CN115749794A - High-pressure gas expansion rock breaking method and small-clear-distance double-arch tunnel construction method thereof - Google Patents

Abstract

The invention discloses a high-pressure gas expansion rock breaking method and a small-clear-distance double-arch tunnel construction method thereof, belonging to the technical field of tunnel construction, wherein the rock breaking method comprises the following steps: the method comprises the steps that a cavity expanding groove is formed in the middle of an excavation area, blasting layers are divided from the cavity expanding groove to the edge of the excavation area circle by circle, blasting holes are drilled and high-pressure gas expansion pipes are buried, the blasting is carried out layer by layer from the cavity expanding groove to the edge direction of the excavation area, and after each blasting layer is blasted, mechanical excavation and slag discharging are carried out on a fractured rock mass; the construction method comprises the following steps: the method comprises the steps of excavating the first-row holes by adopting a reserved core soil up-and-down step method, excavating the second-row holes by adopting a single-side wall pit guiding method, and excavating all excavation areas on the tunnel face by adopting a high-pressure gas expansion rock breaking method. The cavity expanding groove can provide a blank face and a compensation space for blasting cracking, peripheral rocks are guided to crack and throw towards the cavity expanding groove, the best blasting effect is achieved, layer-by-layer blasting can enable each blasting to form a new blank face, the final blasting effect is guaranteed, overbreak is avoided, and disturbance is reduced.

Description

High-pressure gas expansion rock breaking method and small-clear-distance double-arch tunnel construction method thereof

Technical Field

The invention relates to the technical field of tunnel construction, in particular to a high-pressure gas expansion rock breaking method and a small-clear-distance double-arch tunnel construction method thereof.

Background

With the continuous development and improvement of the traffic track facilities in China, the intersection influence among the traffic complexes is more and more complicated. When a shallow-buried small-clear-distance double-arch tunnel is excavated in a broken soft rock environment, the surrounding rock at the tunnel opening section is seriously weathered and broken, the strength and the stability are poor, collapse is easy to occur during excavation, and once the stratum collapses too much, the soil body above the tunnel sinks, so that the normal use of the existing traffic facilities above the tunnel is inevitably influenced. Therefore, in the construction process, it becomes important to reduce the disturbance to the pilot tunnel and the surrounding rock of the tunnel and ensure the stability of the tunnel support, and the key to reduce the disturbance lies in the implementation mode of the concrete construction method selection and excavation method of the tunnel.

The construction method of the mountain tunnel mainly comprises a full section method, a step method, a reserved core soil method, a CD method and the like, and when the excavation construction method is selected, a proper scheme needs to be selected according to a specific site environment and the comprehensive ratio of advantages and disadvantages of different construction methods. The mountain tunnel excavation method mainly comprises a drilling and blasting method and a mechanical method, wherein the drilling and blasting method has high efficiency and short construction period compared with the mechanical method, so that the drilling and blasting method has a great proportion. Therefore, an environment-friendly rock breaking technology, namely a high-pressure gas cracking method, is gradually created in recent years, a carbon dioxide blasting tube is arranged in a blasting hole, then an activating agent is excited to heat the carbon dioxide to enable the liquid carbon dioxide to expand instantly to generate high pressure, and a high-pressure air wedge is generated to throw, move and crack the rock, so that the function of breaking the rock is realized. When a tunnel is excavated by adopting a high-pressure gas fracturing method at present, a common method is that blasting holes are directly distributed on a blasting area on a tunnel face, then, a carbon dioxide blasting tube is buried in the blasting holes and then the blasting is directly carried out, for example, the patent number is '201911064828.2', the patent name is 'a device for filling holes in high-pressure gas rock breaking of the tunnel and a method thereof', and the attached drawing 3 shows, but the method has large loss and low efficiency, and has great optimization and improvement space in the aspects of disturbance during blasting, blasting precision and over-short excavation.

Disclosure of Invention

The invention aims to solve the technical problems and provides a high-pressure gas expansion rock breaking method and a small-clear-distance double-arch tunnel construction method thereof.

