A tunnel pre-splitting microseismic control blasting excavation method for bedding joint development

Abstract

The present application belongs to the technical field of tunnel construction, and particularly relates to a layering joint development tunnel pre-splitting microseismic control blasting excavation method. The present application adopts the pre-splitting blasting mode for blasting in the layering joint development tunnel excavation, and compared with smooth blasting, the present application can effectively reduce the disturbance to the surrounding rock, reduce overbreak, and further effectively reduce the slag discharge amount, sprayed concrete amount, reduce the overall cost and speed up the construction progress. Meanwhile, the blasting excavation method of the present application also improves the roundness of the surrounding rock after excavation, reduces stress concentration, and is safer.

Description

Technical Field

[0001] This invention belongs to the field of tunnel construction technology, specifically relating to a pre-splitting micro-vibration controlled blasting excavation method for tunnels with well-developed bedding and joints. Background Technology

[0002] Currently, the drill-and-blast method remains the mainstream method for tunnel excavation. To minimize disturbance to the surrounding rock and effectively reduce over- and under-excavation, smooth blasting is applied to tunnel blasting excavation. Smooth blasting has a good smooth blasting effect, which can largely control over- and under-excavation, and ensure a smooth and even outline, reducing stress concentration.

[0003] However, in tunnels with well-developed bedding, joints, and fissures, traditional smooth blasting suffers from the inability of the blast stress wave and explosive gases to effectively cut along the tunnel excavation outline due to geological factors. Most of the energy is lost along the bedding and joints, resulting in significant over- or under-excavation. Adjusting the charge quantity to correct over- or under-excavation can lead to problems such as an excessively large blasting funnel at the bottom of the borehole or borehole snagging. Adjusting the minimum resistance line of the peripheral boreholes can cause even greater over- or under-excavation. Therefore, smooth blasting cannot guarantee excavation quality in such surrounding rock conditions. Summary of the Invention

[0004] The purpose of this invention is to provide a pre-splitting micro-vibration controlled blasting excavation method for tunnels with well-developed bedding and joints. To ensure the quality of blasting excavation, reduce over- and under-excavation, and guarantee the outline, based on the explosive detonation mechanism and the principle of pre-splitting blasting, this invention's tunnel pre-splitting micro-vibration controlled blasting excavation method effectively solves the problem of significant over- and under-excavation in smooth blasting of tunnels with well-developed bedding and joints by adopting pre-splitting blasting, without increasing construction costs.

[0005] This invention adjusts the detonator segment and changes the detonation sequence. Specifically, the peripheral holes are detonated at a low segment first, followed by the slotted holes, auxiliary holes, and bottom holes in sequence. Pre-splitting blasting is employed, with only one free face at the orifice of the peripheral holes. The blasting effect is not limited by the resistance line, effectively creating a through-crack between the peripheral holes beforehand, reducing the disturbance of the surrounding rock by the auxiliary holes, and guiding the blasting energy generated outside the rock by the auxiliary holes to perform secondary cutting of the through-crack, thus improving the pre-splitting effect.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for pre-splitting micro-vibration controlled blasting excavation of tunnels with well-developed bedding and joints, comprising the following steps:

[0007] S1. Determine the excavation outline and the location of the blast holes;

[0008] S2. Drill blast holes. According to the blast hole distribution design, drill slot holes, auxiliary holes and peripheral holes in sequence from the center outward along the radial direction of the excavation face, as well as drill bottom plate holes for the outline at the bottom of the tunnel face, and clean the drilled slot holes, auxiliary holes, peripheral holes and bottom plate holes.

[0009] S3. Explosives are loaded into the slotted holes, auxiliary holes, peripheral holes, and bottom holes and connected in parallel. The detonation method adopts a hybrid network detonation method. Among them, the peripheral holes use uncoupled interval charges. The interval charges in the peripheral holes can reduce the detonation capability and reduce the destructive effect of the peripheral holes on the surrounding rock.

