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GUIDELINES FOR EXCAVATION WORK
Introduction
This guideline provides a standard for proper sloping and shoring of trenches and excavations. It is intended to give excavation contractors and workers practical information relating to the requirements of the regulations pertaining to excavation work.
This guideline contains general information about excavation work. For specific regulatory requirements regarding excavation work please consult the regulations adopted under the Workplace Safety and Health Act.
Table of Contents
PART I: DEFINITIONS
PART II: HAZARDS TO EXCAVATION WORKERS
PART III: WHAT TO DO PRIOR TO EXCAVATING
- Make sure you are a registered contractor
- Notify the Division prior to excavating
- Obtain clearance from the public utilities
- Obtain engineering approvals
- Plan for dangerous conditions
- Train the workers
- Appoint an experienced supervisor
PART IV: GENERAL SHORING REQUIREMENTS
- Personal protective equipment
- 'Observer' to be on the job
- Access/egress
- Location of excavated material & equipment
- Public protection & traffic control
- First aid
- Engineering information
PART V: TRENCH AND OPEN EXCAVATIONS
PART VI: SHAFT AND TUNNEL EXCAVATIONS
PART VII: CAISSON EXCAVATIONS (DEEP FOUNDATION)
Deep Foundation means a foundation unit that provides support for a building by transferring loads either by end bearing to soil or rock at considerable depth below the building, or by adhesion or friction or both, in the soil or rock in which it is placed.
Excavation means a man-made cavity or depression in the earth's surface formed by earth removal, and includes a trench, deep foundation, tunnel, shaft, or open excavation, but does not include borrow pits, gravel pits and quarries, unless specified by a safety and health officer.
Open Excavation means an excavation where the width is equal to or greater than the depth.
Pile or Caisson means a slender deep foundation unit made of materials such as wood, steel or concrete or combination thereof, which is either premanufactured and placed by driving, jacking, jetting or screwing, or cast-in-place in a hole formed by driving, excavation or boring.
Professional engineer means a person who is a member of the Association of professional Engineers of Manitoba and registered as a professional engineer under The Engineering Profession Act or who, being a non-resident, is in possession of a subsisting license granted under The Engineering Profession Act.
Shaft means a vertical or inclined opening excavated below ground level.
Sheathing means a continuous row of wood or steel sheets in close contact to provide a tight wall to resist the pressure of the walls of an excavation.
Shoring means a construction procedure used specifically to maintain the stability of the walls of an excavation and provide protection to workers who may enter the excavation.
Strut means a horizontal cross-member of a shoring system that directly resists pressure from a wale or upright.
Support Structure means a shoring system required to maintain the stability of the walls and ceiling of an excavation and includes a trench cage.
Trench means an excavation having a depth which exceeds its width measured at the bottom.
Trench Cage means an approved steel support structure designed to resist the pressure from the walls of a trench and capable of being moved as a unit.
Trench Jack means a screw or hydraulic jack used as a brace in a shoring support structure.
Tunnel means a generally horizontal excavation more than 1 metre in length located below ground level.
Uprights means the vertical members of shoring that are placed up against and directly resist pressure from a wall of a trench.
Waler means a shoring member that is placed against and directly resists pressure from sheathing or uprights.
PART II - HAZARDS TO EXCAVATION WORKERS
Why do serious injuries and fatalities to workers continue to occur in the excavation industry?
It is because both employers and workers often forget that when they remove earth from the ground, they are creating a situation where extreme pressures may be generated at the face of an excavation. There is no longer material available to support the walls of the excavation. Engineering controls must be utilized to provide a safe and healthy workplace within the excavation.
REMEMBER
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PART III - WHAT TO DO
PRIOR TO EXCAVATING?
All employers undertaking excavation work are required to notify the Workplace Safety and Health Division and obtain a registration number. Once this number is obtained, the employer is considered a registered excavation contractor. If an employer is not performing excavation work safely, then a Safety and Health Officer may revoke the registration and the employer cannot do any more excavation work.
An employer may re-apply for registration, but must prove to the satisfaction of a Safety and Health Officer that he/she understands the requirements of the excavation regulation and will perform excavation work safely. Contact the Division if you are not registered!
