An asymmetric high-stress tunnel face advance blasting pressure relief rock burst control method

Abstract

The application provides a kind of asymmetric high stress tunnel face advance blasting pressure relief rock burst control method, and relates to the technical field of tunnel engineering.The application is based on the tunnel engineering geological survey report, according to the tunnel original rock initial ground stress, excavation disturbance stress field distribution and tunnel section geometric characteristics, determines the stress concentration area of tunnel face;Based on the tunnel engineering geological survey report, using rock burst intensity evaluation method, the rock burst grade of surrounding rock is predicted;Based on the stress concentration area of tunnel face and the rock burst grade of surrounding rock, the tunnel blasting pressure relief rock burst control method is determined;The method solves the problem that the tunnel face is in asymmetric high stress condition in actual engineering, the adverse effect of stress concentration area on advance pressure relief, compared with the uniform distribution of face hole, reduces the number of stress release holes, more effectively improves the stress distribution in front of tunnel face, the stress concentration area shifts to the inside, improves the safety and construction efficiency of tunnel excavation construction, ensures the safety of construction personnel and equipment.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering technology, and in particular to a method for controlling rockburst during pre-blasting decompression at the working face of an asymmetric high-stress tunnel. Background Technology

[0002] Rockburst is a phenomenon that occurs when tunnels and underground engineering projects pass through hard surrounding rock in areas of high ground stress. Originally in a true triaxial high-stress environment, the surrounding rock undergoes a change in stress path due to excavation, releasing ground stress and causing sudden rock bursts. This is accompanied by the ejection, throwing, and sonic booms of rock fragments, releasing significant internal elastic strain energy. Its main characteristics are its intensity and suddenness. The impact of rockbursts on tunnel construction is primarily manifested in a deterioration of the construction environment, damage and destruction of personnel, equipment, and initial tunnel support, increased safety risks, and reduced construction efficiency.

[0003] With the increasing risk of rockbursts, especially strong and extremely strong rockbursts, it is impossible to completely control their occurrence solely through support. The blasting stress relief method is an effective means of controlling rockbursts. This method is a method of weakening the surrounding rock. By pre-drilling and using appropriate explosives, the surrounding rock structure is modified, reducing the stiffness of the rock mass in the stress concentration area near the tunnel face. The rock mass within the borehole and blasting influence range becomes a weaker force-transmitting medium, increasing deformation. This adjusts the energy distribution within the local surrounding rock, improves the stress concentration level, and shifts the concentration area forward of the tunnel face, thereby achieving the purpose of preventing rockbursts. During tunnel excavation, the stress at the tunnel face is often asymmetrical. Current blasting stress relief methods mainly use a uniform hole layout at the tunnel face, neglecting to place stress relief holes in the stress concentration areas formed by asymmetrical high stress at the tunnel face. This results in a large number of stress relief holes being placed, wasting manpower and resources, and even prematurely inducing rockbursts due to improper placement. Therefore, this application specifies the layout of holes for different rockburst levels and stress concentration areas. Compared with uniform hole layout at the tunnel face, this reduces the number of stress relief holes, more effectively improves the stress distribution in front of the tunnel face, shifts the stress concentration area inward, improves the safety and efficiency of tunnel excavation, and ensures the safety of construction personnel and equipment. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an asymmetric high-stress tunnel face pre-blasting decompression rockburst control method. This effectively improves the stress distribution in front of the tunnel face at the risk of rockburst, shifting the stress concentration zone inwards, thereby enhancing the safety and efficiency of tunnel excavation and ensuring the safety of construction personnel and equipment.

[0005] A method for controlling rockburst during pre-blasting decompression at the working face of an asymmetric high-stress tunnel, specifically including the following steps:

[0006] Step 1: Based on the tunnel engineering geological survey report, determine the stress concentration area at the tunnel face according to the initial ground stress of the original rock, the distribution of excavation disturbance stress field, and the geometric characteristics of the tunnel cross section;

[0007] Step 1.1: Based on the tunnel engineering geological survey report, the initial ground stress of the original rock and the stress field distribution of excavation disturbance are inverted through numerical simulation to determine the stress distribution at the tunnel face during the tunnel excavation project;

[0008] Step 1.2: Based on the spatial relationship between the stress distribution at the tunnel face and the geometry of the tunnel face, the stress concentration area at the tunnel face is obtained.