In order to achieve the purpose, the invention provides the following scheme: the invention discloses a high-pressure gas expansion rock breaking method, which comprises the following steps:

opening a cavity expanding groove in the middle of an excavation area, dividing a blasting layer from the cavity expanding groove to the edge of the excavation area circle by circle, and drilling a blasting hole in the blasting layer;

burying a high-pressure gas expansion pipe in the blast hole;

blasting layer by layer from the cavity expanding groove to the edge direction of the excavation area, and mechanically excavating the fractured rock mass and discharging slag after blasting of each layer of blasting layer.

Preferably, high-pressure gas expansion pipes are fully or intermittently filled in the blasting holes, and the method is determined according to the grade of surrounding rocks and the blasting effect.

Also discloses a small-clear-distance double-arch tunnel construction method, which comprises the following steps: excavating the first-row holes by adopting a reserved core soil up-and-down step method, and excavating the second-row holes by adopting a single-side-wall pit guiding method; when the advancing tunnel and the backward tunnel are excavated, the high-pressure gas expansion rock breaking method is adopted in each excavation area on the tunnel face.

Preferably, the distance between the tunnel faces of the front tunnel and the rear tunnel is more than three times of the tunnel excavation width.

Preferably, when the pilot hole is excavated: firstly, excavating an upper step vault pilot pit area, correcting the end face contour line of a tunnel face, and constructing primary support; secondly, excavating upper step side wall pit guiding areas on two sides of the upper step core soil area, correcting the end face contour line of the tunnel face, and performing primary support; thirdly, excavating a core soil area of a lower step; fourthly, excavating lower step side wall pit guiding areas on two sides of the lower step core soil area, and constructing primary support; and fifthly, excavating the inverted arch, and backfilling the inverted arch after the supporting of the inverted arch is finished.

Preferably, when the cavity expanding groove of the pilot hole is excavated, a drill bit is used for drilling the cut holes in the cavity expanding groove arrangement area, and the adjacent cut holes are mutually occluded and overlapped to form the cavity expanding groove.

Preferably, when the backward cave is excavated: firstly, excavating a first upper step pit guiding area close to the pilot tunnel, and timely constructing primary support and installing a steel frame after excavation; secondly, excavating a second upper step pit guiding area far away from the pilot tunnel, and timely constructing primary support and installing a steel frame after excavation; thirdly, excavating a first lower step pit guiding area close to the pilot tunnel, constructing primary support in time and lengthening the steel frame in the first step; fourthly, excavating a second lower step pit guiding area far away from the pilot tunnel, constructing primary support in time and lengthening the steel frame in the second step; and fifthly, excavating an inverted arch, dismantling the temporary steel frame and backfilling the inverted arch after supporting the inverted arch.

Preferably, when the cavity expanding groove of the backward hole is excavated, firstly, drilling cut holes at intervals by using drill bits in the cavity expanding groove arrangement area, then, burying a high-pressure gas expansion pipe in the cut holes and triggering, and then, excavating the cavity expanding groove by using an instrument.

Preferably, advance supports are required to be constructed before the excavation of the front tunnel and the rear tunnel.

Preferably, before advance support, settlement observation points are arranged at the top of the tunnel entrance and exit section, the mechanical parameters and the stability of surrounding rocks in the influence position of the face to be excavated are obtained according to geological exploration and advanced hole coring test results, and the settlement observation points are monitored at any time in the excavation process of the advance tunnel and the backward tunnel.

Compared with the prior art, the invention achieves the following technical effects:

1. according to the high-pressure gas expansion rock breaking method, the cavity expanding groove is formed in the middle of the excavation area, a blank face and a compensation space are provided for subsequent high-pressure gas blasting cracking, so that the peripheral central rock is guided to crack and be thrown out towards the cavity expanding groove, the optimal blasting effect is achieved, meanwhile, disturbance is reduced, a layer-by-layer blasting mode is adopted from the cavity expanding groove to the edge of the excavation area, a new blank face can be formed in each blasting after mechanical slag is discharged, the optimal blasting effect can be achieved in each blasting, the blasting effect is finally guaranteed, the disturbance is reduced, and the problem of overbreak is avoided.

