WO2022083096A1

WO2022083096A1 - Tunnel excavation method for upper-soft and lower-hard stratum

Info

Publication number: WO2022083096A1
Application number: PCT/CN2021/090852
Authority: WO
Inventors: 张帅; 王建辉; 阳凯; 宋新海; 于建; 王纪伟
Original assignee: 中铁十九局集团第五工程有限公司; 中铁十九局集团有限公司
Priority date: 2020-10-20
Filing date: 2021-04-29
Publication date: 2022-04-28
Also published as: CN112431599A; ZA202305430B; CN112431599B

Abstract

A tunnel excavation method for an upper-soft and lower-hard stratum. The section of a tunnel is divided into an upper portion and a lower portion. The excavation step comprises: S1, constructing advanced support on an arch portion of the tunnel; S2, excavating a lower step (1) on the lower section of the tunnel in a multi-time cyclic footage blasting manner, wherein a lower step primary support and a temporary support of a temporary arch portion (11) of the lower step (1) are constructed after each time of cyclic footage blasting is completed; and S3, excavating an upper step (2) on the upper section of the tunnel in the multi-time cyclic footage blasting manner, wherein the corresponding temporary support is removed before each time of cyclic footage blasting, an upper step primary support is constructed after each time of cyclic footage blasting is completed, and the upper step primary supports and the lower step primary supports are closed to form rings.

Description

Tunnel excavation method for upper soft and lower hard stratum

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of the Chinese patent application with the application number 202011125816.9, filed on October 20, 2020, and the invention titled "Tunnel Excavation Method for Upper Soft and Lower Hard Ground", which is incorporated herein by reference in its entirety.

technical field

The present application relates to the technical field of tunnel construction, and in particular, to a tunnel excavation method for upper soft and lower hard strata.

Background technique

During tunnel construction, various tunnel excavation methods are used. In order to control the impact of construction on the surrounding environment, personnel, ground pipelines and building settlement on the basis of appropriate project cost and construction speed. Among them, the excavation section of the undercut tunnel often has a composite stratum with soft upper and lower hard layers, that is, the upper part of the tunnel section is a soft soil layer, and the lower part is a relatively hard soil layer or rock. For example, the section of a subway tunnel is generally buried at a depth of about 20m. In addition, there are many pipelines under the road. The main pipelines include rainwater, water supply, sewage, natural gas and culverts. There are multi-storey residential buildings, street-facing shops and office buildings on both sides of the road. There is a thick water-rich sand layer above, the geological conditions are extremely complex, and the overlying rock in the arch is thin and broken. However, if the excavation is carried out according to the traditional step method or CD method, safety accidents such as collapse and water and mud inrush are very likely to occur, and the consequences are very serious.

SUMMARY OF THE INVENTION

The embodiment of the present application provides a tunnel excavation method for upper soft and lower hard strata, which is used to solve safety accidents such as collapse and water inrush and mud inrush when the traditional tunnel excavation method is easily excavated in the upper soft and lower hard stratum. The problem.

The embodiment of the present application provides a tunnel excavation method for upper and lower hard strata, the tunnel section is divided into upper and lower parts, and the excavation step comprises:

S1, perform advanced support on the arch of the tunnel;

S2, the lower section of the tunnel is excavated by means of multiple cycle footage blasting; wherein, after each cycle footage blasting is completed, the initial support of the lower step and the temporary arch of the lower step are used as temporary support. support;

S3, the upper section of the tunnel is excavated by means of multiple cycle footage blasting; wherein, before each cycle footage blasting, the temporary support corresponding to the cycle footage blasting length is removed; After the cyclic footage blasting, the initial support for the upper step is applied and closed to form a ring with the initial support for the lower step.

According to the tunnel excavation method for upper soft and lower hard strata according to an embodiment of the present application, after each cycle footage blasting is completed, the initial support for the lower step and the temporary support for the temporary arch of the lower step are performed, specifically include:

shotcrete at the temporary arch of the lower steps;

Apply lower step grille support on the bottom surface and side wall of the lower step;

An I-beam is arranged on the temporary arch of the lower step, and both ends of the I-beam are respectively supported and fixedly connected to the lower step grille at the side wall;

The bottom surface and side walls of the lower steps are sprayed concrete for sealing.

