Posted By Robert Woods Does anyone have any information on sprayed concrete lined tunnels.

Posted By Ciaran McAleenan Robert, I lifted the following from the Institution of Civil Engineers website, "Sprayed Concrete Linings A. Background "Sprayed Concrete Linings" (SCL) is the ICE-recommended name for the lining of tunnels by this method in soft ground urban areas, in preference to "New Austrian Tunnelling Method." * The New Austrian Tunnelling Method (NATM) originated in hard rock tunnelling and utilises rockbolts and shotcrete applied immediately after blasting. This is often followed by a cast in-situ concrete lining using formwork. It is neither new, nor particularly Austrian, having been used in Australia, USA, Switzerland and many other countries. * There are significant differences between SCL in soft ground and the original NATM. In particular, it is not possible to use the NATM philosophy of mobilising inherent ground strength through deformation. The lower strength of soft ground means that work has to proceed in short stages, with no delay in completing the primary support and ground deformation being reduced as much as possible. * In 1994 growing concern developed over the use of the NATM following the collapse of two tunnels during construction at Heathrow and Munich. * As a result an ICE Commission on Tunnelling in Soft Ground in Urban Areas was formed. It examined NATM design and construction principles and their applicability to soft ground; and it produced a design guide for the proper use of SCL in soft ground in urban areas with specific reference to London clay. B. Issues * Good design and supervision are crucial if sprayed concrete linings are to realise their full potential with acceptable risk. Particular attention should be paid to the control of the quality of the sprayed concrete mix and its application to excavation joints. * There are no fundamental design or construction impediments that should preclude the use of sprayed concrete linings beneath urban areas in a wide range of soft ground conditions, including London clay. * Primary risks associated with SCL tunnelling are: ground loading differing from the loading anticipated; lack of integrity of the primary lining and incoherent geometry of the primary lining. These must be controlled by careful specification. Provided appropriate specifications are included in the contract document, then all standard forms of contract can be used for the procurement of SCL tunnels. * SCL cannot be treated as temporary works, which are normally under the control of the contractor. Instead, it is in the interest of employers that there is discretion for instructions to be given by the engineer as a "supervisor" of construction, particularly for safety and potential third party damage limitation. * There are two design approaches for SCL: the empirical and the analytical. Only the latter is usable in the UK because of the requirements of the Construction (Design and Management) Regulations 1994 that SCL dimensions be demonstrated at the outset of construction as being fully adequate for the foreseeable circumstances, the empirical approach may be more difficult to demonstrate. However, using the empirical approach, followed by observation and adaptation during construction, may be just as safe and reliable. * The key components of SCL design for soft ground are: excavation and primary support carried out in short lengths; completion of primary support undertaken as soon as practicable, particularly closure of the support ring; and the limiting of settlement at surface. * There should be continuous interaction between the designer and contractor during an SCL tunnel's construction. * For face areas greater than 30 sq.m. there should be four basic excavation sequences: Type 1, which is the one used most often, divides the face into four parts: two sidewall drifts, the central core and the crown arch. The drifts are advanced concurrently, but staggered so as to avoid the two working faces being side by side, followed by the crown arch and finally the central core. Where tunnels are to provide earlier access to other work areas a circular or near circular SCL or segmental pilot Tunnel may, followed later by SCL enlargement to full section. It is essential that the risks be identified and fully understood; the design must minimise the risks and the construction must be closely supervised to ensure the designer's instructions are followed as closely as possible. Care in the design, construction and supervision of such tunnels should be paramount. C. References 1. Sprayed Concrete Linings (NATM) for Tunnels in Soft Ground, an ICE Design and Practice Guide (Thomas Telford 1996). Check out the following URL you will find other geotechnical and tunnelling information plus a lot of good hyperlinks; http://www.icenet.org.uk...org.uk/public/bslist.asp or go to http://www.ice.org.uk/ and search for tunnelling. Regards Ciaran mailto:ciaran@confinedspaces.com

Posted By Ken Urquhart Robert. There is lots of Tunneling going on all around the world. Some of the references and information that you have been given will help you, but for the Bigger Picture try some of the following sites: tunnelbuilder.com - marketing resources for the world's tunnelling industry Tunneling news and projects from around the world. Built by professionals for professionals. more hits from: http://www.tunnelbuilder.com/ (673 B) Sorry Robrt I lost the link to the Internet, However suggest that you try a search on www.alltheweb.com and enter Tunnelling Information and Construction, it comes up with lots of interesting sites including the international Tunnelling Society/Association. Hope this helps. Regards. ken

Posted By Robert Woods Thanks to everbody who responded your contributions are much appreciated. Bob Woods.