Supporting tunnelling and subterranean projects

Recently, you may have seen tunnelling covered more extensively in the news, following developments in two of the UK’s major civil engineering projects, HS2 and Thames Tideway; and tunnelling looks set to continue to be at the forefront of construction with increased public investment in rail, water and energy infrastructure over the next 10-15 years.
   

In this blog, we dig deeper (excuse the pun!) into how tunnels are constructed, some common tunnelling excavation methods, how Conquip can support subterranean infrastructure projects and how we have supported them in the past.


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Range of tunnelling equipment for large scale infrastructure project, Sydney Metro.

So, what are tunnels and what is tunnelling?

Tunnels are underground passages that usually pass through hills, or under buildings, roads, and bodies of water. Their purposes include, traversing obstacles, creating additional routes for transit systems, such as, London Underground’s Northern Extension Line, or providing underwater connections, like the Euro Tunnel.

Tunnelling is the construction process of creating passageways that provide an alternative access method to bridges. Historically tunnels were created using explosives and intensive manual labour but technological advancements and modern methods now provide much quicker, safer and far more efficient solutions than these traditional methods.


How is a tunnel constructed?

    Well, that depends on a few variables, such as, the scale or route length, the ground or groundwater conditions, the depth and space that is available and the planned construction period.

    There are three main tunnel construction methods:

    • Cut-and-cover tunnel: This method involves construction of a shallow trench that is then covered over with an overhead support system durable enough to withstand the load above.
    • Bored tunnel: Constructed without removing the ground above. Method involves digging a tube-shaped passage through the earth, usually using Tunnel Boring Machines (TBMs).
    • Immersed tube tunnel: These are sunk into a body of water and either placed on or planted just under its bed.

    Various other tunnelling methods exist, including, roadheaders, open-cut method, pipe-jacking, box-jacking, auger-boring, microtunnelling, and mined tunnel.


    How is a tunnel excavated?

    Drill-and-blast excavation and mechanised tunnelling using TBMs are common methods of tunnel excavation.

    Drill-and-blast excavation

    Drill-and-blast excavation is the most common technique of medium to hard rock excavation. During this process, the drilling rig bores the blast holes which are then loaded with explosives and detonated sequentially. After one blasting cycle is complete, it creates breakout material which is removed via the ‘mucking’ process.

    So, tunnel blasted, loose rock dislodged – time to excavate! Conquip have a range of high-quality equipment to support large excavations. Check out what we can offer here

    Mechanised tunnelling

    Mechanised tunnelling is a process using purpose-designed tunnel boring machines (TBMs) to excavate the complete cross-section required. The TBMs are specifically designed for a project depending on the geological makeup of the surrounding environment. Although this incurs high purchase and maintenance costs, TBMs provide greater excavation efficiency and require less operatives, much like the BulkX!

    In Phase One of HS2, a total of ten TBMs are to be launched from six main tunnelling worksites. The Chiltern tunnel will use four TBMs alone and at 32 miles, it will be the longest tunnel of the HS2 project.




    What are the benefits of tunnels?

    • Tunnels provide more direct routes between destinations and less disruption to the landscape.
    • Tunnelling construction is more economical in nature, compared to other methods such as open cut trenching, Hindhead Tunnel, being a prime example of this.
    • Tunnelling ensures high-speed construction with lower power consumption.
    • Noise pollution is dramatically reduced.



    How can Conquip support tunnelling projects?

    We offer a diverse selection of equipment that suits many infrastructure applications. Our in-house design and manufacturing capabilities ensure we can offer bespoke solutions to help overcome challenges that can be presented during projects. Below are examples of some of the UK’s largest civil engineering projects we have already supported.


    What subterranean projects have Conquip supported in the past?

    Conquip have played a vital role by providing a range of solutions that have improved both the efficiency of these projects and reduced the environmental impact they have had on local communities.

    Crossrail

    For inner city projects, like Crossrail, BulkX has proved to be the most efficient solution of waste removal. Its versatile system options help to overcome any logistical challenges presented on sites where space is restricted and local disruption needs to be kept to a minimum. BulkX can also be crane-lifted up and down shafts where conveyor access is not possible.

    Stepney Green was one of the largest drive shaft sites for the Tunnel Boring Machines (TBMs) on the Crossrail project. The BulkX Fixed Gantry System, enabled the discharge of 10,000 litres of spoil in just 5 seconds, axing 12 weeks off the dig programme.

    "It was a pleasure to have Conquip on site, the communication was first class and the solution provided (BulkX) really turned this project around." 
    Glenn, Site Manager.

    BulkX also starred in the West End, showing off a bespoke gantry system that allowed the skip to hook onto the gantry on one side to discharge, rather than both ends. This provided a choice of discharge locations ensuring the most efficient excavation solution for Crossrail at the Tottenham Court Road site.

    The CantiDeck solutions for Crossrail have been predominately used for muck away and goods loading and unloading but they have also provided pedestrian access.

    BulkX lowered over gantry at Crossrail Stepney Green site to discharge spoil from tunnel into muck bay
    BulkX skip being loaded with spoil from tunnelling excavation by excavator

    Northern Extension Line

    The Crane Forks Cage was designed following many load failures and near misses using traditional methods for lifting brick and blocks, such as, safety restraint nets. Close collaboration with leading contractors Ferrovial Laing O’Rourke JV enabled us to design a solution that is fail-safe and considered best-practice for the industry. After a successful trial on the Northern Line Extension project, the Crane Forks Cage is now a popular sight on many construction sites. Advancements to the design ensure it is ideal for subterranean projects such as the access ramp feature for easy loading and working under reduced ceiling height.

    Two site operatives unloading palletised material from Crane Forks Cage in tunnel at Northern Line Extension site
    FLO JV site operatives monitoring Crane Forks Cage being lifted from shaft on Northern Line Extension project

    Thames Tideway

    For the Thames Tideway project, we manufactured a bespoke, modified Fixed Flush CantiDeck loading platform. This was positioned in the entrance of the tunnel, where it intersects with the shaft enabling quick and efficient load-out for materials and tools.

    Another product our design team specifically created for Thames Tideway is the Excavator Lifting Platform, a robust steel platform that facilitates the safe transport of excavators in out of shafts, tunnels, basement excavations and other underground sites.

    London Power Tunnels

    We are currently developing other bespoke products for London Power Tunnels, such as the Tunnel Access Ladder, stay tuned for further updates on this!

    Hinkley Point C

    Our range of personnel lifting solutions have been used extensively across large tunnelling projects, such as Hinkley Point C, as we are one of the only hire providers in the UK offering a fully-compliant, 12 person Access Cage.

     

    These are just a few examples of the solutions Conquip can provide into tunnelling and other underground projects…how can we help you?


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    Need reliable support on your project? Get in touch by email sales@cqegroup.com