Trench Blasting Guide
Document type: Guide

Trench Blasting
with DYNAMITE

A TRADITION OF INNOVATION

Dyno Nobel’s roots reach back to every signiﬁcant in-
novation in explosives safety and technology. Today,
Dyno Nobel supplies a full line of explosives products
and blasting services to mines, quarries and contractors
in nearly every part of the world.

DYNAMITE
 PRODUCT OF CHOICE
 FOR TRENCH BLASTING
One explosive product has survived the test of time to
become a true classic in the industry. DYNAMITE! The
dynamite products manufactured today by Dyno Nobel
are similar to Alfred Nobel’s original 1860s invention
yet, in selected applications, they outperform any other
commercial explosives on the market. The high energy,
reliability and easy loading characteristics of dynamite
make it the product of choice for difﬁcult and demand-
ing trench blasting jobs. Look to Unigel®, Dynomax Pro®
and Unimax® to make trench blasting as effective and
efﬁcient as it can be.

DISCLAIMER
The information set forth herein is provided for informational purposes
only. No representation or warranty is made or intended by DYNO NOBEL
INC. or its afﬁliates as to the applicability of any procedures to any par-
ticular situation or circumstance or as to the completeness or accuracy of
any information contained herein. User assumes sole responsibility for all
results and consequences.

®
Cover photo depicts a trench blast using Primacord detonating cord, MS
 ®
Connectors and Unimax dynamite.

SAFE BLASTING REMINDERS

Blasting safety is our ﬁrst priority. Review these remind-
ers frequently and make safety your ﬁrst priority, too.
• Dynamite products will provide higher energy value
than alternate products used for trenching due to their
superior energy, velocity and weight strength.
• All explosives bearing the 1.1 UN classiﬁcation (High
Explosives) are sensitive to shock and heat; therefore,
dynamites must be treated with care. They must never
be removed from the factory cartridge nor should they
ever be tamped vigorously.
• Read and understand the “Always and Nevers” docu-
ment contained in each case of Dyno Nobel dynamite.
When in doubt, always consult the manufacturer.

Causes of Unsafe and Ineffective Trench Blasting
• Drilling Accuracy: Check every borehole for borehole
drift from vertical with instrument or inverted ﬂashlight on
loading tape. Borehole deviation is a signiﬁcant safety
problem because of the possibility of ﬂyrock, which is
compounded in trench blasting due to heavy conﬁnement
and close proximity of all the holes.
• Underloading Boreholes: Shoot the trench on paper
with the recommended formula for column height, pow-
der factor, stemming and delay pattern before drilling and
loading the shot. In addition, test shooting a small section
of the trench will improve hole pattern and product selec-
tion success.
• Overloading Boreholes: Consider using blasting mats
or debris-free dirt cover for added safety against ﬂyrock.
• Geological Analysis: Failure to properly evaluate the
rock properties, prominent seams or joining planes may
cause poor results.
• Improper Product Selection: Using explosives that
deadpress, that have insufﬁcient energy per unit or too
little density may cause product failure or poor breakage.

GUIDELINES FOR SUCCESSFUL

EXPLOSIVES SELECTION
Successful trench blasting depends upon proper ex-
plosive selection, correct powder factor, proper vertical
explosives distribution, correct delay pattern and drilling
accuracy.

UNIGEL is recommended for rock conditions that are soft
to medium hard, horizontally bedded, laminated and/or
fractured formations and where water conditions are not
excessive.
DYNOMAX PRO is recommended when saturated ground
or severe water conditions are encountered, where drill
patterns are reduced for controlled blasting or in hard,
massive rock formations. Dynomax Pro should be con-
sidered where dead pressing or propagation is a potential
problem.
UNIMAX is recommended for all trenching applications
where soft, medium, hard and very hard rock are encoun-
tered. Drill patterns may be adjusted to accommodate
rock types. Unimax is best suited for massive rock forma-
tions, surface or moderate water conditions, and where
drill patterns can be kept within design parameters.

The best initiation system for trench blasting, electric or
nonelectric, uses detonators designed to resist transient
dynamic shock. Dyno Nobel NONEL® and Electric Super
detonators have built-in safeguards to minimize damage
from dynamic shock.

SUBDRILLING
Subdrilling is required for proper ﬂoor control and is
dependent on the depth of the trench.
• Trench depths of 4’ to 12’: subdrilling = 3’
• Trench depths over 12’: subdrilling = 4’
Note: these recommendations are based on borehole
diameters of 3.5” or less.

