CN113984532A - A method and system for determining potential damage zones of surrounding rock of deep-buried fractures - Google Patents
A method and system for determining potential damage zones of surrounding rock of deep-buried fractures Download PDFInfo
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Abstract
本发明涉及一种深埋裂隙围岩的潜在破坏分区确定方法及系统，包括：对工程岩体的围岩裂隙进行采样，确定各围岩裂隙的围岩裂隙信息；根据各所述围岩裂隙信息确定多个目标半径值；所述目标半径值为同组的所有围岩裂隙中的最大半径值；对所述工程岩体进行围岩断裂韧度测试，确定围岩断裂韧度；对所述工程岩体进行岩体应力场测试，确定所述工程岩体的平均应力场；根据所述最大半径值和所述平均应力场利用断裂力学公式确定最大应力强度因子；根据所述最大应力强度因子和所述围岩断裂韧度确定围岩潜在破坏分区。本发明能够提高破坏分区的精度。
The invention relates to a method and system for determining potential damage zones of surrounding rock with deep buried fissures. The information determines a plurality of target radius values; the target radius value is the largest radius value among all the surrounding rock fissures in the same group; the surrounding rock fracture toughness test is performed on the engineering rock mass to determine the surrounding rock fracture toughness; The rock mass stress field test is carried out on the engineering rock mass to determine the average stress field of the engineering rock mass; the maximum stress intensity factor is determined by the fracture mechanics formula according to the maximum radius value and the average stress field; according to the maximum stress intensity The factor and the fracture toughness of the surrounding rock determine potential failure zones of the surrounding rock. The present invention can improve the precision of the destruction zone.
Description
Technical Field
The invention relates to the technical field of engineering surrounding rocks, in particular to a method and a system for determining potential damage subareas of deeply buried fractured surrounding rocks.
Background
In the underground engineering construction, due to the difference of the shape, the Excavation speed and the Excavation means of the Excavation engineering, some Excavation damaged areas (EDZ) are formed around the Excavation section. Under the condition of excavation unloading of deep brittle surrounding rocks, the stress redistribution causes the expansion and penetration of the pre-existing cracks of the rock mass until the formation of regular fracture damage. The stress condition and the rock mass structure are the most main factors for controlling the fracture damage. On one hand, high ground stress is a main characteristic of deep underground engineering, and on the other hand, excavation is accompanied with the adjustment of the structural state of a rock body, and a series of processes such as closure, opening, expansion, connection and the like of microscopic cracks are caused by large-scale excavation, and finally macroscopic brittle failure is formed. At present, the main determination methods of the EDZ comprise acoustic wave testing, stress displacement measurement, borehole shooting and the like, the methods basically need extra workload to be matched with testing work, and the testing range is limited. The existing EDZ partition determination method mainly considers the influence of one of two factors, the analysis method based on the stress condition does not consider the influence of the existing cracks in the rock mass, and the traditional rock mass crack statistical measurement ignores the reconstruction of the existing cracks of the surrounding rock under the high-stress excavation condition. Therefore, a method for determining the potential damage subareas of the deeply buried fractured surrounding rock based on the stress condition and the rock mass structure is needed to be provided.
Disclosure of Invention
The invention aims to provide a method and a system for determining a potential damage subarea of a deeply buried fractured surrounding rock so as to improve the precision of the damage subarea.
In order to achieve the purpose, the invention provides the following scheme:
a potential damage subarea determination method for deeply buried fractured surrounding rock comprises the following steps:
sampling surrounding rock fractures of the engineering rock mass, and determining surrounding rock fracture information of each surrounding rock fracture;
determining a plurality of target radius values according to the surrounding rock fracture information; the target radius value is the maximum radius value in all the surrounding rock fractures in the same group;
performing a surrounding rock fracture toughness test on the engineering rock mass to determine the surrounding rock fracture toughness;
performing rock mass stress field test on the engineering rock mass, and determining the average stress field of the engineering rock mass;
determining a maximum stress intensity factor by utilizing a fracture mechanics formula according to the maximum radius value and the average stress field;
and determining a potential damage subarea of the surrounding rock according to the maximum stress intensity factor and the fracture toughness of the surrounding rock.