According to an embodiment of the tunnel excavation method for upper soft and lower hard strata, after the bottom surface and side walls of the lower step are sealed by spraying concrete, the method further includes: respectively placing side walls on both sides of the lower step. The lower step grille support at the place is set up with locking foot anchor pipes and grouted.

According to the tunnel excavation method for upper soft and lower hard strata according to an embodiment of the present application, before each cyclic footage blasting, the temporary support corresponding to the cyclic footage blasting length is removed, specifically comprising: removing the engineering The connecting bolts between the steel beam and the lower step grille support at the side wall are cut off or the I-beam is cut off from the root.

According to the tunnel excavation method for upper soft and lower hard strata according to an embodiment of the present application, the S1 specifically includes:

From the ground, a water-stop curtain is installed in the stratum within the set range of the tunnel vault, and grouting reinforcement is performed in the area surrounded by the water-stop curtain; or, from the inside of the tunnel, the tunnel vault is Apply half-section curtain grouting reinforcement in the stratum within the set range;

The advanced middle pipe shed support is applied along the excavation outline of the tunnel.

According to the tunnel excavation method for upper soft and lower hard strata according to an embodiment of the present application, the performing initial support for upper steps includes:

An upper step grille support is applied to the arch of the upper step and is fixedly connected with the lower step grille support;

The arches of the upper steps are sprayed concrete for sealing.

According to an embodiment of the present application, the tunnel excavation method for upper soft and lower hard strata further includes applying advanced small conduit support to the arch of the tunnel after completing one or more cycles of footage blasting;

Wherein, while the arch of the upper step is supported by the upper step grid, the PVC pipe is pre-buried in the initial support of the upper step; after the arch of the upper step is sealed by spraying concrete, Drill holes are drilled in the PVC pipe, and a small lead pipe is arranged in the hole.

According to the tunnel excavation method for upper soft and lower hard strata according to an embodiment of the present application, the steel arches supported by the upper step grid and/or the steel arches supported by the lower step grid are Use socket connection.

According to an embodiment of the tunnel excavation method for upper soft and lower hard strata, the cyclic footage blasting of the lower step adopts an electronic detonator water pressure control blasting method, and the cyclic footage blasting of the upper step adopts the electronic detonator layer-by-layer peeling control. blasting method.

According to the tunnel excavation method for upper soft and lower hard formations according to an embodiment of the present application, the diameter of the part of the middle pipe shelter intruding into the contour line of the initial support of the upper step is smaller than the diameter of the part of the middle pipe shelter intruding into the stratum .

The tunnel excavation method for the upper soft and lower hard stratum provided by the embodiment of the present application is a reverse step construction method of excavating the lower step first, and then performing the upper step excavation, and both the lower step and the upper step are adopted. Multiple cycle footage blasting. After each blasting of the lower steps, the initial support of the lower steps and the temporary support of the temporary arch of the lower steps shall be applied. The corresponding temporary supports shall be removed before each blasting of the upper steps so that the The force is released to the excavated lower steps, thereby greatly reducing the reaction force on the tunnel arch when the upper steps are blasted, reducing the risk of collapse and water and mud inrush, and improving the safety of construction.

Description of drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the accompanying drawings used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are some embodiments of the present application. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without any creative effort.

Fig. 1 is the schematic flow chart of the tunnel excavation method of upper soft and lower hard strata in the embodiment of the present application;

2 is a schematic cross-sectional view of a tunnel excavation method for upper soft and lower hard strata in the embodiment of the present application;

3 is a schematic longitudinal cross-sectional view of a tunnel excavation method for upper soft and lower hard strata according to an embodiment of the present application.

Reference number:

1. Lower steps; 2. Upper steps; 121. Lower steps grid support; 122. Locking anchors; 111. Concrete; 11. Temporary arches; 3. Middle pipe shed; 4. Leading small pipes; 211. Upper step grille support; 112, I-beam; 5, waterproof layer; 6, secondary lining.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments It is a part of the embodiments of the present application, but not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

In the description of the embodiments of the present application, it should be noted that, unless otherwise expressly specified and limited, the terms "first" and "second" are used to clearly describe the numbering of product components and do not represent any substantial difference. Those of ordinary skill in the art can understand the specific meanings of the above terms in the embodiments of the present application according to specific situations.

