In situ soil cementation with ureolytic bacteria by surface percolation

Abstract

The possibility of using microbiological processes to improve the mechanical properties of soil by undisturbed in-situ application has gained attention over recent years. This paper describes a new variation of in-situ soil reinforcement technology based on Microbially Induced Carbonate Precipitation (MICP), which involves both the hydrolysis of urea by soil bacteria enzyme and calcium carbonate precipitation in the presence of dissolved calcium ions. In contrast to other previously published approaches, the current work uses surface percolation for in-situ placement of bacteria and cementation solution. Bacteria could be immobilised over the full length of a 1 m column by surface percolation. To accomplish this it was necessary to percolate alternate solutions containing either bacteria or fixation solution containing calcium ions.The biologically triggered cementation resulted in homogeneous cementation over the entire length of the 1-meter sand column. The efficiency of calcite crystals to form strength was found to be related to the pore water content of the continuously drained column with less water content enabling more efficient strength formation. Scanning electron microscopy supported the idea that lower water contents lead to selective positioning of crystals at the bridging points between sand grains. These findings imply that the cost of MICP technology can be reduced by optimizing the conditions for effective crystals precipitation. This is expected to make this technology more readily acceptable for large scale applications

Upscaling Effects of Soil Improvement by Microbially Induced Calcite Precipitation by Surface Percolation

“…The previous research (Cheng and Cord-Ruwisch, 2012) demonstrated that after primary treatments (2 flushes) a homogenous strength could be achieved in the 1 m fine sand column with 6 layers of bacterial placement. As discussed previously (Cheng and Cord-Ruwisch, 2012), with increasing column length a larger number of alternating layers of bacterial suspension and cementation solution for bacterial immobilization are needed.…”

“…Surface percolation associated with bacterial placement with multiple layers has been demonstrated in short columns (Cheng and Cord-Ruwisch, 2012). However, for large scale application depths of more than 1 m may need to be achieved.…”

“…A method of applying MICP specifically to unsaturated sandy soil by using surface percolation has been developed and demonstrated in the scale of 1 m depth (Cheng and Cord-Ruwisch, 2012). In comparison to the saturated flow MICP application, the unsaturated zone created in the surface percolation MICP treatment provided environmental conditions more conducive to the formation of effective crystals (Cheng et al 2013).…”

Improving the Strength of Sandy Soils via Ureolytic CaCO<sub>3</sub> Solidification by <i>Sporosarcina ureae</i>

“…6). It has been shown that MICP treated sands remain some porosity in materials (Cheng and Cord-Ruwisch 2012;Chu et al, 2012) and that good strength maintenance in seasonal water saturation and freeze-thaw is possible with porous materials (Cornforth 2005). Further studies may wish to investigate the permeability of hardened sands via S. ureae at various levels of CaCO 3 precipitation to strike a balance between 650 porosity, peak strength and endurance overtime in weather simulations.…”

“…Indeed, it has been 85 commented that the type of bacteria utilized is one of the major considerations and potential limitations in large scale geotechnical operations (Mitchell and Santamarina, 2005). Therefore, the search for new bacteria by which to achieve viable levels of MICP is important for optimizing the protocol best suited (in terms of performance, economics and environmental impact) for marketing in green industry (Cheng and Cord-Ruwisch 2012;Patel 2015;van Paassen et al, 2010). Following a literature review of the nine documented species of 90…”