Every excavator who intends to make trench excavation in excess of 1.8 metres (6 feet) or an open excavation exceeding 2.4 metres (8 feet) in which a worker may enter must notify the Division not more than 48 hours prior to beginning the excavation. The Division will assign a serial number for that excavation.
The following information must be provided to the Division at the time of notification:
 | the excavation contractors registration number
| the name and address of the owner of the land where the proposed
excavation is to be made
| the name and address of the employer, principal contractor,
municipality, public utility, or agency of the government proposing to
excavate
| the location of the proposed excavation and the date of the
commencement of the work
| a description of the proposed depth, length, and width of the
excavation
| a description of the proposed method of shoring, including the type
of shoring materials to be used
| verification that the appropriate utilities have been notified and
that the location of any pipes, conduits, or previous excavations in or
adjacent to the proposed site has been determined and
| the name of the on-site worker supervising the excavation. | |
Serious accidents have occurred in the past when excavators have made contact with a gas or energized electrical line causing fires, explosions, and injuries.
An excavation cannot be started until all the public utilities (including telephone, hydro, gas, steam, etc.) have been notified and the accurate location of all underground facilities has been determined.
If damage to any pipe, cable, or other underground facility occurs once the excavation has started, the employer must contact the utility immediately and advise them of the contact. No further excavation work should proceed until the utility has undertaken an on-site inspection. The workers must be evacuated from the worksite if an energized cable is exposed or dangerous fluids or gases are released.
| Where a worker or any portion of excavating machinery or equipment may come closer than 3 metres (10 feet) to an overhead or underground electrical power line, the public utility must be contacted and permit authorization obtained. |
An employer must engage a professional engineer to provide design information and approvals for shoring support structures where a worker or workers are required to enter an excavation:
A hazard assessment must be undertaken to determine the risks associated with workers entering an excavation. Possible hazards include:
If a risk assessment reveals that there is a confined entry hazard in an excavation, then a proper work plan must be developed.
For example, in cases where a toxic or hazardous atmosphere may exist or could reasonably be expected to exist in an excavation, the employer must test the atmosphere and control worker exposure to the hazard. (For example, this may occur in excavations where there are accumulations of gasoline vapors due to leaking underground tanks. There are also situations where there may be elevated carbon monoxide (CO) levels or a lack of sufficient oxygen in the excavation.)
What to do:
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(Refer to Workplace Safety and Support Services Division "Guidelines for Confined Entry Work" for more detailed information).
An effective training program must be developed and delivered to excavation workers. Prior to a worker beginning excavation work, the employer must instruct each worker in proper and safe work procedures. This includes making the worker aware of the hazards associated with excavations and any emergency procedures or rescue methods that may have to be utilized.
The employer must ensure that an experienced and trained worker is designated to directly supervise each excavation project. This worker must be familiar with all aspects of excavation work, from shoring requirements to emergency rescue procedures. The supervisor must directly supervise all excavation work during the entire period the workers are in the excavation.
PART IV - GENERAL
SHORING REQUIREMENTS
All workers doing excavation work must wear CSA approved Grade 1 safety footwear and safety headwear. Additional personal protective equipment may be required, depending on the risk assessment for the work to be undertaken (i.e. hearing protection, hand protection, etc.).
The employer is required to ensure that there is always an experienced worker designated to be the "observer" for trench excavations. This worker is responsible to remain on the surface and keep the trench and workers under observation for unsafe conditions.
If workers are required to cross-over an excavation, then a proper walkway with suitable guardrails on all exposed sides must be provided.
All excavated materials must be piled in a manner so that the material cannot roll back into the excavation. The material must never be closer than 1 metre (8 feet) from the edge of the excavation, and should be placed as far away from the excavation as possible.
Tools, equipment, and heavy machinery shall not be placed or used near an excavation where they may fall into the excavation or affect the structural stability of the walls of the excavation.
All excavations, where the public has access, shall have a means provided to guard the public from the hazards of the excavation project. This includes barriers and signage to protect the public from falls, falling material, and excavating equipment. Proper covers or fencing must be provided to prevent the public from access to the excavation during "off" hours.
In public traffic areas, adequate signage and barricades meeting the requirements of the municipal or provincial highway authorities must be provided.
First aid and emergency supplies must be kept at the excavation project at all times. It is recommended that at least one worker per shift be a trained first aider with CPR certification.
