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Innovative offsite methods of construction used in the rail and road sectors are often restricted by approval authorities. Here, a comparative case study explores the key challenges, main drivers and constraints for offsite adoption and implementation.
Offsite techniques in the building sector have seen great development in the past decade. However, in infrastructure, offsite exploitation has generally been limited to precast concrete or steel bridge sections. Many barriers have been identified including the inflexibility of the approval authorities to change and adjust. To address the resulting challenges, two offsite case studies were analysed [1,3]. Forming culverts and underbridges by reinforced concrete box-jacking may not be completely new and innovative solutions in themselves but in conjunction with an array of organisational and legislative problems and limitations, this type of offsite solution can become extremely demanding and complicated to apply.
The projects reviewed and compared as case studies have many similarities, but one major difference. First, the same contractor, consultant and subcontractor were involved in both schemes. Second, the challenges faced were ground-breaking. However, in one of the projects the box was jacked into position under a live motorway  (Figure 1). In the other it was jacked under a railway line during a precise time-window closure of 101 hours  (Figure 2). In both projects the margin for error was minimal. Thus, very strict approval protocols had to be addressed in order to minimise risk and increase confidence so that the governmental approval agencies would authorise the works underneath and around their assets.
For several months prior to commencing the design and build works, all parties involved had been engaged in discussions to determine exactly what the approval authority wanted as a final outcome and what their priorities were. Technical risk and execution risk were unofficially divided into subcategories. Structural design was not considered as a challenge but due to unconventional soil conditions such as contaminated ground and toxic carbons the 'geotechnical risk' had to be analysed.
Insert Image 2 here - Figure 2 - Box jacked under a railway line
Close comparison of the two case studies suggested that, if the approval body is also the client, they have an increased vested interest in the completion of the project. Consequently the approval authority/client has a greater interest in seeing the project through to a successful, timely and cost-effective completion rather than solely maintaining and protecting their assets available to the public. In contrast, where the client is not also the approval body, then there may be additional barriers to overcome since the approval body may take less of an interest in the operation and delivery of the project. Nevertheless, this overlapping of roles should be considered an advantage because approval bodies focus on completing the new works and also returning their existing asset to the public which leads to a more holistic approach.
The key knowledge of an individual, authorised by a government approval body to assess and update regulations, has direct influence on innovation in a specific sector. The interpersonal relationship between the individuals representing the industry consortium and the approver representing the government authority could be the key factor to accelerate the introduction of innovation.
By considering the differences in approach towards innovation and approval systems for the governmental approval agencies responsible for motorways and railways, the parties involved can align their programmes of work and methods to help fulfil their clients' needs, facilitating more lean working processes throughout the procurement, design and construction stages . Understanding the ways that such organisations influence the sector's confidence regarding innovative construction methods and materials could help accelerate their development in the design and construction process, and hence also maximise the possibilities of modernisation in the sector .
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1. Allenby, D and Ropkins, JWT., (2004) The use of jacking-box tunnelling under a live motorway. "Procs of - Geotechnical Engineering", 157, 229-238
2. Brunsden, R., Higgs, D., Allenby, D. and Ropkins JWT., (2003) Jacked box tunneling under the M1 motorway at Junction 15A, Northampton." Procs of Underground Construction", 373-384
3. Ogborn, S, Sreeves, J and Beech, S., (2011) Jacking the box: a 101 h squeeze under the West Coast main line. "Procs of the Institute of Civil Engineers", 164, 27-34
4. Vernikos, V K, Goodier, C I, Gibb, A G F, Robery, P C and Broyd, T W., (2011) Offsite innovation in UK infrastructure: The role of the approvals process in box jacking projects. Procs 27th Annual ARCOM Conference, 53-62
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