A method for determining hole spacing in chamber blasting considering ground stress unloading effect

Abstract

The application provides a method for determining the hole spacing of chamber blasting caving considering the effect of ground stress unloading, measures and records the original ground stress and rock mechanics parameters of the underground chamber blasting excavation engineering; establishes a stress analysis model with a slotting cavity according to the measured ground stress and caving blasting pre-design; carries out ground stress unloading calculation on the stress analysis model and establishes a ground stress redistribution model; constructs an explosion stress wave propagation model according to the rock material parameters and explosive material parameters and calculates the explosion stress superposition field between adjacent caving holes; calculates the maximum hole spacing of adjacent holes of caving blasting producing through cracks according to the rock strength fracture criterion. Through the calculation and analysis of the maximum effective distance of hole cracking under the coupling effect of ground stress redistribution and explosion load, the hole spacing design is avoided to be too small to cause large surrounding rock damage, the hole spacing design is avoided to be too large to be insufficient to form through cracks between holes, and the expected blasting excavation effect cannot be achieved.

Description

Technical Field

[0001] This invention relates to the field of rock blasting engineering technology, and in particular to a method for determining the spacing of collapse holes in tunnel blasting that takes into account the effect of ground stress unloading. Background Technology

[0002] In high-stress rock mass collapse blasting projects, the rational design of hole spacing is a core challenge to ensure both blasting effectiveness and construction safety. This is particularly relevant in high-stress environments (typically...). s Hmax >30MPa), the cavity formed by the slotting blast will trigger the unloading of ground stress, which in turn induces stress redistribution, resulting in a significant non-uniformity of the surrounding rock stress field (such as stress release in the plastic zone reaching 40%-70% and stress concentration coefficient in the elastic zone rising to 1.5-2.0). Traditional design methods are mostly based on static assumptions or simplified mechanical models, making it difficult to accurately quantify the coupling effect of dynamic adjustment of ground stress and superposition of blast stress waves.

[0003] In existing technologies, such as patent CN117329941A, the arrangement of boreholes is optimized through multi-stage slotting, but the effect of ground stress on crack propagation suppression is not quantified. Although this method simplifies the design process, it does not consider the stress redistribution caused by ground stress unloading and its impact on crack propagation paths, especially at the boundary between the plastic and elastic zones, where the calculation of crack driving force deviates significantly. Patent CN119514255A calculates the range of the crushing and fractured zones of the rock based on crack propagation characteristics under a coupled model, and then uses MATLAB to establish a crack propagation analysis model to predict the crack propagation path, thereby determining the borehole arrangement. This method requires personnel to first perform coupled stress field analysis, then perform micro-element point stress analysis, and simultaneously calculate the radii of the crushing and fractured zones. After that, MATLAB programming is used to predict and calculate the crack propagation path to finally determine the borehole arrangement. The process is relatively complex and requires a certain level of technical expertise, making it inconvenient for on-site personnel to make adjustments. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a method for determining the spacing of blasting collapse holes in caverns that takes into account the effect of ground stress unloading. By calculating and analyzing the maximum effective distance for crack formation between holes under the coupled effect of ground stress redistribution and explosive load, this method avoids excessively small hole spacing, which would cause significant damage to the surrounding rock, and excessively large hole spacing, which would not be sufficient to form through cracks between holes and fail to achieve the expected blasting excavation effect. This method is particularly suitable for optimizing the design of blasting collapse hole spacing in caverns in high ground stress environments such as water conservancy, mining, and transportation. By quantifying the coupling effect of stress redistribution caused by ground stress unloading and the superposition of explosive stress, the maximum effective distance for crack propagation between holes is accurately calculated, guiding the design and layout of blasting holes.

[0005] To achieve the aforementioned technical features, the objective of this invention is as follows: a method for determining the spacing of blasting collapse holes in a tunnel considering the effect of ground stress unloading, characterized in that...

[0006] Step 1: Measure and record the original geostress and rock mechanics parameters of the underground cavern blasting excavation project.

[0007] Step 2: Establish a stress analysis model with cut-out cavities based on the measured ground stress and the pre-design of the collapse blasting.

[0008] Step 3: Perform stress unloading calculation on the slotted cavity using the stress analysis model, and establish a stress redistribution model.

