A method for determining the charge density of a pre-splitting blasting line for a fractured rock mass

Abstract

The present application relates to underground cavern excavation rock mass blasting construction field, disclose a kind of for fissure development rock mass's presplitting blasting line charge density determination method, suppose that the longitudinal wave velocity of rock mass and actual rock uniaxial compressive strength there is certain relationship and carry out fitting, again with the traditional common experience formula in hydropower engineering as foundation, the actual rock compressive strength obtained by rock mass integrity analysis is brought into experience formula, that is, the presplitting blasting charge calculation formula considering rock mass integrity can be obtained, based on field blasting test data is fitted, each parameter in the formula applicable to specific engineering can be obtained.The present application optimizes charge structure according to the segmentation integrity analysis in blast hole, can reduce the damage and destruction influence to the rock mass of reserved area on the basis of ensuring good presplitting blasting seam forming effect, ensures the overall blasting forming effect, and carries out application in the underground powerhouse, surge chamber, main transformer room of hard beam package engineering and achieves very good effect.

Description

Technical Field

[0001] This invention relates to the field of rock blasting construction for underground cavern excavation, specifically to a method for determining the charge density of a pre-splitting blasting line for rock masses with developed fractures. Background Technology

[0002] There are three main methods for determining the linear charge density: theoretical calculation, empirical formula calculation, and engineering analogy. The theoretical calculation method, based on the theory of impact stress waves within the borehole, calculates the optimal linear charge density while ensuring the borehole wall rock mass is not crushed. However, this method is not mature, and the calculated linear charge density has not proven ideal in engineering applications. The engineering analogy method determines the linear charge density by drawing analogies from actual experience data from completed projects, considering topographical and geological conditions, drilling machinery, blasting requirements, and blasting scale. This method also has limitations, requiring a certain degree of similarity between different project conditions during the analogy process. Currently, the empirical formula calculation method is the most effective in engineering applications. Based on the rock's compressive strength, borehole spacing, and borehole diameter, the linear charge density can be calculated. Commonly used empirical formulas include those from the Yangtze River Scientific Research Institute, the Gezhouba Dam Engineering Bureau, and the Wuhan University of Hydraulic and Electric Engineering.

[0003] In existing technology, Central South University proposed "A Deep-Hole Blasting Construction Technology in Fractured Rock Mass" (CN201110131635.1). This invention utilizes borehole imaging technology to first locate information such as the occurrence, development degree, and spatial location of joints and fractures on the inner wall of the blast hole. Then, based on the occurrence of joints and fractures in each blast hole, it optimizes blasting parameters such as the charge quantity, charge structure, explosive roll length, and detonation sequence, thereby improving blasting effect, reducing the impact of fractures on blasting quality, and reducing blasting costs. However, this method, which optimizes charge parameters by acquiring the joint and fracture conditions of each borehole, is cumbersome and costly. Furthermore, it does not establish a relationship between rock mass integrity and charge parameters, and its applicability is limited. Summary of the Invention

[0004] The technical problem this invention aims to solve is that when performing pre-splitting blasting in areas with well-developed fractured rock masses, the charge design is usually based on empirical formulas commonly used in hydropower engineering. However, when the rock mass has well-developed fractures and poor integrity, the traditional empirical formulas for pre-splitting blasting charge design do not take into account the influence of various fracture joints on rock strength. As a result, it is often difficult to achieve good fracture formation in pre-splitting blasting, and it is easy to cause significant damage to the rock mass surrounding the pre-splitting hole, which is not conducive to the formation of the tunnel.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is to provide a method for determining the charge density of pre-splitting blasting lines in fractured rock masses, comprising the following steps:

[0006] Step S1: Rock samples and acoustic testing are performed at multiple blasting points. The compressive strength of the rock is calculated by converting the results of the point load strength test. The longitudinal wave velocities of the rock and rock mass were measured using an acoustic wave detector. The rock mass integrity coefficient was calculated. ;in,

[0007] Rock compressive strength Rock samples were taken at the pre-splitting blasting test sites, and on-site point load strength tests were conducted and converted to obtain the results.

