Method and system for quantitatively evaluating rock mass quality by using resistivity

Abstract

The invention is suitable for the technical field of water conservancy and hydropower engineering geophysical prospecting, and provides a method and system for quantitatively evaluating rock mass quality by using resistivity, and the method comprises the following steps: obtaining resistivity data of a target rock mass; selecting a corresponding conversion model according to the rock mass pore space connectivity and the water-containing state; converting the resistivity data into equivalent wave velocity data by using a conversion model; calculating a rock mass quality evaluation index according to the equivalent wave velocity data; performing quantitative evaluation on the rock mass quality based on the rock mass quality evaluation index; according to the method, direct comparison of an earthquake type method and an electromagnetic type method on the digital level and the mapping effect is facilitated, mutual verification and mutual complementation of results of different geophysical prospecting methods are facilitated, and conditions are created for multi-method data fusion.

Description

TECHNICAL FIELD

[0001] The application relates to a method and system for quantitatively evaluating rock mass quality by resistivity. BACKGROUND

[0002] In the field of construction engineering, the main basis for evaluating the weathering degree, completeness, rock mass quality grade and surrounding rock classification of rock mass is the field characteristics, core characteristics, rock test data and wave velocity of rock mass. The field characteristics are generally subjective and non-unique, and are mainly described qualitatively. The core characteristics and rock test data often need to be obtained by using auxiliary systems such as drilling, adit excavation, coring and sample preparation, which are time-consuming and destructive, and the coverage and sampling quantity of the data are limited. In addition, the drilling process and test results are also disturbed by many random factors. The elastic wave longitudinal wave velocity (V p ) can be directly used for quantitative evaluation of rock mass quality and classification of surrounding rock. The wave velocity can be converted into the weathering wave velocity ratio (K v ), the completeness coefficient (K w ) and the dynamic elastic modulus (E d ), which are important quantitative indicators for the classification of weathering degree and completeness of rock mass and the only quantitative indicators at present. The wave velocity can be obtained by ground geophysical prospecting, hole testing, adit wall testing and penetration testing, and the acquisition process is not easy. The ground geophysical prospecting is often affected by site conditions, test environment, budget, physical structure and other factors. Many scenes do not have the conditions to carry out seismic exploration, such as the seismic reflection wave method, fast-paced engineering survey field, exploration depth requirement and velocity profile calculation which have high requirements for seismic energy and supercomputing capability, and the seismic refraction wave method is limited by topography and stratigraphic structure. The in-hole and inter-hole testing are also limited by the location and conditions of the drill hole and adit.

[0003] Among the geophysical prospecting methods, the electric (magnetic) method has many derivatives, such as the magnetotelluric method and the high-density resistivity method, which can meet the needs of different exploration depths and accuracies, adapt to different application scenarios, and have relatively low cost of field testing and data processing, higher cost performance, clear and intuitive resistivity profile results, and are more widely used in the exploration, detection and testing of underground caverns, slopes and foundations. However, there are many factors affecting the resistivity, such as the composition, structure and structure of rock mass, weathering, unloading, crushing, dissolution, water content and connectivity of pore space of stratum, which will greatly affect the resistivity of rock mass, generally causing the order of magnitude change of the resistivity of rock mass, and the anisotropy of measured resistivity in different directions when the occurrence of stratum and structure surface is different. At present, the resistivity profile is mainly used for positioning and subjective qualitative description of weak links in rock mass, and the resistivity value cannot be directly used for quantitative evaluation of rock mass quality.

[0004] In summary, the field characteristics (such as rock mass color, hardness, structural plane development degree, structural plane properties, secondary minerals, structure and the like), core characteristics (such as core recovery rate RQD, structural plane, color, structure and the like), in-situ test and rock test characteristics (such as standard penetration value, compressive strength) and the like for rock mass quality evaluation often have strong subjectivity, high acquisition cost, limited representativeness, strong randomness of test results and the like, and generally need the wave velocity value as a quantitative index for comprehensive discrimination. In many application scenarios, the acquisition of effective elastic wave velocity value is difficult or costly, and the multi-solution of inversion also makes the elastic wave velocity value need to be verified by other methods. The electric (magnetic) geophysical method can infer the rock mass structure by measuring and inverting the formation resistivity, and is a collaborative method of the seismic method in engineering exploration. In many application scenarios, the electric (magnetic) method has stronger site adaptability, lower cost, and more intuitive results. However, the rock mass resistivity value cannot be directly used for rock mass quality classification due to the complex influencing factors, large range, and no significant linear relationship with rock mass integrity.

