed, storing a file of the ANASYWorkbench platform, and finding a result file of static calculation;
Seventh step: opening AUTODYN software, importing a three-dimensional grid model stored in the first step, setting the unit as mm, setting various related parameters of materials including but not limited to density, elastic modulus, poisson ratio, tensile strength and compressive strength, and describing the breaking behavior of the rock by adopting a maximum principal stress criterion and a maximum shearing stress criterion. Importing a result file of static force calculation in an initial boundary condition part, setting boundary conditions which are the same as those of the static force calculation in the boundary condition part, applying displacement boundary conditions to nodes, establishing a set of left end face and a set of right end face of a model in a stress condition, then calling parallel calculation of AUTODYN software, and calculating multiple cores and multiple threads of the digital model;
Eighth step: setting a result to be output, setting a period of calculation time for verifying whether a stable stress field is obtained, calculating for a period of time by AUTODYN software to obtain stress distribution of surrounding rock of the composite type slit tunnel containing I/II, taking alpha=45 DEG as an example, wherein the stress distribution is consistent with the result obtained by a static calculation module, when the stress of the original rock is increased, the stress value of each position of a rock sample is increased, the integral stress distribution is not changed, and successfully obtaining the stable static stress field of the slit tunnel under different original rock stress conditions;
Ninth step: and selecting a file which is not calculated yet, establishing a model related to dynamic load loading, and selecting a model for realizing dynamic loading of the drop hammer impact system. And establishing models such as an incident rod, a transmission rod, an energy absorption rod and the like in AUTODYN software, restraining displacement of the whole model in the normal direction, applying a dynamic impact stress wave obtained by a preliminary test on the top surface of the incident rod model to correspond to the test, setting the energy absorption rod to be a reflection-free boundary condition, setting the calculation time of monitoring points, and calculating after finishing the adjustment of the result required to be output.
Tenth step: carrying out calculation of sigma θθ radial stress and sigma rr hoop stress by taking stress data sigma x、σy and tau xy around tunnel surrounding rock into theoretical formulas (1) and (2), and then carrying out sigma θθ and sigma rr under different angles into a polar coordinate system according to the angle of the polar coordinate, so as to finally obtain a tunnel surrounding rock dynamic stress concentration distribution coefficient DSCF under the polar coordinate condition, as shown in fig. 12-18;
Eleventh step: according to the dynamic stress concentration coefficient of the tunnel surrounding rock, the stability of the tunnel surrounding rock is evaluated, and from the graph, the dynamic stress concentration coefficient of the tunnel surrounding rock is in a butterfly shape, the dynamic stress concentration coefficients of the crack tunnel surrounding rock are greatly different under different crack inclination angles theta, especially in a vault and arch shoulder area, the dynamic stress concentration coefficient is also larger at the arch foot and arch foot positions of the tunnel, the dynamic stress concentration coefficient of the tunnel arch foot is gradually increased along with the increase of static side pressure, the dynamic stress concentration coefficient of the tunnel surrounding rock is changed under different crack inclination angles, the right side pressure stress of the surrounding rock is reduced along with the increase of crack inclination angles, the tensile stress concentration coefficient is increased, and the stability of the tunnel surrounding rock is evaluated according to the tensile stress concentration coefficient;
Twelfth step: taking crack tip opening displacement time course curves of displacement data u x、uy and u xy of the crack tip of the tunnel surrounding rock, substituting the crack tip opening displacement time course curves into theoretical models (9) and (10) to calculate an I/II composite stress intensity factor of the crack tip of the crack surrounding rock, so as to obtain a stress intensity factor curve of the I/II composite crack tip of the real-time crack tip, and then determining equivalent dynamic fracture toughness K eff of the I/II composite crack according to the initiation moment of the crack tip in the tunnel crack surrounding rock, wherein as shown in fig. 19, alpha=15° is the gradual decrease of the equivalent dynamic fracture toughness along with the increase of the ground stress, which means that the stability of the crack tunnel surrounding rock is gradually decreased along with the increase of the ground stress, and alpha=30°,45 DEG and 60 DEG are the gradual decrease of the equivalent dynamic fracture toughness along with the increase of the ground stress, which means that the stability of the crack tunnel surrounding rock tip is gradually increased, and when alpha=60°, the equivalent dynamic fracture toughness K eff of the crack tunnel surrounding rock is larger, which means that the stability of the crack tip of the tunnel surrounding rock is the best.
The dynamic response of the crack tunnel model is different under the same original rock stress, but the variation trend of the maximum principal stress curve of the crack tip is consistent with the result of the I-shaped crack tunnel surrounding rock model, and the crack initiation time of the same structural model is increased along with the increase of the original rock stress, so that the method can effectively identify different model structures and static stress and obtain feedback in the dynamic response characteristics of the model structures and static stress, and the achievement has important theoretical value in the aspect of dynamic disaster early warning in each underground tunnel engineering and has wide application prospect in the aspects of deep underground mining, tunnel group excavation and the like.
The present invention is not limited to the above-mentioned embodiments, but is not limited to the above-mentioned embodiments, and any person skilled in the art can make some changes or modifications to the equivalent embodiments without departing from the scope of the technical solution of the present invention, but any simple modification, equivalent changes and modifications to the above-mentioned embodiments according to the technical substance of the present invention are within the scope of the technical solution of the present invention.