[0010] S4. Pre-splitting blasting is adopted, that is, the detonation sequence is as follows: peripheral holes, cut holes, auxiliary holes, and bottom holes.

[0011] The technical solution of the present invention also includes: the drilling angle of the peripheral eye is less than 3°, and the peripheral eye is drilled in intact surrounding rock, avoiding bedding and joints.

[0012] The technical solution of the present invention also includes: when the distance between two adjacent peripheral eyes is greater than 1.2 times the peripheral eye distance E, a hollow eye is made in the middle position, and the size of the hollow eye is the same as that of the peripheral eye.

[0013] The technical solution of the present invention also includes: the slotting hole adopts a straight eye plus three-stage wedge composite slotting, the slotting hole includes a straight eye slotting set on the center line of the excavation face and a pair of first-level slots, a pair of second-level slots, and a pair of third-level slots symmetrically set on both sides of the center line of the excavation face, wherein the first-level slots, second-level slots, and third-level slots are all oblique eye slotting.

[0014] The depth of the slotted hole is 0.5-1 meter deeper than that of the surrounding holes and auxiliary holes, and the depth is perpendicular to the working face.

[0015] The technical solution of the present invention also includes: the peripheral hole spacing E = (8~12)d, in cm, where d is the hole diameter in cm, the minimum resistance line W = E / m in cm, where m is the hole density coefficient and the linear charge density. The unit is kg / m³. This represents the ultimate compressive strength of the rock, measured experimentally, and is expressed in MPa.

[0016] The technical solution of the present invention also includes: in step S1, the standard for setting the excavation outline is: net radius R1 + design secondary lining thickness + initial support thickness + reserve + (3~5), in cm.

[0017] The technical solution of the present invention also includes: the peripheral eye uses MS1 segment detonators, and the detonator segments in the blasting network of the peripheral eye, slotting eye, auxiliary eye and bottom plate eye are spaced apart by two segment differences according to the detonation sequence.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention uses pre-splitting blasting in the excavation of tunnels with developed bedding joints. Compared with smooth blasting, the present invention can effectively reduce the disturbance to the surrounding rock, reduce over-excavation, and thus effectively reduce the amount of slag and shotcrete, thereby reducing the overall cost and accelerating the construction progress.

[0019] Meanwhile, the blasting excavation method of this invention improves the roundness of the surrounding rock after excavation, reduces stress concentration, and is safer.

[0020] The technological principle of this invention:

[0021] ① Explosion mechanism

[0022] a. Dynamics theory

[0023] When an explosive detonates, the powerful shock wave impacts and compresses the surrounding rock mass, generating intense stress waves within it. When these stress waves reach the free surface, they reflect off to form tensile stress waves. When the intensity of these waves exceeds the ultimate compressive strength of the rock mass, tensile fracturing failure occurs.

[0024] b. Statics theory

[0025] When explosives detonate, they produce a large amount of high-temperature, high-pressure explosive gases. The pressure generated by the expansion of these gases acts on the surrounding rock walls, causing radial displacement of rock particles. Due to unequal forces, different radial displacements occur, leading to shear stress in the rock. When the shear stress exceeds the rock's ultimate shear strength, it will cause the rock to fracture. When the thrust of the explosive gases becomes large enough, it will cause the rock to heave and be thrown.

[0026] c. The theory of combined dynamic and static effects

[0027] Stress wave tensile failure, combined with the thrust and wedge action of explosive gases, varies in degree depending on the properties of the rock mass. In well-integrated, dense, and tough rock masses, due to their high wave impedance and good stress wave propagation performance, the degree of rock damage mainly depends on the stress wave tensile failure. In rock masses with relatively fragmented and poor integrity, due to their low wave impedance and the presence of different media, the stress wave propagation performance is poor, and the degree of rock damage mainly depends on the action of the explosive gases.

