Trenching and Excavation

223. This Part applies to all excavating and trenching operations.

224. No person shall enter or be permitted to enter an excavation that does not comply with this Part.

225. Work shall not be performed in a trench unless another worker is working above ground in close proximity to the trench or to the means of access to it.

226. (1) For the purposes of this Part, soil shall be classified as Type 1, 2, 3 or 4 in accordance with the descriptions set out in this section.

(2) Type 1 soil,

(a) is hard, very dense and only able to be penetrated with difficulty by a small sharp object;

(b) has a low natural moisture content and a high degree of internal strength;

(c) has no signs of water seepage; and

(d) can be excavated only by mechanical equipment.

(3) Type 2 soil,

(a) is very stiff, dense and can be penetrated with moderate difficulty by a small sharp object;

(b) has a low to medium natural moisture content and a medium degree of internal strength; and

(c) has a damp appearance after it is excavated.

(4) Type 3 soil is,

(a) previously excavated soil; or

(b) soil that is stiff to firm or compact to loose in consistency and has one or more of the following characteristics:

(i) It exhibits signs of surface cracking.

(ii) It exhibits signs of water seepage.

(iii) If it is dry, it may run easily into a well-defined conical pile.

(iv) It has a low degree of internal strength.

(5) Type 4 soil,

(a) is soft to very soft and very loose in consistency, very sensitive and upon disturbance is significantly reduced in natural strength;

(b) runs easily or flows, unless it is completely supported before excavating procedures;

(c) has almost no internal strength;

(d) is wet or muddy; and

(e) exerts substantial fluid pressure on its supporting system.

[O. Reg. 345/15, s. 24]

228. (1) Before an excavation is begun,

(a) the employer excavating shall ensure that all gas, electrical and other services in and near the area to be excavated are located and marked;

(b) the employer and worker locating and marking the services described in clause (a) shall ensure that they are accurately located and marked; and

(c) if a service may pose a hazard, the service shall be shut off and disconnected.

(2) If a service may pose a hazard and it cannot be shut off or disconnected, the owner of the service shall be requested to supervise the uncovering of the service during the excavation.

(3) Pipes, conduits and cables for gas, electrical and other services in an excavation shall be supported to prevent their failure or breakage.

[O. Reg. 443/09, s. 6]

229. (1) If an excavation may affect the stability of an adjacent building or structure, the constructor shall take precautions to prevent damage to the adjacent building or structure.

(2) An engineer shall specify in writing the precautions required under subsection (1).

(3) Such precautions as the engineer specifies shall be taken.

[O. Reg. 375/22, s. 5]

230. Every excavation that a worker may be required to enter shall be kept reasonably free of water.

234. (1) The walls of an excavation shall be supported by a support system that complies with sections 235, 236, 237, 238, 239 and 241.

(2) Subsection (1) does not apply with respect to an excavation,

(a) that is less than 1.2 metres deep;

(b) that no worker is required to enter;

(c) that is 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 is cut in sound and stable rock;

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

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

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

(h) that is not a trench and is not made in Type 4 soil and with respect to which an 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.

(3) The opinion in clause (2)(h) shall include details of,

(a) the specific project and the location thereon;

(b) any specific condition for which the opinion applies; and

(c) the frequency of inspections.

(4) The constructor shall keep on the project a copy of every opinion given by an engineer for the purpose of clause (2)(h) while the project is in progress.

(5) The engineer who gives an opinion described in clause (2)(h), or a competent worker designated by him or her, shall inspect the excavation to which the opinion relates as frequently as the opinion specifies.

[O. Reg. 142/17, s. 26; 375/22, s. 5]

235. (1) Subject to subsection (2), a support system shall consist of,

(a) timbering and shoring that meets the requirements of subsection 238(2), if no hydrostatic pressure is present in the soil, and if the width and depth of the excavation are equal to or less than the width and depth indicated in the Table to section 238;

(b) a prefabricated support system that complies with sections 236 and 237;

(c) a hydraulic support system that complies with sections 236 and 237; or

(d) an engineered support system that complies with section 236.

(2) Where the excavation is a trench and the depth exceeds six metres or the width exceeds 3.6 metres, the support system shall consist of an engineered support system designed for the specific location and project.

[O. Reg. 631/94, s. 7]

236. (1) Every prefabricated, hydraulic or engineered support system shall be designed by an engineer.

(2) Every prefabricated, hydraulic or engineered support system shall be constructed, installed, used and maintained in accordance with its design drawings and specifications.

(3) The design drawings and specifications for a prefabricated, hydraulic or an engineered support system,

(a) shall indicate the size of the system and the type and grade of materials of which it is to be made;

(b) shall indicate the maximum depth and the types of soil for which it is designed;

(c) shall indicate the proper positioning of the system in the excavation, including the maximum allowable clearance between the walls of the support system and the walls of the excavation; and

(d) shall indicate how to install and remove the system.

(e) Repealed. [O. Reg. 85/04, s. 21]

(4) In addition to the requirements of subsection (3), the design drawings and specifications for a hydraulic support system,

(a) shall indicate the minimum working pressure required for the system; and

(b) shall require the use of a device to ensure the protection of workers if a loss of hydraulic pressure occurs in the system.

(5) Before a variation from the design drawings and specifications for a prefabricated, hydraulic or an engineered support system is permitted, the variation shall be approved in writing by an engineer.

(6) If the soil conditions on a project differ from those assumed by the engineer in designing a prefabricated, hydraulic or an engineered support system, an engineer shall modify the design drawings and specifications for the actual soil conditions or shall approve the support system for use in the actual soil conditions.

(7) The constructor shall keep the design drawings and specifications for a prefabricated, hydraulic or an engineered support system at a project while the system is on the project.

(8) Repealed. [O. Reg. 443/09, s. 7]

[O. Reg. 145/00, s. 32; 85/04, s. 21; 443/09, s. 7; 375/22, s. 5]