A method for determining parameters of the rock Hoek-Brown criterion considering the effects of blasting and water-rich disturbance

Abstract

The present invention discloses a method for determining the parameters of the Hoek-Brown criterion for rock, taking into account the effects of blasting and water-rich disturbance. The present invention determines the blasting disturbance factor by evaluating the blasting disturbance level in the excavation disturbance zone, establishes a connection between the water-rich disturbance factor and the water content of the rock by conducting indoor tests on the rock in the excavation disturbance zone, and then combines the above two effects to obtain a new disturbance factor. Furthermore, the Hoek-Brown criterion parameters of rock under the combined effects of different blasting and water-rich disturbance levels can be directly obtained through theoretical calculation. The present invention can be preferably used to predict the deformation of the surrounding rock after water enrichment on the tunnel excavation face, providing a reference for assessing subsequent construction risks.

Description

Technical Field

[0001] The present invention belongs to the field of rock mechanics and engineering technology, and particularly relates to a method for determining rock Hoek-Brown criterion parameters taking into account the effects of blasting and water-rich disturbance. Background Art

[0002] During tunnel blasting and excavation, blast stress waves and excavation unloading inevitably cause disturbances near the tunnel excavation face, forming a disturbance zone. The mechanical properties of the rock within this disturbance zone deteriorate, affecting the stability of the tunnel's surrounding rock. This is exacerbated by tunneling in water-rich strata. The cracks created by blasting can easily connect this tunnel excavation disturbance zone with the water system, altering the water content of the surrounding rock. As the excavation face becomes increasingly water-rich, water-rock interactions further weaken the rock's mechanical properties, increasing construction risks. Therefore, obtaining reliable rock mechanical parameters in areas affected by blasting and water-rich disturbances is crucial for evaluating the stability of surrounding rock, supporting design, and construction in water-involved tunnels.

[0003] Among the many methods for obtaining rock mechanical parameters, the most direct and accurate is conducting large-scale in-situ field tests. However, such tests are associated with long lead times and high costs. Practice has proven that using indoor rock mechanical testing as a benchmark, while comprehensively considering the influence of joints, fissures, and size effects within the rock mass, can meet engineering needs. Among these methods, the Hoek-Brown criterion is the most well-developed, as it comprehensively reflects the influence of rock structural characteristics on rock strength. The key to applying the Hoek-Brown criterion is determining the geological strength index (GSI) and the rock mass disturbance factor (D) within the strength criterion. Therefore, determining the Hoek-Brown criterion parameters for rock that accounts for the effects of blasting and waterlogging is crucial for obtaining rock mechanical parameters within the blasting and waterlogging-affected zones, and thus, is of great significance for studying the stability of surrounding rock after waterlogging at the tunnel excavation face.

[0004] Extensive research has examined the Hoek-Brown criterion parameters for rocks subjected to blasting disturbances. However, when the rock mass is in a water-rich state, the water-rock interaction can also damage the rock's integrity, causing damage and disturbances that can alter the Hoek-Brown criterion parameters (especially for soft rock). Currently, few methods exist for determining the Hoek-Brown criterion parameters for rocks that consider both blasting and water-rich disturbances, necessitating further research. Summary of the Invention

[0005] In order to solve the problems of the existing technology, the present invention provides a method for determining the parameters of the Hoek-Brown criterion for rock considering the influence of blasting and water-rich disturbance. The method can substitute the superimposed influence of blasting and water-rich into the criterion in the form of a composite influencing factor for calculation, and obtain the key parameters of the Hoek-Brown criterion considering the influence of blasting and water-rich disturbance.

[0006] The present invention comprises the following steps:

[0007] Step 1: Observe the disturbed area of ​​the blasting excavation face to assess the level of rock disturbance after blasting;

[0008] Step 2: Collect uniform and complete rock blocks near the disturbed area of ​​the excavation surface and process them into standard rock samples;

[0009] Screening of apparent and longitudinal wave velocities of standard rock samples;

[0010] Obtain the average saturation of rock samples at different immersion times, and then fit the rock sample water absorption curve;

[0011] Step 3: Select multiple groups of saturations based on the water absorption curve of the rock sample; perform wave velocity tests on the rock sample at different saturations to determine the wave velocity value of each standard rock sample at different saturations.

