Construction altered granite strength prediction method based on multiple linear regression

Abstract

The invention discloses a tectonic altered granite strength prediction method based on multiple linear regression, and belongs to the technical field of altered rock engineering geology. The method comprises the following steps: step 1, determining altered granite with different alteration degrees from a macroscopic view, and sampling; step 2, performing slice identification, SEM microstructure feature analysis and XRD mineral composition analysis on the rock sample, and performing alteration type classification in combination with macroscopic features; step 3, carrying out a dry density test, a porosity test, a water absorption test and a longitudinal wave velocity test on the collected rock sample; and 4, constructing a multivariate regression-based altered granite uniaxial compressive strength prediction model. According to the method, on the basis of research on the engineering geological characteristics of the altered granite, the multi-parameter indexes are selected and the multi-parameter variable indexes are input, so that the rock mass strength of the altered granite can be comprehensively predicted, and the prediction accuracy can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of altered rock engineering geology, and in particular relates to a method for predicting the strength of tectonic altered granite based on multiple linear regression. Background Art

[0002] Alteration causes the mineral composition and structural structure of rocks to change to varying degrees, thus affecting the physical and mechanical properties of rocks. In particular, clay-altered rocks often constitute major geological defects in engineering rock masses. Granite is easily altered under the action of tectonic dynamics, which leads to changes in the physical and mechanical properties of rock masses. Tectonic dynamic alteration, also known as dynamic metamorphism, is generally defined as a process in which rocks undergo varying degrees of fracture, crushing, or ductile deformation and dynamic recrystallization under the action of tectonic stress. At the same time, due to the frictional heating of faults and the influence of solutions in rocks, it is sometimes accompanied by certain chemical changes, forming some new minerals.

[0003] With the development of transportation and water conservancy projects in the southwest region, a large number of engineering problems such as landslides and large deformations of altered granite have been encountered during engineering construction. Therefore, the research on the engineering properties of altered granite has received more and more attention. Granites with different degrees of alteration have completely different physical and mechanical properties. With the increase of the degree of alteration, the porosity and water absorption of the altered granite increase, the block density and strength decrease, and the mechanical properties decrease exponentially. At present, there are relatively many studies on the engineering properties of hydrothermal altered granite, and it is believed that the degree of clayification is the main factor controlling its physical and mechanical properties; there are relatively few research results on the engineering properties and mechanical property degradation of tectonic altered rocks, which mainly focus on rock mineralogical characteristics, physical and mechanical property testing and engineering response research.

[0004] At present, although many scholars at home and abroad have carried out a lot of work on the engineering problems of altered rocks, there are few studies on the strength prediction methods of tectonic altered granite, and it is difficult to objectively and comprehensively predict the strength of tectonic granite rock mass.

[0005] A Chinese patent with publication number CN202110215980.7 and publication date March 22, 2024 discloses an altered rock, an altered rock strength prediction method based on short-wave infrared spectroscopy technology, by establishing a short-wave infrared spectral curve characteristic of altered rock-uniaxial compressive strength data relationship model, and then based on the model, the strength of the altered rock samples to be tested can be quickly, accurately and conveniently predicted in grades, which can greatly save detection costs and construction cycles, and has important practical significance for large-scale engineering construction in altered rock areas.

[0006] The altered rock strength prediction method disclosed in this patent introduces short-wave infrared spectroscopy technology into the altered rock strength prediction, which solves the problem of single evaluation method and large influence of human factors in the existing technology, and provides a basis for engineering survey, design and management. However, the selection of its prediction index is too single and one-sided, making it difficult to accurately predict the strength of altered rocks. Summary of the invention

[0007] The object of the present invention is to provide a classification method for altered granite.

[0008] Another object of the present invention is to provide a method for constructing a prediction model of the strength of tectonic altered granite based on multiple linear regression.

[0009] Another object of the present invention is to provide a method for predicting the strength of tectonic altered granite based on multiple linear regression.

[0010] According to a method for classifying altered granite according to a specific embodiment of the present invention, the method comprises the following steps:

[0011] Step 1: Obtain rock samples of granite in the study area and determine the degree of granite alteration based on macroscopic characteristics;

[0012] Step 2: Conduct microscopic analysis on the obtained rock samples, including thin section identification, SEM microstructural characteristics analysis and XRD mineral composition analysis;

[0013] Combining the results of macro-analysis and micro-analysis, the alteration type of the altered granite is determined.

