One of the main advantages with a wider shield is a reduction in the number of components on the face, an improvement of around 11%, according to Horst Ringleff, division manager roof support systems.

DBT's standard Pittsburgh seam shields are normally 1.75m in width and weigh about 23 tons. The new 2m shield weighs 25 tons.

"For Pittsburgh seam shields you do not need a very high support density. Therefore, sufficient support density can be generated in the 2m width shield without using the largest legs currently available from DBT. However, all the other cylinders in the shield are bigger compared to the standard," Ringleff said.

One of the design challenges to be overcome was ensuring that the hinges could withstand higher forces. These are the connections between canopy, gob shield, lemniscate links and base.

"On a wider shield, the wider stance presents the possibility to generate higher torsional stresses. If you simulate one-sided (offset) loading for example, you get higher forces at the hinge points. On the positive side, with a wider shield you get more space inside the shield. This additional space creates more opportunities for mounting the hydraulic and electronic controls in areas that provide easy access for maintenance. Also the hosing configuration can be made much cleaner which results in less damage during operation," he said.

To accommodate the wider shield, pan lines also have had to be made wider. DBT will be monitoring this longwall closely to see how the flexibility of the pan line is affected in situ.

The wider shield is predicted to deliver a 15-20% time saving in face relocations, depending on various factors. Effectively for every ten 1.75m shields moved, a mine could move roughly 8-9 of the 2m shields. In addition, along with the reduction in the number of shields on the face comes an equivalent reduction in maintenance costs. The combined reduction in face relocation times and maintenance costs will help the Cumberland mine to improve its profitability.

In addition, through its new DBT Diesel division in Australia, DBT is now able to supply the most appropriate shield mover, Ringleff said.

Looking ahead, DBT has no plans to go to wider shields and Ringleff predicts that for the next five years 2m shields would be sufficient. He said at seam heights of greater than 6m other methods of support might become an option.