Here is a story that I was told long ago–the details are shrouded in the mists of history, but the story is worth repeating for the lessons learnt are always relevant.
Dikes were being constructed on soft clays. A series of open tube piezometers (standard in those distant days) were installed in the clay to monitor pore pressure increases as the dike was constructed and to monitor pore pressure dissipation as the clay consolidated and gained sufficient strength to support the dike. The tubes were stapled to a board and a technician was instructed to read the water levels and phone the results in to the engineers of record.
One week there was no phone call from site. The engineer called to find out why. He was told ”the technician is off work as he fell of the ladder trying to read the water level in the tubes. And he broke his leg in the fall.”
The engineer immediately recognized that the high water levels implied high pore pressures in the clay and probably a low strength—the water in the tubes was so high that a step ladder was required to read the top point. This was a danger to both the technician and to the stability of the dikes. A few frantic phone calls to be assured the technician was OK and to stop construction–placement of fill—until the pore pressures could dissipate and the clay gain strength enough to support another lift.
The point of this story is that we had and we have today the technologies to instrument, to monitor, to measure, and to quantify the impacts of construction of geotechnical facilities. Thus if we are building earthworks for mine geowaste facilities such as tailings impoundments, waste rock dumps, and heap leach pads, we can observe, instrument, monitor, and proceed on the basis of information. Sometimes this may mean application of the Observational Method.
There are thus two issues:
- Who does the observing, the monitoring, and the measuring?
- How and when is this information transmitted to engineers who understand what the data means and how have power to respond?
One way is to put the professional engineer on site during construction. In most instances this is prohibitively expensive. But on a big geotechnical job, the cost is trivial. Twice I have spent extended periods on civil construction jobs involving primarily earthworks. The first was the Cannon Mine tailings impoundment 300-ft high rockfill embankment.
The second was the closure of the Operating Industries Inc. Landfill in Los Angeles. On both projects my job was simple: look at the soils, decide what to do with the soils, and make sure the soils were placed properly. In practice, it was more complex, but I know that by seeing the soil and its placement on a daily basis I was able to make timely decisions that saved my client millions.
Thus my conclusion: if you are undertaking a large, complex, and/or innovative job on a mine involving soils and rocks, what may be called geotechnical construction, make sure your consultant provides a fully qualified person, preferably a professional geotechnical engineer, to be on site as much as possible to observe, record, and make recommendations for change and response to actual conditions.