Rock mass grouting evaluation method based on geological structure, engineering property and environmental factors

Abstract

The invention belongs to the technical field of grouting engineering, and particularly relates to a rock mass grouting evaluation method based on geological structures, engineering properties and environmental factors. The GGI value is calculated according to the formula # imgabs0 #, wherein Jn represents the number of rock mass joint groups, RQD represents the rock mass quality index, Lu represents the permeability of water, Fc represents the flow efficiency ratio of cement paste, Pw represents the underground water pressure, and sigma v represents the field stress; the rock mass groutability is evaluated according to the GGI value, the higher the GGI value is, the better the rock mass groutability is, and the lower the GGI value is, the poorer the rock mass groutability is. According to the method, the comprehensive influence of geological structures, engineering properties and environmental factors is considered, the limitation of single parameter evaluation is broken through, multi-dimensional and multi-level representation of rock mass groutability evaluation is realized, and the grouting capacity of rock mass can be comprehensively reflected.

Description

Technical Field

[0001] The present invention belongs to the technical field of grouting engineering, and specifically relates to a rock mass grouting evaluation method based on geological structure, engineering properties and environmental factors. Background Art

[0002] As the core technology to ensure the structural safety of water conservancy projects, the quality control of dam grouting is directly related to the anti-seepage property and overall stability of the dam foundation. However, this technology faces double dilemmas in practical applications: from the aspect of engineering attributes, grouting operations are concealed construction, and the diffusion process of grout in rock mass fractures is invisible, making it difficult to monitor the grouting effect in real time; from the aspect of theoretical support, current grouting parameter design mainly relies on engineering experience and uses the engineering analogy method. For example, according to the previous geological exploration results, grouting parameters are designed based on experience. However, under special geological conditions such as strong unloading zones and deep gentle dip fractures, the applicability of empirical formulas is significantly reduced. According to statistics, the cost of secondary supplementary grouting caused by misjudgment of rock mass groutability in a certain extra-high arch dam project accounts for a large proportion of the project cost, and there is also a potential risk of inducing seepage failure. Therefore, it is urgent to establish a new grouting evaluation model to scientifically guide grouting construction.

[0003] At present, the index for measuring the groutability of rock masses mainly relies on the results of the water pressure test of rock masses. Based on this, scholars have carried out the analysis and research on the groutability of rock masses by combining other factors. The literature "Saeidi O, Khalokakaie R. A new rock-engineering index to assess jointed rock mass groutability[J]. European journal of environmental and civil engineering, 2013, 17(5): 374-397." proposed a Rock Mass Groutability Index (RGI) based on the Rock Engineering Systems (RES) to evaluate the groutability of jointed rock masses. Parameters such as joint dip angle, hydraulic aperture, roughness, spacing, and trace length are used as rock mass geological structure parameters, and parameters such as grouting pressure, viscosity, and cohesion are used as grouting engineering parameters. The literature "Azimian A, Ajalloeian R. Permeability and groutability appraisal of the Nargesi dam site in Iran based on the secondary permeability index, joint hydraulic aperture and Lugeon tests[J]. Bulletin of Engineering Geology and the Environment, 2014, 74(3): 845-859." carried out the permeability and groutability evaluation according to the Secondary Permeability Index (SPI), Joint Hydraulic Aperture (JHA), and Lugeon permeability.

[0004] However, the existing analysis methods for the groutability of rock masses mainly consider geological structure and engineering properties, while ignoring the influence of environmental factors (such as groundwater stress and in-situ stress) on groutability. Therefore, the present invention comprehensively considers the influences of geological structure, engineering properties, and environmental factors, and proposes a rock mass grouting evaluation method. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the technical problem to be solved by the present invention is to provide a rock mass grouting evaluation method based on geological structure, engineering properties, and environmental factors.

[0006] The present invention solves the above-mentioned technical problem by adopting the following technical solutions:

[0007] A method for evaluating rock mass grouting based on geological structure, engineering properties and environmental factors, characterized in that the method calculates the GGI value according to formula (1), the higher the GGI value, the better the groutability of the rock mass, and the lower the GGI value, the worse the groutability of the rock mass;

[0008]

[0009] In the formula, J n represents the number of rock mass joint sets, a dimensionless parameter; RQD represents the rock mass quality index, a dimensionless parameter; Lu represents the water permeability, with the unit of L / (min·MPa·m); F c represents the flow efficiency ratio of the cement slurry, with the unit of m 2 / (s·Pa); P w represents the groundwater pressure, with the unit of MPa; σ v represents the in-situ stress, with the unit of MPa.

