A real granite GBM modeling method considering mineral layer structure

Abstract

The application discloses a real granite GBM modeling method considering mineral layer structure and relates to the technical field of rock mechanics, and comprises the following steps: obtaining the morphological characteristics, structural characteristics and distribution positions of quartz, feldspar and mica minerals through high-precision nanometer CT; introducing the mineral information into PFC2d discrete element software to perform real GBM modeling; introducing various contact models in the real GBM model to reproduce the process of mineral particle deformation and micro-crack evolution; correcting the mesoscopic mechanics parameters of the real GBM model through indoor experiments to reproduce the process of mineral particle deformation and micro-crack evolution; obtaining the influence law of the mineral layer structure on the rock mechanics characteristics and cracking behavior based on the real GBM model, obtaining the change conditions of the mineral scale crack propagation and the force chain network structure; and combining the high-precision nanometer CT and the discrete element modeling to restore the real layer structure and crystal form of the minerals, and improving the precision and reliability of rock rupture simulation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of rock mechanics, and particularly relates to a real granite GBM modeling method considering a layered structure of minerals. BACKGROUND

[0002] In recent years, with the progress of characterization technology, it is found that minerals have a significant influence on the macroscopic mechanical properties and deformation and fracture characteristics of crystalline rocks.

[0003] In the prior art, the discrete element method is used to construct a crystalline model GBM, which has become a mainstream means for exploring the fracture mechanism of crystalline rocks from the mineral scale, however, there is a fundamental limitation in the existing research: the focus is excessively concentrated on the influence of the macroscopic mechanical properties of minerals on the overall behavior of rocks, and the key meso-structural characteristics of the layered structure of mica is completely ignored.

[0004] In the modeling process, researchers usually simplify minerals as a homogeneous granular assembly, and this processing method causes the model to be unable to reflect the existence of the weak surface inside the mica, and further causes the mechanical response of the rock, the initiation and propagation path of the crack and the final failure mode in the numerical simulation to be significantly deviated from the observed actual situation, which greatly limits the authenticity and reliability of the prediction of the mineral-scale crack propagation and the change of the force chain network structure.

[0005] Therefore, the present application provides a real granite GBM modeling method considering a layered structure of minerals to solve the above problems. SUMMARY

[0006] The purpose of the present application is to provide a real granite GBM modeling method considering a layered structure of minerals, which can construct a GBM model capable of truly reflecting the layered structure of minerals, so as to accurately simulate the mesoscopic mechanical behavior of mica in rocks and its influence on the macroscopic fracture characteristics.

[0007] To achieve the above purpose, the present application provides a real granite GBM modeling method considering a layered structure of minerals, comprising the following steps:

[0008] S1: high-precision nanometer CT scanning of a granite sample to obtain mineral information;

[0009] S2: importing the mineral information into PFC2d discrete element software to perform real GBM modeling;

[0010] S3: introducing a plurality of contact models in the real GBM model to reproduce the process of deformation and micro-crack evolution of mineral particles;

[0011] S4: correcting the mesoscopic mechanical parameters of the real GBM model through a trial-and-error method by means of indoor experiments;

[0012] S5: Based on the real GBM model, multi-working condition rock fracture simulation is carried out, the influence law of mineral layered structure on rock macro-mechanical properties and cracking behavior is obtained, and the change of mineral scale crack propagation and force chain network structure is obtained.

[0013] Preferably, step S1 specifically comprises the following steps:

[0014] S11: Image information of the mineral layered structure is collected by high-precision nanometer CT to obtain a CT image;

[0015] S12: The spatial distribution information of different minerals is extracted according to the gray value of the CT image, a representative two-dimensional slice is selected for digital image processing, and the position and shape information of different minerals in the slice are extracted based on the threshold marked watershed segmentation method;

[0016] S13: The geometric contour of the mica mineral is extracted, the long axis direction of the geometric contour of the mica mineral is calculated based on the coordinates of each pixel point in the geometric contour, and the long axis direction is determined as the cleavage surface inclination of the mica mineral;

[0017] S14: The shape characteristics and distribution positions of feldspar, quartz and mica minerals are extracted.

