CN116465732A - Method and system for taking value of mechanical parameters of rock mass joint unit - Google Patents

Abstract

The invention belongs to the technical field of rock and soil mechanics, and specifically discloses a method and a system for acquiring mechanical parameters of rock mass joint units. The method includes: obtaining the macroscopic mechanical parameters of the complete rock based on the basic rock mechanics test in the laboratory; classifying the engineering rock mass according to the rock mass quality classification standard to obtain the equivalent rock mass mechanical parameters; deriving the elastoplastic stiffness matrix of the joint unit according to the Mohr-Coulomb criterion and the associated flow law; calculating the mechanical parameters of the joint unit according to the homogenization theory and the ultimate strain theory, and verifying the rationality of the mechanical parameters of the joint unit. Based on the idea of an equivalent continuous model, the present invention treats the structural surface as a weak interlayer with a certain thickness, divides the rock mass into an elastic rock unit and an elastic-plastic joint unit, and obtains the mechanical properties of the joint unit through the analysis of the entire jointed rock unit, which can not only meet the engineering calculation accuracy, but also facilitate the direct application of laboratory test data.

Description

A method and system for obtaining mechanical parameters of rock mass joint units

technical field

The invention belongs to the technical field of rock and soil mechanics, and more specifically relates to a method and system for acquiring mechanical parameters of rock mass joint units.

Background technique

As a geological body with a long history of diagenesis, rock mass usually has a large number of fractures and joint fissures distributed inside it. These micro-cracks are large in number, small in size, and have a high cutting degree to the rock mass, which directly affects the mechanical properties and deformation characteristics of the rock mass. However, due to the large number of joints and fissures, it is not feasible to simulate one by one. Therefore, how to accurately and efficiently simulate the rock mass structure with many joints and fissures has become an urgent problem to be solved in the field of rock mass engineering.

At present, there are two main approaches to solve the equivalent rock mass structure. The first idea is based on the understanding of the ubiquity of defects in rock and soil materials, and establishes the rock mass representation unit method by analyzing the influence of discontinuous structures on the overall mechanical behavior of materials (Zhou Chuangbing, Yu Sansan. On the rock mass representation unit volume REV-a basic problem of rock mass mechanical parameters [J]. Journal of Engineering Geology, 1999, 7(4): 332-336.). This method divides rock mass grades through the national standard BQ, GSI and RQD indicators and other rock mass quality classification standards, obtains rock mass mechanical parameters, and combines numerical simulation analysis to determine rock mass representation unit volume (REV), and takes the mechanical parameters of rock mass representation unit as mechanical parameters of engineering scale rock mass (Kulatilake PH S W.Estimating elastic constants and strength of discontinuous rock[J].Journal of geotechnical engine ering,1985,111(7):847-864.He Manchao,Xue Tinghe,Peng Yanfei.Research on the Method of Determination of Mechanical Parameters of Engineering Rock Mass[J].Journal of Rock Mechanics and Engineering,2001(02):225-229.). In addition, Chinese patent CN113946958A discloses a method based on the discrete fracture network method to obtain the rock mass representation unit REV. This method can reasonably reflect the macroscopic mechanical behavior of the general fractured rock mass. It is a popular method in the engineering field. However, due to the size effect, the rock mass laboratory test data cannot be used as the main basis for parameter selection. The second way of thinking regards the rock mass as a two-phase composition of complete rock and structural plane. Among them, rock units and structural plane units are regarded as isotropic bodies, but the rock mass units formed by the two are anisotropic bodies. This method unifies the two failure forms of failure along the joint surface and rock failure through the principle of strength equivalence, and obtains the mechanical parameters of the whole rock mass. The strength equivalence method mentioned above is the frontier of academic research at present. Among them, the rock mechanical parameters are obtained through indoor mechanical tests, and the value of the mechanical parameters of the joint unit becomes the key to whether the model can accurately characterize the mechanical properties and failure characteristics of the rock mass structure.

To sum up, the current methods for solving the equivalent rock mass structure still have certain defects, which are mainly reflected in: (1) joints are widely distributed in natural rock mass, and the analyzed medium has discrete uncertainties. If they are all treated as joint units, it will bring great difficulties to numerical modeling and calculation; (2) affected by the size effect, the REV value of rock mass is usually very large or even does not exist, and the test results of laboratory samples cannot be directly used as the basis for the mechanical parameters of rock mass characterization units.

