Below you'll find the
Workman's Compensation Board's regulations for excavations. These regs are from British
Columbia, Canada. But they apply in almost all jurisdictions of North America. Please feel
free to print out copies for your own use.
Deeper is not cheaper, and to shallow is malo.
(1) Excavation work must be in accordance with the written instructions of a professional
(a) the excavation is more than 6 m (20 ft) deep,
(b) support structures other than as specified in section 20.81 are used in the excavation,
(c) an improvement or structure is adjacent to the excavation,
(d) the excavation is subject to vibration or hydrostatic pressure likely to result in
ground movement hazardous to workers, or
(e) the ground slopes away from the edge of the excavation at an angle steeper than 3
horizontal to 1 vertical.
(2) The written instructions required in subsection (1) must
(a) be certified by a professional engineer,
(b) be available at the site, and
(c) specify the support and sloping requirements, and the subsurface conditions expected
to be encountered.
[Amended by B.C. Reg. 253/2001, effective January 28, 2002.]
20.79 Underground utilities
(1) Before excavating or drilling with powered tools and equipment, the location of all
underground utility services in the area must be accurately determined, and any danger to
workers from the services must be controlled.
(2) Excavation or drilling work in proximity to an underground service must be undertaken
in conformity with the requirements of the owner of the service and with the requirements
of the applicable regulations of the provincial or federal authority having jurisdiction.
(3) Pointed tools must not be used to probe for underground gas and electrical services.
(4) Powered equipment used for excavating must be operated so as to avoid damage to
underground utility services, or danger to workers.
20.80 Removing nearby hazards
Trees, utility poles, rocks and similar objects adjacent to an area to be excavated must
be removed or secured if they could endanger workers.
20.81 Sloping and shoring requirements
(1) Before a worker enters any excavation over 1.2 m (4 ft) in depth or, while in the
excavation, approaches closer to the side or bank than a distance equal to the depth of
the excavation, the employer must ensure that the excavation sides are sloped or supported
as specified by a professional engineer, or that the sides of the excavation are
(a) sloped at angles, dependent on soil conditions, which will ensure stable faces, but in
no case may the slope or combination of vertical cut and sloping exceed that shown in Figure 20-1
(b) benched as shown in Figure 20-2
(c) supported in accordance with the minimum requirements of section 20.85 or
(d) supported by manufactured or prefabricated trench boxes or shoring cages, or other
(2) If the end of a trench over 1.2 m (4 ft) in depth is not adequately sloped, end
shoring must be installed unless
(a) a worker in the trench is not required to approach closer to the end of the trench
than a distance equal to the depth of the trench at that end,
(b) where, for the prevailing soil conditions at the end of the trench, the permissible
spacing of uprights equals or exceeds the width of the trench, or
(c) otherwise authorized in writing by a professional engineer.
(3) If end shoring is required, the walers for the end shoring must be installed to bear
against the walers that extend along the sides of the trench, or in a manner that will
provide equivalent structural restraint.
(4) End shoring must be designed by a professional engineer if the end shoring waler
length exceeds 1.8 m (6 ft).
(5) Shoring must extend from at least 30 cm (1 ft) above ground level to as close to the
bottom of the trench as the material being installed will allow, but in no case more than
60 cm (2 ft) from the bottom.
(6) Shoring need not extend above ground level where traffic crossing plates need to be
used, provided that other measures are taken to prevent excavated or other material from
entering the excavation.
[Amended by B.C. Reg. 253/2001, effective January 28, 2002.]
20.82 Timber shoring and grades
(1) Timber shoring materials must be lumber graded Number 2 or better from the following
species groups: Douglas fir-larch, hemlock-fir, spruce-pine-fir or coast-Sitka-spruce.
(2) All lumber must be graded to the National Lumber Grades Authority Standard Grading
Rules for Canadian Lumber, or other grading rules acceptable to the board.
20.83 Safe shoring procedures
(1) Shoring materials must be installed from the top down and removed in reverse order.
(2) Workers must not enter an excavation to remove shoring materials if ground conditions
have deteriorated so as to make entry for shoring removal unsafe.