[0012] Step 4: Average the wave velocity values ​​of multiple standard rock samples at the same saturation, and fit the relationship between the average wave velocity and saturation.

[0013] Step 5: Determine the blasting disturbance factor D based on the blasting excavation disturbance assessment in step 1 and the relationship between the average wave velocity of the rock sample and the saturation in step 4. b and rich water disturbance factor D w ;

[0014] Step 6: Based on the strain equivalence principle, define the blasting disturbance as the first influencing factor and the water-rich disturbance as the second influencing factor, and calculate the composite influencing factor D that takes into account the influence of both blasting and water-rich disturbance. s ;

[0015] Step 7: Based on the composite impact factor D s , the rock Hoek-Brown criterion parameters considering the effects of blasting and water-rich disturbance are calculated.

[0016] The present invention has the following beneficial effects: the present invention determines the blasting disturbance factor by evaluating the blasting disturbance level in the excavation disturbance zone, establishes the connection between the water-rich disturbance factor and the water content of the rock by conducting indoor tests on the rock in the excavation disturbance zone, and then combines the above two effects to obtain a new disturbance factor, and then directly obtains the Hoek-Brown criterion parameters of the rock under the combined action of different blasting and water-rich disturbance levels through theoretical calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of the present invention.

[0018] Figure 2 1 is a curve showing the relationship between the average saturation of the rock sample and the soaking time in the embodiment of the present invention.

[0019] Figure 3 This is the relationship between the wave velocity and saturation of the rock sample in the embodiment of the present invention.

[0020] Figure 4 It is a numerical simulation vertical displacement cloud map in an embodiment of the present invention.

[0021] Figure 5 This is a numerical simulation horizontal displacement cloud map in an embodiment of the present invention.

[0022] Figure 6 This is the on-site measurement of tunnel vault subsidence in the embodiment of the present invention.

[0023] Figure 7 This is an on-site measurement of tunnel perimeter convergence in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The specific implementation methods of the present invention are further described below in conjunction with the embodiments and drawings so that those skilled in the art can better understand the present invention.

[0025] The technical solution adopted by the present invention is:

[0026] Step 1: Observe the disturbed area of ​​the blasting excavation face to assess the level of rock disturbance after blasting.

[0027] Step 2: Collect uniform and intact rock blocks near the disturbed area of ​​the excavation surface and process them into standard rock samples; screen the standard rock samples for apparent and longitudinal wave velocity, and select rock samples with small differences in appearance and wave velocity for indoor water immersion tests; obtain the average saturation of rock samples under different immersion times, and then fit the rock sample water absorption curve, and divide the water absorption stages according to the change law.

[0028] Step 3: Select multiple saturation groups based on the rock sample water absorption curve. Perform wave velocity tests on the rock samples at different saturations to determine the wave velocity values ​​of each standard rock sample at different saturations.

[0029] Step 4: Average the velocity values ​​of multiple standard rock samples at the same saturation, and fit the relationship between the average velocity and saturation (i.e., V d -V ud =f(S r ), where V d is the average longitudinal wave velocity of rock at different saturations, in km / s; V udis the average longitudinal wave velocity of rock under dry conditions, in km / s; f(S r ) is a functional relationship related to saturation).

[0030] Step 5: Determine the blasting disturbance factor D according to the blasting excavation disturbance assessment in step 1 and the relationship between the average wave velocity of the rock sample and the saturation in step 4. b and rich water disturbance factor D w .

[0031] Step 6: Based on the strain equivalence principle, define the blasting disturbance as the first influencing factor and the water-rich disturbance as the second influencing factor, and calculate the composite influencing factor D that takes into account the influence of both blasting and water-rich disturbance. s .