Engineered design specifications for shorting support structures, including trench cages, must be forwarded to the Division before using the structures, and made available at the excavation site to a Safety and Health Officer.
Design specifications shall include:
| The employer is required to construct all
shoring systems in accordance with the engineering design information
provided. |
PART V - TRENCH AND
OPEN EXCAVATIONS
Shoring, or the proper sloping of an excavation must be provided where a worker is to enter an excavation that is considered to be:
OR
The shoring support structure must be designed to withstand all external forces that may be caused by:
Unless approved by a professional engineer, shoring support structures must be installed so that they are in firm contact with the walls of the excavation. This may require backfilling of voids in the excavation up to the shoring support structure.
| FROZEN GROUND IS NOT CONSIDERED
AN ALTERNATIVE TO PROPER SHORING |
For purposes of establishing shoring tables for trench excavations, soils in Manitoba have been categorized into three main types:
Check here for more information about Manitoba soils
Instead of a shoring support structure, a safe method to protect workers in an excavation is to slope the walls of the excavations at a grade of 1:1 (45 degrees) or flatter. The 45 degree slope is required no matter what type of soil conditions exist. (Fig. 2)
A combination 1:1 (45 degree) slope and vertical face may be used, as long as the vertical face does not exceed 1 metre (3 feet) and the overall depth of the excavation is not greater than 5 metres (15 feet) (Fig. 3).
| To calculate the overall width of a
sloped excavation, use the following formula: WIDTH = (2 X DEPTH) + BOTTOM TRENCH WIDTH
|
The majority of wood shoring used in trenches in Manitoba is comprised of full dimension poplar planks and timbers. Spruce lumber is also acceptable as shoring material provided it meets the shoring table requirements. The lumber must be construction grade No.2 or better. Plywood used as sheathing material in loose soils must be a minimum of 2Omm (8/4 inch).
Steel trench jacks maybe used as struts, as long as they are equivalent in strength to the wood struts specified in the shoring tables. The longer dimension of the trench jack "foot" must be located perpendicular to the grain of the wood on the upright. (Fig. 5)
Check here for more information about types of soil collapse
The shoring tables and diagrams indicate the allowable size and spacing of wood classifications of soil in Manitoba.
When installing shoring within a trench type excavation, proper methods and procedures must be followed to provide for a safe excavation. (Fig. 11)
| Uprights, struts (screw jacks), wales,
and plywood must be installed in accordance with the shoring
tables based on the soil conditions, depth, and width of the
trench excavation. |
Installation of Shoring (Fig. 12)
When shoring is in progress, the bucket of the excavation machine must be placed in the trench directly in front of the shoring being installed. The bucket will serve as additional protection if a cave-in occurs.
A proper ladder must be provided in a trench or open excavation. The ladder must extend at least 1 metre (3 feet) above ground level and be within 3 metres (10 feet) of a worker's working position.
It is essential that shoring struts/jacks be installed from the top down. It is important that the top (first) strut/jack be placed approximately 0.5 metres (18 inches) below the surface, then the second strut/jack placed according to the shoring table. The installation of the first and second strut/jack to support the vertical uprights is very important as it stabilizes the excavation walls.
When plywood is used, the jacks or struts must never be installed directly on to the plywood. (If the walls move, the jack or strut could push through the plywood). Where plywood is used, the jacks must be placed on the uprights that support the plywood.
Once the worker has a minimum of two struts/jacks placed on each set of uprights, the worker can proceed to install the bottom strut/jack. There must never be less than two struts/jacks used on each set of shoring.
This procedure is to be followed with each set of shoring. Using this method, the worker is protected by the bucket of the digging machine and the shoring already installed.
Removal of Shoring (Fig. 12a)
When removing shoring, the reverse procedure is used. That is, the struts are removed from the bottom to the top. Remember, there MUST never be less than two sets of uprights in place and the worker must always remain within the shoring in place for protection.
If there is undue pressure felt when removing a strut or jack, it means that the soil has moved and the trench must be backfill led up to the bottom jack before it is removed; then up to the next jack and so forth. Remember, do not try to remove a jack with undue pressure! as it may cause a sudden collapse.