[0028] ② Pre-splitting blasting principle

[0029] Pre-splitting blasting is initiated before other blast holes, pre-forming a continuous fracture. Using uncoupled, intermittent charges, when the outer auxiliary holes blast, the explosive gases and stress waves reach the continuous fracture. Due to the change in medium, the stress waves attenuate significantly as they pass through different media, greatly reducing the stress acting on the surrounding rock. Furthermore, the stress waves are reflected upon reaching the continuous fracture due to the change in medium, resulting in superposition and enhanced rock-breaking action. The explosive gases, upon reaching the continuous fracture, wedge along the existing fracture, reducing the impact on the surrounding rock and allowing for secondary cutting of the continuous fracture. Attached Figure Description

[0030] Figure 1 This is a diagram showing the connection of the pre-splitting blasting holes described in this invention;

[0031] Figure 2 This is a schematic diagram of the tunnel outline described in this invention;

[0032] Figure 3 This is a schematic diagram of the slotted hole structure described in this invention;

[0033] Figure 4 This is a schematic diagram of the peripheral ocular drug delivery structure described in this invention;

[0034] Figure 5 This is a schematic diagram of the excavation outline of the left and right tunnels described in Embodiment 1 and Comparative Examples 1-3 of the present invention;

[0035] Figure 6 This is a schematic diagram of the pre-splitting blasting perimeter hole arrangement as described in Embodiment 1 of the present invention;

[0036] Figure 7 This is a cross-sectional view of the working face at section K57+794 of the right tunnel as described in Embodiment 1 of the present invention;

[0037] Figure 8 This is a cross-sectional view of the working face at section K57+797 of the right tunnel as described in Embodiment 1 of the present invention;

[0038] Figure 9 These are actual working face diagrams of the right tunnel sections K57+794 and K57+797 as described in Embodiment 1 of the present invention;

[0039] Figure 10 This is a schematic diagram of the peripheral eye arrangement for smooth blasting as described in Comparative Example 1 of the present invention;

[0040] Figure 11 This is a cross-sectional view of the working face of the right tunnel at K57+789 as described in Comparative Example 1 of the present invention;

[0041] Figure 12 This is a real-world diagram of the working face of the right tunnel section K57+789 described in Comparative Example 1 of the present invention;

[0042] Figure 13This is a cross-sectional view of the working face of the left tunnel ZA3K57+842 section as described in Comparative Example 2 of the present invention;

[0043] Figure 14 This is a real-world diagram of the working face of the left tunnel ZA3K57+842 section as described in Comparative Example 2 of this invention;

[0044] Figure 15 This is a cross-sectional view of the working face of the left tunnel ZA3K57+845 section as described in Comparative Example 3 of the present invention;

[0045] Figure 16 This is a cross-sectional view of the working face of the left tunnel ZA3K57+849 section as described in Comparative Example 3 of the present invention;

[0046] Figure 17 These are actual working face diagrams of the ZA3K57+845 and ZA3K57+849 sections of the left tunnel as described in Comparative Example 3 of this invention;

[0047] Figure 18 This is a comparison diagram of the blasting effect of the left tunnel as described in this invention;

[0048] Figure 19 This is a comparison diagram of the blasting effect of the right tunnel described in this invention;

[0049] In the diagram, 1 is the slotting hole, 11 is the straight slotting hole, 12 is the first-level slotting hole, 13 is the second-level slotting hole, 14 is the third-level slotting hole; 2 is the auxiliary slotting hole, 3 is the peripheral slotting hole, and 4 is the bottom slotting hole. Detailed Implementation

[0050] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the embodiments of the present invention, the left tunnel is a complete rock tunnel excavation section, and the right tunnel is a stratified tunnel excavation section.

[0051] Terminology introduction: (1) Roof finding: This means removing loose or weak surrounding rock and stones on the tunnel cross section.

[0052] (2) Hanging at the opening: This is a common situation where the blasting effect of the borehole body is good, but the opening is a complete blast hole. The reason for the hanging at the opening is that the force generated by the explosion of the explosive is insufficient to break the rock.

