CN117905481A - Large-section tunnel excavation structure and excavation method - Google Patents

Abstract

The invention discloses a large-section tunnel excavation structure. A first excavation area and two second excavation areas are formed in a geological body to be excavated. The two second excavation areas are spaced apart on both sides of the first excavation area, and the first excavation area and the two second excavation areas are arranged between the arch waists on both sides of the tunnel. The first excavation area and the two second excavation areas each include at least two excavation guide tunnels sequentially distributed along the direction from the arch crown to the invert arch of the tunnel, and the excavation guide tunnels adjacent to the invert arch in the first excavation area form a temporary step. When the invention is used, the large-section tunnel is excavated in sections, and the excavation span and excavation height of each section are reduced. The section support system can be ringed in time, and multiple disturbances to weak surrounding rocks are reduced. The deformation of the surrounding rocks is effectively controlled, the safety of the excavation operation is ensured, and the use of supporting materials is reduced. The invention also discloses a large-section tunnel excavation method, which reduces engineering costs and improves construction efficiency.

Description

Excavation structure and excavation method of large-section tunnel

Technical Field

The invention belongs to the technical field of tunnel construction, and relates to a large-section tunnel excavation structure and an excavation method.

Background technique

In recent years, with the leapfrog development of my country's transportation, the traffic volume of urban traffic has increased. Traditional two-lane and three-lane highway tunnels can no longer meet the needs of peers. Newly built and expanded highway tunnels have been widely used, and the cross-section of highway tunnels has also increased to eight lanes in both directions. Large-span and ultra-large cross-section tunnel construction technology has emerged accordingly, becoming the main technology and research hotspot for tunnel construction. In view of the situation of ultra-large cross-sections in the process of tunnel construction, the single-side wall pilot pit method, double-side wall pilot pit method, CD method, CRD method and other partial excavation methods are generally used on site.

Taking the double-side wall pilot tunnel excavation method as an example, this method divides the tunnel section into 9 parts for excavation. It has problems such as complicated construction procedures, many process connections, low degree of mechanization, low construction efficiency, long construction period, high project cost, and many construction safety hazards.

Summary of the invention

The purpose of the present invention is to provide a large-section tunnel excavation structure to solve the technical problems in the prior art such as complicated construction procedures, many process connections, low degree of mechanization, low construction efficiency, long construction period, high project cost and many construction safety hazards.

Another object of the present invention is to provide a large-section tunnel excavation method.

The first technical solution adopted by the present invention is a large-section tunnel excavation structure, including a geological body to be excavated, in which a first excavation area and two second excavation areas are formed, the two second excavation areas are distributed at intervals on both sides of the first excavation area, and the first excavation area and the two second excavation areas are arranged between the arch waists on both sides of the tunnel, the first excavation area and the two second excavation areas each include at least two excavation guide tunnels distributed in sequence along the direction from the tunnel arch to the invert arch, and the excavation guide tunnels adjacent to the invert arch in the first excavation area form temporary steps.

The second technical solution adopted by the present invention is a large-section tunnel excavation method, which adopts a large-section tunnel excavation structure and is specifically implemented in the following steps:

Step 1, excavating two excavation guide tunnels in the second excavation areas to form a first molding structure and a second molding structure in the second excavation areas respectively; a side of the first molding structure close to the first excavation area is a first temporary structure; a side of the second molding structure close to the first excavation area is a second temporary structure;

Step 2, excavating the excavation guide tunnel near the arch of the tunnel in the first excavation area to form a temporary step corresponding to the excavation guide tunnel near the invert arch of the tunnel in the first excavation area;

Step 3, dismantling the first temporary structure and the second temporary structure and performing initial support construction on the arch corresponding to the first excavation area, the first temporary structure and the arch waist of the second temporary structure;

Step 4: Continue excavating the temporary steps and the tunnel invert to form a tunnel structure.

The second technical solution of the present invention is also characterized in that:

The forming of the first forming structure in step 1 is specifically as follows:

In any of the two second excavation areas, the pilot tunnels are sequentially excavated in the direction from the arch to the invert of the tunnel to form the first forming structure in the second excavation area. Specifically, the excavation pilot tunnel close to the arch direction of the tunnel is excavated to a first preset depth in the direction from the arch to the invert of the tunnel and initial support construction is performed to form a first tunnel structure; the first tunnel structure includes a first temporary invert and a first temporary structure, the first temporary invert is formed at the bottom end of the first tunnel structure, and the first temporary structure is formed on one side of the first tunnel close to the first excavation area;

