Effect of bio-cementation on geophysical and cone penetration measurements in sands

Abstract

Microbially induced calcite precipitation (MICP) is a potentially environmentally conscious ground improvement method that can improve the engineering properties of granular soils through the precipitation of calcite. In this study, an experiment involving two 1.7 m diameter tank specimens was completed to investigate the effect of bio-cementation on cone penetrometer and geophysical measurements in sands. Following nonuniform bio-cementation treatments, specimens achieved calcite contents ranging from 0.5% to 5.3% by mass, shear wave velocity (Vs) values between 131 and 967 m/s, and mid-depth cone penetration resistances (qc) ranging between 3.6 and 32.1 MPa. At calcite contents exceeding 5.0%, qcand Vsimprovements were as high as 527% and 686%, respectively. Although cone penetration resistance, sleeve friction, and friction ratio measurements exhibited limited sensitivity to bio-cementation at calcite contents of less than 3.0%, Vsmeasurements successfully detected bio-cementation at calcite contents near 1.0%. When qcand Vsmeasurements were compared at similar locations, increases in an empirical parameter (KG) enabled improved detection of bio-cementation at calcite contents near 0.5%. Large increases in normalized tip resistances (Qtn) and small decreases in normalized friction ratios (Fr) with increasing bio-cementation resulted in cemented materials plotting near and within the gravelly sand and sand-like dilative soil behavioral type regions using two soil behavior type (SBT) charts.