[0005] In this case, resistivity data is often used for rock mass quality evaluation in the following ways:

[0006] (1) According to the drilling verification data and empirical values, the segmented calibration is performed. For example, in a limestone stratum in a certain area, according to the drilling verification, it can be considered that the resistivity of 20-120 Ω.m is a karst development stratum, 120-300 is a fracture zone, 300-2500 is a poor integrity stratum, and greater than 3000 is a relatively complete stratum. This way has strong subjectivity, limited scope, and is not suitable for complex strata;

[0007] (2) Simple data transformation and normalization processing is performed to make the converted data related to the rock mass integrity coefficient in terms of distribution and magnitude. For example, the data is cubed or logarithmically processed, and then normalized according to the range value and mean value. This way realizes the correlation between resistivity and integrity coefficient in form, but has a large deviation in mechanism;

[0008] (3) Through joint inversion, the physical parameters are converted into other parameters, different method data are constrained to each other, the model is constantly modified, and the optimal result is finally obtained. This method is actually only at the level of digital processing, and the final result has great uncertainty, and the composite result obtained is not directly related to the rock mass quality.

[0009] Therefore, in view of the above status, it is urgent to provide a method and system for quantitatively evaluating rock mass quality by resistivity to overcome the deficiencies in current practical applications. SUMMARY

[0010] The present application aims to provide a method and system for quantitatively evaluating rock mass quality by resistivity, effectively solving the problems in the background art.

[0011] The present application is implemented by a method for quantitatively evaluating rock mass quality by resistivity, comprising the following steps:

[0012] Obtaining resistivity data of the target rock mass;

[0013] Classifying and organizing the resistivity according to engineering sites, rock mass structures, and underground water levels, and labeling the data;

[0014] Determining the background wave velocity, resistivity, rock mass water content, and water saturation of rock skeleton and pore filler of different lithology, different sites, and different elevations, and estimating the electrical measurement connected porosity according to the statistical results of the structure surface occurrence;

[0015] Converting the resistivity into wave velocity according to the corresponding conversion model selected according to the application scene type;

[0016] Calculating the rock mass quality evaluation index according to the converted wave velocity;

[0017] Quantitatively evaluating and grading based on the rock mass quality evaluation index.

[0018] As a further scheme of the present application, the conversion model includes a saturated connected model, a non-saturated connected model, a saturated non-connected model, and a mixed model.

[0019] As a further scheme of the present application, the conversion equation of the saturated connected model is:

[0020]

[0021] wherein V is the measured wave velocity of the rock mass when converting the wave velocity into resistivity, and V is the converted wave velocity V when converting the resistivity into wave velocity. h V1 is the rock skeleton wave velocity, V2 is the pore filler wave velocity, ρ is the measured resistivity, ρ1 is the rock skeleton resistivity, ρ2 is the pore filler resistivity, and ψ is the rock porosity.

[0022] As a further scheme of the present application, the conversion equation of the non-saturated connected model is:

[0023]

[0024] wherein K l is the linear fissure rate, S is the saturation, i.e., the proportion of water-containing pores in the total pores, and V3 is the wave velocity of air.

[0025] As a further scheme of the present application, the conversion equation of the saturated non-connected model is:

[0026]

[0027] As a further scheme of the present application: the conversion equation of the mixed model is:

[0028]

[0029] Wherein, V1 * is the corrected rock skeleton wave speed, K l1 is the saturated connectivity fracture line fracture ratio, which can be converted by the electrical parameter.

[0030] As a further scheme of the present application: the rock mass quality evaluation index includes rock mass conversion wave speed, weathering wave speed ratio, integrity coefficient and dynamic elastic modulus.

[0031] As a further scheme of the present application: the application scene type is determined according to the connectivity of the rock mass pore space, the water saturation and the development direction of the structural plane and the relationship with the observation system.

[0032] As a further scheme of the present application: the resistivity data is obtained by the magnetotelluric method, the high-density electrical method, the resistivity logging and the like.

