Last reviewed 30 Sept 2026 · 7 min read
What a metro station is, structurally
A metro station is a building that has to do three things at once: carry passengers safely and comfortably, support the track (viaduct or tunnel) and its heavy dynamic loads, and house equipment — ticketing, signalling, ventilation, power, lifts and escalators. Its structural design mixes bridge engineering (viaduct and trains), building engineering (floors, columns, roofs) and, for underground stations, basement and earth-retaining engineering.
Types of stations
| Type | Description |
|---|---|
| Elevated | Track and platforms above street level on a viaduct; a concourse level below the platform; access by stairs, escalators and lifts. Usually an RCC frame with steel roof |
| At-grade | Station at ground level, on the same level as the surrounding land; used in suburban stretches |
| Underground (cut-and-cover) | Rectangular RCC box excavated from the surface; the roof is at or below road level; platforms at depth |
| Underground (mined / deep-level) | Caverns or bored tunnels for stations under difficult ground or heavy buildings |
Platform arrangements
- Island platform — one platform between two tracks; economical in width, the station box is narrower.
- Side platforms — one platform on the outer side of each track; simple passenger flow; the box is wider.
- Stacked / multi-level — platforms on different levels at interchange stations.
Structural systems
Elevated stations
- Foundations: piles (bored cast-in-situ) or open footings on rock, with pile caps.
- Substructure: columns (often circular or oval, with a portal to save space above roads) supporting the viaduct girders and the station floors; some stations have an independent viaduct and station structure to avoid vibration coupling.
- Superstructure: concourse slab and platform slab (RCC flat slab or beams and slab, sometimes PSC), stair/escalator openings, plant rooms, and an overall roof of steel trusses or light framing with cladding.
- Separation: expansion/movement joints at the interface between the viaduct and the station building; isolation of the platform structure from the track structure limits vibration and noise transmission.
Underground stations (cut-and-cover)
A rectangular RCC box with:
- Roof slab (with earth cover and the road above),
- Concourse slab and platform slab as intermediate floors,
- Base (raft) slab,
- Side walls (in-situ or diaphragm-wall retaining structure), and interior columns and shear walls.
The box is a rigid frame that is analysed as a 2D (transverse) frame in the ground, and as a 3D model where the layout is irregular.
Loads on a metro station
- Dead load (DL): self-weight of slabs, walls, columns, roof; finishes, services, partitions, false ceiling; super-imposed dead load (SIDL) such as waterproofing and earth cover.
- Live load (LL): crowd loading on concourse, platform and stairs — of the order 5 kN/m² (assembly occupancy); other floors as per occupancy; plant rooms as per equipment; roof live load.
- Train loads: vertical live load of the train on the viaduct or slab, dynamic (impact) factor, braking and traction (longitudinal) forces, centrifugal force on curved track, nosing / lateral force, and the derailment load in the design of track supports.
- Earth pressure: for underground boxes — at-rest pressure on walls (K₀ ≈ 0.4–0.6 depending on soil), surcharge from roads, buildings and traffic.
- Water pressure: at the design ground-water level (highest expected, including flood or monsoon); buoyancy / uplift on the base slab.
- Wind: on elevated stations and canopies (IS 875 Part 3); temperature (uniform and gradient); shrinkage and creep.
- Seismic: per the code for the building, and racking for underground boxes.
- Construction loads: cranes, heavy construction plant, stockpiles near the excavation, stage loading.
- Accidental: impact of vehicles on columns, fire, blast (for security), flooding.
The live load values, train loads and design life (100 years for permanent metro structures) come from the metro authority's design criteria and the codes (IS 875, IRC:6, Indian Railways Bridge Rules where relevant).
Load combinations
The structure is checked for combinations of the type
- DL + SIDL + LL (normal service);
- DL + SIDL + LL + earth pressure + water pressure;
- DL + SIDL + train loads + braking/traction;
- DL + wind, DL + LL + wind (elevated);
- DL + seismic (with a fraction of LL);
- Temperature, shrinkage and creep together with the above;
- Construction stages: excavation, dewatering, casting sequence.
Load factors follow the limit state format (for example, 1.5 for DL + LL at ultimate in IS 456, and reduced factors for combinations with wind or seismic) and serviceability combinations control crack width, deflection and water-tightness.
Seismic weight in IS 1893: the full dead load plus a fraction of the imposed load — 25 % of the live load where it does not exceed 3 kN/m² and 50 % where it exceeds 3 kN/m². (Check the current edition.)
Flotation (uplift) check for an underground box
A box below the water table experiences buoyancy. The weight of the structure and any earth above it must exceed the uplift by a safety factor (usually at least 1.1 without considering skin friction on the walls, and 1.2 where the water level is uncertain):
External width = 20 m. The base is 14 m below the design water level, so the uplift kN/m.
Weight per metre: roof slab 1.0 m thick → 1.0×20×25 = 500 kN; base slab 1.5 m → 1.5×20×25 = 750 kN; two walls 1.0 m thick × 10 m high → 2×1.0×10×25 = 500 kN; earth cover 3 m at 18 kN/m³ → 3×20×18 = 1080 kN.
= 500 + 750 + 500 + 1080 = 2830 kN/m → — not enough (needs 1.1).
Options: thicken the base slab or roof, add earth cover or ballast concrete, use tension piles (or anchors) or reduce the water head by permanent dewatering. Adding 0.3 m to the base slab adds 150 kN/m → = 1.06; adding tension piles for 350 kN/m brings above 1.1.