Continue to excavate the excavation pilot tunnel located below the first tunnel structure to a second preset depth along the direction from the arch to the invert of the tunnel until the corresponding second excavation area is excavated; the second preset depth is less than the first preset depth;

The first temporary invert is removed and initial support construction is performed on the second excavation area that has been excavated to obtain a first formed structure;

The forming of the second forming structure in step 1 is specifically as follows:

The other second excavation area excavates the pilot tunnels in sequence along the direction from the arch to the invert of the tunnel, so as to form a second forming structure in the other second excavation area, specifically: for the other second excavation area, the excavation pilot tunnels close to the arch direction of the tunnel are excavated to a first preset depth along the direction from the arch to the invert of the tunnel and initial support construction is performed to form a second cave structure; the second cave structure includes a second temporary invert and a second temporary structure, the second temporary invert is formed at the bottom end of the second cave structure, and the second temporary structure is formed on one side of the second cave close to the first excavation area;

Continue to excavate the excavation pilot tunnel located below the second tunnel structure to a second preset depth along the direction from the arch to the invert of the tunnel until the corresponding second excavation area is excavated;

The first temporary invert is removed and initial support construction is performed on the second excavation area that has been excavated to obtain a second formed structure;

The forming of the temporary step in step 2 is as follows:

Excavating the excavation pilot tunnel near the tunnel vault in the first excavation area to a first preset depth and performing initial support construction to obtain a third tunnel body; the first temporary structure and the second temporary structure are enclosed together with the geological body located at the tunnel vault to form the third tunnel body;

A third temporary invert is constructed at the bottom of the third tunnel body, so that a temporary step is formed in the geological body corresponding to the excavation guide tunnel of the invert close to the tunnel in the first excavation area;

The tunnel structure formation in step 4 is specifically as follows:

Excavating the temporary steps and the tunnel invert to a third preset depth; the third preset depth is less than the second preset depth;

Carry out support construction on the first excavation area and two second excavation areas where excavation construction has been completed to form a tunnel structure;

In step 4, support construction is performed on the first excavation area and the two second excavation areas, where excavation construction has been completed, to form a tunnel structure as follows: initial support construction is performed on the inverted arch of the first excavation area and the two second excavation areas, and secondary lining construction is performed on the tunnel to form a tunnel structure;

The secondary lining construction to form the tunnel structure is as follows:

Carry out initial support construction on the inverts of the first excavation area where excavation construction has been completed and the two inverts of the second excavation area, and carry out secondary lining construction on the tunnel;

Repeat the step of sequentially excavating each pilot tunnel in any second excavation area along the direction from the arch to the invert of the tunnel to form a first forming structure in the second excavation area until the tunnel is bored through to form a tunnel structure;

The inverted arches in the first excavation area and the two inverted arches in the second excavation area that have been excavated are initially supported and the tunnel is relined to form a tunnel structure as follows:

The invert arch of the first excavation area and the invert arches of the two second excavation areas that have been excavated are relined to form a tunnel structure for support construction;

Filling the invert of the tunnel that has been excavated with slag, and performing road surface construction on the invert after the slag filling has been completed, to form a tunnel structure;

Wherein, for any second excavation area, each guide tunnel is excavated in sequence along the direction from the arch crown to the invert arch of the tunnel to form a first forming structure in the second excavation area, and the method also includes using an advance support component with preset parameters to perform advance support construction on the first excavation area and the two second excavation areas.

The beneficial effects of the present invention are:

The large-section tunnel excavation structure of the present invention forms a first excavation area and two second excavation areas in a geological body to be excavated, the two second excavation areas are spaced apart on both sides of the first excavation area, and the first excavation area and the two second excavation areas are arranged between the arch waists on both sides of the tunnel, the first excavation area and the two second excavation areas each include at least two excavation guide tunnels sequentially distributed along the direction from the arch top to the invert of the tunnel, and the excavation guide tunnels adjacent to the invert in the first excavation area form temporary steps, so that the present invention adopts partial excavation for the large-section tunnel when in use, reduces the excavation span and excavation height of each part, and the partial support system can be ringed in time, reduces multiple disturbances to the weak surrounding rock, effectively controls the deformation of the surrounding rock, and ensures the safety of the excavation operation; at the same time, the excavation guide tunnel connected to the invert of the tunnel in the first excavation area is used as a temporary step, so that the present invention can give full play to the bearing capacity of the lower surrounding rock when in use, and the temporary support system is composed of the reserved soil of the lower step and the temporary steel frame support of the upper step, which reduces the use of support materials, reduces the engineering cost, and improves the construction efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic structural diagram of a large-section tunnel excavation structure of the present invention;

FIG2 is a flow chart of a large-section tunnel excavation method according to the present invention;