Based on the above defects and deficiencies, there is an urgent need in this field to propose a new method for determining the mechanical parameters of rock mass joint elements, so as to overcome the discrete uncertainty of the analytical medium and the inaccuracy of determining values based on test results in the prior art.

Contents of the invention

In view of the above defects or improvement needs of the prior art, the present invention provides a method and system for obtaining mechanical parameters of rock mass joint units. Based on the idea of equivalent continuous model, the structural surface is treated as a weak interlayer with a certain thickness, and the rock mass is divided into elastic rock units and elastic-plastic joint units. Through the analysis of the entire joint rock mass unit, the mechanical properties of the joint unit are obtained comprehensively. This method combines indoor mechanical tests and rock quality classification, which can not only meet the accuracy of engineering calculations, but also facilitate the direct application of indoor test data.

In order to achieve the above object, according to one aspect of the present invention, a method for obtaining the mechanical parameters of a rock mass joint unit is proposed, comprising the following steps:

S1 is based on indoor basic rock mechanics tests to obtain macroscopic mechanical parameters of intact rocks;

S2 Classify the engineering rock mass according to the rock mass quality classification standard, and obtain equivalent rock mass mechanical parameters;

S3 derives the elastic-plastic stiffness matrix of the joint element according to the Mohr-Coulomb criterion and the associated flow rule;

S4 According to the homogenization theory, the complete rock mechanical parameters, the equivalent rock mass mechanical parameters and the elastic-plastic stiffness matrix of the joint unit are substituted to calculate the strength parameters of the joint unit, and at the same time, the equivalent rock mass ultimate strain is calculated based on the ultimate strain theory and the equivalent rock mass mechanical parameters;

S5 calculates the fracture energy of the physical unit according to the equivalent rock mass ultimate strain and the strength parameters of the joint unit, and determines the mechanical parameters of the joint unit based on this.

As further preferred, in step S1, the indoor rock basic mechanics test includes rock uniaxial compression and rock Brazilian splitting test, according to the rock uniaxial compression test to obtain the elastic modulus E ^r and Poisson's ratio v ^r of the complete rock; according to the rock Brazilian splitting test to obtain the tensile strength f _t ^r of the complete rock.

As a further preference, in step S2, the equivalent rock mass mechanical parameters include elastic modulus E ^m , Poisson's ratio v ^m , cohesion c ^m , internal friction angle and tensile strength f _t ^m .

As further preferred, step S3 includes the following steps:

S31 Construct the yield function f and the expression of the first material parameter m(κ) and the second material parameter σ _c (κ), select the Mohr-Coulomb criterion as the yield criterion of the joint element, and construct the yield function:

f(σ ₁ ,σ ₃ ,κ)=m(κ)σ ₁ -σ ₃ -σ _c (κ)=0

In the formula, σ ₁ and σ ₃ are the maximum principal stress and minimum principal stress of the material, respectively, and the internal variable κ represents the degree of hardening of the material;

S32 constructing the elastic-plastic stiffness matrix of the joint element, wherein the plastic deformation adopts the flow law associated with the yield surface, and the calculation model of the elastic-plastic stiffness matrix [K ^ep ] of the joint element is as follows:

where [K ^e ] is the elastic stiffness matrix of the joint element, R is the hardening modulus, and σ is the vector representation of the stress of the joint element.

As further preferably, step S4 includes the following steps:

S41 Calculation of joint element stiffness: according to the principle of equivalent stiffness of continuous media, the normal stiffness K _N and tangential stiffness K _S of the joint element are calculated;

S42 Calculate the tensile strength and shear strength of the joint unit: According to the homogenization theory, the yield point of the joint unit and the equivalent rock mass unit should be consistent, and the tensile strength f _t , initial cohesion c ₀ and initial internal friction of the joint unit should be constructed calculation formula.

As a further preference, the calculation formulas of the normal stiffness K _N and the tangential stiffness K _S of the joint element are as follows:

In the formula, h is the thickness of the equivalent rock mass unit, E ^r and v ^r are the elastic modulus and Poisson's ratio of the intact rock, respectively, E ^m and v ^m are the elastic modulus and Poisson's ratio of the engineered rock mass, respectively;

As a further preference, the tensile strength f _t , initial cohesion c ₀ and initial internal friction of the joint unit The calculation formulas are respectively:

f _t =f _t ^m

In the formula, f _t ^m , c ^m and /> are the tensile strength, cohesion and internal friction angle of the equivalent rock mass unit, respectively, /> is the shear strain of the equivalent rock mass at the initial yield point.