[0053] (3) Secondary lining: "Secondary lining" is a term in tunnel construction. When excavating a tunnel, the tunnel is advanced along the tunnel face, and the four sides of the excavated tunnel need to be reinforced. "Secondary lining" refers to the work of further reinforcing the four sides of the tunnel after it has been reinforced.

[0054] Generally speaking, depending on the surrounding rock conditions and the stress conditions of the primary and secondary linings, tunnel support can be divided into two types: 1. The primary lining is fully stressed, and the secondary lining is constructed after the surrounding rock deformation stabilizes and the primary support is fully stressed; 2. The primary and secondary linings are stressed together.

[0055] (4) Arch foot and arch waist: The arch line is the arch foot, which is the junction of the road surface and the tunnel wall; the arch foot is just two points on a cross surface, while the arch line connects these points and runs through the entire tunnel.

[0056] The midpoint of the arc from the tunnel arch to the arch foot is called the arch waist.

[0057] The construction method of the pre-splitting micro-vibration controlled blasting excavation method for tunnels with well-developed bedding and joints, as described in this invention, includes the following specific steps:

[0058] 1) Laying out and positioning, determining the excavation outline and the location of blast holes.

[0059] ① Determine the actual allowance by using construction monitoring and measurement data. Based on the principle of similarity of surrounding rock, monitoring and measurement data from sections of similar surrounding rock can be used as the basis for determining the excavation outline. See details below. Figure 2 .

[0060] ② The net clearance radius R1 + design secondary lining thickness + initial support thickness + allowance + (3-5) cm is used as the standard for the excavation outline. Among them, (3-5) cm is the allowance to ensure that the secondary lining does not encroach on the limit.

[0061] 2) Drilling, charging, and wiring

[0062] like Figure 1 As shown, boreholes were drilled. Based on the borehole distribution design, cut holes 1, auxiliary holes 2, and peripheral holes 3 were drilled radially outward from the center of the excavation face. A bottom plate hole 4, outlining the tunnel face, was also drilled. The drilled cut holes 1, auxiliary holes 2, peripheral holes 3, and bottom plate holes 4 were cleaned, and explosives were filled and connected in place. A YT28 pneumatic rock drill was used, with an A42mm diameter drill bit. The drill bit was made of "I"-shaped hard alloy steel, and the drill rod was a hollow hexagonal type with lengths of 2m, 3m, 4m, and 5m.

[0063] Hole-shaped opening: such as Figure 1 and Figure 3As shown, the cut hole 1 adopts a composite cut method consisting of a straight cut and a three-stage wedge cut. The cut hole 1 includes a straight cut 11 located on the center line of the excavation face and a pair of primary cuts 12, a pair of secondary cuts 13, and a pair of tertiary cuts 14 symmetrically located on both sides of the center line of the excavation face. The primary cuts 12, secondary cuts 13, and tertiary cuts 14 are all oblique cuts, with angles perpendicular to the working face of 65°, 70°, and 75° respectively. To ensure the cut effect and improve the utilization rate of the blast holes, the depth of the cut hole 1 perpendicular to the working face is 0.5 meters to 1 meter deeper than that of the surrounding holes 3 and auxiliary holes 2. The composite cut method aims to enhance the cut effect of the straight cut 11 and the primary cut 12, providing a larger free face for subsequent blast hole detonation.

[0064] Peripheral holes: Ensure that the drilling angle of peripheral holes 3 is less than 3°. Do not drill holes at bedding planes or joints. Avoid these areas. Drill holes in intact surrounding rock. If the distance between two adjacent peripheral holes 3 is greater than 1.2 times the peripheral hole spacing E, a hollow hole can be drilled in the middle as a guide.

[0065] Peripheral hole 3 uses decoupled interval charges and MS1 detonators, detonated in front of all boreholes. Other boreholes are charged using conventional methods. See details below. Figure 1 and Figure 4 The specific charge amount and detonator usage are shown in Table 1. The specific charge amount and number of detonators are determined according to the surrounding rock conditions. The specific method is based on existing technology and will not be elaborated here.