FIG3 is a flow chart of forming the first forming structure in step 1 of the large-section tunnel excavation method of the present invention;

FIG4 is a schematic diagram of a tunnel cross section in step 1.1 of the large-section tunnel excavation method of the present invention;

FIG5 is a schematic diagram of the tunnel cross section in step 1.2 of the large-section tunnel excavation method of the present invention;

FIG6 is a flow chart of forming the second forming structure in step 1 of the large-section tunnel excavation method of the present invention;

7 is a schematic diagram of a tunnel cross section when a second tunnel structure is formed in the large-section tunnel excavation method of the present invention;

FIG8 is a schematic diagram of a tunnel cross section when a second excavation zone is formed in the large-section tunnel excavation method of the present invention;

FIG9 is a schematic diagram of a process for forming a temporary step in a large-section tunnel excavation method of the present invention;

FIG10 is a schematic diagram of a tunnel cross section when a third tunnel body is obtained in the large-section tunnel excavation method of the present invention;

FIG11 is a schematic diagram of a tunnel cross section when a temporary step is formed in the large-section tunnel excavation method of the present invention;

FIG12 is a flow chart showing the completion of the tunnel structure design in the large-section tunnel excavation method of the present invention;

13 is a schematic diagram of a tunnel cross section when excavating to a third preset depth in the large-section tunnel excavation method of the present invention;

FIG14 is a schematic diagram of a tunnel cross section after secondary lining construction in the large-section tunnel excavation method of the present invention;

FIG15 is a flow chart of secondary lining construction in the large-section tunnel excavation method of the present invention;

FIG16 is an overall flow chart of the large-section tunnel excavation method of the present invention after adding a preparation workflow;

FIG17 is a schematic diagram of a tunnel section formed after the large-section tunnel excavation method of the present invention is implemented;

FIG18 is a schematic diagram of the tunnel section formed under different working conditions of the large-section tunnel excavation method of the present invention.

In the figure, 1. geological body to be excavated, 2. first excavation area, 3. second excavation area, 4. first temporary structure, 5. second layer of initial support, 6. second temporary structure, 7. temporary steps, 8. first layer of initial support, 9. secondary lining.

Detailed ways

The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

The present invention provides a large-section tunnel excavation structure, as shown in the following embodiments:

Example 1, large cross-section tunnel excavation structure is as follows:

In this embodiment, as shown in FIG1 , a large-section tunnel excavation structure includes a geological body 1 to be excavated, a first excavation area 2 and two second excavation areas 3 are formed in the geological body 1 to be excavated, the two second excavation areas 3 are distributed at intervals on both sides of the first excavation area 2, and the first excavation area 2 and the two second excavation areas 3 are arranged between the arch waists on both sides of the tunnel, the first excavation area 2 and the two second excavation areas 3 each include at least two excavation guide tunnels distributed in sequence along the direction from the arch crown to the invert arch of the tunnel, and the excavation guide tunnels adjacent to the invert arch in the first excavation area 2 form a temporary step 7;

In this embodiment, a first excavation area 2 and two second excavation areas 3 are formed in the geological body 1 to be excavated, the two second excavation areas 3 are spaced apart on both sides of the first excavation area 2, and the first excavation area 2 and the two second excavation areas 3 are arranged between the arch waists on both sides of the tunnel, the first excavation area 2 and the two second excavation areas 3 each include at least two excavation guide tunnels sequentially distributed along the direction from the arch crown to the invert arch of the tunnel, and the excavation guide tunnels adjacent to the invert arch in the first excavation area 2 form a temporary step 7, so that the present invention can be used for large-section tunnels when in use. The tunnel is excavated in sections to reduce the excavation span and excavation height of each section. The section support system can be ringed in time, reducing multiple disturbances to the weak surrounding rock, effectively controlling the deformation of the surrounding rock, and ensuring the safety of the excavation operation. At the same time, the excavation guide tunnel connected to the tunnel invert in the first excavation area 2 is used as a temporary step 7, so that the bearing capacity of the lower surrounding rock can be fully utilized when the present invention is used. The temporary support system is composed of the reserved soil of the lower step and the temporary steel frame support of the upper step, which reduces the use of support materials, reduces the engineering cost, and improves the construction efficiency.

