Culvert underground excavation construction method under roadbed backfilling condition

Abstract

The invention discloses a culvert underground excavation construction method under a roadbed backfill condition, and aims to solve the technical problem that culvert underground excavation construction is difficult to safely and quickly carry out under complex and poor-stability geological conditions such as backfill soil and stone stratums. According to the technical scheme, a double-layer self-propelled pipe shed is adopted to form a stable ring; after excavation, an upper step is subjected to temporary cross brace supporting, a lower step is subjected to permanent cross brace supporting, exposed surrounding rocks are closed in time, a stable ring is formed, small guide pipe radial grouting reinforcement and cavity backfilling are adopted, and the stability of the surrounding rocks is improved; and finally, secondary lining is conducted in time, and construction safety is ensured. According to the technical scheme, shallow-buried excavation construction can be safely and efficiently completed under the condition that open excavation is not allowed or earth surface damage is not allowed on the upper portion of an existing line.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel engineering construction, and in particular to a culvert dark excavation construction method under backfill roadbed conditions. Background Art

[0002] In modern urban construction, culvert construction is often required under complex geological conditions such as backfill soil and rocky strata. Especially in strata with extremely poor stability and shallow burial depth, the construction difficulty and safety risks are significantly increased. Backfill soil has the characteristics of high compressibility and low bearing capacity, which makes it easy for collapse and roof falls to occur during construction, bringing many challenges to culvert construction. Collapse will not only cause construction interruption and affect the progress of the project, but also seriously threaten the lives of construction workers. Roof falls may cause obstruction of upper vehicle traffic and even cause traffic accidents.

[0003] Traditional support construction methods often fail to meet the safety requirements of culvert excavation under backfill roadbed conditions. In addition, if the support measures are not appropriate during the excavation process, it is very easy to cause the stratum to become unstable and cause collapse. In addition, the looseness of the backfill soil and stone strata makes it particularly difficult to control the settlement during the construction process. Once the settlement is uneven, it will not only affect the structural safety of the culvert, but also pose a potential threat to vehicles passing above.

[0004] The information disclosed in this background technology section is only used to deepen the understanding of the background technology of the present disclosure, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art known to those skilled in the art. Summary of the invention

[0005] The present invention provides a method for dark excavation of culverts under backfill roadbed conditions, aiming to solve the technical problem that it is difficult to safely and quickly carry out dark excavation of culverts under complex and unstable geological conditions such as backfill soil and rocky strata.

[0006] According to one aspect of the present disclosure, a culvert dark excavation construction method based on backfill roadbed conditions is provided, comprising the following steps: (1) Re-test the control piles and set up monitoring points before excavation; (2) constructing a double-layer self-propelled pipe shed at the entrance and exit of the culvert, and pouring cement slurry into the double-layer self-propelled pipe shed; (3) Use excavators and crushers to carry out underground excavation of the backfill roadbed. After the underground excavation is completed, it is supported once and temporary cross bracing is installed. Cement slurry is used to grout the loose rock mass on the back of the arch to ensure the stability of the rock mass, and concrete slurry is sprayed to seal it; (4) Use excavators and crushers to carry out underground excavation of the backfill roadbed. After the underground excavation is completed, it is supported once and permanent cross bracing is installed. Cement slurry is used to grout the loose rock mass on the back of the arch to ensure the stability of the rock mass, and concrete slurry is sprayed to seal it; (5) After the excavation step reaches 6-8 m, secondary lining construction is carried out; (6) Repeat steps (3) to (5) to start the next excavation cycle.

[0007] In some embodiments of the present disclosure, in step (2), the diameter of the double-layer self-propelled pipe rack is Φ100~110mm, the circumferential spacing of the pipe rack is 35~40 cm, the pipe rack layer spacing is 45~50 cm, the pipe rack angle is 3°~5°, and the cement slurry is formed by mixing water and cement with a water-cement ratio of 1:1~0.5. After grouting, an arch ring (stabilization ring) of 1~1.2 m is formed to ensure the stability of the free surface after excavation.