[0009] Step 2: Based on the tunnel engineering geological survey report, use the rockburst intensity assessment method to predict the rockburst level of the surrounding rock;

[0010] Step 2.1: Based on the tunnel engineering geological survey report, obtain the actual condition of the surrounding rock of the tunnel, specifically including the burial depth, stratum lithology, initial in-situ stress, uniaxial compressive strength of the rock, surrounding rock classification, and hydrogeological conditions of the surrounding rock at the tunnel face.

[0011] Step 2.2: Based on the actual conditions of the surrounding rock of the tunnel, draw a comprehensive judgment table of tunnel rockburst intensity, and comprehensively analyze and predict the rockburst level of the surrounding rock. The rockburst level of the surrounding rock specifically includes no rockburst, slight rockburst, moderate rockburst, and severe rockburst.

[0012] Step 3: Based on the stress concentration area at the tunnel face and the rock burst level of the surrounding rock, determine the tunnel blasting pressure relief control method;

[0013] Step 3.1: Determine the location of the pre-blasting stress relief holes based on the stress concentration area at the tunnel face;

[0014] Step 3.2: Based on the rockburst level of the surrounding rock, compare and match different rockburst control schemes for advance blasting and decompression at the tunnel face, and determine the rockburst control scheme.

[0015] The tunnel face pre-blasting decompression rockburst control scheme specifically includes:

[0016] (1) For tunnel faces with no rockburst or minor rockburst, the blasting stress relief method is not used;

[0017] (2) For tunnel faces with medium rockburst level, 9 to 14 shallow holes of extended excavation blasting are arranged in the stress concentration area for advance blasting and pressure relief.

[0018] (3) For tunnel faces with strong rockburst, 3 to 5 deep holes are laid out for advance blasting to relieve pressure in the stress concentration area. If the intensity of the rockburst increases, it is used in conjunction with 9 to 14 shallow holes for advance blasting to relieve pressure in the extended tunneling blasting holes, that is, shallow holes are laid out around the stress concentration area.

[0019] It should be noted that the construction basis for the tunnel face pre-blasting pressure relief rockburst control scheme includes the construction cross-section diagram, pressure relief hole layout diagram and blasting parameter table;

[0020] Step 4: Effect Check; After each blast, investigate the blasting effect:

[0021] (1) Check for misfires; if misfires are found, handle them according to the misfire handling procedure in the "Blasting Safety Regulations".

[0022] (2) If there is no misfire, observe the blast crushing zone and the blast fracture zone:

[0023] Based on observations at the borehole opening, the blasting crushing zone, with a diameter of 50–70 mm centered on the original borehole centerline, showed an increase in fissures within a diameter range of 100–160 mm, indicating that the blasting caused the cracks. The rock mass within this range exhibited significant loosening. Based on the rock mass damage in this area, it was identified as the blasting fracture zone. The confining pressure within the blasting fracture zone and the blasting vibration zone loosened, and the high ground stress within them was effectively released.

[0024] The beneficial effects of adopting the above technical solution are as follows:

[0025] This invention provides a method for controlling rockburst during pre-blasting pressure relief at the tunnel face in asymmetric high-stress tunnels. Based on the tunnel engineering geological survey report, this method determines the stress concentration area at the tunnel face according to the initial ground stress of the original rock, the distribution of the excavation disturbance stress field, and the geometric characteristics of the tunnel cross-section. Based on the tunnel engineering geological survey report, it uses a rockburst intensity assessment method to predict the rockburst level of the surrounding rock. Based on the stress concentration area at the tunnel face and the rockburst level of the surrounding rock, it determines the tunnel blasting pressure relief control method. This method solves the problem of the adverse effects of stress concentration areas on pre-blasting pressure relief in actual engineering projects where the tunnel face is under asymmetric high-stress conditions. Compared to uniformly distributing holes at the tunnel face, it reduces the number of stress relief holes, more effectively improves the stress distribution in front of the tunnel face, shifts the stress concentration area inward, improves the safety and efficiency of tunnel excavation, and ensures the safety of construction personnel and equipment. Attached Figure Description

[0026] Figure 1 This is a flowchart of the asymmetric high-stress tunnel face pre-blasting decompression rockburst control method provided in the implementation case of this application;

[0027] Figure 2 This is a schematic diagram of the main stress concentration areas of the surrounding rock at the working face under asymmetric initial geostress conditions provided in the implementation case of this application;

[0028] Figure 3 This is a schematic diagram comparing the stress distribution in front of the tunnel face before and after decompression under asymmetric initial geostress conditions, provided in the implementation case of this application.