It is preferable to have the worker who installed the struts to be the one who removes them. That worker will know if there has been a change in conditions, undue pressure on struts or other potentially dangerous conditions.
A trench cage is a self-contained steel structure placed in an excavation (prior to a worker entering) that is designed to withstand soil pressures and protect the worker(s) against soil cave-ins. (Fig. 13)
Trench cages must be designed by a professional engineer and constructed inspected and maintained in accordance with the engineering specifications. The design criteria for a trench cage is normally based on 75 pounds per square foot of earth pressure, per foot of depth of the excavation.
Where trench cages are designed to be "stacked" in deep excavations. these must be secured in a manner to transmit the loading condition between cages.
Trench cages shall have continuous sides and extend at least 600 mm (24 inches) above the vertical wall of the excavation.
Hoisting hookup and drag points on trench cages must be designed and engineer approved. Workers working in a trench cage that is to he dragged forward, must be protected against rigging failure by suitable protective screening or other means.
| NO WORKER IS TO WORK OUTSIDE
THE PROTECTION OF THE TRENCH CAGE! |
Hydraulic and pneumatic shoring systems are advantageous because a worker does not have to enter the excavation in order to put the supports in place. These systems are often made of lighter weight material such as aluminum and can be handled easily. Care must be taken to ensure that the systems are property maintained and not damaged when in use.
Hydraulic and pneumatic shoring systems must be certified by a professional engineer to be equivalent to the requirements as specified in the trench shoring tables for the particular soil conditions.
Excavations that are not considered to be trenches, caissons, shafts, or tunnels may be classified as open excavations. A basement or foundation excavation for a building or structure is a good example of an open excavation. If an open excavation exceeds 2.4 metres (8 feet) in depth, then the walls of the excavation must be vee'd-out or a shoring support structure designed and installed.
A shoring support structure for an open excavation must be designed by a professional engineer. Typical structures consist of heavy wood lagging supported by steel I-beams properly installed into the foundation. The engineering specifications must include complete details on the correct procedures to install the support structure and on-going inspection criteria to ensure the shoring is maintained in a safe condition.
| BE AWARE! An open excavation may become a trench excavation as the project proceeds. A concrete basement wall constructed in an open excavation 2.0 metres (6.6 feet) deep, now requires shoring or veeing-out if workers are required to work on the outside wall between the concrete and earth. (Fig. 14) |
PART VI - SHAFT AND
TUNNEL EXCAVATIONS
Shaft and tunnel excavations are used primarily in sewer, water, and other utility work and include such procedures as vertical circular shafts, "hand" tunneling operations and fully mechanized excavating systems ("moles").
The requirements outlined in Part III and Part IV of this guideline apply to shaft and tunnel excavations. It is especially important to ensure that the following requirements are actioned.
Shaft and tunnel excavations are to be considered confined entry situations and a hazard assessment and risk control analysis must be undertaken.
Where monitoring of hazardous atmospheres is required, the job site supervisor must be equipped with suitable testing equipment (i.e. explosive meter, oxygen, and toxic gas detectors) and be trained in proper monitoring procedures. It is recommended that continuous monitoring devices be used where monitoring is necessary.
Ventilation systems must be put in place to provide a safe atmosphere where there may be a lack of oxygen or unsafe accumulations of toxic vapours, gases, dusts, or other harmfull substances.
| The ventilation rate at the work face
of the tunnel shall not be less than 2.75 cubic metre/second per
square metre of face area (50 cubic feet/minute per square foot of
face area). |
Due to the nature of the work, it is important that proper first aid supplies be provided at the excavation worksite. A first aid kit shall be provided at each shaft location. It is recommended that at least one worker on each shift shall be a certified first aider with CPR training. A basket stretcher and blankets must also be provided at each worksite, as well as a "parachute-type" full body harness for hoisting a worker to the surface, if necessary.
Workers shall be instructed on rescue procedures to be undertaken in case of a serious accident or injury occurring in a shaft or tunnel.
The wash-up facilities at excavation worksites must be kept in a sanitary condition. Provisions must be made to provide a supply of clean and warm running water, hand cleaners, soap, and towels for the workers to use.