Embodiment 2, the excavation method of the large-section tunnel excavation structure is as follows:

The present invention proposes a large-section tunnel construction method, which is applied to a large-section tunnel excavation structure. To facilitate understanding of the present invention, the following description is made by taking an example in which the first excavation area 2 and the two second excavation areas 3 each include two excavation guide tunnels stacked vertically in sequence, as shown in FIG2 :

Specifically, the following steps are implemented:

Step 1, as shown in FIG3 , for any second excavation area 3 , guide tunnels are excavated in sequence along the direction from the arch to the invert of the tunnel to form a first forming structure in the second excavation area 3 ; a first temporary structure 4 is formed on one side of the first forming structure close to the first excavation area 2 ;

In this embodiment, the tunnel section is divided into upper and lower steps (wherein the upper and lower guide tunnels are both excavation guide tunnels) from the arch line position according to the left guide tunnel, the middle guide tunnel and the right guide tunnel (wherein the left and right guide tunnels are the second excavation area 3, and the middle guide tunnel is the first excavation area 2), the left guide tunnel is excavated in 2 parts, the middle guide tunnel is excavated in 2 parts, and the right guide tunnel is excavated in 2 parts, a total of 6 parts are excavated and supported separately; the upper step of the left guide tunnel is excavated by drilling and blasting first, and the excavation footage is controlled within the distance of 1 steel frame. After the excavation is completed, the first layer of the main tunnel is constructed. Initial support 8, forming the first temporary structure 4: φ25 hollow grouting anchor rod, anchor rod length 4.5m, spacing 100×60mm, plum blossom arrangement 18 per ring, φ8 steel mesh: spacing 200×200mm, I22b steel arch frame: spacing 0.6m, full ring construction, protective layer thickness between the surrounding rock 4cm, protective layer thickness 2cm on the side facing the air, locking anchor rod: 8 φ42 grouting small pipes with a length of 4.5m, and finally spraying 28cm thick C20 concrete;

After the excavation support length of the upper step of the left guide tunnel is greater than 30m, it is necessary to specifically and clearly explain that the first preset depth in the example in the embodiment is 30m, and the excavation of the surrounding rock of the lower step of the left guide tunnel is carried out; when the bearing capacity of the surrounding rock of the lower step of the middle guide tunnel meets the requirements of temporary steel frame support, a 4m wide lane is reserved at the upper end of the excavation of the lower step of the left guide tunnel, and the lower end is excavated to the design contour line, and the excavation footage is 1 steel frame distance. After the excavation is completed, the support parameters of the first temporary structure 400 are used for initial support to form a first forming structure;

When the excavation step distance of the left and right guide tunnels is not less than 30m, the upper step excavation of the right guide tunnel is carried out, and the excavation advance is controlled within the distance of one steel frame. After the excavation is completed, the support parameters of the first temporary structure 4 are used for initial support to obtain the second temporary structure 6;

As shown in FIG6 , the pilot tunnels are sequentially excavated in the other second excavation area 3 in the direction from the arch to the invert of the tunnel, so as to form a second forming structure in the other second excavation area 3; wherein the second forming structure is close to the first excavation area 2 on one side thereof as a second temporary structure 6;

In this embodiment, after the excavation support length of the upper step of the right guide tunnel is greater than 30m, the excavation of the surrounding rock of the lower step of the right guide tunnel is carried out. When the bearing capacity of the surrounding rock of the lower step of the middle guide tunnel meets the requirements of temporary steel frame support, a 4m wide driving lane is reserved at the upper end of the excavation of the lower step of the right guide tunnel, and the lower end is excavated to the design contour line. The excavation advance is 1 steel frame distance. After the excavation is completed, the first layer of initial support 8 is applied using the support parameters of the first temporary structure 4 to obtain the second forming structure;

Step 2, as shown in FIG9 , excavating the excavation guide tunnel near the arch of the tunnel in the first excavation area 2, so that the geological body corresponding to the excavation guide tunnel near the invert of the tunnel in the first excavation area 2 forms a temporary step 7;

In this embodiment, when the left and right pilot tunnels are 6m to 8m apart from the middle pilot tunnel, it should be particularly and clearly stated that when the third preset depth is 6m to 8m, independent synchronous excavation and support can be performed; the middle pilot tunnel excavation safety step distance for IV grade surrounding rock is 40m, and for V grade surrounding rock is 50m, and the excavation footage of the upper step of the middle pilot tunnel is 1 steel frame distance. After the excavation is completed, the support parameters of the first temporary structure 4 are used to apply the first layer of initial support 8;

Step 3, dismantling the first temporary structure 4 and the second temporary structure 6 and performing initial support construction on the arch corresponding to the first excavation area 2, the first temporary structure 4 and the arch waist of the second temporary structure 6;

