A hard surrounding rock classification method for hydropower projects based on high ground stress reduction coefficient

Abstract

The application discloses a kind of hard surrounding rock classification methods of hydropower engineering based on high ground stress reduction coefficient, according to investigation exploration, underground cavern surrounding rock lithology index, rock wave velocity, and structure surface state, structure surface occurrence, groundwater condition are obtained by test, calculate surrounding rock quality value;Using surrounding rock strength stress ratio S and surrounding rock shear strength ratio W to determine the high ground stress reduction coefficient F of corresponding interval;On the basis of surrounding rock quality value, score reduction correction is carried out, and the surrounding rock category is determined.The application carries out surrounding rock classification for hydropower engineering underground powerhouse under high ground stress condition, provides basis for determining underground powerhouse cavern construction excavation scheme and system support design scheme;By introducing high ground stress reduction coefficient F as additional correction reduction value, replace the simple degradation mode of traditional surrounding rock strength stress ratio, solve the problem that traditional method forced degradation result is too aggressive or conservative.

Description

Technical Field

[0001] This application relates to the fields of hydropower engineering and geological exploration, and in particular to a classification method for hard surrounding rock in hydropower engineering based on a high ground stress reduction coefficient. Background Technology

[0002] With the deepening construction of major hydropower projects in high mountain and canyon areas, the development and utilization of large underground powerhouse caverns are becoming increasingly widespread. High ground stress areas refer to regions with initial ground stress of 20-30 MPa. The excavation and support of underground caverns under high ground stress environments have always been a research hotspot in the field of hydropower engineering.

[0003] The underground cavern construction environment is characterized by "high ground stress and strong unloading effect". The large underground powerhouse cavern group of hydropower projects has the following characteristics: (1) large cross-section, prominent cavern size effect; (2) dense and intertwined cavern group, which affects each other; (3) high sidewalls, and the excavation scheme affects the stability of the surrounding rock; (4) complex geological environment conditions, with large ground stress and complex rock mass structure.

[0004] The properties and condition of the surrounding rock in hydropower projects directly affect the stability and safety of underground caverns, which differs from that of single tunnels or caverns in industries such as transportation and mining. During the construction of underground cavern complexes, various deformation and damage problems inevitably occur due to the influence of geological environmental conditions such as ground stress, rock mass structure, and groundwater, as well as the construction plan.

[0005] The accuracy and adaptability of hard surrounding rock classification methods are fundamental to dynamic control measures for the surrounding rock of large underground powerhouse caverns in hydropower projects, and are important bases for the design and construction of underground caverns. Currently, the main methods used for classifying the surrounding rock of large underground caverns in my country's hydropower projects include the HC method, Q method, RMR method, and BQ method. The way these methods consider in-situ stress factors differs: the HC method uses the ratio of surrounding rock strength to stress as a limiting criterion to consider the influence of in-situ stress.

[0006] Taking the HC method (GB50287-2016) as an example, the HC method, as a national standard, is widely used in the water conservancy and hydropower industry. However, it has the following shortcomings:

[0007] (1) The HC method is not applicable to underground caverns with a burial depth less than twice the cavern diameter or span, and is not applicable to special rocks (expanding rocks, salt rocks), karst caves, or soil caverns. (2) The HC method has certain limitations in classifying rock masses in areas with extremely high stress. (3) When classifying the surrounding rock of large-span caverns, the HC method can also be compared with internationally accepted surrounding rock classifications (such as the Q system classification).

[0008] The Q method considers the influence of in-situ stress through the stress reduction factor (SRF); the RMR method does not directly consider in-situ stress factors; and the BQ method considers the influence of in-situ stress through a stress correction factor. The classification results of RMR, HC, and BQ show a linear relationship under medium- and low-stress conditions, but the correlation coefficients are very low under high-stress conditions. Currently, the classification methods for surrounding rocks under medium- and low-stress conditions are relatively mature, and the obtained classification results are quite satisfactory. However, the classification methods for surrounding rocks under high-stress conditions are not yet mature, and existing surrounding rock classification methods lack adaptability and specificity, and cannot be fully applied to the classification of hard surrounding rocks under high-stress conditions.

