1. Introduction to Steel Bellows
The prefabricated steel corrugated culvert has the advantages of high strength, thin pipe section, light weight, easy transportation and storage, simple construction process, fast assembly speed and short construction period. In order to solve the problem of frost heave damage to bridges and culverts in cold northern regions and uneven foundation settlement damage to culverts in the south, the inner and outer surfaces of the corrugated pipe sections and the fastening bolts are hot-dip galvanized before leaving the factory to prevent rust. The thickness of the galvanized layer is ≥63μm and the average thickness of the galvanized layer is 84μm; asphalt coating is added during construction and installation, and its design service life is 100 years.
The corrugated steel pipe (plate) culvert is a pipe-soil effect formed by the pipe body and the surrounding backfill soil. The pipe body and the surrounding backfill soil are indispensable. If the reaction force of the surrounding backfill soil is insufficient or uneven, it will cause the corrugated steel plate to deform beyond the allowable range.
Construction technology
Excavation → Construction layout → Foundation cushion filling → Pipe installation → Culvert backfill → Opening paving
Digging the base
1.1 When there are design requirements, excavate the foundation in accordance with the design requirements; when there are no design requirements, the thickness of the foundation cushion and the width of the groove refer to the table below. In order to facilitate mechanical rolling, it is recommended to use the standard width of the foundation.
Geological conditions | Minimum foundation thickness (cm) | Minimum base width | Basic standard width | |
High-quality land base | The foundation can be directly used as the foundation | 2×1.0+ø m | 2×3.0+ø m | |
general | Pipe diameter ø＜0.9m | 20 | 2×1.0+ø m | 2×3.0+ø m |
0.9m≤pipe diameter ø≤2.0m | 30 | 2×1.0+ø m | 2×3.0+ø m | |
Pipe diameter ø＞2.0m | 0.2ø | 2×1.0+ø m | 2×3.0+ø m | |
Rock foundation | 20-40cm, but when the fill height is greater than 5m, the thickness increases by 4cm for every 1.0m increase in fill height | 2×1.0+ø m | 2×3.0+ø m | |
Soft soil foundation | 0.3-0.5ø or more than 50cm | 2×1.0+ø m | 2×3.0+ø m | |
1.2 Excavation of foundation pit shall be carried out as required. When the base soil is poor soil layer such as silt, it shall be replaced and over-excavation shall be avoided. If over-excavation occurs, the loose parts shall be removed and the treatment plan shall be submitted to the supervision and design unit for approval.
1.3 The earth foundation pit dug to the elevation shall not be exposed, disturbed or soaked for a long time, and the size, elevation and bearing capacity of the foundation pit shall be checked in time. If they meet the requirements, foundation construction shall be carried out immediately.
1.4 Treatment methods for various soil foundations
1) High-quality land foundation
Unscreened sand, crushed stone, gravel and sandy soil are ideal foundation materials, but hard objects such as stones over 10 cm in diameter must be removed.
2) General soil foundation
Ordinary foundations with low bearing capacity need to have a foundation of a certain thickness. However, if the original soil of the culvert foundation trench is strictly compacted (the compaction degree is more than 90% of the heavy compaction density), the corrugated pipe can be placed directly on the foundation.
3) Rock foundation
Except as specified in the design requirements, the corrugated pipe cannot be placed directly on the rock or concrete foundation bed, because the overly rigid support will not only reduce the good flexibility of the pipe wall itself, but also reduce the bearing capacity of the culvert. Therefore, a part of the soft rock should be dug out of the rock foundation, replaced with a layer of high-quality soil, and carefully compacted. When excavating soft rock trenches, high explosives and deep-hole blasting cannot be used to avoid loosening too much of the outer layer. The rock weathering layer foundation cannot be used as a foundation and needs to be replaced with a fill of 3 times the diameter .
4) Soft soil foundation
When the culvert is located on a soft soil foundation, the soft soil roadbed needs to be treated. According to the thickness of the soft foundation, when the depth is less than 5 meters, the dredging and stone throwing treatment method is adopted; when the depth is greater than 5 meters, CFG foundation piles are used for reinforcement, and then a layer of high-quality gravel cushion with a thickness of more than 50cm is filled on it and compacted tightly.
1.5 Reserved arch
Corrugated pipes buried on ordinary soil foundations often sink after a period of time, and the middle of the pipe is often larger than the ends. Therefore, the pipe body of the corrugated pipe laid under the embankment should be set with a reserved camber. Its size is based on the possible settlement of the foundation soil, the longitudinal slope of the culvert bottom and the fill height. It can usually be 0.2% to 1% of the pipe length to ensure that there is no concavity or landslide in the middle of the pipe.
2. Construction layout
Level the construction site, arrange the storage sites for various materials, and organize the necessary machinery and equipment. Before construction, organize surveyors to lay out the culvert axis according to the design documents, drive the center and side piles, sprinkle white gray lines on the center axis of the culvert and the edge of the foundation range, and measure the original ground elevation.
3. Foundation cushion filling
The foundation cushion material is crushed stone soil or gravel.
4. Pipe body installation
4.1 Preparation before installation
Prepare the installation tools and necessary accessories: box wrench (16-18 and 22-24), adjustable spanner, small crowbar (ø16mm round steel with a length of about 50cm), crowbar (ø50mm steel pipe with a length of about 1.8m), hammer, chisel, screwdriver (flat head), jack, screws and rubber asbestos pads, and 0.5kg of binding wire.
Check whether the cumulative length and diameter of each section of the corrugated pipe are consistent with the culvert at that location.
