In London, Improvement addresses the challenges of variable superficial deposits overlying London Clay, Lambeth Group sands, and river terrace gravels. Schemes must comply with Eurocode 7 and the UK National Annex, alongside Environment Agency groundwater protection requirements. Typical techniques include stone column design to reinforce soft alluvium and made ground, and deep soil mixing for stabilising contaminated or weak cohesive soils while controlling settlement beneath foundations.
These methods are essential for residential and commercial basements, infrastructure cuttings, and embankment foundations where excavation and replacement are impractical. For granular soils beneath vibration-sensitive structures, vibrocompaction design offers densification without spoil removal. A robust ground investigation and serviceability limit state assessment remain critical to validate performance on London’s complex post-glacial and anthropogenic terrain.
Soil improvement comprises a set of techniques aimed at modifying the mechanical, hydraulic or strength properties of the ground, allowing construction on soils that originally would not meet design requirements. Its application is common in zones with soft, loose, expansive, collapsible soils or those with liquefaction potential under seismic loading.
Densification techniques include vibrocompaction for granular soils (improves relative density), dynamic compaction through controlled mass drop, and stone columns (vibroreplacement) which provide reinforcement and vertical drainage. Their effectiveness is verified through SPT, CPT tests and settlement measurements during and post-treatment.
Grouting (jet grouting, permeation, compaction grouting) modifies soil through cementitious, chemical or resin slurries that fill voids, increase strength and reduce permeability. Applications include excavation support, impermeable cutoffs, improvement of existing foundations and consolidation of collapsible or soft terrains.
Accelerated drainage techniques (prefabricated vertical drains, sand drains) reduce consolidation times in saturated cohesive soils, complemented with static surcharge. Monitoring of settlements, pore pressures and lateral deformations through specific instrumentation allows validation of acceptance criteria compliance and proceeding with construction on improved soil.