Layout of underground chambers is determined by the structural capacity of the sandstone pillars [shown in white] to support the material above and of the limestone roof layer to clear span the space. The clear work spaces between the pillars are about sixty five feet wide.

The layout is also determined by the necessity for providing adequate access, egress and ventilation for people and vehicles.

The result is a basic planning unit of approximately four hundred by four hundred and twenty feet.

 
 
 
 
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