A method for supporting tunnel intersections in soft rock

Abstract

This invention discloses a construction method for supporting soft rock tunnel intersections, comprising interconnected civil engineering excavation and supporting arch support. The civil engineering excavation includes the excavation of an adit, a pilot tunnel, and the main tunnel. The adit is designed and arranged on the side of the main tunnel to form an intersection, and a pilot tunnel is excavated above the main tunnel at the intersection. In the intersection excavation and support process, this invention uses a steel support gantry connected to the main tunnel steel support to form an effective initial support closed loop. The pilot tunnel is constructed from the end of the adit, and the main tunnel is supported by a combination of the pilot tunnel steel support frame and the steel support gantry. This method effectively closes the intersection support construction in advance when large machinery cannot enter the tunnel, solving the difficulties in excavation and support caused by adverse geological conditions, and addressing the frequent occurrence of rockfalls, collapses, and deformations during construction. It also overcomes the slow construction progress caused by site and space limitations, improving the on-site construction quality.

Description

Technical Field

[0001] This invention belongs to the field of water conservancy and hydropower construction technology, and in particular to the field of water conservancy and hydropower tunnel excavation and construction technology. It relates to the excavation and support construction of tunnel intersections in water conservancy projects, specifically a support structure for soft rock tunnel intersections and its construction method. Background Technology

[0002] Tunnel intersection excavation is frequently encountered in water conservancy and hydropower projects. Currently, the conventional method for excavating and supporting tunnel intersections involves excavating the entire length of the adit into the main tunnel, followed by widening the excavation from the adit to the main tunnel. A problem arises when encountering areas with poor surrounding rock during the excavation from the adit to the main tunnel; this can easily lead to rockfalls, collapses, and deformations, compromising the safety of construction workers. Furthermore, the excavation and support speed is severely delayed, preventing timely support of the excavation face. The progress of the main tunnel excavation is also affected by the limited operating space and construction platform within the tunnel, impacting both the project schedule and construction quality, while also posing significant safety hazards. Therefore, rapid and safe excavation and support construction of tunnel intersections becomes a crucial procedure, with safety and efficiency becoming critical factors affecting the project's progress. Summary of the Invention

[0003] This invention addresses the aforementioned problems in existing technologies by providing a support structure and construction method for soft rock tunnel intersections. This invention effectively solves the safety issues associated with inclined shaft construction during soft rock tunnel intersection support construction and improves construction efficiency.

[0004] This invention is achieved through the following technical solution:

[0005] A method for constructing a support structure at a soft rock tunnel intersection, characterized in that: the construction method includes interconnected civil engineering excavation and supporting arch frame construction, wherein the civil engineering excavation includes the excavation of adit tunnels, pilot tunnels, and the main tunnel; the adit tunnels are designed and arranged on the side of the main tunnel to form an intersection, and a pilot tunnel is designed and excavated above the main tunnel at the intersection; the method includes the following technological processes:

[0006] First, the adit is excavated and supported. The adit is excavated and supported to the intersection with the main tunnel. A rectangular steel support gantry is installed at the intersection. After the steel support gantry is completed, the pilot tunnel is excavated and supported. After the pilot tunnel is excavated and supported, the main tunnel section of the pilot tunnel is supported. Then, the sidewall support of one side of the pilot tunnel is removed to form the excavation face of one side of the main tunnel. After the excavation face of one side of the main tunnel meets the space requirements, the sidewall support of the other side of the pilot tunnel is removed to form the upstream and downstream double working faces of the main tunnel. After the excavation space of the main tunnel is sufficient, the excavation and support below the arch of the main tunnel are carried out.

[0007] The support structures for the auxiliary tunnel and the main tunnel are made of steel arch frames.

