Study on Mechanism of Cumulative Directional Blasting of Brittle Karst Limestone in the Guizhou Province

Table 1

The lithology distribution table of the Taoziya tunnel.

	Roof depth (m)	Length (m)	Columnar	Rock stratum	Rock properties	Excavation prone problems
1	0–58	110		Clay	Gray-black, plastic, crushed stone powder, fragmentation	Collapse, blocks falling, roof fall
2	58–192	295		Mudstone	Gray-black, silty, moderately weathered carbonaceous	Loose deformation, crushing damage, collapse
3	192–243	160		Sandstone	Deep gray, fragile rock	Without self-stability, water gushing of fault
4	243–467	395		Mudstone, limestone	Gray, containing plant debris, silty sand	There are hidden caves, water gushing, mud inrush
5	467–693	480		Limestone	Gray-white, medium-weathered limestone, hard rock	Rock burst, loose deformation, fly rocks
6	673–762	430		Limestone	Dark gray, broken rock, hard rock	Rock burst, gas outburst, high-energy water inrush
7	762–778	360		Marl, limestone	Black, carbonaceous	Loose deformation, crush damage