Streetworks

Note:- New BS EN 12591
Wearing Course = Surface Course; Base Course = Binder Course; Roadbase = Base

By employing sound excavation methods the risks of subsequent reinstatement failure can be avoided. Below are some basis principles to adopt.

Safe Excavation
The Health and Safety Executive has produced and recently revised guidance for excavation work HSG (47), this guide applies whether excavation work is on the highway or otherwise. This guide should be followed as failure to do so has lead to injury, death and prosecution. Reference can also be made to Construction Health Safety and Welfare Regulations 1996.

Summary of HSG (47) Avoiding Danger From Underground Services
Below are the main principles to adopt before excavation work commences.

A Suitable and sufficient assessment of the risks involved must be undertaken and safe systems of work made clear to those involved in the works
Utility plans showing the location of underground services must be obtained
The plans need to be interpreted by a competent person
Where the plans cannot be interpreted the utility company must be consulted for advice
A cable locator must be used to mark the position of the services up to 1 metre outside the excavation area
Where an unknown or unmarked service is located it must be reported to the likely utility company, tracing it to a source will also help in identifying it
Local authority plans showing drainage, fowl water, etc must also be obtained
Suitable excavation equipment should be used and trial hole dug to confirm the location of the services
Mechanical excavation should not be used closer than 0.5 metre to the service
In the event of a service being damaged the utility company must be informed. The area may need to be evacuated and the emergency services called where there is a risk to life or property
If excavating through any concrete any service lines should be made safe
Exposed services must be supported and protected to prevent movement and the risk of damage by other works

In addition to the above summary of HSG 47 the risk of trench collapse must be continually assessed. Past legislation suggested that when an excavation reached 1.4 metres the use of trench support is required. In the light of recent changes to legislation the depth is irrelevant as a trench in poor ground or high water tables may also pose a risk.

Personnel working in deep trenches near the traffic lanes are also at risk from carbon-monoxide poisoning and steps should be taken in accordance with the Confined Spaces Regulations to ensure that no person is put at risk.

The time between opening the highway and reinstatement should be kept to a minimum to prevent the subgrade and exposed faces from drying out.

The surface material should be cut with a pavement saw cleanly and vertically. the use of a breaker should be avoided as this can damage the surface edge and sometimes cause undercutting.

The sides of the excavation should be vertical and the bottom flat to allow for even compaction during reinstatement.

Ground and surface water must be controlled by pumping or diverting. Water left in the trench when reinstatement is carried out will cause the material to 'sponge' and full compaction difficult to achieve.

Excavated materials for re-use must be either removed for storage or adequately protected on-site to prevent drying, wetting or contamination. Material for disposal should be removed from site as soon as possible. Material must be kept at least 1 metre from the trench to prevent overloading the unsupported sides.

The trench should be made large enough to accommodate the work activities undertaken.

A trench by virtue of its nature may be defined as a confined space, reference should be made to the Confined Spaces Regulations and safe working practices employed on site.

There should be adequate and safe means of access and egress into the trench.

Deep excavations may need covering with steel sheets or a more rigid barrier provided to prevent unauthorised access or where the risks of falling in are high.