[0008] The steel support gantry installed at the intersection is a rectangular frame support structure consisting of gantry columns, bottom cross braces, and gantry cross braces. Two gantry columns are fixed to the side walls on both sides of the intersection. Bottom cross braces are fixed between the bottom of the two gantry columns, and gantry cross braces are fixed between the top of the two gantry columns. Several gantry reinforcement columns are fixed at intervals between the gantry cross braces and the top beam supporting the tunnel. The gantry cross braces are connected and fixed to the main tunnel steel support extension beam at the top of the main tunnel.

[0009] The pilot tunnel support consists of an array of pilot tunnel steel support frames that are erected as the tunnel is excavated along the excavation direction. Each set of pilot tunnel steel support frames includes a left column of the pilot tunnel support, a right column of the pilot tunnel support, and a pilot tunnel top horizontal brace fixed between the tops of the two columns. The pilot tunnel top horizontal brace is set below the pre-installed pre-grouting small guide pipe in the main tunnel and is welded and fixed to the main tunnel steel support at the top of the main tunnel.

[0010] The sidewalls and arches of the branch tunnels, pilot tunnels, and main tunnels were all protected with shotcrete after excavation.

[0011] In the construction method of this invention, the supporting columns of the side walls of the branch tunnel, the guide tunnel and the main tunnel are all anchored by anchor pipes anchored to the rock mass.

[0012] In the construction method of this invention, the shotcrete facing is formed by a steel mesh arranged on each excavation surface and concrete solidified by spraying; wherein the steel mesh is welded and fixed to the corresponding column by steel support connecting bars.

[0013] In the construction method of this invention, after the sidewall supports on both sides of the pilot tunnel are removed to form the upstream and downstream double working faces of the main tunnel, the main tunnel section of the pilot tunnel is divided into the remaining part of the top of the main tunnel, the middle step of the main tunnel, and the lower step of the main tunnel, which are excavated and supported in sequence, and then the main tunnel is excavated through the double working faces.

[0014] The beneficial effects of the construction method of this invention are as follows: During the excavation and support of the intersection, the steel support gantry is used to connect with the main tunnel steel support to form an effective initial support closed loop. The main tunnel is supported by a combination of the guide tunnel steel support frame and the steel support gantry, which is used to construct the guide tunnel from the end of the branch tunnel. When large machinery cannot enter the tunnel for construction, an effective closed loop is formed in advance for the intersection support construction. This effectively solves the difficulties in excavation and support caused by adverse geological conditions during the excavation process, solves the frequent occurrence of phenomena such as rockfall, collapse, and deformation during the excavation and support construction of soft rock tunnel intersections, solves the problem of slow construction progress due to site and space limitations, improves the on-site construction quality, and innovates the excavation and construction method for soft rock tunnel intersections. Attached Figure Description

[0015] Figure 1 This is a schematic cross-sectional view of the intersection in an embodiment of the present invention;

[0016] Figure 2 This is a schematic diagram showing the positional relationship between the main tunnel, branch tunnel, and guide tunnel in an embodiment of the present invention;

[0017] Figure 3 This is a schematic cross-sectional view of the steel support gantry structure at the intersection in an embodiment of the present invention;

[0018] Figure 4 This is a schematic cross-sectional view of the steel support frame for the guide tunnel in an embodiment of the present invention.

[0019] Explanation of reference numerals in the attached diagram: 1 is the steel support gantry; 2 is the gantry column; 3 is the auxiliary tunnel steel support; 4 is the gantry reinforced column; 5 is the main tunnel steel support; 6 is the bottom horizontal brace; 7 is the gantry horizontal brace; 8 is the guide tunnel; 9 is the guide tunnel steel support frame; 10 is the guide tunnel support left column; 11 is the guide tunnel support right column; 12 is the pre-grouting small guide pipe; 13 is the anchor pipe; 14 is the guide tunnel top horizontal brace; 15 is the steel support connecting bar; 16 is the hanging steel mesh; 17 is the shotcrete; 18 is the remaining part of the main tunnel top; 19 is the main tunnel middle step; 20 is the main tunnel lower step; 21 is the auxiliary tunnel backfill road; 22 is the auxiliary tunnel; 23 is the main tunnel. Detailed Implementation

[0020] The present invention will be further described below with reference to specific embodiments. These specific embodiments are further explanations of the principles of the present invention and are not intended to limit the present invention in any way. Any technology that is the same as or similar to the present invention does not exceed the scope of protection of the present invention.