[0008] In some embodiments of the present disclosure, in step (3), the excavation advance per cycle is controlled at 0.3-0.7 m, the step distance of the upper and lower steps is controlled within 3 m, the upper and lower steps are both supported by I20a I-beams, and the thickness of the shotcrete is 15-20 cm, that is, the excavation and reinforcement are promptly sealed to ensure the stability of the surrounding rock. Cement paste is a mixture of water and cement at a water-cement ratio of 1:1-0.5. Since the stability of the backfill soil and stone strata is extremely poor, it is easy to cause collapse after excavation. Therefore, grouting is used for backfilling and reinforcement to ensure the stability of the rock mass.

[0009] In some embodiments of the present disclosure, in step (5), the length of each compartment of the secondary lining construction is 5 to 6 m. Since the culvert is shallowly buried and the primary support strength is weak, in order to avoid roof collapse accidents during culvert construction and ensure safe construction, the secondary concrete lining construction should be carried out in a timely manner.

[0010] One or more technical solutions provided in the embodiments of the present application have at least any of the following technical effects or advantages: 1. Through the double-layer self-propelled pipe shed: ① Due to the complex internal structure of the surrounding rock of backfill soil and stone strata, ordinary follow-up pipes and top pipes are prone to drill jams and pipe breakage, which makes construction difficult. The use of self-propelled pipe sheds can effectively avoid drill jams and pipe breakage, and the success rate of pipe shed construction is high; ② After grouting, the double-layer pipe shed can form a stable circle with a thickness of 1m to 1.2m, which can ensure the stability of the surrounding rock during the later excavation process.

[0011] 2. By adding temporary cross bracing to the upper steps and permanent cross bracing to the lower steps and closing them, a closed loop is formed in time to increase the stability of the surrounding rock and ensure construction safety.

[0012] 3. Through radial grouting consolidation and backfilling, the integrity of the surrounding rock is increased and the stability of the surrounding rock is ensured.

[0013] 4. When there are existing lines on the upper part that do not allow open excavation or do not allow surface damage, the construction method provided in this application can ensure construction safety and improve construction efficiency, and complete shallow buried excavation construction safely and efficiently. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a flowchart of the dark excavation construction of a culvert based on backfill roadbed conditions in one embodiment of the present application.

[0015] Figure 2 This is a schematic diagram of the construction plan layout of each process in an embodiment of the present application.

[0016] Figure 3 The figure is a schematic diagram of the arrangement of lateral measuring points for surface settlement in one embodiment of the present application.

[0017] Figure 4 This is a diagram of the settlement and convergence installation in one embodiment of the present application.

[0018] Figure 5 Schematic diagram of the structure of a self-propelled pipe-roof drill bit in one embodiment of the present application; wherein, A: a front view of the self-propelled pipe-roof drill bit; B: a cross-sectional view of the self-propelled pipe-roof drill bit.

[0019] Figure 6 This is a schematic diagram of the structure of culvert construction support in one embodiment of the present application.

[0020] In the above figures, 1 is the drill cutter of the self-propelled pipe-roof drill bit; 2 is the overflow hole of the self-propelled pipe-roof drill bit; 3 is the self-propelled pipe-roof drill bit; 4 is the Φ42 grouting small guide tube; 5 is the primary support system; 6 is the reinforcement ring; 7 is the temporary support for the upper step; 8 is the permanent support for the lower step; 9 is the secondary lining; 10 is the backfill soil and stone foundation. DETAILED DESCRIPTION

[0021] The specific implementation methods of the present invention are described below in conjunction with examples, but the following examples are only used to illustrate the present application in detail and do not limit the scope of the present application in any way.

