Recently released a new plugin for Spigot. This plugin aims to increase the danger of mining underground in Minecraft. A strenuous underground experience while mining deeply.
It introduces a few new concept mechanics.
Safety Checks - Force player's to reinforce their mines with wood to ensure there are not cave-ins.
Ceiling Collapses - When the player does not meet required safety checks there is a elevated probability of collapses. This will also cause player's to lose important ores.
Intelligent Mining Checks - The plugin will determine how deep a player is underground, what safety threshold they must meet, and the total safety value of the structural integrity around them.
Scaling Depth System - As a player goes further underground the safety required increases.
Light System - In the dark player's are unable to mine without proper lighting.
You can grab it over on the spigot website.
or if you're feeling adventurous...