[0008] Longitudinal wave velocity Detection holes were set at the pre-splitting blasting test sites, and the longitudinal wave velocity of the rock mass in the fractured area was measured using an acoustic wave detector equipped with one transmitting transducer and two receiving transducers. The longitudinal wave velocity of a single rock in a fractured region is The calculation formula is as follows:

[0009] (1);

[0010] (2);

[0011] Where S is the installation distance between the two receiving transducers, which is a known quantity;

[0012] t1 is the time difference when the two receiving transducers receive the sound wave in the rock mass environment, and it is a known quantity;

[0013] t2 is the time difference when the two receiving transducers receive the sound wave in a rocky environment, and it is a known quantity;

[0014] Rock mass integrity coefficient The calculation formula is as follows:

[0015] (3);

[0016] Step S2, based on the existing known rock P-wave velocities The relationship between the rock's compressive strength P and the rock's compressive strength P

[0017] (4);

[0018] Assuming the P-wave velocity of a rock mass with developed fractures Actual compressive strength of rocks in fractured areas The same mathematical pattern exists between them as in equation (4), thus,

[0019] =A (5);

[0020] In equation (5), A and T are constant coefficients, which are the data sets recorded in step S1. Substituting into equation (5), and simultaneously based on the data group in step S1... Directly fitting the longitudinal wave velocity of the rock mass With the actual compressive strength of the rock The curve is obtained by formula (5), and the values ​​of A and T are obtained from it.

[0021] Step S3, the charge density Q of the push wire is related to the rock compressive strength P and the rock mass integrity coefficient. Actual compressive strength of rocks with well-developed fissures The relationship between constant coefficients A and T;

[0022] By combining equations (3), (4), and (5), we can obtain: (6); Based on existing empirical formulas, the following can be used for rock masses with compressive strength between 20 and 200 MPa: (7); Combining equations (6) and (7), we can obtain:

[0023] (8);

[0024] In equations (7) and (8), a is the borehole spacing, which is a fixed known quantity;

[0025] Equation (8) is the rock mass integrity coefficient. The relationship between the linear charge density Q and the charge density Q, where A and T are the values ​​of A and T obtained in step S2;

[0026] Step S4: Finally, acoustic wave detection is performed at the blasting point to obtain the longitudinal wave velocity of the rock mass in the blasting area. and rock longitudinal wave velocity ,according to Substituting the calculated rock compressive strength value into the formula and using the longitudinal wave velocity of the rock mass... and rock longitudinal wave velocity The rock mass integrity coefficient is obtained and substituted into the formula. This allows us to determine the linear charge density Q, which takes into account the integrity of the rock mass in areas with well-developed rock fissures.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] The measurement method proposed in this invention is based on previous research. It assumes that there is a certain relationship between the longitudinal wave velocity of the rock mass and the actual uniaxial compressive strength of the rock, and fits the relationship. Then, based on the commonly used empirical formulas in hydropower engineering, the actual rock compressive strength obtained through rock mass integrity analysis is substituted into the empirical formula to obtain the calculation formula for pre-splitting explosive charge considering rock mass integrity. By fitting the data from field blasting tests, the parameters in the formula applicable to specific projects can be obtained. Blasting design and numerical simulation based on this formula ensure that the formula has high reliability.

[0029] Based on the results of field blasting experiments, and combined with the charge density of the pre-splitting blasting line and the corresponding rock mass integrity coefficient, a calculation formula for pre-splitting blasting charge considering rock mass integrity was obtained, providing a reference formula for determining the charge parameters of rock masses in fractured areas.

[0030] Further optimization of the charge structure based on the integrity analysis of the segments within the blast holes allows for the design of pre-splitting blasting parameters for underground caverns in fractured rock masses. This approach reduces damage to the rock mass in the reserved area while ensuring good pre-splitting blasting results, thus guaranteeing the overall blasting formation effect. It has been successfully applied in the underground powerhouse, pressure regulating chamber, and main transformer room of the Hard Beam Bao project. Attached Figure Description

[0031] Figure 1 The results show the experimental results of the integrity coefficient of the underground powerhouse rock mass and the corresponding pre-splitting blasting charge parameters in a certain embodiment.

[0032] Figure 2 According to Figure 1 The experimental results yielded a fitting curve between the longitudinal wave velocity of the rock mass and the actual compressive strength of the rock.

[0033] Figure 3 This is a schematic diagram of single-hole acoustic wave detection. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, so as to provide a better understanding of the concept of the present invention, the technical problem solved, the technical features constituting the technical solution, and the technical effects brought about.

[0035] A method for determining the charge density of a pre-splitting blasting line used in fractured rock masses includes the following steps:

[0036] Step S1: Rock samples and acoustic testing are performed at multiple blasting points. The compressive strength of the rock is calculated by converting the results of the point load strength test. The longitudinal wave velocities of the rock and rock mass were measured using an acoustic wave detector. The rock mass integrity coefficient was calculated. ,like Figure 3 As shown; where,

[0037] Rock compressive strength Rock samples were taken at the pre-splitting blasting test sites, and on-site point load strength tests were conducted and converted to obtain the results.

