Design considerations of corrugated pipe culverts

Weakness or excessive treatment of soft foundation. One is that the calculated design foundation bearing capacity is too small, resulting in insufficient depth and limited range of treatment for weak foundations, leading to excessive settlement in the middle of the culvert; Another approach is to overly consider the impact of foundation settlement and deformation, where the foundation of the culvert is too strong relative to the roadbeds on both sides after treatment, resulting in defects such as misalignment and uneven lateral settlement of the culvert body. Unreasonable parameters such as wall thickness, wave distance, and wave height of steel corrugated pipe culverts result in cracks or deformations in the pipe body. Improper selection and handling of culvert inlet forms during design. The design of the entrance did not fully consider adverse factors such as initial deformation, freeze-thaw and frost heave, erosion, and flood modulation and diversion of the steel corrugated pipe culvert. Unreasonable treatment of longitudinal slope and inlet/outlet of culvert bottom. If a reasonable longitudinal slope at the bottom of the culvert cannot be selected in the design, and the ground outside the inlet and outlet cannot be excavated properly to connect with the inlet and outlet of the culvert, it is easy to cause siltation at the bottom of the culvert or the culvert cannot perform its drainage function. The measures for anti-corrosion of the culvert body are insufficient, such as inadequate rust removal treatment of steel plates, insufficient galvanizing thickness, erosion caused by floods carrying sand and gravel on the culvert, and adverse factors such as long-term water accumulation and frost heave. To reduce the erosion of water flow on the bottom of the pipe, the longitudinal slope of the pipe bottom should generally not exceed 5 °.

(1) Improper selection of parameters such as specific thickness, wave distance, and wave height for steel corrugated pipe culverts during design and construction. All steel corrugated pipe culverts in this project have the same wall thickness, when filled with soil at different heights, resulting in pipe cracks or deformation in the later stage.

(2) It is not good Treatment methods for soft soil foundation in design and construction. There are two common errors in the treatment of soft soil foundation for culverts: one is that the additional stress at the top of the culvert is not considered, resulting in a calculated design foundation bearing capacity that is too small, and the depth and scope of soft soil foundation treatment are insufficient; Another situation is that excessive consideration is given to the impact of foundation settlement and deformation, and the design is too conservative. Some reinforcement measures are taken on the foundation, which increases the bearing capacity of the foundation but also leads to an increase in the stiffness of the entire culvert structural system. This makes the settlement deformation of the soil on the top of the culvert smaller than that on both sides of the culvert, resulting in defects such as misalignment and uneven lateral settlement of the culvert pipe body.

(3) Poor selection and handling of the inlet and outlet forms of pipe culverts during design. All steel corrugated pipe culverts in this section will adopt a sloping upward opening form with the same slope rate as the roadbed slope, and the slope surface will be constructed with dry masonry. Although this method can better ensure the adaptability of the pipe body to deformation, due to the difficulty of water ingress into the corrugated pipe mouth compared to the cover culvert, without protection and anti erosion waterproof walls, it is easy to cause serious damage and peeling of the dry masonry under water flow erosion and winter icing, resulting in problems such as suspended pipe body or difficulty in collecting water at the culvert opening.

(4) The treatment way of longitudinal slope and inlet/outlet of corrugated pipe culverts is not right during design and construction. Compared with slab culverts, corrugated pipe culverts have significant differences in water inlet and bottom roughness. For example, if a reasonable longitudinal slope cannot be selected in the design, and the ground outside the inlet and outlet cannot be excavated properly during construction to connect with the inlet and outlet of the culvert, it is easy to cause sedimentation at the bottom of the culvert or the culvert cannot perform its drainage function.

1. Strengthen the geological exploration work at the location of the steel corrugated pipe culvert, and determine a reasonable aperture based on the investigation Accurate ground line measurement is fundamental to ensuring the safety of culverts and roadbeds Choose a reasonable form of entrance and exit based on the terrain of the culvert site. Based on the inlet and outlet forms of individual culverts in this project and the usage of reinforced concrete circular pipe culverts, it is recommended to use a straight wall connected to an eight shaped wall or a tapered slope form for the inlet and outlet of steel corrugated pipe culverts.

2. Reasonable parameters such as steel corrugated pipe wall thickness, wave distance, and wave height should be selected according to the different filling heights of each culvert during design. To reduce the siltation of the culvert bottom, it is recommended to use a longitudinal slope of 1% -5% for the steel corrugated pipe culvert bottom. The steel corrugated pipe bottom is relatively rough, and when the longitudinal slope of the culvert bottom is gentle, it is easy to cause poor water flow or siltation.

Steel corrugated pipe culverts should be constructed during the warm season, with a minimum temperature above zero degrees. Due to the fact that the material of steel corrugated pipes is metal and the wall thickness is relatively thin, the quality of anti-corrosion treatment will directly affect the service life of steel corrugated pipe culverts. It is recommended that the construction unit and the supervision unit inspect the anti-corrosion treatment of the corrugated pipe before it leaves the factory. Pay attention to the foundation treatment at the culvert site. The bearing capacity of the foundation will directly affect the use of culverts in the later stage. To prevent the occurrence of diseases, special foundation treatment schemes such as replacement and dynamic compaction should be adopted based on the soil characteristics of weak foundations. Strengthen the supervision of steel corrugated pipe construction. During the assembly of steel corrugated pipes, the supervisor should be present on site to inspect whether the rubber sealing ring or asbestos sealing strip is tightly sealed and whether there are any missing bolts. Ideal filling materials and filling techniques should be selected for the pipe side during construction. Gravel soil and sandy soil are ideal materials for back filling. For high-altitude permafrost areas, graded gravel materials are used for filling within 2 meters around culverts. Fill soil should be spread in layers and compacted layer by layer using a small vibratory compactor. The recommended thickness for each layer is 20cm, and the compaction degree should be greater than 95%, consistent with the compaction degree of the roadbed at that location. During the compaction process, observe the deformation of the pipe body at any time in order to adjust the filling or compaction method in a timely manner.

The normal maintenance cost of steel corrugated pipe culverts is relatively low, and attention should be paid to routine inspection and evaluation, as well as regular anti-corrosion maintenance. When the preliminary design is reasonable and the construction control is good, the culvert will not have significant damage.