L TRENCH BLASTING

POWDER FACTOR
 Power factor is expressed as pounds of explosive per cu-
 bic yard of rock and is depth dependent. Cubic yardage
 is calculated: Burden (ft) x Spacing (ft) x Hole Depth (ft)
 (not including subdrill) ÷ 27
 • Trench depths of 4’ to 12’: powder factor = 3.5
 • Trench depths of 12’ to 20’: powder factor = 4.0
 • Trench depths over 20’: powder factor = 5.0
 Notes:
 1 - Trench depth does not include subdrilling; hole
 depth does.
 2 - In trenches where the overburden is not removed,
 the overburden is included in the cubic yard calculations.
 3 - These recommendations are based on borehole
 diameters of 3.5” or less.
 4 - Recommended subdrill is 6” more than the trench
 advance.
 5 - Recommend no more than 1” difference between the
 borehole diameter and powder diameter.

STEMMING
 Stemming material should always be clean, minus ⅜”
 crushed stone to improve fragmentation and reduce
 ﬂyrock potential. Drill cuttings will yield less than satisfac-
 tory results and increase the potential of ﬂyrock and poor
 blasting results.
 Stemming depths should be at least 20 times the bore-
 hole diameter -or- one foot below the top of the rock with
 overburden, when the depth of the overburden is at least
 20 times the borehole diameter.
 DECKING
 In boreholes that are decked, the decks should consist
 of at least 2.5 feet of clean, minus ⅜” crushed stone to
 avoid interaction of explosive charges.
 The ﬁring sequence should be top-to-bottom. Top deck
 ﬁrst, bottom deck last.

EXPLOSIVE COMPARISON

 DYNAMITE EMULSION ANFO

 DYNOMAX PRO

 BLASTEX

 DYNO TX

 DYNOMIX
 UNIMAX

Density UNIGEL
 1.51 1.45 1.30 1.26 1.17 0.82
 DYNOMAX PRO

 BLASTEX

 DYNO TX

 DYNOMIX
 UNIMAX

 UNIGEL

Energy
RWS
 1.20 1.20 1.09 0.84 1.14 1.00
 DYNOMAX PRO

 BLASTEX

 DYNO TX
 UNIMAX

 DYNOMIX
 UNIGEL

Energy
RBS
 2.10 2.10 1.72 1.29 1.63 1.00

 FOUR REASONS FOR POOR TRENCH BLASTING

DYNAMITE EMULSION ANFO

 DYNOMAX PRO

 BLASTEX

 DYNO TX

 DYNOMIX
 UNIMAX

Detonation UNIGEL
Velocity
 ft/sec 19,700 19,700 14,100 16,400 16,400 12,800
 m/sec 6,000 6,000 4,300 5,000 5,000 3,900
 DYNOMAX PRO

 BLASTEX

 DYNO TX

 DYNOMIX
 UNIMAX

 UNIGEL

 Detonation
 Pressure
 Kbars 136 130 60 79 73 31
 DYNOMAX PRO

 DYNOMIX
 BLASTEX

 DYNO TX
 UNIMAX

 UNIGEL

 Gas
 Volume
 moles/kg 32 32 37 44 32 43

1. Underloading the boreholes.
2. Overloading the boreholes.
3. Failure to deck through a prominent seam or joint.
4. Poor product selection for the application.

UNIMAX
 ®
 TECHNICAL
Best All Around
EXTRA GELATIN NITROGLYCERIN DYNAMITE
MSDS #1019

 2 x 16 Convolute Shell Tamptite

 Properties

 Density (g/cc) 1.51

 Energy (cal/g) 1,055
 (cal/cc) 1,510

 Relative Weight Strength 1.20

 Relative Bulk Strength 2.10

 Velocity (ft/sec) 19,700
 (m/sec) 6,000

 Detonation Pressure (Kbars) 136

 Gas Volume (moles/kg) 32

 Water Resistance Excellent

 Fume Class IME1 & NRCan1

 Unimax is susceptible to sympathetic deto-
 nation when used in very wet conditions.

INFORMATION
Packaging
 Diameter x Length Cartridge Cartridge
 Weight Weight
 inches mm lbs kg
 1x 8 25 x 200 0.34 0.16
1⅛ x 8 29 x 200 0.44 0.20
1¼ x 8 32 x 200 0.54 0.25
1¼ x 16 32 x 400 1.07 0.49
1½ x 8 40 x 200 0.77 0.35
1¾ x 8 45 x 200 1.05 0.48
 2x 8 50 x 200 1.37 0.62
 2 x 16 50 x 400 2.74 1.24
2¼ x 16 60 x 400 3.47 1.57
2½ x 16 65 x 400 4.28 1.94
2¾ x 16 70 x 400 5.18 2.35
 3x 8 75 x 200 3.08 1.40
 3 x 16 75 x 400 6.17 2.80

Borehole Loading Calculation
 Explosive Pounds of Kilograms
 Diameter UNIMAX per of UNIMAX
 Foot of Blast- per Meter of
inches (mm) hole Blasthole