[0010] Furthermore, the flow efficiency ratio of the cement slurry is calculated by the following formula:

[0011]

[0012] In the formula, μ represents the dynamic viscosity of the cement slurry, with the unit of Pa·s; ρ represents the density of the cement slurry, with the unit of kg / m 3 ; ν c represents the kinematic viscosity of the cement slurry, with the unit of m 2 / s; τ0 represents the initial yield stress of the cement slurry, with the unit of Pa.

[0013] Compared with the prior art, the beneficial effects of the present invention are:

[0014] (1) The present invention takes into account the comprehensive influence of geological structure (J n / RQD), engineering properties (Lu / F c ) and environmental factors (P w / σ v ), and proposes a brand-new evaluation index GGI for rock mass groutability, breaking through the limitations of single-parameter evaluation, realizing multi-dimensional and multi-level characterization of rock mass groutability, and being able to comprehensively reflect the grouting ability of the rock mass. Compared with the traditional single-parameter evaluation, the non-linear relationship characterization method of GGI can more comprehensively reflect the actual effect of rock impregnation ability. The higher the GGI value, the looser the rock mass and the better the groutability; on the contrary, the denser the rock mass, the worse the groutability. According to the GGI value, the impregnation scheme can be optimized to improve the engineering effect, which has important engineering practical value and theoretical significance.

[0015] (2) Based on the traditional Lu value (Lugeon unit), the present invention proposes the flow efficiency ratio F cAs a parameter for evaluating the flow characteristics of cement slurry. Different from the traditional single-factor evaluation method (for example, only considering dynamic viscosity or initial yield stress), the flow efficiency ratio comprehensively combines the viscosity characteristics and penetration ability of cement slurry, and can more comprehensively reflect the flow characteristics of cement slurry in rock fractures. Research shows that the flow efficiency ratio changes significantly with the increase of the water-cement ratio (W / C). Especially when W / C is less than 1.0, the flow efficiency ratio is particularly sensitive to the water-cement ratio.

[0016] (3) As a dimensionless index, GGI has the significant advantage of eliminating the differences in dimension and unit, can better reflect the actual changes in the rock grouting ability, and can be used to evaluate the groutability of different grouting projects. With the improvement of rock groutability, the GGI value shows a gradually increasing trend, reflecting the improvement of the penetration ability of the rock to cement slurry. Through theoretical analysis and numerical simulation, the effectiveness of the present invention is verified, which can accurately reflect the relationship between grouting effect and construction conditions under different geological conditions, provides a more systematic decision-making basis for deep bedrock grouting projects, and can comprehensively evaluate the groutability of bedrock. Description of the Drawings

[0017] Figure 1 is a graph showing the relationship between the flow efficiency ratio of cement slurry and the water-cement ratio;

[0018] Figure 2 is a two-dimensional model diagram of the penetration of cement slurry in rock fractures;

[0019] Figure 3 is a graph showing the relationship between the maximum permeability of cement slurry and the equivalent flow conversion coefficient and GGI under different initial yield stresses and grouting pressures;

[0020] Figure 4 is a graph showing the relationship between the grouting pressure and the equivalent flow conversion coefficient and GGI under different initial yield stresses and maximum permeabilities. Detailed Embodiments

[0021] The following provides specific embodiments in conjunction with the drawings. The specific embodiments are only used to introduce the technical solutions of the present invention in detail, and do not limit the protection scope of this application.

[0022] The present invention provides a method for evaluating rock mass grouting based on geological structure, engineering properties and environmental factors. Calculate the GGI value according to the following formula. The higher the GGI value, the looser the rock mass and the better the groutability; the lower the GGI value, the denser the rock mass and the worse the groutability;

[0023]

[0024] In the formula, J nrepresents the number of joint sets in rock mass, a dimensionless parameter; RQD represents the rock mass quality index, a dimensionless parameter; Lu represents the water permeability, with the unit of L / (min·MPa·m); F c represents the flow efficiency ratio of cement slurry, with the unit of m 2 / (s·Pa); P w represents the groundwater pressure, with the unit of MPa; σ v represents the in-situ stress, with the unit of MPa;

[0025] represents the number of effective fractures in rock mass, characterizing the fractures actually used for water flow, quantifying the water diversion capacity of geological structure, and serving as a geological structure parameter;

[0026] represents the equivalent flow conversion coefficient, characterizing the conversion relationship between water injection volume and grouting volume, realizing the quantitative evaluation of slurry migration efficiency, and being an engineering property parameter;

[0027] represents the degree of influence of stress on rock mass, characterizing the influence of stress on the compactness of rock mass, reflecting the environmental constraint effect, and serving as an environmental factor parameter.

