GB2611425A

GB2611425A - Three-step cut blasting structure and method for ultra-hard rock tunnel

Info

Publication number: GB2611425A
Application number: GB2214010.7A
Authority: GB
Inventors: Zhang Xin; Sun Jinshan; Zhang Xiangping
Original assignee: China Railway 18th Bureau Group Co Ltd
Current assignee: China Railway 18th Bureau Group Co Ltd
Priority date: 2022-08-31
Filing date: 2022-09-26
Publication date: 2023-04-05
Anticipated expiration: 2042-09-26
Also published as: CN115325894A; CN115325894B; GB202214010D0; GB2611425B

Abstract

The blasting structure includes drilling cuts or holes perpendicular to a tunnel cross section; the cuts include a first-step cut 1-1, second-step cuts 1-2 provided on a periphery of the first-step cut and third-step cuts1-3 provided on a periphery of the second-step cuts ; and explosives are loaded in the first-step cut and the third-step cuts, with the second-step cuts in the absence of explosive. Also disclosed is a circular cover or cap (1-11 Figure 4) to fix the explosives in place. Legs or arms 1-122 extend from the circular cover into the hole.

Description

THREE-STEP CUT BLASTING STRUCTURE AND METHOD FOR ULTRA-HARD

ROCK TUNNEL

BACKGROUND OF THE INVENTION

1. Technical Field

[0001] The present disclosure relates to the technical field of tunnel construction blasting, in particular to a three-step cut blasting structure and method for an ultra-hard rock tunnel.

2. Description of Related Art

[0002] Since an ultra-hard rock/hard rock is a rock having a hardness coefficient f=15-20, there are technical problems of poor cut basting effect, long residual blasthole and short footage during ultra-hard rock tunnel blasting.

[0003] At present, a construction method for II-class surrounding rocks employs a two-step wedge-shaped cut blasting method, in which a first-step cut has a depth of 1.5 m, a second-step cut has a depth of 3.0 m, the other blastholes each have a depth of 2.8 m, there are 63 blastholes on a full section, 96 Kg of explosives are loaded, each blasting footage is 1.8 m-2.0 m, a remaining blasthole length is 0.7 m-0.8 m, and a blasthole utilization rate is 64.3%-71.4%. An existing construction method has the following defects: although the cut has a depth of 3.0 m, a remaining blasthole length is 1.0 m-1.2 m after blasting, rending a poor cut basting effect. Moreover, a wedge cut is difficult to drill because of a short section and a narrow site, only a short drill pipe can be used to carry out drilling by 1.6 m at first, and then a long drill pipe is used to continue drilling to a designed depth. Each blasting footage is only 1.8 m-2.0 m, and only 60 m-70 m of task can be completed each month, such that a construction progress is slow, and a construction period is prolonged. On account of a short footage and long residual blastholes, explosive consumption is certainly high. In addition, due to a poor smooth blasting effect, the quantity of sprayed concrete for primary support is increased, causing cost waste and obvious loss.

BRIEF SUMMARY OF THE INVENTION

[0004] The present disclosure provides a three-step cut blasting structure and method for an ultra-hard rock tunnel. The blasting structure includes cuts perpendicular to a tunnel section; the cuts include a first-step cut, second-step cuts provided on a periphery of the first-step cut and third-step cuts provided on a periphery of the second-step cuts; and explosives are loaded in the first-step cut and the third-step cuts, with the second-step cuts in the absence of explosive (e.g. no explosive is loaded in the second-step cuts).

[0005] On the basis of the above solution, the first-step cut, the second-step cuts and the third-step cuts have the same depth.

[0006] On the basis of the above solution, a circular cover is fixed at each of two ends of the explosives in the first-step cut, and each circular cover is a round metal plate having a certain thickness.

[0007] On the basis of the above solution, fixed arms are fixed on the circular covers respectively. Each fixed arm is in a shape of I (e.g. U-shaped)and includes a transverse portion and extension portions formed by extending two ends of the transverse portion in a direction towards the explosives.

[0008] The present disclosure further provides a three-step cut blasting method for an ultra-hard rock tunnel, and specifically, the above blasting structure is used. Specific steps are as follows: [0009] the method includes the following steps: [0010] Si: carrying out blasthole construction [0011] drilling blastholes on a tunnel section by a pneumatic drill; where a first-step cut is positioned at a center, second-step cuts are positioned on a periphery of the first-step cut, and third-step cuts are positioned on a periphery of the second-step cuts; the blastholes further include several cut spreader holes provided on a periphery of the third-step cuts, several auxiliary holes provided on a periphery of the cut spreader holes, several periphery holes provided on a periphery of the auxiliary holes and several bottom holes positioned at a bottom of the tunnel section; and the first-step cut, the second-step cuts and the third-step cuts have the same depth, and the depth is greater than that of the other blastholes; and [0012] clearing residual debris and water from each blasthole after drilling is completed.