Claims (9)
1. The stability evaluation method of the tunnel surrounding rock under dynamic and static combined stress is characterized by comprising the following steps of:
S1, establishing a two-dimensional numerical model of a rock mass part of a tunnel surrounding rock by adopting a finite element preprocessing module, and entering a grid dividing module to divide a structural grid;
S2, importing a statics calculation module, inputting engineering geological material numerical model parameters, carrying out statics loading on the statics calculation module, setting boundary conditions, and carrying out statics calculation;
S3, importing static calculation data into a dynamics calculation module, performing dynamics numerical simulation analysis by using a difference method, and analyzing according to a theoretical model to obtain a stress field of units around the tunnel surrounding rock and a maximum main stress time path curve of crack tips of the tunnel surrounding rock after static load is applied to the tunnel surrounding rock;
s4, calculating a dynamic stress concentration coefficient based on a stress field of units around the tunnel surrounding rock after static load is applied to the tunnel surrounding rock;
s5, calculating a stress intensity factor curve of the crack tip based on a maximum principal stress time curve of the crack tip of the tunnel surrounding rock;
S6, determining the dynamic fracture toughness of the crack tip according to the dynamic fracture moment, and comprehensively evaluating the dynamic stability of the crack tunnel surrounding rock according to the dynamic stress concentration coefficient and the dynamic fracture toughness of the crack tip.
2. The method for evaluating the stability of the tunnel surrounding rock under the dynamic and static combined stress according to claim 1, wherein the specific steps of the step S1 are as follows:
S11, a preprocessing software ICEM CFD module establishes a two-dimensional geometric model according to actual tunnel engineering, performs structural grid division, and stretches grids along a normal direction to form a three-dimensional grid model;
s12, importing a two-dimensional geometric numerical model file into a geometric module, and stretching the model along a normal direction to form a three-dimensional geometric model;
s13, opening the three-dimensional grid model, and importing the calculation grid.
3. The method for evaluating the stability of tunnel surrounding rock under dynamic and static combined stress according to claim 1, wherein the engineering geological material numerical model parameters comprise density, elastic modulus, poisson ratio, tensile strength and compressive strength.
4. The method for evaluating the stability of the tunnel surrounding rock under the dynamic and static combined stress according to claim 1, wherein the specific steps of the step S4 are as follows:
S41, determining horizontal stress, vertical stress and shear stress of units around the tunnel surrounding rock according to the stress field of the units around the tunnel surrounding rock after static load is applied to the tunnel surrounding rock;
S42, calculating radial stress and hoop stress of the surrounding units of the tunnel surrounding rock according to the horizontal stress and the vertical stress of the surrounding units of the tunnel surrounding rock and the shear stress;
s43, calculating the dynamic stress concentration coefficient of the surrounding units of the tunnel surrounding rock according to the radial stress and the hoop stress of the surrounding units of the tunnel surrounding rock.
5. The method for evaluating the stability of the tunnel surrounding rock under the dynamic and static combined stress according to claim 4, wherein the calculation formula in the step S42 is as follows:
σθθ＝σxcos2θ+σysin2θ-2τxysinθcosθ
σrr＝σxcos2θ+σysin2θ+2τxysinθcosθ
Wherein: σ θθ is the hoop stress of the tunnel surrounding rock in polar coordinates; σ rr represents the radial stress at the polar coordinates of the tunnel surrounding rock; σ x、σy and τ xy are the horizontal stress, the vertical stress and the shear stress of the monitoring unit in the planar coordinate system, respectively.
6. The method for evaluating the stability of the tunnel surrounding rock under dynamic and static combined stress according to claim 4, wherein the calculation formula in the step S43 is as follows:
DSCF＝σθθσ
wherein: σ θθ is the hoop stress of the tunnel surrounding rock in polar coordinates; sigma is the input initial stress; DSCF is the dynamic stress concentration factor.
7. The method for evaluating the stability of the tunnel surrounding rock under the dynamic and static combined stress according to claim 1, wherein the specific steps of the step S5 are as follows:
S51, obtaining a crack tip opening displacement time-course curve based on a maximum main stress time-course curve of the crack tip of the tunnel surrounding rock;
s52, substituting the crack tip opening displacement time course curve into a theoretical model to calculate the stress intensity factor of the crack tip, and obtaining a stress intensity factor curve of the real-time crack tip.
8. The method for evaluating the stability of the tunnel surrounding rock under dynamic and static combined stress according to claim 7, wherein the theoretical model in the step S52 is as follows:
wherein: q I and Q R are the real and imaginary parts of the constant Q 0, respectively; r k and I k are the real and imaginary parts, respectively, of the imaginary number C k; y I and Y II are dimensionless stress intensity factors of K I and K II, respectively.
9. The method for evaluating the stability of the tunnel surrounding rock under the dynamic and static combined stress according to claim 1, wherein in the step S6, the tunnel surrounding rock is broken and closely related to the distribution of the circumferential tensile stress, and the condition of the distribution of the circumferential tensile stress around the tunnel under the action of stress waves in different directions is focused, namely, the dynamic stress concentration coefficient around the tunnel is researched, wherein the positive value of the dynamic stress concentration coefficient represents the compressive stress concentration, and the negative value represents the tensile stress concentration; when tensile stress is concentrated, the smaller the value of DSCF, the greater the degree of tensile stress concentration.
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