Construction method for forked tunnel gradually changing from small section to large section

Abstract

The invention discloses a construction method for a forked tunnel gradually changing from a small section to a large section, and belongs to the technical field of tunnel construction.The method specifically comprises the following steps that firstly, expanding excavation planning is conducted on the section contour of the small section, primary supporting is applied when the gradually-changed section is formed, and on the premise that the follow-up section expanding excavation construction operation space is guaranteed, secondary supporting is conducted on the section contour of the small section; and secondary primary support is constructed on the front-section expanded excavation section, and the outline of the secondary primary support is kept consistent with the original design outline of the small tunnel. And then lower step construction of the large-section tunnel is conducted, and finally an inverted arch and a secondary lining are constructed. By the adoption of the construction method, construction safety at the interface of the variable-cross-section tunnel is guaranteed, potential safety hazards caused by sudden change of the cross section are avoided, arch step type expanding excavation is adopted, steel arch support construction is matched, and construction operability and applicability are high. The specification and form of the steel frame are easy to adjust, and the construction matching technology is mature.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel construction, and in particular relates to a method for constructing a bifurcated tunnel with a gradual change from a small cross-section to a large cross-section. Background Art

[0002] With the rapid development of my country's railway construction, especially high-speed railways, due to the limitations of mountainous terrain and usage functions, the construction of tunnels with different cross-sections in the same section will inevitably increase. The safe and efficient transition to tunnels with different cross-sections for construction is the focus and difficulty of variable cross-section tunnel construction, especially for conditions where the span difference of the tunnel junction section is too large, such as super-large span tunnels and ordinary single-track tunnels. Reasonable construction method selection is crucial to ensure the safe construction of tunnels. When encountering construction conditions from small cross-section to large cross-section, the existing technology mostly directly adopts top-lifting construction to expand the tunnel, and the safety factor of this construction method is relatively low. Summary of the invention

[0003] In view of this, the purpose of the present invention is to provide a method for constructing a bifurcated tunnel with a gradual change from a small cross-section to a large cross-section, thereby ensuring the construction safety at the interface of the variable-section tunnel and avoiding the safety hazards caused by the sudden change of the cross-section.

[0004] In order to achieve the above object, the present invention provides the following technical solutions: The invention discloses a method for constructing a bifurcated tunnel with a gradual change from a small cross section to a large cross section, comprising the following steps: S1, excavation of the first gradual expansion section, specifically including: S1.1, advance small duct support is applied according to the preset annular spacing; S1.2, excavate the upper step and the excavated part of the first gradual excavation section, and construct the primary support of the corresponding section; S2, excavate the second gradual expansion section to the junction of the large section and the small section, specifically including: S2.1, advance small duct support is applied according to the preset annular spacing; S2.2, excavate the upper step and the excavated part of the second gradual excavation section, and construct the primary support of the corresponding section; S2.3, measure data and correct support parameters; S2.4, repeat the above excavation steps to the junction of the large section and the small section according to the excavation step setting; S3, excavation of the third gradual expansion section, specifically including: S3.1, advance small duct support is applied according to the preset annular spacing; S3.2, excavate the upper step and the expanded part of the third gradual expansion section, and construct the primary support of the corresponding section; S3.3, measure data and correct support parameters; S3.4, after climbing the slope, enter the large-section tunnel standard section construction; S4, construction of lower steps, including: S4.1, control the step distance of the lower step excavation according to the construction mileage of the secondary primary support, and excavate the lower step at a staggered distance; S4.2, construct initial support around the lower step.

[0005] Furthermore, the measurement data and correction of support parameters in step S2.3 and step S3.3 include measuring the deformation of the steel frame at the primary support and the contact pressure between the steel frame and the surrounding rock, judging the safety of subsequent construction, and guiding the selection of secondary primary support parameters at the primary support, as well as the primary support parameters of the subsequent expanded excavation section.

[0006] Furthermore, in step S3.4, the slope of the climbing construction is 13%.

[0007] Furthermore, in step S4.1, the distance between the lower bench excavation surface and the secondary primary support is not less than 10m.

