Hole Design for Rocks

General Concepts For Breaking Of Boulders

d 38 - 44 mm
1 1 / 2 "- 1 3 / 4 "
D 70 % of Height
...
(1) Soft Rock
(Tensile Strength: < 60 kg/cm² : 85 psi)
...
(2) Middle Hard Rock
(Tensile Strength: 60 - 100 kg/cm² : 80 - 140 psi)
...
(3) Hard Rock
(Tensile Strength: > 100 kg/cm² : 140 psi)

Underground Excavation

d 38 - 44 mm
1½ "- 1¾ "
L 30 - 60 cm
1 '- 2 '
D Shown in Figure
...
(1) Above ground boulder
d 38 - 51 mm
1½ "- 2 '
L 60 - 90 cm
2 '- 3 '
D 90 % of Height
...
(2) Mostly below ground boulder   (3) Underground boulder

Splitting of Large Boulders

d 32 - 35 mm 44 - 51 mm
1¼ "- 1 3/8 " 1¾ " - 2 "
L 30 - 40 cm 60 - 90 cm
1 '- 1 ' 4 " 2 '- 3 '
D 70 % of Height
...

Cutting Into Slabs

d 32 - 35 mm 44 - 51 mm
1¼ "- 1 3/8 " 1¾ " - 2 "
L 20 - 30 cm 40 - 50 cm
8 "- 1 ' 1'4 "- 1'8"
D 90 % of Height
...

Breaking of Virgin Rock

d 44 - 51 mm
1¾ " - 2 "
L 1 30 - 40 cm
1 '- 1'4"
L 2 60 - 90 cm
2 '- 3 '
D Add 5 % of Height
80° - 90°
...

The toe should be drilled at closer hole spacing and successively broken from the front row. No drilling will cause poor breakage. The front holes (up to the sixth row) may be simultaneously filled in. It is more effective for removal to fill in one hole and then each two rows (2, 3) after a delay of 6 - 20 hours.

Trenching And Tunnelling

d 38 - 51 mm
1½ "- 2 "
L 30 - 60 cm
1 '- 2 '
D 1 - 1.8 m
3 '- 6 '
45° - 60°
...
Reliever holes are necessary when trench is deep
...
Repeat the same procedure for deeper case
d 38 - 51 mm
1½ "- 2 '
L 1 40 - 60 cm
1'4 "- 2 '
L 2 30 - 40 cm
1 '- 1'4"
D 1 - 1.8 m
3 '- 6 '
...
d 38 - 44 mm
1½ "- 1¾ "
L 30 - 60 cm
1 '- 2 '
...