[0013] S2: Loading explosives, [0014] where the explosives are loaded in the first-step cut, the third-step cuts, the cut spreader holes, the auxiliary holes, the periphery holes and the bottom holes, with the second-step cuts (1-2) in the absence of explosive; [0015] when the explosives in the first-step cut are loaded, a circular cover is fixed at each of two ends of the explosives, and each circular cover is a round metal plate having a certain thickness; fixed arms are fixed on the circular covers respectively; each fixed arm is in a shape of I (e.g. U-shaped) and includes a transverse portion and extension portions formed by extending two ends of the transverse portion in a direction towards the explosives; and the extension portions are fixedly connected to the explosives; and [0016] plugging the blastholes after the explosives are loaded. A specific plugging method includes: [0017] plugging each of the first-step cut and the third-step cuts by means of one section of stemming, one plug, one section of stemming, one plug and one section of stemming in sequence from inside to outside to plug each blasthole; [0018] plugging each of the cut spreader holes, the auxiliary holes and the bottom holes by means of one section of stemming and one plug; and [0019] plugging each of orifices of the periphery holes by means of 0.3 m of water stemming.

[0020] 53: Carrying out blasting, [0021] where a blasting sequence is: the first-step cut, the third-step cuts, the cut spreader holes, the auxiliary holes, the periphery holes and the bottom holes.

[0022] According to the blasting structure and method in the present disclosure, aiming at blasting of the ultra-hard rock tunnel, three steps of same-depth parallel horizontal cylinder type cuts are used such that drilling may be simultaneously carried out by a plurality of drill machines without interference, and a long drill pipe may be used for drilling and hole-forming at one time, so as to raise drilling efficiency. A unique cut blasting action mechanism of this patent: by using barrel covers processed by round steel and steel plates and a unique cover-barrel type loading structure of stemming and plug plugging, gathering of blasting energy at a lower portion of the blastholes are guaranteed. Due to a plurality of free cylinders in second-step empty holes, a breaking range at a lower portion of the ultra-hard rock may be effectively expanded, and ballast throwing is smoothly realized after third-step blasting, such that the whole cut blasting effect is guaranteed, "barrel pulling is eliminated, and a cut blasting depth is guaranteed. Only 0.3 m of an orifice of each periphery blasthole is plugged by means of soft and wet water stemming, such that cracks between adjacent periphery holes are through, rocks may smoothly peel off along an excavation contour line, and a desirable smooth blasting effect is guaranteed. A blasting footage is increased from 1.8 m-2.0 m to 3.2 m-3.4 m, a blasthole utilization rate is increased from 70% to 92%, and monthly construction progress is increased from 60 m-70 m to 170 m-190 m, and may reach 220 m mostly. A desirable smooth blasting effect is achieved, over-excavation and under-excavation are reduced, the quantity of sprayed concrete for primary support is reduced, primary support time is shortened, and construction cost is saved

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0023] Fig. 1 is a schematic diagram of arrangement of blastholes on a tunnel section in the present disclosure (the tunnel section is in a vertical wall-circular arch type); [0024] Fig. 2 is a schematic diagram of positions and distances of blastholes on a tunnel section in the present disclosure (the tunnel section is in a vertical wall-circular arch type); [0025] Fig. 3 is a schematic diagram of an explosive loading structure in a

first-step cut in the present disclosure;

[0026] Fig. 4 is a schematic structural diagram of a circular cover and fixed

arms in the present disclosure;

[0027] Fig. 5 is a schematic diagram of loading and plugging structures in a

first-step cut in the present disclosure; and

[0028] Fig. 6 is a smooth blasting effect diagram of a tunnel in an application

example in the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

[0029] The present disclosure will be described in further detail in combination with the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present disclosure, and are not intended to limit it.

[0030] Embodiment 1 [0031] As shown in Fig. 1, the embodiment provides a three-step cut blasting structure for an ultra-hard rock tunnel. Specifically, the ultra-hard rock or hard rock in the present disclosure refers to a rock having a hardness coefficient f'=15-20.

