Occupational Health and Safety Code

The Occupational Health and Safety Code provides specific technical health and safety rules and requirements for Alberta workplaces.

Alberta Regulation 191/2021

Part 32 Excavating and Tunnelling

Contents

 

Disturbing the ground

 

441

For the purpose of this Part, ground is disturbed if a work operation or activity on or under the existing surface results in a disturbance or displacement of the soil, but not if the disturbance or displacement is a result only of

(a) routine, minor road maintenance,

(b) agricultural cultivation to a depth of less than 450 millimetres below the ground surface over a pipeline, or

(c) hand‑digging to a depth of no more than 300 millimetres below the ground surface, so long as it does not permanently remove cover over a buried facility.

 

Classification of soil type

 

442(1)

For the purpose of this Part, soil is classified as “hard and compact” if it closely exhibits most of the following characteristics:

(a) it is hard in consistency and can be penetrated only with difficulty by a small, sharp object;

(b) it is very dense;

(c) it appears to be dry;

(d) it has no signs of water seepage;

(e) it is extremely difficult to excavate with hand tools;

(f) if has not been excavated before.

442(2)

For the purpose of this Part, soil is classified as “likely to crack or crumble” if

(a) it has been excavated before but does not exhibit any of the characteristics of “soft, sandy or loose” soil, or

(b) it closely exhibits most of the following characteristics:

(i) it is stiff in consistency and compacted;

(ii) it can be penetrated with moderate difficulty with a small, sharp object;

(iii) it is moderately difficult to excavate with hand tools;

(iv) it has a low to medium natural moisture content and a damp appearance after it is excavated;

(v) it exhibits signs of surface cracking;

(vi) it exhibits signs of localized water seepage.

442(3)

For the purposes of this Part, soil is classified as “soft, sandy or loose” if it closely exhibits most of the following characteristics:

(a) it is firm to very soft in consistency, loose to very loose;

(b) it is easy to excavate with hand tools;

(c) it is solid in appearance but flows or becomes unstable when disturbed;

(d) it runs easily into a well‑defined conical pile when dry;

(e) it appears to be wet;

(f) it is granular below the water table, unless water has been removed from it;

(g) it exerts substantial hydraulic pressure when a support system is used.

442(4)

If an excavation contains soil of more than one soil type, for the purposes of this Part an employer must operate as if all of it is the soil type with the least stability.

 

Soil stabilization

 

443(1)

Subject to subsection (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.

443(2)

An employer may stabilize the soil in an excavation, tunnel, underground shaft or open pit mine using an artificial soil stabilization technique, including freezing soil by artificial means or grouting if the process used is

(a) designed by a professional engineer to control soil conditions, and

(b) performed in accordance with the professional engineer’s specifications.

443(3)

A person must not use natural freezing of the soil as an alternative or partial alternative to a temporary protective structure, or to stabilize the soil in an excavation, tunnel or underground shaft.

 

Marking an excavation

 

444

If there is a danger of a worker or equipment falling into an excavation, an employer must ensure that workers are made aware of the excavation through flagging, marking, safeguards or other appropriate and effective means.

 

Water hazard

 

445

An employer must ensure that an excavation that a worker may be required or permitted to enter is kept free of an accumulation of water that may pose a hazard to the worker.

 

Worker access

 

446(1)

An employer must provide workers with a safe means of entering and leaving an excavation, tunnel or underground shaft.

446(2)

An employer must ensure that a worker does not enter an excavation, tunnel or underground shaft that does not comply with this Part.

446(3)

A worker must not enter an excavation, tunnel or underground shaft that does not comply with this Part.

 

Locating buried or concrete‒embedded facilities

 

447(1)

For the purposes of subsection (1.1) and section 448, an owner means an owner or the owner’s designate of a pipeline that is within 30 metres of the work site or any other buried or concrete‑embedded facility that may be affected by the ground disturbance or removal of existing concrete.

