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HomeMy WebLinkAboutHUR130-006 Trenches and ExcavatingCitq o CITY PROCEDURE Procedure Title: Trenches and Excavating Procedure Number: HUR 130-006 Reference: Occupational Health & Safety Act Date Originated: January 30, 2009 Date Revised: Approval: Chief A minis i Officer Point of Contact: Coordinator, Health & Safety Procedure Objective: To establish procedures and standards for excavations and trenches that protect the safety of employees and that comply with the Occupational Health & Safety Act and the Construction Project Regulation. Index 01 Definitions 02 Procedures Appendix 1 Table — Excavation Shoring and Timbering (Metric Sizes) 01 Definitions 01.01 Engineered Support System - An excavation or trench shoring system, designed for a specific project or location, assembled in place and which cannot be moved as a unit. 01.02 Hydraulic Support System - A system capable of being moved as a unit, designed to resist the earth pressure from the walls of an excavation by applying a hydraulic counter pressure through the struts. 01.03 Prefabricated Support System - A trench box, trench shield or similar structure, composed of pieces connected to each other and capable of being moved as a unit, and designed to resist the pressure from the walls of an excavation but does not include a hydraulic support system. 01.04 Pressure - In relation to a wall of an excavation, means the lateral pressure of the earth on the wall calculated in accordance with generally accepted engineering principles and includes hydrostatic pressure and pressure due to surcharge. 01.05 Sheathing — Shoring that is placed up against the walls of an excavation to directly resist the pressure exerted from the walls of the excavation. 01.06 Soil Type — Refers to the consistency, density, hardness and moisture levels of soil, and is classified by visual and physical examination of the soil, at the walls of the excavation; and within a horizontal distance from each wall equal to the depth of the excavation measured away from the excavation. 01.07 Strut — Shoring that directly resists pressure from a wale. 01.08 Wale - Shoring that is placed against the sheathing to directly resist the pressure from the sheathing. 02 Procedures 02.01 Working Alone No employee may perform work in a trench unless another employee is working above ground in close proximity to the trench or close to means to access the trench. 02.02 Locating and Marking Services Before an excavation is begun, gas, electrical and other services in and near the area to be excavated must be accurately located and marked. If a service may pose a hazard, the service must be shut off and disconnected. The owner of the service should be requested to locate and mark the service. If a service may pose a hazard and cannot be shut off or disconnected, the owner of the service shall be requested to supervise the uncovering of the service during the excavation. Pipes, conduits and cables for gas, electrical and other services in an excavation shall be supported to prevent their failure or breakage. Procedure Title: Trenches and Excavating Page 2 of 9 Procedure Number: HUR 130-006 02.03 General Requirements Every excavation that a worker may be required to enter shall be kept reasonably free of water. An excavation in which a worker may work shall have a clear work space of at least 45 centimetres between the wall of the excavation and any formwork or masonry or similar wall. The walls of an excavation shall be stripped of loose rock or other material that may slide, roll or fall upon a worker. The walls of an excavation cut in rock shall be supported by rock anchors or wire mesh if support is necessary to prevent the spalling of loose rock. A level area extending at least one metre from the upper edge of each wall of an excavation shall be kept clear of equipment, excavated soil, rock and construction material. The stability of a wall of an excavation shall be maintained where it may be affected by stockpiling excavated soil or rock or construction materials. No person shall operate a vehicle or other machine and no vehicle or other machine shall be located in such a way as to affect the stability of a wall of an, excavation. If a person could fall into an excavation that is more than 2.4 metres deep, a barrier at least 1.1 metres high shall be provided at the top of every wall of the excavation that is not sloped. 02.04 Soil Types Soil is to be classified in one of the four types described below. Prior to commencing excavation or trench work, the written opinion of a geotechnical engineer must be obtained to determine the soil type unless the support system to be used is sufficient as though the soil type is deemed to be Type 4 soil. 02.05 Type 1 Soil: a) is hard, very dense and only able to be penetrated with difficulty by a small sharp object; Procedure Title: Trenches and Excavating Page 3 of 9 Procedure Number: HUR 130-006 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. 02.06 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. 02.07 Type 3 Soil a) is stiff to firm and compact to loose in consistency or is previously -excavated soil; b) exhibits signs of surface cracking; c) exhibits signs of water seepage; d) if it is dry, may run easily into a well-defined conical pile; and e) has a low degree of internal strength. 