[0009] Step 4: Construct an explosion stress wave propagation model based on rock material parameters and explosive material parameters, and calculate the explosion stress superposition field between adjacent collapse holes;

[0010] Step 5: Calculate the maximum hole spacing between adjacent holes that produce through-cracks in the rock collapse blasting according to the rock strength fracture criterion.

[0011] Preferably, in step 1, the original in-situ stress of the surrounding rock is measured, and the measured original in-situ stress in the vertical direction is set as... s 竖 The measured original horizontal ground stress is set as s 平 ;

[0012] The density of the rock was obtained by conducting material parameter calibration tests on the rock samples from the field. r 岩 Longitudinal wave velocity of rocks C 岩 Poisson's ratio of rocks m 岩 Dynamic tensile strength of rock s t ;

[0013] The density of the explosives used r 炸 The detonation velocity of explosives C 炸 Insulation index c .

[0014] Preferably, in step 1, the lateral pressure coefficient is calculated based on the original ground stress. X ;

[0015] (1)

[0016] Preferably, the radius of the cut cavity generated by the on-site cut blasting in step 2 is set to a The distance between the center of the blast hole in the collapse zone and the center of the cut cavity is set asb The borehole radius is set to r The spacing between the caving holes is set to s .

[0017] Preferably, in step 3, a polar coordinate system is established with the center of the grouted cavity as the origin and the horizontal direction as the polar axis. The radial stress on the rock element at the center of the line connecting any collapse hole is calculated according to formula (2). s 径 Size is calculated using the following formula:

[0018] (2)

[0019] in, i Polar angles are different angles in a polar coordinate system established with the radius in the horizontal direction, which is the origin of the slotted cavity, as the polar axis.

[0020] Preferably, in step 4, the explosive load generated on the borehole wall by the explosive is first calculated according to formula (3). P 爆 :

[0021] (3)

[0022] Collapse hole at any distance L The rock element at that location is subjected to radial compressive stress by a single borehole. s j for:

[0023] (4)

[0024] Collapse hole at any distance L The rock element at that location is subjected to circumferential tensile stress by a single borehole. s h for:

[0025] (5)

[0026] In the formula, α The attenuation coefficient is... l The lateral stress coefficient is... l = m a / (1- m a ),and m a =0.8 m 岩 ;

[0027] The rock element in the middle of the line connecting any two adjacent collapse holes is subjected to the combined action of the two adjacent boreholes. Therefore, considering the superposition effect of the explosion stress, the radial compressive stress on the rock element between the holes is calculated. s j1 and circumferential tensile stress s h1 ;

[0028] (6)

[0029] The formation of inter-pore cracks in the collapse hole is influenced by the circumferential tensile stress generated by the explosion. s h1 And the radial stress generated by the redistribution of ground stress is s 径 The combined effect of these factors controls the formation of cracks, and the basis for judging the occurrence of cracks is formula (7):

[0030] (7)

[0031] Preferably, in step 5, the hole spacing s of the through cracks generated in the collapse blasting is obtained according to the criterion formula (7) and in combination with formulas (1) to (6):

[0032] (8)

[0033] Preferably, the method further includes step 6, which calculates the maximum hole spacing that satisfies the formation of a through crack in the collapse hole based on equation (8) given in step 5 and the physical parameter data measured on site.

[0034] The present invention has the following beneficial effects:

[0035] 1. Traditional methods, by neglecting the dynamic adjustment of in-situ stress and the superposition effect of stress waves, often result in excessively large borehole spacing (preventing the formation of through-cracks). This invention quantifies in-situ stress unloading and its redistribution, determining the coupling effect of stress redistribution and the superposition of explosive stress, thereby increasing the probability of through-crack formation between adjacent collapse boreholes. Based on the coupling criterion of dynamic tensile strength of rock and composite stress field, and by introducing a dynamic redistribution model of in-situ stress, the prediction error of borehole spacing is reduced.

[0036] 2. This invention supports real-time parameter adjustment, with a single-condition calculation time of ≤20 minutes (while numerical simulation methods take longer), and can quickly respond to changes in the stress field at the working face, making it suitable for complex engineering scenarios such as deep mines and long tunnels.

