Emery Mills Dam Repair Update 11/5/19

Here’s update #3 from Alex Hammerle from the City of Sanford on the Emery Mills Dam project:

· As anticipated, the concrete cap was removed last Wednesday with no significant vibration noted.
· Thursday and Friday, materials and equipment were staged at the dam for the boring and grouting work.
· Boring and grouting began Monday. 16 primary locations were identified and marked. The holes are being drilled to a depth of about 13 feet, and the first hole was completed by around 10 in the morning. During the boring process, water was used to keep the bit cool and to wash drilled material out of the hole. The first hole was drilled without any water coming out on either the upstream or downstream side of the dam, so this hole did not enter any of the void areas we are concerned about. As the second location was drilled, at about 4 feet down from the surface, we began to notice some of the drill water appearing on the downstream side of the dam, indicating that the drill had entered one of the void areas. The drilling continued until the final depth was reached at around noon. Drill water continued to seep through the downstream face throughout the drilling process. At about 1:00, the contractors began pumping grout, a cement like material, into the 2nd hole. We continued to observe the areas where drill water had appeared and eventually some grout appeared at the main location where we had seen drill water. The contractor stopped pumping the grout so that the opening in the downstream face could be plugged. The opening was plugged using oakum, which is a loose fibrous material that expands as it gets moist. Oakum has many uses, but was often used to fill the gaps between logs in log homes and between the boards in wooden ships, to prevent leaking. When the hole plugging was complete, the grout pumping resumed. In all, more than 1,100 gallons of grout were pumped into the second hole before it was completely filled. This is very good news because it means that we found and filled one of the major void areas in the dam. When the grout hardens, the dam will be much more stable in this area because the grout has filled the spaces between the large stones. Also, the hardened grout should substantially reduce the amount of leakage through the dam.
· We also had Commercial Divers at the site on Monday. They were there to clean the debris from the trash racks and perform routine fall maintenance, but we also had them watching for any grout penetration in the area where the control gates are located. We wanted to ensure that grout material, if it did enter the gate area, would create problems with the gate operating mechanisms. Fortunately, no grout was observed in that area while the grout was being pumped. The control gates had to be closed for the day since we had divers in the water by the gates. After the work was completed, the gates were opened more than normal because the lake level had risen almost 9” from recent rains, and the elevated water level was beginning to encroach on the work area. We plan to lower the level by about 6” this week so that the remaining upstream work can be completed.
· Boring and grouting operations are continuing. As of this morning, 11 locations had been bored and the twelfth was underway. Only one of the locations bored Tuesday entered a void, and this one was much smaller, about 250 gallons of grout. With hole 12, some drill water has again been observed on the downstream side of the dam, so we may have found another large void. We’ll know more when we have the information on how much grout gets pumped into this hole.
· The 16 primary boring and grouting locations will probably be completed tomorrow. The plumb bobs, crack gauges, and vibration monitors are all indicating that there hasn’t been any movement in the dam since they were installed. Engineers are reviewing the data to determine if any of 9 secondary locations will need to be bored and grouted.
· We are still on schedule for beginning to raise the water on the 23rd.

Thank you to Alex for these very informative updates.

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