[0032] Step 7: Based on the theoretical derivation formula and the composite impact factor D in step 6 s , the rock Hoek-Brown criterion parameters considering the effects of blasting and water-rich disturbance are calculated.

[0033] In some embodiments: the method of observing the disturbed area of ​​the blasting excavation face and evaluating the blasting disturbance level in step 1 includes observing the loosening of the surrounding rock, observing the degree of fragmentation, and conducting on-site drilling wave velocity testing.

[0034] In step 2, water immersion tests should be carried out on no less than three standard rock samples to obtain the average saturation of the rock samples at different immersion times. Then, the water absorption curve of the rock samples is fitted to obtain the change law of saturation at different immersion times, and the water absorption stages are divided according to the change law.

[0035] When selecting saturation groups in step 3, the number of saturation groups should be increased as much as possible. Based on the saturation change trends during different water absorption stages, more significant changes should be selected, while fewer changes should be selected during moderate changes. At least three saturation groups should be selected for the significant changes to ensure a good fit between the subsequent average velocity and saturation. Furthermore, when preparing standard rock samples at different saturations, a water immersion method should be used to achieve the selected saturation.

[0036] In certain embodiments, before averaging the velocity values ​​of multiple standard rock samples at the same saturation, step 4 should include eliminating discrete data and ensuring that at least three valid data points are present for each saturation. If fewer than three valid data points are present for a single selected saturation, the rock sample should be replaced and re-prepared and the velocity measured.

[0037] When fitting the relationship between the average velocity and saturation of the rock sample in step 4, the fitting relationship V should be as high as possible (fitting coefficient greater than 0.9) while ensuring that the fitting correlation coefficient is high. d -V ud =f(S r )concise.

[0038] In some embodiments: Step 5 is as follows:

[0039] First, according to the blasting excavation disturbance assessment in step 1, the blasting disturbance factor D is determined by referring to the blasting disturbance factor empirical table proposed by Hoek and Brown. b .

[0040] Table 1 Blasting disturbance factor D b The value of

[0041]

[0042] Then, the rich water disturbance factor D is determined by theoretical formula derivation. w The relationship between rock modulus and disturbance factor D in the 2002 Hoek-Brown strength criterion is expressed as follows:

[0043]

[0044] Where, E m is the rock deformation modulus, σ ci is the uniaxial compressive strength, GSI geological strength index value;

[0045] Formula (1) takes into account the plasticity of rock. w Replace D, and if the deformation modulus of the rock mass affected by water-rich disturbance is expressed as E d , the unaffected ones are represented by E ud , we can get:

[0046]

[0047] Xia Kaizong, Barton et al. studied the rock deformation modulus E m The relationship between Q and rock mass quality index Q and the relationship between Q and longitudinal wave velocity V is:

[0048]

[0049] Q=10 V-3.5 (4)

[0050] Combining equations (2) to (4), we get:

[0051]

[0052] From step 4, we can know that the fitting formula of the change of rock average wave velocity with saturation is:

[0053] V ud -V d =f(S r) (6)

[0054] Finally, by substituting formula (6) into formula (5), the calculation formula of the rich water disturbance factor can be obtained as follows:

[0055]

[0056] At that time, the water-rich disturbance influence factor D under different water content states can be determined w .

[0057] The specific process of step 6 is as follows:

[0058] According to the strain equivalence principle, the blasting disturbance effect is defined as the first disturbance effect, and the water-rich disturbance effect is defined as the second disturbance effect. Then, the composite influence factor D considering both the blasting and water-rich disturbance effects can be obtained from formula (8): s :

[0059] D s =D b +D w -D b D w (8)

[0060] The specific process of step 7 is as follows:

[0061] If we want to obtain the m in the rock Hoek-Brown criterion considering the influence of blasting and water-rich disturbance, b , s, α three parameters (Formula 9), in addition to the need to obtain the composite impact factor D s In addition, it is also necessary to obtain the geological strength index GSI value and m i Value. Among them, m i The value can be obtained by looking up Table 2 based on the evaluation results of step 1, combined with the rock lithology, strength, structural surface and crushing conditions.