447(1.1)

Before the ground is disturbed or existing concrete is removed at a work site, an employer must

(a) contact the owner,

(b) advise the owner of the proposed activities,

(c) ask the owner to identify and mark the location of the buried or concrete-embedded facility, and

(d) not begin disturbing the ground or removing the existing concrete until buried or concrete-embedded facilities have been identified and their locations marked.

447(2)

An employer must ensure that workers are aware of locate marks for buried or concrete‑embedded facilities.

447(3)

An employer must ensure that steps are taken to re‑establish the locate marks for buried or concrete‑embedded facilities if activities at the work site move or destroy the locate marks.

447(4)

Despite subsection (1.1), an employer may use as built record drawings of the buried or concrete‑embedded facilities for locating the buried or concrete‑embedded facilities if

(a) the work does not require excavation or removal of the soil, ground or existing concrete, and

(b) the ground is penetrated to a depth of 1 metre or less or the existing concrete is penetrated to a depth of 150 millimetres or less.

447(5)

The as‑built record drawings referred to in subsection (4) must be certified by the owner of the buried or concrete‑embedded facility as the most current drawings of record that indicate the constructed location of the buried or concrete‑embedded facility.

 

Exposing buried facilities

 

448(1)

An employer must ensure that work with mechanical excavation equipment is not permitted within the hand expose zone of a buried facility until the buried facility has been exposed to sight

(a) by hand digging,

(b) by a non‑destructive technique acceptable to the owner of the buried facility, or

(c) by a method equivalent to clause (a) or (b).

448(2)

Despite subsection (1), an employer may use mechanical excavation if doing so does not present a hazard and

(a) if the buried facility is an electrical cable or conduit, the employer must ensure that

(i) it is grounded and isolated so that its disconnection is visible, and

(ii) the owner of the electrical cable or conduit is notified of the operation before it begins,

or

(b) if the buried facility is not an electrical cable or conduit, the employer ensures that

(i) it is no longer in use, and

(ii) the owner of the buried facility gives the employer written consent to excavate or remove the facility.

(c) - (e) Repealed.

448(3)

An employer may reduce the width of a hand expose zone for a high pressure pipeline to within 1 metre on each side of the pipeline locate marks if

(a) the high pressure pipeline is not governed by the Pipeline Act, and

(b) the employer obtains written approval from the owner of the high pressure pipeline.

448(4)

If the ground that will be disturbed lies within a pipeline right of way, an employer must

(a) contact the operator or licensee of the pipeline, and

(b) get their consent to disturb the ground.

448(5)

An employer must not allow the use of mechanical excavation equipment within 600 millimetres of a buried pipeline unless the use of the equipment is under the direct supervision of a representative of the owner of the buried pipeline.

448(5.1)

If an employer, on behalf of an electric utility, undertakes emergency work that

(a) involves ground disturbance to a depth of no more than 500 millimetres below the ground surface,

(b) is on the horizontal alignment or right of way of an electric utility structure, and

(c) is determined by the employer to be in a location where no buried facilities are present in the area affected by the work,

the employer is exempt from the requirements of subsections (1) to (5).

448(6)

An employer must ensure that any exposed buried facilities are protected and supported so that workers are not injured.

448(7)

If a pipeline is exposed during a work operation, an employer must notify the pipeline operator or licensee before backfilling the excavation.

 

Exemption

 

449

Sections 450 to 459 and sections 461 to 464 do not 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.

 

Methods of protection

 

450(1)

Before a worker begins working in an excavation that is more than 1.5 metres deep and closer to the wall or bank than the depth of the excavation, an employer must ensure that the worker is protected from cave‑ins or sliding or rolling materials by

(a) cutting back the walls of the excavation to reduce the height of the remaining vertical walls, if any, to no more than 1.5 metres for “hard and compact soil” and “likely to crack or crumble soil”,

(b) installing temporary protective structures, or

(c) using a combination of the methods in clauses (a) and (b).

