Nature-inspired bridge scour countermeasures: Streamlining and biocementation

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.