Optionally, a plurality of target radius values are determined according to the information of the surrounding rock fractures; the target radius value is the maximum radius value in all surrounding rock fractures of the same group, and specifically comprises the following steps:
projecting the rock mass fracture information on a Schmidt equal-area declination projection network according to a normal line, and grouping the rock mass fractures according to the density value line of the Schmidt equal-area declination projection network;
performing track length conversion on the same group of the traces of the rock mass fractures to determine the radius of the rock mass fractures;
and sequencing and regression analysis are carried out on the radius of the rock mass fractures in the same group, and the maximum radius value of each group of surrounding rock fractures is determined.
Optionally, it is right the engineering rock mass carries out the test of surrounding rock fracture toughness, confirms surrounding rock fracture toughness, specifically includes:
carrying out central straight crack semicircular disc fracture toughness test on a test sample of the engineering rock body by using a rock mechanics testing machine, and determining I-type fracture toughness in the surrounding rock fracture toughness;
and carrying out a triaxial compression shear test on the test sample of the engineering rock body by using a rock mechanics testing machine to determine the II-type fracture toughness in the surrounding rock fracture toughness.
Optionally, the rock mass stress field test comprises a hydraulic fracturing method and a stress relieving method.
Optionally, the rock mass stress field test is performed on the engineering rock mass to determine the average stress field of the engineering rock mass, and the method specifically includes:
performing rock mass stress field test on the engineering rock mass, and determining the normal stress and the shear stress of a crack surface;
and determining an average stress field according to the normal stress and the shear stress.
Optionally, determining a surrounding rock potential failure zone according to the maximum stress intensity factor and the surrounding rock fracture toughness specifically includes:
judging whether the maximum stress intensity factor meets a first judgment condition or whether the maximum stress intensity factor meets a second judgment condition to obtain a first judgment result; the first judgment condition is that the type I stress intensity factor or the type III stress intensity factor in the maximum stress intensity factor is greater than the type I fracture toughness; the second judgment condition is that the II-type stress intensity factor in the maximum stress intensity factor is greater than the II-type fracture toughness;
and if the first judgment result shows that the maximum stress intensity factor meets the first judgment condition or the maximum stress intensity factor meets the second judgment condition, determining that the fracture is damaged, wherein the surrounding rock fracture is a surrounding rock potential damage subarea.
A potential damage zone determination system for deeply buried fractured surrounding rock, comprising:
the sampling module is used for sampling the surrounding rock fractures of the engineering rock body and determining surrounding rock fracture information of each surrounding rock fracture;
the maximum radius value determining module is used for determining a plurality of target radius values according to the surrounding rock fracture information; the target radius value is the maximum radius value in all the surrounding rock fractures in the same group;
the surrounding rock fracture toughness testing module is used for carrying out surrounding rock fracture toughness testing on the engineering rock mass and determining the surrounding rock fracture toughness;
the rock mass stress field testing module is used for performing rock mass stress field testing on the engineering rock mass and determining the average stress field of the engineering rock mass;
the maximum stress intensity factor determining module is used for determining a maximum stress intensity factor by utilizing a fracture mechanics formula according to the maximum radius value and the average stress field;
and the surrounding rock potential damage subarea determining module is used for determining a surrounding rock potential damage subarea according to the maximum stress intensity factor and the surrounding rock fracture toughness.
Optionally, the maximum radius value determining module specifically includes:
the projection and grouping unit is used for projecting the rock mass fracture information on a Schmidt equal-area declination projection network according to a normal line and grouping the rock mass fractures according to the density value line of the Schmidt equal-area declination projection network;
the trace length conversion unit is used for performing trace length conversion on the same group of traces of the rock mass cracks and determining the radius of the rock mass cracks;
and the sequencing and regression analysis unit is used for sequencing and regression analysis on the rock mass fracture radii of the same group and determining the maximum radius value of each group of surrounding rock fractures.