 1 (25) 0.51 0.76
1⅛ (29) 0.65 0.97
1¼ (32) 0.80 1.19
1½ (40) 1.16 1.72
1¾ (45) 1.57 2.34
 2 (50) 2.06 3.07
2¼ (60) 2.60 3.87
2½ (65) 3.21 4.78
2¾ (70) 3.89 5.79
 3 (75) 4.63 6.89

DYNOMAX PRO
 ®

Best In Water
DESENSITIZED EXTRA GELATIN
NITROGLYCERIN DYNAMITE
MSDS #1019

 2 x 16 Spiral Tube Shell with Tapered End

 Properties

 Density (g/cc) 1.45

 Energy (cal/g) 1,055
 (cal/cc) 1,510

 Relative Weight Strength 1.20

 Relative Bulk Strength 2.10

 Velocity (ft/sec) 19,700
 (m/sec) 6,000

 Detonation Pressure (Kbars) 130

 Gas Volume (moles/kg) 32

 Water Resistance Excellent

 Fume Class Not for under-
 ground use

 Dynomax Pro minimizes sympathetic deto-
 nation when used in very wet conditions.

TECHNICAL INFORMATION
Packaging
 Diameter x Length Cartridge Cartridge
 Weight Weight
 inches mm lbs kg
 1x 8 25 x 200 0.33 0.15
1¼ x 8 32 x 200 0.50 0.23
1¼ x 16 32 x 400 1.03 0.47
1½ x 8 40 x 200 0.75 0.34
1¾ x 8 45 x 200 1.00 0.45
 2x 8 50 x 200 1.30 0.59
 2 x 16 50 x 400 2.60 1.18
2¼ x 16 60 x 400 3.30 1.50
2½ x 16 65 x 400 4.00 1.81
2¾ x 16 70 x 400 5.00 2.27
 3x8 75 x 200 3.00 1.36
 3 x 16 75 x 400 6.00 2.72
All Dynomax Pro shells have a built-in capwell, and in-
corporate a barrier ﬁlm to reduce nitroglycerin exposure.

Borehole Loading Calculation
 Explosive Pounds of Kilograms of
 Diameter Dynomax Pro Dynomax Pro
 per Foot of per Meter of
 inches (mm) Blasthole Blasthole

 1 (25) 0.49 0.73
 1¼ (32) 0.77 1.15
 1½ (40) 1.11 1.65
 1¾ (45) 1.51 2.25
 2 (50) 1.97 2.93
 2¼ (60) 2.50 3.72
 2½ (65) 3.09 4.61
 2¾ (70) 3.73 5.55
 3 (75) 4.44 6.61

UNIGEL
 ®
 TECHNICAL
Most Economical
SEMI-GELATIN NITROGLYCERIN DYNAMITE
MSDS #1019

 2 x 16 Bullet Nose Tube Shell

 Properties

 Density (g/cc) 1.30

 Energy (cal/g) 955
 (cal/cc) 1,240

 Relative Weight Strength 1.09

 Relative Bulk Strength 1.72

 Velocity (ft/sec) 14,100
 (m/sec) 4,300

 Detonation Pressure (Kbars) 60

 Gas Volume (moles/kg) 37

 Water Resistance Good

 Fume Class IME1 & NRCan1

 Unigel is susceptible to sympathetic deto-
 nation when used in very wet conditions.

INFORMATION
Packaging
 Diameter x Length Cartridge Cartridge
 Weight Weight
 inches mm lbs kg

 1x8 25 x 200 0.30 0.14
1⅛ x 8 29 x 200 0.38 0.17
1¼ x 8 32 x 200 0.46 0.21
1½ x 8 40 x 200 0.66 0.30
 2x8 50 x 200 1.18 0.54
 2 x 16 50 x 400 2.36 1.07
2¼ x 16 60 x 400 2.99 1.36
2½ x 16 65 x 400 3.69 1.67
2¾ x 16 70 x 400 4.47 2.03
 3 x 16 75 x 400 5.3 2.41

Borehole Loading Calculation
 Explosive Pounds of Kilograms
 Diameter UNIGEL per of UNIGEL
 Foot of Blast- per Meter of
inches (mm) hole Blasthole

 1 (25) 0.44 0.65
 1⅛ (29) 0.56 0.83
 1¼ (32) 0.69 1.03
 1½ (40) 1.00 1.49
 1¾ (45) 1.36 2.02
 2 (50) 1.77 2.63
 2¼ (60) 2.24 3.33
 2½ (65) 2.77 4.12
 2¾ (70) 3.35 4.98
 3 (75) 3.98 5.92

SHOT DIAGRAM
2.5 ft Straight Line Pattern
Maximum trench size for this pattern: 2.5 ft wide x
10.0 ft deep. This pattern is generally used for narrow
and shallow trenches. To minimize risk of propagation,
only use Dynomax Pro in this pattern.