[0018] Preferably, step S2 specifically comprises the following steps:

[0019] S21: The spatial distribution information of different minerals and the characteristic information of the mineral layered structure are simultaneously imported into the PFC2d discrete element software;

[0020] S22: A Voronoi polygon is generated in the mica area by the Neper software, and the particles inside the Voronoi polygon are filled by the PFC2d discrete element software;

[0021] S23: The filling result is compared with the mineral crystal form of the CT image, the missing particles are supplemented, and the redundant particles are deleted;

[0022] S24: The mineral crystal form is reproduced, and a real GBM model with mineral crystal form and spatial distribution is generated.

[0023] Preferably, in step S13, the joint structure form of the mica mineral is reproduced, specifically comprising the following steps:

[0024] Step 1: Define the connected mica particles as a single mica mineral crystal, calculate the arithmetic mean of the coordinates of all particles in the mineral crystal, and obtain the centroid of the mineral crystal;

[0025] Step 2: Calculate the distance between all particles and the centroid of the mineral crystal, define the maximum distance as the radius, and define the centroid as the center to obtain the circumscribed circle of the mineral crystal;

[0026] Step 3: Based on the distribution angle of the layered structure, parallel lines are generated within the circumscribed circle, and the interval of the parallel lines is set to 0.1 mm;

[0027] Step 4: Calculate the convex hull area of the mineral crystal, determine the distribution range of the parallel lines based on the convex hull area, and divide the mineral crystal into multiple mica sheets by the parallel lines;

[0028] Step 5: Delete the original randomly distributed particles inside the mineral crystal, refill the mica sheet with particles of different sizes, and obtain the joint morphology of the mica mineral;

[0029] Step 6: Repeat steps 1 to 5 until all joint morphologies of the mica mineral are reproduced.

[0030] Preferably, step S3 specifically includes the following steps:

[0031] S31: Introduce a parallel bond model PBM to calculate the normal moment and tangential moment to reproduce the fracture and anisotropy inside the mineral layer;

[0032] S32: Introduce a smooth joint model SJM to calculate the normal force and tangential force to simulate the behavior of relative sliding of different mineral crystals;

[0033] S33: Introduce a linear model of adhesion and rolling resistance ARRLM to calculate the van der Waals force and rolling resistance moment to bond the mica sheet layers.

[0034] Preferably, in step S31, the normal moment and tangential moment are specifically set as:

[0035] ;

[0036] ;

[0037] wherein represents the normal bond strength, represents the tangential bond strength, and represent different cross-sectional moments of inertia, represents the normal rotation increment, represents the tangential rotation increment.

[0038] Preferably, in step S32, the normal force and tangential force are specifically set as:

[0039] ;

[0040] ;

[0041] wherein, represents the contact area, represents the normal displacement, represents the tangential displacement.

[0042] Preferably, in step S33, the van der Waals force and the rolling resistance moment are specifically set as:

[0043] ;

[0044] ;

[0045] wherein, represents the bonding strength, represents the rolling friction coefficient, represents the particle radius.

[0046] Preferably, step S4 specifically comprises the following steps:

[0047] S41: Obtain the macro-mechanical parameters and deformation and failure modes of the mineral layer through uniaxial compression and Brazilian splitting experiments, to provide macro-standards for parameter correction;

[0048] S42: Obtain the meso-mechanical properties of different minerals through nanoindentation experiments, to provide quantitative basis for parameter correction, and the meso-mechanical properties include elastic modulus, hardness and fracture toughness;

[0049] S43: Correct the meso-mechanical parameters of the real GBM model until the macro-mechanical parameters and deformation and failure modes obtained by the real GBM model are consistent with the laboratory test results.

[0050] Therefore, the present application adopts the above-mentioned real granite GBM modeling method considering the layered structure of the mineral layer, and has the following beneficial effects:

[0051] (1) The present scheme obtains the real layered structure information of the mineral through high-precision nanometer CT, combines gray scale analysis and crystal long axis direction, extracts the spatial distribution and bedding angle of the mineral, and realizes high reduction of the layered structure and crystal form of the mineral;

[0052] (2) The present scheme introduces the parallel bonding model, the smooth joint model and the linear model of bonding and rolling resistance, respectively simulates the rupture in the mineral layer, the interlayer sliding and the interlayer bonding behavior, and effectively avoids the problem of mechanical response distortion caused by the fact that the traditional homogeneous model cannot reflect the layered structure.

