DEM method for rock creep impact failure based on subcritical crack growth theory

Abstract

The present invention provides a rock creep impact failure DEM method based on subcritical crack extension theory, by establishing a rock creep model based on rock subcritical crack extension theory and a rock periodic impact model based on impact disturbance stress wave waveform; unifying the time scale and variable time step scheme, and uniformly solving the creep model and the impact disturbance model in the software; obtaining the macroscopic mechanical parameters of the rock and correcting the microscopic mechanical parameters according to the test results of uniaxial compression test, sound wave propagation velocity test, Brazilian splitting test, shear test, etc.; carrying out double torsion test to determine the subcritical crack extension constant A and stress corrosion index n, and inverting the critical crack length a of rock microcrack creep fracture based on trial and error method. mcr and the expected life span of rock specimens t f ; Finally, the geometric model is determined according to the engineering geological conditions, and the numerical simulation of the subcritical crack growth process of rock under impact disturbance is carried out to analyze the scope of creep impact instability damage of tunnel surrounding rock.

Description

Technical Field

[0001] The invention relates to the field of stability analysis of deep underground engineering tunnels, and in particular to a rock creep impact failure DEM method based on subcritical crack extension theory. Background Art

[0002] In deep rock engineering, as the mining depth increases, the deep rock mass is in a high ground stress environment, and the deadweight stress and tectonic stress field together constitute a deep high stress field. The deep rock mass is subjected to high static loads, and the rock creep characteristics, that is, the time effect, are more obvious. The surrounding rock is poorly stable and is easily disturbed and breaks the equilibrium state.

[0003] Under the action of "high static stress" and "periodic impact load", the non-steady-state, nonlinear deformation, damage and energy evolution of deep rock mass are very complex. On the one hand, the rheology of rock mass is accompanied by the deformation and stress adjustment of surrounding rock, which is a process of damage accumulation and energy dissipation. The impact disturbance causes new crack expansion and local damage in the rock mass. The equilibrium state of the rock mass in the stable creep stage is slowly broken, which accelerates the process of rock creep damage accumulation, resulting in the gradual instability and destruction of the rock after the impact disturbance. On the other hand, the rock mass in a strong rheological state has accumulated enough strain energy inside and is in a critical state of instability and destruction. At this time, even a slight impact disturbance can cause instantaneous rock burst in the rock mass, thereby causing deep rock mass dynamic disasters. In order to ensure the safety and long-term stability of deep geotechnical engineering projects, it is crucial to accurately describe and predict the damage of surrounding rock under the action of excavation disturbance.

[0004] At present, the existing creep models include empirical models, component combination models, damage fracture rheological models, endogenous time rheological models and elastic viscoplastic models. Among them, the most commonly used empirical models and component combination models can only reflect the creep deformation trend but cannot reflect the nature of creep instability failure.

[0005] The creep model based on subcritical crack extension theory can not only reflect the creep deformation trend, but also further reveal the nature of creep damage, but it is rarely used in existing creep numerical simulations.

[0006] Secondly, in the analysis and numerical simulation methods of the damage and destruction range of deep underground surrounding rocks, there is no comprehensive solution for the coupling effects of rock creep, impact disturbance and subcritical crack extension, and it is not used to analyze the stability of the surrounding rocks, which makes it difficult to meet the actual needs of numerical simulation of subcritical crack extension of underground surrounding rocks under stable stress and impact disturbance. Therefore, in view of the various shortcomings of the existing numerical simulation methods for long-term stability of underground surrounding rocks, the present invention proposes a discrete element simulation method for rock creep impact failure based on subcritical crack extension theory, so as to more accurately perform numerical simulation analysis of long-term stability of underground surrounding rocks. Summary of the invention

[0007] In order to solve the above problems in the prior art, the present invention provides.

[0008] The technical solution of the present invention is:

[0009] A rock creep impact failure DEM method based on subcritical crack extension theory includes the following steps:

[0010] S1, according to the actual engineering geological conditions of the mine, the mine geometric model is established in UDEC and discretized into blocks, and the rock parameters of the blocks are assigned;

[0011] S2, based on the rock subcritical crack extension theory, the creep load and the rock layer contact degradation and failure process are given to the mine geometry model, a rock creep model is established, and a failure criterion of the rock layer contact is set for the rock creep model;

[0012] S3, according to the impact on the surrounding rock of the mine tunnel, based on the impact disturbance stress wave waveform, establishing a rock periodic impact model of the mine geometric model;

[0013] S4, establishing a numerical model for coupling solution of rock subcritical crack growth and impact disturbance in UDEC, coupling the creep load of the mine geometry model with the action time of the impact load, and based on the rock subcritical crack growth theory, solving the rock creep model and the rock periodic impact model in a unified manner;

[0014] S5, performing numerical simulation of the mine geometry model under creep impact in UDEC, analyzing the stability of the surrounding rock mass of the mine geometry model based on the result of the numerical simulation, and obtaining the creep impact instability damage range of the mine geometry model.