[0014] According to the classification method of altered granite in a specific embodiment of the present invention, in step 1, the macroscopic characteristics used include hammer reaction, rock type, rock mass structure and structural plane spacing.

[0015] Preferably, the degree of alteration of granite includes slight alteration, weak alteration, moderate alteration, relatively strong alteration, and strong alteration.

[0016] The above-mentioned classification of alteration degree is a qualitative classification method. Micro-alteration, weak alteration, moderate alteration, strong alteration and strong alteration represent the gradual increase in the degree of alteration, which is common knowledge in this field.

[0017] According to the classification method of altered granite of a specific embodiment of the present invention, the alteration types of altered granite include micro-altered granite, catacladic granite, catacladic granite, granite breccia and granite porphyry.

[0018] Specifically, when the degree of corrosion is microalteration,

[0019] The hammering reaction is a crisp sound and a vibration.

[0020] The rock type is hard rock.

[0021] The spacing between structural surfaces is 1 to 2 groups of structural fissure cuts, with a block size of more than 30 cm.

[0022] The rock mass type is massive-sub-massive.

[0023] Clay mineral content < 10%, and

[0024] The microscopic characteristics are that the mineral grains are complete and tightly interlocked, with a small amount of microcracks developed within the crystals.

[0025] It is judged to be slightly altered granite;

[0026] When the degree of erosion is weak,

[0027] The hammering reaction is a crisp sound and the hammering is fragile.

[0028] The rock type is hard rock.

[0029] The distance between the structural surfaces is cut by more than 2 groups of structural fissures, with a block size of 10 to 30 cm.

[0030] The rock mass type is mosaic structure, and the dislocation of the fracture surface is not obvious.

[0031] Clay mineral content 10-15%,

[0032] The microscopic characteristics are that the mineral particles are broken to a certain extent, mostly serrated transcrystalline cracks, extending mainly in parallel, with close intercrystalline intercalation, and

[0033] It is judged to be fragmented granite;

[0034] When the degree of erosion is moderate,

[0035] The hammering reaction is a crisp sound and the hammering is easy to break.

[0036] The rock type is medium hard rock.

[0037] The spacing between structural planes is that structural fissures are developed, with a block size of 3 to 10 cm.

[0038] The rock mass type is a fragmented structure with a straight fracture surface and slight dislocation.

[0039] Clay mineral content 15-20%,

[0040] The microscopic characteristics are obvious mineral fracture, multi-crystalline microcracks, relatively tight intercalation between grains, no obvious orientation, and significantly increased density, extension and opening of microcracks.

[0041] It is judged to be crushed granite;

[0042] When the degree of erosion is strong,

[0043] The hammering reaction is a dull sound and the hammering is easy to break.

[0044] The rock type is relatively soft rock.

[0045] The spacing between structural planes is that structural fissures are developed in large numbers, with a block size of 1 to 3 cm.

[0046] The rock mass type is a loose structure, with straight cracks and obvious dislocation, and rust-red and dark green scratches can be seen.

[0047] Clay mineral content 20-30%,

[0048] The microscopic characteristics are broken grains, serious contact damage between grains, loose interlocking, a large number of microcracks, and some openings. The broken base is rounded to a certain extent, indicating that the rock has been subjected to obvious shearing and grinding. The sericite alteration of plagioclase is more obvious.

[0049] It is judged to be granite breccia;

[0050] When the degree of erosion is strong,

[0051] The hammering reaction is that it breaks when the hammer is lightly struck.

[0052] The rock type is soft rock.

[0053] The rock mass type is a loose rock mass with a dense block structure from a distance, and a large number of micro cracks can be seen from a close distance.

[0054] Clay mineral content 30-50%,

[0055] The microscopic characteristics are that the grain boundaries are unclear, the mineral particles are ground to less than 10μm, there are a lot of pores, the mineral particles are strongly broken, fine-grained, and mostly rounded, the matrix is ​​diffusely distributed, the content is 50-90%, and

[0056] It is judged to be granite porphyry.

[0057] According to the method for classifying altered granite according to a specific embodiment of the present invention, in step 1, the rock sample of granite collected is a cylindrical sample.