[0053] (3) The present scheme corrects the mesoscopic mechanical parameters of the GBM model through experimental data, ensures that the model is consistent with the actual situation in terms of macroscopic mechanical response and failure mode, realizes cross-scale simulation verification from the mineral scale to the macroscopic behavior, and improves the authenticity and reliability of the model prediction.

[0054] The method scheme of the present application will be further described in detail below with the help of the accompanying drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1 A flowchart of the real granite GBM modeling method considering the layered structure of minerals of the present application;

[0056] Figure 2 A schematic diagram of extracting spatial distribution information of different minerals of the present application, wherein (a) is a CT image, (b) is a watershed schematic diagram, and (c) is a schematic diagram of spatial distribution information of different minerals;

[0057] Figure 3 A schematic diagram of obtaining characteristic information of the layered structure of minerals of the present application;

[0058] Figure 4 A schematic diagram of self-tracing particle filling of the present application, wherein (a) is a schematic diagram of a magnified mineral layer region, and (b) is a schematic diagram of mineral grouping after particle filling;

[0059] Figure 5 A schematic diagram of generating a real GBM model with layered mica mineral crystal morphology and spatial distribution of the present application, wherein (a) is a schematic diagram of a magnified mineral layer region, (b) is a schematic diagram of mineral grouping after particle filling, and (c) is a schematic diagram of a real GBM model with layered mica mineral crystal morphology and spatial distribution;

[0060] Figure 6 A comparison schematic diagram of stress-strain curves and failure modes of experiments and numerical simulations of the present application, wherein (a) is a comparison schematic diagram of stress-strain curves and overall failure modes, (b) is a comparison schematic diagram of local cracking modes in region I, and (c) is a comparison schematic diagram of local cracking modes in region II;

[0061] Figure 7 A schematic diagram of the evolution process of microcracks of the present application, wherein (a) is the spatial distribution of microcracks at the crack initiation stress , (b) is the spatial distribution of microcracks when the stress is 23.8 MPa, (c) is the spatial distribution of microcracks at the damage stress , (d) is the spatial distribution of microcracks at the peak stress , (e) is the spatial distribution of microcracks at 0.9 Spatial distribution of microcracks at different time, (f) 0.2 s after the peak Spatial distribution of microcracks at different time;

[0062] Figure 8 The proportion of each type of microcrack and the normalized crack coefficient at different loading stages of the present application K i The proportion of each type of microcrack and the normalized crack coefficient at different loading stages of the present application K i The proportion of each type of microcrack and the normalized crack coefficient at different loading stages of the present application K i The proportion of each type of microcrack and the normalized crack coefficient at different loading stages of the present application K i The proportion of each type of microcrack and the normalized crack coefficient at different loading stages of the present application

[0063] Figure 9 The influence of the layered structure of mica on the propagation of microcracks, wherein (a) the observed crack propagation along the cleavage plane of mica and crack deflection phenomenon in the experiment, (b) the observed crack propagation along the cleavage plane of mica and crack deflection phenomenon in the simulation, (c) the process of microcrack initiation and propagation along the cleavage plane of mica mineral in GBM, (d) the process of microcrack deflection in GBM;

[0064] Figure 10 The influence of the layered structure of mica on the propagation of microcracks, wherein (a) the observed crack propagation termination in mica mineral or the formation of transcrystalline cracks in the experiment, (b) the observed crack propagation termination in mica mineral or the formation of transcrystalline cracks in the simulation, (c) the process of microcrack propagation termination in mica mineral and the evolution of transcrystalline cracks in GBM;

[0065] Figure 11 The influence of the layered structure of mica on the propagation of microcracks, wherein (a) the observed crack propagation termination in mica mineral or the formation of transcrystalline cracks in the experiment, (b) the observed crack propagation termination in mica mineral or the formation of transcrystalline cracks in the simulation, (c) the process of microcrack propagation termination in mica mineral and the evolution of transcrystalline cracks in GBM; DETAILED DESCRIPTION

[0066] The method scheme of the present application is further described below by means of the accompanying drawings and examples.

[0067] Unless otherwise defined, the method terms or scientific terms used in the present application shall have the usual meaning understood by a person with ordinary skill in the art to which the present application belongs.