As a further preference, in step S4, the calculation of the equivalent rock mass ultimate strain includes: according to the ultimate strain theory, using the numerical limit analysis method to solve and />

In the formula, is the lateral strain of the equivalent rock mass unit under unidirectional compression, ^cm is the cohesion of the equivalent rock mass unit, /> is the internal friction angle of the equivalent rock mass unit, and E ^m and v ^m are the elastic modulus and Poisson's ratio of the equivalent rock mass, respectively.

As a further preference, in step S5, the type I fracture energy G _I and type II fracture energy G _II of the joint unit are calculated according to the stress-strain curve of the joint unit:

In the formula, f _s and f _s ' are the initial shear strength and residual shear strength of the joint element, respectively; Δε and Δγ are the normal cumulative strain and tangential cumulative strain of the joint element from the initial yield point to the failure point, respectively.

As a further preference, it also includes: based on the finite-discrete element coupling software/program, numerical simulation of uniaxial compression and Brazilian splitting tests is performed to verify the applicability and rationality of the mechanical parameters of the joint unit.

According to another aspect of the present invention, a system for obtaining values of mechanical parameters of rock mass joint units is also provided for realizing the above-mentioned method.

Generally speaking, compared with the prior art, the above technical solution conceived by the present invention mainly has the following technical advantages:

1. The present invention is based on the idea of the equivalent continuous model, processes the structural plane in the engineering rock mass into a weak interlayer with a certain thickness, and divides the equivalent rock mass unit into an elastic rock unit and an elastic-plastic joint unit, so that the anisotropic equivalent rock mass unit can be divided into two interacting isotropic units. The established equivalent rock mass model not only considers the influence of joints on the mechanical properties of rock mass, but also can be regarded as a continuum macroscopically, so as to overcome the problems of modeling difficulties and low calculation efficiency of traditional methods in simulating general jointed and fractured rock mass.

2. The present invention considers the influence of joints on the rock mass mechanical properties, adopts the Mohr-Coulomb criterion and the associated flow law to describe the elastoplastic deformation of the joint unit, and based on the homogenization theory and the limit strain theory, through the comprehensive analysis of the whole joint rock mass unit, deduces the calculation formula of the joint unit mechanical parameters. The derivation process comprehensively considered the indoor mechanical test and rock mass quality classification, so as to overcome the inaccuracy of the traditional method of directly using the indoor mechanical test results, and can more accurately reflect the macroscopic mechanical behavior of the jointed rock mass.

3. The calculation parameters in the joint element mechanical parameter value formula derived by the present invention have clear physical meanings, and can be obtained through rock mechanics test results and rock mass quality classification standards. The value results can be verified by finite-discrete element coupling software/programs. The method is simple and convenient, has strong practicability, and is easy to popularize. It is a joint rock mass equivalent parameter analysis method that can not only meet engineering calculation accuracy, but also facilitate direct application of laboratory test test data.

Description of drawings

Fig. 1 is a flow chart of a method for obtaining values of mechanical parameters of a rock mass joint unit related to an embodiment of the present invention;

(a) in Fig. 2 is a schematic diagram of an indoor uniaxial compression test, and (b) in Fig. 2 is a schematic diagram of an indoor Brazilian splitting test;

(a) in Fig. 3 is the variation trend diagram of the cohesion parameter of the joint unit involved in the method of the present invention with κ, and (b) in Fig. 3 is the variation trend diagram of the joint unit internal friction angle parameter involved in the method of the present invention with κ;

(a) in Fig. 4 is the normal stress-strain curve of the joint unit, and (b) in Fig. 4 is the tangential stress-strain curve of the joint unit;

(a) in Fig. 5 is the FDEM-uniaxial compression numerical simulation model figure involved in the present invention, and (b) in Fig. 5 is the FDEM-Brazil splitting numerical simulation model figure involved in the present invention;

(a) in Fig. 6 is the finite-discrete element stress-strain curve of numerical simulation of uniaxial compression involved in the present invention, and (b) in Fig. 6 is the finite element stress-strain curve of numerical simulation of Brazilian splitting involved in the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

As shown in Figure 1, a method for obtaining the mechanical parameters of a rock mass joint unit provided by an embodiment of the present invention includes the following steps:

Step 1. Obtain the macro-mechanical parameters of the complete rock based on the basic indoor rock mechanics test. That is, the macroscopic mechanical parameters of the complete rock are obtained based on the basic mechanical tests of the rock in the laboratory. Specifically, in the step 1, the rock mechanics test includes uniaxial compression and Brazilian splitting test, as shown in FIG. 2 . The elastic modulus E ^r and Poisson's ratio v ^r of the intact rock are obtained from the rock uniaxial compression test; the tensile strength f _t ^r of the intact rock is obtained from the Brazilian splitting test of the rock. In the present invention, both uniaxial compression and Brazilian splitting tests belong to the prior art, and conventional uniaxial compression and Brazilian splitting tests can meet the requirements for obtaining rock parameters of the present invention. Its specific structure and method will not be repeated in the present invention.

