A construction method for the transition section of a single-track to double-track railway tunnel in an ultra-shallow buried railway tunnel

Abstract

The present invention relates to the field of building construction, and specifically to a construction method for a transition section from a single line to a double line in an ultra-shallow buried railway tunnel. The expansion of the shallow buried transition section is reinforced by advance support of a pipe shed, and then the upper step of the transition section uses special-shaped arch frames with different cross-sections to form a gradual transition section according to the single- and double-line contours, and finally reaches the double-line contour. After the excavation is completed, the gradual transition section is increased with the single-line excavation contour as a reference to increase the initial support, and the expansion of the gradual section is backfilled with concrete. The present invention can avoid large deformation caused by sudden changes in cross-sections, and at the same time use advanced middle pipe sheds and small guide tubes to reinforce the surrounding rock to prevent the expansion of the loose circle from causing collapse, thereby reducing construction risks and construction period costs. The expansion of the gradual section of the present invention does not need to be dismantled and replaced again. After another layer of single-line support is erected inside, the expansion is filled with concrete, and the construction is relatively safe.

Description

Technical Field

[0001] The invention relates to the field of building construction, and in particular to a construction method for a transition section of an ultra-shallow buried railway tunnel from a single track to a double track. Background Art

[0002] Railway tunnels are converted from small sections to large sections. Due to the sudden change in the excavation section, the stress of the surrounding rock is redistributed, which can easily cause collapse if not handled with care. This is especially true for soft surrounding rock and shallow tunnels, which are more prone to deformation and have higher safety risks. Summary of the invention

[0003] In order to overcome the above problems existing in the construction of converting a small section into a large section, the present invention provides a construction method for a transition section of a single-track to double-track ultra-shallow buried railway tunnel. The process can improve the safety of tunnel penetration construction in a fault fracture zone and reduce construction safety risks.

[0004] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a construction method for a transition section from a single line to a double line in an ultra-shallow buried railway tunnel, characterized in that the expansion of the shallow buried transition section is reinforced by advance support of a pipe shed, and then a step on the transition section is formed into a gradual transition section according to the single-line and double-line contour lines with special-shaped arch frames of different cross sections, and finally the double-line contour line is reached. After the excavation is completed, the gradual transition section is increased with the single-line excavation contour line as the reference for initial support, and the expansion of the gradual section is backfilled with concrete, which specifically includes the following steps:

[0005] ⑴ A Φ60mm middle pipe shed is adopted for the front of the shallow buried transition section and the side of the expansion excavation. The pipe shed is 9m long per pipe, and 21 pipes are set in one ring. The external insertion angle and deflection angle are detailed in the construction parameter table of the middle pipe shed in the transition section. Before the construction of the middle pipe shed, the face is sealed with shotcrete, and an I22a steel frame is installed to locate the hole position; before the construction of the transition section, a middle pipe shed construction platform is built on the upper step, and the construction platform is continuously trimmed with the drilling position to meet the construction requirements; after the construction of the middle pipe shed is completed, an advanced small guide tube is constructed in the gap between the holes of the middle pipe shed. The number and drilling angle of the advanced small guide tube are the same as those of the middle pipe shed;

[0006] Transition section pipe shed construction parameter table

[0007]

[0008] (2) The transition section excavation construction adopts the three-step method, with the upper step advancing 0.6m per cycle, the upper step construction height of 3.3m, and the excavation depth of each time of 0.6m. Under the advanced support of the middle pipe shed, the excavator cooperates with manual or pneumatic pick to excavate the upper section;

[0009] ⑶ After the transition section is excavated, arch support is adopted; because the gradual transition section is shallowly buried and the section is gradually widened, I22a steel frame is used for initial support, and the spacing between steel frames is 60cm; after the upper step is excavated according to the requirements of the gradual transition section, the spraying, anchoring and net system support is carried out in time, the steel frame is erected and the concrete is sprayed to the designed thickness. After the upper step is excavated for 5m, the middle step is excavated and supported. After the middle step is excavated for 5m, the lower step is excavated and supported;

[0010] ⑷ Post-processing of the transition section: During the construction of the second lining, because the expansion of the section on the right side of the heading is much larger than the expansion on the right side of the line, in order to ensure construction safety, before pouring the second lining, the original single-line tunnel I18 steel frame is used to support the expanded part of the transition section according to the original design, and shotcrete is used for filling.