2. In the small-clear-distance double-arch construction method, the pilot tunnel is excavated by adopting the reserved core soil bench, the tunnel face is stabilized by using the core soil, the deformation of the tunnel face can be better restrained, the stability of rock mass of the tunnel face is better maintained, the deformation around the tunnel is reduced, so that the stability of the excavated tunnel face of the tunnel under the shallow-buried weak surrounding rock is ensured, meanwhile, the excavation process adopts a high-pressure gas fracturing auxiliary mechanical method for construction, and compared with the traditional drilling and blasting method, the vibration of excavation is reduced to a certain extent; the method is suitable for shallow-buried soft surrounding rock tunnels with small ground surface subsidence requirements, timely constructed supports close to one side of the pilot tunnel are favorable for surrounding rock stability, ground surface subsidence, clearance displacement and vibration influence on adjacent pilot tunnels caused by construction are reduced, disturbance of excavation on the surrounding rocks and the pilot tunnel is reduced as much as possible, stability of the existing structure is guaranteed, safety, efficiency and quality are considered, pollution is low, noise is low, and control is easy.

3. According to the small-clear-distance double-arch construction method, settlement observation points are arranged on the top of the tunnel entrance and exit section before construction, the mechanical parameters and the stability of surrounding rocks in the influence direction of the face of a tunnel to be excavated are obtained according to geological exploration and the core test result of the advanced exploratory hole, and the settlement observation points are monitored at any time in the excavation process of the advanced tunnel and the backward tunnel so as to formulate a proper dynamic construction scheme, so that the safety of tunnel construction can be effectively ensured, and disasters such as collapse, excessive settlement and the like are avoided.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.

FIG. 1 shows the section of the pilot tunnel and the arrangement of high-pressure gas-induced cracking and blasting holes;

FIG. 2 is a backward hole excavation section and a high-pressure gas fracturing blast hole arrangement;

fig. 3 is a flow chart of tunnel excavation construction.

Description of reference numerals: 1. an upper step vault pit guiding area; 2. a side wall pit area of the upper step; 3. a core soil area of an upper step; 4. a lower step core soil region; 5. a lower step side wall pit guiding area; 6. a first upper step pit guiding area; 7. a second upper step pit guiding area; 8. a first lower step pit area; 9 a first lower step pit guiding area; 10. a cavity expanding groove; 11. cutting holes; 12. and (4) blasting holes.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

The embodiment provides a high-pressure gas expansion rock breaking method, as shown in fig. 1 to 3, comprising the following steps:

the middle part of the excavation area is provided with a cavity expansion groove 10, blasting layers are divided from the cavity expansion groove 10 to the edge of the excavation area circle by circle, blasting holes 12 are drilled in the blasting layers, the cavity expansion groove 10 provides a blank surface in the middle part of the excavation area to form a compensation space, so that rocks around the cavity expansion groove 10 are guided to crack and throw towards the direction of the rocks when the subsequent high-pressure gas blasting cracks, and the optimal blasting effect is achieved;

burying a high-pressure gas expansion pipe into the blast hole 12;

blasting layer by layer from the cavity expansion groove 10 to the edge direction of the excavation area, mechanically excavating the fractured rock mass and discharging slag after blasting of each blasting layer, namely triggering a high-pressure gas expansion pipe around the cavity expansion groove 10, mechanically excavating and discharging slag after fracturing the rock mass adjacent to the cavity expansion groove 10 by high-pressure gas expansion, continuously triggering the high-pressure gas expansion pipe adjacent to a new temporary vacant surface on the basis of the newly formed temporary vacant surface, excavating and discharging slag after fracturing by high-pressure gas, and repeating the operation until the high-pressure gas expansion pipe on the outline line of the excavation area is triggered, excavating and discharging slag, so that blasting is completed.

