The Challenge

A sinkhole and surface depression developed within the car park. Investigations identified two affected areas with voiding extending to depths of 2.5m. Drainage defects, including displaced joints and open connections, had caused washout of supporting soils, while 21 penetrometer tests confirmed widespread loose ground beneath the site.

The Solution

• Conducted CCTV drainage surveys, GPR utility mapping and ground testing to identify the extent and cause of the sinkhole.

• Repaired defective drainage pipework and manhole structures.

• Filled voids adjacent to the affected manhole to eliminate ground loss pathways using Teretek® resin injection strengthening and improving ground conditions beneath the car park across a 114m² area.

Monitoring & Validation

• Pre and post-injection dynamic penetrometer testing.

• Continuous laser monitoring sensitive to 0.5mm movement.

• Digital recording of injection volumes, depths and treatment data.

• Validation of ground improvement through measured increases in ground resistance and controlled uplift from depth.

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Outcome

• Sinkhole successfully remediated without major excavation in a single mobilisation over a 3 week programme.

• Defective drainage infrastructure repaired to address the source of ground washout.

• Significant voids filled and loose ground improved using Teretek® resin injection.

• Ground conditions enhanced across both identified treatment zones supported by a 20-year material warranty.

Sustainability & Asset Performance

By combining drainage repairs with targeted ground improvement, Mainmark addressed both the cause and consequence of the sinkhole. The Teretek® solution avoided extensive excavation, reduced waste generation and preserved the existing car park infrastructure while delivering long-term ground improvement.