[0015] Furthermore, establishing the rock creep model includes the following steps: S1, giving the rock creep model rock contact and evenly distributing rock microcracks in the contact; S2, defining the length of the rock microcracks and making the length value randomly and evenly distributed; S3, writing the rock subcritical crack growth rate equation into the rock creep model, and establishing the corresponding relationship between the rock microcrack growth rate and the stress intensity factor; S4, writing the contact strength degradation process into the rock creep model, and establishing the contact strength degradation relationship of the contact strength changing with time; S5, giving the rock creep model a criterion for contact degradation failure.

[0016] Furthermore, the method for defining the length of the rock microcracks is: using the loop statement in the fish function to traverse each contact in the rock creep model, and setting the length of the rock microcracks to 0 to c times the length of the contact where it is located, where the value of c is random and obeys a uniform distribution.

[0017] Furthermore, the rock subcritical crack growth includes mode I with only normal stress and mode II with only shear stress. In mode I, the corresponding relationship between the rock microcrack growth rate and the stress intensity factor is expressed as: In mode II, the corresponding expression of the rock microcrack growth rate and stress intensity factor is: Where, ν Ⅰ , ν Ⅱ is the subcritical crack growth rate of rock, A I , A II is the model fracture extension constant, K I , K II is the model stress intensity factor, K IC , K IIC is the model fracture toughness, n I 、n II is the model stress corrosion index.

[0018] Furthermore, the rock subcritical crack extension also includes a mixed mode of normal stress and shear stress; in mode I, the contact strength degradation relationship expression is:

[0019]

[0020] In mode II, the contact strength degradation relationship expression is:

[0021]

[0022] In the mixed mode, the contact strength degradation relationship expression is:

[0023]

[0024] In the formula, F ni is the normal force on contact i; F si is the shear force on contact i; β i is the inclination angle of contact i; A I , A II is the model fracture extension constant, K IC , K IIC is the model fracture toughness, is the instantaneous tensile strength of contact i, is the instantaneous cohesive strength of contact i, λ 1i is the contact degradation constant of the tensile strength of contact i, λ 2i is the contact degradation constant of the cohesive strength of contact i, L i is the length of contact i, a i is the length of the microcrack on contact i.

[0025] Furthermore, the criterion for contact degradation failure of the rock creep model is:

[0026]

[0027] In the formula, a i is the length of the microcrack on contact i, L i is the length of contact i, K IC , K IIC is the fracture toughness of the model.

[0028] Furthermore, the model fracture extension constant A I , A II and model stress corrosion index n I 、n II The model fracture toughness K was determined by double torsion test. IC and K IIC Determined by Brazilian splitting test; the double torsion test comprises the following steps: a. preparing a rock sample, applying a stable torsion load to the rock sample, making the crack stably expand, and recording the torsion angle and torque data; b. measuring the crack expansion length, repeating step a, and obtaining the crack expansion curve under different torsion loads; c. drawing a double logarithmic coordinate diagram of the crack expansion rate da / dt and the stress intensity factor K according to the test data, and determining the slope n and intercept ln(A) of the double logarithmic coordinate diagram through linear fitting, thereby calculating the model fracture expansion constant A I , A II and model stress corrosion index n I 、n II ; The Brazilian splitting test comprises the following steps:

[0029] a. Calculate the model fracture toughness K in modes I and II by the following formula IC and K IIC :

[0030]

[0031]

[0032]

[0033]

[0034] b. As a and θ change, when N I ≠0,N II = 0, the subcritical crack extension form is mode I; when N I =0,N II When ≠0, it is mode II; the expressions of fracture toughness under the two modes are obtained as follows:

[0035]

[0036] Where P is the maximum load in the Brazilian splitting test, a is the half length of the microcrack, r is the radius of the disk, B is the thickness of the disk, and θ is the inclination angle of the crack relative to the load direction.

[0037] Furthermore, the calculation formula of the stress intensity factor K is:

[0038] In the formula, a m is the initial macro crack length, W is the rock specimen width, and σ is the tensile stress;

[0039] The expected life span t of the rock sample is calculated by the following formula: f :

[0040]

[0041] In the formula, K IC is the model fracture toughness, a mi is the elapsed time t i The macro crack length after I is the model fracture extension constant.

[0042] Furthermore, the impact of the surrounding rock of the mine tunnel includes the impact stress waveform, the impact point, the impact load and the impact load action time; the rock periodic impact model is established based on the impact stress waveform, including the following steps: S1, according to the actual situation of the tunnel surrounding rock body engineering, the coal rock body is subjected to the impact disturbance and its actual impact stress wave waveform is detected; S2, through the microseismic monitoring system, the impact load and impact point of the microseismic event are collected to determine the waveform of the impact stress wave; S3, the impact load is calculated according to the elastic wave theory by the following formula: σ d =ρC ps v, where ρ is the density of the surrounding rock medium of the tunnel; C ps is the velocity of the mine shock wave, which is obtained through on-site measurement; v is the peak velocity of the particle movement of the tunnel surrounding rock caused by the mine shock wave transmitted to the surrounding rock.

