Erosion is relevant to a variety of infrastructure problems such as bridge scour, roadway shoulder erosion, coastal erosion, and riverbank and slope stability. This research investigated the feasibility of using microbial-induced calcite precipitation (MICP) as an erosion countermeasure. MICP is a natural phenomenon in which calcite precipitation occurs as a consequence of microbial metabolic activity. The precipitated calcite modifies the soil fabric and provides an additional bonding force between soil particles. In this paper, a preliminary experimental study on the erosional behavior of MICP-treated sand is presented. A standard soil, Ottawa graded sand, was treated with a bacterium (Sporosarcina pasteurii) in a full-contact reactor-one in which the soil in a fabric mold was fully immersed in the bacteria and cementation solution. The morphologies and crystalline structures of the precipitated calcite in porous sediments were characterized using microscopic imaging techniques. The treated soil samples were tested in a flume to investigate the erosional behavior; both surface erosion and bridge scour tests were conducted. Although the untreated soil is highly erodible, the erosion of the treated sand was found to be negligible under the circumstances of the test; however, some concerns were raised regarding practical applications. Efforts will be made in the future to identify alternative treatment procedures that are more applicable to the field.
Bridge scour has long been identified as the major cause of bridge failures. Bridge scour refers to the loss of sediment around bridge foundations, and it occurs when the erosive force from the flow exceeds the resistance from the soil. This article presents an experimental study on the effectiveness of two nature-inspired countermeasures for scour control and prevention, namely, streamlining and biocementation. On one hand, inspired by the streamlined form of the boxfish and the blue shark, this study introduced streamlining features (i.e., sloped nose and concaved sidewalls) for bridge piers in order to reduce the erosive forces in the vicinity of the piers. On the other hand, inspired by the natural process of microbial-induced carbonate precipitation (MICP) in soil, a polymer-modified MICP method is developed to “cement” the coarse-grained sand in order to increase the erosion resistance. Accordingly, two series of experimental tests were conducted to evaluate the performance of these two countermeasures: (1) based on the numerical results of a pier streamlining optimization study, four small-scale pier models with different streamlining levels were constructed using 3D printing techniques, and flume tests were conducted to characterize the scour process around these models; (2) Ottawa graded sand treated via the polymer-modified MCIP method was tested in the flume to investigate its effectiveness on bridge scour control. The experimental results revealed that both streamlining and biocementation could significantly reduce or even fully prevent the scour around the model bridge piers under the laboratory testing conditions.
Bridge scour has long been identified as the major cause to bridge failures. This paper presents the results of an experimental study on the effectiveness of two newly-proposed scour countermeasures, namely streamlining and biocementation, which are inspired by nature. On one hand, borrowing ideas from the streamlined body shape of boxfish and blue shark, this study introduces streamlining features to bridge piers in order to reduce the flow intensities in the vicinity of bridge piers. Based on the numerical results of a pier streamlining optimization study previously conducted, four small-scale pier models with different streamlining levels were constructed using 3D printing techniques and flume tests were conducted to characterize the scour process around these models. On the other hand, microbial induced carbonate precipitation (MICP) is an emerging technique in geotechnical engineering. It precipitates carbonate that binds soil particles together and thus improves soil properties. In this study, a standard soil, Ottawa graded sand, was treated with bacteria (Sporosarcina pasteurii) in a full-contact reactor where the soil in a fabric mold was fully immersed in bacteria and cementation solution. The treated sample was tested in a flume to investigate the effectiveness of MICP on bridge scour control. The experimental results reveal that both streamlining and biocementation can significantly reduce or even fully prevent the scour around the model bridge piers under the laboratory testing conditions.
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