In this embodiment, after the initial support arch deformation is stable, the first temporary structure 4 and the second temporary structure 6 are dismantled, and the arch settlement measurement is strengthened during the dismantling process to ensure the safety of the tunnel; firstly, the method of dismantling 1m every 3m is adopted, and 3m to 5cm is cut on the top of the steel frame of the two side walls or the middle partition wall to measure the deformation and deformation rate of the tunnel; when the deformation and deformation rate of the tunnel are within the normal range, the method of dismantling 1m every 1m is adopted, and the top of the supporting steel frame of the two side walls or the middle partition wall is cut to observe the deformation and deformation rate of the tunnel; it is strictly forbidden to cut the steel frame continuously to prevent the temporary support from suddenly becoming unstable and collapsing and injuring people; after the deformation is stable, the monitoring measurement results are analyzed to ensure the stability of the initial support of the tunnel;

Step 4, as shown in FIG12 , continues to excavate the temporary step 7 and the invert of the tunnel to form a tunnel structure:

In this embodiment, after the first temporary structure 4 and the second temporary structure 6 are removed, the lower step of the middle guide tunnel is excavated, and the excavation advance is controlled within the distance of one steel frame. After the excavation is completed, the support parameters of the first temporary structure 4 are used to apply the first layer of initial support 8;

After the initial support of the lower step of the middle guide tunnel is completed and reaches the designed strength, the second layer of initial support 5 is constructed. Before the construction of the second layer of initial support 5, the invert is backfilled and leveled with tunnel slag to provide a site for the construction of the second layer of initial support 5. The second layer of initial support adopts I22b steel arch frame: 60cm/frame, φ8 steel mesh with a spacing of 200×200mm and 24cm thick C20 concrete sprayed. The thickness of the protective layer of the steel frame on the surrounding rock side (outside of the tunnel) is not less than 4cm, and on the air side (inside of the tunnel) is not less than 2cm; the present invention adopts a double-layer initial support form, which effectively ensures the stability of the surrounding rock when the tunnel is shallow and the excavation section is large, and the double-layer initial support can be timely constructed to form a closed ring, which reduces the risk of tunnel collapse and improves construction safety;

After the second initial support is completed, the secondary lining construction will be carried out. The construction of the secondary lining 9 should be carried out after the deformation of the surrounding rock and the double-layer initial support is basically stable through monitoring and measurement; the second lining adopts a 70cm thick C30 reinforced concrete structure, and is poured as a whole using a formwork trolley and pressurized concrete pumping. During the pouring process, the continuous supply of electricity and materials is guaranteed, and the pouring shall not be interrupted;

In this embodiment, a first excavation area 2 and two second excavation areas 3 are formed in the geological body 1 to be excavated, the two second excavation areas 3 are spaced apart on both sides of the first excavation area 2, and the first excavation area 2 and the two second excavation areas 3 are arranged between the arch waists on both sides of the tunnel, the first excavation area 2 and the two second excavation areas 3 each include at least two excavation guide tunnels sequentially distributed along the direction from the arch crown to the invert arch of the tunnel, and the excavation guide tunnels adjacent to the invert arch in the first excavation area 2 form a temporary step 7, so that the present invention can be used for large-section tunnels when in use. The tunnel is excavated in sections to reduce the excavation span and excavation height of each section. The section support system can be ringed in time, reducing multiple disturbances to the weak surrounding rock, effectively controlling the deformation of the surrounding rock, and ensuring the safety of the excavation operation. At the same time, the excavation guide tunnel connected to the tunnel invert in the first excavation area 2 is used as a temporary step 7, so that the bearing capacity of the lower surrounding rock can be fully utilized when the present invention is used. The temporary support system is composed of the reserved soil of the lower step and the temporary steel frame support of the upper step, which reduces the use of support materials, reduces the engineering cost, and improves the construction efficiency.

Example 3

As shown in Figure 16, the large-section tunnel excavation method is specifically implemented in the following steps:

Step 1 is specifically implemented according to the following steps, as shown in Figures 4 and 5:

Step 1.1, for any second excavation area 3, excavate a first preset depth in the excavation pilot tunnel in the direction from the tunnel vault to the invert and perform initial support construction to form a first tunnel structure; wherein the first tunnel structure includes a first temporary invert and a first temporary structure 4, the first temporary invert is formed at the bottom of the first tunnel structure, and the first temporary structure 4 is formed on one side of the first tunnel close to the first excavation area 2;

Step 1.2, continue to excavate the excavation pilot tunnel located below the first cave structure to a second preset depth along the direction from the arch to the invert of the tunnel until the corresponding second excavation area 3 is excavated; the second preset depth is less than the first preset depth;

Step 1.3, dismantling the first temporary invert and performing initial support construction on the excavated second excavation area 3 to obtain a first formed structure;

As shown in Figure 7 and Figure 8:

Step 1.4, for another second excavation area 3, excavate a first preset depth in the excavation pilot tunnel in the direction from the tunnel vault to the invert and perform initial support construction to form a second tunnel structure; wherein the second tunnel structure includes a second temporary invert and a second temporary structure 6, the second temporary invert is formed at the bottom of the second tunnel structure, and the second temporary structure 6 is formed on one side of the second tunnel close to the first excavation area 2;

Step 1.5, continue to excavate the excavation pilot tunnel located below the second tunnel structure to a second preset depth along the direction from the arch to the invert of the tunnel, until the corresponding second excavation area 3 is excavated;

Step 1.6, dismantling the first temporary invert and performing initial support construction on the second excavation area 3 that has been excavated to obtain a second formed structure;

In this embodiment, the large-section tunnel is excavated in sections to reduce the excavation span and height of each section. The section support system can be ringed in time, reducing multiple disturbances to the soft surrounding rock, effectively controlling the deformation of the surrounding rock, and ensuring the safety of the excavation operation.

Step 2 is specifically implemented according to the following steps, as shown in Figures 10 and 11:

Step 2.1, excavating the excavation pilot tunnel near the arch of the tunnel in the first excavation area 2 to a first preset depth and performing initial support construction to obtain a third tunnel body; wherein the first temporary structure 4 and the second temporary structure 6 and the geological body located at the arch of the tunnel are enclosed together to form the third tunnel body;

Step 2.1, constructing a third temporary invert at the bottom of the third tunnel body, so that the geological body corresponding to the excavation guide tunnel of the invert close to the tunnel in the first excavation area 2 forms a temporary step 7;

In this embodiment, the bearing capacity of the lower surrounding rock is fully utilized, and a temporary support system is formed by the reserved soil of the lower step and the temporary steel frame support of the upper step, which reduces the support material and reduces the engineering cost;

Step 3, dismantling the first temporary structure 4 and the second temporary structure 6 and performing initial support construction on the arch corresponding to the first excavation area, the first temporary structure and the arch waist of the second temporary structure;

Step 4 is specifically implemented according to the following steps, as shown in Figures 13 and 14:

Step 4.1, continue to excavate the temporary step 7 and the invert of the tunnel to a third preset depth; wherein the third preset depth is less than the second preset depth;

Step 4.2, performing initial support construction on the inverted arch of the first excavation area 2 and the two inverted arches of the second excavation area 3, and performing secondary lining construction on the tunnel to form a tunnel structure;

In this embodiment, the reserved soil of the lower step is used as a bearing wall and also as a construction path for the upper steps of the left and right guide pits, so that each working surface can be constructed at the same time. Compared with the traditional double-side wall excavation, only a small number of excavations are required to complete the excavation, reducing the temporary support of the lower part of the two side walls, simplifying the process, effectively reducing the multiple disturbances to the surrounding rock, and significantly accelerating the construction efficiency;

As shown in FIG. 15 , step 4.2 is as follows:

Step 4.2.1, perform initial support construction on the inverts of the first excavation area 2 and the two inverts of the second excavation area 300, and perform secondary lining construction on the tunnel;

Step 4.2.2, repeatedly executing the step of excavating each pilot tunnel in sequence along the direction from the arch to the invert of the tunnel for any second excavation area 3 to form a first forming structure in the second excavation area 3, until the tunnel is penetrated to form a tunnel structure;

Example 4

Step 4.2 The construction of the tunnel structure specifically includes:

Step 4.2.1, secondary lining construction is performed on the inverted arch of the first excavation area 2 and the two inverted arches of the second excavation area 3, to form a tunnel structure for support construction;

Step 4.2.2, filling the invert of the tunnel that has been excavated with slag, and performing pavement construction on the invert after the slag filling has been completed, to form a tunnel structure;

In this embodiment, the favorable factors of safety and stability of the tunnel surrounding rock during the partial excavation of the double side walls are fully utilized, the excavation divisions are simplified when there are many partial excavation processes, the working space of each partial excavation is increased, the mechanized operation efficiency is greatly improved, and the construction progress is accelerated.

In the above embodiment, before step 1, as shown in FIG16 , the following further includes:

Using advance support components with preset parameters to perform advance support construction on the first excavation area 2 and the two second excavation areas 3;

In this embodiment, before the tunnel excavation construction, a professional advanced geological prediction team is set up on site, and this work is included in the construction process management; a mode combining ground prediction and in-tunnel advanced prediction is adopted, mainly in-tunnel advanced prediction, which is mainly carried out by means of TSP203 geological advanced prediction system, advanced drilling, etc.