Optionally, the surrounding rock fracture toughness test module specifically includes:
the I-type fracture toughness determination unit is used for carrying out central straight crack semicircular disc fracture toughness test on a test sample of the engineering rock body by utilizing a rock mechanics testing machine to determine I-type fracture toughness in the surrounding rock fracture toughness;
and the II-type fracture toughness determination unit is used for performing a triaxial stamping shear test on the test sample of the engineering rock body by utilizing a rock mechanics testing machine to determine the II-type fracture toughness in the surrounding rock fracture toughness.
Optionally, the rock mass stress field test comprises a hydraulic fracturing method and a stress relieving method.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention provides a method and a system for determining a potential damage subarea of a deeply buried fissure surrounding rock, which are used for determining a maximum radius value of a fissure according to rock mass fissure information; performing a surrounding rock fracture toughness test on the engineering rock mass to determine the surrounding rock fracture toughness; performing rock mass stress field test on the engineering rock mass to determine the average stress field of the engineering rock mass; determining a maximum stress intensity factor by utilizing a fracture mechanics formula according to the maximum radius value and the average stress field; and determining the potential damage subarea of the surrounding rock according to the maximum stress intensity factor and the fracture toughness of the surrounding rock. By considering the fracture toughness of the surrounding rock and the stress information of the engineering rock mass when determining the potential damage subarea of the surrounding rock, the structural information of the rock mass is considered, so that the precision of the damage subarea is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a flow chart of a method for determining potential damage zones of deeply buried fractured surrounding rock according to the present invention;
FIG. 2 is a schematic view of a wire layout of a precision wire measurement method provided by the present invention;
FIG. 3 is a normal equal-area stereographic projection of the structure provided by the present invention;
FIG. 4 is a schematic diagram of statistical results of the underground engineering surrounding rock fractures provided by the present invention;
FIG. 5 is a schematic diagram of a specimen model required by the rock fracture toughness test provided by the invention;
fig. 6 is a schematic diagram of type iiii stress intensity factors of specific six points in the surrounding rock provided by the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide a method and a system for determining a potential damage subarea of a deeply buried fractured surrounding rock so as to improve the precision of the damage subarea.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
The failure of the high stress rock mass EDZ is initiated mostly by fracture failure, and after the cracks in the rock mass expand, the adjacent small cracks are communicated into a through large crack to cut each other, thereby destroying the integrity and strength properties of the rock mass. Rock fractures typically begin with an existing fracture. The existing fractures mainly refer to structural fractures formed in geological history period or unloading fractures caused by excavation. These fractures can all be grouped by their cause.
The same set of fractures often have the same or similar occurrence. According to the theory of fracture mechanics, for a certain group of fractures, the maximum stress intensity factor of the fractures in the rock mass is calculated, and the positive stress sigma on the fracture surface needs to be calculated firstlynAnd shear stress τ. According to the fracture mechanics theory, the stress intensity factor of a fracture is proportional to the fracture radius to the power of 0.5, and the longer the fracture radius α, the larger the stress intensity factor. Therefore, the maximum fracture radius alpha of each group of fractures of the rock mass can be determined through fracture statisticsm. On the basis of the stress state sigma obtained by numerical calculationijThe longest radius alpha of each group of cracksmAnd substituting the maximum stress intensity factor into a fracture mechanics formula for calculation to obtain the maximum stress intensity factor in the surrounding rock. The maximum stress intensity factor varies depending on the type of fracture and the grouping of fractures. And finally, determining the fracture toughness of the surrounding rock through a fracture mechanics test of the surrounding rock sample, thereby determining the position of the surrounding rock where fracture damage is most likely to occur. The method can guide an engineer to obtain a key reinforced area through random crack statistical analysis before excavation, and the fracture instability of the surrounding rock is prevented.
As shown in fig. 1, the method for determining the potential damage subarea of the deeply buried fractured surrounding rock provided by the invention comprises the following steps:
step 101: and sampling the surrounding rock fractures of the engineering rock mass, and determining surrounding rock fracture information of each surrounding rock fracture.
Step 102: determining a plurality of target radius values according to the surrounding rock fracture information; the target radius value is the maximum radius value in all the surrounding rock fractures of the same group. Determining a plurality of target radius values according to the fracture information of the surrounding rock; the target radius value is the maximum radius value in all surrounding rock fractures of the same group, and specifically comprises the following steps:
and projecting the rock mass fracture information on a Schmidt equal-area declination projection network according to a normal line, and grouping the rock mass fractures according to the density value line of the Schmidt equal-area declination projection network.
