Rockburst control method for advanced blasting pressure relief of tunnel face under asymmetric high stress

Abstract

The present invention provides a rockburst control method for advanced blasting pressure relief of a tunnel face under asymmetric high stress, and relates to the technical field of tunnel engineering. The method according to the present invention includes the following steps: based on a tunnel engineering geological survey report, determining stress concentration zones of the tunnel face according to initial in-situ stress of virgin tunnel rocks, distribution of an excavation-induced stress field, and geometrical characteristics of tunnel cross-sections; based on the tunnel engineering geological survey report, predicting a grade of rockburst of surrounding rocks by using a rockburst intensity assessment method; based on the stress concentration zones of the tunnel face and the grade of the rockburst of the surrounding rocks, determining a rockburst control scheme for blasting pressure relief of tunnels; and after each blast, inspecting a blasting effect.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to the technical field of tunnel engineering, and in particular to a rockburst control method for advanced blasting pressure relief of a tunnel face under asymmetric high stress.THE PRIOR ARTS

[0002] Rockburst refers to a phenomenon that when tunnels and underground engineering traverse hard surrounding rocks and are in high in-situ stress zones, tunnel surrounding rocks originally in a true triaxial high-stress occurrence environment have a change in a stress path due to excavation, in-situ stress is released to suddenly destroy the surrounding rocks, along with release of large elastic strain energy inside rock masses, such as ejection, throwing and acoustic emission, with primary characteristics being violent nature and abruptness. Impact of the rockburst on tunnel construction is manifested primarily as deterioration of the construction environment, damage and destruction to personnel, equipment, and initial tunnel supports, increased safety risks and reduced construction efficiency.

[0003] As rockburst risks increase, the rockburst particularly intense rockburst and extremely-intense rockburst cannot be fully controlled by supports alone, and a blasting stress relief method is an effective rockburst control means. The method is a surrounding rock weakening method, and reconstructs a surrounding rock structure by pre-drilling holes and charging with appropriate explosives, thereby reducing stiffness of the rock masses within stress concentration zones near the tunnel face, transforming the rock masses within the influence range of drilling and blasting into a weaker stress-transfer medium, enhancing deformation to adjust an energy distribution state in local surrounding rocks, and improve a stress concentration degree, and enabling the concentration zone to transfer to a position ahead of the tunnel face, so as to achieve the objective of rockburst prevention and control. During tunnel excavation, the stress of the tunnel face is frequently in an asymmetric state, but current blasting stress relief methods predominantly adopt a uniform hole arrangement manner across the tunnel face instead of arranging stress relief holes across the stress concentration zones formed by asymmetric high stress of the tunnel face, leading in arrangement of a large quantity of stress relief holes, such that labor and material resources are wasted, and even the rockburst is induced in advance due to improper hole arrangement. Therefore, in the present invention, standardized hole arrangement is performed on the stress concentration zones according to different grades of rockburst, compared with uniform hole arrangement of the tunnel face, the standardized hole arrangement reduces the quantity of the stress relief holes, more effectively improves stress distribution ahead of the tunnel face, enables the stress concentration zones to transfer inwards, improves construction safety and construction efficiency during tunnel excavation operations, and ensures safety of the construction personnel and the equipment.SUMMARY OF THE INVENTION

[0004] To overcome defects in the prior art, the present invention provides a rockburst control method for advanced blasting pressure relief of a tunnel face under asymmetric high stress, thereby effectively improving stress distribution ahead of the tunnel face with rockburst risks, enabling stress concentration zones to transfer inwards, improving construction safety and construction efficiency during tunnel excavation operations, and ensuring safety of construction personnel and equipment.

[0005] The rockburst control method for advanced blasting pressure relief of a tunnel face under asymmetric high stress specifically includes the following steps.