[0058] The present invention also provides a method for constructing a prediction model of the strength of tectonic altered granite based on multiple linear regression, comprising the following steps:

[0059] Step 1: Obtain rock samples of granite in the study area and determine the degree of granite alteration based on macroscopic characteristics;

[0060] Step 2: Conduct microscopic analysis on the obtained rock samples, including thin section identification, SEM microstructural characteristics analysis and XRD mineral composition analysis;

[0061] Combining the results of macroscopic and microscopic analysis, the alteration type of the altered granite can be determined;

[0062] Step 3, performing a uniaxial compressive strength test on the obtained rock sample;

[0063] Step 4: According to the alteration type of the altered granite, the rock samples are respectively subjected to dry density test, porosity test, water absorption test and longitudinal wave velocity test;

[0064] Step 5, using dry density, longitudinal wave velocity, and point load strength as independent variables, a bivariate nonlinear regression analysis is performed to predict the strength of altered granite with different alteration types;

[0065] Step 6: Establish a nonlinear regression model with a power function relationship of four independent variables including dry density, longitudinal wave velocity, and point load intensity to obtain the R w The prediction model is as follows:

[0066] R w =7.768(ρ d 1.514 +w -0.358 +I s(50) 1.4 +v p 1.135 )-41.968;

[0067] ρ d is the dry density, w is the water absorption rate, I s(50) Point load strength, v p is the longitudinal wave velocity.

[0068] According to the method for constructing a prediction model for the strength of tectonic altered granite based on multivariate linear regression according to a specific embodiment of the present invention, in step 1, the macroscopic characteristics used include hammer response, rock type, rock mass structure and structural plane spacing.

[0069] According to the method for constructing a prediction model of the strength of tectonic altered granite based on multivariate linear regression in a specific embodiment of the present invention, the alteration types of altered granite include micro-altered granite, catacladic granite, catacladic granite, granite breccia and granite porphyry.

[0070] According to the method for constructing a prediction model for the strength of tectonic altered granite based on multivariate linear regression in a specific embodiment of the present invention, cylindrical samples of φ50mm×100mm are prepared for micro-altered granite and fragmented granite; cylindrical samples of φ25mm×50mm are prepared for fragmented granite; and cylindrical samples of φ40mm×80mm are prepared for granite porphyry and granite breccia.

[0071] The present invention also provides a prediction model for the strength of tectonic altered granite based on multiple linear regression, comprising the following steps:

[0072] Step 1: Obtain rock samples of granite in the study area and determine the degree of granite alteration based on macroscopic characteristics;

[0073] Step 2: Conduct microscopic analysis on the obtained rock samples, including thin section identification, SEM microstructural characteristics analysis and XRD mineral composition analysis;

[0074] Combining the results of macroscopic and microscopic analysis, the alteration type of the altered granite can be determined;

[0075] Step 3, according to the alteration type of the altered granite, the rock samples are respectively subjected to dry density test, porosity test, water absorption test and longitudinal wave velocity test;

[0076] Step 4: Based on the indicators obtained in step 3, the prediction model of formula (1) is used to calculate the R of tectonic altered granite. w :

[0077] R w =7.768(ρ d 1.514 +w -0.358 +I s(50) 1.4 +v p 1.135 )-41.968(1);

[0078] ρ d is the dry density, w is the water absorption rate, I s(50) Point load strength, v p is the longitudinal wave velocity.

[0079] Beneficial effects of the present invention:

[0080] 1. The present invention combines macroscopic and microscopic analysis and can accurately identify the alteration type of altered granite based on the study of the engineering geological characteristics of altered granite.

[0081] 2. The present invention introduces SEM electron microscope scanning test, XRD ray diffraction and thin section identification test into the classification of altered granite types. Compared with the traditional empirical judgment, it is scientific and objective, and provides a good theoretical basis for in-depth understanding of the correlation between the mechanical characteristics of altered granite and the alteration type.

[0082] 3. The present invention establishes a multi-parameter multiple regression prediction model for altered granite for the first time. By inputting multi-parameter variable indicators, it can make a comprehensive prediction of the rock mass strength of altered granite, which is beneficial to improving the accuracy of judgment.

[0083] 4. The present invention predicts rock mass strength through multiple parameters, making the prediction result more accurate. It is suitable for the prediction research of various types of altered rocks deep underground and has good universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0084] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0085] Figure 1 It is a schematic diagram of the process of the present invention;

[0086] Figure 2 It shows the microscopic characteristics of tectonic altered granite of different alteration types, among which:

[0087] (a) is the microscopic characteristics of micro-altered granite. The left picture shows slight clay alteration of plagioclase; the right picture shows microcracks developed in quartz crystals. Pl = plagioclase; Kfs = potassium feldspar; Qtz = quartz.