[0022] Embodiment 1 The culvert connecting the Songgui Toll Station of the Shanghe Expressway under the Xianglushan drainage channel in a certain city is about 39.35 m long and 4-6 m deep. It adopts a double-hole flow form of an underpass culvert (gate-shaped) + an original ramp culvert (square), and the horizontal spacing between the new and old culverts is 4.11 m; the cross-section of the newly added culvert is a gate-shaped, and the clearance size after lining is a semicircle with a radius of 2.6 m at the top and a U-shaped section of 4.5m*2.5 m at the bottom; the elevation of the bottom plate of the culvert inlet is 1987.94 m, and the elevation of the bottom plate of the culvert outlet is 1987m. Since the toll station connecting line is a backfill line and the roadbed conditions are poor, it is difficult to achieve safe and rapid underpassing with traditional support construction methods, and the risk of collapse and roof collapse is extremely high. To this end, a culvert dark excavation construction method is proposed to solve the problem of culvert underpass under unstable address conditions such as backfill roadbed, see Figure 1 , Figure 2 As shown, the specific steps include: 1. Before excavation, re-survey the control piles and set up monitoring points. According to the existing national control points in the survey area or the available control points of other engineering construction projects near the survey area, determine the joint survey plan and the location of the control network points. After the network layout plan is initially determined, the accuracy of the control network can be estimated and the initial control points can be adjusted if necessary. Then go to the field to explore, check, modify and finalize the points. The selection of the control point location should meet the basic requirements of the corresponding project: (1) There should be line of sight between adjacent wire points. For steel ruler distance wires, the terrain between adjacent points should also be flat to facilitate the measurement of the side length; (2) The wire points should be selected in places with hard and stable soil to facilitate the preservation of point marks and the placement of instruments; (3) The wire points should be selected in places with high terrain and wide vision to facilitate encryption, expansion, search and fragmentation measurement and construction layout.

[0023] Monitoring points must be established on stable rock mass outside the deformation zone. Monitoring points in areas with unstable soil and geology should be reinforced. Monitoring points should be as close to the deformation zone as possible (the closer the monitoring point is to the deformation zone, the more referenceable and reliable the monitoring data is, and the monitoring data can better reflect the deformation law of the tunnel).

[0024] The monitoring contents include surface settlement monitoring and in-tunnel monitoring: (1) Ground subsidence monitoring The ground settlement monitoring points should be buried and the original data should be collected fifteen days before the culvert is excavated. The spacing between the ground settlement monitoring points is 3 m × 3 m ( Figure 3 ), the monitoring point is a steel measuring nail with a smooth convex spherical surface on the top. The measuring nail driven into the soil must be of sufficient length (preferably 0.8 to 1 m), and no looseness is allowed between the measuring nail and the soil.

[0025] If conditions permit, the monitoring points should be arranged together with the benchmark points to form a leveling route that is attached or closed. The leveling route closing error should be less than ±1.0 mm (n is the number of measuring stations). Then, the elevation of each point is obtained by leveling according to the measuring stations. Before construction, the initial elevation of the surface settlement observation point is measured by leveling from the base point. The elevation measured during the construction process is. The height difference is the surface settlement value.

[0026] After obtaining the surface settlement value, a settlement-time curve is drawn. When the settlement-time curve tends to be flat, a suitable function can be selected for regression analysis to predict the maximum settlement. Based on the measured maximum settlement, it is determined whether it exceeds the safety control standard and the reliability of the adopted engineering measures.

[0027] (2) In-tunnel monitoring Culvert roof subsidence monitoring: The monitoring benchmark in the tunnel should use the leveling benchmark in the tunnel as much as possible. Observation method: After the observation element is firmly buried and the reflector is attached, the initial elevation of the arch roof settlement observation point is measured by the total station through non-contact measurement. H0 (Take the average of three observations). The elevation measured during the construction process is H , then the height difference △H=Hn-H0 = ... Figure 4 .

[0028] Culvert clearance change monitoring: Culvert clearance changes are measured by non-contact total station. Use the side measurement function of the total station to measure the measuring element with a reflector and read the distance between the left and right measuring points. The initial reading is determined by taking the average of three readings. The cumulative horizontal convergence value is obtained by subtracting the initial value from each subsequent reading. Five convergence measuring points are set for each monitoring section. Measuring point layout.

[0029] All monitoring operations should continue for 1 to 3 weeks after the deformation is basically stable, and the monitoring frequency shall be carried out in accordance with the provisions of Table 1.