02.08 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. Procedure Title: Trenches and Excavating Page 4 of 9 Procedure Number: HUR 130-006 02.09 Support Systems Where No Support System is Required: The walls of an excavation do not require a support system if: a) the excavation is less than 1.2 metres deep; b) no worker is required to enter it; c) it is cut in sound and stable rock; d) it is 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; e) it is 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; f) it is 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 g) it is not a trench and is not made in Type 4 soil and a professional engineer has given a written opinion that the walls of the specific excavation are sufficiently stable that no worker will be endangered if no support system is used. 02.10 Types and Uses of Support Systems In all other cases, a support system is required and must be constructed with a type of support system that is appropriate in the specific circumstances, as described below. In the case of any prefabricated support system, hydraulic support system or engineered support system, the system must be designed by a professional engineer. The system must be constructed, installed, used and maintained in a manner consistent with the design specifications. Before the system is used, two copies of the design drawings and specifications must be delivered to the closest Ministry of Labour office. Procedure Title: Trenches and Excavating Page 5 of 9 Procedure Number: HUR 130-006 A support system for the walls of an excavation shall be installed, progressively in an excavation in Type 1, 2 or 3 soil, and in advance of an excavation in Type 4 soil, if practicable. A support system for the walls of an excavation shall provide continuous support for it. No support system for the walls of an excavation shall be removed until immediately before the excavation is backfilled. A competent person shall supervise the removal of a support system for the walls of an excavation. If a support system is used for the walls of an excavation, a ladder for access to or egress from the excavation shall be placed within the area protected by the support system. A support system for the walls of an excavation shall extend at least 0.3 metres above the top of the excavation unless otherwise permitted or required by this section. If an excavation is located where there is vehicular or pedestrian traffic and if the excavation will be covered when work on or in it is not in progress, the support system for the walls of the excavation shall extend at least to the top of the excavation. 02.11 Timbering and Shoring Timbering and shoring may be used if no hydrostatic pressure is present in the soil and if the specifications as to its use are consistent with the table at the end of this procedure. Sheathing, struts and wales used should be made of sound Number 1 Grade spruce. Sheathing must be placed against the side of the excavation so that it is vertical, must be secured in place by wales, and must be driven into the soil and firmly secured in place if the excavation is made in Type 3 or Type 4 soil. Struts must be placed in the excavation so they are horizontal and at right angles to wales, cut to proper length and held in place by at least two wedges driven between the strut and the wales, and must be cleated using cleats that extend over the top of the strut and rest on the wales or that are attached securely to the wales by spikes or bolts. Procedure Title: Trenches and Excavating Page 6 of 9 Procedure Number: HUR 130-006 Wales must be placed in the excavation so that they are parallel to the bottom of the excavation and supported by either cleats secured to the sheathing or posts set on the wale below it (or if it is the lowest wale, on the bottom of the excavation). 02.12 Prefabricated Support System A prefabricated support system should never be used in type 4 soil. It may be used for repairing underground pipe breaks if: a) it has four side walls; b) is designed for a maximum depth of 3.6 metres; c) is not used ata depth greater than 3.6 metres; d) is designed to resist all hydrostatic and earth pressures found in type 4 and type 4 soils; e) is installed so as to extend to the bottom of the excavation; f) is installed so that the walls of the system touch the walls of the excavation; and g) is not pulled forward after being installed in the excavation. The space between the walls of a prefabricated support system and the walls of the excavation must be restricted to the minimum clearance required for the forward progression of the support system. 02.13 Hydraulic Support System A hydraulic support system should never be used in type 4 soil. It may be used for repairing underground pipe breaks if: a) it has four side walls; b) is designed for a maximum depth of 3.6 metres; c) is not used at a depth greater than 3. 6 metres; d) is designed to resist all hydrostatic and earth pressures found in type 4 and type 4 soils; Procedure Title: Trenches and Excavating Page 7 of 9 Procedure Number: HUR 130-006 e) is installed so as to extend to the bottom of the excavation; f) is installed so that the walls of the system touch the walls of the excavation; and g) is not pulled forward after being installed in the excavation. 02.13 Engineered Support System 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. Procedure Title: Trenches and Excavating Page 8 of 9 Procedure Number: HUR 130-006 APPENDIX 1 TABLE EXCAVATION SHORING AND TIMBERING (METRIC SIZES) Column 1 Column 2 Column 3 Column 4 Excavation Depth Soil Type Sheathing Struts Width of Excavation at Strut Location Strut Spacing Wales 1.8 m to 3.6 m Up to 1.8 m Vertical Horizontal 3.Omor less 1 50mmx200 mm at 1.2 m o/c 200 mm x 200mm 150 mm x 150mm 1.2 m * 2.4 m *200 mm x 200mm 2 50mmx200 mm at 1.2 m o/c 200mmx 200 mm 150mmx 150 mm 1.2 m * 2.4 m *200mmx 200 mm 3 50 mm x 200 mm at 10 mm gap 200 mm x 200 mm 200 mm x 200 mm 1.2 m 2.4 m 250 mm x 250 mm 4 75 mm x 200 mm at 10 mm gap 250 mm x 250 mm 200 mm x 200 mm 1.2 m 2.4 m 300 mm x 300 mm Over3.Om to 4.5 m 1 50mmx200 mm with 10 mm gap 200 mm x 200 mm 150 mm x 150 mm 1.2 m 2.4 m 200 mm x 200 mm 2 50 mm x 200 mm with 10 mm gap 200 mm x 200 mm 200 mm x 200 mm 1.2 m 2.4 m 250 mm x 250 mm 3 50 mm x 200 mm with 10 mm gap 250 mm x 250 mm 250 mm x 250 mm 1.2 m 2.4 m 250 mm x 250 mm Over 3.0 m to 4.0 m 4 75 mm x 200 mm with 10 mm gap 300 mm x 300 mm 300 mm x 300 mm 1.2 m 2.4 m 300 mm x 300 mm Over 4.5 m to 6.0 m 1 50 mm x 200 mm with 10 mm gap 200 mm x 200 mm 200 mm x 200 mm 1.2 m 2.4 m 200 mm x 200 mm 2 50 mm x 200 mm with 10 mm gap 250 mm x 250 mm 250 mm x . 250 mm 1.2 m 2.4 m 250 mm x 250 mm 3 50 mm x 200 mm with 10 mm gap 300 mm x 300 mm 300 mm x 300 mm 1.2 m 2.4 m 300 mm x 300 mm Procedure Title: Trenches and Excavating Procedure Number: HUR 130-006 Page 9 of 9