[0033] A system for quantitatively evaluating rock mass quality by resistivity, which is used to execute the method for quantitatively evaluating rock mass quality by resistivity as described above.

[0034] Compared with the prior art, the present application has the beneficial effects that:

[0035] The present application creatively proposes the conversion equation of the resistivity and the wave speed of the rock under different scenes by studying the conduction law and the influence mechanism of the rock wave and the current. On the basis of not needing complex conversion algorithm and inversion theory, the equivalent conversion of the wave speed and the resistivity can be quickly realized, the conversion value has direct linear correlation with the rock mass quality, then the rock mass weathering wave speed ratio and the integrity coefficient are calculated by the conversion wave speed, and the rock mass quality is quantitatively evaluated and the rock mass classification is divided according to the above.

[0036] The present application is beneficial to directly comparing the digital level and the mapping effect of the seismic method and the electromagnetic method, facilitating the mutual verification and mutual complement of the results of different geophysical prospecting methods, and creating conditions for multi-method data fusion.

[0037] Compared with other technologies, the present application is not a subjective and empirical segmentation of resistivity values, nor a simple logarithmic or exponential conversion and numerical normalization processing. The mutual conversion equation of resistivity and wave velocity of the present application is established on the basis of rock physics. In addition to considering the wave velocity and resistivity of rock skeleton and pore filler, the rock porosity, water saturation, and connected porosity ratio are also taken as variables in the equation. The conversion result is closer to the real physical property value of the rock, and the problem of anisotropy of rock geophysical parameter measurement is solved, so that the conversion value can more truly and objectively evaluate the rock mass quality. In addition, the relationship between rock mass wave velocity, resistivity, and rock parameters such as porosity, water saturation, and connected porosity ratio is established in the method implementation, which provides a way for using wave velocity and resistivity to jointly invert porosity, water saturation, and connected porosity ratio, and expands the application of geophysical methods. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the specific embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0039] Figure 1 Figure 1 is an example of resistivity and wave velocity conversion curve for a saturated connected model, and a comparison curve of real calculation and speed calculation;

[0040] Figure 2 Figure 2 is an example of resistivity and wave velocity conversion curve for a non-saturated connected model, and a comparison curve of real calculation and speed calculation;

[0041] Figure 3 Figure 3 is an example of resistivity and wave velocity conversion curve for a saturated non-connected model;

[0042] Figure 4 Figure 4 is an example of resistivity and wave velocity conversion curve for a mixed model;

[0043] Figure 5 Figure 5 is a comparison graph of converted wave velocity curve and measured wave velocity curve;

[0044] Figure 6 Figure 6 is a borehole structural plane rose diagram;

[0045] Figure 7 Figure 7 is a comparison graph of converted wave velocity profile and measured wave velocity profile;

[0046] Figure 8 Figure 8 is a workflow diagram. DETAILED DESCRIPTION

[0047] The technical solutions of the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0048] The present application will be further explained and described below with reference to specific embodiments.

[0049] Please refer to Figures 1-8 The method for quantitatively evaluating rock mass quality provided by the embodiments of the present application comprises the following steps:

[0050] Obtaining the resistivity data of the target rock mass;

[0051] Classifying and sorting the resistivity according to the engineering site, rock mass structure and underground water level, and making data labels;

[0052] Determining the background wave velocity, resistivity, rock mass water content and water saturation of the rock skeleton and pore filler of different lithology, different parts and different elevations, and estimating the electrical measurement connected porosity according to the statistical results of the occurrence of structural planes;

[0053] Converting the resistivity into wave velocity according to the corresponding conversion model selected according to the application scenario type;

[0054] Calculating the rock mass quality evaluation index according to the converted wave velocity;

[0055] Quantitatively evaluating and grading based on the rock mass quality evaluation index; the conversion model comprises a saturated connected model, a non-saturated connected model, a saturated non-connected model and a mixed model.

[0056] The rock mass quality evaluation index comprises rock mass conversion wave velocity, weathering wave velocity ratio, integrity coefficient and dynamic elastic modulus; the application scenario type is determined according to the connectivity of the pore space of the rock mass, water saturation and the relationship between the development direction of the structural plane and the observation system; the resistivity data is obtained by the magnetotelluric method, high-density electrical method, resistivity logging and the like.