[0029] Figure 4 This is a schematic diagram of the 9-14 hole extension auxiliary shallow hole pre-blasting pressure relief provided in the implementation case of this application;

[0030] Figure 5 This is a schematic diagram of 3-5 hole deep hole pre-blasting pressure relief provided in the implementation case of this application;

[0031] in Figure 5 a is a plan view of the tunnel face. Figure 5 b is a longitudinal section view at the tunnel face;

[0032] Figure 6 This is a schematic diagram of the internal action and damage zones of a single blasting pressure relief hole provided in the implementation case of this application. Detailed Implementation

[0033] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0034] A method for controlling rockburst from pre-blasting decompression at the tunnel face in asymmetric high-stress tunnels, such as... Figure 1 As shown, the specific steps include:

[0035] Step 1: Based on the tunnel engineering geological survey report, determine the stress concentration area at the tunnel face according to the initial ground stress of the original rock, the distribution of excavation disturbance stress field, and the geometric characteristics of the tunnel cross section;

[0036] Step 1.1: Based on the tunnel engineering geological survey report, the initial ground stress of the original rock and the stress field distribution of excavation disturbance are inverted through numerical simulation to determine the stress distribution at the tunnel face during the tunnel excavation project;

[0037] Step 1.2: Based on the spatial relationship between the stress distribution at the tunnel face and the geometry of the tunnel face, the stress concentration area at the tunnel face is obtained.

[0038] This embodiment is in Figure 2 In the process, based on the stress distribution at the tunnel face, if the magnitude and direction of the maximum principal stress σ1 are known, Figure 2The maximum principal stress σ1 runs through the left arch foot to the right arch crown of the tunnel face. Based on spatial relationships, the stress concentration area is located in the shaded area at the upper left corner of the tunnel face. If the stress distribution cloud map of the tunnel face is known, the stress concentration area can be directly delineated at the high stress point based on the stress cloud map.

[0039] Step 2: Based on the tunnel engineering geological survey report, use the rockburst intensity assessment method to predict the rockburst level of the surrounding rock;

[0040] Step 2.1: Based on the tunnel engineering geological survey report, obtain the actual condition of the surrounding rock of the tunnel, specifically including the burial depth, stratum lithology, initial in-situ stress, uniaxial compressive strength of the rock, surrounding rock classification, and hydrogeological conditions of the surrounding rock at the tunnel face.

[0041] Step 2.2: Based on the actual conditions of the surrounding rock of the tunnel, draw a comprehensive judgment table of tunnel rockburst intensity, and comprehensively analyze and predict the rockburst level of the surrounding rock. The rockburst level of the surrounding rock specifically includes no rockburst, slight rockburst, moderate rockburst, and severe rockburst.

[0042] In this embodiment, for the theoretical analysis of rockburst prediction, domestic and foreign experts have proposed many judgment criteria. Each project will adopt different existing criteria to predict the rockburst level based on its own tunnel characteristics. For example, for a certain tunnel, considering all factors, four criteria applicable to the tunnel are selected, as shown in the following four tables. A comprehensive judgment table of rockburst intensity is drawn to make a comprehensive prediction of the rockburst level of the surrounding rock. If the four rockburst level predictions for a certain section of the tunnel are inconsistent, the majority prediction result shall be taken as the standard.

[0043] 1) Burial depth

[0044] Burial depth H (m) <320 320～485 485～886 >886 Rockburst intensity No rockburst Minor rock burst Moderate rockburst Intense rock burst

[0045] 2) Uniaxial compressive strength of rock

[0046]

[0047] 3) Surrounding rock grade

[0048] Surrounding rock level Ⅳ～Ⅴ Ⅲ～Ⅳ Ⅱ～Ⅲ Ⅰ～Ⅱ Rockburst intensity No rockburst Minor rock burst Moderate rockburst Intense rock burst

[0049] 4) Stress ratio σ max / σ c (σ max σ represents the magnitude of the maximum principal stress at the tunnel face. c (Uniaxial compressive strength of rock at the tunnel face)

[0050] <![CDATA[Stress ratio σ max / σ c > <0.15 0.15～0.25 0.2～0.35 >0.35 Rockburst intensity No rockburst Minor rock burst Moderate rockburst Intense rock burst

[0051] Step 3: Based on the stress concentration area at the tunnel face and the rock burst level of the surrounding rock, determine the tunnel blasting pressure relief control method;

[0052] Step 3.1: Determine the location of the pre-blasting stress relief holes based on the stress concentration area at the tunnel face;

[0053] Step 3.2: Based on the rockburst level of the surrounding rock, compare and match different rockburst control schemes for advance blasting and decompression at the tunnel face, and determine the rockburst control scheme.