[0009] Therefore, it is urgent to propose a new classification method for hard surrounding rock in high-stress areas of hydropower projects, and to systematically study and optimize the surrounding rock classification method to improve the scientificity and reliability of underground cavern design and construction. This has important engineering significance and practical value for ensuring the construction safety of large underground powerhouse caverns in high-stress areas of hydropower projects, guaranteeing the construction period, and improving the economic benefits of the project. Summary of the Invention

[0010] Purpose of the invention: To address the problem that existing rock classification methods are not fully applicable to the classification of hard rock under high ground stress conditions, this invention proposes a classification method for hard rock in hydropower projects based on a high ground stress reduction coefficient. This method determines the category of hard rock in hydropower projects in high ground stress areas, providing a basis for determining the excavation scheme and system support design scheme for the construction of large underground powerhouse caverns.

[0011] Technical solution: This invention provides a classification method for hard surrounding rock in hydropower projects based on a high ground stress reduction coefficient, comprising the following steps:

[0012] (1) The surrounding rock quality value T is calculated based on the judgment basis parameters of the surrounding rock quality of underground caverns in hydropower projects obtained from on-site investigation and exploration and indoor tests. These judgment basis parameters include the saturated uniaxial compressive strength of rock, lithological index, rock wave velocity, as well as the state of structural planes, the occurrence of structural planes, and groundwater conditions.

[0013] (2) Determine the high ground stress reduction coefficient F for the corresponding interval by the strength stress ratio S and the shear strength ratio W of the surrounding rock;

[0014]

[0015] W = σ θ / σ c

[0016] In the formula: R b K represents the saturated uniaxial compressive strength of the rock (MPa). v σ is the rock mass integrity coefficient, which is the square of the ratio of the P-wave velocity of the rock mass to the P-wave velocity of the corresponding rock; mrepresents the maximum principal stress of surrounding rock (MPa), which is replaced by self-weight stress when no measured data is available; W is the shear strength ratio of surrounding rock; σ θ is the maximum tangential stress; σ c is the uniaxial compressive strength of rock.

[0017] (3) On the basis of the surrounding rock quality value T of the underground powerhouse cavern in hydropower projects, score reduction correction is performed to obtain the final rock mass category.

[0018] Wherein, the high geostress reduction coefficient F represents the reduction of surrounding rock grade score for hard rock in high and extremely high geostress areas due to potential rockburst risk. In step (2), the high geostress reduction coefficient F is:

[0019] When the strength-stress ratio S>7 or W<0.3, the value range of F is 0 to -5;

[0020] When the strength-stress ratio 4<S<7 or 0.3<W<0.5, the value range of F is -5 to -15;

[0021] When the strength-stress ratio 2<S<4 or 0.5<W<0.6, the value range of F is -15 to -25;

[0022] When the strength-stress ratio S<2 or 0.6<W<0.7, the value range of F is -25 to -30;

[0023] When the strength-stress ratio S<2 or W>0.7, the value of F is -35.

[0024] In step (3), the surrounding rock classification result is obtained according to the final score T' of the rock mass, and the surrounding rock category is distinguished according to the following discrimination criteria:

[0025] T'=T+F

[0026] Wherein, T represents the surrounding rock quality value, and F represents the high geostress reduction coefficient.