And performing track length conversion on the same group of the traces of the rock mass fractures to determine the radius of the rock mass fractures.
And sequencing and regression analysis are carried out on the radius of the rock mass fractures in the same group, and the maximum radius value of each group of surrounding rock fractures is determined.
Step 103: and carrying out a surrounding rock fracture toughness test on the engineering rock mass to determine the surrounding rock fracture toughness. Wherein, it is right the engineering rock mass carries out the test of surrounding rock fracture toughness, confirms surrounding rock fracture toughness, specifically includes:
and carrying out central straight crack semicircular disc fracture toughness test on the test sample of the engineering rock mass by using a rock mechanics testing machine, and determining I-type fracture toughness in the surrounding rock fracture toughness.
And carrying out a triaxial compression shear test on the test sample of the engineering rock body by using a rock mechanics testing machine to determine the II-type fracture toughness in the surrounding rock fracture toughness.
Step 104: and carrying out rock mass stress field test on the engineering rock mass, and determining the average stress field of the engineering rock mass. Wherein, the rock mass stress field test comprises a hydraulic fracturing method and a stress relieving method.
In practical application, the rock mass stress field test is carried out on the engineering rock mass, and the average stress field of the engineering rock mass is determined, and the method specifically comprises the following steps:
and carrying out rock mass stress field test on the engineering rock mass, and determining the normal stress and the shear stress of the crack surface.
And determining an average stress field according to the normal stress and the shear stress.
Step 105: and determining a maximum stress intensity factor by utilizing a fracture mechanics formula according to the maximum radius value and the average stress field.
Step 106: and determining a potential damage subarea of the surrounding rock according to the maximum stress intensity factor and the fracture toughness of the surrounding rock. Determining a surrounding rock potential damage subarea according to the maximum stress intensity factor and the surrounding rock fracture toughness, wherein the method specifically comprises the following steps:
judging whether the maximum stress intensity factor meets a first judgment condition or whether the maximum stress intensity factor meets a second judgment condition to obtain a first judgment result; the first judgment condition is that the type I stress intensity factor or the type III stress intensity factor in the maximum stress intensity factor is greater than the type I fracture toughness; and the second judgment condition is that the II-type stress intensity factor in the maximum stress intensity factor is greater than the II-type fracture toughness.
And if the first judgment result shows that the maximum stress intensity factor meets a first judgment condition or the maximum stress intensity factor meets a second judgment condition, determining that the fracture is damaged, wherein the surrounding rock fracture is a surrounding rock potential damage subarea.
The invention also provides a method for determining the potential damage subareas of the deeply buried fractured surrounding rock, which is a more specific method in practical application.
The method comprises the following steps: surrounding rock fracture sampling statistics
1.1 rock mass immediate fracture accurate survey line sampling
Firstly, according to a rock mass structure plane spacing method suggested in appendix B of engineering rock mass grading standard GBT50218-2014, performing field random sampling statistics on a target tunnel surrounding rock fracture by adopting a fine survey line method, as shown in figure 2. The accurate measurement method comprises the steps of arranging a measuring line on the exposed surface of the rock mass, sequentially measuring the intersection position, the inclination and dip angle positions, the trace length and the gap width of the structural surface on the measuring line, and identifying the roughness, the filling material and the filling degree of the structural surface, thereby obtaining the fracture information of the rock mass.
1.2 determining random fracture grouping according to attitude projection
According to the principle that the same group of fractures often has the same or similar occurrence, the random fracture occurrence in the collected rock fracture information is projected on a stringy projection network with equal area of the Schmidt according to a normal line, as shown in FIG. 3, the structure can be defined and grouped according to density value lines of points (poles), so that the rock fractures are divided into different groups according to the difference of the occurrence, and the dominant occurrence, namely the inclination and the dip angle, of each fracture group can be obtained.
