Tilford Street is a narrow, but busy country lane connecting Tilford with the B3001 to Farnham, Surrey. The width of the road, with minimal space in the verges due to tree roots and services, meant that there would be insufficient space for a conventional solution without extensive excavation of the roadway itself.
Surrey County Council wanted to install non-traditional, sustainable solutions to not only reduce the risk of flooding and future maintenance, but also increase biodiversity through creation of habitat. Any highway drainage solution that could increase the amount of surface water kept on site and allow it to infiltrate into the surrounding land would therefore contribute to those objectives. Learning of the capability and versatility of Hydrorock, the team also wanted to pursue a minimal-design approach, effectively creating a solution on site in real time.
The verges alongside the road are narrow and there are tree roots and other services underground, that any excavation and drainage installation had to safely work around.
In terms of sustainability, the Council wished to minimise the use of plastic in favour of natural materials and, whilst needing to ensure that the roadway stayed clear of standing water, they wanted to infiltrate as much of the surface water on site without discharging into existing drainage or natural water courses.
The versatility of Hydrorock’s natural aquifer D blocks (without plastic channels and connectors) empowered a more innovative, improvised approach to reach a solution in which a high-level design was set but execution was a collaboration between engineers and contractors on site, developing the solution block by block. They understood the characteristics and capabilities of Hydrorock and conceived different ways in which it could be deployed.
Standard density blocks were used in both verges, varying the number of blocks side-by-side to work around obstacles like tree roots, and linked them together using high density blocks stacked three high under the highway. As every block was in contact with at least one other, a large volume unitary aquifer could be created, sufficient to buffer and infiltrate the required volume of run off.
In addition to its flexibility, the speed of installation of Hydrorock meant that the drainage elements of the project completed within the four-week timeline.
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