[0006] Step 1: based on a tunnel engineering geological survey report, determining stress concentration zones of the tunnel face according to initial in-situ stress of virgin tunnel rocks, distribution of an excavation-induced stress field, and geometrical characteristics of tunnel cross-sections;

[0007] Step 1.1: based on the tunnel engineering geological survey report, inverting the initial in-situ stress of the virgin tunnel rocks and the distribution of the excavation-induced stress field by a numerical simulation method, so as to determine stress distribution situations of the tunnel face in tunnel excavation engineering; and

[0008] Step 1.2: obtaining the stress concentration zones of the tunnel face according to a spatial relationship between the stress distribution situations of the tunnel face and a geometrical shape of the tunnel face;

[0009] Step 2: based on the tunnel engineering geological survey report, predicting a grade of rockburst of surrounding rocks by using a rockburst intensity assessment method;

[0010] Step 2.1: based on the tunnel engineering geological survey report, obtaining actual conditions of the surrounding rocks specifically including a buried depth of the surrounding rocks of the tunnel face, formation lithology, the initial in-situ stress, uniaxial compressive strength of rocks, classification of the surrounding rocks, and hydrogeological conditions; and

[0011] Step 2.2: according to the actual conditions of the surrounding rocks, compiling a comprehensive tunnel rockburst intensity assessment table, and comprehensively analyzing and predicting the grade of the rockburst of the surrounding rocks, wherein the grade of the rockburst of the surrounding rocks specifically includes: no rockburst, mild rockburst, moderate rockburst, and intense rockburst;

[0012] Step 3: based on the stress concentration zones of the tunnel face and the grade of the rockburst of the surrounding rocks, determining a rockburst control scheme for blasting pressure relief of tunnels;

[0013] Step 3.1: determining arrangement positions of advanced blasting stress pressure relief holes according to the stress concentration zones of the tunnel face; and

[0014] Step 3.2: matching different rockburst control schemes for advanced blasting pressure relief of the tunnel faces according to the grade of the rockburst of the surrounding rocks, so as to determine the rockburst control scheme.

[0015] The rockburst control scheme for advanced blasting pressure relief of the tunnel faces specifically includes:

[0016] (1) For tunnel faces with the grades of no rockburst and mild rockburst, a blasting stress relief method is not used;

[0017] (2) For tunnel faces with the grade of moderate rockburst, 9-14 shallow extended-driven blast holes are arranged within the stress concentration zones for advanced blasting pressure relief; and

[0018] (3) For tunnel faces with the grade of intense rockburst, 3-5 deep holes are arranged within the stress concentration zones for advanced blasting pressure relief, if an intensity of the grade of the rockburst increases, the 3-5 deep holes are arranged for use in combination with 9-14 shallow extended-driven blast holes for advanced blasting pressure relief, that is to say, the shallow holes are arranged in peripheral zones of the stress concentration zones.

[0019] It shall be noted that a construction basis for the rockburst control scheme for advanced blasting pressure relief of the tunnel face includes a construction cross-section drawing, a pressure relief hole arrangement drawing, and a blasting parameter table.

[0020] Step 4: effect inspection: after each blasting, inspecting a blasting effect.

[0021] (1) Inspecting whether a misfire detonation phenomenon occurs, if the misfire detonation phenomenon occurs, treating the misfire detonation phenomenon according to misfire treatment procedures specified in Safety Regulations for Blasting; and

[0022] (2) If no misfire detonation phenomenon occurs, observing a blasting crushing zone and a blasting fracture zone are observed.

[0023] According to observations from a borehole, the blasting crushing zone is defined in a manner that a central line of an original borehole is used as an axis, and a diameter thereof is in a range of 50-70 mm; within a range of the diameter being 100-160 mm, an increase in fractures is observed and determined to be caused by blasting, rock masses within the range exhibit significant loosening, and according to a rock mass damage condition within the range, the zone is determined as the blasting fracture zone; and confining pressure loosening is observed in the blasting fracture zone and a blasting vibration zone, and high in-situ stress in the blasting fracture zone and high in-situ stress in the blasting vibration zone are both effectively released.

[0024] Implementation of the above technical solution has the beneficial effects.