[0028] The flow efficiency ratio of cement slurry is calculated by the following formula:

[0029]

[0030] In the formula, μ represents the dynamic viscosity of cement slurry, with the unit of Pa·s; ρ represents the density of cement slurry, with the unit of kg / m 3 ; ν c represents the kinematic viscosity of cement slurry, with the unit of m 2 / s; τ0 represents the initial yield stress of cement slurry, with the unit of Pa;

[0031] It can be seen from formula (2) that the flow efficiency ratio comprehensively considers the dynamic viscosity and initial yield stress of cement slurry, and can more accurately reflect the flow ability of cement slurry in rock mass fractures; the larger the flow efficiency ratio, the greater the viscosity of cement slurry and the poorer the fluidity.

[0032] The interpretability of using GGI to evaluate the groutability of rock mass is as follows:

[0033] Basis for the selection of geological structure parameters:

[0034] The seepage behavior of rock mass can be analyzed through the geological structure characterizing the fracture occurrence. The seepage tensor model based on the cubic law is:

[0035]

[0036] where k is the seepage tensor of fractured rock mass, δ is the Kronecker function tensor, and n i and n j are the unit normal vectors of the i-th and j-th groups of fractures, b i and s i are the average aperture and average spacing of the i-th group of fractures, g is the acceleration due to gravity, and v is the kinematic viscosity of the fluid;

[0037] It can be seen from Equation (3) that the smaller the average spacing of fractures, the larger the number of fractures, and the greater the seepage tensor of the rock mass. Therefore, the lower the RQD value and the greater the fracture density of the rock mass, the greater the permeability; J n The larger the value, the more complex the fracture distribution and the more seepage channels, and the greater the permeability; therefore, can be regarded as the permeability function of fractured rock mass and used as a parameter to reflect geological structures.

[0038] Basis for the selection of engineering property parameters:

[0039] The flow of water exhibits Newtonian fluid behavior, and its viscosity remains constant regardless of the shear rate. It can flow uniformly in fractures without the risk of blockage or sedimentation; while the flow of cement slurry exhibits non-Newtonian fluid behavior. Therefore, based on the mechanical equilibrium equation and without considering the groundwater pressure, the maximum permeability of cement slurry is estimated according to the following formula;

[0040]

[0041] where I is the maximum permeability of cement slurry in m; P g is the grouting pressure in MPa; h is the fracture aperture in m;

[0042] When analyzing the groutability of rock mass, the properties of the slurry are usually considered as an important influencing factor. Therefore, is selected as the slurry flow characteristic to characterize the influence of slurry properties on the groutability of rock mass. In order to comprehensively reflect the influence of slurry flow characteristics on the grouting effect through rheological parameters, the flow efficiency ratio F of cement slurry is defined c as a parameter to reflect engineering properties.

[0043] From Figure 1 it can be seen that when the water-cement ratio is less than 1, the flow efficiency ratio of cement slurry is greatly affected by the water-cement ratio. Therefore, an equivalent flow conversion coefficient is proposed based on the water pressure test to convert the permeability of water into the effective permeability of cement slurry. When the equivalent flow conversion coefficient increases, it indicates that the rock mass has strong permeability and good slurry fluidity, and the GGI increases accordingly, ensuring that the rock mass is more easily grouted.

[0044] Basis for the selection of environmental factor parameters:

[0045] Since the fluid stress in pores can cause effective stress in rock masses, resulting in changes in the broken structure of rock masses, such as increasing the openness and connectivity of fractures, thereby affecting the permeability of fluids; the fracture aperture under the action of water-hydro-mechanical coupling is expressed as:

[0046]

[0047] In the formula, b n is the fracture aperture under the action of water-hydro-mechanical coupling, b0 is the initial fracture aperture, b r is the residual fracture aperture, σ' n is the effective normal stress, and ξ is the stress-aperture correlation coefficient;

[0048] It can be seen from Equation (5) that the fracture aperture is controlled by the effective normal stress, and the effective normal stress is equal to the difference between the total normal stress and the fluid pressure. Then there is:

[0049] σ n = σ n - p(6)

[0050] In the formula, σ n represents the total normal stress, and p represents the fluid pressure;

[0051] It can be seen from Equations (5) and (6) that the fracture aperture is proportional to the groundwater pressure and inversely proportional to the in-situ stress. Also, it can be seen from Equation (3) that the larger the fracture aperture, the better the permeability and groutability of the rock mass. Therefore, environmental factor parameters are defined to quantify the influence of environmental stress on the fracture aperture.

[0052] In summary, considering the influences of geological structure, engineering properties, and environmental factors, GGI is provided as an index for evaluating groutability to qualitatively analyze the groutability of rock masses.