[0008] Furthermore, when the three gradually enlarged excavation sections were being excavated, the soil pressure at each longitudinal position on the top of the tunnel was monitored in real time according to the step distance, and the support parameters of the small-pipe support with the next step distance were guided.

[0009] Furthermore, when monitoring the soil pressure at various longitudinal positions on the top of the tunnel, first, a monitoring hole is constructed at the same angle as the slope of the climbing construction and the hole is cleaned. Then, a monitoring tube is inserted along the monitoring hole. Pressure monitoring points are installed on the monitoring tube according to the step distance. The position of the pressure monitoring point is adjusted so that it fits with the inner wall of the monitoring hole, and then the value of the pressure monitoring point is reset to zero.

[0010] Furthermore, an air hole is opened on the monitoring tube, and the air hole is closed by an airbag. A pressure monitoring point is installed on the surface of the airbag. Specifically, when adjusting the position of the pressure monitoring point, the airbag is expanded by ventilating into the monitoring tube, so that the pressure monitoring point fits against the inner wall of the monitoring hole, and then the outer end of the monitoring hole is sealed.

[0011] Furthermore, after the excavation of the gradual expansion section is completed, grouting is continuously injected into the monitoring hole until the air bag ruptures, and the slurry is filled into the monitoring hole and then the hole is sealed.

[0012] The beneficial effects of the present invention are: 1. The method of the present invention adopts the step-by-step expansion of the arch part. Compared with the traditional transitional top construction, it avoids the generation of "inverted triangle" dangerous blocks, and cooperates with the steel arch support construction, and the construction operability and applicability are strong. The specifications and forms of the steel frame are easy to adjust, and the matching technology is mature. It can be applied to various cross-section forms, with the characteristics of flexible layout and wide application range.

[0013] 2. The present invention adopts double-layer initial support, which is highly safe. Specifically, drilling is performed by drilling rigs, followed by installation of steel pipe grouting, and initial support is performed for the gradual section at this stage after excavation to ensure the safety of subsequent expansion. After excavation to a large-section tunnel, a secondary lining steel frame is installed and concrete is sprayed to form a standard section. At this time, the primary support and the secondary support can form a stable overall reinforcement area.

[0014] 3. In the present invention, by measuring the deformation of the steel frame at the primary support and the contact pressure between the steel frame and the surrounding rock, the primary and secondary primary support parameters of the subsequent excavation section can be adjusted according to the pressure value during the excavation process, thereby ensuring the stability of the support and the safety of the construction.

[0015] Other advantages, objectives and features of the present invention will be described in the following description and will be apparent to those skilled in the art to some extent, or those skilled in the art may be taught from the practice of the present invention. The objectives and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to make the purpose, technical solution and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration: Figure 1 This is a schematic diagram of the tunnel face mileage of the first gradual expansion section; Figure 2 This is a schematic diagram of the excavation section and steel frame support of the first gradual excavation section; Figure 3 This is a schematic diagram of the tunnel face mileage of the second gradual expansion section; Figure 4 This is a schematic diagram of the excavation section and steel frame support of the second gradual excavation section; Figure 5 This is a schematic diagram of the tunnel face mileage of the third gradual expansion section; Figure 6 This is a schematic diagram of the excavation section and steel frame support of the third gradual excavation section; Figure 7 for Figure 1 Enlarged view of point A in the middle.

[0017] The markings in the attached drawing are as follows: steel frame 1, monitoring hole 2, monitoring tube 3, air hole 4, air bag 5, monitoring point 6. DETAILED DESCRIPTION

[0018] like Figures 1 to 7As shown, the present embodiment discloses a method for constructing a bifurcated tunnel with a gradual transition from a small section to a large section, which is applied to the Dashanpo Tunnel of the Chongqing-Kunming High-speed Railway Yanjin Section to Yiliang Section. The whole tunnel consists of a combined widening section (or a large-span transition section) and a branch repair section (single-line tunnel), and mainly passes through strata containing grade III, IV, and V surrounding rock. The maximum excavation area of ​​the section tunnel is 339.7m 2 The corresponding excavation span is 25.84m, the minimum excavation span is 11.20m, and the maximum span difference of the tunnel interface is 14.64m.

