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DAY 66 - APRIL 26, 2010


OMB Rockfort Hearing for April 26th, 2010

Evidence in Chief of Alex Naudts; Expert on the Grout Curtain for the CCC:

  • A barrier in rock needs to divide one side from the other, and be tied to itself (as in a circle) to prevent lowering of the water table. There are many methods--concrete, plastic, ice curtains, etc. to name a few.
  • He recommends that a curtain is installed prior to any construction, in the absence of flow conditions is the most effective. Under flow conditions, there is major disruption going on so it is more desirable to construct under no flow. Most jobs (95%) are grouting under no flow conditions. Grouting under no flow is predictable if you do everything right.
  • For grout curtains at dams, you choose the best geo-technical place to put the dam. At the quarry location, once you start excavating you create flow conditions of the water.
  • When you design the grout curtain you consider the geology, testing of the permeability of the test holes to identify the porosity, angles of drilled holes, etc. If there are many tiny holes in the rock, it can be very porous, like a sponge. If the amenability of the formation will allow water through to a high degree, it shows you whether you can use regular cement based grout or if you need chemical grout which will set-up faster.
  • You can estimate the amount of grout you are going to use depending on how the apertures intersect. By grouting some primary holes you can test this and then calculate the amenability of the formation. The thicker the grout, the more difficult it is to get into the formation. It typically takes 3-4 weeks at most to design the curtain.
  • Causes for failure of "good" grout curtains; use of unbalanced grouts, erosion of silty/clay pockets, and improper grouting practices. There are a lot of grout curtains that fail over time. Limestone is some of the most variable and difficult mediums to grout into.
  • Some examples of failed curtains are Stewartville dam and the lower Baker dam. The Rockfort curtain is 3,200x40 m=128,000m squared. The anticipated failure rate at Rockfort is every 13 to 65 days. The cost to repair each failure is $2 million per occurrence because grouting under flow conditions is unpredictable and costly.
  • Grouting under flow conditions is difficult because the flowing water will dilute the cohesion of the grout and the influences of hydrostatic pressure. These conditions will blow out the grout from some seams. The water is a major disruptive force to the operation. As you start narrowing down the aperture of the curtain, the water starts moving faster (like putting your thumb on the hose). There is a point with cement based grout, will not hold.
  • Madame Chair disallows slides pertaining to the grout test under flow conditions because it was not provided in the witness statement in such detail.
  • There are various types of grouts and other solution grouts like sodium silicates, polyurethanes, acrylamides, epoxys and resins, etc. and they all have their challenges. Flow conditions can be very difficult plus they can be a vehicle for moving some of these additives downstream. Even cement can impact the PH of the water and could impact fish because they are very PH sensitive.
  • Another problem is that the curtain is like a chain which is only as strong as the weakest link. At Rockfort, if there is a blowout, you can expect a velocity very much higher than indicated, because of the mud pockets affecting the permeability.
  • Partial grout curtains do not really work very well. Naudts shows an example where a grouting operation did not really work until they had installed the last drill hole. Also at the Millville quarry in the USA, showed you don't need a big hole to allow large amounts of water to flow into the quarry.  At the Rockfort grout demonstration, if they had finished all the walls and pumped heavily, they would have seen how difficult closing the under flow conditions. If you used hot bitumen it is more environmentally friendly.
  • JDCL is planning an average permeability of 10 Lugeon. His opinion is that average permeability is a dangerous term because the chain is only as strong as the weakest link. His opinion is that the lower the number is picked then the lower the probability of. You should choose a target as low as is reasonably possible, to provide more protection. The more water you allow to go through, the higher risk of more erosion and inflow. In a project near Ottawa a tunnel was constructed in limestone and a curtain was specified to not allow more than 1 meter of water. The water table started dropping and the grout curtain did not hold back the water.
  • At the Millville water was inflowing from the Shenandoah River. They injected high amounts of grout to stop the infiltration and it didn't make much difference. They tried a number of phases over a 13-month period.  They finally managed with hot bitumen to close it but it was VERY expensive and in 2002 it again failed and has been abandoned.
  • At Burritos Rapids they tried to inject a cement-based grout, but it washed out. They increased the cohesion in the grout with additives of polyurethane, which also washed out. MOE was not happy and the project was eventually abandoned.
  • At Rockfort there is a bit of a disconnect in the plans between grouting under flow or no flow conditions in putting the curtain in. Dr Bruce originally indicated it would not be under flow conditions and then the plans changed and indicated it will be under flow conditions. The repairs would be under flow and the cost and technique is considerably more than cement based.
  • What are missing in the revised AMP is the environmental issues once moving to adding chemicals to the grouts.
  • His opinion is that the NAMP although improved, is fundamentally flawed.
  • The Chair will not hear further testimony on the water treatment, as he is not an expert witness on that subject. She hears clearly that Mr. Naudts has experience that there may be issues of impact on the water quality when grouting under flow conditions occurs.
  • Looking at the grout demonstration holes A and TB series in 1999, 15 out of 19 had serious challenges. An average of 10 days was required to complete drilling (normally it would take 2 days). The worst hole took 17 days and the best hole took 5 days. Construction grout was used to facilitate local plugging of pervious features.
  • In the series B holes should have been better but they weren't, where 3 out of 5 holes had to be downstaged (unexpected).
  • The worst hole took 14 days (very bad) and even the best hole took 10 days as an average. These holes would indicate serious problems with the formation and / or the technique.
  • C series holes were an average of 3.75 days per hole was required.
  • On the D holes and average of 4 days was required to complete the drilling.
  • The drilling criteria of the angles on drilling the holes was relaxed during the test.
  • The verification holes after 4-5 holes of grouting, showed high Lugeon numbers (high permeability), and did not even achieve the permeability targets they set.
  • His conclusion was that it would take many many years to build the curtain even in the absence of flow conditions.  The test shows it is a difficult formation.
    31% of the holes (high) encountered blockage or collapsing. 25 out of 42 holes experienced problems. The window test does not demonstrate what it was meant to. Voids and fissures were encountered in different places. All this adds up to red flags about the difficulty of the grouting job.