The high-pressure gas expansion pipe can be a high-pressure gas expansion pipe commonly used in the market, and can also be a high-pressure gas expansion pipe and a cracking device disclosed in patent CN211178157U (gas energy pipe and cracking device). When carrying out rock and send and split, the gas generating agent in the inner tube produces gas, because the setting of gas energy pipe salient makes the gas that produces can concentrate the effect in gas energy pipe salient department to the setting of a plurality of gas energy pipe salient makes the gas that produces fully produce mechanical action to the rock with a plurality of concentrated directions, improves the ability of sending and splitting hard rock of gas energy pipe. The high-pressure gas expansion pipe is buried and blocked by a method in patent CN110779407A (a device and a method for plugging a hole for breaking rock by high-pressure gas in a tunnel) for consolidating and blocking a high-pressure gas rock breaking device.

In this embodiment, as shown in fig. 1 to 3, high-pressure gas expansion pipes are buried in the blast holes 12 at all or at intervals. The specific way of filling is selected according to construction requirements, and the cost is effectively reduced through interval filling. Depending on the grade of the surrounding rock and the blasting effect.

Example 2

The embodiment provides a construction method of a small-clearance double-arch tunnel, as shown in fig. 1 to fig. 2, which includes the following steps: excavating the first tunnel by adopting a reserved core soil up-and-down step method, and excavating the subsequent tunnel by adopting a single side wall pit guiding method (CD); when the first-row hole and the second-row hole are excavated, the high-pressure gas expansion rock breaking method provided by the embodiment 1 is adopted in each excavated area on the tunnel face. The forepoling adopts and leaves the excavation of core soil terrace, utilizes the stable tunnel face of core soil, can restraint the deformation of tunnel face better, maintains the stability of tunnel face rock mass better, reduces tunnel hole week and warp. The rear-going hole is excavated by a single-side-wall pilot tunnel (CD) method, the method is suitable for shallow-buried soft surrounding rock tunnels with small ground surface subsidence requirements, timely support applied to one side close to the front-going hole is beneficial to surrounding rock stability, and ground surface subsidence, clearance displacement and vibration influence on adjacent pilot holes caused by construction are reduced.

In this embodiment, as shown in fig. 1 to 3, the distance between the tunnel faces of the leading tunnel and the trailing tunnel should be greater than three times the tunnel excavation width, so as to minimize the disturbance of tunnel excavation on surrounding rocks and supports.

In this embodiment, as shown in fig. 1 to 3, when excavating the pilot tunnel, the tunnel face of the pilot tunnel is divided into six excavation regions, including an upper-step vault pit guiding region 1, an upper-step side-wall pit guiding region 2 on the left side, an upper-step side-wall pit guiding region 2 on the right side, an upper-step core soil region 3, a lower-step core soil region 4, a lower-step side-wall pit guiding region 5 on the left side, and an upper-step side-wall pit guiding region 2 on the right side.

The construction sequence is as follows: firstly, drilling blast holes 12 at the contour line at a certain interval on the face of a tunnel along the contour line of an upper step vault guide pit area 1, then excavating a cavity expansion groove 10 in the middle of the upper step vault guide pit area 1, triggering a high-pressure gas expansion pipe around the cavity expansion groove 10 in the middle of the upper step vault guide pit area 1, fracturing a rock body adjacent to the cavity expansion groove 10 by using high-pressure gas expansion, discharging slag, continuously triggering a high-pressure gas expansion pipe adjacent to a new temporary empty surface on the basis of the newly formed temporary empty surface, mechanically discharging slag by using high-pressure gas to fracture, repeating the operation until the blast holes 12 at the contour line are triggered, finishing the face contour line of the face of the tunnel, avoiding the occurrence of an over-excavation and under-excavation phenomenon in the high-pressure gas rock breaking process, finishing by using a hydraulic rock drill, and immediately performing initial support after the excavation is finished; secondly, excavating upper step side wall pit guiding areas 2 at two sides of an upper step core soil area 3 by adopting the excavating method, correcting the end surface contour line of the tunnel face, and performing primary support; thirdly, excavating the lower step core soil area 4 by adopting the excavating method; fourthly, excavating lower step side wall pit guiding areas 5 on two sides of the lower step core soil area 4 by adopting the excavating method, and applying primary support; and fifthly, excavating the inverted arch by adopting machinery, and backfilling the inverted arch after completing the supporting and closing of the inverted arch.