450(2)

Subsection (1) does not apply if a trench is constructed in solid rock throughout the entire trench.

 

Cutting back walls

 

451

If the walls of an excavation are cut back, an employer must ensure that

(a) if the soil is classified as “hard and compact soil”, the walls are sloped to within 1.5 metres of the bottom of the excavation at an angle of not less than 30 degrees measured from the vertical,

(b) if the soil is classified as “likely to crack or crumble soil”, the walls are sloped to within 1.5 metres of the bottom of the excavation at an angle of not less than 45 degrees measured from the vertical, and

(c) if the soil is classified as “soft, sandy or loose soil”, the walls are sloped from the bottom of the excavation at an angle of not less than 45 degrees measured from the vertical.

 

Loose materials

 

452

An employer must ensure that loose materials are scaled and trimmed from the sides of an excavation if workers may be on or near the sides.

 

Spoil piles

 

453

An employer must ensure that a spoil pile is piled so that

(a) the leading edge of the pile is at least 1 metre away from the edge of the excavation,

(b) the slope of a spoil pile adjacent to the excavation is at an angle of not more than 45 degrees from the horizontal, and

(c) loose materials are scaled and trimmed from the spoil pile.

 

Power pole support

 

454

An employer must ensure that work that disturbs the ground in the vicinity of an overhead power line is performed in a manner that does not reduce the original support provided for power line poles.

 

Safe entry and exit

 

455(1)

An employer must ensure that if a worker is required to enter a trench that is more than 1.5 metres deep, a safe point of entering and leaving is located not more than 8 metres from the worker.

455(2)

An employer must ensure that if a worker is in a trench that is more than 1.5 metres deep, the trench is supported or sloped so that the worker can reach the safe point in order to enter and leave.

 

Temporary protective structures

 

456(1)

An employer must ensure that temporary protective structures in an excavation

(a) 3 metres deep or less are of sufficient strength to prevent the walls of the excavation from caving in or otherwise moving into the excavation, and

(b) more than 3 metres deep are designed, constructed and installed in accordance with the specifications of a professional engineer.

456(2)

The specifications of a professional engineer for subsection (1)(b) must include

(a) the size and specifications of the structure, including the type and grade of materials used in its construction, and

(b) the loads for which the structure is designed.

456(3)

An employer must ensure that, before beginning an excavation, a foundation that may be affected by the excavation is supported by a temporary protective structure designed, constructed and installed in accordance with the specifications of a professional engineer.

 

Alternatives to temporary protective structures

 

457(1)

Despite section 456, an employer may install the following as temporary protective structures in trenches:

(a) if the trenches vary in depth from 1.5 metres to 6 metres, shoring, stringers and bracing constructed of lumber that complies with Schedule 9, or a material that has equal or greater properties to those of the lumber;

(b) exterior grade plywood as a substitute for 38 millimetre shoring elements if

(i) the plywood meets the requirements of CSA Standard O121‑08, Douglas Fir Plywood or CSA Standard O151‑04, Canadian Softwood Plywood,

(ii) the plywood is at least 19 millimetres thick,

(iii) the trench is not more than 2.7 metres deep,

(iv) uprights are installed at intervals of not more than 600 millimetres centre‑to‑centre,

(v) cross braces do not bear directly on the plywood, and

(vi) cross braces bearing on uprights or walers are located at all joints in the plywood sheathing.

457(2)

Despite subsection (1)(a), screw jacks, hydraulic equipment or other apparatus may be used as shoring, stringers or bracing if they are at least equivalent in strength and reliability to the shoring, stringers or bracing described in Schedule 9.

457(3)

Despite subsection (1)(a) if the trench is less than 2.4 metres deep and in soil classified as “hard and compact” an employer does not have to use stringers.

457(4)

Despite section 456, an employer may install additional protection certified by a professional engineer in trenches to compensate for passing vehicular traffic, working machinery or a heavy object placed within a distance equal to the depth of the trench, measured from the near edge of the bottom of the trench to the traffic, machinery or heavy object.