1.3 determining fracture radius calculation from trace length conversion calculation
The trace of the rock mass fracture is the intersection line of the fracture and the measuring surface, the length of the intersection line is called the length of the trace l (m). According to the principle of the fracture expansion circle-approaching effect, the shape of the fracture can be assumed to be circular, and the fracture centroids are randomly distributed in a three-dimensional space, so that the fracture trace length obtained by the survey line is the chord length of the circle. According to the formula (1),
wherein d and a are the diameter and radius (m) of the rock fracture, and the radius of the fracture can be calculated according to the measured fracture trace length by the formula (1).
1.4 statistical ordering of same set of fracture radii
According to the grouping situation of sampling, assuming field random sampling statistics, wherein the size of a group of fracture samples is n, the radius values of the n fractures are arranged into a sequence as follows:
a1＜a2＜a3＜a4＜.....＜an
it is assumed that the distribution of radius a following the density function f (a) is obtained by regression analysis. The distribution function is as formula (2):
1.5 maximum radius of fracture calculation
Maximum function max (a) according to statistical theory1，a2，a3.....an) The radius a of the set of fractures is maximized such that anThe probability of < a is:
P(an＜a)＝P{max(a1，a2，a3.....an)＜a}
＝P(a1＜a，a2＜a，a3＜a，.....，an＜a)
＝P(a1＜a)P(a2＜a)P(a3＜a).....P(an＜a)
＝[F(a)]n＝G(a)
g (a) is the maximum distribution function of a. The distribution density function of the maximum value of a obtained by differentiating the formula G (a) with respect to a is
G(a)′＝g(a)＝nf(a)[F(a)]n-1
Let g (a)' (0) have
(n-1)f2(a)＝-f′(a)F(a)
Thus, the maximum radius value a of the set of fracturesmThe solution of the following system of equations can be written.
Where f (a) is a density function of the fracture radius a, which may be specified as a different functional form, such as a normal distribution, an exponential distribution, a logarithmic distribution, a polynomial distribution, and the like.
Taking a brocade screen primary hydropower station as an example, the cracks of surrounding rocks of an underground factory building mainly develop 3 groups, and on the surrounding rocks with complete rock masses, the trace lengths of the 3 groups of cracks are within 2 m. With the surrounding rocks with better integrity as research objects, statistical work is carried out on the surfaces of the surrounding rocks. The occurrence of three sets of fractures is shown in table 1:
TABLE 1 fracture occurrence table
| Fracture set | First set of fractures | Second set of fractures | Third set of fractures |
| The state of birth | 154°∠71° | 24°∠75° | 223°∠63° |
After the statistical work is finished, regression analysis needs to be carried out on the statistical fracture radius. In the regression analysis, a proper density function f (a) is selected according to actual data of field statistics, so that higher fitting degree is obtained. According to the situation of field statistical data, the invention adopts an exponential function: (a) Ae-BaRegression analysis is carried out on the statistical data of the underground powerhouse, and satisfactory fitting degree is obtained. The regression analysis result of the surrounding rock fracture statistical data of the underground powerhouse of the brocade power station is shown in figure 3.
Using formulas
The maximum trace length of each set of fractures, i.e., the aforementioned maximum fracture radius am, was calculated, where B is a fitting parameter for the exponential function, and the results are shown in table 2.