[0068] The terms such as "comprising" or "including" or similar words in the present invention mean that the elements before the word encompass the elements listed after the word, and do not exclude the possibility of also encompassing other elements. The orientations or positional relationships indicated by the terms "in", "on", "upper", "lower", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present invention. When the absolute position of the described object changes, the relative positional relationship may also change accordingly. In the present invention, unless otherwise explicitly specified and limited, the term "attached" and other terms should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present invention can be understood according to the specific circumstances.

[0069] Embodiment

[0070] As Figures 1 to 5 shown, the present invention provides a real granite GBM modeling method considering the layered structure of minerals, comprising the following steps:

[0071] S1: Obtain mineral information by high-precision nanometer CT scanning of granite samples;

[0072] Step S1 specifically comprises the following steps:

[0073] S11: Obtain CT image by high-precision nanometer CT acquisition of image information of the layered structure of minerals;

[0074] S12: The density of minerals is different, and different gray areas are shown on the CT image. The spatial distribution information of different minerals is extracted according to the gray value of the CT image, and a representative two-dimensional slice is selected for digital image processing. The position and shape information of different minerals in the slice are extracted based on the threshold marked watershed segmentation method;

[0075] S13: The layered structure of mica minerals will cause the single mineral crystal to be flat. In digital image processing, the geometric contour of the mica mineral is extracted, the long axis direction of the geometric contour of the mica mineral is calculated based on the coordinates of each pixel point in the geometric contour, the long axis direction is determined as the cleavage surface inclination of the mica mineral, and the joint structure morphology of the mica mineral is reproduced;

[0076] In step S13, the joint structure morphology of the mica mineral is reproduced, specifically comprising the following steps:

[0077] Step 1: the connected mica particles are defined as a single mica mineral crystal, the density of the mica particles is consistent, and the distribution is uniform, so the arithmetic mean of the coordinates of all particles in the mineral crystal is calculated to obtain the centroid of the mineral crystal;

[0078] Step 2: the distance between all particles of the mineral crystal and the centroid is calculated, the maximum distance is defined as the radius, and the centroid is defined as the center of the circle to obtain the circumscribed circle of the mineral crystal;

[0079] Step 3: based on the distribution angle of the layered structure, parallel lines are generated within the circumscribed circle, the parallel lines are modeled by walls in the PFC2d discrete element software, and the spacing of the parallel lines is set to 0.1mm;

[0080] Step 4: the convex hull area of the mineral crystal is calculated, the distribution range of the parallel lines is determined based on the convex hull area, and the mineral crystal is divided into multiple mica sheets by the parallel lines, in this embodiment, the mica mineral crystal is divided by seven parallel lines, indicating that the mineral crystal is composed of eight mica sheets;

[0081] Step 5: delete the original randomly distributed particles inside the mineral crystal, refill the mica sheets with particles of different sizes to obtain the joint morphology of the mica mineral;

[0082] Step 6: repeat steps 1 to 5 until the joint morphology of all mica minerals is reproduced.

[0083] S14: extract the morphological characteristics and distribution positions of feldspar, quartz and mica minerals.

[0084] S2: import the mineral information into the PFC2d discrete element software to perform real GBM modeling;

[0085] Step S2 specifically includes the following steps:

[0086] S21: import the spatial distribution information of different minerals and the characteristic information of the layered structure of the minerals into the PFC2d discrete element software at the same time;

[0087] S22: generate a Voronoi polygon in the mica area by Neper software, and fill particles in the Voronoi polygon by PFC2d discrete element software;

[0088] S23: the filled particles cannot reproduce the real mineral crystal morphology at this time, compare the filling result with the mineral crystal morphology of the CT image, supplement the missing particles and delete the redundant particles, and finally perfectly reproduce the crystal morphology of the mineral;

[0089] S24: reproduce the mineral crystal morphology to generate a real GBM model with mineral crystal morphology and spatial distribution.

