KNOW THE LAWS: When Shoring Is Required in Trenches and Excavations

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For more information on this topic, see “TRENCHES & EXCAVATIONS: How to Comply with Shoring Requirements

KNOW THE LAWS: When Shoring Is Required in Trenches and Excavations

Here’s what the OHS laws in each jurisdiction say as to when shoring is required in trenches and/or excavations:

FED Canada OHS Regulations:

1. In a tunnel or in an excavation or trench that’s more than 1.4 m deep and whose sides are sloped at an angle of 45° or more to the horizontal:

a. the walls of the tunnel, excavation or trench, and

b. the roof of the tunnel

must be supported by shoring and bracing that’s installed as the tunnel, excavation or trench is being excavated [Sec. 3.12(3)].

2. The above doesn’t apply in respect of a trench where the employer provides a system of shoring composed of steel plates and bracing, welded or bolted together, that can support the walls of the trench from the ground level to the trench bottom and can be moved along as work progresses [Sec. 3.12(4)].

AB OHS Code 2009:

1. Subject to Sec. 443(2), an employer must stabilize the soil in:

a. an excavation by shoring or cutting back; or

b. a tunnel, underground shaft or open pit mine by shoring [Sec. 443(1)].

2. Secs. 450-459 and Secs. 461-464 don’t apply to an excavation if a professional engineer certifies that the ground formation is and will remain stable, free from cave-ins, sliding or rolling materials and other hazards associated with the workings that may compromise worker safety [Sec. 449].

BC OHS Regs.:

1. Subject to Sec. 20.78, 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 sides of the excavation are:

a. sloped as specified in writing by a qualified registered professional;

b. 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 slope exceed that shown in Figure 20-1;

c. benched as shown in Figure 20-2;

d. supported as specified in writing by a professional engineer;

e. supported in accordance with the minimum requirements of Sec. 20.85; or

f. supported by manufactured or prefabricated trench boxes or shoring cages, or other effective means [Sec. 20.81(1)].

2. If the end of a trench over 1.2 m (4 ft.) in depth isn’t adequately sloped, end shoring must be installed unless:

a. a worker in the trench isn’t 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 or professional geoscientist [Sec. 20.81(2)].

MB Workplace Safety & Health Reg.:

1. An employer who requires or permits a worker to enter an open excavation that has a depth of 1.5 m or less must ensure that the excavation has a support structure installed in it, but only if there is a danger of cave-in, collapse or material sliding or rolling into the excavation due to soil or work conditions at the construction project site [Sec. 26.15(1)].

2. An employer who requires or permits a worker to enter an open excavation that has a depth of more than 1.5 m but not more than 3 m must ensure that:

a. the walls of the excavation are sloped at an angle not greater than 45° measured from the horizontal plane;

b. a combination of slope and vertical face is used for stabilizing the walls of the excavation, so that the vertical face isn’t more than one metre high and the remaining walls are sloped at an angle not greater than 45° measured from the horizontal plane;

c. shoring that’s constructed of components that meet the minimum requirements for the applicable soil conditions set out in the Schedule to this Part is installed;

d. a support structure other than shoring is installed; or

e. the walls of the excavation are stabilized in a manner that has been designed and certified by a professional engineer [Sec. 26.15(2)].

3. An employer who requires or permits a worker to enter an open excavation that has a depth of more than 3 m must ensure that:

a. a support structure or an alternative method for stabilizing the walls has been designed and certified by a professional engineer for the excavation; and

b. as applicable, the support structure or alternative method is constructed, installed, used, maintained and dismantled in accordance with specifications provided by the professional engineer [Sec. 26.15(4)].

4. An employer who requires or permits a worker to enter a trench that has a depth of 1.5 m or less must ensure that a support structure is installed in it, but only if there’s a danger of cave-in, collapse or material sliding or rolling into the trench due to soil or work conditions at the construction project site [Sec. 26.16(1)].

5. An employer who requires or permits a worker to enter a trench that has a depth of more than 1.5 m but not more than 4.5 m must ensure that:

a. shoring that’s constructed of components that meet the minimum requirements for the applicable soil conditions set out in the Schedule to this Part is installed; or

b. an alternative that is designed and certified by a professional engineer is used for stabilizing the walls of the trench [Sec. 26.16(2)].