[0025] The present invention provides the rockburst control method for advanced blasting pressure relief of a tunnel face under asymmetric high stress. In the method, based on a tunnel engineering geological survey report, stress concentration zones of the tunnel face are determined according to initial in-situ stress of virgin tunnel rocks, distribution of an excavation-induced stress field, and geometrical characteristics of tunnel cross-sections; based on the tunnel engineering geological survey report, the grade of the rockburst of surrounding rocks is predicted by using a rockburst intensity assessment method; and based on the stress concentration zones of the tunnel face and the grade of the rockburst of the surrounding rocks, a rockburst control scheme for blasting pressure relief of tunnels is determined. This method solves the problem that during practical engineering, the tunnel face is under asymmetric high-stress conditions, and the stress concentration zones have poor effect on advanced pressure relief effects. Compared with uniform hole arrangement of the tunnel face, this method reduces the quantity of the stress relief holes, more effectively improves stress distribution ahead of the tunnel face, enables the stress concentration zones to transfer inwards, improves construction safety and construction efficiency during tunnel excavation operations, and ensures safety of the construction personnel and the equipment.BRIEF DESCRIPTION OF DRAWINGS

[0026] FIG. 1 is a flowchart of a rockburst control method for advanced blasting pressure relief of a tunnel face under asymmetric high stress according to an embodiment of the present invention.

[0027] FIG. 2 is a schematic diagram of a primary stress concentration zone of surrounding rocks of a tunnel face under asymmetric initial in-situ stress conditions according to an embodiment of the present invention.

[0028] FIG. 3 is a comparative schematic diagram of stress distribution ahead of a tunnel face under asymmetric initial in-situ stress conditions before and after pressure relief according to an embodiment of the present invention.

[0029] FIG. 4 is a schematic diagram of advanced blasting pressure relief using 9-14 shallow extended relief holes according to an embodiment of the present invention.

[0030] FIG. 5 is a schematic diagram of advanced blasting pressure relief using 3-5 deep holes according to an embodiment of the present invention, wherein (a) is a plan view of a tunnel face, and (b) is a longitudinal cross-sectional view of the tunnel face.

[0031] FIG. 6 is a schematic diagram of internal action failure zones of a single blasting pressure relief hole according to an embodiment of the present invention.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0032] The specific implementations of the present invention are described in more detail below with reference to the accompanying drawings and embodiments. The following embodiments are provided to illustrate the invention but are not intended to limit the scope of the present invention.

[0033] A rockburst control method for advanced blasting pressure relief of a tunnel face under asymmetric high stress, as shown in FIG. 1, specifically includes the following steps.

[0034] Step 1: based on a tunnel engineering geological survey report, determining stress concentration zones of the tunnel face according to initial in-situ stress of virgin tunnel rocks, distribution of an excavation-induced stress field, and geometrical characteristics of tunnel cross-sections.

[0035] Step 1.1: based on the tunnel engineering geological survey report, inverting the initial in-situ stress of the virgin tunnel rocks and the distribution of the excavation-induced stress field by a numerical simulation method, so as to determine stress distribution situations of the tunnel face in tunnel excavation engineering.

[0036] Step 1.2: obtaining the stress concentration zones of the tunnel face according to a spatial relationship between the stress distribution situations of the tunnel face and a geometrical shape of the tunnel face.

[0037] In the embodiment, in FIG. 2, according to in-situ stress distribution situation of the tunnel face, if a magnitude and an orientation of a maximum principal stress σ1 are given, the maximum principal stress σ1 in FIG. 2 traverses through the tunnel face from a left haunch to a right crown, and a spatial relationship determines that the stress concentration zones are at an upper-left corner shaded region of the tunnel face; and if a stress distribution nephogram of the tunnel face is given, the stress concentration zones can be directly delineated at high-stress zones according to the stress distribution nephogram of the tunnel face.

[0038] Step 2: based on the tunnel engineering geological survey report, predicting a grade of rockburst of surrounding rocks by using a rockburst intensity assessment method.

[0039] Step 2.1: based on the tunnel engineering geological survey report, obtaining actual conditions of the surrounding rocks specifically including a buried depth of the surrounding rocks of the tunnel face, formation lithology, the initial in-situ stress, uniaxial compressive strength of rocks, classification of the surrounding rocks, and hydrogeological conditions.

[0040] Step 2.2: according to the actual conditions of the surrounding rocks, compiling a comprehensive tunnel rockburst intensity assessment table, and comprehensively analyzing and predicting the grade of the rockburst of the surrounding rocks, wherein the grade of the rockburst of the surrounding rocks specifically includes: no rockburst, mild rockburst, moderate rockburst, and intense rockburst.