[0090] S3: Introducing various contact models in the real GBM model to reproduce the process of mineral particle deformation and micro-crack evolution;

[0091] Step S3 specifically comprises the following steps:

[0092] S31: Introducing the parallel bond model PBM, applying the parallel bond model PBM to the interior of the mineral crystal, calculating the normal force moment and the tangential force moment to reproduce the rupture and anisotropy inside the mineral layer;

[0093] In step S31, the normal force moment and the tangential force moment are specifically set as:

[0094] ;

[0095] ;

[0096] wherein, denotes the normal bond strength, denotes the tangential bond strength, and denote different cross-sectional moments of inertia, denotes the normal rotation increment, denotes the tangential rotation increment.

[0097] S32: Introducing the smooth joint model SJM, applying the smooth joint model SJM between different mineral crystals, calculating the normal force and the tangential force to simulate the behavior of relative sliding of different mineral crystals, thereby avoiding unrealistic cracking behavior;

[0098] In step S32, the normal force and the tangential force are specifically set as:

[0099] ;

[0100] ;

[0101] wherein, denotes the contact area, denotes the normal displacement, denotes the tangential displacement.

[0102] S33: Introducing the linear model of adhesion and rolling resistance ARRLM, calculating the van der Waals force and the rolling resistance moment to bond between mica sheet layers.

[0103] In step S33, the van der Waals force and the rolling resistance moment Specifically set to:

[0104] ;

[0105] ;

[0106] wherein, represents the bonding strength, represents the rolling friction coefficient, represents the particle radius.

[0107] S4: Through indoor experiments, the mesoscopic mechanical parameters of the real GBM model are corrected by trial and error;

[0108] Step S4 specifically includes the following steps:

[0109] S41: Obtain the macroscopic mechanical parameters and deformation and failure modes of the mineral layer through uniaxial compression and Brazilian splitting experiments, to provide macroscopic standards for parameter correction;

[0110] S42: Obtain the mesoscopic mechanical properties of different minerals through nanoindentation experiments, to provide quantitative basis for parameter correction, and the mesoscopic mechanical properties include elastic modulus, hardness and fracture toughness;

[0111] S43: The mesoscopic mechanical parameters of the real GBM model are corrected until the macroscopic mechanical parameters and deformation and failure modes obtained by the real GBM model are consistent with the results of indoor experiments, and then the parameter correction is completed.

[0112] S5: Based on the real GBM model, simulate rock rupture under multiple working conditions, specifically including uniaxial compression, Brazilian splitting and triaxial compression, to obtain the influence law of mineral layered structure on rock macroscopic mechanical properties and cracking behavior, and to obtain the change of mineral scale crack propagation and force chain network structure.

[0113] Finally, the effectiveness of the embodiment is verified, and the verification process specifically includes the following steps:

[0114] (1) Comparison and verification of simulation and experimental results

[0115] For example Figure 6As shown, the peak strength, peak strain and elastic modulus obtained from the indoor experiment are 51.62 MPa, 0.1063% and 54.86 GPa, respectively, while the results obtained from the numerical simulation are 52.93 MPa, 0.1059% and 52.65 GPa, respectively, and the errors are all less than 5%. In terms of the overall failure mode of the sample, a macroscopic crack appears, leading to splitting tensile failure of the sample, and the crack is mainly intracrystalline crack, and the aggregation phenomenon appears at the bottom of the sample. These characteristics of the experiment are highly consistent with the numerical simulation results. Further analysis shows that, as can be seen from the figure, the model obtained by the modeling method proposed in the embodiment can accurately reproduce the actual crack propagation behavior, especially for the transcrystalline and intercrystalline cracks in the mica mineral. The modeling method proposed in the embodiment can effectively capture the above results. The above results show that the GBM modeling method considering the layered structure of the mica mineral and the meso-parameter calibration method can better reproduce the macro-mechanical response and failure mode of the hard and brittle granite.

[0116] (2) Progressive expansion of micro-cracks

[0117] In the numerical model, the initiation and expansion process of different types of micro-cracks can be described by the fracture of contact bonds. The types, number and spatial distribution of micro-cracks generated in the GBM sample during uniaxial compression are statistically analyzed in detail.