[0053] GGI is a dimensionless parameter that can eliminate scale and unit differences. Its dimensionless property is verified by the following formula;

[0054]

[0055] In the formula, 1unit represents dimensionless, L represents the dimension of length, T represents the dimension of time, and M represents the dimension of mass;

[0056] All parameters in the GGI calculation formula can be measured. Moreover, as a dimensionless parameter, GGI does not need to consider unit or engineering scale differences, and can directly compare the groutability of rock masses, eliminating the interference of dimensions on the results and highlighting the internal relationship between parameters, making the evaluation model more focused on the essence of the geological-engineering relationship; geological structure, slurry rheological properties, and in-situ stress environment usually belong to different disciplinary fields. The dimensionless design enables their quantification and synergy under a unified framework, and can more accurately characterize the groutability of grouting materials in geological strata.

[0057] To verify the effectiveness of the present invention, a theoretical relationship between the maximum permeability of GGI and cement slurry and the grouting pressure was established based on a two-dimensional flat plate model to verify the feasibility of the method of the present invention in a fracture network. It is assumed that the fracture is a smooth flat plate, the fracture aperture does not change, the fluid flow is a stable flow, and the flow only occurs within the fracture; by modeling the flow characteristics of cement slurry and water in the fracture, the model is shown in Figure 2 , and the flow characteristics of cement slurry and water are further clarified to verify whether GGI can quantitatively reflect the comprehensive influence of the geological structure of the rock mass, engineering properties, and environmental factors on the penetration of cement slurry.

[0058] Existing studies have shown that in fractures, there is the following approximate relationship for the water permeability Lu:

[0059] Lu ∝ a·K(8)

[0060] In the formula, a represents an empirical coefficient, and K represents the permeability coefficient of the fracture;

[0061] The permeability coefficient of the fracture is calculated by the following formula:

[0062]

[0063] In the formula, v w represents the kinematic viscosity of water;

[0064] According to formula (9), the fracture aperture h is expressed as:

[0065]

[0066] Combining formulas (4) and (10), the maximum permeability of the cement slurry can be expressed as:

[0067]

[0068] Combining formulas (8), (9), and (11), the water transmissivity Lu is expressed as:

[0069]

[0070] Substituting the flow efficiency ratio F of the cement slurry c into formula (12), we can obtain:

[0071]

[0072] In the formula, both a1 and b are fitting constants.

[0073] According to formula (13), at different initial yield stresses τ0 and grouting pressures P g , the maximum permeability I of the cement slurry is respectively related to the equivalent flow conversion coefficient For the relationship with GGI, see Figure 3 ; Under different initial yield stresses and maximum permeabilities, the grouting pressure P g respectively with the equivalent flow conversion coefficient f engi For the relationship with GGI, see Figure 4 . It can be seen from Figure 3 that as GGI or the equivalent flow conversion coefficient increases, the maximum permeability of the cement slurry will increase significantly; when the grouting pressure increases, the increase in the maximum permeability of the cement slurry is more significant when GGI is higher. It can be seen from Figure 4 that at the same maximum permeability, an increase in GGI can significantly reduce the grouting pressure. Figure 3 , 4 Taken together, a high GGI means that the rock mass is more easily grouted, and a larger minimum permeability can be achieved at a lower grouting pressure; on the contrary, a low GGI requires a higher grouting pressure to achieve the same permeation effect, reflecting poor groutability under dense rock mass structures or high stress conditions.

[0074] Matters not described in the present invention apply to the prior art.

Claims

1. A method for evaluating rock mass grouting based on geological structure, engineering properties and environmental factors, characterized in that, The method calculates the GGI value according to Equation (1). The higher the GGI value, the better the groutability of the rock mass; the lower the GGI value, the worse the groutability of the rock mass. In the formula, J n represents the number of rock mass joint sets, a dimensionless parameter; RQD represents the rock mass quality index, a dimensionless parameter; Lu represents the water permeability, with the unit of L / (min·MPa·m); F c represents the flow efficiency ratio of cement slurry, with the unit of m 2 / (s·Pa); P w represents the groundwater pressure, with the unit of MPa; σ v represents the field stress, with the unit of MPa.

2. The rock mass grouting evaluation method based on geological structure, engineering properties and environmental factors according to claim 1, characterized in that, The flow efficiency ratio of the cement slurry is calculated by the following formula: Wherein, μ represents the dynamic viscosity of the cement slurry, with the unit of Pa·s; ρ represents the density of the cement slurry, with the unit of kg / m 3 ; ν c represents the kinematic viscosity of the cement slurry, with the unit of m 2 / s; τ0 represents the initial yield stress of the cement slurry, with the unit of Pa.

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