[0043] Furthermore, the rock creep model and the rock periodic impact model are uniformly solved, including the following steps: S1, coupling the action time of the rock creep load and the impact load by a unified time scale method; S2, based on the rock creep model, causing the mine geometry model to be unstable and damaged by the action of stable creep stress, and recording the mechanical time required for its damage; S3, calculating the expected life t of the rock sample f, and compare it with the time of rock instability and failure in the laboratory uniaxial creep experiment to obtain the proportional magnitude of the two; S4, based on the rock periodic impact model, the impact time and period are reduced or amplified through the proportional magnitude, and the impact effect is controlled by the mechanical time.

[0044] Furthermore, the total mechanical time can be obtained by the following formula: total =N C ×Δt, where T total is the total mechanical time, N C is the creep time step number, Δt is the creep time step; the rock creep model and the rock periodic impact model are improved by a variable time step scheme for unified solution, including the following steps: setting the minimum time step Δt min With the maximum time step Δt max , to ensure the actual time step Δt b Within this range; when the maximum unbalanced force is too small, increase the actual time step and set Δt b =2*Δt b-1 ; When the unbalanced force is too large, let Δt b =Δt min ; Among them, the critical value of the maximum unbalanced force is defined by whether the ratio of the maximum unbalanced force exceeds 0.001.

[0045] Furthermore, the impact stress waveform is a half-sine wave, and the unified solution expression of the rock creep model and the rock periodic impact model is:

[0046]

[0047] In the formula, σ j is the creep load, k is a natural number, T C is the period of a single shock, σ dmax is the peak compressive stress, k is a natural number, and N is the total number of time steps.

[0048] Furthermore, the establishment of the mine geometry model includes the following steps: S1, establishing the mine geometry model through the block createpolygon command; S2, using the block cut Voronoi command to discretize the mine geometry model, dividing it into blocks, and preferably dividing it into Thiessen polygon blocks; S3, using the block zone generate command to divide the grid units, and using the block property material and block contact property material commands to assign rock parameters to the blocks and contacts; S4, setting boundary conditions through the block gridpoint apply velocity-x / y and blockgridpoint apply viscous-x / y commands, setting the bottom and both sides of the mine geometry model as viscous damping boundary conditions, and setting the damping coefficient to prevent the reflection of the impact load.

[0049] Furthermore, the rock parameters include macroscopic mechanical parameters and microscopic mechanical parameters; the rock parameters are determined by the following steps: S1, determining the macroscopic mechanical parameters of the rock by conducting indoor tests on rock samples; the indoor tests include uniaxial compression tests, sound wave propagation velocity tests, Brazilian splitting tests, and shear tests; the macroscopic mechanical parameters include Young's modulus E, Poisson's ratio μ, density ρ, cohesion c, friction angle And tensile strength σ t ; S2, establish a rock sample model, the microscopic mechanical parameters are inverted by UDEC numerical simulation, and the macroscopic mechanical parameters are substituted into the rock sample model by the following command:

[0050] block property material number (custom number) young p (E) poisson p (μ) density p (ρ)

[0051] block contact property material number (custom number) stiffness-normal p (k n )stiffness-shear p(k s )cohesion p(c)friction p tension p(σ t )

[0052] In the above command, p is the corresponding parameter in the brackets;

[0053] S3, use the block fix all command to simulate the top / bottom platen with a rigid body, and use the block apply velocity-y command to apply a downward velocity to the top platen to simulate the uniaxial compression test and the Brazilian splitting test; S4, use the fish function loop statement to traverse the blocks in the rock specimen model to monitor the rock stress, strain and volume changes; and continuously adjust the contact normal stiffness k by trial and error. n , shear stiffness k s , so that the simulated curve shape and failure shape are close to the experimental ones, and the simulated compressive strength reaches the experimental results, so as to invert the contact normal stiffness k of the block in UDEC n , shear stiffness k s .

[0054] The beneficial effects of the present invention are:

[0055] Through the method recorded in the present invention, in engineering practice, for example, for tunnel surrounding rock, the location and range of the tunnel surrounding rock damage area under the action of creep and impact loads can be analyzed by numerical simulation methods, so that the damage and destruction of the tunnel rock under the action of mine shock waves during underground coal mining in this area can be clarified. Through the analysis of the results of the standard specimen numerical simulation model and the analysis of the results of the engineering example numerical simulation, combined with the discrete element simulation support method, such as anchor rods, etc., the damage range of the tunnel surrounding rock under the action of mine shock waves and creep can be clarified, and the damage and destruction location and area can be determined, so as to formulate a suitable support plan, which can effectively guide engineering operations and avoid casualties and property losses during operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 : Schematic diagram of rock crack development process based on the creep model of subcritical crack growth theory;

[0057] Figure 2 : Schematic diagram of creep-impact stress curve;

[0058] Figure 3 : Schematic diagram of rock stress-time curve under creep impact load;

[0059] Figure 4 : Schematic diagram of the calculation process of the method of the present invention;

[0060] Figure 5 : Schematic diagram of tunnel surrounding rock creep and impact load loading;

[0061] Figure 6 : Schematic diagram of damage of tunnel surrounding rock under impact and creep. DETAILED DESCRIPTION

[0062] The contents of the present invention are described in detail below with reference to the accompanying drawings.

[0063] As attached Figure 1 To Attachment Figure 6 As shown, the present invention records a rock creep impact failure DEM method based on subcritical crack extension theory.