[0118] As shown in Figure 7 , the morphological structure and spatial distribution of minerals in granite have a significant control effect on the evolution of micro-cracks. Specifically, when the stress reaches the cracking stress , micro-cracks first initiate between the mica layers, mainly at the two ends of the sample. With the increase of load to 23.8 MPa, intercrystalline tensile cracks begin to appear at the boundary between quartz and mica minerals, and intracrystalline tensile cracks also appear in the quartz mineral adjacent to the mica mineral. This is because the elastic modulus of quartz mineral is higher, and the elastic modulus of mica mineral is lower, and the stiffness difference between them is large, which is easy to cause stress concentration at the boundary between quartz and mica minerals, thereby inducing the initiation and expansion of micro-cracks. When the stress reaches the damage stress , intercrystalline shear cracks first appear at the boundary of quartz mineral. After the damage stress, micro-cracks enter the non-stable expansion stage, and gradually diverge from the layered mica mineral to the interior of other minerals. At the peak stress , micro-cracks have gathered in the local area. In the post-peak stage, some intercrystalline cracks appear in the layered mica mineral, and the micro-cracks further connect and penetrate, eventually forming a macroscopic crack. The expansion of micro-cracks in the post-peak stage is extremely rapid, leading to rapid stress release, which is manifested as a sharp decline after the peak in the stress-strain curve.

[0119] As shown in Figure 8 , at the damage stress Before, the mica interlayer crack ratio was 100% and 53.6% respectively, which occupied the dominant position, which showed that the mica cleavage as a pre-existing weak plane in granite had a significant control effect on the initiation of micro-cracks, and after the loading point B, the sum of intracrystalline and intercrystalline tensile crack ratio increased from the initial 46.4% to 88.6%, with an increase of 90.9%, which showed that the two types of tensile cracks were the main reason for the failure of the model.

[0120] From the quantitative statistics, the number of intracrystalline micro-cracks was much higher than that of intercrystalline micro-cracks. Further analysis of the mineral correlation of the cracks showed that the intracrystalline cracks were mainly derived from quartz and feldspar minerals, and the intercrystalline cracks were mainly produced in strong grain boundaries, while the number of micro-cracks in weak grain boundaries was relatively small.

[0121] However, the number of micro-cracks was closely related to the content of minerals in the model. By introducing the normalized crack coefficient K i The influence of mineral content can be eliminated, and the damage degree of different minerals and grain boundaries can be quantitatively characterized, K i The greater the value, the more serious the damage, K i The calculation formula is as follows:

[0122] Wherein, i represents the type of micro-crack (intracrystalline crack: mica intracrystalline, feldspar intracrystalline, quartz intracrystalline; intercrystalline crack: mica-mica intercrystalline, quartz-mica intercrystalline, feldspar-mica intercrystalline, quartz-feldspar intercrystalline, quartz-quartz intercrystalline, feldspar-feldspar intercrystalline), is the number of i type micro-crack, is the total number of contact bonds of i type micro-crack.

[0123] The calculation results show that the damage degree of mineral grain boundary ( K i =7.145%) after the failure of the sample is significantly higher than that in the mineral crystal ( K i =4.045%), because the mineral grain boundary as a weak area in the rock, its strength is lower than that of the mineral crystal itself, and the grain boundary of different minerals is easy to produce local stress concentration, leading to the damage and destruction of the grain boundary. In the mineral crystal, the K i value of the mica mineral is always higher than that of the quartz and feldspar minerals, and after the failure of the sample, the K i value of the mica mineral is 15.243%, followed by the feldspar and quartz minerals, and the K i value of the quartz mineral is the smallest, which is 2.858%.K i The values ​​were 4.665% and 2.837%, respectively, indicating that weakly chained minerals like mica are more prone to damage and destruction during uniaxial compression. Furthermore, the weak grain boundaries... K i The value was consistently higher than that of strong grain boundaries, indicating that the damage to weak grain boundaries was more severe than that to strong grain boundaries. After sample failure, the damage to weak grain boundaries... K i The value is 11.60%, indicating strong grain boundaries. K i The value was 6.39%, but the difference between the two was less than the difference in damage within the mineral crystals.

[0124] (3) Classification of crack propagation modes

[0125] like Figures 9 to 11 As shown, based on the crack propagation behavior observed in mica minerals and at their boundaries through experiments and numerical simulations, the influence of mica minerals on crack initiation and propagation modes can be summarized into the following three types.