[0088] (b) is the microscopic characteristics of fragmented granite. The left picture shows closed, nearly parallel microcracks; the right picture shows microcracks developed along the crystal boundary, and the quartz shows slight wavy disappearance.

[0089] (c) is the microscopic characteristics of cataclasite granite. The left picture shows interlaced shear cracks; the right picture shows deformation lines on quartz grains.

[0090] (d) is the microscopic characteristics of granite breccia. The left picture shows a porphyroblast-matrix fabric; the right picture shows broken plagioclase particles with obvious sericite alteration; Ser = sericite;

[0091] (e) is the microscopic characteristics of granite porphyroblasts / granular rocks. In the left picture, most of the matrix particles are rounded to a certain extent, with a content of more than 50%; in the right picture, pores are well developed;

[0092] Figure 3 is the bivariate nonlinear regression curve of tectonic altered granite S, where

[0093] (a) Display R w and ρ d Relevance;

[0094] (b) Display R w Correlation with w;

[0095] (c) Display R w with I s(50) Relevance;

[0096] (d) Display Rw With v p Relevance. DETAILED DESCRIPTION

[0097] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0098] Example 1

[0099] See also Figure 1 The method for predicting the strength of tectonic altered granite based on multivariate linear regression of the present invention comprises the following steps:

[0100] Step 1: Find the location of the altered granite in the tunnel through on-site geological surveys. First, determine the altered granite with different alteration degrees from a macroscopic perspective based on the macroscopic characteristics of the altered granite on site, and take rock samples of different altered granites at the test points;

[0101] Step 2: Conduct thin section identification, SEM microstructure characteristics analysis, and XRD mineral composition analysis on the rock samples taken; and classify the alteration types based on the macro and micro characteristics;

[0102] Step 3, conducting a uniaxial compressive strength test on the rock samples taken;

[0103] Step 4: Conduct dry density test, porosity test, water absorption test and longitudinal wave velocity test on the rock samples taken;

[0104] Step 5, using dry density, longitudinal wave velocity, and point load strength as independent variables, a bivariate nonlinear regression analysis is performed to predict the strength of altered granite with different alteration types;

[0105] Step 6: Establish a nonlinear regression model of the power function relationship of four independent variables including dry density, longitudinal wave velocity, and point load intensity to obtain the Rw prediction model of tectonic altered granite:

[0106] R w =7.768(ρ d 1.514 +w -0.358 +I s(50) 1.4 +v p 1.135 )-41.968, among which,

[0107] ρ d is the dry density, w is the water absorption rate, Is(50) Point load strength, v p is the longitudinal wave velocity.

[0108] In step 1, the macroscopic characteristics of the altered granite are hammering reaction, rock type, rock mass structure and spacing between structural planes.

[0109] In step 2, a Prisma E environmental scanning electron microscope and a Rigaku Ultima IV diffractometer were used. Some of the selected samples were ground into powder to prepare for X-ray diffraction. The rock samples ground into powder were analyzed for mineral composition, and the altered diabase was analyzed for microstructural characteristics using a scanning electron microscope (SEM).

[0110] In step 3, the test equipment for the uniaxial compressive strength test of rock is a program-controlled servo rock mechanics testing machine, and the rock sample needs to be prepared into a cylindrical sample for measurement. The equipment for the uniaxial compressive strength test is mainly the MTS program-controlled servo rock mechanics testing machine, and the granite fragments / grained rock uses a geotechnical triaxial instrument. φ50mm×100mm cylindrical samples are prepared for micro-altered rocks and fragmented rocks; φ25mm×50mm cylindrical samples are prepared for fragmented rocks, and the sample is prepared by the drilling coring method. φ40mm×80mm cylindrical samples are prepared for granite fragments / grained rock by manual dry cutting and dry grinding. Considering the two test conditions of dryness and saturation, the natural immersion method is used to saturate the samples. In order to prevent the disintegration of the granite fragments / grained rock samples during immersion, a geotechnical saturator is used to assist in saturation.

