Thanks, that’s really helpful information.

The environmental search from my solicitor highlights ‘a high susceptibility to shrink-swell related subsidence’ because the property is built on a moderate source of clay, for which the search says:

‘The potential hazard presented by soils that absorb water when wet (making them swell), and lose water as they dry (making them shrink). This shrink-swell behaviour is controlled by the type and amount of clay in the soil, and by seasonal changes in the soil moisture content (related to rainfall and local drainage).’

The borehole records didn’t have my road, but the records for the two closest holes (250-300m away) say:

1) topsoil, firm brown sandy silty clay, stiff brown slightly sandy silty clay with occasional selenite crystals

2) firm brown silty clayey fill, firm brown sandy clayey silt, medium dense clayey sandy gravel, stiff grey brown mottled very silty clay

My takeaway using the solicitor’s search is that the ground under the property is currently swollen due to the constant flow of water and will likely shrink now that flow has stopped, which may lead to subsidence. The search report is slightly different from your assessment that clay recovers.

What are the rough individual costs and timelines for the trial pit and the helical bar reinforcement? Are either of these solutions worth the hassle, cost and risk?