Step 2. Classify the rock mass based on the rock mass quality classification standard, and obtain the macroscopic mechanical parameters of the engineering rock mass. That is: according to the rock mass quality classification standard, the engineering rock mass is graded to obtain the equivalent rock mass mechanical parameters. Specifically, the rock mass quality classification standards include the national standard BQ, GSI and RQD indicators. According to the rock mass quality classification standard, classify the rock mass in the project, and obtain the elastic modulus E ^m , Poisson's ratio v ^m , cohesion c ^m , and internal friction angle of the engineering rock mass and tensile strength f _t ^m .

Step 3. Based on the Mohr-Coulomb criterion and the associated flow rule, the elastic-plastic stiffness matrix of the joint element is derived. Specifically, the elastic-plastic stiffness matrix of the joint element can be solved according to the following steps:

Step 3.1. Construct the expressions of the yield function f and the first material parameter m(κ) and the second material parameter σ _c (κ): choose the Mohr-Coulomb criterion as the yield criterion of the joint element, then the yield function f(σ ₁ ,σ ₃ ,κ) can be expressed as:

f(σ ₁ ,σ ₃ ,κ)=m(κ)σ ₁ -σ ₃ -σ _c (κ)=0 (1)

Among them, σ ₁ and σ ₃ are the maximum principal stress and minimum principal stress of the material, respectively; the internal variable κ represents the hardening degree of the material, which determines how the yield surface of the hardened/softened material will change, and its value is usually related to the plastic strain; the first material parameter m(κ) is the ratio of the characteristic compressive strength to the characteristic tensile strength; the second material parameter σ _c (κ) represents the unconfined compressive strength. The expressions of the first material parameter m(κ), the second material parameter σ _c (κ) and the internal variable κ are:

Among them, c(κ) and are the cohesion and internal friction angle of the jointed rock mass, respectively, and are linear functions of the internal variable κ in the elastic-plastic stage, that is, they decrease with the increase of the internal variable κ, but the degree of decrease is different, as shown in Figure 3. c ₀ and /> are the initial cohesion and initial internal friction angle of the joint unit, respectively, /> and κ _r are the internal friction angle and internal variable when the element is completely destroyed, respectively; and dε ^p are the equivalent plastic strain and plastic strain increment, respectively.

Step 3.2, constructing the stiffness matrix K of the joint element: the plastic deformation adopts the flow law associated with the yield surface, then the expression of the elastoplastic stiffness matrix [K ^ep ] of the joint element is:

Among them, [K ^e ] is the elastic stiffness matrix of the joint element, K _N and K _S are the normal stiffness and tangential stiffness coefficients of the joint element; R is the hardening modulus, and at the yield point, R is 0; σ is the vector representation of the stress of the joint element.

Step 4. Calculate the mechanical parameters of the joint element based on the homogenization theory and the ultimate strain theory. Among them, in the present invention, the homogenization theory is to combine the units with two different mechanical properties into a new unit by using the homogenization criterion, stress balance and motion constraint conditions. According to the homogenization theory, the relative displacement between the joint and the rock occurs inside the joint unit, and the two interfaces remain completely bonded. The homogenization theory requires that the yield point of the joint unit and the equivalent rock mass unit be consistent, that is, when the joint unit reaches the yield strain, the stress state of the joint unit and the rock mass unit at this moment both satisfy the yield function. The ultimate strain theory takes the ultimate strain under unidirectional stress as the criterion for the failure of rock and soil materials under unidirectional stress. The ultimate strain theory believes that when the material just reaches yield, it is the initial yield and has an elastic limit strain. With the development of plasticity, the material is destroyed, and the strain reaches the ultimate strain at this time. The equivalent rock mass unit and the joint unit of the present invention adopt elastic-plastic constitutive structure, therefore, it is feasible to calculate the ultimate strain of the rock mass unit and the joint unit by using the ultimate strain theory.