[0111] In step 4, the point load strength test equipment is a WH-1000 point load meter. Irregular rock blocks are used for testing. The sample is in a natural water-containing state. For extremely soft rock, the natural point load strength is taken as 0.01MPa based on experience. The dry density test adopts the volumetric method and the wax sealing method; the porosity is calculated after the particle density is measured by the pycnometer method; the water absorption rate is determined by the direct immersion method, and the granite porphyry / grained rock is determined by the filter paper wrapping method; the longitudinal wave velocity is tested by the cylindrical specimen penetration method.

[0112] In step 5, a nonlinear regression analysis algorithm is used to establish a saturated uniaxial compressive strength prediction model for altered rock, and the saturated uniaxial compressive strength of rock is predicted by easily measurable indicators such as dry density, longitudinal wave velocity, water absorption, point load strength, and porosity.

[0113] In this method, multivariate nonlinear regression analysis was used to establish an easily measurable index (dry density ρ d , porosity n t , water absorption w, point load strength I s(50) , longitudinal wave velocity v p ) and the saturated uniaxial compressive strength R of tectonic altered granite wBefore building the model, perform data testing, perform collinearity diagnosis on the independent variables, and calculate the independent variable variance inflation factor VIF:

[0114] (VIF) i =(1-R i 2 ) -1 ;

[0115] Among them, R i 2 is the determination coefficient.

[0116] Furthermore, the power function is selected as: R w =a×bX c ; The logarithmic function is selected as: R w =aInX+b;

[0117] The linear function is selected as: R w =aX+b; the exponential function is selected as: R w =a X +b. Among them, a, b, c are constants, and X is the selected prediction indicator.

[0118] Furthermore, according to the results of bivariate nonlinear regression analysis, we can determine the R w And easy to measure index (dry density ρ d , porosity n t , water absorption w, point load strength I s(50) , longitudinal wave velocity v p ), and a multiple linear regression model is established based on the functional relationship.

[0119] This embodiment is the most basic implementation method. Compared with the prior art, it selects multi-parameter indicators based on the study of the engineering geological characteristics of altered granite by combining macro and micro aspects. By inputting multi-parameter variable indicators, it is possible to make a comprehensive prediction of the rock mass strength of the altered granite, which is conducive to improving the prediction accuracy.

[0120] The present invention is described below by taking the altered granite of the Yingliangbao Hydropower Station in Sichuan Province as a specific example.

[0121] The Yingliangbao Hydropower Station project area is located in the Dadu River Basin in the north of the Kangdian axis. The geotectonic structure is located at the junction of the western edge of the Yangtze Platform and the Songpan-Ganzi orogenic belt. The area has experienced multiple large-scale geological tectonic movements from Jinning to the Himalayas, forming a complex fault system, among which the Dadu River fault is the most prominent. The fault zone is nearly SN-trending and consists of multiple discontinuous and parallel secondary faults, which control the overall trend of the tectonic line in the project area.

[0122] The Yingliangbao Hydropower Station is a low-gate water diversion power station project. The water diversion system is distributed on the left bank of the Dadu River and consists of two diversion tunnels with a diameter of 13.5m and a length of 14.4km. The diversion tunnels mainly expose intermediate-acid intrusive rocks of the Jinning-Chengjiang period, and the lithology is various mixed granites, including ostrich granite, biotite monzonite, syenogranite, etc. Affected by multiple tectonic activities, the granite in the project area generally develops tectonic alteration rock belts of different scales and degrees of alteration.

[0123] A total of 123 altered rock belts were revealed during the tunnel excavation process, including 5 large-scale Grade II altered rock belts and 37 Grade III altered rock belts. These altered rock belts have different properties due to different degrees of alteration. The engineering properties of the weakly altered rock belts are slightly weaker than the original rock, while the strength of the strongly altered rock belts is rapidly lost. Their effects on the stability of the tunnel surrounding rock are also significantly different.

[0124] Steps 1 and 2 are based on macroscopic judgments of the site, including hammer response, rock type, rock mass structure and structural plane spacing, and microscopic characteristics including mineral grain integrity, microcracks, clay mineral content ( Figure 2 , Table 1), it is determined that the alteration types of altered granite are divided into five types: micro-altered granite, catacladic granite, catacladic granite, granite breccia, and granite porphyry (Table 2);

[0125] Table 1 Mineral composition of tectonic altered granite Unit: %

[0126]

[0127] Pl = plagioclase; Kfs = potassium feldspar; Qtz = quartz; Ser = sericite; Qtz-quartz; Pl-plagioclase; Kfs-potassium feldspar; Bt-biotite; Kao-kaolinite; Chl-chlorite; Sem-secondary minerals (Kao+Chl).