[0032] The blasting structure includes cuts 1 perpendicular to a tunnel section. The cuts 1 are in a form of three steps of same-depth cylinder (barrel) type cuts, and the cuts 1 include a first-step cut 1-1, second-step cuts 1-2 provided on a periphery of the first-step cut 1-1 and third-step cuts 1-3 provided on a periphery of the second-step cuts 1-2. Explosives are loaded in the first-step cut 1-1 and the third-step cuts 1-3, with the second-step cuts (1-2) in the absence of explosive.

[0033] A cut blasting effect is the most important during blasting construction of a full excavation section (a tunnel section), and therefore the cut blasting problem during blasting construction for an ultra-hard rock is to be solved at first in the present disclosure. During blasting, a traditional method is to directly load explosives in cuts 1, but the second-step cuts 1-2 in this patent are only used as empty slots, and no explosive is placed therein. In this way, a breaking range may be expanded during blasting of the first-step cut 1-1, and ballast throwing and cut blasting effects may be achieved during blasting of the third-step cuts 1-3, thereby solving the problems of poor cut blasting effect, long residual blasthole and short footage of the ultra-hard rock tunnel.

[0034] As a specific implementation solution, the first-step cut 1-1, the second-step cuts 1-2 and the third-step cuts 1-3 in this patent have the same depth.

[0035] During blasting, a traditional method is to directly load explosives in the cuts 1, but a blasting effect is not ideal in the face of ultra-hard rock/hard rock. Therefore, this patent provides a technical solution for enhancing a blasting effect, specifically, a circular cover 1-11 is fixed at each of two ends of the explosives in the first-step cut 1-1, and each circular cover 1-11 is specifically a round metal plate having a certain thickness, such as a steel plate having a thickness of 6 mm In this way, energy is gathered in the first-step cut 1-1 during blasting, such that a blasting effect is enhanced.

[0036] In order to better fix the circular covers 1-11 to the explosives, as shown in Figs. 3 and 4, fixed arms 1-12 are fixed on the circular covers 1-11 respectively, and the fixed arms 1-12 extend in a direction towards the explosives. In order to enhance strength of the circular covers 1-11, as an implementable solution, each fixed arm 1-12 is in shape of L..J (e.g. U-shaped) and includes a transverse portion 1-121, and two ends of the transverse portion 1-121 extend in a direction towards the explosives to form extension portions 1-122. The transverse portion 1-121 is welded to the circular covers 1-11 (as shown in Fig. 3) such that the transverse portions 1-121 of the fixed arms 1-12 may effectively enhance strength of the circular covers 1-11, and the extension portions 1-122 are fixed to the explosives. Specifically, each fixed arm 1-12 may be formed by bending round steel having a diameter of 8 mm. When the circular covers 1-11 and the fixed arms 1-12 that are welded together are fixed to the explosives, an adhesive tape is used to wind and fix the extension portions 1-122 extending in a direction towards the explosives and the explosives. Due to an explosive cartridge and the circular covers 1-11 that are fixed together, energy is gathered when the explosives explodes, such that a blasting effect is enhanced.

[0037] As a specific application example, the first-step cut 1-1 has a diameter of 45 mm, a conventional explosive cartridge has a diameter of 35 mm, and each circular cover 1-11 has a diameter of 40 mm. In this way, an energy gathering effect of the circular covers 1-11 may be guaranteed, and the explosives with the circular covers 1-11 may be placed into the first-step cut 1-1. Since a difference between the diameter of each circular cover 1-11 and the diameter of the first-step cut 1-1 is only 5 mm, and the first-step cut 1-1 is horizontal it is difficult to load the explosives into a bottom of the first-step cut 1-1 during placement. In order to conveniently place the explosives, a handle 1-13 is fixed on one side, away from the explosives, of the circular cover 1-11 close to an outer side portion in the first-step cut 1-1, and the handle 1-13 may also be made of round steel having a diameter of 8 mm (as shown in Fig. 3).

[0038] After the explosives in the first-step cut 1-1 are loaded, the first-step cut 1-1 is completely blocked by means of one section of stemming, one plug, one section of stemming, one plug and one section of stemming in sequence, which is as shown in Fig. 5. According to this plugging method in the present disclosure, friction between the whole of the stemming and the plugs and a hole wall is increased, such that explosion gases, explosion stress waves, shock waves and detonation waves generated when the explosives explode are not prone to rush out, action time in the blasthole is prolonged, the rock is fully broken, and a cut blasting effect is fully exerted. After the explosives in the third-step cuts 1-3 are loaded, the third-step cuts are plugged in the same way as the first-step cut 1-1.

