Since the introduction of sprayed concrete as a means of providing tunnel support we have lived with the ever present challenge of defeating gravity. When the ground conditions, shotcrete mix and physical application all align, sprayed concrete is a highly effective means of placing a tunnel lining. Unfortunately this perfect meeting of constraints isn’t always achievable, even with every effort made by the construction team to ensure the highest quality of the lining and the outcome can be collapses of fresh or green shotcrete or the ground it is designed to support.
Teams utilising sprayed concrete have previously managed the process of preventing injury to personnel from falling materials with a number of methods that have had no industry wide adoption or consensus.
The construction teams undertaking the work and exposed to the risks can also be desensitised to the risk and the need for a robust system of prevention that is adhered to.
On numerous occasions I am sure many SCL team leaders have been advised how to manage face access and then have those giving the advice stumped when they watch the work in progress and see the viability of their proposal evaporate. The constantly advancing face and presence of heavy machinery makes a viable solution to controlling access into the area of high risk a challenge that doesn’t have an easy fi x. A viable solution relies on the cooperation and understanding of all personnel involved in the process from operative to the senior members of the client’s team.
The fi rst step to success is communicating the risk, and the reason for operating an exclusion zone. Anyone who has worked in an SCL tunnel will have seen shotcrete falls but still, so often, personnel feel justifi ed in “just popping” into the high risk zone beneath exposed ground or green shotcrete because they think they are helping, saving time, or that it won’t happen to them. No one’s luck holds out for ever and every time someone enters that danger zone there is the potential that they won’t be walking out, however briefl y they enter for. It also then creates the additional risk for colleagues or emergency teams wanting to assist them.
The unfortunate death of Rene Tkacik on a Crossrail worksite made the risk very apparent to everyone and was the catalyst to bring all parties together to agree a unifi ed solution to manage exclusions zones.
The gathering of so many companies and individuals on Crossrail presented an opportunity to develop a document that could become industry wide guidance with agreement from a large percentage of the industry before its publication.
We mustn’t forget that with the development of ever more effi cient lining designs and the need to verify geotechnical conditions and shotcrete performance and early strength gain essential to maximise productivity and reduce costs it is easy to take the simple option and require personnel to visit the face.
The presence of this guide will remind all that access should be a last resort and alternative means to gather the data need to be adopted rather than the easy one (pleasingly there are plenty of initiatives looking to develop solutions that eradicate the need to access the face).
The document forms a reference to guide and inform future projects of the issues to be considered when establishing exclusions zones for Sprayed Concrete Lining works. There remains the need for every project to review the specifi c conditions under which they will operate to ensure that the process is fully applicable to their works. When every scheme is aligned with this process, its application will become second nature to all and not seen as a hurdle to completing the works. I was pleased to read a short, concise and clear document that is easy for all to follow and understand.
I hope that the document becomes common place on all projects and when it was discussed amongst the British Tunnelling Society committee it was a simple decision to make this document available to all of our members and the wider tunnelling community through our website and the greater the awareness of its presence the greater the chance of the desired blanket adoption.
I am sure that the present review of BS6164 [the British Standard for health and safety in tunnelling] will take note of this document and we are likely to see some of its content appearing in the British Standard in the next revision. Congratulations to Crossrail and everyone involved with the guide
