Abstract
Tangential flow-induced interface erosion poses a major threat to a wide variety of engineering structures, such as earth-filled embankment dams, and oil- and gas-producing wells. This study explores the applicability of microbial induced calcium carbonate (CaCO3) precipitation (MICP) by way of the ureolytic soil bacterium Sporosarcina pasteurii as a method for enhancing the surface erosion resistance of fine sand. Specimens were treated with cementation solution concentrations between 0·02 and 0·1 M, and the erosional behaviour examined in a flume under surface-parallel flow and increasing shear stress. Photographs, cumulative height eroded-time series and erosion rates were obtained as a function of specimen height, MICP treatment formulation and calcium carbonate content. Results showed that while untreated specimens eroded primarily in particulate and mass form, MICP-treated specimens were characterised by a block erosion mechanism. Further, erodibility was found to depend on the calcium carbonate content and the cementation solution concentration. To understand this, a systematic study of the calcium carbonate crystal sizes and distributions was undertaken through X-ray computed tomography. Fundamentally, the effectiveness of MICP for erosion control was found to be dominated both by the precipitated calcium carbonate content and microstructural features, with higher contents and larger crystals yielding lower erodibility values. Additionally, crystal growth mechanisms varied depending on the cementation solution concentration.
Highlights
Tangential flow-induced interface erosion poses a major threat to a wide variety of engineering structures, including earth-filled embankment dams, and oil- and gas-producing wells
Results consistently showed that the coarse-fine sand interface was heavily cemented, with CaCO3 contents approximately 2-times greater than in the bulk fine material. This “preferential” cementation was consistent with the results presented in two previous studies by the authors, where coarse-fine sand specimens were treated with increasing number of injections of urea-CaCl2 solution
Erosion tests of MICP-treated fine sand were conducted using a newly designed Erosion Function Apparatus (EFA) and the sample structure was investigated with XRCT
Summary
Tangential flow-induced interface erosion poses a major threat to a wide variety of engineering structures, including earth-filled embankment dams, and oil- and gas-producing wells. This process occurs at the surface between soil and water or at the interface between two soil types (Regazzoni & Marot, 2013). The latter, termed contact erosion, generally starts along the interface between two different soils (e.g. coarse-fine soil interface), leading to the formation of a cavity. In hydrate-bearing reservoirs, such as the Daini-Atsumi Knoll
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