[0057] In the embodiments, the specific analysis of each model is as follows:

[0058] 1. Saturated connected model

[0059] It refers to the pore space in the rock mass being connected and in a saturated state, which is mainly suitable for the scene that the pore space is mainly composed of medium and low angle fissures and holes developed along the structural plane.

[0060] The conversion relationship between the resistivity and the rock mass quality evaluation index parameters is as follows:

[0061]

[0062] wherein,

[0063] k w —weathering wave velocity ratio;

[0064] k v —integrity coefficient;

[0065] V1—rock skeleton wave velocity, or unfractured fresh intact rock mass wave velocity, m / s;

[0066] V—wave velocity conversion resistivity is the measured wave velocity of rock mass, resistivity conversion wave velocity is conversion wave velocity V h , m / s;

[0067] V1—rock skeleton wave velocity, which is close to the value of unfractured fresh intact rock mass wave velocity V pr , m / s;

[0068] V2—rock pore filler wave velocity, m / s, generally refers to air, water and mud, and the value of the detrital filling material is taken according to the degree of cementation;

[0069] ψ—rock porosity, which refers to the conversion porosity and can be used as an independent achievement. The volume fracture porosity, surface fracture porosity and linear fracture porosity related to the present application.

[0070] The conversion process of ψ is:

[0071]

[0072] ρ—wave velocity conversion resistivity is conversion resistivity ρ h , resistivity conversion wave velocity is the measured resistivity, Ω.m;

[0073] ρ1—rock skeleton resistivity, or unfractured fresh intact rock mass resistivity, Ω.m;

[0074] ρ2—rock pore filler resistivity, Ω.m, and water and mud have a greater impact on resistivity.

[0075] The conversion method of wave velocity and resistivity is:

[0076]

[0077] Of course, if the influence factors such as rock pore space structure, water content, structure surface distribution are not considered in daily life, only a rough equivalent and rapid conversion of resistivity and wave velocity is needed, and the following quick calculation formula can be used:

[0078]

[0079] wherein, V p —measured wave velocity, m / s;

[0080] V pr —fresh intact rock mass resistivity, similar in value to V1, m / s;

[0081] Figure 1 In the figure, V1=6600 m / s, V2=1500 m / s, ρ1=20000 Ω.m, ρ2=20 Ω.m are set according to the measured results, and the comparison results of the actual calculation and the rapid calculation are shown in Figure 1

[0082] It can be seen from Figure 1 that under the saturated connected model, the trend of the simple rapid calculation equation is consistent with the actual calculation result, and the numerical value is close. The simple rapid calculation equation can basically meet the accuracy requirements of most application scenarios.

[0083] 2. Non-saturated connected model

[0084] It refers to the connected pore space in the rock mass, but the pore space is in a non-saturated state, which is mostly applicable to the scenario where the pore space is generally a medium or low angle fracture.

[0085] The conversion relationship between resistivity and rock mass quality evaluation index parameters is:

[0086]

[0087] Among them, the newly appeared variables:

[0088] V3—air wave velocity, m / s;

[0089] S—saturation, the proportion of water-filled pores to total pores.

[0090] In the above formula:

[0091]

[0092] Among them, K l is the linear fracture ratio.

[0093] In general, if the influence factors such as rock pore space structure, structure surface occurrence and test orientation are not considered, only a rough equivalent rapid conversion of resistivity and wave velocity is needed, and the following rapid calculation formula can be used:

[0094]

[0095] Figure 2 In the figure, the comparison results of the actual calculation and the rapid calculation when S=90% are shown. The lower the porosity and the higher the saturation, the closer the rapid calculation method to the actual situation. When the pore saturation is less than 80%, it is no longer recommended to use the rapid calculation method.

[0096] ​3. Non-continuous model of water-saturated

[0097] It refers to the state of water-saturated but non-continuous in the pore space of rock mass. The continuity refers to the electrical continuity of the pore filling, not the continuity of seepage. It is generally believed that the isolated pores, the steeply inclined fractures with the direction perpendicular to the direction of electrical measurement, the pores filled with insulators such as air and plastic rubber are non-continuous pore spaces. The main consideration in rock mass is the steeply inclined fractures with the direction perpendicular to the direction of electrical measurement.