In the step 4, the rock element adopts the elastic constitutive structure, and the rock mass element adopts the ideal elastic-plastic constitutive structure, and the mechanical parameters of the joint element can be calculated according to the following steps:

Step 4.1. Solve the stiffness of the joint element: According to the equivalent principle of stiffness of the continuum, the calculation formulas of the normal stiffness K _N and the tangential stiffness K _S of the joint element are as follows:

In the formula:

Among them, h is the thickness of the equivalent rock mass unit; E ^r and v ^r are the elastic modulus and Poisson's ratio of the intact rock, respectively, and their values are based on the initial straight line section of the stress-strain curve of the indoor uniaxial compression test; E ^m and v ^m are the elastic modulus and Poisson's ratio of the equivalent rock mass, respectively, and their values are based on the rock mass quality classification standard.

Step 4.2, Solve the tensile strength and shear strength of the joint unit: according to the homogenization theory, the yield point of the joint unit and the equivalent rock mass unit are consistent, then the tensile strength f _t , initial cohesion c ₀ and initial internal friction of the joint unit The calculation formula is:

f _t = f _t ^m (16)

In the formula:

Among them, f _t ^m , c ^m and are the tensile strength, cohesion and internal friction angle of the equivalent rock mass unit respectively, and the values are taken according to the rock mass quality classification standard;/> is the shear strain of the equivalent rock mass at the initial yield point, see step 4.3 for the specific value.

Step 4.3, solving the fracture energy of the joint unit: Fig. 4 is the stress-strain curve of the joint unit, and the area enclosed by the stage after the curve yields is the fracture energy of the unit, then the calculation formulas of the type I fracture energy G _I and the type II fracture energy G _II of the joint unit are:

Among them, f _s and f _s ' are the initial shear strength and residual shear strength of the joint element, respectively; Δε and Δγ are the normal cumulative strain and tangential cumulative strain of the joint element from the initial yield point to the failure point, respectively. The calculation formulas of Δε and Δγ are as follows:

Among them, t is the thickness of the joint element; and /> is the tensile strain at the initial yield point and the complete failure point of the equivalent rock mass unit; /> and /> is the shear strain at the initial yield point and the complete failure point when the equivalent rock mass unit is sheared. According to the ultimate strain theory, /> and /> It can be solved by numerical limit analysis method, and their relational expressions are as follows:

in, is the lateral strain of the equivalent rock mass unit under unidirectional compression.

Step 5. Based on the finite element-discrete element coupling software, perform numerical simulation on the uniaxial compression and Brazilian splitting tests, and verify the applicability and rationality of the method for obtaining the mechanical parameters of the joint element of the present invention. In the step 5, using the finite-discrete element software, the complete rock mechanical parameters in the above step 1 are used as the input parameters of the solid element, and the mechanical parameters of the joints calculated in the above steps 3 to 4 are used as the input parameters of the joint element, and numerical simulations of uniaxial compression and Brazilian splitting are performed. The numerical model is shown in (a) (b) in Fig. 5, and the stress-strain curve results of the model are shown in (a) and (b) in Fig. 6. By comparing the finite-discrete element simulation results with the quality classification results of engineering rock mass, the applicability and rationality of a method for obtaining mechanical parameters of rock mass joint units proposed by the present invention are verified.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims (10)

1. The method for evaluating the mechanical parameters of the rock mass joint unit is characterized by comprising the following steps of:

s1, acquiring macroscopic mechanical parameters of the complete rock based on an indoor rock basic mechanical test;

s2, classifying the rock mass of the engineering rock mass according to the rock mass quality classification standard to obtain equivalent rock mass mechanical parameters;

s3, deducing an elastic-plastic rigidity matrix of the joint unit according to Mohr-Coulomb criterion and associated flow rule;

s4, substituting the mechanical parameters of the complete rock, the mechanical parameters of the equivalent rock and the elastic-plastic rigidity matrix of the joint unit to calculate the strength parameters of the joint unit according to the homogenization theory, and simultaneously, calculating the limit strain of the equivalent rock based on the limit strain theory and the mechanical parameters of the equivalent rock;

s5, calculating the fracture energy of the joint unit according to the ultimate strain of the equivalent rock mass and the strength parameter of the joint unit, and determining the mechanical parameter of the joint unit according to the fracture energy.