[0041] For theoretical analysis on rockburst prediction in the embodiment, multiple assessment criteria have been proposed by global experts. Appropriate existing criteria are selected for individual projects according to specific tunnel characteristics to pre-judge the grade of the rockburst. For example, for a certain tunnel, after comprehensive consideration, four applicable criteria are selected as shown in four (4) tables below, so as to compile a comprehensive rockburst intensity assessment table, thereby performing comprehensive pre-judgment on the grade of the rockburst of the surrounding rocks. If pre-judgment results of the 4 grades of the rockburst for a given tunnel section conflict, a pre-judgment result is determined by majority principle.

[0042] 1) Buried depthBuried depth <320320-485485-886>886H (m)RockburstNo Mild ModerateIntenseintensityrockburstrockburstrockburstrockburst2) Uniaxial compressive strength of rocksUniaxial<8080-120120-180>180compressivestrength of rocksσc (MPa)RockburstNo Mild ModerateIntenseintensityrockburstrockburstrockburstrockburst3) Grade of surrounding rocksGrade ofIV-VIII-IVII-IIII-IIsurroundingrocksRockburstNo Mild ModerateIntenseintensityrockburstrockburstrockburstrockburst4) Stress ratio σmax / σc (where σmax refers to the magnitude of maximum principal stress at the tunnel face, and σc refers to the uniaxial compressive strength of rocks at the tunnel face)Stress ratio<0.150.15-0.250.2-0.350.35σmax / σcRockburstNo rockburstMild rockburstModerateIntenseintensityrockburstrockburstStep 3: based on the stress concentration zones of the tunnel face and the grade of the rockburst of the surrounding rocks, determining a rockburst control scheme for blasting pressure relief of tunnels.Step 3.1: determining arrangement positions of advanced blasting stress pressure relief holes according to the stress concentration zones of the tunnel face.Step 3.2: matching different rockburst control schemes for advanced blasting pressure relief of the tunnel faces according to the grade of the rockburst of the surrounding rocks, so as to determine the rockburst control scheme.The rockburst control scheme for advanced blasting pressure relief of the tunnel faces specifically includes the followings.

[0050] Based on domestic literature and related rockburst control schemes for tunnel blasting pressure relief, because a blasting stress relief method is complex in construction procedures, and conventional support schemes can effectively prevent and control rockburst, blasting stress relief is unnecessary for sections having mild rockburst; surrounding rock support measures are sufficient for rockburst prevention for the grade of the mild rockburst, but cannot prevent and resist rockburst occurrence for the moderate rockburst and above, an additional measure is needed, that is to say, an advanced blasting pressure relief method is used to weaken the surrounding rocks and transfer stress. Compared with the conventional advanced blasting pressure relief method adopting uniform arrangement, the present invention aims to provide a manner of arranging holes only in the stress concentration zones so as to achieve the purposes of achieving better effects even if the quantity of the arranged holes is reduced, weakening the surrounding rocks, and inducing a rockburst fracture zone and stress to move to a position ahead of the tunnel face to achieve the stress transfer effect in FIG. 3. Due to low occurrence risks of the mild rockburst and minimal hazards associated with the mild rockburst, shallow-hole blasting is adopted for the sections with moderate rockburst, and deep-hole blasting is predominantly adopted for the sections with intense rockburst. A stress transfer distance using the shallow-hole blasting is shorten than that using the deep-hole blasting, but construction procedures of the shallow-hole blasting are simpler than those of the deep-hole blasting, and the grade of intense rockburst exhibits a larger destructive scope and a magnitude than the grade of moderate rockburst, and after the comprehensive consideration, the scheme is implemented as follows:

[0051] in the embodiment, a normal driven blasting cyclic advance length L for a given tunnel is 3 meters.

[0052] For the grades of moderate rockburst and above, a construction principle of “shorter advance, reduced-intensity blasting” is universally adopted in rockburst prevention measures. Consequently, a driven blasting cyclic advance length / in the sections having moderate rockburst and above is set as 1.5 meters.

[0053] (1) For tunnel faces with the grade of no rockburst and mild rockburst, a blasting stress relief method is not used.

[0054] (2) For tunnel faces with the grade of moderate rockburst, 9-14 shallow extended-driven blast holes are arranged within the stress concentration zones for advanced blasting pressure relief.