[0019] Combination Figure 1 , the construction process of the construction method of the embodiment of the present invention is as follows: construction preparation → excavate to 10m before the large section → apply Ф42mm advance small conduit support with an annular spacing of 0.4m → excavate the upper step and the expanded excavation part, and apply the corresponding section primary support → excavate to the junction of the large section and the small section → apply Ф42mm advance small conduit support with an annular spacing of 0.4m → measure the deformation of the steel frame 1 at the place where the primary support has been applied and the contact pressure between the steel frame 1 and the surrounding rock, judge the safety of subsequent construction, and guide the secondary primary support parameter value at the place where the primary support has been applied, as well as the primary support parameters of the subsequent expanded excavation section → excavate to the mileage YDK315+069.4 → apply Make a 42mm Ø small duct support with a length of 3m and an annular spacing of 0.4m → excavate the upper step and the expanded part, and apply the primary support of the corresponding section → measure the deformation of the steel frame 1 at the primary support and the contact pressure between the steel frame 1 and the surrounding rock, judge the safety of subsequent construction, and guide the selection of the secondary primary support parameters at the primary support, and the primary support parameters of the subsequent expanded section → climb 25m with a slope of 13% and enter the standard section construction of the corresponding construction method of the large-section tunnel → control the excavation step of the lower step with the secondary primary support mileage, excavate the lower step at a staggered distance → apply the primary support around the lower step → monitor and measure → apply the secondary lining. Among them, YDK represents the construction mileage of the right line, and 315 represents the number of kilometers, that is, 315 kilometers have passed from the starting point of the line to this point. +069.4 means that 69.4 meters have been moved forward at 315 kilometers.

[0020] In the embodiment of the present invention, when the three gradually expanded excavation sections are expanded, the soil pressure at each longitudinal position of the tunnel top is monitored in real time according to the step distance, and the support parameters of the small pipe support in the next step distance are guided. Specifically, when monitoring the soil pressure at each longitudinal position of the tunnel top, the monitoring hole 2 is first constructed and cleaned at the same angle as the slope of the climbing construction. The distance between the monitoring hole 2 and the tunnel top is 0.5m. Then, a 20mm monitoring tube 3 is inserted along the monitoring hole 2. The monitoring tube 3 is installed with a pressure monitoring point 6 according to the step distance. The position of the pressure monitoring point 6 is adjusted to make it fit with the inner wall of the monitoring hole 2, and then the value of the pressure monitoring point 6 is reset to zero. The monitoring tube 3 is provided with an air hole 4, which is closed by an air bag 5. The surface of the air bag 5 is installed with a pressure monitoring point 6. Specifically, when adjusting the position of the pressure monitoring point 6, the air bag 5 is expanded by ventilating the monitoring tube 3, so that the pressure monitoring point 6 fits with the inner wall of the monitoring hole 2, and then the outer end of the monitoring hole 2 is sealed. After the excavation of the gradual expansion section is completed, grouting is continuously injected into the monitoring hole 2 until the airbag 5 ruptures, and the grout is filled into the monitoring hole 2 and then sealed, which can play a certain supporting role. According to the actual situation, multiple monitoring holes 2 can be set, and the monitoring holes 2 are evenly arranged around the tunnel.

[0021] The construction method disclosed in the present invention first plans the excavation of the small-section cross-sectional profile, and applies a primary support when the cross-section is gradually changed. On the premise of ensuring the subsequent cross-section excavation construction work space, a secondary primary support is applied to the front section of the excavation cross-section, and the secondary primary support profile is consistent with the original design profile of the small tunnel. Then, the lower step of the large-section tunnel is constructed, and finally the invert arch and secondary lining are constructed. The construction method of the present invention ensures the construction safety at the interface of the variable-section tunnel, avoids the safety hazards caused by the sudden change of the cross-section, adopts the step-by-step excavation of the arch, and cooperates with the steel arch frame support construction, so the construction operability and applicability are strong. The specifications and forms of the steel frame are easy to adjust, and the supporting construction technology is mature.

