Improving non-uniform gravelly sand using microbially induced carbonate precipitation: An outdoor cubic-meter scale trial by engineering contractors
Guijie Sang, Rebecca J. Lunn, Gráinne El Mountassir, James M. Minto, Erica McLachlan, David J. Bradley, Kenneth W. Henderson
Abstract
Soil improvement using microbially induced carbonate precipitation (MICP) remains largely confined to the laboratory, with only a very small number of large-scale experiments having been completed under field conditions and none by engineering contractors. This study presents a cubic-meter scale improvement of heterogeneous natural sand collected from a local quarry, with a wide variation in grain size, via MICP. The MICP trial was conducted by engineering contractors in a cubic test cell under variable temperatures ranging from 5 °C to 19 °C. The upscaling of cultivation of Sporosarcina pasteurii (600 L for each treatment cycle) under non-sterile conditions, as performed by engineering contractors, achieved an optical density (OD 600 ) of 0.89 and a specific urease activity of 2.5 mM urea/min/OD 600 . Post-MICP-treated sands were subjected to a series of coring, block sampling and laboratory tests. The block sampling process indicated that the majority of sand was effectively cemented, with a small region near a side wall forming a less well-cemented zone, likely induced by less effective fluid delivery in this region. The unconfined compressive strengths of three cores (diameter: 10 cm, length: 22 cm) were 3.6, 4.4, and 7.6 MPa. Consolidated-drained triaxial tests on sub-sampled cores also demonstrated rock-like material behaviour, with a peak friction angle of 43.6° and peak cohesion of 0.64 MPa, and ultimate state frictional angles of 42.0° and ultimate cohesion of 0.12 MPa. The increased shear parameters of the bio-cemented samples (relative to the untreated samples) have many implications for mitigation of geotechnical hazards such as soil liquefaction. The study marks a step forward industrial implementation of MICP for soil improvement by engineering contractors without prior knowledge of MICP. • A m 3 -scale MICP trial on heterogenous soil was performed outdoors at 5–19 °C. • MICP improved soil cohesion, peak and ultimate state frictional angles. • Engineering contractors can conduct field MICP trials without prior knowledge.