In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it may be a fixed connection or a detachable connection, Or integrally connected; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal communication between the two components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood in specific situations.

The following describes the tunnel excavation method for upper soft and lower hard strata provided by the embodiments of the present application with reference to FIGS. 1 to 3 .

As shown in FIG. 1 , it is a schematic flow chart of a tunnel excavation method for upper soft and lower hard strata in the embodiment of the application. In the embodiment of the application, the tunnel section is divided into upper and lower parts, and the lower step 1 is excavated first and then the upper step is excavated. 2 way cycle excavation. FIG. 2 is a schematic cross-sectional view of the tunnel excavation method for upper soft and lower hard strata according to an embodiment of the present application, and FIG. 3 is a longitudinal cross-sectional schematic diagram of the tunnel excavation method for upper soft and lower hard strata according to an embodiment of the present application. The excavation steps include:

S1, implement advance support on the arch of the tunnel.

S2, the lower section of the tunnel is excavated by the method of multiple cycle footage blasting; wherein, after each cycle footage blasting is completed, the initial support of the lower step and the temporary support of the temporary arch 11 of the lower step 1 are applied. protect.

Specifically, the lower bench 1 is excavated by means of cyclic footage blasting at the lower section of the tunnel, and the length of one excavation of the lower bench 1 can be determined according to the length of the advance support. For example, if the length of the middle pipe shed 3 used for the advanced support is 10m, and the longitudinal overlap is 4m, the length of one excavation of the lower step 1 is about 6m. If the footage is blasted 1m per cycle, it will take 6 blasts to complete the excavation of the next step 1. After each blasting, a temporary arch 11 with a length of 1 m will be formed on the top of the lower step 1 . After each cycle footage blasting is completed, the initial support of the descending steps and the temporary support of the temporary arch 11 are completed in time. In order to further improve the safety of construction, vertical I-beams such as I18 I-beams may also be arranged between the temporary arch 11 and the bottom surface of the lower step as a temporary support roof.

Among them, the cyclic footage blasting of the lower step 1 adopts the electronic detonator hydraulic blasting method. The electronic detonator can freely set the delayed initiation time (such as 50 milliseconds), which can realize precise blasting control and control of construction noise and blasting vibration. Each cycle footage blasting of the lower step 1 adopts the blasting method of 2 holes and 1 stage, and the middle hole is blasted first to reduce the reaction force of the subsequent blasting on the arch. Hydraulic blasting is used for control, the utilization rate of explosives is improved, the amount of single-shot blasting charges is reduced, the degree of blasting and crushing is uniform, and the on-site dust removal is faster. In the embodiment of the present application, a corresponding number of water bags are added to the blast hole according to the design requirements, and the blast hole is sealed with the blast mud.

S3, on the upper section of the tunnel, the upper step 2 is excavated by means of multiple cycle footage blasting. Among them, before each cycle footage blasting, the temporary support corresponding to the cycle footage blasting length is removed first; after each cycle footage blasting is completed, the upper step initial support is applied and closed with the lower step initial support. .

Specifically, since the upper step 2 is in a relatively soft stratum, and the overlying rock of the arch is very weak, in order to reduce the blasting risk as much as possible, in the embodiment of the present application, the cyclic footage blasting of the upper step 2 adopts the electronic detonator layer-by-layer stripping blasting method. For example, each cycle footage is 0.5m, and the excavation length of the upper step 2 and the lower step 1 is the same. If the excavation length of the upper step 2 is 6m, 12 blasts are required to complete the excavation of the upper step 2. Each cycle footage blasting of the upper step 2 adopts a single-hole single-stage blasting method, and the middle hole is blasted first to reduce the reaction force of the subsequent blasting on the arch. Before each cycle shot blasting, remove the temporary support of the temporary arch within the range of 0.5m, so that most of the energy during blasting of the upper step 2 is released in the direction of the excavated lower step 1, which can be larger The degree of reduction of the blasting reaction force on the arch. After each cycle footage blasting is completed, the initial support for the upper step is completed in time and the initial support for the lower step is closed into a ring.