[0066] Table 1. Blasting Parameters for Upper Bench

[0067]

[0068]

[0069] 3) Detonation method

[0070] The detonation method adopts a hybrid network detonation method. Peripheral holes are detonated using a non-electric millisecond detonator-detonating cord detonation network, while other holes are detonated using non-electric millisecond detonators. Non-electric millisecond detonators are selected as the detonating equipment. When designing the blasting network, such as... Figure 1 As shown, designed according to sections 1 to 17, the peripheral eye 3 uses MS1 section detonators. The detonator sections in the blasting network of peripheral eye 3, slotted eye 1, auxiliary eye 2, and base plate eye 4 are spaced two sections apart according to the detonation sequence; this two-section difference is the optimal configuration. The detonator sections are designed to reflect the section differences; different sections have different detonation time differences. Higher-section detonators detonate later, while those detonated earlier can form a free surface, ensuring the effectiveness of subsequent detonations. The detonation sequence is: peripheral eye 3, slotted eye 1, auxiliary eye 2, and base plate eye 4.

[0071] Example 1

[0072] like Figure 1 As shown, in this embodiment, sections K57+794 and K57+797 of the right tunnel are selected, which are of the Class IV reinforced lining type, with a lining thickness of 40cm, initial support of I18 I-beams, and shotcrete thickness of 24cm, with a designed allowance for deformation of 8cm. The rock in the right tunnel is bedding-jointed rock, and the pre-splitting micro-vibration controlled blasting excavation method for bedding-jointed tunnels of the present invention is adopted.

[0073] During construction, based on the surrounding rock conditions and monitoring data, a 5cm deformation allowance was reserved, and the bench excavation method was used. The actual excavation outline is as follows: Figure 2 As shown. Before drilling, surveyors used a total station to lay out the outline of the excavation face and marked the hole positions with red paint to ensure drilling accuracy.

[0074] The peripheral eye blasting parameters are as follows:

[0075] The surrounding hole spacing E = (8-12)dcm, where d is the hole diameter (42mm), E = 33.6-50.4cm, taken as 40cm, the hole density coefficient m = 0.8, the minimum resistance line W = E / W = 50cm, and the linear charge density... The ultimate compressive strength of the rock was obtained from the test. Then q = 0.367 × (4.2) 0.5 ×0.042 0.36 =0.24, take q as 0.25kg / m.

[0076] Therefore, the following parameters are obtained: perimeter hole spacing E = 40cm, minimum resistance line W = 50cm, linear charge density q = 0.25kg / m, hole density coefficient m = 0.8, MS-1 non-electric millisecond detonating cord detonators are used for the perimeter holes of the dome, and two detonators are used in the hole to achieve intermittent charging. See details. Figure 6 The surrounding eye layout diagram.

[0077] After the right tunnel was excavated and the roof was found, the cross-section of the tunnel face was scanned. The actual over-excavation and under-excavation are shown below:

[0078] like Figure 7 As shown in the cross-sectional diagram of the K57+794 working face, the over-excavation in this cycle was relatively small, with a maximum over-excavation of 11.3 cm, located at the left shoulder. The linear average over-excavation was 7.6 cm, and the over-excavation was 1.56 m per linear meter. 3 .

[0079] like Figure 8 As shown in the cross-sectional diagram of the K57+797 working face, the over-excavation control in this cycle was relatively good. The maximum over-excavation was 18.5cm, located at the right shoulder, with a linear average over-excavation of 9cm, or 1.85m of over-excavation per linear meter. 3 .

[0080] like Figure 9As shown, based on the analysis of the actual images taken at the tunnel face, after the blasting excavation of the right tunnel, the blast hole retention rate is high, the pre-cracked area of ​​the arch crown reaches 100%, and the over-excavation is relatively small. However, the maximum over-excavation in both cycles occurred at the arch shoulder, which is the stratification junction.