[0064] According to the actual engineering geological conditions of deep mines, a mine geometry model is established in the geotechnical engineering software UDEC, and based on the subcritical crack growth theory, a discrete element simulation is performed on the destruction process of the tunnel surrounding rock under the combined action of creep load and impact load, so as to clarify the destruction range of the tunnel surrounding rock under the action of mine shock wave and creep. The specific steps include the following steps.

[0065] S1, according to the actual engineering geological conditions of the deep mine, the mine geometry model is established in the geotechnical engineering software UDEC, including the following steps:

[0066] S11, establish the mine geometry model through the block create polygon command;

[0067] S12, using the block cut Voronoi command to discretize the mine geometry model, dividing it into blocks, and preferably dividing it into Thiessen polygon blocks;

[0068] S13, use the block zone generate command to divide the grid cells, and use the block property material and block contact property material commands to assign rock parameters to the blocks and contacts;

[0069] S14, set the boundary conditions through the block gridpoint apply velocity-x / y and block gridpoint applyviscous-x / y commands, set the bottom and both sides of the mine geometry model as viscous damping boundary conditions, and set the damping coefficient to prevent the transflection of the impact load.

[0070] S2, determine the rock parameters in the mine geometry model, which include macroscopic mechanical parameters and microscopic mechanical parameters.

[0071] Specifically:

[0072] S21, making a rock sample and establishing a rock sample model in UDEC software. The steps of establishing the rock sample model refer to step S1.

[0073] The macroscopic mechanical parameters of the rock are determined by conducting indoor tests on rock samples. The indoor tests include but are not limited to uniaxial compression tests, sound wave propagation velocity tests, Brazilian splitting tests, shear tests and other tests.

[0074] The macroscopic mechanical parameters of rocks include but are not limited to Young's modulus E, Poisson's ratio μ, density ρ, cohesion c, friction angle And tensile strength σ t .

[0075] S221, micromechanical parameters of rock are inverted by UDEC numerical simulation.

[0076] Substitute the rock macroscopic mechanical parameters determined by the experiment into the rock specimen model using the following command:

[0077] block property material number (custom number) young p (E) poisson p (μ) density p (ρ)

[0078] block contact property material number (custom number) stiffness-normal p (k n )stiffness-shear p(k s )cohesion p(c)friction p tension p(σ t )

[0079] In the above command, p is the corresponding parameter in the brackets.

[0080] S222, the top / bottom platens are simulated with rigid bodies using the block fix all command, and the block applyvelocity-y command applies a downward velocity to the top platen to simulate the uniaxial compression test and the Brazilian split test.

[0081] S223, using the fish function loop statement to traverse the blocks in the rock sample model, so as to monitor the stress, strain and volume change of the rock;

[0082] The contact normal stiffness k is adjusted by trial and error. n , shear stiffness k s , so that the simulated curve shape and failure shape are close to the experimental ones, and the simulated compressive strength reaches the experimental results, so as to invert the contact normal stiffness k of the block in UDEC n , shear stiffness k s .

[0083] S23, referring to step S221, substitute the determined macroscopic and microscopic mechanical parameters into the mine geometry model.

[0084] S3, based on the rock subcritical crack extension theory, is programmed through fish language, and the creep load and rock contact degradation and failure process are given to the mine geometry model to establish a rock creep model.

[0085] The following steps are involved:

[0086] S31, assign rock contact to the rock creep model according to the actual rock contact type in deep mines;

[0087] S32, setting rock microcracks so that they are evenly distributed in the contact areas of each rock;

[0088] S33, define the length of the rock microcracks by using the loop statement in the fish function to traverse each contact in the rock creep model, and set the length of the rock microcracks to 0 to c times the length of the contact where it is located, where the value of c is random and obeys a uniform distribution.

[0089] Through the settings of steps S31 to S33, the rock creep model can simulate the initial microcracks naturally existing in the rock mass, reflecting the heterogeneity of the rock.

[0090] S34, write the rock subcritical crack growth rate equation into the rock creep model, and establish the relationship between the rock microcrack growth rate and the stress intensity factor.

[0091] The equation for the subcritical crack growth rate of rock is expressed based on the empirical power law relationship. When the temperature is constant and only the two-dimensional case is considered, the subcritical crack growth rate of rock can be divided into mode I with only normal stress, mode II with only shear stress, and a mixed mode of normal stress and shear stress.

[0092] in,

[0093] The rock subcritical crack growth rate equation of mode I is expressed as:

[0094]

[0095] The rock subcritical crack growth rate equation of mode II is expressed as:

[0096]

[0097] In the formula,

[0098] ν Ⅰ , ν Ⅱ is the subcritical crack growth rate of rock;

[0099] A I , AII is the model fracture extension constant;

[0100] K I , K II is the model stress intensity factor;

[0101] K IC , K IIC is the model fracture toughness;

[0102] n I 、n II is the model stress corrosion index.

[0103] S351, rock contact strength, that is, contact tensile strength J T and cohesive strength J C , decreases with the increase of the length of rock microcracks. This process is the contact strength degradation process of rock. The contact strength degradation process is written into the rock creep model to establish the relationship between contact strength and time.

