Project Sheet: Erddig



  • OPUS International Consultants

Works Undertaken

  • Site Investigation
  • Organisation and supervision of the excavation of trial pits, soakaway testing and CBR testing
  • Geotechnical and environmental recommendations for the development

Description of Project

GroundSolve Ltd were approached by OPUS International Consultants to assist them with the investigation of a proposed development site off Wrexham Road in Rhostyllen, with some 226 conventional houses planned on site. 

Before development work could commence, a detailed design of the road and drainage was required. This involved the following testing:

  • Californian Bearing Ratio (CBR) 
  • Soakaway testing
  • Laboratory testing.

GroundSolve Ltd were appointed to organise and supervise this work. 

A total of 64 machine dug trial pits were excavated, some as deep as 3.60m. They were logged by a chartered geologist from GroundSolve Ltd. Soil samples were taken in several pits that were then sent to the laboratory for chemical analysis.

Three soakaway tests were carried out in all trial pits in accordance with BRE Digest 365, using a 1100-gallon water bowser capable of filling a pit in approximately 2 minutes. A pipe (3m long) was placed into each trial pit and gravel backfill was used around the pipe. The pit was then filled with water from the bowser and the time taken for it to empty was recorded. 

The CBR tests were carried out in 20 locations across the site and these were tested using the conventional TRL probe. 

The site investigation showed the ground conditions to be variable across the site. However, the site was suitable for soakaways and the use of traditional spread foundations for the properties.


ollowing the works a geotechnical interpretive report was issued, including geotechnical and environmental recommendations for the proposed development.

Trial Pit 4
Trial Pit 4
Infilling in progress during a soakaway test
Infilling in progress during a soakaway test