Structural engineering, BIM and detailing for metro and rail.

Building next to a running railway

A metro programme is rarely built on a clear site. Station boxes, entrances and viaducts are usually constructed next to, above or below a railway that is still running, which makes the possession, not the structure, the thing that actually limits progress.

• Work happens inside possessions. Track-side and over-line work is only accessible during possessions agreed with the operator, and a package has to be sequenced to what one possession can complete.
• Every interface is an agreement, not an assumption. Structural interfaces with the existing railway, support of excavation, track slab tie-ins, overhead line structures, are governed by interface agreements with the operator, not by the structural design alone.
• Diaphragm walls and station boxes carry heavy reinforcement. Station box walls, base slabs and roofs are amongst the most heavily reinforced concrete on any programme, resolved in three dimensions before they reach the cage.
• Handover means asset data, not just drawings. The operator typically requires structured asset information for the life of the railway, not only a construction record.

The structures a rail programme covers

A rail programme is a set of very different structures held together by one operator's standards, and each of them fails in its own way.

• Underground stations are a reinforcement problem. Box walls, base slabs, roof slabs and the entrances that break through them are congested, and they are cast inside a support-of-excavation sequence that decides what can be poured and when.
• Elevated and viaduct sections are a repetition problem. Piers, pier heads, bearings and deck units repeat across kilometres, so a detail error is copied down the alignment long before the first span is inspected.
• Commuter, regional and street-running light rail add long stretches of lower-intensity work along an existing corridor, platform extensions, footbridges, retaining structures and utility diversions, usually delivered in short possessions on a line carrying passengers the next morning.
• High-speed rail tightens tolerance rather than load. Track slab, alignment and the stiffness of everything supporting them are held to limits that make setting-out and survey part of the structural deliverable, not a site activity.
• Interchanges and transit hubs stack rail, bus and pedestrian movement onto one structure, with long-span roofs and transfer structures sitting directly over an operational railway.
• Depots and stabling yards read as industrial sheds until the maintenance regime is drawn: inspection pits, jacking points, overhead line supports and crane rails all land in the structure.

The packages a metro programme needs

Most metro structures are heavily reinforced concrete, with steel roof and canopy structures at stations and viaducts detailed alongside them.

• Rebar detailing for station boxes, diaphragm walls, base slabs, viaduct piers and deck units, where congestion resolution is the largest part of the drawing effort.
• BIM modelling and coordination across structure, systems and architecture, built to the asset data structure the operator's handover requirements set.
• Drafting and CAD production for the controlled issue set and the interface drawings an operator approval requires.
• Steel detailing for station roofs, canopies, footbridges and depot structures.

Standards, operator requirements and asset data

Metro structures sit under the general structural code, the operator's own engineering standards, and an asset information requirement that runs well beyond construction.

Structurally, that is the Eurocodes, EN 1992 for concrete and EN 1993 for steel, with the National Annex and EN 1090-2 execution class, or BS EN Eurocodes with the UK National Annex. Operators typically maintain their own standards for structures built within or adjacent to the running railway, covering clearances, support of excavation and structural gauge. Information management runs under ISO 19650, with the operator's asset information requirements setting the classification, naming and data structure that the model and the handover package have to follow from the first issue, not just at completion. Depot and stabling yard structures are typically detailed to the same operator standards as the running line, even though they sit outside the passenger-carrying route.

Fire and life safety is the standard most often missed on a structural package. NFPA 130 governs fixed guideway transit and passenger rail systems in the United States and is widely referenced elsewhere; it sets evacuation times, means-of-egress capacity and the fire resistance and smoke control provisions that decide stair widths, shaft positions and slab openings well before the architecture settles. Where an alignment carries a bridge or viaduct in North America the deck is designed to AASHTO LRFD alongside the operator's own loading, with FRA requirements applying on the national network. Elsewhere the same structures run to IS 456 and the Indian Railways standards, or to JIS and GB standards, and the operator's own manual still sits on top of whichever national code applies.

Congestion, interfaces and what we check

Metro packages fail either in the reinforcement or at the interface with the existing railway, so the checks concentrate on both.

• Reinforcement congestion in 3D. Station box and diaphragm wall reinforcement is resolved in the model before it reaches the cage, with bar clashes and cover reported rather than discovered on site.
• Interface geometry against the operator's asset. Every new structure is checked against the current survey of the existing railway, not the record drawings, which are frequently out of date.
• Possession sequencing. Packages are checked against the possessions calendar so a crew arriving for a booked window has a complete, checked issue waiting for it.
• Asset data completeness. Model and drawing data is checked against the operator's asset information requirement before handover, not assembled retrospectively at completion.

The check record is issued with the package, and a senior engineer reviews and signs it before it goes out.

Delivering to a possessions calendar

A metro programme is paced by possessions that are booked months in advance and rarely repeated if missed, so a late issue does not cost a day, it costs the next available window. The repetitive parts of the drawing set, typical viaduct spans, repeated station box bays, are produced by an AI-driven system, which is what keeps a possession-paced programme affordable to run without the quality dropping under time pressure.

Accountability stays with one partner across the whole programme. BuildTwin delivers the structural and BIM scope, one delivery lead, one register, one programme, working to your possessions calendar and your operator's asset information requirement.