Taking the length of a single excavation step as an example of 6m, first excavate a 6m-long lower step 1 on the lower section of the tunnel, and then excavate a 6m-long upper step 2 on the upper section of the tunnel, which is regarded as the completion of one tunnel excavation. Cycle, perform multiple excavation cycles according to the length of the tunnel to be excavated. Further, after the above steps S1-S3 are completed, a waterproof layer 5 and a secondary lining 6 are also laid on the tunnel that has been excavated at the rear.

In the embodiment of the present application, performing advance support on the arch of the tunnel in S1 includes the steps:

S11, when there is a working space on the ground above the tunnel, the method of applying advanced support from the ground is adopted, that is, a water-stop curtain is installed from the ground in the stratum of the set range of the tunnel vault, and the water-stop curtain is surrounded by the water-stop curtain. Grouting reinforcement is carried out in the designated area. Specifically, on the corresponding ground above the tunnel, the water-stop curtains of the rotary jet piles and the stirring jet piles are applied within the set range along the width direction and length direction of the tunnel to form a water-stop body such as a mouth-shaped, a sun-shaped or a mesh-shaped water body. Then, according to the hole position and drilling parameters in the design drawing, drill holes in the area enclosed by the water-stop curtain, and perform single-liquid cement grouting reinforcement in the hole, and the grouting reinforcement area covers the excavation contour line surrounding the tunnel. A range is set on the outside to form a continuous water stop coaxial with the tunnel. Specifically, according to the hole position and drilling parameters in the design drawing, drill holes directly on the corresponding ground above the tunnel, and then grouting is carried out in the holes.

When the ground above the tunnel is not suitable for construction, such as when there is a road or a building above the road, the method of applying advanced support from the tunnel is adopted, that is, the half-section is applied from the stratum within the set range of the tunnel vault within the tunnel. Curtain grouting reinforcement. For example, the grouting pipe extends from the upper section of the tunnel to the outside of the tunnel excavation outline, and grouting is performed outside the excavation outline and within the set range along the length of the tunnel, so as to form a continuous stop coaxial with the tunnel. Water body.

Specifically, according to the hole position and drilling parameters in the design drawing, the drilling position is released on the working face (the upper section of the tunnel) and calibrated with paint. The orifice pipe is buried at the calibration position, and the orifice pipe is tightly consolidated with the installation surface to ensure no leakage or stringing of slurry. The burying method is as follows: use a drilling rig to drill at the calibrated drilling position, insert the orifice tube with the orifice flange and expose it for 20-30cm after the hole is formed, and wrap the outer wall of the orifice tube with geotextile. The drilling rig pushes the orifice pipe into the borehole, pours the double-liquid slurry, and finally completes the burial of the orifice pipe. For example, the diameter of the borehole is 115mm and the length is about 4m. The orifice pipe is made of seamless steel pipe with a diameter of 108mm and a length of 3m. The thickness of the geotextile is about 1-3cm and the length is about 30cm. match.

After the orifice pipe is all buried, replace the drill bit, drill the hole in the orifice pipe to the design depth, insert the grouting pipe into the hole and connect it with the orifice flange of the orifice pipe to complete the orifice pipe and grouting system Connection. Then, the tightness of the pipeline of the grouting pipe is detected by the pressurized water, and the cracks in the rock are flushed, the slurry passage is enlarged, and the compactness of the slurry flushing is increased. After the hole is cleared, the grouting construction is started. For example, make sure that the final hole diameter of the drilled hole is not less than 75mm. The grouting pipe adopts a PVC pipe with a diameter of 42 mm, wherein the grouting pipe is provided with grouting ports with a plum-shaped distribution at intervals of 50 cm along the length direction of the grouting pipe, and the diameter of the grouting port is 10 mm. The grouting pressure of the pressure sand layer is 0.5-1.0MPa. When the rock layer is grouted on site, choose 1.0-1.5MPa. The grouting sequence is: the outer ring is injected first, the inner ring is injected later, and the same ring is applied at intervals from bottom to top. In this way, the subsequent holes can check the grouting effect of the previous holes.

S12, implement advanced middle pipe shed support along the excavation outline of the tunnel. After the curtain grouting is completed, the middle pipe shed support is applied. For example, the middle pipe shed 3 is made of steel pipes with a diameter of 89 mm, a length of 10 m, and a thickness of 5 mm. The middle pipe shed 3 is symmetrically arranged along the excavation contour with a circumferential spacing of 0.25 m within the range of the tunnel arch not less than 150°.

