Summary
A collapsed Victorian sewer running below the A74 London Road, Glasgow caused significant localised softening of the soils due to water ingress. The main contractor excavated along the 50 m length of damaged sewer, taking the excavation down to 4.00 m below the existing road level. In addition there was redundant railway tunnel running adjacent to the excavation that could not be damaged during the injection works.
Objectives
Stabilise 150 m² to a depth of 7.00 m below the base of the excavation, using a combination of compaction PowerPiles and Deep Injection to improve the ground so that it can support the new sewer construction loads of 100 kN/m2
Technology Applied
62 Geobear PowerPiles were installed in the weak shallow soils to improve the bearing capacity. Additional Geobear Deep Injection works were carried out between the PowerPiles to achieve the required increase in bearing capacity. By using a combination of Deep Injection and PowerPiles we were able to avoid damaging the tunnel and limit the amount of polymer that migrated into the tunnel structure.
Outcome
The installation of 62 PowerPiles in combination with 80 Deep Injection locations successfully increased the bearing capacity of the shallow soils. The improvement of soil bearing capacity was confirmed by pre and post treatment dynamic penetrometer testing. All the Polymer treatment works were completed within a few weeks allowing the road to open on time.