[0011] In the step (1), the pipe sheds are numbered from left to right on the face starting with G1, the drilling rig must be parallel to the hole direction set on the steel frame, and drilling is allowed only after the drilling rig position is accurately confirmed; because the arch height and the right radius gradually increase, in order to ensure that the pipe shed has an advanced support effect and does not affect the subsequent arch support after the construction is completed, after the construction of the middle pipe shed is completed, an advanced small guide tube is constructed in the hole spacing gap of the middle pipe shed, and the number and drilling angle of the advanced small guide tube are the same as those of the middle pipe shed.

[0012] In step (3), locking foot anchor pipes are added to the middle and lower steps of the arch frame. In order to enhance the stability of the surrounding rock during construction, two Φ89mm large locking feet are added at the connection of each unit steel arch frame. Each foot is 6m long and has a driving angle of 45°. Grouting is required after driving.

[0013] In the step (4), when backfilling with concrete, the masonry height each time shall not exceed 1.5m, and the next layer of concrete backfilling can be carried out only after the previous layer of backfill concrete reaches the strength; the backfill concrete of the gradual transition section and the section where the thickness of the second lining is increased must be dense, and the second lining construction can be carried out after the concrete backfilling is completed.

[0014] The present invention can avoid large deformation caused by sudden changes in the ground stress due to sudden changes in the cross section, and at the same time use the advanced middle pipe shed and small pipe to reinforce the surrounding rock to prevent the expansion of the loose circle and cause collapse, thereby reducing construction risks and construction period costs. The expansion of the gradual section of the present invention does not need to be dismantled and replaced again. After another layer of single-line support is erected inside, the expansion is filled with concrete, which is safer to construct. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a cross-sectional view of the middle pipe shed during the construction process of the present invention;

[0016] Figure 2 It is a schematic diagram of excavation during the construction process of the present invention;

[0017] Figure 3 It is a plan view of the transition section steel frame layout during the construction process of the present invention;

[0018] Figure 4 It is an elevation view of the transition section steel frame arrangement during the construction process of the present invention;

[0019] Figure 5 This is a plan view of the initial support backfill of the transition section during the construction process of the present invention. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below with reference to the accompanying drawings. Example

[0021] The construction length of a certain tunnel is 403m, with single-mouth excavation and few working surfaces. The construction mileage is from 432km 500.6m to 432km 484m from the starting point. The surrounding rock grade of the above section is Grade V, with a buried depth of only 7-11m. The junction mileage of the single and double lines is 432km 494m from the starting point. The entire tunnel is a shallow buried tunnel with great safety risks. The single-line segment is transformed into a double-line segment using a gradual transition segment for construction.

[0022] (1) A Φ60mm middle pipe shed is adopted for the front of the shallow buried transition section and the side of the expansion excavation. The pipe shed is 9m long per pipe shed, and 21 pipes are set in one ring. For details of the external insertion angle and deflection angle, please refer to the construction parameter table of the transition section middle pipe shed. Before the construction of the middle pipe shed, the face is sealed with shotcrete, and an I22a steel frame is installed to locate the hole. The middle pipe shed construction can only be carried out after the steel frame is accepted. The materials used for the construction of the middle pipe shed must be qualified after the test sampling before entering the site. The steel flower pipe must be completed before the drilling is completed; before the construction of the transition section, a middle pipe shed construction platform is built on the upper step, and the construction platform is continuously adjusted with the drilling position to meet the construction requirements; after the construction of the middle pipe shed is completed, an advance small guide tube is constructed in the gap between the holes of the middle pipe shed. The number and drilling angle of the advance small guide tube are the same as those of the middle pipe shed;

