Civil Engineering

DRAINAGE PROJECT

M180 Filter Drain Refurbishment

In-situ recycling & stabilisation in Area 12

Carnell collaborated with National Highways to undertake in-situ filter drain refurbishment, in Area 12.

A number of flooding hot-spots were identified on the network, and after teaming up with Carnell, a scheme was developed and passed through the Value Management process.

Carnell undertook the remediation works on the M180 between J1 & J4, along sections of both verges and the central reservation. This comprised the removal of surface vegetation and the recycling of the combined surface and groundwater filter drain. With the asset returned to its optimum performance, the filter media was also reinforced using Carnell’s TRL approved StableDrain solution.

To minimise the network occupancy, two StoneMaster units were used in tandem, halving the overall duration of the schemes. In total the two crews covered a distance of 6,800 linear metres which resulted in over 11,800 tonnes of aggregate being recycled and immediately reinstated to the drain.

This provided an estimated reduction of more than 1300 HGV movements on the network and a Carbon saving of over 70 tonnes.

The need for remediation

The functionality of all filter drains, especially those not constructed to specification, will diminish over time. Silt from surface run-off and fine particles from the carriageway sub-layers fill the voids between the aggregate.

Vegetation / overburden will grow on the surface of the filter drain to further restrict water reaching the carrier pipe.

With an impermeable barrier formed in the filter drain, it will hold water, leading to surface ponding and during times of heavy rainfall, standing water in the running lanes. Road user safety and network resilience will both be compromised as a result.and immediately reinstated to the drain. This provided an estimated reduction of more than 1300 HGV movements on the network and a Carbon saving of over 70 tonnes.

Preliminary surveys

Knowing the benefits which could be gained from remediating the asset, A-one+ undertook preliminary surveys to determine the locations of filter drain along the carriageway, the surface condition and carriageway profile to determine the primary drainage asset.

Subsequent trial excavations assessed the filter drain dimensions and the depth of silt. Samples were taken by Carnell to ensure the material in the drain could be efficiently recycled (grading profile), whilst others were sent for independent chemical analysis to ensure compliance with waste management and environmental legislation.

Innovative solutions

The sustainable StoneMaster process has advantages over the traditional ‘dig-out & replace‘ method, in that only arisings containing silt, fines and aggregate not conforming to type B specification are removed from site. The vehicle movements associated with the import and export of material was reduced by 80% overall.

StableDrain reinforces the newly refurbished filter drain so that the surface is able to withstand vehicles which stray onto it at speed. Subsequent risks resulting from stone scatter and recovery operations are therefore significantly reduced.