[0081] Comparative Example 1

[0082] The K57+789 section of the right tunnel was selected. The design type, excavation outline, and blast hole layout were the same as in Example 1. The difference from Example 1 was that smooth blasting was used and the blasting parameters of the peripheral holes were different.

[0083] The peripheral eye blasting parameters are as follows:

[0084] The borehole spacing E = 50cm, the minimum resistance line W = 60cm, the linear charge density q = 0.25kg / m, the borehole density coefficient m = 0.83, and the peripheral holes use MS-15 non-electric millisecond detonating cord detonators. Two detonators are used in each hole for spaced charging. See details. Figure 10 The surrounding eye layout diagram.

[0085] After the right tunnel was blasted and excavated to find the roof, the cross-section of the tunnel face was scanned. See details. Figure 11 Cross-sectional view of the working face.

[0086] like Figure 11 As shown in the diagram, analysis of the tunnel face cross-section reveals significant over-excavation in this cycle, with a maximum over-excavation of 27.7 cm located at the arch waist. Over-excavation at the arch crown is also severe, with multiple locations exceeding 20 cm. Calculations indicate a linear average over-excavation of 19 cm, with an excavation cross-section arc length of 20.56 meters, resulting in an over-excavation of 3.91 m per linear meter. 3 .

[0087] like Figure 12 As shown, analysis of the actual footage taken at the working face shows that there was a complete over-excavation at the arch crown, especially at the arch shoulder. The on-site analysis indicates that the rock is a horizontally bedding rock layer. The shape was acceptable after excavation, but there was significant rockfall after the crown was found, and the flatness of the surrounding rock was poor.

[0088] Comparative Example 2

[0089] The ZA3K57+842 section of the left tunnel was selected. Unlike Example 1, smooth blasting was used. The lining design, excavation method, actual excavation outline, blast hole layout, and blasting parameters were the same as those in Comparative Example 1.

[0090] After the left tunnel was blasted and excavated to find the roof, the cross-section of the tunnel face was scanned. See details. Figure 13 Cross-sectional view of the tunnel face. Analysis of the cross-sectional view shows that over-excavation control was relatively good in this cycle. The maximum over-excavation was 18.2 cm, located at the arch crown, with a linear average over-excavation of 10.8 cm, or 2.22 m per linear meter. 3 .

[0091] like Figure 14 As shown, analysis of actual footage taken at the tunnel face reveals some under-excavation and hanging at the arch. Although some holes remain, there are blasting marks between them, indicating varying degrees of over-excavation and under-excavation. Overall, over-excavation is relatively controllable.

[0092] Comparative Example 3

[0093] Sections ZA3K57+845 and ZA3K57+849 of the left tunnel were selected and pre-splitting blasting was carried out in the same manner as in Example 1. The lining design, excavation method, actual excavation outline, blast hole layout, blasting parameters, etc. were the same as in Example 1.

[0094] After the left tunnel was excavated and the roof was found, the cross-section of the tunnel face was scanned, and the actual over-excavation and under-excavation are shown below.

[0095] like Figure 15 As shown in the cross-sectional diagram of the ZA3K57+845 working face, the over-excavation in this cycle was slightly greater than that of smooth blasting, with a maximum over-excavation of 25.2 cm located at the arch crown. The linear average over-excavation was 13.6 cm, and the over-excavation was 2.8 m per linear meter. 3 .

[0096] like Figure 16 As shown in the cross-sectional diagram of the ZA3K57+849 working face, the over-excavation control in this cycle was relatively good. The maximum over-excavation was 29.1 cm, located at the arch shoulder, with a linear average over-excavation of 12.6 cm, and an over-excavation of 2.59 m per linear meter. 3 .

[0097] like Figure 17 As shown, analysis of the actual footage taken at the working face reveals that there is some over-excavation at the arch, but the over-excavation is controllable. The main reason is the angle of the external insertion of the surrounding holes.