[0054] The tunnel face pre-blasting decompression rockburst control scheme specifically includes:

[0055] Based on domestic literature and relevant tunnel blasting stress relief rockburst control schemes, the blasting stress relief method has a relatively complex construction process, and conventional support schemes can effectively prevent rockbursts. Therefore, it is unnecessary in sections with minor rockbursts. For minor rockbursts, surrounding rock support measures are sufficient to prevent rockbursts. However, for moderate and severe rockbursts, surrounding rock support cannot prevent or resist rockbursts, requiring additional measures. The advanced blasting stress relief method weakens the surrounding rock and transfers stress. The goal of this invention is to propose, compared to the uniform arrangement of current advanced blasting stress relief methods, to only drill holes in stress concentration areas, thereby reducing the number of holes while achieving better results. This weakens the surrounding rock, induces rockburst fracture zones, and transfers stress towards the tunnel face, achieving... Figure 3 The stress transfer effect is considered. Minor rockbursts have a lower risk and cause less damage; therefore, shallow-hole blasting is used in moderate rockburst sections, while deep-hole blasting is more common in severe rockburst sections. This is because the stress transfer distance of shallow-hole blasting is shorter than that of deep-hole blasting. However, the construction process for shallow-hole blasting is simpler than that for deep-hole blasting. Severe rockbursts have a larger destructive range and greater intensity than moderate rockbursts. Considering all factors, the following solutions are proposed:

[0056] In this embodiment, a normal tunneling blasting cycle advance of L = 3 meters.

[0057] For rockburst levels of medium to high, the principle of "short advance and weak blasting" is often followed in the rockburst prevention measures during construction. Therefore, the advance of the tunneling blasting cycle in sections with medium to high rockburst levels is l = 1.5 meters.

[0058] (1) For tunnel faces with no rockburst or minor rockburst, the blasting stress relief method is not used;

[0059] (2) For tunnel faces with medium rockburst level, 9 to 14 shallow holes of extended excavation blasting are arranged in the stress concentration area for advance blasting and pressure relief.

[0060] In the stress concentration area located on the left side of the tunnel face, 9-14 shallow blasting relief holes were pre-drilled using the existing tunnel drilling rig with a depth of 3 times the original blasting borehole depth and a cycle advance of 3l. The blasting parameters and layout diagrams are shown in Table 1 and Table 2, respectively. Figure 4As shown. The stress blasting release holes are shallow holes, 4.5m deep and Φ42mm in diameter. They are drilled above the blast holes in the tunneling face, extending from them and inclined at a 15° angle towards the face outline. This ensures a blasting loosening zone of at least two cycles (3m) ahead of the tunneling face, pre-loosening the surrounding rock and releasing stress. The placement of the control holes, the number of shallow holes, and the blasting parameters can be adjusted based on the actual rockburst conditions and microseismic monitoring data.

[0061] Table 1. Parameters for Pre-blasting and Pressure Relief Blasting of Shallow Holes with 9-14 Extended Auxiliary Eyes

[0062]

[0063] (3) For tunnel faces with strong rockburst, 3 to 5 deep holes are laid out for advance blasting to relieve pressure in the stress concentration area. If the intensity of the rockburst increases, it is used in conjunction with 9 to 14 shallow holes for advance blasting to relieve pressure in the extended tunneling blasting holes, that is, shallow holes are laid out around the stress concentration area.

[0064] In the stress concentration area located on the left side of the tunnel face, 3-5 15-meter deep blasting relief Φ108 holes were pre-drilled using a ZY880 down-the-hole drill. The blasting parameters and layout diagrams are shown in Table 2. Figure 5 As shown, the drill holes are staggered from the blasting holes to ensure that there is always a loosening zone of at least four cycles (6m) ahead of the working face, which is used to pre-loosen the surrounding rock and release stress. The control position, the number of deep holes, and the blasting parameters can be adjusted based on the actual rockburst situation and microseismic monitoring data.

[0065] Table 2. Parameters for Pre-blasting and Pressure Relief Blasting in Deep Holes (3-5 Holes)

[0066]

[0067] It should be noted that the construction basis for the tunnel face pre-blasting pressure relief rockburst control scheme includes the construction cross-section diagram, pressure relief hole layout diagram, and blasting parameter table, as shown in Table 1 and... Figure 4 As shown.

[0068] Step 4: Effect check; blasting will create blast crushing zones, blast fracture zones, and blast vibration zones, such as... Figure 6 As shown.

