The self-certification documentation for the secondary lining, and other activities such as the snagging works, membrane installation, finishing works and walkway construction, was less time consuming and significantly easier for the engineer to complete than for the primary lining. This was mainly due to:
– a longer time interval between stages in the construction cycle that require approval and;
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– familiarity with the self-certification procedures.
The inspection and test plan for construction of the secondary lining vault identifies two main hold points. These are before the concrete pour can start, and before the shutter can be struck. Before a pour begins a number of checks must be made, such as checking that the waterproofing membrane and water bars are intact, the stop end is built correctly and the shutter is positioned accurately. Once these checks have been made and self-certification documentation completed, the pour can begin.
A permit to strike the shutter is issued when the concrete strength reaches 7N/mm2. The concrete strength is determined by carrying out tests on cubes made with the final load of concrete used in the pour. The cubes are stored in a water bath on the shutter and the temperature of the water is controlled to match that of the in-situ concrete by a series of thermocouples and a data logger. This replicates the curing conditions within the shutter and ensures the shutter is not struck before all the concrete in the pour has reached the specified minimum strength.
For each 12m length of secondary lining, one sheet details all the inspections and checks required by the section engineer or foreman. At the following stages approval, inspection or test results are required before work can go ahead: pre-concrete checks; approval to pour; permit to strike; concrete finish inspection; post remedial checks; approval of section.
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By GlobalDataWith one pour carried out each shift, it is clear that there are significantly fewer hold points to be approved per shift during secondary lining construction than for the primary lining. This meant that previous difficulties with the volume of paperwork were no longer an issue.
For each section of secondary lining, all stages of approval are included on one sheet and this sheet is not complete, ie: the section of secondary lining is not fully approved, until remedial works have been carried out and final concrete checks have been made.
Defects and remedial works
The HSE‘s report on its investigation into the collapse of New Austrian Tunnelling Method tunnels at Heathrow Airport stated that “repairs were permitted without sufficient inspection, engineering analysis and design, and without recording and certificating the repair work that was completed. The unsatisfactory conduct of remedial works … demonstrate[s] the ease with which such errors can be made and remain undetected in the absence of suitable management control systems”.
In the CTRL project, the identification of defects and remedial works are controlled by a non-conformance reporting (NCR) system, central to the self-certification system. The daily meeting, in which the RESS sheet was produced to allow construction to continue, was a key part of project control, and covered defects and remedial works.
It is the contractor’s responsibility to ensure all defects are identified and resolved. Non-conformance reports must be raised for any work that does not comply with the specification or agreed working procedures. This includes a description of the defect, its cause, and when it was discovered, action required both to rectify the defect and prevent it happening again. The NCR remains open until these actions are complete.
One of the specific CTRL contract requirements is that all non-conformance reports raised by Eurolink are to be reviewed by RLE. This is vital because of an important clause in the payment procedures for the project, relating to remedial works.
The contract includes an incentive to the contractor to report defects. If the contractor raises an NCR within 72 hours of discovering a defect, then it is paid for putting the work right. If not, the client will raise the NCR and the cost of remedial work will be considered a disallowed cost, ie: it will be payable by Eurolink. This is seen as another way of encouraging the contractor to take responsibility for its work and continuously feed back and develop the self-certification process. To date, around 350 NCRs have been raised for the North Downs tunnel. About 25% of NCRs concerned environmental issues such as oil spills and were closed within a week. Although everyone can bring up an NCR, most were raised by engineers.
Internal audits and surveillance
As part of the Eurolink quality control procedures, and as an additional check on the correct implementation of self-certification, internal audits and surveillance were carried out. Aside from the external audits by the client or nominated third parties, each section of work had to be audited at least every six months, in accordance with the method statement, to ensure compliance with quality, safety and environmental procedures. Internal audits were generally carried out by the quality and environmental managers and were aimed at ensuring that the work complied with the plans and procedures associated with that activity.