 (view from above, not to scale)

Typical ﬁring sequence of holes

Problems that typically occur when the trench is too wide
or too deep for this pattern.

SHOT DIAGRAM
2.5 ft x 4.5 ft Staggered Pattern
Maximum trench size for this pattern: 5.0 ft wide x 15
ft deep. This pattern is generally used as trenches get
wider and/or deeper than those using straight line pat-
terns.

 (view from above, not to scale)

Typical ﬁring sequence of holes

Problems that typically occur when the trench is too wide
or too deep for this pattern.

SHOT DIAGRAM
2.5 ft x 4.5 ft Box Pattern
Maximum trench size for this pattern: 5.0 ft wide x 20
ft deep. This pattern is generally used as trenches get
wider and/or deeper than those using staggered patterns.
To minimize risk of propagation, only use Dynomax Pro.

 (view from above, not to scale)

Typical ﬁring sequence of holes

Problems that typically occur when the trench is too wide
or too deep for this pattern.

SHOT DIAGRAM
2.5 ft x 5.0 ft Diamond Pattern (5 Dice)
Maximum trench size for this pattern: 5.0 ft wide x
25.0 ft deep. This pattern is generally used as trenches
get wider and/or deeper than those using box patterns.

 (view from above, not to scale)

Typical ﬁring sequence of holes

Problems that typically occur when the trench is too wide
or too deep for this pattern.

SHOT DIAGRAM
3.0 ft x 3.0 ft Three Hole Box Pattern
Use this pattern for trenches 6.0 ft and wider x 25.0 ft
and deeper. This pattern is generally used as trenches get
wider and/or deeper than those using three spot patterns.
To minimize risk of propagation, only use Dynomax Pro.

 (view from above, not to scale)

Typical ﬁring sequence of holes

Typical results

Weights of Various Solid Materials

 Weight Weight Loose Weight
 lbs/ft3 lbs/yd3 lbs/yd3

Basalt 180-185 4860-5075 —
Bauxite 100-160 2700-4325 2020-3240
Diabase 160-185 4200-5075 —
Dolomite 175-180 4725-4860 —
Granite 170 4500 3000-2520
Gypsum 145-205 3915-5535 —
Limestone, massive/hard 160 4200 —
Limestone, seamy/punky 150 4000 2680
Limestone 120-145 3240-3920 2400-2900
Sandstone 155 4140 2980-2610
Shale, riprap 150-175 4050-4725 —
Traprock 185 5075 3400

 Speciﬁc Swell Percent Suggested
 Gravity Factor of Swell Dynamite*

Basalt 2.8-3.0 — — Unimax
Bauxite 1.6-2.5 .75 33 Unimax
Diabase 2.6-3.0 — — Unimax
Dolomite 2.8-2.9 — — Unimax
Granite 2.7 .67-.56 50-80 Unimax
Gypsum 2.3-3.3 — — Unigel
Limestone, massive/hard 2.6 .60-.57 67-75 Unimax
Limestone, seamy/punky 2.4 .67 50 Unigel
Limestone 1.9-2.1 .74 35 Unigel
Sandstone 2.5 .72-.63 40-60 Unigel
Shale, riprap 2.4-2.8 .75 33 Unigel
Traprock 3.0 .67 50 Unimax
* Use Dynomax Pro where water saturated conditions exist, regard-
less of rock type, to minimize the risk of propogation.

We’d like to

a few myths
 EXPLODE
about the future of
 DYNAMITE
myth: Dynamite will soon be unavailable.
fact: Alfred Nobel invented dynamite over 130 years ago and
Dyno Nobel has been manufacturing it ever since. Both Dyno
Nobel and its afﬁliated companies are committed to supplying
dynamite far into the future.

myth: Dynamite can be easily replaced with other explosives.
fact: Dynamite is superior to any other explosive in difﬁcult
blasting conditions. Its high energy, proven reliability and rug-
gedness dramatically reduce the risk of poor blast results. These
unique performance characteristics will always separate dyna-
mite from other explosives.

myth: Dynamite is too expensive.
fact: In difﬁcult conditions, the consequences of not using
dynamite often include excessive digging time, oversize muck,
undetonated explosives in the muck pile, poor fragmentation,
not pulling to grade and missed holes. All of which can be very
expensive. As we have in the past, Dyno Nobel will continue to
sell dynamite at a fair price.

 Dyno Nobel Inc.
 2650 Decker Lake Boulevard, Suite 300
 Salt Lake City, UT 84119
 800 732 7534

 www.dynonobel.com

 © Dyno Nobel 2003
 REVISED FEBRUARY 2006