(3) Shoring or manufactured or prefabricated support systems must be installed in firm
contact with the faces of the excavation, and in a manner which ensures no loss of soil
from behind or below the bottom of the shield or shoring while the excavation is open.
(4) Unless otherwise indicated by the manufacturer or a professional engineer, in writing,
voids between the shoring and the excavation face must be backfilled or blocked.
20.84 Manufactured shoring
Manufactured equipment for supporting an excavation must be used, inspected, repaired, and
maintained in accordance with the manufacturer's instructions or those of a professional
20.85 Trench support structures
(1) Trench support structures, other than those designed by a professional engineer, must
comply with Table 20-1 for the
following relevant soil conditions:
Soil type Description of soil
A hard and solid
B likely to crack or crumble
C soft, sandy, filled or loose
Table 20-1 is to be used
for a combination of supporting and sloping, the selection of shoring elements must be
based on the overall depth of the excavation, and the arrangement must conform to Figure
(3) Cross braces and trench jacks must be installed in a horizontal position and must be
secured against dislodgment.
(4) The minimum number of cross braces at each cross bracing location is determined by the
trench depth as follows:
Depth at location Number of braces
up to 2.4 m (8 ft) 2
2.4 m to 3.7 m (8 ft to 12 ft) 3
3.7 m to 4.6 m (12 ft to 15 ft) 4
4.6 m to 6 m (15 ft to 20 ft) 5
Table 20-1 includes
an allowance for 60 cm (2 ft) of spoil pile adjacent to the excavation. In such cases
shoring or shielding will be deemed acceptable if rated adequate for a tabulated depth
equal to the depth of the excavation plus the average depth of the spoil pile minus 60 cm
(2 ft). For other systems consult the manufacturer's instructions.
(5) At each cross bracing location the cross braces must be less than 1.2 m (4 ft) apart,
and the uppermost cross brace must be within 60 cm (2 ft) of ground level.
(6) Manufactured trench jacks extended by a screw, hydraulic or pneumatic means must be
used in accordance with the instructions of the manufacturer or a professional engineer.
(7) Hydraulic or pneumatic trench jacks must have a means of ensuring that they will not
collapse in the event of loss of internal pressure.
(8) Uprights must not spread outwards more than 15 degrees from the vertical when viewed
along the trench.
(9) Plywood may be substituted for two inch thick shoring elements provided that
(a) the plywood is not less than 19 mm (3/4 in) thick,
(b) the trench is not over 2.7 m (9 ft) in depth,
(c) uprights are installed at not over 60 cm (2 ft) centres,
(d) cross braces do not bear directly on plywood, and
(e) cross braces bearing on uprights or walers are located at all joints in plywood
20.86 Spoil piles
If the average depth of a spoil pile which is adjacent to a supported excavation exceeds
60 cm (2 ft), the selection of the shoring or shielding must take into account the
resulting increase in lateral soil pressure.
20.87 Entry and exit
(1) Safe means of entry and exit must be provided for an excavation a worker enters.
(2) If workers are required to enter a trench over 1.2 m (4 ft) deep, the safe point of
entry and exit must be located within 8 m (25 ft) of the workers and the excavation must
be safely supported or sloped to the entry and exit location.
(3) Walkways must be secured to prevent dislodgment.
(4) The open side of an access route into an excavation used by mobile equipment must have
If an excavation is a hazard to workers, it must be effectively covered or guarded.
20.89 Excavation crossings
A walkway across an excavation must be at least 50 cm (20 in) wide, and if crossing an
excavation over 1.2 m (4 ft) deep, be equipped with guardrails on both sides.
20.90 Excavated materials
(1) Excavated material must be kept back a minimum distance of 60 cm (2 ft) from the edge
of a trench excavation and 1.2 m (4 ft) from any other excavation.
(2) Under no circumstances may excavated material be piled so that it endangers workers.
20.91 Use of skips or buckets
If a skip or bucket is used to remove material from an excavation, horizontal shoring
members must be shielded from dislodgment with vertical planking.
20.92 Scaling and trimming
The sides of an excavation must be scaled and trimmed or otherwise stabilized to prevent
slides of material or falls of rock which could endanger workers.
20.93 Height limitations
In pits, quarries and similar excavations the height of unstable faces must not exceed the
maximum safe reach of the excavating equipment being used.