[0128] Table 2 Methods for determining alteration types

[0129]

[0130]

[0131] Note: Clay mineral content refers to secondary minerals - Kao + Chl.

[0132] Step 3: Conduct a uniaxial compressive strength test on the rock samples taken.

[0133] Uniaxial compressive strength tests were carried out on granites with five degrees of alteration classified above.

[0134] With reference to the Standard for Engineering Rock Test Methods (GB / T 50266-2013), the equipment for uniaxial compressive strength test is mainly the MTS program-controlled servo rock mechanics testing machine, and the geotechnical triaxial apparatus is used for granite porphyry / grained rock.

[0135] Micro-altered rock and fragmented rock were used to prepare φ50mm×100mm cylindrical specimens; fragmented rock was used to prepare φ25mm×50mm cylindrical specimens, and the drilling coring method was used to prepare the specimens. Granite porphyroblasts / fragmented rock were prepared by manual dry cutting and dry grinding to prepare φ40mm×80mm cylindrical specimens. Considering the two test conditions of dryness and saturation, the natural immersion method was used to saturate the specimens. In order to prevent the disintegration of the granite porphyroblasts / fragmented rock specimens during immersion, a geotechnical saturator was used to assist in saturation.

[0136] Step 4: Conduct dry density test, porosity test, water absorption test and longitudinal wave velocity test on rock samples

[0137] The dry density test adopts the volumetric product method and wax sealing method.

[0138] The porosity was calculated after measuring the particle density using the pycnometer method.

[0139] The water absorption rate was determined by direct immersion method, and the granite porphyry / grained rock was determined by filter paper wrapping method.

[0140] The longitudinal wave velocity is tested by the cylindrical specimen penetration method.

[0141] The point load strength test equipment is the WH-1000 point load meter. Irregular rock blocks are used for the test. The samples are in a natural water-containing state. For extremely soft rocks, the natural point load strength is taken as 0.01MPa based on experience.

[0142] The test results of uniaxial compressive strength, point load strength and physical indexes of granite with different alteration types are shown in Table 3.

[0143] Table 3 Physical and mechanical test results of tectonic altered granite

[0144]

[0145]

[0146] Step 5: Construct a prediction model for the uniaxial compressive strength of altered granite based on multivariate regression to predict the strength of altered granite with different alteration types.

[0147] The multivariate nonlinear regression analysis was used to establish an easy-to-measure index (dry density ρ d , porosity n t , water absorption w, point load strength I s(50) , longitudinal wave velocity v p ) and the saturated uniaxial compressive strength R of tectonic altered granitew The correlation relationship.

[0148] Before building the model, data testing is performed, collinearity diagnosis is performed on the independent variables, and the variance inflation factor VIF of the independent variables is calculated:

[0149] (VIF) i =(1-R i 2 ) -1

[0150] Among them, the dry density ρ d The VIF value is 42.54, and the porosity n t The VIF value is 40.73, which is much larger than 10, indicating that there is a serious multicollinearity problem between the two indicators. The reason is that there is no large amount of hydrophilic clay minerals in the tectonic altered granite, and its dry density ρ d The change of depends mainly on the development of pores. Therefore, it is not advisable to select ρ d and n t As an independent variable, considering the dry density ρ d The data is easier to obtain, so the independent variable porosity n is deleted. t , and perform collinearity diagnosis again. At this time, the VIF values ​​of the independent variables are all less than 10.

[0151] A bivariate nonlinear regression analysis prediction model was established. Four models, including linear, logarithmic, power function and exponential function, were used for regression analysis. After a total of 16 regression analyses, the coefficient of determination (R 2 ) was selected as the best fitting model (Table 4, Figure 3 ).

[0152] Table 4 Bivariate nonlinear regression model of tectonic altered granite

[0153]

[0154] From the results of the bivariate nonlinear regression analysis, it can be seen that Rw is a power function relationship with dry density, longitudinal wave velocity, and point load intensity. Therefore, a nonlinear regression model with four independent variables in a power function relationship is established:

[0155] R w =A(ρ d B +w C +I s(50) D +v p E )+F;

[0156] Where A, B, C, D, E, and F are fitting parameters. After 48 iterations, the tectonic altered granite R w Prediction Model:

[0157] R w =7.768(ρ d 1.514 +w -0.358 +I s(50) 1.4 +v p 1.135 )-41.968;

[0158] The coefficient of determination of this model, R 2 The prediction accuracy is 0.977, and the model passes the F test and t test, which can be used to predict the R w .