[0055] For the stress concentration zones at the left crown of the tunnel face, 9-14 shallow blasting pressure relief holes of which the hole depth is 3 times of the cyclic advance length (3 l) and of which the hole diameter is the hole diameter of the driven blast holes are pre-drilled by an original rock drilling rig for drilling and driving blast holes of tunnels, where blasting parameters and arrangement drawings are shown in Table 1 and FIG. 4, respectively. The blasting stress relief holes (namely shallow holes) have the hole depth of 4.5 m, and the hole diameter of Φ42 mm. The holes are drilled at driven blast hole positions, in a direction extending from the driven blast holes, the blast holes close to an outline of the tunnel face are obliquely arranged at 15 degrees towards the direction of the outline of the tunnel face, a blasting loosening zone of at least two cyclic advance lengths (3 m) is always kept ahead of a driven working face so as to pre-loosen the surrounding rocks and relieve stress. In combination with actual in-situ rockburst conditions and micro-vibration monitoring data, hole arrangement positions can be adjusted, the quantity of the shallow holes can be increased, and the blasting parameters can be changed.TABLE 1Blasting parameter table of 9-14 shallow extended relief holes for advanced blasting pressure reliefQuantity ofexplosivesHoleDiameter of a Arrangement charged in Pluggingdepth / mdrilled hole / mmparametereach hole / kglength / m4.542 (identical to Uniform arrangement of3.751.5driven blasting relief holes within stressparameters)concentration zones(3) For tunnel faces with the grade of intense rockburst, 3-5 deep holes are arranged within the stress concentration zones for advanced blasting pressure relief, if an intensity of the grade of the rockburst increases, the 3-5 deep holes are arranged for use in combination with 9-14 shallow extended-driven blast holes for advanced blasting pressure relief, that is to say, shallow holes are arranged in peripheral zones of the stress concentration zones.

[0057] For the stress concentration zones at the left crown of the tunnel face, 3-5 15-meter blasting pressure relief deep holes of @108 are pre-drilled by using a ZY880 down-the-hole drill, and the blasting parameters and the arrangement drawing are respectively shown in Table 2 and FIG. 5. The drilling positions and the driven blasting holes are staggered, and a blasting loosening zone of at least 4 cyclic advance lengths (6 m) is always kept ahead of a driven working face so as to pre-loosen the surrounding rocks and relieve stress. In combination with actual in-situ rockburst conditions and micro-vibration monitoring data, hole arrangement positions can be adjusted, the quantity of deep holes can be increased, and the blasting parameters can be changed.TABLE 2Blasting parameter table of 3-5 deep holes for advanced blasting pressure reliefQuantity of HoleDiameter explosivesdepth / of a drilled Arrangement charged in Pluggingmhole / mmparametereach hole / kglength / m15108The holes are uniformly25-307distributed in the stress concentration zones, with a hole space being 1 m

[0058] It shall be noted that a construction basis for a rockburst control scheme for advanced blasting pressure relief of the tunnel face includes a construction cross-section drawing, a pressure relief hole arrangement drawing, and a blasting parameter table, as shown in Table 1 and FIG. 4.

[0059] Step 4: effect inspection: blasting may form a blasting crushing zone, a blasting fracture zone and a blasting vibration zone, as shown in FIG. 6. After each blast, a blasting effect is inspected.

[0060] (1) Inspecting whether a misfire detonation phenomenon occurs, if the misfire detonation phenomenon occurs, treating the misfire detonation phenomenon according to misfire treatment procedures specified in Safety Regulations for Blasting.

[0061] (2) If no misfire detonation phenomenon occurs, observing a blasting crushing zone and a blasting fracture zone.

[0062] According to observations from a borehole, the blasting crushing zone is defined in a manner that a central line of an original borehole is used as an axis, and a diameter thereof is in a range of 50-70 mm; within a range of the diameter being 100-160 mm, an increase in fractures is observed and determined to be caused by blasting, rock masses within the range exhibit significant loosening, and according to a rock mass damage condition within the range, the zone is determined as the blasting fracture zone; and confining pressure loosening is observed in the blasting fracture zone and a blasting vibration zone, and high in-situ stress in the blasting fracture zone and high in-situ stress in the blasting vibration zone are both effectively released.

[0063] The preceding description merely presents preferred embodiments of the present invention and explains the technical principles applied. Persons skilled in the art should appreciate that the coverage of the present invention involved in the embodiments of the present invention extends beyond the technical solutions formed by specific combinations of the above technical features, but also covers any other technical solutions formed by arbitrary combinations of the above technical features or their equivalent features without departing from the inventive concept described herein, such as the technical solutions formed by interchangeably replacing the aforementioned features with technical features having similar functions (including but not limited to those disclosed in the embodiments of the present invention).