20.94 Positioning equipment
Whenever possible, power machines excavating banks must be positioned so that the operator
is on the side away from the bank and with the boom positioned closest to the side of the
20.95 Water accumulation
(1) Water must not be allowed to accumulate in an excavation if it might affect the
stability of the excavation or might endanger workers.
(2) Erosion of slopes by surface water must be prevented if workers may be endangered.
Table 20-1: Trench support structures
Size and spacing of members1
(metric figures)UPRIGHTSWALERSCROSS BRACESTrench depth (m)Minimum dimensions (mm)2Maximum
spacing (m)Minimum dimensions (mm)2Maximum vertical spacing (m)Width of trench (m) Up to
1.8 1.8-3.7 Minimum dimensions (mm)2Maximum spacing (m)VerticalHorizontalType A:
Hard and solid soil1.2-3 338 x 2351.889 x 1401.289 x 89140 x 1401.21.83-4.638 x
2351.2140 x 1401.289 x 140140 x 19126.96.36.199-638 x 235Close tight140 x 1401.2140 x 191191
x 1911.21.8Type B: Soil likely to crack or crumble1.2-3 338 x 2351.289 x 1401.289 x
140140 x 1401.21.83-4.638 x 2350.9140 x 1911.2140 x 140140 x 19188.8.131.52-638 x 235Close
tight140 x 1911.2140 x 191191 x 1911.21.8Type C: Soft, sandy, filled or loose soil1.2-3
338 x 235Close tight140 x 1911.2140 x 140140 x 1911.21.83-4.638 x 235Close tight191 x
1911.2140 x 191191 x 19184.108.40.206-664 x 235Close tight191 x 2411.2140 x 191191 x 2411.21.8
Size and spacing of members1 (imperial figures)UPRIGHTWALERSCROSS
BRACESTrench depth (feet)Minimum dimensions (inches)2Maximum spacing (feet)Minimum
dimensions (inches)2Maximum vertical spacing (feet)Width of trench (feet) Up to 6 6-12
Minimum dimensions (inches)2Maximum spacing (feet)VerticalHorizontalType A: Hard and
solid soil4-10 32 x 1064 x 6 444 x 46 x 64610-152 x 1046 x 644 x 66 x 84615-202 x
10Close tight6 x 646 x 88 x 846Type B: Soil likely to crack or crumble4-10 32 x
1044 x 644 x 66 x 64610-152 x 1036 x 846 x 66 x 84615-202 x 10Close tight6 x 846 x 88 x
846Type C: Soft, sandy, filled or loose soil4-10 32 x 10Close tight6 x 846 x 66 x
84610-152 x 10Close tight8 x 846 x 88 x 84615-203 x 10Close tight8 x 1046 x 88 x 1046
1 The dimensions shown are minimum and
must be increased if necessary to meet job conditions.
2 The dimensions of members in millimetres are actual dimensions for surfaced dry
materials. The dimensions in inches are the nominal values for surfaced dry materials.
3 Trenches less than 1.2 m (4 ft) deep must be shored when hazardous ground movement may
be expected, as in ground subject to hydrostatic pressure or vibration.
4 Walers may be omitted in trenches not exceeding 2.4 m (8 ft) in depth provided that it
has been confirmed that the soil is sufficiently hard and solid to safely permit waler
deletion, and provided that the trench is not in proximity to previously excavated ground.
Sloping in lieu of shoring
Case 1 (trench or bulk
excavation) - maximum slope of excavated face, shown as line AB, in hard and solid soil is
3 horizontal to 4 vertical.
Case 2 (trench or bulk excavation), maximum height of vertical portion, shown as line AB
is 1.2 metres (4 feet).
For Case 2 (trench or bulk excavation), the maximum permissible slope of the excavated
face BC for the corresponding height of the lower vertical cut AB is as follows:
Height of line ABMaximum slope of
line BC (in hard and solid soil)centimetresfeetup to 30up to 11 horizontal (H) to 1
vertical (V)30 to 601 to 23H to 2V60 to 902 to 32H to 1V90 to 1203 to
43H to 1V
Benching in lieu of shoring
20-3: Combined supporting and sloping