2. The method for evaluating mechanical parameters of a rock mass joint unit according to claim 1, wherein in step S1, the indoor rock basic mechanical test comprises a rock uniaxial compression test and a rock brazil split test, and the elastic modulus Er and poisson ratio v of the whole rock are obtained according to the rock uniaxial compression test ^r The method comprises the steps of carrying out a first treatment on the surface of the Obtaining the tensile strength f of the complete rock according to the Brazilian rock splitting test _t ^r 。

3. The method for evaluating mechanical parameters of a rock mass joint unit according to claim 1, wherein in step S2, the equivalent rock mass mechanical parameters include an elastic modulus E ^m Poisson ratio v ^m Cohesive force c ^m Angle of internal frictionAnd tensile strength f _t ^m 。

4. The method for evaluating mechanical parameters of a rock mass joint unit according to claim 1, wherein the step S3 comprises the steps of:

s31 building a yield function f and a first material parameter m (kappa) and a second material parameter sigma _c (kappa) expression, selecting Mohr-Coulomb criterion as yield criterion of the joint unit, constructing yield function:

f(σ ₁ ,σ ₃ ,κ)＝m(κ)σ ₁ -σ ₃ -σ _c (κ)＝0

in sigma ₁ Sum sigma ₃ The maximum principal stress and the minimum principal stress of the material are respectively, and the internal variable kappa represents the hardening degree of the material;

s32, constructing an elastoplastic stiffness matrix of the joint unit, wherein the elastoplastic stiffness matrix [ K ] of the joint unit is constructed by adopting a flow rule associated with a yielding surface through plastic deformation ^ep ]The calculation model of (2) is as follows:

in [ K ] ^e ]The elastic stiffness matrix of the joint unit is represented by R, R and sigma, wherein R is the hardening modulus, and sigma is the vector representation of the stress of the joint unit.

5. The method for evaluating mechanical parameters of a rock mass joint unit according to claim 1, wherein step S4 comprises the steps of:

s41, solving joint unit rigidity: solving the normal rigidity K of the joint unit according to the rigidity equivalent principle of the continuous medium _N And tangential stiffness K _S ；

S42, solving the tensile strength and the shear strength of the joint unit: according to the homogenization theory requirement, the yield points of the joint unit and the equivalent rock mass unit are kept consistent, and the tensile strength f of the joint unit is constructed _t Initial cohesion c ₀ And initial internal friction forceIs a calculation formula of (2).

6. The method for evaluating mechanical parameters of a rock mass joint unit according to claim 5, wherein the normal stiffness K of the joint unit _N And tangential stiffness K _S The calculation formula of (2) is as follows:

in the method, in the process of the invention,h is the thickness of the equivalent rock mass unit, E ^r And v ^r Elastic modulus and poisson ratio of the complete rock, E ^m And v ^m The elastic modulus and the poisson ratio of the equivalent rock mass are respectively;

tensile strength f of the joint unit _t Initial cohesion c ₀ And initial internal friction forceThe calculation formulas of (a) are respectively as follows:

f _t ＝f _t ^m

in the method, in the process of the invention,f _t ^m 、c ^m and->Tensile strength, cohesion and internal friction angle of equivalent rock mass units, respectively +.>Is the shear strain of the equivalent rock mass at the initial yield point.

7. The method according to claim 1, wherein the mechanical parameter of the rock mass joint unit is a valueThe method is characterized in that in step S4, the calculating the equivalent rock mass limit strain comprises: according to the limit strain theory, solving by adopting a numerical limit analysis methodAnd->

In the method, in the process of the invention,c is the lateral strain of the equivalent rock mass unit under the unidirectional compression condition ^m As the cohesion of the equivalent rock mass unit,is the internal friction angle of the equivalent rock mass unit E ^m And v ^m The elastic modulus and poisson ratio of the equivalent rock mass are respectively.

8. The method for evaluating mechanical parameters of a rock mass joint unit according to claim 1, wherein in step S5, the type I breaking energy G of the joint unit is calculated from the stress-strain curve of the joint unit _I And type II break energy G _II ：

Wherein f _s And f' _s The initial shear strength and the residual shear strength of the joint unit are respectively; delta epsilon and delta gamma are the normal and tangential cumulative strains of the joint unit from the initial yield point to the failure point, respectively.

9. The method for evaluating mechanical parameters of a rock mass joint unit according to any one of claims 1 to 8, further comprising: based on finite-discrete element coupling software, carrying out numerical simulation on uniaxial compression and Brazilian split tests, and verifying the applicability and rationality of the mechanical parameter values of the joint units.

10. A system for the valuing of mechanical parameters of a rock mass joint unit, characterized by implementing the method of any one of claims 1-9.