[0039] As a specific implementation solution, there are one first-step cut 1-1, four second-step cuts 1-2 and eight third-step cuts 1-3. A position relation between the first-step cut 1-1, the second-step cuts 1-2 and the third-step cuts 1-3 will be described below by taking Fig. 1 as an example: the four second-step cuts 1-2 are positioned on a small circumference with the first-step cut 1-1 as a circle center, and the four second-step cuts 1-2 are uniformly distributed on the small circumference. The eight third-step cuts 1-3 are positioned on a large circumference with the first-step cut 1-1 as a circle center, and the eight third-step cuts 1-3 are uniformly distributed on the large circumference. A connecting line between any one of the third-step cuts 1-3 and the first-step cut 1-1 does not pass through the second-step cuts 1-2. Through this structural design of the cuts in the present disclosure, since no explosive and detonator is loaded in the second-step cuts, and the second-step cuts are empty holes, a free surface is provided for the first-step cut, and the first-step cut is assisted in fully breaking rocks. Therefore, a clamping effect of the rocks at a bottom of the first-step cut is reduced, a blasting effect of this hole is enhanced, and the third-step cuts may continue to playing a role of expanding the cuts.

[0040] The special cut structure and the explosive loading method aiming at blasting of the ultra-hard rock tunnel in this patent is described above in detail. During actual blasting, besides the cuts 1, other auxiliary blastholes will be also provided on the blasting section. For example, as shown in Figs. 1 and 2, the blastholes further include several cut spreader hole 2 provided on a periphery of the third-step cuts 1-3, several auxiliary holes 3 provided on a periphery of the cut spreader holes 2, several periphery holes 4 provided on a periphery of the auxiliary holes 3 and several bottom holes 5 positioned at a bottom of the tunnel section. The cut spreader holes 2, the auxiliary holes 3, the periphery holes 4 and the bottom holes 5 have the same depth in a direction perpendicular to the tunnel section, and the depth is less than that of the cuts 1. For example, the cuts 1 has a depth of 3.8 m, and the cut spreader holes 2, the auxiliary holes 3, the periphery holes 4 and the bottom holes 5 each have a depth of 3.6 m.

[0041] All the cuts I, the cut spreader holes 2, the auxiliary holes 3, the periphery holes 4 and the bottom holes 5 each have a blasthole diameter of 45 mm.

[0042] The cut spreader holes 2, the auxiliary holes 3 and the bottom holes 5 are each plugged by means of one section of stemming and one plug, and an orifice of each periphery hole 4 is plugged by means of 0.3 m of water stemming. Since only 0.3 m of an orifice of each periphery hole 4 is plugged by means of water stemming, cracks between the adjacent periphery blastholes are through such that rocks may smoothly peel off along an excavation contour line, and a desirable smooth blasting effect is guaranteed.

[0043] On the tunnel section, the cuts 1 are provided at a lower middle portion of the tunnel section, and the tunnel section may be in a vertical wall-circular arch type, a vertical wall-three-centered arch type, an arc wall-arc arch type, an inclined wall-elliptical arch type and other types.

[0044] Embodiment 2 [0045] A three-step cut blasting method for an ultra-hard rock tunnel is provided below, and specific steps are as follows: [0046] Si: Carry out blasthole construction [0047] Drill blastholes (that are cuts 1, cut spreader holes 2, auxiliary holes 3, periphery holes 4 and bottom holes 5) on a tunnel section by a pneumatic drill; where a first-step cut 1-1 is positioned at a center, second-step cuts 1-2 are positioned on a periphery of the first-step cut 1-1, and third-step cuts 1-3 are positioned on a periphery of the second-step cuts 1-2; the blastholes further include several cut spreader holes 2 provided on a periphery of the third-step cuts 1-3, several auxiliary holes 3 provided on a periphery of the cut spreader holes 2, several periphery holes 4 provided on a periphery of the auxiliary holes 3 and several bottom holes 5 positioned at a bottom of the tunnel section; the cut spreader holes 2, the auxiliary holes 3, the periphery holes 4 and the bottom holes 5 have the same depth in a direction perpendicular to the tunnel section, and the depth is less than that of the cuts 1; as a preferred solution, the cuts 1 has a depth of 3.8 m, and the cut spreader holes 2, the auxiliary holes 3, the periphery holes 4 and the bottom holes 5 each have a depth of 3.6 m; and [0048] the specific number of the cuts 1 is: there are one first-step cut 1-1, four second-step cuts 1-2 and eight third-step cuts 1-3; and [0049] clear residual debris and water from each blasthole after drilling is completed.