When curtain grouting and advanced mid-pipe shed support are used for advance support, the length of advance support is determined by the length of curtain grouting and mid-pipe shed advance support construction. For example, if the length of the middle pipe shed 3 is 10m, and the longitudinal overlap is 4m along the length of the tunnel, the length of the primary support of the middle pipe shed is about 6m. In the case that the length of one curtain grouting should not be less than 6m, and the length of one advance support reaches 6m, then the length of one excavation lower step 1 and one excavation upper step 2 are both 6m.

In the embodiment of the present application, in step S2, after each cycle footage blasting is completed, the initial support of the lower step and the temporary support of the temporary arch 11 of the lower step 1 are applied, specifically including:

S21 , spraying concrete 111 on the temporary arch 11 of the lower step 1 .

S22, the lower step grid support 121 is applied to the bottom surface and side walls of the lower step 1.

S23, an I-beam 112 is provided on the temporary arch 11 of the lower step 1, and the I-beam 112 is fixedly connected to the lower step grille support 121 at the side wall.

S24, spraying concrete on the bottom surface and side wall of the lower step 1 for sealing.

Wherein, after each completion of one cycle footage blasting, the temporary arch 11 is immediately sprayed with concrete 111 to reinforce the temporary arch and ensure construction safety. For example, the thickness of the shotcrete 111 is 150 mm. The I-beam 112 is connected with the lower step grille support 121 at the side wall through a connecting plate and bolts. During construction, ensure that the I-beam 113 is firmly connected to the grille arch, and is closely attached to the temporary arch 11, and the non-compact places are sealed and compacted with shotcrete. For example, I-beam 112 adopts I18 I-beam. The longitudinal spacing of the I-beams 112 is 1m along the excavation footage direction of the tunnel. If the cyclic footage of each blasting is 1m, then after each cycle footage is blasted, an I-beam is installed in the temporary arch 11 . The thickness of sprayed concrete is 250mm on the bottom surface and side wall of the lower step 1.

Before each cycle footage blasting of the lower step 1, first remove the temporary support corresponding to the cycle footage blasting length, specifically including: cutting off the connecting bolts between the I-beam 112 and the lower step grille support 121 at the side wall Or cut the I-beam 112 from the root. Wherein, before removing the I-beam 112, the shotcrete at the connection plate between the I-beam 112 and the lower step grille support 121 at the side wall is cleaned by hand and a breaking hammer.

Further, after the bottom surface and side walls of the lower step 1 are sealed with sprayed concrete, it also includes setting up locking foot anchor pipes 122 on the lower step grid supports 121 at the side walls on both sides of the lower step 1 and grouting. For example, the length of the foot-locking anchor pipe 122 is 3.5 m, two foot-locking anchor pipes 122 are erected on each side, and the grouting pressure is 0.5-1.0 MPa.

On the basis of the above embodiment, in step S3, the initial support for the upper steps is performed, which specifically includes:

S31, the upper step grille support 211 is applied to the arch of the upper step 2 and fixedly connected to the lower step grille support. For example, the upper step grid and the lower step grid are connected by connecting plates, so that the upper step grid and the lower step grid are closed into a ring.

S32, spraying concrete on the arch of the upper step 2 for sealing. For example, the thickness of shotcrete in the arch 21 of the upper step 2 is 250 mm, wherein the arch of the upper step 2 includes a vault and side walls connected to the vault on both sides of the upper step 2 .

Further, step S3 also includes:

S33, after each completion of one or more cycles of footage blasting, a small advanced duct support is applied to the arch of the tunnel. Among them, if the number of leading small pipes 4 is 34 and the length is 3.5m, it will take about 4 hours from drilling to the end of grouting. However, the overlying rock of the tunnel arch itself is thin, and the sand layer above it needs to be closed as soon as possible. Therefore, when the arch of the upper step 2 is used as the upper step grille support 211, according to the design position and angle of the advanced small conduit 4, the PVC pipe is pre-buried in the initial support of the upper step, and the arch of the upper step 2 is pre-buried. After the part of the sprayed concrete is sealed, a hole is drilled in the PVC pipe, and the drilled hole is used to set the leading small conduit 4 . This can reduce the risk of collapse caused by the exposure of surrounding rock for too long, and ensure the safety of the project.