TABLE 2 maximum trace length table for each set of fractures
The statistical result of the underground engineering surrounding rock fractures is shown in fig. 4, wherein the abscissa in the graph is the trace length of the tested fractures, the ordinate is the number of fractures corresponding to the corresponding trace length, x is the trace length and is expressed in units of l/m, y is the number of fractures and is expressed in units of n/piece. Fig. 4(a) shows the first statistics for the first set of fractures (26 total fractures, n-26), where y-24.782361 e-8.92907x. Fig. 4(b) shows the second statistics for the first set of fractures (47 total fractures, n-47), where y-24.02915 e-13.45693x. FIG. 4(c) shows the third statistic for the first set of fractures, (25 fractures total, n-25) where y-23.42015 e-8.80847x. FIG. 4(d) shows the first statistic for the second set of fractures, (23 total fractures, n-23), where y-31.77098 e-7.50258xFig. 4(e) shows a second statistic for the second set of fractures (38 total fractures, n-38), where y-34.11937 e-8.40944xFig. 4(f) shows the third statistic for the second set of fractures, (43 fractures total, n-43), where y-31.2851 e-3.1847x. FIG. 4(g) shows the first statistic for the third set of fractures, (38 total fractures, n 38), where y 73.26811e-7.40506x. Fig. 4(h) shows the second statistic for the third set of fractures (42 total fractures, n-42), where y-57.74979 e-12.16382x. FIG. 4(i) shows the third statistic for the third set of fractures, (63 fractures total, n-63), wherein y-82.48519 e-8.94419x。
Step two: testing of fracture toughness of surrounding rock
The test sample is processed indoors by collecting the surrounding rock blocks on site. According to the rock fracture toughness test method recommended by international society for rock mechanics and engineering (ISRM)2014, a rock mechanics testing machine is utilized to carry out the central straight crack semicircular disc fracture toughness test on the surrounding rock sample, as shown in fig. 5, so that the type I fracture toughness K of the surrounding rock is obtainedIc. Rock fracture toughness recommended by international society for rock mechanics and engineering (ISRM) in 2012The method comprises the steps of utilizing a rock mechanics testing machine to carry out a triaxial compression shear test on a surrounding rock sample to determine the II-type fracture toughness K of the surrounding rockIIcAs shown in fig. 5. Fig. 5(a) is a schematic plane view of a central straight-crack semicircular disk fracture toughness test, fig. 5(b) is a schematic cross-sectional view of the central straight-crack semicircular disk fracture toughness test, fig. 5(c) is a plan view of a triaxial compression-shear test, fig. 5(d) is a plan view of a triaxial compression-shear test sample, and fig. 5(e) is a plan view of the triaxial compression-shear test sample.
Step three: maximum stress intensity factor calculation
Obtaining stress intensity factor, and solving the positive stress sigma on the structural surface in the rock masseAnd shear stress taue. The method comprises the following specific steps:
3.1 acquisition of the ground stress field
Because of the difficulty of obtaining the stress field by numerical calculation (the numerical calculation must master the outer boundary conditions of all rock masses, accurately master the spatial positions and mechanical properties of all structural surfaces in the rock masses, and accurately master the mechanical parameters of the rock masses so as to accurately calculate the internal stress field of the rock masses), the method for directly measuring the internal stress field of the rock masses by adopting the field stress test has a plurality of advantages. The field test means can avoid the difficult problem in numerical calculation, the precision of the test result depends on the precision of the test means and the test method, and the problem of mutual interference of stress fields of complex structural surfaces does not need to be considered. At present, the main rock stress field testing methods are a hydraulic fracturing method, a stress relieving method and the like. And after the ground stress test data is obtained, the average stress field in the rock mass is obtained.
3.2 calculation of Normal and shear stresses at the fracture plane
Projecting the average stress field onto the crack surface by using the inclined plane stress formula (Cauchy formula) to obtain the positive stress sigma on the crack surfaceeAnd shear stress taue. All mass points in the rock mass are in an average stress field environment. The average stress field can be expressed by tensor, wherein the average stress field is the stress state as follows:
solving stress field normal stress sigma on structural surface by inclined plane stress formula (Cauchi formula)eAnd shear stress taue：
px＝σxl+τyxm+τzxn
py＝τxyl+σym+τzyn
pz＝τxzl+τzym+σzn
Wherein p isx，py，pzIs stress sigmavComponent in x, y, z direction:
normal stress on oblique section: sigmae＝pxl+pym+pnn, shear stress on oblique section:
from this, the normal stress and the shear stress on the structural surface can be calculated. Stress field normal stress sigma on structural surfaceeAnd shear stress taueAnd both the positive and shear stresses on the structural plane are the positive stress sigma on the fracture planeeAnd shear stress taue。
3.3 maximum stress intensity factor calculation
Calculating the average stress field sigma obtained by testing in the surrounding rockijThe longest radius a of each group of cracksmAnd substituting the maximum stress intensity factor into a fracture mechanics formula for calculation to obtain the maximum stress intensity factor in the surrounding rock. The maximum stress intensity factor varies depending on the type of fracture and the grouping of fractures. The invention takes underground engineering as an example, 3 groups of fractures are shared in an engineering area, so that 9 pairs of graphs are needed to represent the maximum stress intensity factors of I, II and III types of fractures of each group, three fracture modes are defined in fracture mechanics and respectively correspond to the three stress intensity factors, wherein I is tensile fracture, II is shear fracture, and III is mixed fracture.