Underground excavations must be provided with a source of electrical illumination for the full length of the tunnel and at the working face of the tunnel excavation [minimum 25 lux (2.5 foot-candles) of illumination]. In the event of electrical failure, an emergency lighting system must be in place. This may consist of battery operated flashlights suitably sized and located to assist workers in exiting the tunnels.
All electrical circuits in underground excavations must be installed in accordance with the Manitoba Electrical Code. Light bulbs shall be caged to protect them from physical damage. Due to the moisture accumulations in such excavations, it is essential that electrical wiring systems be properly grounded. Only electrical equipment and tools that are doubly insulated or properly grounded can be used. It is recommended that GFCI's (Ground Fault Circuit Interrupters) he used for electrical circuits underground.
A minimum of two, 2A-1OBC rated multi-purpose type fire extinguishers shall be provided in each shaft and tunnel excavation. Any flammable or combustible liquids must be stored in compliance with the Manitoba Fire Code and dispensed only from safety containers meeting the requirements of CSA Standard B376, "Portable Containers for Gasoline and other Petroleum Fuels".
Combustible scrap materials such as wood shoring components, shall not be allowed to accumulate in the excavation. These shall be removed at least daily.
All blasting operations must be undertaken by a certified blaster who is qualified to handle and use explosives. Explosives must be stored and transported in accordance with both Transport Canada and Energy Mines and Resources Canada regulations.
Vertical drilled shafts, shored with steel sleeves, are normally provided access by a straight fixed vertical ladder. Where the ladder exceeds 5 metres (15 feet) in length a rest platform or proper fall protection must be provided. This can be done by providing a worker with a full-body safety harness secured with a lifeline to a fall- arresting device.
In shaft and tunnel operations, the worker accessway to a shaft must extend the full length of the shaft and be completely separated from the hoistway in a manner so that the load or hoisting device cannot come in contact with the workers. The accesaway must he equipped with a vertical ladder having rungs spaced at 300 mm (12 inches) on centre with a clear space of 150 mm behind each rung, and rest platforms (landings) located every 5 metres (15 feet).
Both accessways and hoistways shall be provided at the surface with proper guardrails having a top rail, mid-rail and toeboard. The accessway must have a secured cover to prevent unauthorized entry and the cover is to be locked at all times when not in use.
All shafts and tunnel support structures shall be designed and approved by a professional engineer in accordance with the provisions of Part III and Part IV.
A shaft that is to be excavated to a depth of 1.8 metres (6 feet) or more shall have shoring installed continuously from 300 mm (12 inches) above the surface of the excavation to the bottom of the shaft.
Soil shall not be exposed in lifts greater than 1.8 metres (6 feet) where workers may enter, without the immediate installation of proper shoring.
Subject to confirmation by a professional engineer, vertical shoring must be equivalent to full 75 mm x 200 mm (3" x 8") close shored timbers supported by 200 mm x 200 mm (8" x 8") horizontal wales [maximum 2.5 metres (8 feet) span not more than 1.8 metres (6 feet) on center and posted at the corners. For spans greater than 2.5 metres (8 feet), the wales must be increased in size in accordance with engineering specifications.
Subject to confirmation by a professional engineer, crown shoring shall not be less than full 75 mm x 200 mm (3" x 8") timbers that extend from the 10 o'clock position around the roof to the 2 o'clock position. The shoring shall be put in place as digging proceeds and as soon as possible after the "monkey hole" has been excavated. Planks shall be fully over lapped at connection points. [75 mm (3") minimum]
Crown shoring shall extend a maximum of 900 mm (3 feet) beyond the concrete framing for the next "push". The maximum length for crown shoring is 3.0 metres (10 feet) under stable soil conditions.
"Face" shoring is to be installed in all tunnels greater than 1.8 metres (6 feet) in diameter and in tunnels at a lesser diameter where soil conditions may be unstable.
Steel sleeves are often used to shore vertical drilled circular shafts in cohesive soils. The sleeves are usually made from unreinforced steel plate and have proved to successfully prevent local "cave-ins" of blocks of soil and wet silt layers. Subject to confirmation by a professional engineer, the following minimum criteria apply;
Note: This type of shoring is temporary and should not be utilized for periods longer than 30 days and should not be used for holes larger in diameter than 4.5 m (15 feet).
