Case Study: Handforth, Cheshire – Soakaway Testing
Client: Confidential
Services: Soil infiltration testing, BRE Digest 365 soakaway testing, trial pitting, ground condition assessment, drainage recommendations
Location: Handforth, Cheshire
Project summary & client purpose:
As part of a proposed residential development in Handforth, Cheshire, Earth Environmental & Geotechnical carried out soakaway testing to support the site’s drainage strategy and planning application.
The proposed development comprised 28 new homes, together with associated roads, landscaping, open space and an attenuation basin. Our investigation assessed whether the underlying ground could accommodate infiltration-based drainage, providing the design team with reliable site-specific data to inform the SuDS strategy.
Our services:
Two soakaway trial pits were excavated to depths of up to 3.00m using an 8-tonne backhoe excavator. Our engineers logged the ground conditions before carrying out infiltration testing in accordance with BRE Digest 365.
Each excavation was filled with water from a bowser and monitored over several hours to measure infiltration performance. The results were analysed and presented alongside practical recommendations to support the proposed drainage design.
The challenges:
The investigation identified cohesive clay deposits beneath the site, which are typically associated with poor infiltration characteristics. Existing land drains were also encountered during the works, adding further consideration to the proposed drainage design.
The key objective was to determine whether soakaways could provide a viable surface water solution or whether alternative drainage measures would be required before the development progressed.
Results:
Testing demonstrated that infiltration rates were extremely low, with water levels falling only marginally throughout the monitoring period. As a result, the ground was found to be unsuitable for soakaway drainage.
By confirming this at an early stage, the project team was able to progress with confidence, selecting a more appropriate surface water drainage solution before detailed design and construction, reducing programme risk and avoiding unnecessary redesign.