6. An employer who requires or permits a worker to enter a trench that has a depth of more than 4.5 m must ensure that the walls of the trench are stabilized using a method designed and certified by a professional engineer [Sec. 26.16(4)].

NB OHS Regulations:

1. An employer must ensure that the walls of an excavation or trench are supported by shoring, bracing or caging except when the excavation or trench:

a. is less than 1.2 m deep;

b. subject to Sec. 181(2), is cut in solid rock;

c. is sloped or benched to within 1.2 m of the bottom of the excavation or trench with the slope or bench not exceeding 1 m of vertical rise to each 1 m of horizontal run; or

d. is one that an employee isn’t required to enter [Sec. 181(1)].

2. An employer must ensure that an employee doesn’t, and no employee may, enter an excavation or trench 1.2 m or more in depth unless:

a. the walls of the excavation or trench are supported by shoring, bracing or caging, the excavation or trench is cut in solid rock or the excavation or trench is sloped or benched to within 1.2 m of the bottom of the excavation or trench with the slope not exceeding 1 m of vertical rise to each 1 m of horizontal run;

b. Secs. 181(2), (3) and (4) have been complied with;

c. loose material that may fall into the excavation or trench has been removed; and

d. a ladder that extends at least 1 m above the excavation or trench is installed no more than 15 m from where the employee is working or some other safe means of access and egress is provided [Sec. 182(1)].

NL OHS Regs. 2012:

A worker shall not enter an excavation over 1.22 metres deep unless:

a. the sides of the excavation are sloped to a safe angle and have been secured by the use of sheet piling, shoring and bracing or a trench box; or

b. the worker is protected by other effective means [Sec. 406(4)].

NS Occupational Safety General Regulations:

Where a person may enter an excavation or trench and a wall of an excavation or trench is greater than 1.2 m in height, an employer must ensure that the wall’s supported by adequate shoring or bracing, or that an adequate trench cage is used, except where the employer is able to establish that the excavation or trench:

a. is cut in sound and stable rock;

b. is sloped:

i. to within 1.2 m of the bottom of the excavation or trench, or

ii. where soil overburden is located above an excavation or trench excavated in sound and stable rock, for the entire overburden,

and the slope doesn’t exceed 1 m of vertical rise to each 1 m of horizontal run; or

c. is one that a person doesn’t enter within a horizontal distance from the walls of the excavation or trench that is equal to the height of the walls [Sec. 166(1)].

NT OHS Regs.:

1. If a worker is present in an excavation that’s more than 1.2 m deep and is required to be closer to the wall or bank than the distance equal to the depth of the excavation, an employer must ensure that the worker’s protected from cave-ins or sliding material by:

a. cutting back the upper portion of the walls of the excavation in accordance with Sec. 266(2);

b. installing a temporary protective structure; or

c. a combination of cutting back the walls to the slope specified in Sec. 266(2) and installing a temporary protective structure that extends not less than 300 mm above the base of the cut-back [Sec. 269(1)].

2. If a worker is present in a trench that’s more than 1.2 m deep, an employer must ensure that the worker’s protected from cave-ins or sliding material by:

a. cutting back the upper portion of the walls of the trench in accordance with Sec. 266(2);

b. installing a temporary protective structure; or

c. a combination of cutting back the walls to the slope specified Sec. 266(2) and installing a temporary protective structure that extends not less than 300 mm above the base of the cut-back [Sec. 270(1)].

NU OHS Regs.:

1. If a worker is present in an excavation that’s more than 1.2 m deep and is required to be closer to the wall or bank than the distance equal to the depth of the excavation, an employer must ensure that the worker’s protected from cave-ins or sliding material by:

a. cutting back the upper portion of the walls of the excavation in accordance with Sec. 266(2);

b. installing a temporary protective structure; or

c. a combination of cutting back the walls to the slope specified in Sec. 266(2) and installing a temporary protective structure that extends not less than 300 mm above the base of the cut-back [Sec. 269(1)].

2. If a worker is present in a trench that’s more than 1.2 m deep, an employer must ensure that the worker’s protected from cave-ins or sliding material by:

a. cutting back the upper portion of the walls of the trench in accordance with Sec. 266(2);

b. installing a temporary protective structure; or

c. a combination of cutting back the walls to the slope specified Sec. 266(2) and installing a temporary protective structure that extends not less than 300 mm above the base of the cut-back [Sec. 270(1)].

