We all know that tunnel construction is not an exact science and that, therefore, monitoring often plays a crucial role in ensuring that the tunnel and surrounding properties are safe and meet the design intent. Monitoring often includes the use of geotechnical instrumentation. If significant decisions are to be based on the monitoring data, data quality must be maximised.
If instrumentation is used, the tasks include:
1. Buying instruments
2. Installing instruments
3. Collecting data
4. Interpreting data
How can we ensure that these tasks are assigned to the people who are most likely to maximise quality?
The golden rule is: ‘The people who have the greatest interest in the monitoring and instrumentation data should be given direct line responsibility for obtaining the data.’ Or, put another way, who has the motivation to do these nit-picking tasks with enough care?
Who are the candidates?
The candidates for this responsibility are the staff of the project owner, the designer, the construction manager, the principal construction contractor, possibly a temporary works contractor, possibly a design-build contractor, and often a specialist geotechnical subcontractor. The selection depends on the specifics of each project, on who has ‘the greatest interest’.
If principal construction contractors, design-build contractors, temporary works contractors or specialist geotechnical subcontractors have initiated the monitoring programme, clearly they have the greatest interest, and all’s well. But if the designer of the project has initiated the programme, personnel in these organisations may not have enough motivation to ensure quality. Let’s look at the options for this situation.
Options for tasks 1, 2 and 3
When the designer of the tunnel has initiated the monitoring programme, the options for assignment of tasks 1, 2 and 3 are as follows.
Let’s call these three tasks of buying and installing instruments and collecting data ‘field instrumentation services’. Use of the conventional low-tender procedure, whereby these tasks are included as items in the bill of quantities, has often led to poor quality data. Is there an alternative? Yes, there is.
There are four specific reasons for assigning responsibility for field instrumentation services to personnel selected by the project owner or designer and under direct contract with the owner.
First reason – quality of data
Principal contractors may not have enough motivation to ensure quality. A few years ago a UK colleague and I put together ideas about how to maximise quality when the designer of the project has initiated the monitoring programme. We made a strong plea for using a qualifications-based selection procedure for field instrumentation services.
If you have any interest, you can download these ideas from www.geotechnicalnews.com/instrumentation_news.php (scroll down to the only entry for 2001).
Our preferred option is that the people responsible for field instrumentation services should be selected by the project owner or designer, and under direct contract with the project owner. Our publication includes many comments from the technical literature in support of a qualifications-based selection procedure, which can be useful when trying to convince decision makers to accept this method.
Second reason – cost
Colleagues in New York discuss the issue from the viewpoint of an instrumentation subcontractor to the principal construction contractor—see www.geotehnicalnews.com/instrumentation_news.php and scroll to Geotechnical Instrumentation News Sept. 2009.
They warn:
“The award of instrumentation work based on the ‘bottom line’ includes little consideration for quality, if any at all […] After the contract is awarded to a construction contractor, potential instrumentation subcontractors are invited to re-bid, so that the construction contractor can compare line item breakdowns. Instrumentation bidders revisit their costs and strip contingencies. The firm ultimately awarded the work is likely to have assumed that the more stringent specification requirements will not be enforced.”
In my own experience as an instrumentation subcontractor in US, this ‘stripping’ can be up to 20 per cent. Let’s look at whether owners get a fair deal if this happens.
As an example, if the amount assigned for field instrumentation services in the construction contractor’s tender is GBP 800,000 (USD 1.294M) the project owner pays that amount, but only receives work that costs GBP 640,000 (USD 1.035M). There’s a strong message for owners there.
Third reason – adequacy of baseline data
If construction work is likely to impact on neighbouring structures, and monitoring with instrumentation is required to mitigate the impact, there’s another important reason for favouring a contract directly with the project owner. If field instrumentation services are included in the principal construction contract, monitoring can’t start until the award of that contract. In that case there’s rarely sufficient time to establish adequate records of pre-construction behaviour (baseline data).
Structures move and groundwater regimes often change from season to season, and monitoring data cannot be interpreted correctly if adequate baseline data are not obtained.
Fourth reason – cost on multiprincipal contracts
For multi-principal contract projects, there would be one monitoring subcontractor for each principal contract, hence greater cost when compared with a single assignment.
Recommendations for tasks 1, 2 and 3
When the designer of the tunnel has initiated the monitoring programme, my recommendations for assignment of tasks 1, 2 and 3 are given in Table 1.
Options for task 4 – interpreting data
Clearly the people who initiated the monitoring programme (in this case the tunnel designer) should have a role in interpreting the data.
However, the principal contractor MUST pursue a parallel effort, and construction documents must specify that the principal contractor has the primary responsibility for interpretations and that it must stay on top of the data flow at all times.
Conclusions
I know very well that it isn’t easy to convince owners (and project managers in design firms, who supposedly have the owner’s interests at heart) that it’s in their interest to adopt the above recommendations, but it is!
Join the campaign to ensure that the people who have the greatest interest in the geotechnical monitoring and instrumentation data should be given direct line responsibility for obtaining the data.
John Dunnicliff Table 1