Preferably, the distance between the blast holes 12 at the contour line is 0.5m, the hole depth is 2m, the hole diameter is 70-90 mm, preferably 80mm, a down-the-hole drill can be adopted for drilling, and the disturbance is small. And (3) drilling the blast holes 12 between the cavity expanding groove 10 and the blast holes 12 at the contour line, wherein the drilling distance is 0.4m, the drilling footage is 2m, the aperture is 70-90 mm, and the preferred option is 80mm. The specific arrangement position is shown with reference to fig. 1.

In this embodiment, as shown in fig. 1 to 3, when the cavity-expanding slot 10 of the pilot hole is excavated, the cut holes 11 are drilled by a drill in the region where the cavity-expanding slot 10 is located, and the adjacent cut holes 11 are mutually overlapped to form the cavity-expanding slot 10. The length of the cavity expansion groove 10 is preferably 1.5m, and the specific size of the cavity expansion groove is determined according to the size of an excavated area, so that a blank surface and a compensation space are provided for high-pressure gas fracturing of a rock body.

In this embodiment, as shown in fig. 1 to 3, when the backward hole is excavated, the tunnel face of the backward hole is divided into four excavation regions, including a first upper step pit guiding region 6 close to the preceding hole, a second upper step pit guiding region 7 far away from the preceding hole, a first lower step pit guiding region 8 close to the preceding hole, and a second lower step pit guiding region 9 far away from the preceding hole.

The construction sequence is as follows: firstly, according to four pre-planned subareas, after determining a central line and a contour line of an excavation surface on a tunnel face, drilling a blast hole 12 at the contour line by using a mechanical drilling machine along the contour line of the subareas, then excavating a cavity expansion groove 10 in the middle of a first upper step pilot pit area 6, drilling a blast hole 12 between the cavity expansion groove 10 and the blast hole 12 at the contour line, triggering a high-pressure gas expansion pipe around the cavity expansion groove 10 firstly during triggering, fracturing a rock body adjacent to the cavity expansion groove 10 by using high-pressure gas, discharging slag, continuously triggering a high-pressure gas expansion pipe adjacent to a new adjacent empty face on the basis of the newly formed empty face, mechanically discharging slag after fracturing by using the high-pressure gas, repeating the operation until the blast hole 12 at the contour line is triggered, trimming the contour line of the end face of the tunnel face, avoiding the occurrence of an overexcitation phenomenon in the high-pressure gas rock breaking process, trimming by using a hydraulic press, immediately performing initial support after the excavation is completed, and installing a steel frame; secondly, excavating a second upper step pilot pit area 7, drilling a blast hole 12 between the cavity expansion groove 10 and the blast hole 12 at the contour line, then triggering excavation according to the first step mode, and timely constructing primary support and installing a steel frame after excavation; thirdly, excavating a first lower step pilot pit area 8, drilling a blast hole 12 between a cavity expansion groove 10 and the blast hole 12 at the contour line, triggering excavation according to the first step mode, and timely applying primary support and lengthening the steel frame in the first step; fourthly, excavating a second lower step pit guiding area 9, drilling a blast hole 12 between the cavity expanding groove 10 and the blast hole 12 at the contour line, triggering excavation according to the first step mode, and timely constructing primary support and lengthening the steel frame in the second step; and fifthly, mechanically excavating an inverted arch, dismantling the temporary steel frame and backfilling the inverted arch after the inverted arch support is closed.

Preferably, when drilling the backward hole excavated by the CD method, the influence on the forward hole and the ground subsidence should be minimized, so that the distance, the diameter and the depth of the blast holes 12 should be reasonably selected. The distance between the blast holes 12 at the contour line is 0.5m, the hole depth is 2m, the aperture is 70-90 mm, preferably 80mm, wherein the distance between the blast holes 12 at the contour line close to one side of the pilot hole is properly increased to 0.6m, so that the number of the blast holes 12 close to one side of the pilot hole is reduced, the disturbance of excavation on surrounding rocks and the pilot hole is reduced, and the stability of the existing structure is ensured. The blasting holes 12 are arranged between the cavity expanding groove 10 and the blasting holes 12 at the contour line, the drilling intervals are 0.4m, the drilling footage is 2m, and the hole diameter is 70-90 mm, preferably 80mm. The specific arrangement position is shown with reference to fig. 2.