[0030] Table 1 Monitoring frequency .

[0031] Monitoring data warning: In general, the monitoring alarm value of each project consists of two parts, namely the cumulative change and the change per unit time. In view of the fact that the culvert is buried at a depth of about 4 m, the tunnel body is mainly the backfill soil of the Songgui toll station connecting line of the expressway, and the ramp has a large dynamic load, it is decided to use the cumulative change of the settlement of the Songgui toll station connecting line and the change per unit time as the main warning data for monitoring and analysis, and the settlement and displacement data of other monitoring parts are used as references. ① The settlement change per unit time of any monitoring point on the Songgui toll station connecting line reaches 3 mm / d or the cumulative change reaches 15 mm; ② The settlement or displacement data of any monitoring point in other parts reaches 15mm / d or the cumulative change reaches 30 mm; In any of the above situations, all operations should be stopped immediately, and the Shanghe Expressway Management Department should be notified to carry out traffic control. At the same time, the monitoring personnel should mark it prominently in the monitoring report, and then immediately notify the four parties involved in the construction to discuss and decide on the treatment measures; after the treatment is completed and the monitoring data settlement is stable, personnel will be organized to carry out construction and cancel traffic control.

[0032] 2. Construct double-layer self-propelled pipe scaffolding 3 ( Figure 5-Figure 6 ), there is no single anchor rod between the double-layer pipe sheds, and the anchor rods (small guide tubes) are arranged radially in the culvert, wherein the double-layer self-propelled pipe shed 3 has a diameter of 108 mm and a length of 25 m. The circumferential spacing between the double-layer self-propelled pipe sheds 3 is 40 cm, and the interlayer spacing is 50 cm. The angle (elevation angle) of the double-layer self-propelled pipe shed 3 is determined according to the specific burial depth, ranging from 3° to 5°. After the construction of the double-layer self-propelled pipe shed 3 is completed, 0.5:1 to 1:1 cement slurry is poured into the double-layer self-propelled pipe shed 3 (the ratio can be flexibly adjusted according to the on-site geological conditions and the amount of slurry consumed by the rock mass), the grouting pressure is between 0.3-1.5 MPa, and the slurry diffusion radius is within the range of 0.5-1.0 m. After grouting, a 1-1.2 m arch ring (stabilization ring) 6 can be formed to ensure the stability of the air surface after excavation.

[0033] 3. After the double-layer pipe shed is constructed, excavation is carried out directly according to the outline of the culvert opening (before excavation, the roadbed corresponding to the culvert opening is a backfill slope). The total height of the culvert is 5.3 m, and the upper and lower steps are used for excavation (the upper step is 3.2m high and the lower step is 2.1m high). This can avoid disturbance of the surrounding rock during excavation; the upper step can be closed in time to improve the stability of the upper structure and ensure the safety of the lower step construction process.

[0034] A small excavator and a crusher are used to carry out dark excavation of the upper step of the backfill roadbed (one-time excavation and forming), and the advance of each cycle is controlled at 0.5 m; after the dark excavation is completed, the upper step is supported once 5 (in the early stage of tunnel construction, 5 cm thick shotcrete operation is first carried out to provide temporary support, and then mesh and arch frame are installed to enhance the stability of the structure; then locking anchor rods and system anchor rods are constructed to further reinforce the surrounding rock; finally, secondary shotcrete is carried out until the thickness required by the design is reached, and the primary support is completed, which can better reinforce the surrounding rock and make the rock mass and the small guide tube bond together through slurry to ensure the stability of the surrounding rock), and I20a I-beams are used for temporary cross bracing 7, and the two ends of the temporary cross bracing 7 are welded to the arch foot of the arch frame. After that, the loose rock mass on the back of the arch frame is grouting reinforced by pouring 0.5:1~1:1 cement slurry with a length of 4.5 m and Φ42 grouting pipe 4 to ensure the stability of the rock mass, and 20 cm thick concrete slurry is sprayed for timely sealing to ensure the stability of the surrounding rock.