[0159] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for classifying altered granite, characterized in that: The method comprises the following steps: Step 1: Obtain rock samples of altered granite in the study area and determine the degree of alteration of the rock samples based on their macroscopic characteristics; Step 2: Conduct microscopic analysis on the obtained rock samples, including thin section identification, SEM microstructural characteristics analysis and XRD mineral composition analysis; Combining the macroscopic characteristics with the microscopic analysis results, the alteration type of the altered granite is determined.

2. The method for classifying altered granite according to claim 1, characterized in that: In step 1, macroscopic characteristics including hammer response, rock type, rock mass structure and spacing of structural planes are used to determine the degree of alteration of the rock sample.

3. The method for classifying altered granite according to claim 1, characterized in that: The alteration types of granite include micro-altered granite, fragmented granite, fragmented granite, granite breccia and granite porphyry.

4. The method for classifying altered granite according to claim 1, characterized in that: In step 1, the rock sample of granite collected is a cylindrical sample.

5. A method for constructing a prediction model for the strength of tectonic altered granite based on multivariate linear regression, characterized in that: The method comprises the following steps: Step 1: Obtain rock samples of altered granite in the study area and determine the degree of alteration of the rock samples based on their macroscopic characteristics; Step 2: Conduct microscopic analysis on the obtained rock samples, including thin section identification, SEM microstructural characteristics analysis and XRD mineral composition analysis; Combining macroscopic characteristics with microscopic analysis results, the alteration type of the altered granite is determined; Step 3, performing a uniaxial compressive strength test on the obtained rock sample; Step 4: According to the alteration type of the altered granite, the rock samples are respectively subjected to dry density test, porosity test, water absorption test and longitudinal wave velocity test; Step 5, using dry density, longitudinal wave velocity, and point load strength as independent variables, a bivariate nonlinear regression analysis is performed to predict the strength of altered granite with different alteration types; Step 6: Establish a nonlinear regression model with a power function relationship of four independent variables including dry density, longitudinal wave velocity, and point load intensity to obtain the R w The prediction model is as follows: R w =7.768(ρ d 1.514 +w -0.358 +I s(50) 1.4 +v p 1.135 )-41.968; ρ d is the dry density, w is the water absorption rate, I s(50) Point load strength, v p is the longitudinal wave velocity.

6. The method for constructing a prediction model for the strength of tectonic altered granite based on multiple linear regression according to claim 5, characterized in that: In step 1, macroscopic characteristics including hammer response, rock type, rock mass structure and spacing of structural planes are used to determine the degree of alteration of the rock sample.

7. The method for constructing a prediction model for the strength of tectonic altered granite based on multiple linear regression according to claim 5, characterized in that: The alteration types of altered granite include micro-altered granite, cataclasite granite, fragmented granite, granite breccia and granite porphyry.

8. The method for constructing a prediction model of tectonic alteration granite strength based on multiple linear regression according to claim 7, characterized in that: Cylindrical specimens of φ50mm×100mm were prepared for slightly altered granite and fragmented granite; φ25mm×50mm cylindrical specimens were prepared for fragmented granite; and φ40mm×80mm cylindrical specimens were prepared for granite porphyry and granite breccia.

9. A prediction model for the strength of tectonic altered granite based on multivariate linear regression, characterized in that: The following steps are involved: Step 1: Obtain samples of tectonic altered granite in the study area and perform index detection on the samples; Step 2: Based on the indicators obtained in step 1, the prediction model of formula (1) is used to calculate the R of tectonic altered granite. w : R w =7.768(ρ d 1.514 +w -0.358 +I s(50) 1.4 +v p 1.135 )-41.968(1), among which, ρ d is the dry density, w is the water absorption rate, I s(50) Point load strength, v p is the longitudinal wave velocity.

10. The prediction model of tectonic alteration granite strength based on multivariate linear regression according to claim 9, characterized in that: In step 1, the index tests include dry density, water absorption, point load strength and longitudinal wave velocity.

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