[0027] When T'>85, the surrounding rock category is Class I;

[0028] When 80<T'≤85, the surrounding rock category is Class II, and the surrounding rock subcategory is II 1a ;

[0029] When 75<T'≤80, the surrounding rock category is Class II, and the surrounding rock subcategory is II 1b ;

[0030] When 70<T'≤75, the surrounding rock category is Class II, and the surrounding rock subcategory is II 2a ;

[0031] When 65<T'≤70, the surrounding rock category is Class II, and the surrounding rock subcategory is II2b class;

[0032] When 60<T'≤65, the surrounding rock is of Class III, and the sub-class of surrounding rock is III 1a class;

[0033] When 55<T'≤60, the surrounding rock is of Class III, and the sub-class of surrounding rock is III 1b class;

[0034] When 50<T'≤55, the surrounding rock is of Class III, and the sub-class of surrounding rock is III 2a class;

[0035] When 45<T'≤50, the surrounding rock is of Class III, and the sub-class of surrounding rock is III 2b class;

[0036] When 25<T'≤45, the surrounding rock is of Class IV;

[0037] When T'≤25, the surrounding rock is of Class V.

[0038] In step (1), drilling is performed on the surrounding rock mass of the underground cavern, and core samples are extracted; testing is performed on the core samples and the surrounding rock around the borehole to obtain parameters serving as a basis for judging the rock mass quality of the target underground powerhouse cavern.

[0039] In step (1), the surrounding rock quality value T is calculated based on the HC method specified in the current *Code for Engineering Geological Investigation of Hydropower Projects* (GB50287-2016).

[0040] In step (1), the strength of hard surrounding rock in underground caverns of hydropower projects is represented by the saturated uniaxial compressive strength coefficient of rock.

[0041] In step (2), the value of F, the score of the high ground stress reduction coefficient for surrounding rock with the largest absolute value, is determined by the surrounding rock strength-stress ratio S and the surrounding rock shear stress ratio W.

[0042] In step (2), when the surrounding rock strength ratio S is a value within an interval, the value is obtained according to the linear interpolation method.

[0043] In step (3), multiple sub-classes are divided for surrounding rocks of Class II and Class III, and the sub-class scores are divided into multiple grades.

[0044] In step (3), when the surrounding rock is of Class I, Class IV and Class V, no sub-class is divided.

[0045] Working Principle: This invention introduces a high ground stress reduction factor F as an additional correction reduction value, replacing the simple downgrading method of the traditional surrounding rock strength-stress ratio. This solves the problem that the forced downgrading results of traditional methods are either too aggressive or too conservative. Based on surveys, explorations, and experiments, this invention obtains the saturated uniaxial compressive strength, lithological indicators, rock wave velocity, structural plane state, structural plane occurrence, and groundwater conditions of the surrounding rock of underground caverns to calculate the surrounding rock quality value. It then determines the high ground stress reduction factor F for the corresponding interval using the surrounding rock strength-stress ratio S and the surrounding rock shear strength ratio W. Based on the surrounding rock quality value, a score reduction correction is applied to determine the surrounding rock category. This invention classifies the surrounding rock of underground powerhouses in hydropower projects under high ground stress conditions, providing a basis for determining the excavation scheme and system support design scheme for large underground powerhouse caverns.

[0046] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0047] (1) This invention emphasizes the impact of high ground stress on the potential rockburst safety of hard rock under high ground stress in engineering. It is reflected in the proposed high ground stress reduction coefficient for the reduction of the final score of the surrounding rock grade, so that the sub-class classification results of the surrounding rock classification method under high ground stress conditions are more refined, which is consistent with the actual conditions of engineering, targeted, and more in line with the needs of later research; it fits the on-site construction support treatment, saves costs, and improves efficiency.

[0048] (2) This invention proposes a high ground stress reduction factor to quantify the impact of high ground stress on the surrounding rock classification results. In addition, this method is also applicable to the classification of brittle rock caverns with large spans in high-stress and extremely high-stress areas, and has a wide range of applications. Detailed Implementation

[0049] This invention relates to a classification method for hard surrounding rock in hydropower projects based on high ground stress reduction coefficients, comprising the following steps:

[0050] (1) Based on the parameter acquisition requirements specified in the HC method, determine the parameters for judging the quality of the surrounding rock mass of the target underground powerhouse cavern. Conduct targeted drilling in the area of ​​the surrounding rock mass of the target underground powerhouse cavern and extract core samples. Perform comprehensive and systematic testing on the core samples and the surrounding rock around the borehole to obtain the parameters required for assessing the quality of the rock mass of the target underground powerhouse cavern.