[0050] S2: Load explosives, [0051] where the explosives are loaded in the first-step cut 1-1, the third-step cuts 1-3, the cut spreader holes 2, the auxiliary holes 3, the periphery holes 4 and the bottom holes 5, wherein the second-step cuts (-2) are in the absence of explosive; [0052] as a preferred solution, a usage quantity of explosives in each blasthole is: [0053] 1 Kg -12.4 Kg per first-step cut, 1 Kg -32.1 Kg per third-step cut, 21.8 Kg per cut spreader hole, 31.5 Kg per auxiliary hole, 41.2 Kg per periphery hole, and 51.5 Kg per bottom hole; and [0054] the method in Embodiment 1 is used as an explosive loading method in the first-step cut 1-1, that is, a circular cover 1-11 is installed at each of two ends of explosives for gathering energy, which will not be repeated herein; and [0055] plug the blastholes after the explosives are loaded. A specific plugging method includes: [0056] plug each of the first-step cut 1-1 and the third-step cuts 1-3 by means of one section of stemming, one plug, one section of stemming, one plug and one section of stemming in sequence from inside to outside to plug each blasthole; [0057] plug each of the cut spreader holes 2, the auxiliary holes 3 and the bottom holes 5 by means of one section of stemming and one plug; and [0058] plug an orifice of each periphery hole 4 by means of 0.3 m of water stemming.

[0059] S3: Carry out blasting [0060] A blasting sequence is: the first-step cut 1-1, the third-step cuts 1-3, the cut spreader holes 2, the auxiliary holes 3, the periphery holes 4 and the bottom holes 5.

[0061] Application case [0062] Lotus mountain tunnel is positioned at lotus mountain at an intersection between Hu dons county, Huizhou city, Guangdong province and Shenzhen-Shanwei special cooperation zone, the lotus mountain tunnel has a length of 5200 m, a tunnel clearance section has a size of 4.5 m x 4.5 m (hight x width) and is in a vertical wall-circular arch type, a DN914 gas pipeline is laid in the tunnel, and a designed pressure is 9.2 MPa.

[0063] The surrounding rocks of the lotus mountain tunnel are classified into class II to class VI. The tunnel has a horizontal length of 5200 m, where 11-class surrounding rocks have a length of 1016.69 m, accounting for 19.55% of a total length; HI-class surrounding rocks have a length of 2296.11 m, accounting for 44.15% of the total length; IV-class surrounding rocks have a length of 1116.53 m, accounting for 21.47% of the total length; V-class surrounding rocks have a length of 713.92 m, accounting for 13.73% of the total length; and VI-class surrounding rocks have a length of 57.04 m, accounting for 1.10% of the total length.

[0064] The II-class surrounding rocks are ultra-hard granite. An existing solution is: a two-step wedge-shaped cut blasting method is used, a first-step cut has a depth of 1.5 m, a second-step cut has a depth of 3.0 m, other blasthole each has a depth of 2.8 m, there are 63 blastholes on a full section, 96 Kg of explosives are loaded, each blasting footage is 1.8 m-2.0 m, a remaining blasthole length is 0.7 m-0.8 m, a blasthole utilization rate is 64.3%-71.4%, a footage is over short, and cost is high.

[0065] Construction is carried out by means of the blasting structure in Embodiment 1 of the present disclosure and through the blasting method in Embodiment 2 of the present disclosure, which will be described in detail below.

[0066] S 1: Carry out blasthole construction [0067] Drill holes (that are cuts 1, cut spreader holes 2, auxiliary holes 3, periphery holes 4 and bottom holes 5) by a YT-30 type pneumatic drill, a y 18 mm x 4.5 m hollow hexagonal drill pipe and a cp 42 mm cross type alloy steel drill bit (or a diamond bit) on a tunnel section, where the blastholes are distributed according to the requirements of a design drawing in Fig. 2 (references are made to Fig. 1 for region division and auxiliary lines), and left, right, upper and lower position relations in the following contents are all described on the basis of Fig. 2.

[0068] The tunnel section is divided into an upper portion and a lower portion along a dividing line M, that is, an arched section A at the upper portion and a vertical section B at the lower portion. A whole body is divided into a left portion and a right portion along a middle line N of the tunnel [0069] There are three circles of cuts 1 all provided on the vertical section B, there is one first-step cut 1-1 (numbered as TO), the one first-step cut passes through a middle line N of the tunnel. There are four second-step cuts 1-2 (numbered as 01, 02, 03 and 04) positioned on a periphery of the first-step cut I-I, There are eight third-step cuts 1-3 (numbered as Ti, T2, T3, T4, T5, TO, T7 and T8) positioned on a periphery of the second-step cuts 1-2. As shown in Fig. 2, the four second-step cuts 1-2 are positioned on a small circumference with the first-step cut 1-1 as a circle center, and the four second-step cuts 1-2 are uniformly distributed on the small circumference. The eight third-step cuts 1-3 are positioned on a large circumference with the first-step cut 1-1 as a circle center, and the eight third-step cuts 1-3 are uniformly distributed on the large circumference.

