Within 200m you usually go through transported cover or a highly...

Within 200m you usually go through transported cover or a highly weathered rock, then into transitional rock then into fresh. Even in a Coal setting with lots of clays you are hard pressed to slump 200m of clay. A geological structure that allows toppling so the rock keeps rilling in will normally change direction and become self supporting at some point to the surface. 200m is a long way from the surface, even with clays as they are flexible. We are not talking about nil failure like in an underground mine setting where people work as that's different. In UCG we are talking about definite underground failures as a given but due to geological interpretations from drill cores we can safety model extent of failures. If not we may as well sack all Geotech Engineers and wipe it as a profession and save ourselves a lot on money.

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