[0038] Longitudinal wave velocity Detection holes were set at the pre-splitting blasting test sites, and the longitudinal wave velocity of the rock mass in the fractured area was measured using an acoustic wave detector equipped with one transmitting transducer and two receiving transducers. The longitudinal wave velocity of a single rock in a fractured region is The calculation formula is as follows:

[0039] (1);

[0040] (2);

[0041] Where S is the installation distance between the two receiving transducers, which is a known quantity;

[0042] t1 is the time difference when the two receiving transducers receive the sound wave in the rock mass environment, and it is a known quantity;

[0043] t2 is the time difference when the two receiving transducers receive the sound wave in a rocky environment, and it is a known quantity;

[0044] Rock mass integrity coefficient The calculation formula is as follows:

[0045] (3);

[0046] Step S2, based on the existing known rock P-wave velocities The relationship between the rock's compressive strength P and the rock's compressive strength P is as follows:

[0047] (4);

[0048] Assuming the P-wave velocity of a rock mass with developed fractures Actual compressive strength of rocks in fractured areas The same mathematical pattern exists between them as in equation (4), thus,

[0049] =A (5);

[0050] In equation (5), A and T are constant coefficients, which are the data sets recorded in step S1. Substituting into equation (5), and simultaneously based on the data group in step S1... Directly fitting the longitudinal wave velocity of the rock mass With the actual compressive strength of the rock The curve is obtained by formula (5), and the values ​​of A and T are obtained from it.

[0051] Step S3, the charge density Q of the push wire is related to the rock compressive strength P and the rock mass integrity coefficient. Actual compressive strength of rocks with well-developed fissures The relationship between constant coefficients A and T;

[0052] By combining equations (3), (4), and (5), we can obtain: (6);

[0053] Based on existing empirical formulas, the following can be used for rock masses with compressive strength between 20 and 200 MPa: (7); Combining equations (6) and (7), we can obtain: (8);

[0054] In equations (7) and (8), a is the borehole spacing, which is a fixed known quantity;

[0055] Equation (8) is the rock mass integrity coefficient. The relationship between the linear charge density Q and the charge density Q, where A and T are the values ​​of A and T obtained in step S2;

[0056] Step S4: Finally, acoustic wave detection is performed at the blasting point to obtain the longitudinal wave velocity of the rock mass in the blasting area. and rock longitudinal wave velocity ,according to Substituting the calculated rock compressive strength value into the formula and using the longitudinal wave velocity of the rock mass... and rock longitudinal wave velocity The rock mass integrity coefficient is obtained and substituted into the formula. This allows us to determine the linear charge density Q, which takes into account the integrity of the rock mass in areas with well-developed rock fissures.

[0057] In practical applications, after obtaining A and T, the relationship between the actual rock compressive strength and the rock mass integrity coefficient of the corresponding project can also be obtained and substituted into equation (6). You can get it immediately.

[0058] In a certain rigid beam-supported engineering project of this invention, six point load pressure tests and acoustic wave detection tests were conducted on the third floor of the underground powerhouse. Based on the acoustic wave detection and integrity evaluation of the rock mass, the rock mass integrity coefficient at the corresponding location was calculated. Specific data are as follows: Figure 1 As shown.

[0059] Among them, according to equation (5), combined with Figure 1 The data in the figure yielded the following fitted curve: Figure 2 As shown, its expression is: The correlation coefficient R of the fitted curve 2 The value is 0.97586, indicating that the curve fits well. Where A = 606.2 and T = 0.5.

[0060] Substituting the values ​​of A and T into equation (8), we derive the calculation formula for pre-splitting explosive charges, considering rock mass integrity, applicable to the third layer of the underground powerhouse in the hard beam enclosure project:

[0061] ;

[0062] According to the indoor acoustic wave test, the longitudinal wave velocity of the fresh rock in the third layer of the underground plant is 6.06 km / s. The longitudinal wave velocity of the rock is 6.06 km / s, and the uniaxial compressive strength is P = 146.3 MPa (from equation (4)). Figure 1 Substituting the parameters (obtained) and the borehole spacing of 0.7m into the above formula, we can obtain the complete formula for pre-splitting blasting charge considering the rock mass integrity coefficient:

[0063] ;

[0064] At the same time, the relationship between the actual rock compressive strength and the rock mass integrity coefficient can also be obtained from equations (7) and (8):

[0065] .

[0066] Under the same conditions in subsequent construction, the explosive loading parameters calculated above can be used for loading.