[0062]

[0063] Table 2 m of different rocks i The value of

[0064]

[0065]

[0066] The GSI value can be estimated by the RMR value according to the research of Hashemi et al., as shown in formula (10):

[0067] GSI=RMR 89 -5(RMR 89 >23) (10)

[0068] Where, RMR89 It is the geological classification parameter in the RMR geomechanical classification method.

[0069] According to Barton's RMR 89 The relationship between it and the rock mass quality index Q:

[0070] RMR 89 =15lg Q+50 (11)

[0071] Substituting formula (10) into formula (11), we can obtain:

[0072] GSI=15V-7.5 (12)

[0073] When the rock mass is in water-rich conditions, formula (11) becomes:

[0074] GSI w =15V d -7.5 (13)

[0075] Combining the above formulas, we can get:

[0076]

[0077] If the water content of the rock formation is known, the rock Hoek-Brown criterion parameters considering the effects of blasting and water-rich disturbance can be directly obtained through Equation (14), which can then be used for related design and numerical simulation calculations and evaluations.

[0078] Example:

[0079] This case study involves a mountain highway tunnel construction project located adjacent to a scenic area with abundant water resources. The surrounding rock mass of the tunnel is medium-to-highly weathered crystalline tuff with well-developed joints and fissures. Microscopic analysis indicates that the rock contains a high concentration of clay minerals (which readily swell in the presence of water). Tunnel construction utilizes a double-sidewall pilot tunnel method. During construction of the right side of the tunnel, blasting caused a break in the rock mass at the excavation face, which then became interconnected with the surrounding water system. This resulted in the excavation face becoming increasingly waterlogged and its bearing capacity significantly reduced. To mitigate subsequent construction risks, the Hoek-Brown criterion parameters for the rock were determined and analyzed through numerical simulation and field measurements.

[0080] Step 1: Observe the disturbed area of ​​the blasting excavation face to check the looseness, fragmentation, and joint fissures of the surrounding rock at the tunnel face, conduct necessary borehole wave velocity tests, and comprehensively evaluate the level of rock disturbance after blasting.

[0081] Step 2: Collect uniform, intact rock blocks near the disturbed area of ​​the excavation face and process them into several standard rock samples (50 mm in diameter and 100 mm in height). These standard rock samples were screened for apparent and longitudinal wave velocity. Three rock samples with minimal differences in appearance and velocity were selected for water immersion testing. The average saturation of the rock samples at different immersion times was determined. The water absorption curves of the rock samples were then fitted to determine the saturation variation pattern at different immersion times.

[0082] It can be seen from the water absorption curve that ( Figure 2 ), the rock sample saturation shows a negative exponential growth trend with the immersion time, which can be divided into three stages:

[0083] 1) Stage I: When the immersion time is less than 72 h, the rock sample saturation increases almost linearly with the immersion time;

[0084] 2) Stage II: when the immersion time is between 72 and 240 h, the rock sample saturation increases slowly with the immersion time;

[0085] 3) Stage III: When the immersion time is greater than 240 h, the rock sample saturation almost stops increasing.

[0086] Step 3. According to the saturation change trend of different water absorption stages in step 2, increase the number of saturation groups as much as possible, and select more sections with obvious changes according to the water absorption curve, and appropriately reduce the sections with gentle changes. Therefore, the six groups of water absorption stage I are selected as 0%, 10%, 19%, 27%, 46%, and 60%, the three groups of water absorption stage II are selected as 75%, 85%, and 90%, and one group of water absorption stage III is 100% as the subsequent test saturation. Rock samples with selected saturation are prepared through immersion tests, and wave velocity tests are carried out at different saturations to determine the wave velocity value of each rock sample at different saturations;

[0087] Step 4: Take the average of the wave velocity of 5 standard rock samples at the same saturation (eliminating discrete data) to ensure that there are at least 3 valid data under each saturation. If there are less than 3 valid data under a single group of selected saturation, replace the rock sample and re-prepare and test the wave velocity.