[0070] Cut spreader holes 2 are provided on a periphery of the third-step cuts 1-3, and there are 12 cut spreader holes (with numbers of K1 -K12), where six cut spreader holes are positioned on the vertical section B, three cut spreader holes being positioned on each of a left side and a right side of the third-step cuts 1-3 and being vertically provided in a vertical line, two cut spreader holes are positioned at a junction between the arched section A and the vertical section B, and four cut spreader holes are positioned on the arched section A Eleven cut spreader holes 2 define a city gate shape (two sides are vertical lines, and a top is a circular arch line) sleeving the cuts 1, and the remaining one cut spreader hole 2 positioned on the arched section A is positioned between the circular arch line and the cuts 1 [0071] Two circles of auxiliary holes 3 are provided on a periphery of the cut spreader holes 2, and there are 32 auxiliary holes 3 (15 auxiliary holes are positioned in a first circle with the numbers of Fl-F15, and 17 auxiliary holes are positioned in a second circle with the numbers of F16-F32) A arrangement method of the 15 auxiliary holes in the first circle is: six auxiliary holes are positioned on the vertical section B, three auxiliary holes being provided on each of a left side and a right side of the third-step cuts 1-3 and being vertically provided in a vertical line, two auxiliary holes are positioned at a junction between the arched section A and the vertical section B, seven auxiliary holes are positioned on the arched section A, and the 15 auxiliary holes 3 define a city gate shape (two sides are vertical lines, and a top is a circular arch line) sleev ng the periphery of the cut spreader holes 2. The arrangement method of the 17 auxiliary holes 3 in the second circle is: six auxiliary holes are positioned on the vertical section B, three auxiliary holes being provided on each of a left side and a right side of the third-step cuts 1-3 and being vertically provided in a vertical line, two auxiliary holes are positioned at a junction between the arched section A and the vertical section B, nine auxiliary holes are positioned on the arched section A, and the 17 auxiliary holes 3 define a city gate shape (two sides are vertical lines, and a top is a circular arch line) sleeving the periphery of the first circle of auxiliary holes 3.

[0072] One circle of periphery holes 4 are further provided on a periphery of the second circle of auxiliary holes 3, and there are 21 periphery holes (with the numbers of Z1-Z21). An arrangement method s six auxiliary holes are positioned on the vertical section B, three auxiliary holes being provided on each of a left side and a right side of the third-step cuts 1-3 and being vertically provided in a vertical line, two auxiliary holes are positioned at a junction between the arched section A and the vertical section B, 13 auxiliary holes are positioned on the arched section A, and 21 periphery holes 4 define a city gate shape (two sides are vertical lines, and a top is a circular arch line) sleeving the periphery of the second circle of auxiliary holes 3.

[0073] A transverse row of bottom holes 4 are provided below the vertical section B, and there are nine bottom holes (with the numbers of DI-D9).

[0074] References are made to data in Fig. 2 for information such as positions and distances of blastholes, and the data in Fig. 2 may be directly cited into the contents of this patent. Unit of the data in Fig. 2, such as 325, 400, 500, 550, 600, 650, 700, 850, 1100, 2500 and 2650 is mm.

[0075] Specific surrounding rock parameters and blasting parameters and an expected blasting effect are as shown in Tables 1 and 2.