[0037] The present invention has the following advantages:

[0038] For the first time, the stress redistribution field of the slotted cavity is dynamically coupled with the explosion stress wave propagation model, breaking through the technical limitations of traditional static assumptions and decoupling analysis, and realizing the accurate simulation of the time-varying process of the stress field. A quantitative index system including key parameters such as the dynamic tensile strength of rock, the anisotropy coefficient of ground stress, and the attenuation coefficient of explosion load is established. This method establishes a complete calculation system, from the strength of the rock itself to the effect of hole spacing on the formation and penetration of cracks in the rock mass after blasting, taking into account the parameter data required for each link, ensuring that all key information can be accurately calculated and applied during the design. By constructing a closed-loop calculation framework through formulas (1) to (8), the deterministic solution of hole spacing is realized, reducing the problem of hole spacing being too large due to subjective errors, which prevents the generation of through cracks between holes. Attached Figure Description

[0039] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0040] Figure 1 This is a design drawing of the layout of blast holes for collapse blasting under high ground stress according to the present invention.

[0041] Figure 2 This is a diagram of the stress redistribution analysis model caused by the slotting cavity in this invention.

[0042] Figure 3 This is a diagram of the explosion load and ground stress coupling analysis model of the present invention.

[0043] Figure 4 This is a flowchart illustrating the implementation steps of the present invention.

[0044] Figure 5 This is a comparison diagram of the explosion effects of different methods of the present invention.

[0045] Legend: 1-surrounding rock, 2-cut cavity, 3-collapse hole, 4-original horizontal stress, 5-original vertical stress, 6-radius of cut cavity, 7-distance between the center of the pre-set collapse zone blast hole and the center of the cut cavity, 8-rock element, 9-explosive, 10-hole spacing, 11-radial stress, 12-circumferential tensile stress, 13-polar axis. Detailed Implementation

[0046] The following is in conjunction with the embodiments and appendices Figure 1-3 The technical solution of the present invention will be described in detail, and the implementation process is as follows: Figure 4 As shown, this embodiment uses a collapse blasting test of a granite underground cavern as an example, but it does not constitute a limitation on the scope of protection of this invention.

[0047] Example 1:

[0048] Step 1: Measurement of in-situ stress and rock parameters. The original vertical in-situ stress is obtained based on the in-situ stress measurement of the surrounding rock 1. s 竖 The original horizontal in-situ stress is 20 MPa. s 平 For 20 MPa, such as Figure 1 As shown; the density of the rock was obtained by material parameter calibration tests on the rock samples from the field. r 岩 The longitudinal wave velocity of the rock is 2850 kg / m³. C 岩 The speed is 4800 m / s, and the Poisson's ratio of the rock is... m 岩 The dynamic tensile strength of the rock is 0.23. s t The pressure is 12 MPa; the density of the explosive used is... r 炸 The detonation velocity of the explosive is 1200 kg / m³. C 炸 The adiabatic index is 4500 m / s. c The value is 2.8. The lateral pressure coefficient can be calculated using formula (1). X The value is 1.

[0049] (1)

[0050] Step 2: Establish a stress analysis model for the cut cavity 2, and determine the radius of the cut cavity generated by the on-site cut blasting. a The distance is 1.2 m, which is the preset distance between the center of the blast hole in the collapse zone and the center of the cut cavity 2. b The borehole radius is 2.5 m. r It is 0.04 m.

[0051] Step 3, calculate the redistribution of ground stress. Establish a polar coordinate system with the center of the excavation cavity 2 as the origin and the horizontal direction as the polar axis 13. Calculate the radial stress on the rock element 8 at the center of the line connecting any collapse hole 3 according to formula (2). s 径 size.

[0052] (2)

[0053] Step 4: Construct an explosion stress wave propagation model. First, calculate the explosion load generated by the explosive on the borehole wall according to formula (3). P 爆 Then, the attenuation coefficient is obtained based on relevant literature. α Simultaneously calculate the lateral stress coefficient. l Then, assuming the spacing between the collapse holes is... s Considering the superposition effect of loads from adjacent boreholes, the calculation of the circumferential tensile stress on rock element 8 between adjacent boreholes is given. sh1 Equation (4).

[0054] (3)

[0055] (4)

[0056] Step 5, Coupled analysis of composite stress field: The formation of cracks between the three collapsed holes is influenced by the circumferential tensile stress generated by the explosion. s h1 and radial stress generated by stress redistribution s 径 The combined effect of these factors controls the circumferential tensile stress. s h1 Radial stress generated by ground stress redistribution s 径 The resultant force must be greater than the dynamic tensile strength of the rock. s t Then the condition for the formation of a through crack between the three collapse holes is given by equation (5).