[0023] The pipe shed is numbered from G1 to G21 from left to right on the face. The drilling rig must be parallel to the hole direction set on the steel frame. Drilling is allowed only after the drilling rig position is accurately verified. Use a combination of total station, hanging line, and drill rod guidance to make repeated adjustments to ensure that the axis of the drill rod of the drilling rig coincides with the designed drilling axis. As the arch height and the radius on the right side of the face gradually increase, in order to ensure that the pipe shed has an advanced support effect and does not affect the subsequent arch support after the construction is completed, the original designed drilling angle will be gradually raised by 1 to 3 degrees while ensuring the vertical distance from the pipe shed to the arch. Figure 1 shown.

[0024] Transition section pipe shed construction parameter table

[0025] .

[0026] (2) The transition section is constructed using the three-step method. Figure 2As shown, the advance of each cycle of the upper step is 0.6m. The construction height of the upper step is 3.3m, and the excavation depth is 0.6m each time. Under the advance support of the middle pipe shed, the excavator cooperates with manual or pneumatic pick to excavate. After the excavation of the transition section is completed, arch support is adopted. Because the burial depth of the gradient section is shallow and the cross-section gradually widens. The original I18 steel frame was changed to I22a steel frame for initial support, and the spacing between the steel frames was 60cm. After the upper step is excavated according to the requirements of the gradient section, the spraying, anchoring and net system support is carried out in time. The steel frame is erected and the concrete is sprayed to the designed thickness. After the upper step is excavated for 5m, the middle step is excavated and supported. After the middle step is excavated for 5m, the lower step is excavated and supported. The steel frame gradient is shown in Figure 3 to Figure 4 shown.

[0027] Additional locking foot anchor pipes are installed at the middle and lower steps of the arch frame. In order to enhance the stability of the surrounding rock during construction, two Φ89mm large locking feet are added at the connection of each unit steel arch frame. Each foot is 6m long and the installation angle is consistent with the Φ42mm locking feet. Grouting is required after installation.

[0028] The tunnel bottom is excavated by weak blasting, and initial support is carried out around the tunnel bottom: initial concrete spraying, erection of steel frame, and re-spraying of concrete to the designed thickness.

[0029] Shotcrete construction

[0030] The strength of shotcrete is C25 and the thickness is 25cm. Before the shotcrete operation, the mechanical equipment, air and water pipelines, material delivery pipelines and cable lines are comprehensively inspected and tested. The working area has good ventilation and sufficient lighting.

[0031] The spraying of concrete should be carried out in sections, slices and layers. The spraying sequence should be from bottom to top, and the length of each section should not be greater than 6m. When spraying, first roughly level the low-lying areas, and then spray in layers and reciprocatingly from bottom to top.

[0032] Shotcrete must be sprayed densely to avoid the appearance of voids and to avoid increasing safety hazards. To ensure construction safety during excavation, the excavated surface of the transition section should be initially sprayed and sealed to prevent rocks from falling.

[0033] ⑷ Gradient segment post-processing

[0034] During the construction of the secondary lining of the gradient section, if Figure 3 As shown in the figure, because the expansion of the right side of the line is much greater than that of the left side of the line, the original single-line second lining trolley pouring concrete construction will cause uneven force on the left and right sides, posing a major safety hazard. To ensure construction safety, before pouring the second lining, the original single-line tunnel arch frame is used according to the original design to support the construction mileage: 432 kilometers and 500.6 meters from the starting point to 432 kilometers and 484 meters from the starting point. The steel arch frames are numbered according to the excavation direction, a total of 12 frames, and installed in sequence.

[0035] C20 concrete backfill

[0036] like Figure 5 As shown, when backfilling with concrete, the masonry height each time shall not exceed 1.5m, and the next layer of concrete backfilling can be carried out only after the previous layer of backfilling concrete reaches the strength. The backfilling concrete of the gradient section and the increased thickness section of the secondary lining must be dense, and the secondary lining construction can be carried out after the concrete backfilling is completed.