All cranes and hoisting equipment used for excavation work shall be inspected and maintained in accordance with the manufacturer's maintenance procedures. Records of such inspection and maintenance shall be kept in a crane log book.
All ropes, cables, chains, blocks, and other hoisting equipment shall be rated as hoisting equipment and regularly inspected to ensure that the equipment is not damaged and can continue to be used safely.
The employer shall establish a system of clearly communicated signals which shall be used for all hoisting operations. Workers appointed by the employer and trained in proper hoisting procedures shall be located at both the top and bottom of a shaft at all times hoisting operations are to be undertaken.
A motorized locomotive with an internal combustion engine must be equipped with a properly maintained exhaust conditioner and serviced regularly in order to control hazardous exhaust gases and other emissions (i.e. carbon monoxide, nitrogen oxides).
All haulage locomotives must be equipped with properly maintained braking systems and operator "dead-man" power controls that are operational from the driver's station only. The locomotive must also have an audible horn and warning lights.
No workers shall ride on haulage locomotives, except in seats provided for that purpose. A worker may only ride in a vehicle designed specifically for the transportation of workers. Workers are not allowed to ride in a haulage bucket that is being hoisted to the surface in a shaft.
Haulage buckets shall not be overloaded with mud in a manner where the material is likely to fall out of the bucket.
It is important that rail track placed for haulage locomotives and buckets is constructed in a straight manner, located at a uniform height to the established tunnel grade, and securely fastened to the foundation ties.
PART VII - CAISSON
EXCAVATIONS
Due to the nature of the risks involved in a worker entering a caisson or similar type of deep foundation excavation, it is essential that the employer develop a documented safe work procedure for this type of confined entry work. A documented method of access and egress for a worker is to be available at the worksite prior to a worker entering the excavation.
It is also essential that the excavation be under constant supervision at all times when a worker is in the caisson. An "observer" must be at the surface near the top opening at all times when a worker is in the caisson. (Fig. 15)
The principles established in Part III and IV of this guideline regarding confined entry apply to caisson excavations. Procedures must be developed to deal with a number of potential hazards. The risk assessment must include, but may not be limited, to the following:
A sufficient supply of air suitable for breathing must be provided in a caisson excavation. This is normally provided through a proper piping system from the surface to the working level. An adequate supply of uncontaminated breathable air must be provided throughout the period a worker is working in the excavation. Continuous electronic monitoring of the oxygen content of the air in a caisson must be undertaken prior to a worker entering the excavation and during the time the worker is in the caisson.
Where it is suspected that poisonous or flammable gases may exist in the caisson, continuous testing must also be undertaken.
Precautions must be taken to ensure that exhaust gases from the compressor or other internal combustion engines nearby do not enter the excavation.
The shoring support structure for a caisson excavation must be approved by a professional engineer, prior to a worker entering such an excavation. Steel sleeves of approved dimensions and material are normally used to shore a caisson.
The minimum diameter of a shoring support structure in a caisson is 700 mm (28 inches).
The shoring support structure must extend a minimum of 600mm (2 feet) above ground level to the point where work is to be undertaken.
A worker entering a caisson excavation must be secured to a tripod-type hoist or similar device that is approved by a professional engineer. The tripod hoist must be of a sufficient height to raise the worker completely above the surface of the caisson.
The worker retrieval and fall-arrest device is separate from the "mud bucket hoist and must be capable of supporting a worker with a 4 to 1 factor of safety. The device must be equipped with an adequate braking mechanism capable of arresting the fall of a worker with the same factor of safety. The retrieval system shall be capable of bringing the worker to the surface of the excavation in 2-1/2 minutes or less.
All cables, hooks, shackles, and other components shall be rated by the manufacturer as hoisting components having a 10:1 safety factor. They shall be inspected on a regular basis to ensure that they are not damaged.
The correct number and spacing of wire clips and thimbles must be used when rigging hoisting components.
| All hooks must be equipped with a
positively secured safety latch. Simple spring-type safety latches
that cannot be secured in a closed position are not acceptable.
|
A worker entering a caisson must wear a full-body safety harness attached to an approved lifeline that is secured to a fall-arresting retrieval device located at the surface of the excavation.
The worker must wear CSA approved footwear and headwear at all times. Safety eyewear and other job-specific protective equipment may also be necessary.