[0022] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A method for constructing a bifurcated tunnel with a gradual change from a small cross section to a large cross section, characterized in that: The following steps are involved: S1, excavation of the first gradual expansion section, specifically including: S1.1, advance small duct support is applied according to the preset annular spacing; S1.2, excavate the upper step and the excavated part of the first gradual excavation section, and construct the primary support of the corresponding section; S2, excavate the second gradual expansion section to the junction of the large section and the small section, specifically including: S2.1, advance small duct support is applied according to the preset annular spacing; S2.2, excavate the upper step and the excavated part of the second gradual excavation section, and construct the primary support of the corresponding section; S2.3, provide steel frame support for the expansion section, measure data and correct support parameters; S2.4, repeat the above excavation steps to the junction of the large section and the small section according to the excavation step setting; S3, excavation of the third gradual expansion section, specifically including: S3.1, advance small duct support is applied according to the preset annular spacing; S3.2, excavate the upper step and the expanded part of the third gradual expansion section, and construct the primary support of the corresponding section; S3.3, provide steel frame support for the expansion section, measure data and correct support parameters; S3.4, after climbing the slope, enter the large-section tunnel standard section construction; S4, construction of lower steps, including: S4.1, control the step distance of the lower step excavation according to the construction mileage of the secondary primary support, and excavate the lower step at a staggered distance; S4.2, construct initial support around the lower step.

2. A method for constructing a bifurcated tunnel with a gradual change from a small cross section to a large cross section according to claim 1, characterized in that: The measurement data and correction of support parameters in step S2.3 and step S3.3 include measuring the deformation of the steel frame at the primary support and the contact pressure between the steel frame and the surrounding rock, judging the safety of subsequent construction, and guiding the selection of secondary primary support parameters at the primary support, as well as the primary support parameters of the subsequent expanded excavation section.

3. A method for constructing a bifurcated tunnel with a gradual change from a small cross section to a large cross section according to claim 2, characterized in that: In step S3.4, the slope of the climbing construction is 13%.

4. A method for constructing a bifurcated tunnel with a gradual change from a small cross section to a large cross section according to claim 3, characterized in that: In step S4.1, the distance between the lower bench excavation surface and the secondary primary support is not less than 10m.

5. A method for constructing a bifurcated tunnel with a gradual change from a small cross section to a large cross section according to claim 4, characterized in that: When the three gradually expanded sections are being excavated, the soil pressure at each longitudinal position on the top of the tunnel is monitored in real time according to the step distance, and the support parameters of the next step-by-step advance small duct support are guided.

6. A method for constructing a bifurcated tunnel with a gradual change from a small cross section to a large cross section according to claim 5, characterized in that: Specifically, when monitoring the soil pressure at each longitudinal position on the top of the tunnel, first construct a monitoring hole at the same angle as the slope of the climbing construction and clean the hole, then insert a monitoring tube along the monitoring hole, and install pressure monitoring points on the monitoring tube according to the step distance. Adjust the position of the pressure monitoring point so that it fits the inner wall of the monitoring hole, and then reset the value of the pressure monitoring point to zero.

7. A method for constructing a bifurcated tunnel with a gradual change from a small cross section to a large cross section according to claim 6, characterized in that: An air hole is opened on the monitoring tube, and the air hole is closed by an air bag. A pressure monitoring point is installed on the surface of the air bag. When adjusting the position of the pressure monitoring point, the air bag is expanded by ventilating into the monitoring tube, so that the pressure monitoring point fits against the inner wall of the monitoring hole, and then the outer end of the monitoring hole is sealed.

8. A method for constructing a bifurcated tunnel with a gradual change from a small cross section to a large cross section according to claim 7, characterized in that: After the excavation of the gradual expansion section is completed, grouting is continuously injected into the monitoring hole until the air bag ruptures, and the slurry is filled into the monitoring hole and then the hole is sealed.

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