[0035] 4. After the upper step is processed, the temporary cross brace 7 of the upper step is removed, and the lower step is also excavated by a small excavator and crusher. The offset between the left and right excavation faces is not less than 1m, and the advance per cycle is controlled at 0.5m. After the excavation is completed, it is supported once 5 and I20a I-beam is used for permanent cross brace 8 (set at the bottom of the culvert to make the arch frame into a ring, which can improve the compressive strength of the arch frame and ensure the stability of the surrounding rock exposed by the tunnel). A 4.5m long, Φ42 grouting pipe 4 is used to inject 0.5:1~1:1 cement slurry to reinforce the loose rock mass on the back of the arch frame to ensure the stability of the rock mass, and a 20cm thick concrete slurry is sprayed for timely sealing to ensure the stability of the surrounding rock. The primary support of the upper and lower steps is connected by connecting plates + bolts. The step distance of the upper and lower steps is controlled within 3m.

[0036] 5. As the culvert is shallowly buried and the primary support strength is weak, in order to avoid roof collapse accidents during culvert construction and ensure safe construction, the secondary concrete lining construction is carried out in time. Therefore, the secondary lining construction is carried out after the excavation step (the distance between the upper step face and the lining working surface) reaches 6~8 m. First, the bedrock surface needs to be thoroughly cleaned, and then the inverted arch steel bars are tied, and the formwork is installed and the concrete is poured; after the inverted arch concrete is poured, the side arch steel bars are tied, the formwork is installed and the concrete is poured; finally, after the concrete reaches a certain strength, the formwork is removed and proper maintenance is carried out to ensure the stability of the structure and the final quality of the concrete. The length of each compartment of the secondary lining construction is 6 m.

[0037] The construction method of this application is suitable for situations where there are existing lines on the upper part that do not allow open excavation requirements or do not allow surface damage. It can not only ensure construction safety, but also improve construction efficiency, and complete shallow buried excavation construction safely and efficiently.

[0038] Although some preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0039] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the inventive concept. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A culvert dark excavation construction method under backfill roadbed conditions, characterized in that: The steps include: (1) Re-test the control piles and set up monitoring points before excavation; (2) constructing a double-layer self-propelled pipe shed at the entrance and exit of the culvert, and pouring cement slurry into the double-layer self-propelled pipe shed; (3) Use excavators and crushers to carry out underground excavation of the backfill roadbed. After the underground excavation is completed, it is supported once and temporary cross bracing is installed. Cement slurry is used to grout the loose rock mass on the back of the arch to ensure the stability of the rock mass, and concrete slurry is sprayed to seal it; (4) Use excavators and crushers to carry out underground excavation of the backfill roadbed. After the underground excavation is completed, it is supported once and permanent cross bracing is installed. Cement slurry is used to grout the loose rock mass on the back of the arch to ensure the stability of the rock mass, and concrete slurry is sprayed to seal it; (5) After the excavation step reaches 6-8 m, secondary lining construction is carried out; (6) Repeat steps (3) to (5) to start the next excavation cycle.

2. The culvert dark excavation construction method according to claim 1, characterized in that: In step (2), the diameter of the double-layer self-propelled pipe rack is Φ100-110 mm, the circumferential spacing of the pipe rack is 35-40 cm, the spacing between the pipe rack layers is 45-50 cm, and the angle of the pipe rack is 3°-5°.

3. The culvert dark excavation construction method according to claim 1, characterized in that: In step (3), the excavation depth per cycle is controlled within 0.3-0.7 m, the step distance between the upper and lower steps is controlled within 3 m, and the thickness of the shotcrete is 15-20 cm.

4. The culvert dark excavation construction method according to claim 1, characterized in that: The cement paste is prepared by mixing water and cement in a water-cement ratio of 1:1 to 0.

5.

5. The culvert dark excavation construction method according to claim 1, characterized in that: In step (5), the length of each bin in the secondary lining construction is 5 to 6 m.

6. The culvert dark excavation construction method according to claim 1, characterized in that: The upper and lower steps are supported by I20a I-beams.

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