PODED-G
18 November 1976
GENERAL GUIDELINE FOR DRILLING AND
BLASTING CORAL REEF FOR ARMOR STONE
AT ENEWETOK ATOLL, M.I.
A.
PURPOSE
1.
Based on the Corps drilling and blasting experience in the Marshall
Islands provide
guidance in the planning and execution of a coral recf{
quarry operation.
Under the best controlled drilling and blasting methods
the approximate yield of armor stone size pieces remains low, or about
15 percent.
Consequently, to be sucessful in mining armor stone the quarry
operation must be rigidly controlled,
B.
ASSUMPTIONS
1.
Fully qualified individuals with proven experience shall provide
2.
Control drilling and blasting techniques will be used.
3.
Safety and accident prevention planning and protection will be
the supervision or technical direction.
closely followed.
Cc,
ITEMS TO CONSIDER
1.
Drilling and loading can be successfully done only at times of
low tide levels.
Only four to five days out of every other week will
low tides occur during the daylight hours.
2.
A potential armor stone quarry is generally located in thick reef
crusts on the ocean side of the atoll.
Visually the quarry site should be
selected where the reef is widest and surface elevations are highest.
reef rock will be thickest near the ocean and thinning toward dry land.
The
The higher the reef crust is above low tide the greater is the depth of
calcification and hardening.
3.
The reef structure decreases in hardness with depth and grades
into unconsolidated clastic sediments (silt,
sand, gravel & cobble size
particles) suitable only for concrete aggregates and fill materials.
4.
Freshly mined armor stone pieces are soft and tend to break and
crumble on handling.
Exposure of rock pieces to air for several days causes
further calcification and strengthening (like case hardening). To minimize
breakage, armor stone should be quarried and the individual pieces temporarily stored on the adjacent reef surface,