Part 1: Crown 3 Mine, Illinois, USA

Part 2 (Newstan Colliery, Australia) and Part 3 (Lenina Mine, Russia) will run on ILN later this week.

In February 2006, production was able to return to normal at Freeman United Coal’s Crown 3 mine near Girard in Illinois. The mine had been previously shut for eight days following high carbon monoxide readings. The mine was closed after a “hot spot” was detected and although the exact location was unclear, the situation was soon brought under control by pumping in water and carbon dioxide after the area was sealed off using Minova’s Tekseal system.

Tekseal is a pumpable grout that allows a seal to be erected quickly and safely and also offers cost savings through reduced construction time and transport costs.

A traditional block seal takes eight to 10 man shifts to construct. A pumped seal of the same size takes about half that.

A block seal requires a large amount of work prior to construction such as hitching into the ribs and making a solid footing that may require drilling and shooting to a solid bottom. Once this preparation work has been done, the materials required for the job need to be transported to the site. In a typical working height of 2.7m, a seal requires 360, 20 x 20 x 40cm blocks, each weighing 15kg. Also, a 24-hour drying period is required when the seal is half built, with a second drying period before filling the cavity to the roof.

When using the Tekseal method, no hitching is required and the floor is taken to solid. The form work consists of two walls spaced at least 1.2m apart, depending on the height of the gallery. Each wall consists of 12cm square posts evenly spaced across the opening. Planks of 2 x 15cm in size are then nailed across the posts at 40cm centers.

The final stage of construction involves nailing or stapling brattice cloth to the inside of the form work. It is important that the cloth is overlapped at the edges to provide a seal when the Tekseal grout is pumped in. The cloth is usually nailed in place but can be secured using a metal spring attached to the top plank. Once the back wall is fully constructed, a small opening in the front wall is left as a means of egress for the construction crew.

Once this form work is complete, the Tekseal grout can then be pumped into the form work. The grout is pumped through a placer unit that ensures that the correct amount of water and air is mixed with the powder, giving the grout a specific gravity of 0.5-0.7.

The grout is pumped through a small hatch that has been left at the top of the form work. When the grout reaches the level of this hatch, it is sealed using a pre-cut length of plank. The seal is then pressured through pipes and valves that have been placed along the top of the seal. Any leaks in the formwork can be sealed using rags or paper.

At Crown 3, nine ventilation seals were constructed in less than 17 hours, which enabled the mine to restart production only eight days after closure.

Published in the December 2006 American Longwall Magazine