[0021] Refer to the attached diagram.

[0022] The present invention relates to a method for supporting soft rock tunnel intersections, comprising interconnected civil engineering excavation and supporting arch support. The civil engineering excavation includes the excavation of a branch tunnel 22, a pilot tunnel 8, and a main tunnel 23. The branch tunnel 22 is designed and arranged on the side of the main tunnel 23 to form an intersection, and a pilot tunnel 8 is designed and excavated above the main tunnel 23 at the intersection.

[0023] When the adit 22 is excavated to the intersection with the main tunnel 23, the face support at the intersection is completed first, and a rectangular steel support gantry 1 is installed at the end of the adit 22 at the intersection for the initial support closure of the main tunnel 23 intersection. After the support of the adit 22 and the main tunnel 23 is completed, the pilot tunnel 8 is excavated and supported. The main tunnel support of the subsequent pilot tunnel section is installed using the pilot tunnel 8 as the operating space. The bottom side of the main tunnel steel support 5 at the intersection is connected along the design excavation line to the bottom plate of the main tunnel 23, and the other side is connected to the steel support gantry 1 at the end of the adit 22. Since the steel support gantry 1 has been grounded in advance, the main tunnel 23 support is connected to the steel support gantry 1 to form a complete support closure loop. In addition, the steel supports and gantry in the support structure are connected by connecting bars to form a whole. Locking anchor pipes 13 are used to fix the bottom of each steel support and gantry. The protective shell is formed by hanging steel mesh 16, shotcrete 17, system anchor rods and advanced grouting small pipes 12 to ensure the safety of subsequent face construction.

[0024] During construction: First, the branch tunnel 22 is excavated and supported to the intersection with the main tunnel 23, and a rectangular steel support gantry 1 is installed at the intersection (end of the branch tunnel). After the steel support gantry 1 is completed, the guide tunnel 8 is excavated and supported. The guide tunnel 8 is excavated in a rectangular shape and the excavation of the guide tunnel 8 must meet the requirements of mechanical construction. After the guide tunnel 8 is excavated and supported, the support construction of the main tunnel 23 in the guide tunnel section is completed. After the support construction of the main tunnel 23 in the guide tunnel section is completed, the support measures of the single side wall of the guide tunnel 23 are removed according to the site conditions to form the excavation and support face of the main tunnel 23. After the main tunnel 23 is excavated and supported to a certain extent, the removal of the side wall of the other side of the guide tunnel 8 can continue to be carried out to form the upstream and downstream double working faces of the main tunnel 23. After the excavation space of the main tunnel 23 is sufficient, the subsequent excavation and support below the top arch of the main tunnel 23 can continue.

[0025] The steel support gantry 1 includes a gantry cross brace 7, gantry columns 2, and a base plate cross brace 6, and also includes a gantry reinforcing column 4. The gantry cross brace 7 is located at the top of the gantry and forms an effective connection with the subsequent main tunnel steel support 5. The gantry columns 2 are located on both sides of the steel support gantry 1 to form an effective support loop after the subsequent main tunnel steel support 5 is connected to the top gantry cross brace 7. The gantry reinforcing column 4 is located below the gantry cross brace 7 and above the steel support arch beam of the branch hole 22, and is used to enhance the strength of the top gantry cross brace 7 of the steel support gantry 1. The base plate cross brace 6 is located at the bottom of the steel support gantry 1 and is used to support both sides of the gantry columns 2, ensuring that the gantry columns 2 on both sides will not shift after being subjected to force.