[0051] The parameters used for judgment based on investigation and exploration include the state of the surrounding rock structure of the underground cavern, the orientation of the structure, and the groundwater conditions. The parameters used for judgment based on experiments include the saturated uniaxial compressive strength of the rock, lithological indices, rock wave velocity, state of the structure, orientation of the structure, and groundwater conditions.

[0052] Based on the HC method in the current "Code for Geological Investigation of Hydropower Projects" (GB50287-2016), the rock strength scoring parameters, rock mass integrity scoring parameters, structural plane status scoring parameters, groundwater influence correction coefficient, and the occurrence of the main structural planes are determined according to the rock parameters obtained from the investigation, exploration and test, and the surrounding rock quality value T is calculated.

[0053] (2) Determine the high ground stress reduction coefficient F for the corresponding interval by the strength stress ratio S and the shear strength ratio W of the surrounding rock;

[0054]

[0055] W = σ θ / σ c

[0056] In the formula: R b K represents the saturated uniaxial compressive strength of the rock (MPa). v σ is the rock mass integrity coefficient, which is the square of the ratio of the P-wave velocity of the rock mass to the P-wave velocity of the corresponding rock; m The maximum principal stress of the surrounding rock (MPa) is used as the self-weight stress when no measured data is available.

[0057] In the formula: W is the shear strength ratio of the surrounding rock; σ θ The maximum tangential stress; σ c It represents the uniaxial compressive strength of the rock.

[0058] Wherein: In this example, the high ground stress reduction factor F represents the reduction of the surrounding rock grade score of hard rock in high and extremely high ground stress areas due to the potential rockburst risk.

[0059] The scoring table for the high ground stress reduction factor is shown in Table 1.

[0060] Table 1 Scoring Table for High Ground Stress Reduction Factor F

[0061]

[0062] Specifically, in this embodiment, when the surrounding rock strength-stress ratio S is less than 7, the high ground stress reduction factor F is 0; when the surrounding rock strength-stress ratio S is 7, the high ground stress reduction factor F is -5; when the surrounding rock strength-stress ratio S is 4, the high ground stress reduction factor F is -15; when the surrounding rock strength ratio S is different values ​​within the range, the value is determined by linear interpolation.

[0063] When the surrounding rock shear stress ratio W is less than 0.3, the value of the high ground stress reduction factor F is 0; when the surrounding rock shear stress ratio W is 0.3, the value of the high ground stress reduction factor F is -5; when the surrounding rock shear stress ratio W is 0.5, the value of the high ground stress reduction factor F is -15; when the surrounding rock shear stress ratio is at different values within the interval, the value is obtained according to the linear interpolation method.

[0064] In this example, the high ground stress reduction factor is comprehensively determined by the surrounding rock strength-stress ratio S and the surrounding rock shear stress ratio W, and the value of the surrounding rock high ground stress reduction factor score F with the largest absolute value determined by the two parameters is taken.

[0065] (3) Obtain the surrounding rock classification result according to the final rock mass quality value T'.