[0126] Type 1: Cracks initiate and propagate along the interlayer of mica, accompanied by path deflection. Both experimental and numerical simulation results observe crack propagation along the interlayer of mica, with path deflection due to its layered structure. At lower axial stress levels, microcracks first initiate in the interlayer of mica. As the stress increases to 42.3 MPa, microcracks, primarily tensile cracks, begin to appear in the quartz minerals adjacent to the mica. Upon reaching peak stress, the interlayer microcracks further propagate and locally aggregate. With continued loading, after the peak stress (0.8 MPa), further cracks appear. At that time, interlayer microcracks penetrated the entire mica mineral and gradually extended to the surrounding minerals.

[0127] Furthermore, the layered structure of mica has a significant impact on crack propagation paths. Microcracks first initiate in the interlayers of mica and in adjacent minerals. As the load increases further to the peak stress, microcracks locally aggregate but do not yet form penetrating cracks. In the post-peak stage, simulation results show two different types of crack deflection: the microcrack propagation path deflects along the interlayers of mica and the microcrack propagation path deflects within the mica layer. Corresponding crack deflection modes were also observed in experiments. The first crack deflection mode is easier to understand, mainly due to the weak surface guiding effect provided by the layered structure of mica. The second mode is characterized by the crack not extending completely along the cleavage plane of mica, but penetrating the mica layer, forming an intralayer crack and changing the original propagation path, eventually leading to crack deflection. This is because when the mica deforms along the cleavage plane to a certain extent, it is difficult to deform further due to the restriction of surrounding minerals. At this time, the energy at the crack tip continues to accumulate, and after reaching a critical value, it penetrates the mica layer and continues to propagate.

[0128] Type 2: Crack propagation terminates at mica minerals or forms transgranular cracks, in Type 2, microcracks stop expanding at or across mica minerals, and the numerical model successfully reproduces this kind of microcrack propagation behavior, at a stress of 42.3 MPa, microcracks do not initiate from the mica interlayer, but first appear in the adjacent quartz mineral, with further increase in load (44.9 MPa to 52.9 MPa), only a small amount of microcracks are generated in the mica interlayer, indicating that cracks are difficult to initiate and expand in this kind of mica crystal, until the post-peak 0.85 stage, microcracks struggle to form transgranular cracks by vertically crossing the mica cleavage plane, and part of the microcracks terminate at the mica mineral boundary.

[0129] Type 3: Effect of mica minerals without layer structure on crack propagation, when the mica cleavage plane is parallel to the observation plane, the layer structure is not visible in the plane, at this time, microcracks mainly exhibit two expansion modes, transgranular and intergranular, at the peak stress, almost no microcracks are generated in the mica crystal; until the post-peak stress decreases to 0.98 , obvious microcracks begin to appear in the crystal, which indicates that the lack of interlayer weak plane significantly inhibits the early initiation and expansion of microcracks in the mica, however, microcracks expand rapidly in the post-peak stage, at 0.90 , intergranular and transgranular cracks have been formed, which indicates that after simplifying the mica mineral into a mean grain without layer structure, the damage evolution presents a rapid expansion feature triggered by a threshold: the crack path is mainly controlled by the overall strength and stiffness of the grain, rather than progressive failure along the preset weak plane.

[0130] Type 1 and Type 2 show two different effects of mica layer structure on crack propagation: Type 1 layer mica mineral generally promotes crack propagation, while Type 2 mainly inhibits the expansion of microcracks in it, and Type 3 reflects that without layer structure, the crack behavior of mica mineral is closer to that of homogeneous brittle material, these differences are mainly related to the relative relationship between the mica cleavage angle and the crack propagation direction.

[0131] Therefore, the present application adopts the above-mentioned one kind of true granite GBM modeling method considering the layer structure of mineral, realizes the real reduction of the internal layer structure and weak plane of mica, significantly improves the prediction accuracy of crack propagation, force chain evolution and macroscopic mechanical response in rock failure simulation, and overcomes the simulation deviation problem caused by ignoring the structure characteristics of mica in the traditional method.

[0132] It should be pointed out finally that the above examples are only used to illustrate the method scheme of the present application but not to limit it, and although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those of ordinary skill in the art that the method scheme of the present application can still be modified or equivalently replaced, and these modifications or equivalent replacements cannot make the modified method scheme deviate from the spirit and scope of the method scheme of the present application.

