C+S March 2020 Vol. 6 Issue 3 (web)

and excavations for boxes, shafts and portals. Crossrail is utilizing eight TBMs, six earth pressure balance machines (EPB) and two slurry machines. Transportation was mainly by rail and river barge, then by ship to the landfill, avoiding the use of heavy trucks wherever possible.

Source: https://learninglegacy.crossrail.co.uk

In the case of Crossrail in London, most excavated materials were transported by barge and ship due to the proximity to the River Thames and the access to the waste recovery and landfill site by sea. The ap- proach to material movement will vary by location. Project executives must prepare adequately to respond to those needs in ways that limit impact to communities. Stations Construction of underground stations results in areas of disruption whilst the station is excavated and built. Modern techniques such as top-down construction, when practical, reduce the period of disruption and the amount of temporary works needed. The top-down construction method builds the permanent structural portions of the basement and station along with the excavation from the top to the bottom. The top-down method is particularly suited to the construction of underground stations beneath busy roadways and provides significant savings on overall construction time. This is an important technique for major projects, in which time is of primary importance and surface disruption needs to be minimized. Circular shaped shaft excavations, supported either by diaphragm walls or secant pile walls, provide significant advantages over plane walls. They do not need supports such as struts or tie-back anchors. Such excavation works can be achieved quickly without a complicated construction sequence or coordination between the excavator and the shoring or anchor installer.

Photo: Doha News

school, work, appointments, and other important everyday activities. Businesses suffer when clients and customers find it hard to access them. Everyday emergencies turn critical when ambulances, rescue crews, and fire trucks are not able to travel regular routes. Restrictions on the time of travel for trucks bringing in construction materials and taking away excavated material can help alleviate the impact. In some cities such as Doha, Qatar, overhead conveyors have been used to transport excavated material from the tunnelling opera- tions in the heart of the city to dump sites. Depending on the physical location of the sites, a range of options may exist. Case study: Crossrail, London Crossrail is a new UK railway that runs for over 100 KM from Maidenhead and Heathrow in the west, through new tunnels under central London to Shenfield and Abbey Wood in the east. It is currently Europe’s largest construction project. Work started in May 2009 and over 10,000 people were working across over 40 construction sites. The project is planned to open in 2021. Within Central London, Crossrail is routed through 42 KM of running tunnels. The works in Central London will generate 6,000,000 T of excavated material. 4,500,000 T of this material will be shipped to be deposited at a ‘Waste Recovery’ facility at Wallasea Island approximately 60 KM east of London, where it will be used to create a coastal nature reserve. Material unsuitable for deposition at Wallasea Island or unsuitable for shipping to Wallasea will be transported by road, rail, and/or barge to a number of licensed landfill sites to the east of London.

The excavated material is derived from the tunnel boring machines (TBMs), sprayed concrete lining (SCL) tunnels,

Photo: Ulmaconstruction.net


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