Railway Engineering Design Technology Manual: Culverts and Arch Bridges.

Author: Chief Editor: Liu Qishan
Publisher:
Publish Date: 1999-06-01
Features: Brief Introduction This manual was compiled by the Ministry of Railways, in collaboration with the Survey and Design Institute and Lanzhou Railway College, in accordance with relevant national standards and railway survey and design specifications, based on practical design experiences of culverts and arch bridges. Part 1 covers culverts, mainly consisting of three sections: culvert construction design, culvert structural calculations, and culvert and bridge-tunnel jacking on existing lines. Part 2 discusses arch bridges, listing basic design regulations, requirements, common design calculation methods, optimization design, seismic design, structural analysis, and the introduction of specialized programs and case studies for arch bridge design. Appendices can serve as references for design calculations. Target Audience: Engineering, construction, and research personnel for new and existing railway lines, as well as faculty and students of universities and colleges.
Excerpt: Part 1: Culverts
Chapter: Culvert Construction Design
Section: Culvert Types and Selection
Culverts are generally classified based on structural form, construction materials, flow conditions, the relationship between the culvert axis and the central line of the railway, purpose, and construction methods.
By structural form, culverts can be categorized as circular culverts, slab-box culverts, rectangular culverts, and arch culverts. Among these, arch culverts can be further divided into segmental arches, three-hinged arches (high-rise arches), and five-hinged arches (egg-shaped culverts). By construction materials, they include reinforced concrete culverts, concrete culverts, and masonry culverts. By flow conditions, they are classified as unpressurized culverts, semi-pressurized culverts, and pressurized culverts. Based on the relationship between the culvert axis and the central line of the railway, they are divided into orthogonal culverts and skew culverts. By purpose, they can be categorized as flood drainage culverts, irrigation culverts, overpass culverts (traffic culverts), and flood drainage and overpass culverts. By construction method, they can also be classified as on-site masonry culverts and prefabricated assembled culverts. On existing operational lines, culverts can be constructed by open-cutting under the main line (using falsework such as suspended rails,,, etc.) or by jacking methods (e.g., jacking-in, jacking-pulling, counter-jacking, counter-pulling, intermediate jacking, traction).
In addition to the above, common culvert types include inverted siphons used when irrigation channels cross cuttings, constrained by topographic conditions, and water tunnels adopted when the railway crosses loess gullies or mountain valleys, provided the technical and economic conditions are suitable. All culverts should be designed as permanent structures, and standard drawings (or general drawings, or reference drawings—hereinafter collectively referred to as standard drawings) are generally available for use.
### General Principles for Culvert Type Selection
The selection of culvert types should be based on the characteristics of rivers and streams, terrain, geology, hydrology, and other natural conditions, considering the height of nearby embankments and the fill materials, while taking into account flood drainage, irrigation, and traffic needs. It should also prioritize ease of maintenance and construction, cost savings in construction and maintenance, and ensure the safety of railway operations, nearby factories, villages, houses, and farmland. The general principles for selecting culvert types are as follows:
(1) Prioritize the use of prefabricated circular and rectangular reinforced concrete culverts, which are easy to manufacture centrally. If local sand and gravel materials meet the requirements, slab-box culverts or arch culverts can also be used. In high-altitude regions with sparse populations, cold climates, and short construction seasons, or in arid areas with poor construction conditions, prefabricated assembled culverts should be selected to reduce on-site work, accelerate construction progress, and shorten the project timeline, considering construction equipment and transportation capacity.
(2) When selecting culvert types based on design flow, ensure that water accumulation in front of the culvert does not overflow or form backwater hazards that could endanger the embankment (e.g., long-term erosion, subsidence, culvert penetration, or collapse of embankments). Prevent floods from inundating upstream areas or eroding downstream farmland and villages. In relatively flat terrain, ensure that the terrain conditions allow for flood prevention to avoid overflow. If necessary, use culverts with lower water accumulation or appropriately increase the culvert span.
(3) When installing flood drainage and irrigation culverts in agricultural areas, consider flood retention, concentrated rotation irrigation, sand transport, and annual maintenance dredging. Avoid compressing channel sections or arbitrarily altering water levels. Prioritize slab-box culverts or rectangular culverts, preferably single-span culverts to cross existing channels, minimizing water accumulation to reduce additional channel construction efforts.
(4) Flood drainage and overpass culverts should ideally be installed separately to prevent flood hazards to traffic safety. If combined flood drainage and overpass culverts are necessary, conduct a comprehensive technical and economic comparison based on historical flood data. Culverts for pedestrians, livestock, vehicles, and agricultural machinery should meet the needs of industrial and agricultural development and ensure safety.
(5) For rivers and streams prone to debris flows, sediment transport, floating debris (logs, ice, etc.), or ice cones and ice mounds in cold regions and permafrost areas, bridges are generally preferred over culverts to avoid siltation and embankment hazards. For small streams, if sediment discharge can be ensured without siltation or debris can pass smoothly without blockage, larger-span culverts can be considered, with appropriate increases in clear span if necessary.
(6) For culverts in areas with poor foundation soil (e.g., swamps, soft soils), use lightweight structures with lower base bearing stress, such as circular culverts, rectangular culverts, or slab-box culverts with reinforced concrete foundations.
