Consultation on the use of narrow trenching in Scotland's roads

It would be our suggestion to set this at no less than 100mm. Specialist plant and machinery required to compact the trench and its layers at anything less would be extremely challenging.
The compaction method, material suitability (where non-SROR specified materials are used), and the suitability of the plant to be used should be demonstrated to the Roads Authority for approval.

Due to the narrow width of the trench the technical tolerances should be adjusted accordingly (i.e a reduction of the level of settlement). These should be reviewed and defined by the SROR working group and added to the SROR document.

Testing should also be reviewed with alternative testing techniques suitable for narrow widths introduced, and coring specifications reviewed and adjusted accordingly

For footways constructed to a standard 230mm make up ( 30mm wearing course, 50mm binder and 150mm sub base) we would like to seen the narrow trenching 100mm below this sub base layer. For a footway minimum depth of 380mm cover.

For a type 3 and 4 carriageways we would want to see the absolute minimum of 450mm cover.

We would not want this installed in high speed A- B roads.

The materials to be used would be dependent on the width of the trench and they should be specified on the SROR for different widths. For example, foam concrete on carriageways, or foam concrete with bituminous surface course (as per the SROR).

Evidence in the form of photos/ levels should be provided on the VAULT when the depth of cover is not as per the Guidance

This is dependent on the location and hierarchy of road.

The materials to be used would be dependent on the width of the trench and they should be specified on the SROR for different widths. For example, foam concrete on carriageways, or foam concrete with bituminous surface course (as per the SROR).

Conventional materials should be used when possible

We would want to see detail records kept of any installations, including photos and as built drawings. We would also want the information recorded on the SRWR/ Vault system.

Companies sign up to a charter of dial before you dig to then get them to mark out their apparatus. Plant protection officers should be available to attend sites as and when required.

A preferred route would go through the footway and road verges. The crossing points when required should be agreed with the Roads Authority and only on Type 3 and Type 4 roads.

If a route uses the carriageway this will only be allowed on Type 3 and Type 4 carriageways and restrictions will apply (i.e location away from the wheel tracks).

Restrictions will also apply on conservation areas where the reinstatement materials should match the existing ones exactly.

Restrictions will also apply on roads with engineering difficulties and in certain locations there will be a complete ban for example where a geogrid or a road protection is in place.

We would not want to have an alright ban. However, this is a complex technique that can impact on the road network. We would treat every application on a case by case basis. We would want to be consulted and then we would give careful consideration.

Yes narrow trenching should be Prohibited where certain ground conditions are encountered and looked at on a case by case basis.

All works should comply with existing code of practice and proposed changes to the code.

We would want all companies who are using this technique and promoting the products within to have utility status.
Given this is a relatively new process and is not tried and tested we would want an extended period of warranty from 3 to at least 5. This will allow us to monitor the performance of the reinstatement at no potential cost to us.