[0088] After fitting, the relationship between the average wave velocity and saturation is a linear relationship, and the relationship is: V d -2.02=-0.2S r (unit is km / s), the fitting correlation coefficient is 0.97 (see Figure 3 ).

[0089] Step 5: Determine the blasting disturbance factor D based on the blasting excavation disturbance assessment in step 1 and the relationship between the average wave velocity and saturation in step 4. b and rich water disturbance factor D w The specific process is as follows:

[0090] First, according to the blasting excavation disturbance assessment in step 1, refer to the blasting disturbance factor empirical table proposed by Hoek and Brown (Table 1) to determine the blasting disturbance factor D b is 0.4;

[0091] Then, the water-rich disturbance factor is determined by theoretical derivation. The relationship between the rock modulus and the disturbance factor D of the Hoek-Brown strength criterion is expressed as follows:

[0092]

[0093] Where, E m is the rock deformation modulus, σ ci is the uniaxial compressive strength, GSI geological strength index value;

[0094] Formula (1) takes into account the plasticity of rock. w Replace D, and if the deformation modulus of the rock mass affected by water-rich disturbance is expressed as E d , the unaffected ones are represented by E ud , we can get:

[0095]

[0096] About rock deformation modulus E m The relationship between Q and rock mass quality index Q and the relationship between Q and longitudinal wave velocity V is:

[0097]

[0098] Q=10 V-3.5 (4)

[0099] Combining equations (2) to (4), we get:

[0100]

[0101] From step 4, we can know that the fitting formula of the change of rock average wave velocity with saturation is:

[0102] V d -V ud =-0.2S r (6)

[0103] Finally, by substituting formula (6) into formula (5), the calculation formula of the rich water disturbance factor can be obtained as follows:

[0104]

[0105] At that time, the water-rich disturbance factor D under different water content states can be determined w .

[0106] Step 6: Based on the strain equivalence principle, define the blasting disturbance as the first influencing factor and the water-rich disturbance as the second influencing factor, and calculate the composite influencing factor D that takes into account the influence of both blasting and water-rich disturbance. s ;

[0107] The specific process in step 6 is as follows:

[0108] According to the strain equivalence principle, the blasting disturbance effect is defined as the first disturbance effect, and the water-rich disturbance effect is defined as the second disturbance effect. Then, the composite influence factor D considering both the blasting and water-rich disturbance effects can be obtained from formula (8): s :

[0109] D s =D b +D w -D b D w (8)

[0110] Step 7: Based on the theoretical derivation formula and the composite impact factor D obtained in step 6, the impact of blasting and water-rich disturbance is considered. s , the rock Hoek-Brown criterion parameters considering the effects of blasting and water-rich disturbance are calculated. The specific process is as follows:

[0111] If we want to obtain the m in the rock Hoek-Brown criterion considering the influence of blasting and water-rich disturbance, b , s, α three parameters (Formula 9), in addition to the need to obtain the composite impact factor D s In addition to the value of the geological strength index GSI value and m i Value. Among them, m i The value is obtained from Table 2 based on the evaluation results of step 1 and comprehensive lithology, strength, etc. i =13.

[0112]

[0113] The GSI value is estimated by the RMR value, as shown in formula (10):

[0114] GSI=RMR 89 -5(RMR 89 >23) (10)

[0115] Where, RMR 89 It is the geological classification parameter in the RMR geomechanical classification method.