The process of self-certification allowed Eurolink engineers to assist and meet the requirements of the auditors, given their extensive involvement in the supervision and documentation of every shift. Where an audit identified lack of compliance, a corrective action report (CAR) was issued which, as well as identifying the defect or omission, requires corrective action and that to prevent re-occurrence. The findings of audits, particularly those highlighted through CARs, could then be fed back into the self-certification process by identifying a need for closer monitoring of a particular aspect of the tunnel construction.
Surveillances are described in the associated Eurolink method statement as “a lesser form of an audit which is intended to be localised, less formal, rapid and which focuses on specific areas or work activities”. Surveillances of the tunnel cycle were often carried out by one of the tunnel engineers, either Eurolink or RLE, with either the pit boss or lead miner of the gang on shift. Using a standard Eurolink surveillance report form, aspects of the primary and secondary lining construction were observed through a whole cycle and monitored against the relevant method statement, specification or the RESS. The form included checks on aspects that appeared on standard shift documentation and thus acted as an independent check on the implementation of self-certification. It also included safety, access and environmental issues.
Both audits, and particularly surveillances, were an essential part of the quality system in allowing those involved in supervision of the tunnel advance to stand back from the everyday activity of monitoring and documenting the shift, enabling them to look for possible improvements or identify any failings in the existing system. With the involvement of RLE in the audits and surveillance, the self-certification system developed with the project.
Self-certification: future development
The amount of paper required, because of the frequency of hold points during excavation and primary lining construction, raises the question of where to place the line between fulfilling the self-certification procedures with shift documentation and it becoming too time consuming. As discussed earlier, the quality system must be a tool at the engineer’s disposal and not a procedure that leaves the engineer a slave to the paperwork it requires.
This is an inherent problem with the implementation of self-certification procedures on a process with so many hold points. The issue will be helped if pit bosses begin to share shift documentation with the engineer. A change in attitude and culture is required before the self-certification process can be fully implemented throughout a project. For example, everyone involved in the management of the tunnel advance must enforce a bonus system based not entirely on production, but also on quality of the workmanship, consideration of environmental issues and primarily towards safety. On the North Downs tunnel these issues were a central part of the bonus system.
There is no doubt that everyone became more aware of, and more competent with, the requirements of self-certification. It is certain to have improved the overall quality. It is, however, unlikely that this increase correlates to an increased amount of paperwork. In fact, the opposite is more realistic.
The advances made in terms of training, learning and implementing self-certification on the North Downs tunnel are notable. These are important lessons that the industry cannot afford to lose. Training and involving as many people as possible will help to carry forward the experience gained and allow self-certification to find its place in the tunnelling culture.
Conclusion
The self-certification process can be seen in a number of different lights. Is it an exercise in transferring risk by the client on to the contractor, leaving the responsibility for a quality end product to them? Is it a way of reducing the client’s site supervision costs? Or is it a system that aims to encourage an open working relationship between all parties to the contract, leading to a better and more economical product?
Certainly, most people involved in the tunnel construction have welcomed the removal of the traditional ‘hold points’ for client approval at each stage of the work. However, RLE still maintained a significant site presence, with a tunnel manager and several staff working directly with Eurolink to provide immediate input to the tunnel advance.
For those at the ‘coal face’, roles and responsibilities have been clearly defined through previous jobs, and changing these attitudes and habits will not happen over the course of one project. However, self-certification has required the tunnelling workforce to take direct responsibility for their work. Workmanship, environmental and, most importantly, safety issues have all become an inherent part of the daily routine.
This report highlights that self-certification on the North Downs tunnel has required continuous development to become the smooth system it was intended to be. However, it is clear that from the beginning the self-certification system has worked effectively. The CTRL project has seen the level of contractual correspondence between the contractor and project manager kept to an absolute minimum. Contract 350/410 was the first major civil engineering contract in the UK to complete one million man-hours of work with no reportable accidents. Construction of the tunnel and related works is predicted to finish at least £5M below budget and five months ahead of schedule, in autumn 2001.