Claims

1. A rockburst control method for advanced blasting pressure relief of a tunnel face under asymmetric high stress, comprising the following steps:Step 1: based on a tunnel engineering geological survey report, determining stress concentration zones of the tunnel face according to initial in-situ stress of virgin tunnel rocks, distribution of an excavation-induced stress field, and geometrical characteristics of tunnel cross-sections;Step 1.1: based on the tunnel engineering geological survey report, inverting the initial in-situ stress of the virgin tunnel rocks and the distribution of the excavation-induced stress field by a numerical simulation method, so as to determine stress distribution situations of the tunnel face in tunnel excavation engineering; andStep 1.2: obtaining the stress concentration zones of the tunnel face according to a spatial relationship between the stress distribution situations of the tunnel face and a geometrical shape of the tunnel face:Step 2: based on the tunnel engineering geological survey report, predicting a grade of rockburst of surrounding rocks by using a rockburst intensity assessment method;Step 2.1: based on the tunnel engineering geological survey report, obtaining actual conditions of the surrounding rocks comprising a buried depth of the surrounding rocks of the tunnel face, formation lithology, the initial in-situ stress, uniaxial compressive strength of rocks, classification of the surrounding rocks, and hydrogeological conditions; andStep 2.2: according to the actual conditions of the surrounding rocks, compiling a comprehensive tunnel rockburst intensity assessment table, and comprehensively analyzing and predicting the grade of the rockburst of the surrounding rocks, wherein the grade of the rockburst of the surrounding rocks comprises: no rockburst, mild rockburst, moderate rockburst, and intense rockburst:Step 3: based on the stress concentration zones of the tunnel face and the grade of the rockburst of the surrounding rocks, determining a rockburst control scheme for blasting pressure relief of tunnels;Step 3.1: determining arrangement positions of advanced blasting stress pressure relief holes according to the stress concentration zones of the tunnel face; andStep 3.2: matching different rockburst control schemes for advanced blasting pressure relief of the tunnel faces according to the grade of the rockburst of the surrounding rocks, so as to determine the rockburst control scheme;wherein the rockburst control scheme for advanced blasting pressure relief of the tunnel faces comprises:(1) for tunnel faces with the grades of no rockburst and mild rockburst, a blasting stress relief method is not used;(2) for tunnel faces with the grade of moderate rockburst, 9-14 shallow extended-driven blast holes are arranged within the stress concentration zones for advanced blasting pressure relief; and(3) for tunnel faces with the grade of intense rockburst, 3-5 deep holes are arranged within the stress concentration zones for advanced blasting pressure relief, if an intensity of the grade of the rockburst increases, the 3-5 deep holes are arranged for use in combination with 9-14 shallow extended-driven blast holes for advanced blasting pressure relief, in which the shallow holes are arranged in peripheral zones of the stress concentration zones;wherein a construction basis for the rockburst control scheme for advanced blasting pressure relief of the tunnel face comprises a construction cross-section drawing, a pressure relief hole arrangement drawing, and a blasting parameter table; andStep 4: effect inspection: after each blast, inspecting a blasting effect;wherein the inspecting the blasting effect comprises:(1) inspecting whether a misfire detonation phenomenon occurs, if the misfire detonation phenomenon occurs, treating the misfire detonation phenomenon according to misfire treatment procedures specified in Safety Regulations for Blasting; and(2) if no misfire detonation phenomenon occurs, observing a blasting crushing zone and a blasting fracture zone;according to observations from a borehole, the blasting crushing zone is defined in a manner that a central line of an original borehole is used as an axis, and a diameter thereof is in a range of 50-70 mm; within a range of the diameter being 100-160 mm, an increase in fractures is observed and determined to be caused by blasting, rock masses within the range exhibit significant loosening, and according to a rock mass damage condition within the range, the zone is determined as the blasting fracture zone; and confining pressure loosening is observed in the blasting fracture zone and a blasting vibration zone, and high in-situ stress in the blasting fracture zone and high in-situ stress in the blasting vibration zone are both released.2.-7. (canceled)

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