[0026] The pilot tunnel 8 is rectangular and located above the main tunnel 23 at the intersection. Workers can directly install the main tunnel steel support 5 below the supported pilot tunnel 8. The pilot tunnel 8 is excavated from the end of the branch tunnel 22. The main tunnel steel support 5 of the pilot tunnel section can be effectively connected to the steel support gantry 1 at the end of the branch tunnel 22 through the pilot tunnel 8.

[0027] Combination Figures 1-4The following are preferred embodiments of the construction procedure and support method, which are used to specifically illustrate the construction method for support of soft rock tunnel intersections of the present invention.

[0028] The construction adit of a water conveyance project intersects the main tunnel at an oblique angle of 42.65° and has a width of 13.136m.

[0029] like Figure 1 , Figure 2 As shown, the branch tunnel is 582.23m long and is arranged as an inclined shaft with a slope ratio of 1:2.47 and a downward slope of 22.03°. The cross-section of the inclined shaft is in the shape of a city gate. The cross-section after lining is 6.5×6m, and the unlined cross-section is 7.5×7m. The lining thickness is 50cm.

[0030] The main tunnel has a horseshoe-shaped cross-section, with a lining size of 9.20m × 9.20m and a lining thickness of 0.4m to 0.7m. The tunnel's design flow rate is 125m³ / h. 3 / s, bottom slope i=1 / 4200.

[0031] The lithology of the confluence section consists of (T3ba) strongly weathered silty mudstone and calcareous mudstone, interbedded with thin-layered siltstone and argillaceous sandstone. The rock mass is relatively broken and has poor integrity, posing a risk of deformation, collapse, and rockfall.

[0032] To address the excavation and support requirements at the intersection of this water conveyance project, this invention presents a support structure and construction method for soft rock tunnel intersections. The support structure includes: a steel support gantry 1, a main tunnel steel support 5, a guide tunnel steel support 9, a pre-grouting small guide pipe 12, a locking anchor pipe 13, a steel support connecting bar 15, a steel mesh 16, and shotcrete 17.

[0033] The steel-supported gantry 1 consists of gantry columns 2, branch tunnel steel supports 3, gantry reinforced columns 4, bottom cross braces 6, gantry cross braces 7, anchor pipes 13, steel support connecting bars 15, steel mesh 16, and shotcrete 17. The initial support is connected to the tunnel floor at the junction of branch tunnel 22 and main tunnel 23, creating conditions for the subsequent formation of a closed-loop support for main tunnel 23. The gantry reinforced columns 4 effectively enhance the bending strength of the gantry, ensuring that the support structure meets requirements when the main tunnel steel supports 5 are subsequently connected to the steel-supported gantry 1.

[0034] The main tunnel steel support 5 is connected to the steel support gantry 1 to form a complete support closed loop at the intersection. The intersection protective shell is formed by the advanced grouting small guide pipe 12, the locking foot anchor pipe 13, the top horizontal brace of the guide tunnel 14, the steel support connecting bar 15, the hanging steel mesh 16, and the shotcrete 17, which together with the intersection support closed loop form a complete support type.

[0035] The excavation and support of the adit 22 consists of a steel support gantry 1 and an adit backfill road 21. The steel support gantry 1 is installed at the intersection of the adit 22 and the main tunnel 23 and connects with the main tunnel steel support 5 to form a closed loop for the main tunnel 11 support. The construction of the pilot tunnel 8 uses the adit backfill road 21 as a construction passage.

[0036] The excavation of pilot tunnel 8 consists of pilot tunnel steel supports 9, left-side support columns 10 and 11, pre-grouting small guide pipes 12, anchor pipes 13, top horizontal bracing 14, steel support connecting bars 15, steel mesh reinforcement 16, and shotcrete 17. The excavation of pilot tunnel 8 provides a working face for the subsequent support construction of main tunnel 23. Furthermore, because the pilot tunnel 8 was reinforced in advance, the excavated working face can be promptly supported during the subsequent construction of main tunnel 23. This effectively prevents deformation of the surrounding rock due to prolonged exposure time and large excavation cross-section after the main tunnel 23 excavation, especially under complex geological conditions. Meanwhile, the main tunnel steel supports 5 are constructed after the pilot tunnel 8 excavation and support are completed, maximizing the safety of on-site construction personnel.