[0104] The expression of contact strength degradation process is:

[0105]

[0106] In the formula,

[0107] is the instantaneous tensile strength of contact i;

[0108] is the instantaneous cohesive strength of contact i;

[0109] λ 1i is the contact degradation constant of the tensile strength of contact i;

[0110] λ 2i is the contact degradation constant of the cohesive strength of contact i;

[0111] L i is the length of contact i;

[0112] a i is the length of the microcrack on contact i.

[0113] S352, the two sides of the expression of the contact strength degradation process are simultaneously differentiated with respect to time t, and substituted into the rock subcritical crack growth rate equation to obtain the rock contact strength degradation equation under the rock subcritical crack growth state:

[0114]

[0115] a. In mode I where only positive stress exists in rock subcritical crack extension, the contact strength degradation equation is:

[0116]

[0117] In the formula, F ni is the normal force on contact i;

[0118] b. In mode II where only shear stress exists in the subcritical crack growth of rock, the contact strength degradation equation is:

[0119]

[0120] In the formula, F si is the shear force on contact i;

[0121] c. In the mixed mode of normal stress and shear stress in rock subcritical crack extension, the contact strength degradation equation is:

[0122]

[0123] In the formula, β i is the inclination angle of contact i.

[0124] S36, as the rock microcracks continue to grow, the contact strength of the rock continues to decrease. Regardless of whether the length of the rock microcracks reaches the critical crack length or the critical stress intensity factor, as long as the fracture toughness is reached, the rock microcrack extension rate will increase sharply, causing the contact to be quickly destroyed, causing the stress around the contact to be redistributed, further leading to local stress concentration, and accelerating the deterioration of the adjacent contact strength to destruction.

[0125] The contact failure criterion is:

[0126]

[0127] When the contact is broken, the instantaneous tensile strength of the contact Instantaneous cohesive strength All become 0.

[0128] The contact failure criterion is written into the rock creep model as the crack generation standard of one cycle of the rock creep model.

[0129] S37, through the double torsion test, determine the model fracture extension constant A and model stress corrosion index n; through the Brazilian splitting test, determine the model fracture toughness K in mode I and II IC and K IIC .

[0130] S371, determine the model fracture extension constant A and model stress corrosion index n by double torsion test:

[0131] a. Apply a stable torsional load to the rock sample to allow the crack to expand steadily, and record the torsion angle and torque data;

[0132] b. Measure the crack extension length and repeat the previous steps to obtain the crack extension curves under different torsional loads;

[0133] c. Based on the test data, a double logarithmic coordinate graph of the crack growth rate da / dt and the stress intensity factor K is plotted. Through linear fitting, the slope n and intercept ln(A) of the double logarithmic coordinate graph are determined, from which the parameters A and n can be calculated.

[0134] S372, based on the Brazilian splitting test, the model fracture toughness K in modes I and II is calculated by the following formula IC and K IIC :

[0135]

[0136]

[0137]

[0138]

[0139] Where P is the maximum load in the Brazilian splitting test, a is the half length of the microcrack, r is the radius of the disk, B is the thickness of the disk, and θ is the inclination angle of the crack relative to the load direction;

[0140] As a and θ change, N I or N II Possible zeros:

[0141] When N I ≠0,N II = 0, the subcritical crack extension form is mode I;

[0142] When N I =0,N II When ≠0, it is mode II;

[0143] The expressions of fracture toughness under the two modes are obtained as follows:

[0144]

[0145] S38, through UDEC numerical simulation of rock single-side crack growth, inversion of rock creep model parameters, specifically:

[0146] a. Assign rock parameters using the method from step S221 to step S223, write into the contact strength degradation equation of mode I where only positive stress exists in the subcritical crack extension of rock, apply constant tensile stress and record the time taken for the macro crack to penetrate, and calculate the stress intensity factor K by the following formula in the case of unilateral crack extension

[0147]

[0148] In the formula,

[0149] a m is the initial macro crack length, W is the width of the rock sample, and σ is the tensile stress.

[0150] b. Under constant tensile stress σ, the relationship between crack length and crack growth rate is as follows:

[0151]

[0152] Rearranging and integrating the equation, the crack starts from length a m(i-1) Expand to a mi , and the length a m(i-1) Infinitely close to a mi , then the time Δt i =t i -t i-1 , which can be obtained by the following formula:

[0153]

[0154]

[0155] When the stress intensity factor K is equal to the fracture toughness K IC When the critical crack length is a mcr At this time, the crack growth rate reaches the critical value, and the rock sample is rapidly destroyed. The expected life of the rock sample is t f for:

[0156]

[0157] In the formula, K IC is the model fracture toughness, a mi is the elapsed time t i The macro crack length after I is the model fracture extension constant.

[0158] a mcr K IC Make a preliminary estimate and then use nonlinear iteration to get its value:

[0159]

[0160] S4, determine the impact stress waveform, impact point, impact load, and impact load action time of the tunnel surrounding rock in deep mines under impact disturbance, such as mine earthquake. Based on the impact disturbance stress wave waveform, a rock periodic impact model under the impact stress wave waveform is established in UDEC through fish language programming.