[0098] In summary, as shown in Table 2, each cycle advances 3.2 meters. Smooth blasting of the arch area requires 18 perimeter holes, while pre-splitting blasting requires 22 perimeter holes. This results in an increase of 4 blast holes, 8 detonators, and 3 kg of explosives. The specific cost increases and decreases are shown in Table 2.

[0099] Table 2. Cost Comparison of Smooth Blasting and Pre-splitting Blasting

[0100]

[0101]

[0102] Notes: 1. Cycle advance is 3.2 meters; 2. Cost is based on smooth blasting; 3. Prices of detonators and explosives are market prices and for reference only; 4. Labor costs are calculated per shift, and there is no increase in cost for increasing the number of blast holes.

[0103] (I) Analysis of Excavation Results

[0104] (1) As Figure 18 As shown, after pre-splitting blasting was used in the left tunnel, compared with smooth blasting, the average linear over-excavation increased from 10.6 cm to 13.6 cm and 12.6 cm, respectively, and the over-excavation decreased from 2.22 m. 3 Increased to 2.8m 3 2.59m 3 On average, the over-excavation increased by 0.495m per linear meter. 3 The over-excavation rate increased by 22.3%.

[0105] The maximum over-excavation in the left tunnel increased from 18.2cm to 25.2cm and 29.1cm, and the over-excavation was relatively random, mainly located at the arch crown and arch shoulder.

[0106] (2) Figure 19 As shown, after pre-splitting blasting was used in the right tunnel, compared with smooth blasting, the average linear over-excavation decreased from 19cm to 7.6cm and 9cm, respectively, and the over-excavation decreased from 3.91m. 3 Reduced to 1.56m 3 1.85m 3 On average, the over-excavation was reduced by 2.205m per linear meter. 3 The over-excavation rate was relatively low at 56.4%.

[0107] The maximum over-excavation in the right tunnel decreased from 24.9cm to 11.3cm and 18.5cm, and both were located at the arch shoulder.

[0108] (II) Summary

[0109] Because pre-splitting blasting involves more drilling than smooth blasting, and pre-splitting blasting doesn't have the same proven effectiveness as smooth blasting, those skilled in the art typically use smooth blasting in actual tunnel construction. It's difficult for them to conceive of using pre-splitting blasting in tunnels with well-developed bedding and joints, thus breaking with established experience and yielding unexpected results. Through comparative examples and embodiments, this invention also demonstrates that pre-splitting blasting technology can be applied to tunnels with well-developed bedding, but not to tunnels with intact surrounding rock.

[0110] From an overall perspective, pre-splitting blasting technology can effectively reduce over-excavation at the arch crown and control the overall linear over-excavation to about 10cm, with the maximum over-excavation not exceeding 20cm. After blasting, the surrounding rock contour of the tunnel face is better, smooth and flat, and the over-excavation rate is reduced by nearly 60%. Considering the unavoidable over-excavation factors caused by the external insertion angle of the surrounding holes, this blasting technology has greatly reduced over-excavation.

[0111] From a cost perspective, while pre-splitting blasting increases the amount and cost of explosives and detonators, it significantly reduces the amount and cost of shotcrete, lowering the cost by 900 yuan per linear meter. Simultaneously, it reduces the total concrete consumption and rebound rate; based on a 20% rebound rate stipulated in the quota, this saves 180 yuan, resulting in an overall cost reduction of 1080 yuan per linear meter.

[0112] In terms of progress, the amount of over-excavation was reduced, the time for slag removal was shortened, the time for shotcreting was shortened, and the overall cycle efficiency was improved.

[0113] From a safety perspective, the blasting marks on the arch are nearly 100% preserved, and the rock surface is smooth, which reduces the risk of arch collapse and the concentration of ground stress, thus improving the safety factor.

[0114] In terms of quality, the smooth rock surface reduces the time required for finding the top, allows for initial spraying of the surrounding rock at the first opportunity, ensures stress redistribution, and improves overall quality.