[0098] The conversion relationship between resistivity and rock mass quality evaluation index parameters is:

[0099]

[0100] Among them,

[0101]

[0102] Figure 3 The conversion curve of resistivity and wave velocity of water-saturated non-continuous model, compared with the continuous model, the resistivity of the saturated non-continuous model is more directly related to the porosity, and the conversion of resistivity and wave velocity is more approximately linear in the segmented interval; while the influence of porosity on resistivity of the continuous model is much greater than that of the non-continuous model.

[0103] 4. Mixed model

[0104] First, introduce the non-continuous model without water, such as isolated vertical cracks in concrete that penetrate the concrete, the cracks do not contain water or are filled with plastic, rubber and other materials. When the vertical cracks are measured for resistivity, the current channel is blocked, and the overall resistivity can be considered as +∞.

[0105] For the measurement of wave velocity, there is a limit form. If the measurement direction is consistent with the extension direction of the crack, the wave velocity follows the principle of optimal path, and the measured wave velocity is the matrix wave velocity:

[0106] V = V1

[0107] At this time, no matter how large the porosity is, no matter how the resistivity of the rock mass changes, the measured wave velocity will not change.

[0108] Therefore, for the measurement of resistivity and wave velocity, not only is it related to the continuity and water saturation of the pore space, but also is related to the measurement direction.

[0109] In reality, most of the rocks are mixed models of continuity and non-continuity. The non-water pores can be regarded as insulating channels integrated into the conductive model, which does not contribute to the conductivity of the model. The conductivity of the model mainly depends on the proportion of water-filled cracks.

[0110] The mixed model refers to the model that the connectivity of the pore and fracture space of the rock mass is not limited, the water content is not limited, the development direction of the structural plane is not fixed, and the observation system is not fixed. In this case, the dominant occurrence of the stratum level and the fracture and the proportion of the fracture in different directions need to be considered, the groundwater level and the zonation of the aquifer need to be understood, the water saturation S is segmented and valued according to the elevation and position, and then the solution is obtained. Meanwhile, when the lithology changes, the reference value of the wave velocity and the resistivity of the fresh and complete rock mass should also be valued according to the lithology structure.

[0111] Under the mixed model, the wave motion and the conduction equation of the current satisfy:

[0112]

[0113] wherein,

[0114]

[0115] ρ1 * =ρ1(1-K l2 )+ρ2K l2

[0116] K l2 =ψ2=(1-w)ψ

[0117]

[0118] wherein, w is the proportion of the connectivity fracture, the connectivity of the connectivity guide electricity, in the calculation model, it is considered that the part of the fracture with the strike perpendicular to the measurement direction is the connectivity fracture, which can be obtained by counting the occurrence of the structural plane in the hole according to the geological logging or the digital imaging (hole television) result of the drilling; ψ is the volume fracture rate; ψ1 and ψ2 are the (surface) fracture rates of the saturated connectivity and the non-connectivity fracture respectively; K l1 and K l2 are the linear fracture rates of the saturated connectivity and the non-connectivity linear fracture respectively.

[0119] According to the above equation set, the solution equation set of ψ is derived as follows:

[0120] (1-w)Swρ(ρ1-ρ2)ψ 2 -(ρρ1Sw-ρρ2w+ρ2 2 w-ρ1ρ2w+ρ1ρ2-ρ2 2 )ψ+ρ2(ρ1-ρ)=0

[0121]

[0122] The solution of 1> ψ> 0 is generally as follows:

[0123]

[0124] wherein,

[0125] a = (1 - w)Swp (p1 - p2),

[0126] b = -(p p1 Sw - p p2 w + p2 2 w - p1 p2 w + p1 p2 - p2 2 ),

[0127] c = p2 (p1 - p),

[0128] The solution value of ψ is brought into the above formula, and the value of V can be obtained.

[0129] Figure 4 is Figure 2 and Figure 3 based on the further improvement of the model, the resistivity and wave velocity conversion curve when w = 90%, through the correction of multiple parameters, the conversion wave velocity at this time has basically approached the real wave velocity of the rock mass.