[0057] (5)

[0058] Step 6, Hole spacing optimization calculation: Based on the equation given in Step 5 and combined with various physical parameter data measured on site, the maximum hole spacing that satisfies the formation of through cracks between holes in the collapse hole (3) is calculated to be 1.12 m.

[0059] Example 2:

[0060] According to on-site construction specifications, the traditional empirical formula for determining the spacing between collapse blasting holes is 40 × 0.04 m = 1.6 m. However, considering the suppression effect of ground stress, this invention calculates the maximum hole spacing to be 1.12 m. For example... Figure 5 As shown, compared to traditional methods, the hole spacing calculated by this method effectively solves the problem of some blast holes failing to form through cracks in collapse blasting, thus achieving good excavation results. Furthermore, this method takes 20 minutes to calculate, while patent CN119514255A takes 6 hours to calculate the hole spacing based on ground stress, rock material, and explosive material, significantly longer than this invention, demonstrating its higher computational efficiency.

Claims

1. A method for determining the spacing of blasting collapse holes in a tunnel considering the effect of ground stress unloading, characterized in that, Step 1: Measure and record the original in-situ stress and rock mechanics parameters at the site of the underground cavern blasting excavation; set the measured original in-situ stress in the vertical direction as... σ 竖 The measured original horizontal ground stress is set as σ 平 The density of the rock was obtained by conducting material parameter calibration tests on the rock samples from the site. ρ 岩 Longitudinal wave velocity of rocks C 岩 Poisson's ratio of rocks μ 岩 Dynamic tensile strength of rock σ t The density of the explosives used ρ 炸 The detonation velocity of explosives C 炸 Insulation index γ The lateral pressure coefficient was calculated based on the original ground stress. (1); Step 2: Based on the measured ground stress and the pre-designed caving blasting, establish a stress analysis model with a cut-out cavity; wherein, the radius of the cut-out cavity generated by the on-site cut-out blasting is set as... a The distance between the center of the blast hole in the collapse zone and the center of the cut cavity is set as b The borehole radius is set to r The hole spacing for through-cracks generated during collapse blasting is set as s ; Step 3: Perform stress unloading calculation on the slotted cavity using the stress analysis model, and establish a stress redistribution model. In step 3, a polar coordinate system is established with the center of the grouted cavity as the origin and the horizontal direction as the polar axis. The radial stress on the rock element at the center of the line connecting any collapse hole is calculated according to formula (2). σ 径 Size is calculated using the following formula: （2） in, θ Polar angles are different angles in a polar coordinate system established with the radius in the horizontal direction, which is the origin of the slotted cavity, as the polar axis. Step 4: Construct an explosion stress wave propagation model based on rock material parameters and explosive material parameters, and calculate the explosion stress superposition field between adjacent collapse holes; In step 4, the explosive load generated on the borehole wall by the explosive is first calculated according to formula (3). P 爆 : （3） Collapse hole at any distance L The rock element at that location is subjected to radial compressive stress by a single borehole. σ j for: （4） Collapse hole at any distance L The rock element at that location is subjected to circumferential tensile stress by a single borehole. σ h for: （5） In the formula, α The attenuation coefficient is... λ The lateral stress coefficient is... λ = μ a / (1- μ a ),and μ a =0.8 μ 岩 ; The rock element in the middle of the line connecting any two adjacent collapse holes is subjected to the combined action of the two adjacent boreholes. Therefore, considering the superposition effect of the explosion stress, the radial compressive stress on the rock element between the holes is calculated. σ j1 and circumferential tensile stress σ h1 ; （6） The formation of inter-pore cracks in the collapse hole is influenced by the circumferential tensile stress generated by the explosion. σ h1 And the radial stress generated by the redistribution of ground stress is σ 径 The combined effect of these factors controls the formation of cracks, and the basis for judging the occurrence of cracks is formula (7): （7）； Step 5: Calculate the maximum hole spacing between adjacent holes that produce through-cracks in the rock collapse blasting according to the rock strength fracture criterion. In step 5, based on criterion formula (7) and in conjunction with formulas (1) to (6), the hole spacing s for the through cracks generated during the collapse blasting is obtained as follows: （8）。 2. The method for determining the spacing of blasting collapse holes in a tunnel considering the effect of ground stress unloading, as described in claim 1, is characterized in that... It also includes step 6, which calculates the maximum hole spacing that satisfies the formation of a through crack between the collapsed holes, based on equation (8) given in step 5 and the physical parameter data measured on site.

Images