[0066] T′=T+F

[0067] Surrounding rock classification is carried out according to the following discrimination criteria:

[0068] When T'>85, the surrounding rock is Class I;

[0069] When 80<T'≤85, the surrounding rock is Class II, and the surrounding rock subclass is 1a Class II;

[0070] When 75<T'≤80, the surrounding rock is Class II, and the surrounding rock subclass is 1b Class II;

[0071] When 70<T'≤75, the surrounding rock is Class II, and the surrounding rock subclass is 2a Class II;

[0072] When 65<T'≤70, the surrounding rock is Class II, and the surrounding rock subclass is 2b Class II;

[0073] When 60<T'≤65, the surrounding rock is Class III, and the surrounding rock subclass is 1a Class III;

[0074] When 55<T'≤60, the surrounding rock is Class III, and the surrounding rock subclass is 1b Class III;

[0075] When 50<T'≤55, the surrounding rock is Class III, and the surrounding rock subclass is 2a Class III;

[0076] When 45<T'≤50, the surrounding rock is Class III, and the surrounding rock subclass is 2b Class III;

[0077] When 25<T'≤45, the surrounding rock is Class IV;

[0078] When T'≤25, the surrounding rock category is Class V.

[0079] Based on the characteristics of hydropower projects, and while ensuring construction safety, a more refined classification of the surrounding rock is adopted to better facilitate support design and control project costs. Surrounding rock of categories II and III is divided into four sub-categories, each with a score of 5 points. For example, if the final rock mass quality value T' is within the range of (60, 65), the surrounding rock grade is III. 1a kind.

[0080] The sub-classification of surrounding rock categories provides a more refined and accurate evaluation of the quality grade of engineering rock masses. However, for Type I surrounding rock, where fissures are not developed, the rock mass is intact, exhibiting a monolithic structure, no rockburst phenomena are observed, the cavern is stable, and no support is required, it is not classified. For Type IV and V surrounding rock, where the surrounding rock conditions are poor, joints and fissures are developed, the rock mass is fractured, and there is no rockburst scenario, it is also not classified.

[0081] In practical applications, this invention is suitable for excavating rock masses with large burial depths or high ground stress, such as underground powerhouses and water diversion tunnels in large hydropower projects like Shuangjiangkou and Jinping, and deep-buried caverns in railway and highway engineering. It is applicable to the excavation of hard rock masses in high-stress areas and the determination of surrounding rock types.

[0082] The underground powerhouse cavern complex on the right bank of the Lancang River GX Hydropower Station, currently under construction, is classified as Class III surrounding rock according to the "Code for Geological Investigation of Hydropower Projects" (GB50287). The main powerhouse, main transformer tunnel, surge tank arch, and upstream and downstream sidewalls are predominantly Class III surrounding rock, with some areas near faults classified as Class IV. Class III rock accounts for 92% of the total, while Class IV rock near small faults accounts for 8%. However, using the modified HC classification method proposed in this invention, the surrounding rock of the caverns is classified as Class II (approximately 3%), Class III (approximately 88%), and Class IV (approximately 9%). These proportions are relatively close, with the difference in the proportion of Class III rock before and after the modification being within 5%. The surrounding rock classified as Class III before the modification, accounting for 3%, is now classified as Class II. 2b Based on the high ground stress reduction factor, the class is classified into level II. 2b The revised classification is more in line with actual engineering conditions and is more targeted; the surrounding rock that was previously classified as Class III and accounted for 1% to 3% was classified as Class IV, which emphasizes the influence of high ground stress on the classification results of the surrounding rock.

