Strengthening Ground for a Cinema Seismic Upgrade

Treatment was required to increase cone penetration resistance, expressed as qc, and reduce the liquefaction potential of the identified soils. The ground improvement program targeted a cone resistance of 10 MPa.

The treatment area had already been excavated, requiring an approach that could be delivered within the exposed formation and integrated into the wider strengthening works. The solution needed to achieve consistent improvement across approximately 140 m², with testing used to assess the ground’s response.

Approximately 110 injection points were arranged on a 1.2 m triangular grid to provide coverage across the treatment area. Injections targeted a nominal depth of 1 m, treating soils approximately 0.5-1.5 m below the excavation surface.

An average of approximately 25 kg of expanding polyurethane resin was injected at each point. Resin expansion densified the surrounding soils, with intermediate bulk containers (IBCs) used to provide temporary surcharge loading to assist compaction during treatment.

The injection layout and surcharge approach were selected to support improvement towards the target cone resistance. Post-treatment cone penetration testing (CPT) and dynamic cone penetrometer (DCP) testing assessed the response of the treated ground.

Where testing identified areas requiring further improvement, Mainmark completed additional targeted injections.

The treatment substantially increased ground resistance across the identified area. Post-treatment CPT and DCP testing generally reached refusal, indicating a marked increase in resistance to penetration within the treated ground.

A small number of areas required reinjection to address local variations in treatment response. This targeted follow-up allowed Mainmark to refine the improvement program in response to the verification test results.

The project team reported that the overall results exceeded expectations. The works addressed the weak ground identified as a constraint to the proposed screw pile foundation solution and supported the wider cinema seismic strengthening project.