Various hazards of accidents can follow in operating trenches, foundations, removal of material and other excavations that follow construction.

It is therefore important to carry out a risk assessment where the risks are defined.

Risk can be reduced by optimum preparation, by applying proper working procedures and by walking away from the workplace to avoid risks to staff or others.

The employer shall ensure that the safety and good working environment and health are in the workplace in the utmost possible way. This applies especially to the work, workplace, machinery, equipment and hazardous materials.

The risk of cuts collapsing or from their banks is generally reduced by a suitable angle of departure. Safety requirements concerning soil slope in different situations will be explained. The use of constraints will also be described.

Further details on risk assessment

Important things to do before you start:

• All pipes must be searched for information before digging commences.

• Care must be taken when working near machinery, cranes and other equipment.

• In the event of damage to underground cables or conduits, notify the person concerned immediately.

Read more:

• Enska/English: Act on Working Environment, Health and Safety in Workplaces, No. 46/1980

Organisation and implementation

Those who organise, execute or supervise works should have knowledge and experience of such work.

The person responsible for the execution of a task shall ensure that the highest level of security is maintained.

Checking the weight

Before digging trenches or excavating structures, one must consider the following: the characteristics of the soil, the depth of the excavation, its length and width, the groundwater level, the length of the trench or foundation and the amount of stress that will be exerted on the banks. In some cases soil testing may be necessary.

Preventing collapse

To prevent possible collapse in a trench it is necessary to have a suitable skin or to use yards. The risk of a collapse may also be reduced by digging trenches as short as possible, completing a conduit and then filling it. The risk of collapse of ditches and foundations may also be reduced by placing suitably tight mesh on the sides and banks.

Machinery work

When trenches and foundations are dug, it should be considered that they remain open for as short a period as possible. Excavations must be carried out with particular care and materials not placed too close to the banks of ditches, causing overloading and risking the bank collapsing.

Machinery loads and vibrations during excavations can be a major challenge on the bank of the trench. Therefore, a grave should be driven as little as possible in the vicinity of the canal and it should always be driven from the canal when excavations have been completed.

Taps and machines used for cutting and foundations must be located at suitable distances from banks. Special care is needed when soil is thawing.

Canal wall tilt

When cuts have sloping sides without cuts, the slope must be sufficiently large to prevent the risk of collapse. Soil material should be taken into account in each case. If stones protrude on slopes, it is important to remove them or to restrain them well to ensure a high level of safety.

It is not possible to set absolute rules on what this deficit should be. Many issues are important, such as the composition of the soil, depth of the trench, distance from traffic, distance from structures and other factors.

Examples of dangerous situations. The canal has become deeper than the groundwater level and there is little slope on the sides.

Constraints: general

If the material is loose, the vertical walls of the ditch must be securely restrained either by duct restraints, inclined trays, or by other means that make the work of the ditch safe. Constraints should be strong enough to withstand the ground pressure encountered, and to prevent collapse of the sides of the trench.

Examples of constraints.

Because of digging in wet clay or/wet sand in deep trenches (below groundwater level), the bottom may rupture or cause water to be pushed up from the bottom of a trench. When conditions are such, a bulkhead is to be used.

Special circumstances

When the excavation is longitudinal along a slope, special circumstances may arise. Layers, groundwater and soft clays can pose particular hazards, especially when clays mix with groundwater. Special care is also needed first after frost leaves the ground and when the ground thaws in a short period of time. In such circumstances, it is advisable to obtain advice from someone with good geological knowledge.

In circumstances such as these, it is necessary to restrain both the walls and the wall.

When you dig close to a supporting wall, there may be certain dangers. It is necessary to get advice in such situations as to whether the grave and even the support wall need to be restrained as well. In circumstances such as shown in the above figure, it is necessary to restrain both the walls and the wall.

Excavated material

The material that emerges from the cut increases the pressure on its sides and on placing it at maximum distance. It must not be less than one metre.

Material emerging from the cut must be placed at least one metre away from the edge of the cut.

Loose stones can easily slide into the trench if the material is too close. It should also be possible to walk securely along the banks of the canal without creating the risk of them falling over the person who may be working in the canal.

It should be possible to walk securely along the banks of the canal without creating the risk of them falling over the person who may be working in it.

Constraints removed: Filling

When constraints are removed, try to arrange work methods so that those who work on it do not have to be in the ditch.

Access points

In all cuts deeper than one meter, at least one ladder shall be used in each work area to make it easier for persons to go down into a ditch or shallow and up again. For long cuts, there should be more than one staircase to use. Ladders must extend from the base of a ditch at least one metre above its bank.

Interruption of work

If a break is required, the work area must be well enclosed and secured in accordance with the rules that apply to it.

Warnings

Working on cutting edges requires good lighting. Traffic warning devices shall be installed, in particular for road users and children. In this context, warning signs, warning lights, line and equipment preventing people from falling into ditches, for example in the dark.