[0161] The following steps are involved:

[0162] S41, according to the actual situation of tunnel surrounding rock mass engineering, after the coal rock mass is disturbed by impact, its impact stress waveform can usually be simplified to a half-sine wave.

[0163] Taking the impact stress waveform as a half-sine wave as an example, the period of one impact is set to T C , the sine wave period T is the impulse period T C 1 / 4 of the impact stress waveform of the periodic impact is:

[0164]

[0165] In the formula, σ dmax is the peak value of compressive stress, k is a natural number, and N is the total number of time steps

[0166] S42, through the microseismic monitoring system, collect the impact point of the mine microseismic event and the released mine seismic energy E J , and mine shock frequency, where the mine shock frequency is the action frequency of the impact load; determine the position of the mine shock and express the mine shock as an impact load, so as to formulate a suitable shock wave waveform.

[0167] S43, the calculation method of impact load is as follows:

[0168] According to elastic wave theory, the impact load σ of the mine shock wave at the rock unit is calculated by the following formula: d :

[0169] σ d =ρC ps v

[0170] Where, ρ is the density of the surrounding rock medium of the tunnel; C ps is the velocity of the mine shock wave, which is obtained through on-site measurement; v is the peak velocity of the particle movement of the tunnel surrounding rock caused by the mine shock wave transmitted to the surrounding rock.

[0171] In the above formula,

[0172] The peak velocity v of the particle movement is obtained by inverse calculation of the magnitude of the mine earthquake, and the calculation formula is:

[0173] logRv=log2.6+0.5logML

[0174] Where R is the distance between the impact point and the earthquake source. The R value can be given according to geological conditions and production experience. L is the magnitude of the mine earthquake;

[0175] Based on the mine earthquake energy E J , the corresponding mine earthquake magnitude M under the current energy level is obtained by inversion of the Polish empirical formula L :

[0176] logE J =1.8+1.9M L .

[0177] S5. A numerical model for coupling subcritical crack growth and impact disturbance is established in UDEC. By coupling the action time of creep load and impact load, and based on the rock subcritical crack growth theory, the rock creep model and rock periodic impact model are solved uniformly.

[0178] The following steps are involved:

[0179] S51, coupling the action time of rock creep load and impact load by unified time scale method:

[0180] S511, based on the rock creep model, the mine geometry model is made to fail under the action of stable creep stress, and the mechanical time required for failure is recorded using the model history time-total command;

[0181] S512, the expected life of the rock sample t f , compared with the time of rock instability failure in laboratory uniaxial creep experiments, the proportional magnitude of the two was obtained;

[0182] S513, based on the rock periodic impact model, reduces or amplifies the impact time and period through proportional magnitude, and uses mechanical time to control the impact.

[0183] In the model calculation of the above steps, the total mechanical time can also be obtained by the following formula:

[0184] T total =N C ×Δt

[0185] Where, T total is the total mechanical time, N C is the number of creep time steps, and Δt is the creep time step length.

[0186] S52, the creep load and the impact load are superimposed and applied to the mine geometry model, and the subcritical crack growth theory is substituted to unify the rock creep model and the rock periodic impact model in UDEC.

[0187] Specifically, the constant creep load is superimposed on the changing impact load through the fish function, that is, the impact stress waveform keeps the waveform, period and amplitude unchanged, and moves upward on the y-axis as a whole. The creep plus impact load is applied as shown in the attached figure. Figure 2 shown.

[0188] Taking the impact stress waveform as a half-sine wave as an example, the period of one impact is set to T C , the sine wave period T is the impulse period T C 1 / 4 of the rock creep model and rock periodic impact model, the unified solution expression is:

[0189]

[0190] In the formula, σ j is the creep load, k is a natural number, T C is the period of a single shock, σ dmax is the peak compressive stress, k is a natural number, and N is the total number of time steps.

[0191] In order to further improve the computational efficiency of the numerical model for solving the coupling of subcritical crack growth and impact disturbance, ensure the calculation accuracy and reduce the calculation time, a variable time step scheme can be adopted, specifically:

[0192] a. Set the minimum time step Δt min With the maximum time step Δt max , to ensure the actual time step Δt b within that range;

[0193] b. When the maximum unbalanced force F u If it is too small, increase the actual time step and set Δt b =2*Δt b-1 ; When the unbalanced force F u When Δt is too large, b =Δt min Among them, the critical value of the maximum unbalanced force is defined by whether the ratio of the maximum unbalanced force exceeds 0.001, and multiple trials are performed to obtain the appropriate maximum and minimum time step value range.

[0194] S6, numerical simulation of the mine geometry model under creep impact was carried out in UDEC. Based on the numerical simulation results, the stress field, deformation field and damage field of the surrounding rock of the deep mine tunnel were obtained, the stability of the tunnel surrounding rock was analyzed, and the creep impact instability damage range of the tunnel surrounding rock was obtained.

[0195] Through the steps given in this embodiment, the numerical simulation of the mine geometry model under the creep impact can be performed in the existing discrete element simulation software. Figure 4 The given program logic steps can use discrete element simulation software to perform calculations of the set program and generate graphics or display data, without exceeding the basic functions of discrete element numerical simulation software.