Claims

1. A real granite GBM modeling method considering mineral layer structure, characterized in that, The method comprises the following steps: S1: Obtain mineral information by scanning the granite sample through high-precision nanometer CT; Step S1 specifically comprises the following steps: S11: Obtain CT images by collecting image information of the layered structure of the mineral through high-precision nanometer CT; S12: Extract the spatial distribution information of different minerals according to the gray value of the CT images, select a representative two-dimensional slice for digital image processing, and extract the position and shape information of different minerals in the slice based on the threshold marked watershed segmentation method; S13: Extract the geometric contour of the mica mineral, calculate the long axis direction of the geometric contour of the mica mineral based on the coordinates of each pixel point in the geometric contour, and determine the long axis direction as the cleavage surface inclination of the mica mineral; In step S13, the joint structure morphology of the mica mineral is reproduced, specifically comprising the following steps: Step 1: Define the connected mica particles as a single mica mineral crystal, calculate the arithmetic mean of the coordinates of all particles in the mineral crystal, and obtain the centroid of the mineral crystal; Step 2: Calculate the distance between all particles and the centroid of the mineral crystal, define the maximum distance as the radius, and define the centroid as the center of the circle to obtain the circumscribed circle of the mineral crystal; Step 3: Generate parallel lines in the circumscribed circle based on the distribution angle of the layered structure, and set the interval of the parallel lines to 0.1mm; Step 4: Calculate the convex hull area of the mineral crystal, determine the distribution range of the parallel lines based on the convex hull area, and divide the mineral crystal into multiple mica sheets by the parallel lines; Step 5: Delete the original randomly distributed particles inside the mineral crystal, refill the mica sheets with particles of different sizes, and obtain the joint morphology of the mica mineral; Step 6: Repeat steps 1 to 5 until the joint morphology of all mica minerals is reproduced; S14: Extract the shape characteristics and distribution positions of feldspar, quartz and mica minerals; S2: Import the mineral information into the PFC2d discrete element software to perform real GBM modeling; S3: Introduce various contact models in the real GBM model to reproduce the process of mineral particle deformation and micro-crack evolution; S4: Correct the mesoscopic mechanical parameters of the real GBM model through trial and error based on laboratory experiments; S5: Perform multi-condition rock rupture simulation based on the real GBM model to obtain the influence law of the layered structure of the mineral on the macroscopic mechanical properties and cracking behavior of the rock, and obtain the changes of the mineral scale crack propagation and force chain network structure.

2. The real granite GBM modeling method considering mineral layer structure according to claim 1, characterized in that, Step S2 specifically comprises the following steps: S21: Import the spatial distribution information of different minerals and the characteristic information of the layered structure of the mineral into the PFC2d discrete element software; S22: Generate a Voronoi polygon in the mica area through the Neper software, and fill the particles inside the Voronoi polygon through the PFC2d discrete element software; S23: Compare the filling result with the mineral crystal morphology of the CT image, supplement the missing particles, and delete the redundant particles; S24: Reproduce the mineral crystal morphology to generate a real GBM model with the mineral crystal morphology and spatial distribution.

3. The real granite GBM modeling method considering mineral layer structure according to claim 2, characterized in that, Step S3 specifically comprises the following steps: S31: Introduce parallel bond model PBM, calculate normal moment and tangential moment reproducing the fracture and anisotropy within the mineral layer; S32: Introduce smooth-joint model SJM, calculate normal force and tangential force , simulate the behavior of different mineral crystal phases relative sliding; S33: Introduce the adhesion rolling resistance linear model ARRLM, calculate the van der Waals force and the rolling resistance moment , to bond the mica plate interlayers.

4. The real granite GBM modeling method considering mineral layer structure according to claim 1, characterized in that, Step S4 specifically comprises the following steps: S41: Obtain the macro-mechanical parameters and deformation and failure modes of the mineral layer through uniaxial compression and Brazilian splitting test, and provide macro-standards for parameter correction; S42: Obtain the micro-mechanical properties of different minerals through nanoindentation test, and provide quantitative basis for parameter correction. The micro-mechanical properties include elastic modulus, hardness and fracture toughness; S43: Correct the micro-mechanical parameters of the real GBM model until the macro-mechanical parameters and deformation and failure modes obtained by the real GBM model are consistent with the laboratory test results.

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