For example, the length of the leading small ducts 4 is 3.5m, the circumferential spacing is 0.25m, the leading small ducts 4 are arranged in the range of not less than 150° on the dome of the upper step 2, and the number of the leading small ducts 4 is determined according to the actual size of the tunnel. The longitudinal overlap is 2m, that is, the longitudinal distance is 1.5m. If the blasting length of one cycle footage is 0.5m, it can be blasted three times and then applied to the leading small conduit 4. Of course, in order to increase the safety of construction, the longitudinal distance of the leading small duct 4 can also be shortened to 0.5m or 1 m. After completing one or two cycle footage blasting and initial support of the steps, the leading small duct 4 is applied. support.

The grid support is formed by connecting and fixing a plurality of steel arches arranged along the tunnel excavation direction by connecting steel bars. Generally, the adjacent steel arches are connected by single-sided welding connecting steel bars, and the welding length needs to be reserved for the next circulating connecting steel bars, and the welding length is at least 10 times the diameter of the connecting steel bars. This will lead to a long blasting footage and a long distance between the last grille and the face of the tunnel. The rock mass of this reserved length is in a state of being in the air and unsupported, which brings safety hazards to the construction.

In this regard, in the embodiment of the present application, the steel arches of the upper step grille support 211 and the steel arches of the lower step grille support are connected by sleeves. Specifically, two adjacent steel arches are fixedly connected by two steel bars and a sleeve, one end of the connecting steel bars is provided with an external thread, and the sleeve is provided with an internal thread.

During installation, for example, first stand up the first steel arch, weld the unthreaded end of the connecting steel bar to the first steel arch, and screw the sleeve to the threaded end of the connecting steel bar. Then, before the second steel arch is erected, the other connecting bar is screwed to the sleeve at the end of the previous connecting bar. After the second steel arch is erected, the other connecting bar is connected to the second steel arch. The arches are welded accordingly, so that the two steel arches are welded and fixed in the longitudinal direction by two steel bars and a sleeve. Among them, welding and fixing are carried out at intervals of 1m on the steel arch ring upward. After the last steel arch is erected in each blasting footage, the sleeve is installed on the connecting steel bar, and it is buried in the initial support when spraying concrete. Therefore, it is not necessary to reserve a long single-sided welding length of the lower circulation connecting steel bar, but only a short length of the sleeve needs to be reserved, thereby reducing the welding length of the longitudinal connecting steel bar, thereby reducing a single excavation. The length of the grid arch is as close as possible to the face of the tunnel, reducing the length of the unsupported rock mass facing the tunnel, and enhancing the engineering safety factor.

After the blasting of the upper step 2 is completed, because part of the middle pipe shed 3 intrudes into the initial support outline of the upper step, it needs to be cut off during the excavation process. However, due to the large diameter of the middle tube shed 3, it is difficult to cut it, resulting in a long operation cycle, which is not conducive to the rapid sealing of the upper step 2. Therefore, on the basis of the above-mentioned embodiment, the diameter of the part where the middle pipe shelter 3 intrudes into the initial support contour of the upper step is smaller than the diameter of the part where the middle pipe shelter 3 penetrates into the formation. For example, the tail of the middle pipe shed 3 with a diameter of 89mm needs to be replaced by a steel pipe with a diameter of 42mm and a length of 1.5m. The two sections are welded together by open steel plates, so as to facilitate the cutting of the intrusion-limiting steel pipe in the later construction, thereby promoting the The upper step 2 is quickly and effectively closed into a loop to reduce engineering risks.

The connection between the grid arches in the embodiment of the present application, including the initial support of the lower step and the connection of the I-beam 112, are all made of steel plates and high-strength bolts, and the parts that need to be welded are fully welded with 50 electrodes on one side.

The tunnel excavation method for the upper soft and lower hard stratum provided by the embodiment of the present application, through the reverse step construction method of excavating the lower step first and then excavating the upper step, so that most of the energy during blasting of the upper step is directed to the excavated lower step. The direction release greatly reduces the disturbance of the blasting operation to the tunnel arch and reduces the risk of water inrush and mud inrush; through the precise control of the blasting control technology, the blasting noise and blasting vibration speed are reduced, and the surrounding environment and the surrounding road surface are effectively controlled and pipeline settlement; hydraulic blasting is adopted to reduce the impact of construction dust and toxic and harmful gases on the health of workers; small-diameter steel pipes are installed in the encroachment section of the middle pipe shed, and steel grids are used between the arches. Sleeve connection is simple and easy to operate, and can shorten the construction time, so as to quickly complete the initial support and sealing, and realize the efficient and safe excavation of the tunnel that goes through the soft and hard stratum below.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be The technical solutions described in the foregoing embodiments are modified, or some technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions in the embodiments of the present application.