[0115] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A pre-splitting micro-vibration controlled blasting excavation method for tunnels with developed bedding and joints, solving the problem of over- and under-excavation in smooth blasting in tunnels with developed bedding, joints, and fissures, characterized in that... Includes the following steps: S1. Determine the excavation outline and the location of the blast holes; S2. Drill blast holes. According to the blast hole distribution design, drill slot holes (1), auxiliary holes (2) and peripheral holes (3) in sequence from the center outward along the radial direction of the excavation face, and drill bottom plate holes (4) at the bottom of the tunnel face to form the outline. Clean the drilled slot holes (1), auxiliary holes (2), peripheral holes (3) and bottom plate holes (4). S3. Explosives are loaded into the slotted hole (1), auxiliary hole (2), peripheral hole (3) and bottom hole (4) and connected in parallel. The detonation method adopts the hybrid network detonation method. Among them, the peripheral hole (3) uses uncoupled interval charge. S4. Pre-splitting blasting is adopted, that is, the detonation sequence is as follows: peripheral hole (3), slotting hole (1), auxiliary hole (2), bottom plate hole (4); The cut hole (1) adopts a straight cut hole plus three-stage wedge composite cut hole. The cut hole (1) includes a straight cut hole (11) set on the center line of the excavation face and a pair of first-level cut holes (12), a pair of second-level cut holes (13) and a pair of third-level cut holes (14) symmetrically set on both sides of the center line of the excavation face. The first-level cut hole (12), second-level cut hole (13) and third-level cut hole (14) are all oblique cut holes. The straight-hole cut (11) includes two vertically spaced blast holes, the first-level cut (12) and the second-level cut (13) each include three vertically spaced blast holes, and the third-level cut (14) includes two vertically spaced blast holes and two inclined blast holes, with the two inclined blast holes located outside the two vertically spaced blast holes. The peripheral eye (3) and auxiliary eye (2) are arranged in an arched pattern parallel to the excavation outline and spaced apart from each other. The peripheral eye (3) and auxiliary eye (2) distributed on the same ring adopt the same detonator segment. The first-level cut (12), the second-level cut (13), and the third-level cut (14) are detonated in sequence according to the detonation order; The auxiliary eye (2) detonates sequentially from the inside out; The peripheral eye (3) uses MS1 segment detonators. The detonator segments in the blasting network of the peripheral eye (3), slotted eye (1), auxiliary eye (2) and bottom plate eye (4) are spaced two segments apart according to the detonation sequence.

2. The method for pre-splitting micro-vibration controlled blasting excavation of tunnels with developed bedding and joints according to claim 1, characterized in that: The peripheral eye (3) is drilled at an angle of less than 3°, and the peripheral eye (3) is drilled in intact surrounding rock, avoiding bedding and joints.

3. The method for pre-splitting micro-vibration controlled blasting excavation of tunnels with developed bedding and joints according to claim 1, characterized in that: When the distance between two adjacent peripheral eyes (3) is greater than 1.2 times the peripheral eye distance E, an empty eye is made in the middle position.

4. The method for pre-splitting micro-vibration controlled blasting excavation of tunnels with developed bedding and joints according to claim 1, characterized in that: The depth of the slotted hole (1) is 0.5 mm deeper than the surrounding holes (3) and the auxiliary holes (2). 1 meter.

5. The method for pre-splitting micro-vibration controlled blasting excavation of tunnels with developed bedding and joints according to claim 1, characterized in that: The spacing between the peripheral holes (3) is E = (8~12)d, in cm, where d is the hole diameter in cm, the minimum resistance line W = E / m, in cm, where m is the hole density coefficient, and the linear charge density q = 0.367 ( 压 ) 0.5 d 0.36 The unit is kg / m³. 压 This represents the ultimate compressive strength of the rock, expressed in MPa.

6. The method for pre-splitting micro-vibration controlled blasting excavation of tunnels with developed bedding and joints according to claim 1, characterized in that: In step S1, the standard for setting the excavation outline is: net radius R1 + design secondary lining thickness + initial support thickness + allowance + (3~5), in cm.

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