[0196] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A rock creep impact failure DEM method based on subcritical crack extension theory, characterized in that: The following steps are involved: S1, according to the actual engineering geological conditions of the mine, the mine geometric model is established in UDEC and discretized into blocks, and the rock parameters of the blocks are assigned; S2, based on the rock subcritical crack extension theory, the creep load and the rock layer contact degradation and failure process are given to the mine geometry model, a rock creep model is established, and a failure criterion of the rock layer contact is set for the rock creep model; Establishing the rock creep model includes the following steps: S21, giving the rock creep model rock contact and evenly distributing rock microcracks in the contact; S22, defining the length of the rock microcracks, and making the length values ​​randomly and evenly distributed; S23, writing the rock subcritical crack growth rate equation into the rock creep model to establish a corresponding relationship between the rock microcrack growth rate and the stress intensity factor; S24, writing the contact strength degradation process into the rock creep model to establish a contact strength degradation relationship of the contact strength varying with time; S25, assigning a criterion for contact degradation and failure to the rock creep model; S3, according to the impact on the surrounding rock of the mine tunnel, based on the impact disturbance stress wave waveform, establishing a rock periodic impact model of the mine geometric model; S4, establishing a numerical model for coupling solution of rock subcritical crack extension and impact disturbance in UDEC, coupling the creep load of the mine geometry model with the action time of the impact load, and solving the rock creep model and rock periodic impact model in a unified manner based on the rock subcritical crack extension theory, including the following steps: S41, coupling the action time of rock creep load and impact load by unified time scale method: S42, based on the rock creep model, causing the mine geometry model to be unstable and destroyed through the action of stable creep stress, and recording the mechanical time required for the destruction; S43, the expected life of the rock sample t f , compared with the time of rock instability failure in laboratory uniaxial creep experiments, the proportional magnitude of the two was obtained; S44, based on the rock periodic impact model, reducing or enlarging the impact time and period through proportional magnitude, and using the mechanical time to control the impact; S5, performing numerical simulation of the mine geometry model under creep impact in UDEC, analyzing the stability of the surrounding rock mass of the mine geometry model based on the result of the numerical simulation, and obtaining the creep impact instability damage range of the mine geometry model.

2. The rock creep impact failure DEM method based on subcritical crack extension theory according to claim 1 is characterized in that: The method for defining the length of the rock microcrack is: using the loop statement in the fish function to traverse each contact in the rock creep model, and setting the length of the rock microcrack to 0 to c times the length of the contact where it is located, where the value of c is random and obeys uniform distribution.

3. The rock creep impact failure DEM method based on subcritical crack extension theory according to claim 1 is characterized in that: Subcritical crack growth in rock includes mode I with only normal stress and mode II with only shear stress. In mode I, the corresponding expression of the rock microcrack growth rate and stress intensity factor is: In mode II, the corresponding expression of the rock microcrack growth rate and stress intensity factor is: In the formula, ν Ⅰ , ν Ⅱ is the subcritical crack growth rate of rock, A I , A II is the model fracture extension constant, K I , K II is the model stress intensity factor, K IC , K IIC is the model fracture toughness, n I 、n II is the model stress corrosion index.

4. The rock creep impact failure DEM method based on subcritical crack extension theory according to claim 3 is characterized in that: Subcritical crack growth in rock also includes a mixed mode of normal stress and shear stress; In mode I, the contact strength degradation relationship expression is: In mode II, the contact strength degradation relationship expression is: In the mixed mode, the contact strength degradation relationship expression is: In the formula, F ni is the normal force on contact i; F si is the shear force on contact i; A I , A II is the model fracture extension constant, K IC , K IIC is the model fracture toughness, is the instantaneous tensile strength of contact i, is the instantaneous cohesive strength of contact i, λ 1i is the contact degradation constant of the tensile strength of contact i, λ 2i is the contact degradation constant of the cohesive strength of contact i, L i is the length of contact i, a i is the length of the microcrack on contact i.

5. The rock creep impact failure DEM method based on subcritical crack extension theory according to claim 4 is characterized in that: The criterion for contact degradation failure of the rock creep model is: In the formula, a i is the length of the microcrack on contact i, L i is the length of contact i, K IC , K IIC is the fracture toughness of the model.

6. The rock creep impact failure DEM method based on subcritical crack extension theory according to claim 4 is characterized in that: Model fracture extension constant A I , A II and model stress corrosion index n I 、n II The model fracture toughness K was determined by double torsion test. IC and K IIC Determined by Brazilian split test; The double torsion test comprises the following steps: a. Prepare rock samples and apply stable torsional load to the rock samples to make their cracks expand stably, and record the torsion angle and torque data; b. Measure the crack extension length and repeat step a to obtain the crack extension curves under different torsional loads; c. Based on the test data, a double logarithmic coordinate diagram of the crack growth rate da / dt and the stress intensity factor K is drawn. Through linear fitting, the slope n and intercept ln(A) of the double logarithmic coordinate diagram are determined, from which the model fracture extension constant A can be calculated. I , A II and model stress corrosion index n I 、n II ; The Brazilian split test comprises the following steps: a. Calculate the model fracture toughness K in modes I and II by the following formula IC and K IIC : b. As a and θ change, when N I ≠0,N II = 0, the subcritical crack extension form is mode I; when N I =0,N II When ≠0, it is mode II; the expressions of fracture toughness under the two modes are obtained as follows: Where P is the maximum load in the Brazilian splitting test, a is the half length of the microcrack, r is the radius of the disk, B is the thickness of the disk, and θ is the inclination angle of the crack relative to the load direction.