[0037] After the excavation and support of the main tunnel 23 are completed, the remaining part 18 at the top of the main tunnel is excavated and supported. Then, the left-side support column 10 of the guide tunnel is removed. Immediately after removal, the excavation and support of the main tunnel 23 working face is carried out. After the main tunnel 23 working face is constructed to a certain extent, the right-side support column 11 of the guide tunnel is removed. Immediately after removal, the working face is excavated and supported to form a double working face. After the upstream and downstream working faces are opened, the excavation and support construction of the middle bench 19 and the lower bench 20 of the main tunnel can be carried out according to the actual site conditions.

[0038] During construction, the support for the adit 22 is first extended to the sidewall of the main tunnel 23, i.e., the position of the steel support gantry 1 intersecting with the adit. Once the steel support gantry 1 meets the installation requirements, it is immediately installed. After the steel support gantry 1 is installed, the guide tunnel 8 is excavated. After the guide tunnel 8 is completed, the main tunnel steel support 5 is constructed. One side of the main tunnel steel support 5 is connected to the bottom of the main tunnel 23 along the original design excavation line, and the other side is connected to the gantry cross brace 7. A closed-loop support system at the intersection is formed through the pre-grouting small guide pipe 12, locking anchor pipe 13, steel support connecting bar 15, hanging steel mesh 16, and shotcrete 17. After the above construction is completed, the excavation and support construction of the main tunnel 23 is carried out. For the main tunnel 23 excavation and support, the right-side column 11 of the guide tunnel support is first removed. After removal, the working face excavation and support are immediately carried out to form a double working face. According to the actual site conditions, the excavation and support construction of the main tunnel middle step 19 and the main tunnel lower step 20 are carried out simultaneously, and the backfill road 21 of the adit is excavated. Construction at the intersection is complete.

[0039] Specifically, the construction of the support structure and construction method for soft rock tunnel intersections shall be carried out in the following steps:

[0040] A. The branch tunnel 22 was excavated using the full-section and bench method to extend the support to the side wall of the main tunnel 23.

[0041] B. Install steel support gantry 1 at the side wall position of the main tunnel 23 at the end of the branch tunnel 22. After the steel support gantry 1 is installed, excavate and support the pilot tunnel 8.

[0042] C. After the excavation and support of pilot tunnel 8 are completed, the main tunnel support construction of the pilot tunnel section will be carried out.

[0043] D. After the main tunnel support of the pilot tunnel section is completed, the main tunnel 23 will be excavated and supported. At the construction intersection, when the main tunnel is lowered to the step 20, the backfill road 21 of the auxiliary tunnel will be excavated at the same time.

[0044] E. Construction at the intersection is complete, and normal excavation and support construction is underway upstream and downstream of the main tunnel 23.

[0045] Comparison of engineering examples:

[0046] The construction adit intersects the main tunnel at an oblique angle of 42.65° with a width of 13.136m. The adit has a portal-shaped cross-section, with a lined cross-section of 6.5×6m and an unlined cross-section of 7.5×7m, with a lining thickness of 50cm. The main tunnel has a horseshoe-shaped cross-section, with a lined cross-section of 9.20m×9.20m, a lining thickness of 0.4m~0.7m, and a design flow rate of 125m³ / h. 3 / s, bottom slope i=1 / 4200. Furthermore, the lithology of the intersection section consists of (T3ba) strongly weathered silty mudstone and calcareous mudstone, interbedded with thin layers of siltstone and argillaceous sandstone. The rock mass is relatively fragmented and lacks integrity, posing a risk of deformation, collapse, and rockfall. If the original method of directly excavating and supporting the main tunnel from the branch tunnel is followed, the excavation carries certain risks. During the excavation from the branch tunnel to the main tunnel, if areas with poor surrounding rock are encountered, rockfall, collapse, and deformation are likely to occur during the excavation and support process, compromising the safety of construction personnel. Simultaneously, the excavation and support speed is severely delayed, resulting in the excavation face not receiving timely support construction. The main tunnel excavation progress is affected by the operating space inside the tunnel and the construction platform, impacting the construction schedule and quality, and posing significant safety hazards. After using this soft rock tunnel intersection support structure and construction method, the operating space for construction personnel during the support process meets the construction conditions, improving the quality of excavation and support, and increasing the strength of the intersection support. This improves construction efficiency and quality, and also enhances the safety of construction at soft rock tunnel intersections.