In this embodiment, as shown in fig. 1 to 3, when the cavity expanding slot 10 of the following tunnel is excavated, the slotted holes 11 are drilled at intervals by using a drill in the area where the cavity expanding slot 10 is located, then the high-pressure gas expansion pipe is buried in the slotted holes 11 and triggered, then the cavity expanding slot 10 is excavated by using an instrument, and the cavity expanding slot 10 is formed by using a hydraulic rock drill or a hand-held pneumatic pick to remove slag, so as to provide an adjacent surface for subsequent rock breaking. In order to effectively form the cavity expanding groove 10 and reduce the high-pressure gas cracking vibration, six cut holes 11 are arranged, the row spacing is 70cm, the column spacing is 2.5m, wedge-shaped cut holes 11 are drilled, the depth of each cut hole is deepened to be 0.2-0.5 m on the basis of the depth of a blast hole 12, the preferred depth of each cut hole is 2.3m, and an included angle of 60 degrees is formed between each cut hole and a tunnel face, so that rock breaking and slag discharging are facilitated to form the cavity expanding groove 10.

It should be noted that: no matter the excavation is carried out in advance or in the backward excavation, concrete is sprayed on the face surface of the upper excavation area during the excavation, and the high-pressure gas fracturing excavation of the lower excavation area is carried out after the strength of the concrete reaches 70% -80% of the design strength. When the rock is broken, after the high-pressure gas device is triggered to complete, the blasting waste gas and dust are dissipated, and then the site is recycled for 15min, and the mechanical excavation work is carried out.

In this embodiment, as shown in fig. 1 to 3, advance supports are required to be applied to both the advance tunnel and the backward tunnel before excavation, a long pipe shed is used for a concrete advance support portal section, and a small advance grouting pipe or an advance anchor rod is used in the tunnel. In the process of excavating the shallow tunnel, primary support should be strengthened, blasting vibration should be reduced, the primary support should be constructed in time, the inverted arch should be constructed as early as possible, and the distance between the inverted arch and the tunnel face is not more than 1/2 of the length of the large pipe shed.

Further, in order to ensure the safety of tunnel construction and avoid disasters such as collapse and excessive settlement, in this embodiment, as shown in fig. 1 to fig. 3, before advance support, settlement observation points need to be set at the top of the tunnel entrance and exit section, the mechanical parameters and the stability of surrounding rocks in the influence position of the face to be excavated are obtained according to geological exploration and advanced hole coring test results, and the settlement observation points are monitored at any time in the excavation process of the first-row tunnel and the second-row tunnel.

And in the excavation process, the excavation mode is determined to be adjusted and the support parameters are corrected according to the monitoring and measuring result and timely feedback analysis so as to ensure the safety. And the principle of 'weak blasting, short footage, advanced pipe, strict grouting, less disturbance, strong support, frequent measurement and early sealing' is adopted in the tunnel excavation, the design idea of a 'new Olympic method' is implemented, and the self-stability capability of surrounding rocks is fully protected and utilized. Surrounding rocks at the opening of the hole are weak, rock bodies are broken, stability is poor, and the hole is located in a shallow buried section.

In this embodiment, the whole construction process can be shown in fig. 3, and includes the following steps:

the method comprises the following steps: preparation before construction;

step two: performing advanced support;

step three: excavating the pilot tunnel by adopting a method of reserving core soil for going up and down steps, specifically excavating by adopting a high-pressure gas expansion rock breaking method and assisting in repairing a section and excavating and deslagging by a mechanical method, constructing a primary support during the period, excavating an inverted arch, closing the support and backfilling;

step four: and excavating the backward hole by adopting a CD method, wherein the specific excavating method adopts a high-pressure gas expansion rock breaking method, and is assisted with a mechanical method for section trimming and excavating and slag discharging, and during the period, a primary support is applied, an inverted arch is excavated, and after the support is closed, a temporary steel frame is removed and backfilled.