Claims

A tunnel excavation method for upper soft and lower hard stratum is characterized in that, the tunnel section is divided into upper and lower parts, and the excavation step comprises:

S1, perform advanced support on the arch of the tunnel;

S2, the lower section of the tunnel is excavated by means of multiple cycle footage blasting; wherein, after each cycle footage blasting is completed, the initial support of the lower step and the temporary arch of the lower step are used as temporary support. support;

S3, the upper section of the tunnel is excavated by means of multiple cycle footage blasting; wherein, before each cycle footage blasting, the temporary support corresponding to the cycle footage blasting length is removed; After the cyclic footage blasting, the initial support for the upper step is applied and closed to form a ring with the initial support for the lower step.
The tunnel excavation method for upper soft and lower hard strata according to claim 1, characterized in that, after each completion of one cycle footage blasting, the initial support of the lower step and the temporary support of the temporary arch of the lower step are applied. Support, including:

shotcrete at the temporary arch of the lower steps;

Apply lower step grille support on the bottom surface and side wall of the lower step;

An I-beam is arranged on the temporary arch of the lower step, and both ends of the I-beam are respectively supported and fixedly connected to the lower step grille at the side wall;

The bottom surface and side walls of the lower steps are sprayed concrete for sealing.
The tunnel excavation method for upper soft and lower hard strata according to claim 2, characterized in that, after the bottom surface of the lower step and the side walls are sprayed with concrete, the method further comprises: The lower step grille support at the side walls on both sides is provided with locking foot anchor pipes and grouting.
The tunnel excavation method for upper soft and lower hard strata according to claim 2, characterized in that, before each cyclic footage blasting, the temporary support corresponding to the cyclic footage blasting length is removed, specifically including: The connecting bolts between the I-beam and the lower step grille support at the side wall are cut off or the I-beam is cut from the root.
The tunnel excavation method for upper soft and lower hard strata according to claim 1, wherein the S1 specifically includes:

From the ground, a water-stop curtain is installed in the stratum within the set range of the tunnel vault, and grouting reinforcement is performed in the area surrounded by the water-stop curtain; or, from the inside of the tunnel, the tunnel vault is Apply half-section curtain grouting reinforcement in the stratum within the set range;

The advanced middle pipe shed support is applied along the excavation outline of the tunnel.
The tunnel excavation method for upper soft and lower hard strata according to any one of claims 2 to 5, wherein the performing initial support for the upper step comprises:

An upper step grille support is applied to the arch of the upper step and is fixedly connected with the lower step grille support;

The arches of the upper steps are sprayed concrete for sealing.
The tunnel excavation method for upper soft and lower hard strata according to claim 6, further comprising: after completing one or more cycles of footage blasting, applying an advanced small conduit support to the arch of the tunnel ;

Wherein, while the arch of the upper step is supported by the upper step grid, the PVC pipe is pre-buried in the initial support of the upper step; after the arch of the upper step is sealed by spraying concrete, Drill holes are drilled in the PVC pipe, and a small lead pipe is arranged in the hole.
The tunnel excavation method for upper soft and lower hard strata according to claim 6, characterized in that, between the steel arches supported by the upper step grille and/or the steel arches supported by the lower step grille The frames are connected by sleeves.
The tunnel excavation method for upper soft and lower hard strata according to claim 1, wherein the cyclic footage blasting of the lower step adopts an electronic detonator water pressure control blasting method, and the cyclic footage blasting of the upper step adopts an electronic detonator Layer-by-layer peeling and controlled blasting.
The tunnel excavation method for upper soft and lower hard strata according to claim 1, wherein the diameter of the part of the middle pipe shed intruding into the contour line of the initial support of the upper step is smaller than the diameter of the middle pipe shed intruding into the stratum the diameter of the part.