[0076] Table 1 Design of Blasting Parameters for II-Class Surrounding Rocks Se ria 1 nu m be r Name of Inclin Qua Depth Quantity of Seg Plug Len gth of ste mm ing Blast Con necti ng meth od blasthole ati on ntity (m) loaded men (piece/h ino angle of blast hole (piec explosive t ole) b (°) e) num sequ ber ence of deto nato r Cartri Kg dge/h ole 1 First-step cut 90 1 3.8 8 2.4 1+1 1+1 1.4 I Larg e para1 lel conn ectio n 2 Second-s 4 3.8 0 0 0 0 tep cut 3 Third-ste 90 8 3.8 7 16.8 3 1+1 1.7 II p cut 4 Cut 90 12 3.6 6 21.6 5 1 1.8 III spreader hole Two circles of auxiliary 90 32 3.6 5 48.0 7 1 1.0 IV holes Peripher 6 y hole 91 21 3.6 4 25.2 9 1 0.3 V Bottom 7 hole 92 9 3.8 5 13.5 11 1 2.0 VI [0077] Table 2 Surrounding Rock Parameters and Expected Blasting Effect Serial Name Unit Quantity Serial Name Unit Quantity number number 1 Class of surrounding rock II 11 Plug on full piece 92 section 2 Hardness f 10-19 12 Stemming box 20 of rock on full section 3 Excavated section m2 23.1 13 Quantity of Kg 127.5 loaded explosive on full section 4 Section Semicircular arch 14 Length of m 315.8 type blasthole on full section Water None 15 Each m 3.3 gushing blasthole footage 6 Emulsion (I) 35300300 g 16 Blasthole 0/ 91.6 explosive utilization rate 7 Detonator Digital tube 17 Broken rock M3 76.2 of each circle 8 Pneumatic drill piece 9 18 Unit Kg/m3 1.67 explosive consumption 9 Quantity piece 87 19 Unit piece/m 26.7 of detonator blasthole consumption on full section Quantity piece 88 20 Smooth,0 100 of blasting detonators hole-mark on full rate section [0078] 52: Load explosives [0079] Load the explosives in all the blastholes according to the Table 1, and plug the blastholes according to the contents in the Table I. [0080] A specific plugging methodincludes: [0081] plug each of the first-step cut 1-1 and the third-step cuts 1-3 by means of one section of stemming, one plug, one section of stemming, one plug and one section of stemming in sequence from inside to outside to plug each blasthole; [0082] plug the cut spreader holes 2, the auxiliary holes 3 and the bottom holes 5 by means of one section of stemming and one plug; and [0083] plug an orifice of each periphery hole 4 by means of 0.3 m of water stemming.

[0084] 53 Carry out blasting [0085] Carry out blasting according to a blasting sequence in the Table I, where a blasting effect diagram is as shown in F [0086] According to the blasting structure and method in the implementation, aiming at blasting of the ultra-hard rock tunnel, three steps of same-depth parallel horizontal cylinder type cuts are used such that drilling may be simultaneously carried out by a plurality of drill machines without interference, and a long drill pipe may be used for drilling and hole-forming at one time, so as to raise drilling efficiency. By means of the unique cover-barrel type explosive loading structure of this patent, gathering of blasting energy at a lower portion of the blastsholes is guaranteed, a breaking range of hard rocks at a bottom is deepened, a breaking range of hard rocks at a lower portion is expanded, and a cut blasting depth is guaranteed. A blasting footage is increased from 1.8 m-2.0 m to 3.2 m-3.4 m, a blasthole utilization rate is increased from 70% to 92%, and monthly construction progress is increased from 60 m-70 m to 170 m-190 m, and may reach 220 m mostly. A desirable smooth blasting effect is achieved, over-excavation and under-excavation are reduced, the quantity of sprayed concrete for primary support is reduced, primary support time is shortened, and construction cost is saved.

[0087] With respect to the application case, it can be understood that the present disclosure provides a blasting structure and method for a vertical wall-circular arch type ultra-hard rock tunnel, and references are made to Fig. 2 and the contents of the application case for the specific blasting structure and blasting method.

[0088] What is described above is merely preferred embodiments of the present disclosure, and is not intended to limit the present disclosure in any form. Although the present disclosure is disclosed as above by means of the preferred embodiments, these embodiments are not for defining the present disclosure. Those skilled in the art can make certain alterations or modifications by using the technical contents disclosed above without departing from the scope of the technical solutions of the present disclosure so as to arrive at equivalent embodiments with equivalent changes. However, any simple amendments, equivalent changes, and modifications made to the above embodiments according to the technical essence of the present disclosure without departing from the contents of the technical solutions of the present disclosure still fall within the scope of the technical solutions of the present disclosure.