457(5)

Despite section 456, an employer may install additional protection certified by a professional engineer in a trench to compensate for the stress created because the trench is adjacent to or abuts a building or other structure.

 

Installation of shoring, stringers or bracing

 

458(1)

An employer must ensure that a worker who installs shoring, stringers or bracing uses a ladder and works down from the top of the trench, installing each brace in descending order.

458(2)

An employer must ensure that a worker who removes shoring, stringers or bracing uses a ladder and works upward from the bottom of the trench, removing each brace in ascending order.

458(3)

A worker must install shoring, stringers or bracing in accordance with subsection (1) and remove them in accordance with subsection (2).

458(4)

Despite subsections (2) and (3), if the quality of the ground in which a trench has been dug has deteriorated during operations to the extent that it is unsafe to use the method of removal required by subsection (2), an employer must ensure that the shoring, stringers or bracing are removed using a method that does not require the worker to be in the trench.

 

Access for powered mobile equipment

 

459

An employer must ensure that the open side of an excavation or a route used by powered mobile equipment to gain access to an excavation has a barrier high enough to stop the equipment from sliding or rolling into the excavation.

 

Dumping block

 

460

An employer must ensure that if powered mobile equipment may go over a bank or enter a dump opening while it is discharging its load, the equipment is effectively stopped or controlled by

(a) an anchored block,

(b) a ridge of material acting as a backstop, or

(c) a designated signaller with a stop signal.

 

Underground shafts

 

461(1)

An employer must ensure that, during the excavation of an underground shaft that is between 1.5 metres and 6 metres deep, the walls of the shaft from the top down are retained by temporary protective structures strong enough to prevent the walls from collapsing or caving in.

461(2)

An employer must ensure that, during the excavation of an underground shaft 6 metres or more deep, the walls of the shaft from the top down are retained by temporary protective structures certified by a professional engineer as strong enough to prevent the walls from collapsing or caving in.

461(3)

An employer must ensure that

(a) a solid fence or equally effective means of preventing workers, materials and equipment from falling into the shaft is provided around an underground shaft opening, and

(b) gates not less than 1 metre high are installed at each entrance of an underground shaft and are kept closed when they are not being used.

461(4)

Workers must keep a gate to the entrance of an underground shaft closed when it is not being used.

461(5)

An employer must ensure that an underground shaft is provided with suitable and efficient machinery or another device for keeping the shaft free of accumulations of water.

 

Drilled or bored underground shaft

 

462(1)

An employer must ensure that

(a) a worker who is required to enter a drilled or bored underground shaft is protected by a casing or temporary protective structure, and

(b) the casing or temporary protective structure extends and remains at least 300 millimetres above surface of the ground where the shaft is drilled or bored.

462(2)

An employer must ensure that a casing or temporary protective structure referred to in subsection (1) is certified by a professional engineer as having sufficient strength to resist the shifting of the surrounding materials.

462(3)

Subject to subsection (4), if a worker in a belled area of an underground shaft is exposed to falling materials and is unable to stand clear of the area, an employer must ensure that the worker precedes each load of excavated material to the surface.

462(4)

If a worker referred to in subsection (3) cannot precede each load to the surface, an employer must ensure that

(a) the worker accompanies each load if the equipment is designed to safely transport both the worker and the excavated material simultaneously, and

(b) safe work procedures are prepared that include the procedures to be followed when the worker and the excavated material are moved simultaneously.

 

Prohibition

 

463

A worker must not enter a belled area of a drilled or bored underground shaft if the worker is not protected by temporary protective structures.

 

Tunnel

 

464(1)

An employer must ensure that, during the excavation of a tunnel, the walls of the tunnel from the top down are retained by temporary protective structures certified by a professional engineer as strong enough to prevent the walls from collapsing or caving in.

464(2)

An employer must ensure that a tunnel is provided with suitable and efficient machinery or another device for keeping the tunnel free from accumulations of water.