[0067] The design method for pre-splitting blasting parameters and charge structure, taking into account the integrity of the rock mass, was applied to the underground caverns of the rigid beam enclosure project. The pre-splitting blasting achieved good fracture formation. Although there were areas with severe local crack cutting and no obvious pre-splitting holes, the damage to the rock mass in the rock anchor beam area was reduced while ensuring the basic formation of the protective layer sidewalls, thus guaranteeing the formation of the rock anchor beam platform. The subsequent excavation and formation rate of the rock anchor beam platform reached 94.2%, with no remaining unexploded rock on the wall surface. The average over-excavation was 7.5 cm, and the average half-hole rate was over 94.8%. The half-hole rate of pre-splitting blasting in the sidewall rock mass of the surge tank and main transformer room basically reached 100%, achieving excellent pre-splitting blasting results and meeting the project requirements.

[0068] In step S2, the method for rock mass acoustic detection is as follows: a single-hole acoustic detection method is adopted, and an acoustic detector and a probe with one transmitting transducer and two receiving transducers are inserted into the detection hole. The probe is moved to different depths, the transmitting transducer emits acoustic waves, and the two receiving transducers receive acoustic waves. The longitudinal wave velocity at that location is obtained based on the acoustic wave propagation time, the transducer installation spacing, and the time of receiving the acoustic waves.

[0069] The terms "connection" and "fixing" appearing in the description of this invention can refer to fixed connection, processing and forming, welding, or mechanical connection. The specific meaning of the above terms in this invention should be understood according to the specific circumstances.

[0070] In the description of this invention, the terms "center," "upper," "lower," "horizontal," "inner," and "outer," etc., are used only to indicate the orientation or positional relationship for the convenience of describing this invention and to simplify the description, and do not indicate or imply a specific orientation that the device or element referred to must have, and therefore should not be construed as a limitation of this invention.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining the charge density of a pre-splitting blasting line used in fractured rock masses, characterized in that, Includes the following steps: Step S1: Rock samples and acoustic testing are performed at multiple blasting points. The compressive strength of the rock is calculated by converting the results of the point load strength test. The longitudinal wave velocities of the rock and rock mass were measured using an acoustic wave detector. The rock mass integrity coefficient was calculated. ;in, Rock compressive strength Rock samples were taken at the pre-splitting blasting test sites, and on-site point load strength tests were conducted and converted to obtain the results. Longitudinal wave velocity Detection holes were set at the pre-splitting blasting test sites, and the longitudinal wave velocity of the rock mass in the fractured area was measured using an acoustic wave detector equipped with one transmitting transducer and two receiving transducers. The longitudinal wave velocity of a single rock in a fractured region is The calculation formula is as follows: （1）； （2）； Where S is the installation distance between the two receiving transducers, which is a known quantity; t1 is the time difference when the two receiving transducers receive the sound wave in the rock mass environment, and it is a known quantity; t2 is the time difference when the two receiving transducers receive the sound wave in a rocky environment, and it is a known quantity; Rock mass integrity coefficient The calculation formula is as follows: （3）； Step S2, based on the existing known rock P-wave velocities The relationship between the rock's compressive strength P and the rock's compressive strength P is as follows: （4）； Assuming the P-wave velocity of a rock mass with developed fractures Actual compressive strength of rocks in fractured areas The same mathematical pattern exists between them as in equation (4), yielding... =A （5）； In equation (5), A and T are constant coefficients, which are the data sets recorded in step S1. Substituting into equation (5), and simultaneously based on the data group in step S1... Directly fitting the longitudinal wave velocity of the rock mass With the actual compressive strength of the rock The curve is obtained by formula (5), and the values ​​of A and T are obtained from it. Step S3, the charge density Q of the push wire is related to the rock compressive strength P and the rock mass integrity coefficient. Actual compressive strength of rocks with well-developed fissures The relationship between constant coefficients A and T; By combining equations (3), (4), and (5), we can obtain: （6）； Based on existing empirical formulas, the following can be used for rock masses with compressive strength between 20 and 200 MPa: （7）； Combining equations (6) and (7), we can obtain: （8）； In equations (7) and (8), a is the borehole spacing, which is a fixed known quantity; Equation (8) is the rock mass integrity coefficient. The relationship between the linear charge density Q and the charge density Q, where A and T are the values ​​of A and T obtained in step S2; Step S4: Finally, acoustic wave detection is performed at the blasting point to obtain the longitudinal wave velocity of the rock mass in the blasting area. and rock longitudinal wave velocity ,according to Substituting the calculated rock compressive strength value into the formula and using the longitudinal wave velocity of the rock mass... and rock longitudinal wave velocity The rock mass integrity coefficient is obtained and substituted into the formula. This allows us to determine the linear charge density Q, which takes into account the integrity of the rock mass in areas with well-developed rock fissures.

Images