ON Construction Projects Regulation:

1. The walls of an excavation must be supported by a support system that complies with Secs. 235, 236, 237, 238, 239 and 241 [Sec. 234(1)].

2. The above doesn’t apply with respect to an excavation:

a. that’s less than 1.2 metres deep;

b. that no worker is required to enter;

c. that’s not a trench and with respect to which no worker is required to be closer to a wall than the height of the wall;

d. that’s cut in sound and stable rock;

e. made in Type 1 or Type 2 soil and whose walls are sloped to within 1.2 metres of its bottom with a slope having a minimum gradient of one horizontal to one vertical;

f. made in Type 3 soil and whose walls are sloped from its bottom with a slope having a minimum gradient of one horizontal to one vertical;

g. made in Type 4 soil and whose walls are sloped from its bottom with a slope having a minimum gradient of three horizontal to one vertical; or

h. that’s not a trench and isn’t made in Type 4 soil and with respect to which a professional engineer has given a written opinion that the walls of the excavation are sufficiently stable that no worker will be endangered if no support system is used [Sec. 234(2)].

PE OHS Regs.:

The employer must ensure that the walls of an excavation or trench are supported by adequate shoring and bracing or caging except when an excavation or trench:

a. is less than 1,219 mm (4 ft.) deep;

b. is cut in solid rock;

c. is sloped to within 1,219 mm (4 ft.) of the bottom of the excavation or trench with a slope at the angle of repose that doesn’t exceed 305 mm (1 ft.) of vertical rise to each 305 mm (1 ft.) of horizontal run; or

d. is such that employees aren’t required to enter [Sec. 12.2(1)].

QC Safety Code for the construction industry:

The employer must ensure that the banks of an excavation or trench are shored solidly with quality materials in accordance with the plans and specifications of an engineer. Shoring isn’t required in the following cases:

a. where the trench or excavation is dug out of solid rock or where no workers are required to descend into it;

b. where there’s no risk of the banks of the trench or excavation collapsing and where they slope less than 45º from a point less than 1.2 m from the bottom; and

c. where there’s no risk of the banks of the trench or excavation collapsing and where an engineer attests that it isn’t necessary to shore up the banks, given the slope, nature and stability of the ground. A copy of the engineer’s attestation must be available on the construction site at all times [Sec. 3.15.3(1)].

SK OHS Regulations:

1. Where a worker is present in an excavation that is more than 1.2 metres deep and is required to be closer to the wall or bank than the distance equal to the depth of the excavation, an employer or contractor must ensure that the worker’s protected from cave-ins or sliding material by:

a. cutting back the upper portion of the walls of the excavation in accordance with Sec. 260(2);

b. installing a temporary protective structure; or

c. a combination of cutting back the walls to the slope specified in Sec. 260(2) and installing a temporary protective structure that extends at least 300 millimetres above the base of the cut-back [Sec. 262(1)].

2. Where a worker’s present in a trench that’s more than 1.2 metres deep, an employer or contractor must ensure that the worker is protected from cave-ins or sliding material by:

a. cutting back the upper portion of the walls of the trench in accordance with Sec. 260(2);

b. installing a temporary protective structure; or

c. a combination of cutting back the walls to the slope specified in Sec. 260(2) and installing a temporary protective structure that extends at least 300 millimetres above the base of the cut-back [Sec. 263(1)].

YT OHS Reg.:

1. Before a worker enters any excavation or trench more than 1.2 m (4 ft.) in depth, or where a worker approaches the side or bank within a distance equal to the depth of the excavation, the excavation sidewalls must be sloped or supported, as specified by a professional engineer, or the sidewalls of the excavation shall be, at a minimum:

a. sloped at an angle not steeper than 37 degrees from the vertical;

b. sloped at an angle, 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 10-1;

c. benched as shown in Figure 10-2;

d. supported in accordance with the minimum requirements of Section 10.68; or

e. supported by manufactured or prefabricated trench boxes, shoring cages, or other effective means acceptable to the director [Sec. 10.65(1)].

2. End shoring must be installed if the end of a trench more than 1.2 m (4 ft.) in depth isn’t adequately sloped unless:

a. a worker in the trench isn’t required to approach closer to the end of the trench than a distance equal to the depth of the trench at that end;

b. the permissible spacing of uprights equals or exceeds the width of the trench; or

c. otherwise authorized in writing by a professional engineer [Sec. 10.65(2)].