[0069] After each blast, the effects of the blast are investigated:

[0070] (1) Check for misfires; if misfires are found, handle them according to the misfire handling procedure in the "Blasting Safety Regulations".

[0071] (2) If there is no misfire, observe the blast crushing zone and the blast fracture zone:

[0072] Based on observations at the borehole opening, the blasting crushing zone, with a diameter of 50–70 mm centered on the original borehole centerline, showed an increase in fissures within a diameter range of 100–160 mm, indicating that the blasting caused the cracks. The rock mass within this range exhibited significant loosening. Based on the rock mass damage in this area, it was identified as the blasting fracture zone. The confining pressure within the blasting fracture zone and the blasting vibration zone loosened, and the high ground stress within them was effectively released.

[0073] The above description is merely a preferred embodiment of this disclosure and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in the embodiments of this disclosure is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in the embodiments of this disclosure.

Claims

1. A method for controlling rockburst during pre-blasting decompression at the working face of an asymmetric high-stress tunnel, characterized in that, Includes the following steps: Step 1: Based on the tunnel engineering geological survey report, determine the stress concentration area at the tunnel face according to the initial ground stress of the original rock, the distribution of excavation disturbance stress field, and the geometric characteristics of the tunnel cross section; Step 1.1: Based on the tunnel engineering geological survey report, the initial ground stress of the original rock and the stress field distribution of excavation disturbance are inverted through numerical simulation to determine the stress distribution at the tunnel face during the tunnel excavation project; Step 1.2: Based on the spatial relationship between the stress distribution at the tunnel face and the geometry of the tunnel face, the stress concentration areas at the tunnel face are obtained; Step 2: Based on the tunnel engineering geological survey report, use the rockburst intensity assessment method to predict the rockburst level of the surrounding rock; Step 2.1: Based on the tunnel engineering geological survey report, obtain the actual condition of the surrounding rock of the tunnel, specifically including the burial depth, stratum lithology, initial in-situ stress, uniaxial compressive strength of the rock, surrounding rock classification, and hydrogeological conditions of the surrounding rock at the tunnel face. Step 2.2: Based on the actual conditions of the surrounding rock of the tunnel, draw a comprehensive judgment table of tunnel rockburst intensity, and comprehensively analyze and predict the rockburst level of the surrounding rock. The rockburst level of the surrounding rock specifically includes no rockburst, slight rockburst, moderate rockburst, and severe rockburst. Step 3: Based on the stress concentration area at the tunnel face and the rock burst level of the surrounding rock, determine the tunnel blasting pressure relief control method; Step 3.1: Determine the location of the pre-blasting stress relief holes based on the stress concentration area at the tunnel face; Step 3.2: Based on the rockburst level of the surrounding rock, compare and match different rockburst control schemes for advance blasting and decompression at the tunnel face, and determine the rockburst control scheme; The tunnel face pre-blasting decompression rockburst control scheme specifically includes: (1) For tunnel faces with no rock bursts or minor rock bursts, the blasting stress relief method is not used; (2) For tunnel faces with medium rockburst level, 9 to 14 shallow holes of extended excavation blasting are arranged in the stress concentration area for advance blasting and pressure relief. (3) For tunnel faces with strong rockburst, 3 to 5 deep holes are laid out for advance blasting to relieve pressure in the stress concentration area. If the intensity of the rockburst increases, it is used in conjunction with 9 to 14 shallow holes for advance blasting to relieve pressure in the extended tunneling blasting holes, that is, shallow holes are laid out around the stress concentration area. Step 3.2 specifically includes the following steps: The construction basis for the tunnel face pre-blasting pressure relief rockburst control scheme includes the construction cross-section diagram, pressure relief hole layout diagram, and blasting parameter table; Step 4: Effect check; After each blast, check the blasting effect; Step 4 describes checking the blasting effect; (1) Check if there is a misfire; if there is a misfire, handle it in accordance with the misfire handling procedure in the "Blasting Safety Regulations"; (2) If there is no misfire, observe the blasting crushing zone and the blasting fracture zone: Based on observations at the borehole opening, the blasting crushing zone, with a diameter of 50–70 mm centered on the original borehole centerline, showed an increase in fissures within a diameter range of 100–160 mm, indicating that the blasting caused the cracks. The rock mass within this range exhibited significant loosening. Based on the rock mass damage in this area, it was identified as the blasting fracture zone. The confining pressure within the blasting fracture zone and the blasting vibration zone loosened, and the high ground stress within them was effectively released.

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