[0130] The above four models are based on the fact that the rock is mainly physically weathered, and the lithological composition is mainly ion-conductive mineral. For more complex models, the basic principle is to correct the values of V1 and p1, and correct the parameters S, w, etc. When the amount of measured data is large and complete, Ψ, S, w, etc. can be used as unknown parameters for inversion calculation, which is generally an underdetermined problem.

[0131] Please refer to Figures 1-8 The embodiment of the present application provides a system for quantitatively evaluating rock mass quality by resistivity, which is used to execute the method for quantitatively evaluating rock mass quality by resistivity as described above.

[0132] For the above technical solution, the present application further provides the following verification examples for further discussion:

[0133] Verification Example 1

[0134] Figure 5 In (a), it is a resistivity logging curve of a siliceous dolomite region, Figure 5 In (b), the converted acoustic wave curve and the measured acoustic logging curve are shown at the same time, and the comparison shows that the fitting curves (9-point smoothing) of the converted acoustic logging curve and the measured acoustic logging curve are very close in change trend and value. In the conversion process, V1 = 7000 m / s, V2 = 1500 m / s, V3 = 340 m / s, p1 = 100000 Ω.m, p2 = 20 Ω.m, S = 96%, and w = 94.68%. Among them, V1 and p1 are mainly derived from the measured results of complete formation, V2, V3 and p2 are derived from empirical values, S is derived from comprehensive inference based on geological data and rock test results, the pore space in the rock mass of the engineering area is mainly developed in the form of fissure and fissure-parallel dissolved pore, and w is the statistical result of the structure surface according to the drilling panoramic digital imaging, and the statistical process is as followsFigure 6 As shown.

[0135] The discrepancy between the converted sonic logging curve and the measured sonic logging curve is due to the failure to take into account the detailed changes in lithological composition, structure, and texture.

[0136] Verification Example 2

[0137] Figure 6 From top to bottom, the figures show the measured resistivity profile, the converted resistivity profile, and the measured wave velocity curves along the borehole. The results show that the converted wave velocity is close to the true wave velocity of the rock mass. The converted results can not only reflect the distribution of the fractured zones in the rock mass, but also quantitatively evaluate the integrity of the rock mass based on the magnitude of the converted wave velocity. Figure 6 The values ​​of background parameters of the medium rock mass and Figure 5 Consistent, w is derived from the statistics of structural surfaces inside the boreholes along the survey line, as shown in Table 1. The survey line azimuth is NW324°, so the steeply dipping fractures near NW324° and SE144° are considered to be electrically non-connected fractures.

[0138] Table 1. Statistical results of borehole fractures along the test route.

[0139] Tilt / ° Tilt Average Tilt Average Number Percentage Tilt / ° Tilt Average Tilt Average Number Percentage 0～10 2.75 58.50 8 2.13％ 180～190 187.50 65.50 2 0.53％ 10～20 18.00 24.00 2 0.53％ 190～200 194.67 78.17 6 1.60％ 20～30 25.79 33.74 19 5.05％ 200～210 203.00 49.00 1 0.27％ 30～40 35.19 28.79 47 12.50％ 210～220 212.00 60.00 1 0.27％ 40～50 44.10 28.46 52 13.83％ 220～230 0.00 0.00 0 0.00％ 50～60 53.24 28.20 25 6.65％ 230～240 235.00 71.67 3 0.80％ 60～70 65.25 25.50 12 3.19％ 240～250 248.50 59.00 4 1.06％ 70～80 74.18 25.45 11 2.93％ 250～260 254.86 60.43 7 1.86％ 80～90 85.92 27.38 13 3.46％ 260～270 266.17 64.83 6 1.60％ 90～100 95.00 23.77 13 3.46％ 270～280 275.77 61.08 13 3.46％ 100～110 104.08 23.31 13 3.46％ 280～290 284.39 59.33 18 4.79％ 110～120 112.80 26.90 20 5.32％ 290～300 295.80 62.40 5 1.33％ 120～130 123.36 38.82 11 2.93％ 300～310 306.13 53.88 8 2.13％ 130～140 134.20 47.20 5 1.33％ 310～320 313.25 53.50 12 3.19％ 140～150 144.00 68.60 5 1.33％ 320～330 323.50 49.83 6 1.60％ 150～160 154.50 75.67 6 1.60％ 330～340 336.25 68.25 4 1.06％ 160～170 164.60 77.40 5 1.33％ 340～350 344.71 47.14 7 1.86％ 170～180 178.00 77.00 1 0.27％ 350～360 353.20 63.00 5 1.33％

[0140] According to GB 50487-2008 Code for Geological Investigation of Water Conservancy and Hydropower Projects (2022 Edition) and GB / T50218-2014 Standard for Classification of Engineering Rock Mass, the weathering degree, integrity degree, and engineering geological classification of dam foundation rock mass are shown in Tables 2-4.