Asphalt painting
When the culvert leaves the factory, the culvert and its accessories have been galvanized. The galvanizing thickness is greater than or equal to 63 microns. In the absence of saline water or harmful industrial wastewater immersion and frequent water flow in the culvert, the coating can prevent rust. Otherwise, two coats of asphalt paint or emulsified asphalt can be applied or sprayed on the pipe wall below the water level inside and outside the pipe section to enhance the anti-corrosion effect. From the appearance, the inside and outside of the pipe wall are evenly coated with black pipes. However, it must be installed after the asphalt is dried. The thickness of the general asphalt coating should reach 0.5~1mm.
Check whether the flatness, slope and elevation of the foundation, the axis of the culvert and the direction of the inlet and outlet meet the design requirements, and pay attention to the position of the end pipe section and the middle pipe section. The installation of the culvert must be laid according to the correct axis and slope shown in the drawing.
A culvert installation commander is appointed to direct the lifting and on-site operations of the construction personnel.
4.2 Installation operation method
According to the actual situation of the culvert, lay out the culvert pipe. During installation, lay out the first pipe section from one side so that the center of the pipe is parallel to the longitudinal center line of the foundation. Similarly, place the second pipe in place. When there is a gap of 3-5cm between the adjacent flanges of the two pipes, use a small crowbar to align the bolt holes on the flanges so that the bolt holes on the two pipe flanges are aligned. At this time, use a crowbar to pry the pipe section from the other end of the second pipe section to make it move longitudinally so that the distance between the two flanges is about 2cm. Then put on all the bolts and screw them on, but do not tighten the bolts, and start to inlay the asbestos pad. After that, connect them section by section in this way.
Asbestos pad: Due to the terrain and other reasons, sometimes the distance between two adjacent flanges is small. At this time, use a hammer and chisel to chisel a gap of about 1cm between the two flanges, and use a screwdriver to insert the asbestos pad between the two flanges (the asbestos pad is inserted inside the bolt). Sometimes the distance between the two flanges at the top of the pipe is large, and it is difficult to insert the asbestos pad. Use a binding wire to tie the asbestos pad to the bolt and fix it. Then the worker starts to tighten the screws symmetrically. Until there is only a 2-5mm gap between the two flanges from the outside.
Use a jack to align the entire culvert so that its center is on the specified center line.
4.3 Installation Notes
The pipe body should be installed close to the gravel cushion so that the culvert can be evenly stressed. The slope of the top surface of the foundation is consistent with the design slope, and a reserved camber is set along the horizontal direction of the pipe body to ensure that there is no depression or reverse slope in the middle of the pipeline.
After all the pipe joints are assembled, check whether the positions of the pipe joints meet the design requirements.
5. Backfilling of pipe
The construction process of steel corrugated pipe culvert can be divided into embankment method and reverse slot backfill method.
5.1 Embankment method
In order to ensure the backfill quality of the culvert, there are five options for filling the wedge-shaped parts on both sides of the bottom of the pipe: 1. Use coarse sand "watertight method" oscillator to compact. 2. Use well-graded natural gravel (the water content requirement is about 2% higher than the optimal water content), and use wooden sticks to compact from the outside to the inside of the pipe body. The action point of the wooden stick must be close to the pipe body, and each groove must be compacted in place. 3. Use liquid fly ash for backfill. 4. Use lightweight concrete for backfill. 5. Backfill with graded crushed stone with a maximum particle size of no more than 3cm. Then use a small compacting machine to compact obliquely to ensure the backfill quality of the bottom of the pipe.
The backfill on both sides of the culvert is made of well-graded natural gravel or graded crushed stone. An 18T roller is used to roll 50cm outside the maximum diameter of the pipe body, and a small compacting machine is used to compact within 50cm to avoid the impact of large mechanical equipment such as rollers on the culvert.
The filling should be done in layers and compacted in layers. The thickness of each compacted layer is 20cm. The compaction degree must reach 95% before the next layer can be filled. Before filling, mark the height of each 20cm on both sides of the pipe section with red paint, and control the filling according to the marked lines.
The filling must be carried out synchronously and symmetrically on both sides of the culvert, and the height difference of the backfill soil on both sides shall not be greater than 30cm.
When the thickness of the fill on the top of the pipe is less than 50cm, rollers larger than 6T shall not be used for compaction, and construction machinery is not allowed to pass.
The construction unit must backfill the culvert strictly in accordance with the requirements.
The use of strong compaction machinery is not allowed within 10 meters on both sides and top of the pipe body.
5.2 Reverse Slotting Backfilling Method
In order not to affect the overall progress of roadbed construction during the construction process, the backfill of the steel corrugated pipe culvert can be constructed by the reverse slot backfill method. The main construction techniques of this method are as follows:
1) The slot width is generally (D+100) cm, which is convenient for installation and backfilling.
2) The backfill material is graded gravel or crushed stone.
3) Both sides must be compacted in layers, with each layer being 20cm thick.
6. Tunnel entrance paving and slope protection
The opening adopts the end wall type or the inclined opening with the same slope as the roadbed. The opening paving and slope protection are M7.5 mortar-laid flagstones. The stones with relatively long and short geometric dimensions should be selected to be staggered in the same layer to form a staggered structure to ensure staggered masonry without vertical joints or through joints. The exposed surface should be chiseled with large stones with appropriate texture, fine and uniform color, and no weathering, peeling or cracks to ensure the flatness and accurate geometric dimensions of the exposed surface of the project.
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