It should be specially and clearly stated that the advance support components of the preset parameters in the present embodiment include: the advance support adopts a φ42×4mm advance small conduit, no holes are opened within 0.5m of the pipe mouth, and the rest of the part is staggered with grouting holes at a spacing of 10cm, with a hole diameter of 8mm and a horizontal overlap length of not less than 1m. The small conduit is 4.5m long, with an annular spacing of 35cm to 45cm, 70 per ring (140 double-layer), and the external insertion angles are respectively a gentle angle of 10° to 14° and a steep angle of 30° to 40°. The upper and lower layers are staggered and arranged within the range of 125° of the arch. The temporary support small conduit is 4.5m long, with an annular spacing of 40cm, 30 per ring, and an external insertion angle of 10° to 14°;

In specific implementation, as shown in Figures 17 and 18, after the excavation support length of the upper step of the left guide tunnel is greater than 30m, the surrounding rock of the lower step of the left guide tunnel is excavated; when the bearing capacity of the surrounding rock of the lower step of the middle guide tunnel does not meet the requirements of the temporary steel frame support, grouting is first performed to reinforce the surrounding rock, and when excavating the lower step of the left guide tunnel, a 1.5m width is reserved at the upper end, and a 4m wide roadway is reserved at the lower end (that is, the top surface of the lower step of the left guide tunnel close to the side of the middle guide tunnel has a reserved width of 1.5m, and the bottom of the lower step of the left guide tunnel has a reserved width of 4m as a roadway). The excavation advance is the distance of one steel frame. After the excavation is completed, the first layer of initial support is applied using the support parameters of the first temporary structure 400.

After the excavation support length of the upper step of the right guide tunnel is greater than 30m, the excavation of the surrounding rock of the lower step of the right guide tunnel is carried out. When the bearing capacity of the surrounding rock of the lower step of the middle guide tunnel does not meet the requirements of the temporary steel frame support, grouting is first used to reinforce the surrounding rock. When excavating the lower step of the right guide tunnel, a width of 1.5m is reserved at the upper end and a 4m wide carriageway is reserved at the lower end (that is, the top surface of the lower step of the right guide tunnel close to the side of the middle guide tunnel has a reserved width of 1.5m, and the bottom of the lower step of the left guide tunnel has a reserved width of 4m as a carriageway); the excavation advance is the distance of one steel frame. After the excavation is completed, the first temporary structure 400 support parameters are used to apply the first layer of initial support;

In this embodiment, the excavation process can be dynamically adjusted according to the surrounding rock conditions of the lower step in front of the face. If the bearing capacity of the reserved soil in the lower step does not meet the requirements as a bearing wall, it can be grouting reinforced first, and construction can continue when the bearing capacity meets the requirements.

Claims (10)

1. Big section tunnel excavation structure, its characterized in that, including waiting to excavate geologic body (1), wait to excavate to be formed with first excavation district (2) and two second excavation district (3) in geologic body (1), two second excavation district (3) interval distribution in the both sides of first excavation district (2), just first excavation district (2) and two second excavation district (3) equipartition is arched down between the tunnel both sides, first excavation district (2) and two second excavation district (3) all include two at least edges the excavation pilot tunnel that the direction of tunnel vault to the inverted arch distributes in proper order, with the adjacent excavation pilot tunnel formation temporary step (7) of inverted arch in first excavation district (2).

2. The large-section tunnel excavation method is characterized by adopting the large-section tunnel excavation structure as claimed in claim 1, and is implemented specifically according to the following steps:

Step 1, excavating excavation pilot holes in two second excavation areas to form a first molding structure and a second molding structure in the second excavation areas respectively; a first temporary structure (4) is arranged on one side of the first forming structure, which is close to the first excavation area; a second temporary structure (6) is arranged on one side of the second forming structure close to the first excavation area;

step 2, excavating construction is carried out on an excavation pilot tunnel close to the vault of the tunnel in a first excavation area, so that a temporary step corresponding to the excavation pilot tunnel close to the inverted arch of the tunnel in the first excavation area is formed;

Step 3, dismantling the first temporary structure (4) and the second temporary structure (6) and performing primary support construction on vaults corresponding to the first excavation area, vaults of the first temporary structure and the second temporary structure;

And 4, continuing to excavate the temporary steps and the inverted arch of the tunnel to form the tunnel structure.