[0141] Table 2. Criteria for Classifying the Weathering Degree of Rock Mass

[0142] Weathering Degree Fresh Slightly Weathered Weakly Weathered Strongly Weathered Fully Weathered Kw 0.9～1 0.8～0.9 0.6～0.8 0.4～0.6 <0.4

[0143] Table 3. Criteria for Classifying the Integrity of Rock Masses

[0144] Completeness Complete More Complete Poorly Complete More Fragmented Fragmented Kv >0.75 0.55～0.75 0.35～0.55 0.15～0.35 <0.15

[0145] Table 4 Classification Standards for Engineering Geology of Hard Rock Dam Foundations

[0146]

[0147] Alternatively, the dynamic elastic modulus E of the rock mass can be calculated by converting wave velocity. d This serves as a reference indicator for evaluating rock mass strength. By comparing the rock mass classification and quality evaluation standards in the regulations and specifications, resistivity and wave velocity can be finely calibrated, thus deriving the electrical property standards for rock mass classification. For example, regarding... Figure 7 In a model where the degree of fracture development is relatively uniform, preliminary simulation calculations show that the relationship between resistivity and rock mass wave velocity and integrity in the engineering area is as follows:

[0148] Resistivity 0-300 ohm.m, wave velocity 1500-2730 m / s, integrity coefficient 0-0.15, broken;

[0149] Resistivity 300-1500 ohm.m, wave velocity 2730-4200 m / s, integrity coefficient 0.15-0.35, relatively broken;

[0150] Resistivity 1500-6000 ohm.m, wave velocity 4200-5200 m / s, integrity coefficient 0.35-0.55, poor integrity;

[0151] Resistivity 6000-23000 ohm.m, wave velocity 5200-6080 m / s, integrity coefficient 0.55-0.75, relatively complete;

[0152] Resistivity > 23000 ohm.m, > 6080 m / s, integrity coefficient 0.75-1, complete.

[0153] The use process of the patent is summarized according to the principles and verification examples of the comprehensive method as shown in Figure 8 .

[0154] In summary, the equivalent conversion of resistivity, wave velocity and integrity coefficient is realized, and the idea and way of quantitatively evaluating rock mass quality by resistivity are constructed and opened up; resistivity becomes a new reliable parameter for rock mass quality evaluation and grade division, and the cost is low, the efficiency is high, and the coverage is wide; the algorithm for inversely calculating the formation porosity and water saturation from the wave velocity and resistivity data is provided, and the geophysical prospecting idea and application mode are expanded; and the calibration and unification method of resistivity measurement anisotropy is provided.

[0155] The alternatives of the present application are as follows:

[0156] The method for quantitatively evaluating rock mass quality by resistivity is that resistivity and wave velocity data are obtained by ground (water) surface testing, hole testing, adit testing or penetration testing of different free surfaces; then the data are classified and arranged according to engineering parts, rock mass structure, underground water level, etc., and data labels are prepared; then background wave velocity, resistivity, rock mass water content and water saturation of rock skeleton and filling material of different lithology, different parts and different elevations are given according to measured data, rock test and experience determination, and the connected porosity of electrical measurement can also be estimated according to the statistical results of structure surface occurrence; then the conversion equations under different models are selected according to the application scene type, the mutual conversion of resistivity and wave velocity is realized, and then the weathering wave velocity ratio, integrity coefficient and dynamic elastic modulus and other parameters of rock mass are calculated according to the converted resistivity; on this basis, the resistivity and wave velocity are scaled and graded according to the requirements of national and industry standard specifications by comprehensively considering various parameters, so that the rock mass quality is quantitatively evaluated and the rock mass is graded.

