Consolidation and shearing behaviour of MICP-treated sand – a critical state approach

Microbial-induced carbonate precipitation is a ground improvement method and has the potential to be a sustainable and environmentally friendly alternative to conventional techniques. Several studies have investigated different behavioural aspects of treated soils, and some have used advanced testing such as triaxial shearing. Very limited studies can be found in the literature that have examined the treated soil behaviour from a critical state theory perspective. A series of drained and undrained triaxial tests are conducted on treated and untreated sand. Due to difficulties in obtaining a critical state line (CSL) for treated soil, its behaviour is analysed using the CSL of the untreated soil as a reference. Behavioural characteristics such as brittleness index, characteristic state, dilatancy and instability state are examined. Correlation of the state parameter (derived from the CSL of untreated soil) with peak stress ratio, brittleness index and characteristic state stress ratio is evaluated. Sudden partial or total loss of strength is observed for soil specimens sheared under relatively high confining stress and is attributed to localised failure and subsequent re-adjustment in soil behaviour.