3. The method for excavating a large-section tunnel according to claim 2, wherein the forming of the first forming structure in step 1 is specifically as follows:

Any one second excavation area of the two second excavation areas excavates each pilot tunnel in turn according to the direction from the vault to the inverted arch of the tunnel, so that a first forming structure is formed in the second excavation area, and the method specifically comprises the following steps: excavating the excavation pilot tunnel close to the vault direction of the tunnel to a first preset depth according to the direction from the vault of the tunnel to the inverted arch, and performing primary support construction to form a first tunnel body structure; the first hole body structure comprises a first temporary inverted arch and a first temporary structure (4), the first temporary inverted arch is formed at the bottom end of the first hole body structure, and the first temporary structure (4) is formed at one side of the first hole body close to the first excavation area;

continuing to excavate an excavation pilot tunnel below the first tunnel body structure to a second preset depth according to the direction from the vault of the tunnel to the inverted arch until the second excavation area corresponding to the excavation is completed; the second preset depth is smaller than the first preset depth;

And removing the first temporary inverted arch and performing primary support construction on the excavated second excavation area to obtain the first forming structure.

4. A method of excavating a large-section tunnel according to claim 3, wherein the second molding structure in step 1 is formed as follows:

The other second excavation area excavates each pilot tunnel in turn according to the direction from the vault to the inverted arch of the tunnel so as to form a second molding structure in the other second excavation area, specifically: aiming at the other second excavation area, excavating the excavation pilot tunnel which is close to the vault direction of the tunnel according to the direction from the vault of the tunnel to the inverted arch to the first preset depth, and performing primary support construction to form a second tunnel body structure; the second hole body structure comprises a second temporary inverted arch and the second temporary structure, the second temporary inverted arch is formed at the bottom end of the second hole body structure, and the second temporary structure is formed at one side, close to the first excavation area, of the second hole body;

Continuing to excavate the excavation pilot tunnel below the second tunnel body structure to a second preset depth according to the direction from the vault of the tunnel to the inverted arch until the second excavation area is excavated;

and removing the first temporary inverted arch and performing primary support construction on the excavated second excavation area to obtain the second molding structure.

5. The method for excavating a large-section tunnel according to claim 4, wherein the forming of the temporary step in the step 2 is specifically as follows:

Performing excavation construction on the excavation pilot tunnel close to the tunnel vault in the first excavation area to a first preset depth and performing primary support construction to obtain a third tunnel body; the first temporary structure and the second temporary structure are enclosed together with a geologic body positioned on the vault of the tunnel to form the third hole body;

And a third temporary inverted arch is arranged at the bottom of the third hole body, so that a temporary step is formed in the first excavation area, which is close to the inverted arch of the tunnel, of the geologic body corresponding to the excavation pilot tunnel.

6. The method for excavating a large-section tunnel according to claim 5, wherein the tunnel structure in step 4 is formed as follows:

Excavating the temporary step and the tunnel inverted arch to a third preset depth; the third preset depth is smaller than the second preset depth;

And carrying out supporting construction on the first excavation area and the two second excavation areas which are subjected to excavation construction, so as to form the tunnel structure.

7. The method of excavating a large-section tunnel according to claim 6, wherein in the step 4, the first excavation region and the two second excavation regions where the excavation is completed are subjected to supporting construction, and the tunnel structure is formed specifically as follows: and performing primary support construction on the inverted arch of the first excavation area and the inverted arches of the two second excavation areas after the excavation construction is completed, and performing secondary lining construction on the tunnel to form the tunnel structure.

8. The method for excavating a large-section tunnel according to claim 7, wherein the secondary lining construction is performed, and the tunnel structure is formed specifically as follows:

Performing primary support construction on the inverted arch of the first excavation area and the inverted arches of the two second excavation areas after the excavation construction is completed, and performing secondary lining construction on the tunnel;

And repeatedly executing the step of sequentially excavating guide holes for any second excavation region according to the direction from the vault to the inverted arch of the tunnel so as to form a first forming structure in the second excavation region until the tunnel is opened, so as to form the tunnel structure.

9. The method for excavating a large-section tunnel according to claim 7, wherein the primary support construction is performed on the inverted arch of the first excavated area and the inverted arches of the two second excavated areas, and the secondary lining construction is performed on the tunnel, and the tunnel structure is formed specifically as follows:

performing secondary lining construction on the inverted arch of the first excavation area and the inverted arches of the two second excavation areas after the excavation construction is completed, and forming the tunnel structure for supporting construction;

filling slag soil on the inverted arch of the tunnel after the excavation construction is completed, and performing pavement construction on the inverted arch after the completion of the slag soil filling to form the tunnel structure.

10. The method of any one of claims 2 to 9, further comprising performing advanced support construction on the first excavation region and the two second excavation regions by using an advanced support member having preset parameters before the step of sequentially excavating each pilot tunnel for any one of the second excavation regions in a direction from the crown to the inverted arch of the tunnel to form a first molding structure in the second excavation region.