Claims

What is claimed is: 1. A three-step cut blasting structure for an ultra-hard rock tunnel, comprising: cuts (1) perpendicular to a tunnel section; wherein the cuts comprise a first-step cut (1-1), second-step cuts (1-2) provided on a periphery of the first-step cut (1-1) and third-step cuts (1-3) provided on a periphery of the second-step cuts (1-2); and wherein explosives are loaded in the first-step cut (1-1) and the third-step cuts (1-3), with the second-step cuts (1-2) in the absence of explosive 2. The blasting structure according to claim 1, wherein the first-step cut (1-1), the second-step cuts (1-2) and the third-step cuts (1-3) have the same depth.3. The blasting structure according to claim 1 wherein a circular cover (1-11) is fixed at each of two ends of the explosives in the first-step cut (1-1), and each circular cover (1-11) is a circular metal plate having a certain thickness.4. The blasting structure according to claim 3, wherein fixed arms (1-12) are fixed on the circular covers (1-11) respectively; and each fixed arm (1-12) is in a shape of 1 and comprises a transverse portion (1-121) and extension portions (1-122) formed by extending two ends of the transverse portion in a direction towards the explosives.5. The blasting structure according to claim 4, wherein a handle (1-13) is fixed on one side, away from an explosive cartridge, of the circular cover (1-11) close to an outer side portion in the first-step cut (1-1).6. The blasting structure according to claim 1, wherein after an explosive cartridge in the first-step cut (1-1) is loaded, the first-step cut (1-1) is completely plugged by means of one section of stemming, one plug, one section of stemming, one plug and one section of stemming in sequence; and the third-step cuts (1-3) are plugged in the same way as the first-step cut (1-1).7. The blasting structure according to claim 1, wherein there are one first-step cut (1-1), four second-step cuts (1-2) and eight third-step cuts (1-3); a distance between any one of the second-step cuts (1-2) and the first-step cut (1-1) is the same; and a distance between any one of the third-step cuts (1-3) and the first-step cut (1-1) is the same.8. The blasting structure according to claim 1, further comprising several cut spreader holes (2) provided on a periphery of the third-step cuts (1-3), several auxiliary holes (3) provided on a periphery of the cut spreader holes (2), several periphery holes (4) provided on a periphery of the auxiliary holes (3) and several bottom holes (5) positioned at a bottom of a tunnel section; the cut spreader holes (2), the auxiliary holes (3), the periphery holes (4) and the bottom holes (5) have the same depth in a direction perpendicular to the tunnel section, and the depth is less than that of each cut (1).9. A three-step cut blasting method for an ultra-hard rock tunnel, wherein the blasting structure of any one of claims 1-8 is used.10. The three-step cut blasting method for an ultra-hard rock tunnel according to claim 9, comprising the following steps: S1: carrying out blasthole construction drilling blastholes on a tunnel section by a pneumatic drill; wherein a first-step cut (1-1) is positioned at a center, second-step cuts (1-2) are positioned on a periphery of the first-step cut (1-1), and third-step cuts (1-3) are positioned on a periphery of the second-step cuts (1-2); the blastholes further comprise several cut spreader holes (2) provided on a periphery of the third-step cuts (1-3), several auxiliary holes (3) provided on a periphery of the cut spreader holes (2), several periphery holes (4) provided on a periphery of the auxiliary holes (3) and several bottom holes (5) positioned at a bottom of the tunnel section; and the first-step cut (1-1), the second-step cuts (1-2) and the third-step cuts (1-3) have the same depth, and the depth is greater than that of the other blastholes; and clearing residual debris and water from each blasthole after drilling is completed; S2 loading explosives wherein the explosives are loaded in the first-step cut (1-1), the third-step cuts (1-3), the cut spreader holes (2), the auxiliary holes (3), the periphery holes (4) and the bottom holes (5), wherein the second-step cuts (1-2) are in the absence of explosive; when the explosives in the first-step cut (1 -1) are loaded, a circular cover (1-1 1) is fixed at each of two ends of the explosives, and each circular cover (1-11) is a round metal plate having a certain thickness; fixed arms (1-12) are fixed on the circular covers (1-11) respectively; each fixed arm (1 -1 2) is in a shape of I 1 and comprises a transverse portion (1-121) and extension portions (1-122) formed by extending two ends of the transverse portion in a direction towards the explosives; and the extension portions (1-122) are fixedly connected to the explosives; and plugging the blastholes after the explosives are loaded, wherein a specific plugging method comprises: plugging each of the first-step cut (1-1) and the third-step cuts (1-3) by means of one section of stemming, one plug, one section of stemming, one plug and one section of stemming in sequence from inside to outside to plug each blasthole; plugging each of the cut spreader holes (2), the auxiliary holes (3) and the bottom holes (5) by means of one section of stemming and one plug; and plugging each of orifices of the periphery holes (4) by means of 0.3 m of water stemming; and S3: carrying out blasting sequentially blasting: the first-step cut (1-1) the third-step cuts (1-3), the cut spreader holes (2), the auxiliary holes (3), the periphery holes (4) and the bottom holes (5)