[0116] According to Barton's RMR 89 The relationship between it and the rock mass quality index Q:

[0117] RMR89 =15lg Q+50 (11)

[0118] Substituting formula (10) into formula (11), we can obtain:

[0119] GSI=15V-7.5 (12)

[0120] When the rock mass is in water-rich conditions, formula (11) becomes:

[0121] GSI w =15V d -7.5 (13)

[0122] Combining the above formulas, we can get:

[0123]

[0124] If the water content of the rock formation is known, the value of the rock Hoek-Brown criterion parameter considering the influence of blasting and water-rich disturbance can be directly obtained through formula (14), which can then be used for related design and numerical simulation calculation and evaluation.

[0125] It is known that the water saturation of the rock mass at the excavation face is approximately 47%. Based on the relationship between average wave velocity and saturation in step 4, the rock wave velocity at this time is 1.926 km / s. The initial rock wave velocity is 2.02 km / s. Combining formulas (7), (8), (13), and (14), the HB strength criterion parameters considering the effects of blasting and water-rich disturbance can be obtained, as shown in Table 3.

[0126] Table 3 Calculation results of HB strength criterion parameters considering the effects of blasting and water-rich disturbance

[0127]

[0128] The HB strength criterion parameters considering the influence of blasting and water-rich disturbance obtained in the above steps are used in the numerical simulation of tunnel excavation, and the final displacement results ( Figure 4-5 ) and the measured final displacement ( Figure 6-7 ). The comparison results (Table 4) show that the numerical model established using the HB strength criterion parameters that consider the effects of blasting and water-rich disturbance is reliable and can well reflect the deformation of the surrounding rock after water-rich tunnel excavation, providing a reference for assessing subsequent construction risks.

[0129] Table 4 Comparison of numerical simulation results and field measurements

[0130]

Claims

1. A method for determining the parameters of the rock Hoek-Brown criterion considering the effects of blasting and water-rich disturbance, characterized by The method comprises the following steps: Step 1: Observe the disturbed area of ​​the blasting excavation face to assess the level of rock disturbance after blasting; Step 2: Collect uniform and complete rock blocks near the disturbed area of ​​the excavation surface and process them into standard rock samples; Screening of apparent and longitudinal wave velocities of standard rock samples; Obtain the average saturation of rock samples at different immersion times, and then fit the rock sample water absorption curve; Step 3: Select multiple groups of saturations based on the water absorption curve of the rock sample; perform wave velocity tests on the rock sample at different saturations to determine the wave velocity value of each standard rock sample at different saturations; Step 4: average the wave velocity values ​​of multiple standard rock samples at the same saturation, and fit the relationship between the average wave velocity and saturation; Step 5: Determine the blasting disturbance factor D based on the blasting excavation disturbance assessment in step 1 and the relationship between the average wave velocity of the rock sample and the saturation in step 4. b and rich water disturbance factor D w , the rich water disturbance factor D w The calculation is as follows: Where f(S r ) is a functional relationship related to saturation; Step 6: Based on the strain equivalence principle, define the blasting disturbance as the first influencing factor and the water-rich disturbance as the second influencing factor, and calculate the composite influencing factor D that takes into account the influence of both blasting and water-rich disturbance. s ;D s =D b +D w -D b D w ; Step 7: Based on the composite impact factor D s , the rock Hoek-Brown criterion parameters considering both the blasting and water-rich disturbance are calculated as follows: Where V ud is the average longitudinal wave velocity of rock under dry conditions, m b , s and α are the parameters in the Hoek-Brown criterion.

2. The method according to claim 1, wherein: In step 2, water immersion tests should be carried out on no less than three standard rock samples to obtain the average saturation of the rock samples at different immersion times. Then, the water absorption curve of the rock samples is fitted to obtain the change law of saturation at different immersion times, and the water absorption stages are divided according to the change law.

3. The method according to claim 1, wherein: Step 4: Before averaging the velocity values ​​of multiple standard rock samples at the same saturation, discrete data should be eliminated and at least three valid data should be ensured for each group of saturation. If there are less than three valid data for a single group of selected saturation, the rock sample should be replaced and re-prepared and the velocity tested.

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