Claims

1. A construction method for a transition section from a single track to a double track in an ultra-shallow buried railway tunnel, characterized in that: Through pipe-roof advance support, the expansion of the shallow buried transition section is reinforced, and then the upper step of the transition section uses special-shaped arch frames with different sections to form a gradual transition section according to the single-line and double-line contours, and finally reaches the double-line contour. After the excavation is completed, the gradual transition section is based on the single-line excavation contour line to increase the initial support, and the expansion of the gradual section is backfilled with concrete, which specifically includes the following steps: ⑴ A Φ60mm middle pipe shed is adopted for the front of the shallow buried transition section and the expanded excavation side. The pipe shed is 9m long per pipe, and 21 pipes are set in one ring. The middle pipe shed is constructed according to the preset external insertion angle and deflection angle. Before the construction of the middle pipe shed, the face is sealed with shotcrete, and an I22a steel frame is installed to locate the hole position; before the construction of the transition section, a middle pipe shed construction platform is built on the upper step, and the construction platform is continuously trimmed with the drilling position to meet the construction requirements; after the construction of the middle pipe shed is completed, an advance small guide tube is constructed in the gap between the holes of the middle pipe shed, and the number and drilling angle of the advance small guide tube are the same as those of the middle pipe shed; (2) The transition section excavation construction adopts the three-step method, with the upper step advancing 0.6m per cycle, the upper step construction height of 3.3m, and the excavation depth of each time of 0.6m. Under the advanced support of the middle pipe shed, the excavator cooperates with manual or pneumatic pick to excavate the upper section; ⑶ After the transition section is excavated, arch support is adopted; because the gradual transition section is shallowly buried and the section is gradually widened, I22a steel frame is used for initial support, and the spacing between steel frames is 60cm; after the upper step is excavated according to the requirements of the gradual transition section, the spraying, anchoring and net system support is carried out in time, the steel frame is erected and the concrete is sprayed to the designed thickness. After the upper step is excavated for 5m, the middle step is excavated and supported. After the middle step is excavated for 5m, the lower step is excavated and supported; ⑷ Post-processing of the transition section; during the construction of the second lining, because the expansion of the section on the right side of the heading is much larger than the expansion on the right side of the line, in order to ensure construction safety, before pouring the second lining, the original single-track tunnel I18 steel frame is used to support the expanded part of the transition section according to the original design, and shotcrete is used for filling; when backfilling with concrete, the masonry height each time shall not exceed 1.5m, and the next layer of concrete backfill can only be carried out after the previous layer of backfill concrete reaches the strength; the backfill concrete of the second lining thickness increase section of the gradual transition section must be dense, and the second lining construction can be carried out after the concrete backfill is completed.

2. The method for constructing a transition section from a single track to a double track in an ultra-shallow buried railway tunnel according to claim 1, characterized in that: In the step (1), the pipe sheds are numbered from left to right on the face starting with G1, the drilling rig must be parallel to the hole direction set on the steel frame, and drilling is allowed only after the drilling rig position is accurately confirmed; because the arch height and the right radius gradually increase, in order to ensure that the pipe shed has an advanced support effect and does not affect the subsequent arch support after the construction is completed, after the construction of the middle pipe shed is completed, an advanced small guide tube is constructed in the hole spacing gap of the middle pipe shed, and the number and drilling angle of the advanced small guide tube are the same as those of the middle pipe shed.

3. The method for constructing a transition section from a single track to a double track in an ultra-shallow buried railway tunnel according to claim 1, characterized in that: In step (3), locking foot anchor pipes are added to the middle and lower steps of the arch frame. In order to enhance the stability of the surrounding rock during construction, two Φ89mm large locking feet are added at the connection of each unit steel arch frame. Each foot is 6m long and has a driving angle of 45°. Grouting is required after driving.

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