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EVERY DUNGEON IS A DEATHTRAPOnly a Suicidal Idiot would go into a Dungeon. Most D&D Dungeons fail on the grounds that if you apply real world subsidence rules, the damn things would have caved in during construction.100% Subsidence: Width of Cave/Cover depth=1.1-1.410% Subsidence: Width of Cave/Cover Depth=0.1-0.5The Range depends on the Rock type. The High Thresholds are more likely Granite, midway is Sandstone and Limestone, while the low end of the scale is Dirt/Gravel.That means that a cave with a 50' cross section sitting below 20' of rock has a value of 2.5 (well in excess of 100% Subsidence): Such a cave began to transfer the effects of subsidence to the surface back at 10% so the ground will be sagging and unless this chamber is propped up with columns it will collapse like a sinkhole. Likewise a 10' wide tunnel below 20' of rock has a value of 0.5 (at the upper limit of 10% subsidence). Here the stress of failure has reached the surface - Fine cracks that will probably not be visible at the surface due to topsoil. REDUCING SUBSIDENCE TO 10%Column Width= 0.12 x cover depthGoaf (space between columns) width = 0.6 x cover depth.What does it mean? Our 50' cross-section cave above can be reduced to a subsidence of 10% by including at time of construction columns to support the ceiling.Column Width: 0.12 x 20' = 2.4'Column Spacing: 0.6 x 20' = 12'that is a Chamber supported by 2.4' wide columns spaced 12' apart. Inflict some damage to those columns (beyond the damage inflicted by the existing subsidence) and the entire Dungeon will have to be tested (%percentage roll for each chamber and corridor) as to whether it has collapsed with the mountain coming down on the Adventurers.SUBSIDENCE AT THE SURFACE
Subsidence TypesStepped Terraces: The collapse of large sections separated from one another can result in this.Cracking at the Surface: This is associated with a change in the rate of subsidence.Chimneys and Vertical Shafts: Often associated with the mining of irregular shapes.Slumping: This is more likely to occur where the surface material is loose - Dirt or Gravel.Depression: Often associated with groundwater extraction resulting in gradual compression of the water bearing strata (often associated with wells in cities where surface changes of up to 22' can occur over a period of two hundred years.Sinkholes: Mostly limestone removal under a Karst layer but also the hydrological removal of salt deposits as brine in coastal soils.