(7) In flat desert or grassland areas, in addition to reasonable bridge and culvert layout considering flood conditions, culverts upstream often have poor water accumulation conditions. Use slab-box or rectangular culverts and appropriately increase the span to prevent backwater from endangering embankments.
(8) When installing culverts in loess areas, consider debris flows, waterlogging-induced penetration, erosion, and subsidence. Prefer culverts with lower waterlogging and appropriately increase the span. For culverts in collapsible loess areas, use structures less sensitive to uneven settlement, such as full-slab circular culverts, full-slab rectangular culverts, or full-slab slab-box culverts (use with caution for large spans). Avoid arch culverts.
(9) Culverts have good seismic performance and should be prioritized in seismic zones. Generally, reinforced concrete circular and rectangular culverts or slab-box culverts are preferred.
(10) Within reservoir inundation areas, if the streambed is below the normal water level, culverts are generally not recommended to avoid siltation, prolonged inundation, and increased maintenance difficulties. If the streambed is above the normal water level, consider culverts based on hydrological, geological, and topographic conditions. If the valley is winding and conditions are suitable, elevate the location and construct culverts or water tunnels on one side of the valley. If culverts are within reservoir erosion zones, construct them on embankments designed for dams, using structures less sensitive to uneven settlement, such as rectangular culverts or full-slab slab-box culverts. Avoid full-slab circular culverts with thin walls, as their segments are prone to misalignment.
(11) When the railway crosses deep valleys in mountainous or loess plateau areas, consider both high-bridge and high-fill culvert options. Comprehensively evaluate natural conditions of the river/stream, fill material sources, farmland occupation, labor and material requirements, project costs, military readiness, construction conditions, timeline, and operational maintenance. High-bridge solutions generally save labor, occupy less farmland, and have shorter timelines, but require complex construction and more materials. High-fill culverts have simpler construction, fewer material costs, and are favorable if abundant fill material is available and labor is sufficient. However, poor foundation soil requires more effort in culvert foundation treatment, leading to higher labor and land occupation, longer timelines, significant embankment settlement, and potential subsidence or collapse of culvert bodies, negatively impacting operations and maintenance. When using high-fill culverts, reinforced concrete rectangular culverts (requiring structural redesign if necessary) can be selected. If the foundation soil is good, arch culverts (use egg-shaped culverts with caution in high sediment and abrasion conditions) are preferred. Prefer water tunnels if topographic conditions allow, with appropriately increased spans for easier maintenance and future modifications.
(12) For valleys at tunnel entrances (one or both sides of the tunnel), fully consider factors such as bridge-launching equipment reach, tunnel clear span, spoil disposal, and coordination with bridge, culvert, and tunnel construction timelines. If bridge-launching and spoil disposal are difficult but topography, geology, and hydrology permit, consider large-span culverts.
(13) For rivers and streams within station areas or traffic routes, if topography, geology, and hydrology allow, prioritize culverts but avoid forced installation to prevent severe operational issues.
(14) When constructing second-line culverts or retrofitting existing ones, unless the existing culverts have significant flaws in type, span, or main structure requiring changes, prefer the same type and span as existing culverts or reuse old culverts. On busy operational lines (stable embankments without subsidence), constructing flood drainage or overpass culverts (tunnels) may require jacking methods if falsework construction is impractical or costly, and if geological and technical conditions are suitable. See Chapter 3 of this part for details.
### Usage Conditions for Various Culvert Types
When selecting culvert types, consider their characteristics and actual site needs, with technical and economic comparisons if necessary. New culverts should generally be designed as unpressurized culverts (all standard designs for culverts are based on unpressurized critical flow, with maximum flow designed for unpressurized, semi-pressurized, or pressurized states). Exceptions include inverted siphons, which are pressurized but require sealed joints to prevent leakage, with culvert bodies, embankments, and foundations having anti-permeability and appropriate reinforcement at entrances and exits.
The standard drawings for commonly used railway culverts are listed in Table 1-1-1. The usage conditions for various culverts are as follows:
(1) Integral Reinforced Concrete Circular Culverts (YQJ 5191)
Reinforced concrete circular culverts are easy to manufacture centrally and construct, suitable for streams or channels with gentle gradients and smaller flow rates. Avoid using them if the flow carries silt, stones, or debris that may cause blockage or abrasion. Do not use them in streams prone to ice cones in winter. In mountainous areas with poor transportation before railway construction, transporting culvert segments may be difficult or damaged, so avoid circular culverts. Irrigation channels should not compress existing flow sections, so avoid circular culverts in main or branch canals. Avoid multi-span circular culverts in minor canals.
Reinforced concrete circular culverts (YQJ 5191) have single or double spans of 0.75–2.5 m, three spans of 1.0–2.5 m, with the height from culvert crown to rail bottom fill shown in Table 1-1-2. Under the same drainage capacity, multi-span circular culverts are generally more expensive than single-span ones, with uneven flow distribution prone to issues, so avoid more than two spans. Circular culverts must accommodate transportation, installation, and maintenance requirements. Generally, spans should not exceed 2.0 m or be less than 0.75 m.
For circular culverts with 2.5 m spans in standard drawings, when the fill height (embankment) from culvert crown to rail bottom is 5–15 m, each segment weighs 4.3–5.2 t. Use with caution, considering the transportation and lifting capacity of construction units.