The principle and the implementation mode of the invention are explained by applying a specific example, and the description of the embodiment is only used for helping to understand the method and the core idea of the invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims (10)

1. A high-pressure gas expansion rock breaking method is characterized by comprising the following steps:

opening a cavity expanding groove in the middle of an excavation area, dividing a blasting layer from the cavity expanding groove to the edge of the excavation area circle by circle, and drilling a blasting hole in the blasting layer;

burying a high-pressure gas expansion pipe in the blast hole;

blasting layer by layer from the cavity expanding groove to the edge direction of the excavation area, and mechanically excavating the fractured rock mass and discharging slag after blasting of each layer of blasting layer.

2. The high-pressure gas expansion rock breaking method as claimed in claim 1, wherein the high-pressure gas expansion pipe is fully or intermittently buried in the blast hole.

3. A small-clear-distance double-arch tunnel construction method is characterized by comprising the following steps: excavating the first-row holes by adopting a reserved core soil up-and-down step method, and excavating the second-row holes by adopting a single-side-wall pit guiding method; when the advancing tunnel and the retreating tunnel are excavated, the high-pressure gas expansion rock breaking method is adopted in each excavated area on the tunnel face according to the claim 1 or 2.

4. The method as claimed in claim 3, wherein the distance between the tunnel faces of the front tunnel and the rear tunnel is greater than three times of the tunnel excavation width.

5. The method for constructing a small-clearance double arch tunnel according to claim 3 or 4, wherein when the pilot tunnel is excavated: firstly, excavating an upper step vault pilot pit area, correcting the end face contour line of a tunnel face, and constructing primary support; secondly, excavating upper step side wall pit guiding areas on two sides of the upper step core soil area, correcting the end face contour line of the tunnel face, and performing primary support; thirdly, excavating a lower step core soil area; fourthly, excavating lower step side wall pit guiding areas on two sides of the lower step core soil area, and constructing primary support; and fifthly, excavating the inverted arch, and backfilling the inverted arch after the supporting of the inverted arch is finished.

6. The method as claimed in claim 5, wherein when the cavity-expanding slot of the pilot tunnel is excavated, the cut holes are drilled by a drill in the area where the cavity-expanding slot is installed, and the adjacent cut holes are overlapped with each other to form the cavity-expanding slot.

7. The small-clearance double arch tunnel construction method according to claim 3 or 4, wherein when the backward tunnel is excavated: firstly, excavating a first upper step pilot hole area close to the pilot hole, and timely constructing primary support and installing a steel frame after excavation; excavating a second upper step pilot hole area far away from the pilot hole, and timely constructing primary support and installing a steel frame after excavation; thirdly, excavating a first lower step pilot pit area close to the pilot tunnel, constructing a primary support in time and lengthening a steel frame in the first step; fourthly, excavating a second lower step pit guiding area far away from the pilot tunnel, constructing primary support in time and lengthening the steel frame in the second step; and fifthly, excavating the inverted arch, and after the supporting of the inverted arch is finished, dismantling the temporary steel frame and backfilling the inverted arch.

8. The method as claimed in claim 7, wherein when the cavity-expanding slot of the back-row hole is excavated, the drill bit is used to drill the slotted holes at intervals in the area where the cavity-expanding slot is located, then the high-pressure gas expansion pipe is buried in the slotted holes and triggered, and then the cavity-expanding slot is excavated by an instrument.

9. The method as claimed in claim 3 or 4, wherein forepoling is required before the excavation of the forepoling and the backward tunneling.

10. The small-clear-distance double-arch tunnel construction method according to claim 9, wherein before advance support, settlement observation points are arranged at the top of the tunnel entrance and exit section, the surrounding rock mechanical parameters and the stability of the face of the tunnel to be excavated in the influence direction are obtained according to geological exploration and advanced hole coring test results, and the settlement observation points are monitored at any time in the excavation process of the first tunnel and the second tunnel.

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