Claims

1. A classification method for hard surrounding rock in hydropower projects based on a high ground stress reduction coefficient, characterized in that: Comprising the following steps: (1) Calculating the surrounding rock mass quality value T according to judgment basis parameters of hard surrounding rock quality of underground caverns in hydropower projects obtained through investigation, exploration and laboratory tests, wherein the judgment basis parameters include rock saturated uniaxial compressive strength, lithology index, rock wave velocity, structural plane condition, structural plane occurrence and groundwater condition; (2) Determining the high ground stress reduction coefficient F of the corresponding interval through the surrounding rock strength-stress ratio S and the surrounding rock shear stress ratio W; ； ； In the formula: R b The saturated uniaxial compressive strength of rock is given in MPa and K. v σ is the rock mass integrity coefficient, which is the square of the ratio of the P-wave velocity of the rock mass to the P-wave velocity of the corresponding rock; m σ is the maximum principal stress of the surrounding rock, MPa; when no measured data is available, the self-weight stress is used instead; W is the shear strength ratio of the surrounding rock; σ θ The maximum tangential stress; σ c It represents the uniaxial compressive strength of the rock. In step (2), the high ground stress reduction coefficient F is: When the strength-stress ratio S>7 or W<0.3, the value range of F is 0 to -5; When the strength-stress ratio 4<S<7 or 0.3<W<0.5, the value range of F is -5 to -15; When the strength-stress ratio 2<S<4 or 0.5<W<0.6, the value range of F is -15 to -25; When the strength-stress ratio S<2 or 0.6<W<0.7, the value range of F is -25 to -30; When the strength-stress ratio S<2 or W>0.7, the value of F is -35; Determining the value of the surrounding rock high ground stress reduction coefficient score F with the largest absolute value according to the surrounding rock strength-stress ratio S and the surrounding rock shear stress ratio W; (3) Performing score reduction correction on the basis of the surrounding rock quality value T to obtain the final score T' of the rock mass, and obtaining the final surrounding rock category according to the final score T' of the rock mass; wherein, T'=T+F, T represents the surrounding rock quality value, and F represents the high ground stress reduction coefficient; The process of obtaining the surrounding rock category according to the rock mass score T' is as follows: When T'>85, the surrounding rock category is Class I; When 80 < T' ≤ 85, the surrounding rock category is Class II, and the sub-category of the surrounding rock is Class II. 1a kind; When 75 < T' ≤ 80, the surrounding rock category is Class II, and the sub-category of the surrounding rock is Class II. 1b kind; When 70 < T' ≤ 75, the surrounding rock category is Class II, and the sub-category of the surrounding rock is Class II. 2a kind; When 65 < T' ≤ 70, the surrounding rock category is Class II, and the sub-category of the surrounding rock is Class II. 2b kind; When 60 < T' ≤ 65, the surrounding rock category is Class III, and the sub-category of the surrounding rock is Class III. 1a kind; When 55 < T' ≤ 60, the surrounding rock category is Class III, and the sub-category of the surrounding rock is Class III. 1b kind; When 50 < T' ≤ 55, the surrounding rock category is Class III, and the sub-category of surrounding rock is Class III. 2a kind; When 45 < T' ≤ 50, the surrounding rock category is Class III, and the sub-category of the surrounding rock is Class III. 2b kind; When 25< T '≤45, the surrounding rock category is Class IV; When T '≤25, the surrounding rock category is Class V.

2. The classification method for hard surrounding rock in hydropower projects based on high ground stress reduction coefficient according to claim 1, characterized in that: In step (1), drilling is performed on the surrounding rock mass of the underground cavern, and core samples are extracted; testing is performed on the core samples and the surrounding rock around the borehole to obtain the judgment basis parameters of the rock mass quality of the target underground powerhouse cavern.

3. The classification method for hard surrounding rock in hydropower projects based on high ground stress reduction coefficient according to claim 1, characterized in that: In step (1), the strength of hard surrounding rock of underground caverns in hydropower projects is represented by the rock saturated uniaxial compressive strength coefficient.

4. The classification method for hard surrounding rock in hydropower projects based on high ground stress reduction coefficient according to claim 1, characterized in that: In step (2), when the surrounding rock strength ratio S is a value within the interval, the value is obtained according to the linear interpolation method.

5. The classification method for hard surrounding rock in hydropower projects based on high ground stress reduction coefficient according to claim 1, characterized in that: In step (3), multiple sub-levels are divided for Class II and Class III surrounding rocks, and the sub-level scores are divided into multiple scores.

6. The classification method for hard surrounding rock in hydropower projects based on high ground stress reduction coefficient according to claim 1, characterized in that: In step (3), when the surrounding rock category is Class I, Class IV and Class V, no sub-levels are divided.

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