Claims

1. A method for constructing support at a soft rock tunnel intersection, characterized in that: The construction method includes interconnected civil engineering excavation and supporting arch frame construction. The civil engineering excavation includes the excavation of adit tunnels, pilot tunnels, and the main tunnel. The adit tunnels are designed and arranged on the side of the main tunnel to form an intersection, and a pilot tunnel is excavated above the main tunnel at the intersection. The construction process includes the following techniques: First, the adit is excavated and supported. The adit is excavated and supported to the intersection with the main tunnel. A rectangular steel support gantry is installed at the intersection. After the steel support gantry is completed, the pilot tunnel is excavated and supported. After the pilot tunnel is excavated and supported, the main tunnel section of the pilot tunnel is supported. Then, the sidewall support of one side of the pilot tunnel is removed to form the excavation face of one side of the main tunnel. After the excavation face of one side of the main tunnel meets the space requirements, the sidewall support of the other side of the pilot tunnel is removed to form the upstream and downstream double working faces of the main tunnel. After the excavation space of the main tunnel is sufficient, the excavation and support below the arch of the main tunnel are carried out. The support structures for the auxiliary tunnel and the main tunnel are made of steel arch frames. The steel support gantry installed at the intersection is a rectangular frame support structure consisting of gantry columns, bottom cross braces, and gantry cross braces. Two gantry columns are fixed to the side walls on both sides of the intersection. Bottom cross braces are fixed between the bottom of the two gantry columns, and gantry cross braces are fixed between the top of the two gantry columns. Several gantry reinforcement columns are fixed at intervals between the gantry cross braces and the top beam supporting the tunnel. The gantry cross braces are connected and fixed to the main tunnel steel support extension beam at the top of the main tunnel. The pilot tunnel support consists of an array of pilot tunnel steel support frames that are erected as the tunnel is excavated along the excavation direction. Each set of pilot tunnel steel support frames includes a left column of the pilot tunnel support, a right column of the pilot tunnel support, and a pilot tunnel top horizontal brace fixed between the tops of the two columns. The pilot tunnel top horizontal brace is set below the pre-installed pre-grouting small guide pipe in the main tunnel and is welded and fixed to the main tunnel steel support at the top of the main tunnel. The sidewalls and arches of the branch tunnels, pilot tunnels, and main tunnels were all protected with shotcrete after excavation.

2. The construction method for support at soft rock tunnel intersections according to claim 1, characterized in that: The sidewall support columns of the branch tunnel, pilot tunnel, and main tunnel are all anchored by anchor pipes anchored to the rock mass.

3. The construction method for support at soft rock tunnel intersections according to claim 1, characterized in that: The shotcrete facing with wire mesh is formed by steel mesh arranged on each excavation surface and concrete solidified by spraying; the steel mesh is fixed to the corresponding columns by welding steel support connecting bars.

4. The construction method for support at soft rock tunnel intersections according to claim 1, characterized in that: After the sidewall supports on both sides of the pilot tunnel are removed to form the upstream and downstream working faces of the main tunnel, the main tunnel section of the pilot tunnel is divided into the remaining part of the top of the main tunnel, the middle step of the main tunnel, and the lower step of the main tunnel, which are excavated and supported in sequence. Then the main tunnel is excavated through the double working faces.

Images