Step four: determining a potentially damaging zone of surrounding rock
According to the fracture mechanics theory, the stress intensity factor K of the tensile fracture1Or stress intensity factor K of mixed fracture3Greater than fracture toughness KIcOr stress intensity factor K of shear fracture2Greater than fracture toughness KIIcThe crack is broken. And (3) drawing a surrounding rock potentially-damaged subarea cloud picture by introducing a maximum stress intensity factor and fracture toughness data by using commercial software Tecplot.
As shown in fig. 6, in the foregoing calculation results of the underground powerhouse, a location (point 4 location) in the cavern where fracture damage is most likely to occur is clearly indicated, and it is also indicated that fracture damage is mainly performed along the second group of fractures, so that an engineer can be guided to perform key reinforcement on the second group of fractures at the point 4 location, thereby preventing the surrounding rock from fracture and instability; in the rock burst research of the high-stress hard rock tunnel, the method can also be used for calculating the position where the rock burst is most likely to occur in the surrounding rock of the cavern, and determining the fracture occurrence state which is likely to cause the rock burst, thereby guiding an engineer to take treatment measures. Fig. 6(a) shows six characteristic points at which the surrounding rock of the underground chamber may be damaged, and fig. 6(b) shows calculation results of stress intensity factors of types I, II, and III corresponding to the characteristic points in the six surrounding rocks. In addition, the results in FIG. 6(b) clearly show the magnitude of the stress intensity factor, wherein the stress intensity factor K of the surrounding rock at point 4 is shownII、KIIISignificantly larger than the other portions, are the portions of the fracture where brittle fracture is most likely to occur.
The invention provides a system for determining potential damage subareas of deeply buried fractured surrounding rock, which comprises the following steps:
and the sampling module is used for sampling the surrounding rock fractures of the engineering rock mass and determining the surrounding rock fracture information of each surrounding rock fracture.
The maximum radius value determining module is used for determining a plurality of target radius values according to the surrounding rock fracture information; the target radius value is the maximum radius value in all the surrounding rock fractures of the same group.
And the surrounding rock fracture toughness testing module is used for testing the surrounding rock fracture toughness of the engineering rock mass and determining the surrounding rock fracture toughness.
And the rock mass stress field testing module is used for testing the rock mass stress field of the engineering rock mass and determining the average stress field of the engineering rock mass.
And the maximum stress intensity factor determining module is used for determining the maximum stress intensity factor by utilizing a fracture mechanics formula according to the maximum radius value and the average stress field.
And the surrounding rock potential damage subarea determining module is used for determining a surrounding rock potential damage subarea according to the maximum stress intensity factor and the surrounding rock fracture toughness.
In practical applications, the maximum radius value determining module specifically includes:
and the projection and grouping unit is used for projecting the rock mass fracture information on the Schmidt equal-area declination projection network according to a normal line and grouping the rock mass fractures according to the density value line of the Schmidt equal-area declination projection network.
And the trace length conversion unit is used for performing trace length conversion on the same group of traces of the rock mass cracks and determining the radius of the rock mass cracks.
And the sequencing and regression analysis unit is used for sequencing and regression analysis on the rock mass fracture radii of the same group and determining the maximum radius value of each group of surrounding rock fractures.
In practical application, the surrounding rock fracture toughness test module specifically comprises:
and the I-type fracture toughness determination unit is used for performing central straight crack semicircular disc fracture toughness test on the test sample of the engineering rock body by utilizing a rock mechanics testing machine to determine the I-type fracture toughness in the surrounding rock fracture toughness.
And the II-type fracture toughness determination unit is used for performing a triaxial stamping shear test on the test sample of the engineering rock body by utilizing a rock mechanics testing machine to determine the II-type fracture toughness in the surrounding rock fracture toughness.
In practical application, the rock mass stress field test comprises a hydraulic fracturing method and a stress relieving method.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.
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