[0157] The resistivity and wave velocity conversion model is selected according to the application scene, and four conversion models are: saturated connected model, unsaturated connected model, non-connected model (mainly saturated non-connected model) and mixed model. The four models continuously incorporate new variables, gradually become complex, and gradually approach the real formation physical property model. Under normal circumstances, the saturated connected model and the unsaturated connected model can basically meet the effective conversion of most formation resistivity and wave velocity, and the invention also provides a simple approximate rapid calculation method under the two models. When the formation water content is low, the pore connectivity is poor, and the development trend is perpendicular to the direction of the steeply inclined fracture, the mixed model may be used. In fact, the mixed model has covered the other three models, and the calculation process is relatively complex.

[0158] The method and system for quantitatively evaluating rock mass quality proposed in the application are based on the equivalent conversion of resistivity and wave velocity. At the same time, an algorithm is provided for inversely calculating the formation porosity and water saturation using wave velocity and resistivity.

[0159] The method for inferring the proportion of connected porosity in resistivity measurement by surface and borehole structure surface occurrence statistics, and the calibration and unification method of resistivity measurement anisotropy are both proposed for improving the complex model and providing background parameters for the model. These methods can be used together or independently.

[0160] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the application, and not to limit them; although the application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the application.

Claims

1. A method for quantitatively evaluating rock mass quality using resistivity, characterized in that, The method includes the following steps: Obtain resistivity data of the target rock mass; Resistivity data should be categorized and labeled according to engineering location, rock mass structure, and groundwater level. The background wave velocity, resistivity, rock mass water content, and water saturation of the rock skeleton and pore filling material of different lithologies, locations, and elevations were determined, and the electrical interconnection porosity was estimated based on the statistical results of the structural plane attitude. Select the appropriate conversion model based on the application scenario type to convert the resistivity into wave speed; Calculate the rock mass quality evaluation index based on the converted wave velocity; Quantitative evaluation and classification are based on rock mass quality evaluation indicators.

2. The method for quantitatively evaluating rock mass quality using resistivity according to claim 1, characterized in that, The transformation models include saturated connectivity models, unsaturated connectivity models, saturated non-connected models, and hybrid models.

3. The method for quantitatively evaluating rock mass quality using resistivity according to claim 2, characterized in that, The transformation equation for the water-saturated connectivity model is: Where V is the measured wave velocity of the rock mass when converting wave velocity to resistivity, and V is the converted wave velocity V when converting resistivity to wave velocity. h V1 is the wave velocity of the rock skeleton, V2 is the wave velocity of the pore filling material, ρ is the measured resistivity, ρ1 is the resistivity of the rock skeleton, ρ2 is the resistivity of the pore filling material, and ψ is the rock porosity.

4. The method for quantitatively evaluating rock mass quality using resistivity according to claim 2, characterized in that, The transformation equation for the unsaturated connectivity model is: Among them, K l V3 is the linear porosity, S is the saturation degree, which is the proportion of water-bearing pores to total pores, and V3 is the air wave velocity.

5. A method for quantitatively evaluating rock mass quality using resistivity according to claim 2, characterized in that, The transformation equation for the saturated disconnected model is:

6. The method for quantitatively evaluating rock mass quality using resistivity according to claim 2, characterized in that, The transformation equation for the hybrid model is: Among them, V1 * For the corrected wave velocity of the rock skeleton, K l1 The porosity of the saturated connectivity fracture line can be calculated using electrical parameters.

7. The method for quantitatively evaluating rock mass quality using resistivity according to claim 1, characterized in that, The rock mass quality evaluation indicators include rock mass equivalent wave velocity, weathering wave velocity ratio, integrity coefficient, and dynamic elastic modulus.

8. A method for quantitatively evaluating rock mass quality using resistivity according to claim 2, characterized in that, The application scenario type is determined based on the relationship between the connectivity of the rock mass pore space, water saturation, and the development direction of the structural planes and the observation system.

9. A method for quantitatively evaluating rock mass quality using resistivity according to claim 1, characterized in that, The resistivity data were obtained through magnetotelluric methods, high-density electrical resistivity methods, or resistivity logging methods.

10. A system for quantitatively evaluating rock mass quality using resistivity, characterized in that, This method system is used to perform the method for quantitatively evaluating rock mass quality using resistivity as described in any one of claims 1-9.

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