Stepney Green cavern is an underground junction which contains the junction where

Crossrail Crossrail is a railway construction project mainly in central London. Its aim is to provide a high-frequency hybrid commuter rail and rapid transit system crossing the capital from suburbs on the west to east, by connecting two major railway ...

divides into two branches: one to

Shenfield Shenfield is a commuter suburb of Brentwood, in the borough of Brentwood, Essex, England. In 2020, the suburb was estimated to have a population of 5,396. History The old village (now town), by the church and Green Dragon pub, lies along the ...

and one to

Abbey Wood Abbey Wood is an area in south east London, England, straddling the border between the Royal Borough of Greenwich and the London Borough of Bexley. It is located east of Charing Cross. Toponymy The area takes its name from Lesnes Abbey ...

. It is located below Stepney Green Park. At the time of its completion in 2017, Stepney Green cavern was claimed to have been one of the largest mined caverns in Europe. Construction activity commenced during March 2010, almost two years after the programme's authorisation. The cavern was built using spray concrete lining techniques, and involved the use of multiple

tunnel boring machine A tunnel boring machine (TBM), also known as a "mole", is a machine used to excavate tunnels with a circular cross section through a variety of soil and rock strata. They may also be used for microtunneling. They can be designed to bore throu ...

s (TBMs). During 2013, excavation work was largely completed, while both of the TBMs were dismantled during the following year. During October 2017, it was announced that all major structural work associated with Stepney Green cavern had been completed.

History

The origins of Stepney Green cavern are strongly associated with the

programme. Construction of the railway begun shortly after the

Crossrail Act 2008 The Crossrail Act 2008 (c 18) is an Act of the Parliament of the United Kingdom that authorises the construction of the Crossrail railway from Maidenhead and Heathrow Airport to Shenfield and Abbey Wood. The legislation was introduced by the ...

received

royal assent Royal assent is the method by which a monarch formally approves an act of the legislature, either directly or through an official acting on the monarch's behalf. In some jurisdictions, royal assent is equivalent to promulgation, while in othe ...

during July 2008. In addition to forming one element of the central underground section of the new railway, Stepney Green accommodated a critical junction, requiring care in its design. The engineering of Stepney Green cavern involved overcoming several challenges, as it was one of the largest excavated caverns to be constructed in Europe. Its maximum dimensions are a width , a height of , and a length of . Following an evaluation of various techniques, it was decided to use a tunnelling technique known as spray concrete lining, which involved the excavation and removal of of

subsoil Subsoil is the layer of soil under the topsoil on the surface of the ground. Like topsoil, it is composed of a variable mixture of small particles such as sand, silt and clay, but with a much lower percentage of organic matter and humus, and it ...

along with the application of of

shotcrete Shotcrete, gunite (), or sprayed concrete is concrete or mortar conveyed through a hose and pneumatically projected at high velocity onto a surface, as a construction technique, first used in 1907 invented by Carl Akeley. It is typically ...

to support the walls. Due to the presence of highly permeable water-bearing sand that posed a hazard during the shotcrete application, depressurisation measures were employed. The boring process was largely performed via multiple TBMs. Various measures were taken to support the construction effort. To supply the large quantities of concrete needed, a purpose-built batching plant was constructed to manufacture it on site. A variety of sensors were installed in the vicinity of the cavern to closely monitor any instances of ground movement, vigorous measuring of the applied concrete's strength was also practiced. Furthermore, a specialised cutting tool was used to remove the temporary supports, which generated far less noise than conventional impact hammers. Primary access to the site was via a rectangular access shaft that is located across the twin running tunnels just to the west of the junctions; this space also accommodates various utility spaces, including a ventilation facility, as well as providing an emergency access point. During March 2010, shortly after being awarded the contract to construct the section, the contractor took possession of the site; initial activity centred around the excavation of the first large access and operations shaft. During May 2013, the eastbound section of the cavern was completed ahead of schedule; completion of the westbound section was achieved in August 2013. The first breakthrough of a TBM into the cavern was achieved during the latter half of 2013. During June 2014, it was announced that one of the TBMs had finished its boring activity at Stepney Green; the occasion also marked the structural completion of all tunnels of the line's north east spur. Upon arriving at Stepney Green, the TBMs were disassembled and removed in pieces, before being reassembled elsewhere to work on additional Crossrail elements. During October 2017, Crossrail announced the completion of all work associated with Stepney Green cavern, which was stated to be a major milestone of the overall scheme.

References

External links

Image of Stepney Green cavern via gettyimages.co.uk

Crossrail: tunnelling on an epic scale via ingenia.org.uk
{{coords, 51.517, -0.044, display=title, notes=http://www.dsjv.co.uk/c305stepney.html Crossrail Railway tunnels in England Rail junctions in Great Britain Tunnels in London