7. The rock creep impact failure DEM method based on subcritical crack extension theory according to claim 6 is characterized in that: The calculation formula of the stress intensity factor K is: In the formula, a m is the initial macro crack length, W is the rock specimen width, and σ is the tensile stress; The expected life span t of the rock sample is calculated by the following formula: f : In the formula, K IC is the model fracture toughness, a mi is the elapsed time t i The macro crack length after I is the model fracture extension constant.

8. The rock creep impact failure DEM method based on subcritical crack extension theory according to claim 7 is characterized in that: The impact on the surrounding rock of the mine tunnel includes the impact stress wave waveform, the impact action point, the impact load and the impact load action time; and establishing the rock periodic impact model based on the impact stress wave waveform includes the following steps: S1, according to the actual situation of the tunnel surrounding rock mass engineering, the actual impact stress wave waveform is detected after the coal rock mass is subjected to impact disturbance; S2, through the microseismic monitoring system, collect the impact load and impact point of the microseismic event and determine the waveform of the impact stress wave; S3, the impact load is calculated according to the elastic wave theory by the following formula: σ d =ρC ps v Where, ρ is the density of the surrounding rock medium of the tunnel; C ps is the velocity of the mine shock wave, which is obtained through on-site measurement; v is the peak velocity of the particle movement of the tunnel surrounding rock caused by the mine shock wave transmitted to the surrounding rock.

9. The rock creep impact failure DEM method based on subcritical crack extension theory according to claim 1 is characterized in that: The total mechanical time can be obtained as follows: T total =N C ×Δt Where, T total is the total mechanical time, N C is the number of creep time steps, Δt is the creep time step length; The rock creep model and the rock periodic impact model are improved by a variable time step scheme for unified solution, including the following steps: Set the minimum time step Δt min With the maximum time step Δt max , to ensure the actual time step Δt b Within this range; when the maximum unbalanced force is too small, increase the actual time step and set Δt b =2*Δt b-1 ; When the unbalanced force is too large, let Δt b =Δt min ; Among them, the critical value of the maximum unbalanced force is defined by whether the ratio of the maximum unbalanced force exceeds 0.

001.

10. The rock creep impact failure DEM method based on subcritical crack extension theory according to claim 9 is characterized in that: The impact stress waveform is a half-sine wave, and the unified solution expression of the rock creep model and the rock periodic impact model is: In the formula, σ j is the creep load, k is a natural number, T C is the period of a single shock, σ dmax is the peak compressive stress, and N is the total number of time steps.

11. A rock creep impact failure DEM method based on subcritical crack extension theory according to any one of claims 1 to 10, characterized in that: The establishment of the mine geometric model includes the following steps: S1, build the mine geometry model through the block create polygon command; S2, using the block cut Voronoi command to discretize the mine geometry model into blocks and divide it into Thiessen polygon blocks; S3, use the block zone generate command to divide the grid cells, and use the block property material and block contact property material commands to assign rock parameters to the blocks and contacts; S4, set the boundary conditions through the block gridpoint apply velocity-x / y and block gridpoint apply viscous-x / y commands, set the bottom and both sides of the mine geometry model as viscous damping boundary conditions, and set the damping coefficient to prevent the reflection of the impact load.

12. The rock creep impact failure DEM method based on subcritical crack extension theory according to claim 11, characterized in that: The rock parameters include macroscopic mechanical parameters and microscopic mechanical parameters; the rock parameters are determined by the following steps: S1, determine the macroscopic mechanical parameters of the rock by conducting indoor tests on the rock samples; the indoor tests include uniaxial compression test, sound wave propagation velocity test, Brazilian splitting test, and shear test; the macroscopic mechanical parameters include Young's modulus E, Poisson's ratio μ, density ρ, cohesion c, friction angle And tensile strength σ t ; S2, establish a rock sample model, the microscopic mechanical parameters are inverted by UDEC numerical simulation, and the macroscopic mechanical parameters are substituted into the rock sample model by the following command: block property material number (custom number) young p (E) poisson p (μ) density p (ρ) block contact property material number (custom number) stiffness-normal p (k n )stiffness-shear p(k s )cohesion p(c)friction tension p(σ t ) In the above command, p is the corresponding parameter in the brackets; S3, the top / bottom platens are simulated with rigid bodies by using the block fix all command, and the block apply velocity-y command is used to apply downward velocity to the top platen to simulate the uniaxial compression test and Brazilian split test; S4, using the fish function loop statement to traverse the blocks in the rock sample model, so as to monitor the rock stress, strain and volume changes; the contact normal stiffness k is continuously adjusted by trial and error method. n , shear stiffness k s , so that the simulated curve shape and failure shape are close to the experimental ones, and the simulated compressive strength reaches the experimental results, so as to invert the contact normal stiffness k of the block in UDEC n , shear stiffness k s .

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