Study of biocementation treatment to prevent erosion by concentrated water flow in a small-scale sand slope

• Culverts and deficient road drainage systems can cause concentrated water flows. • Concentrated water flows lead to scour and runoff erosion in soil slopes. • EICP treatment avoid scour and runoff erosion under concentrated water flows. • Riprap and mulching coverage prevent runoff erosion but not scour erosion. Road drainage systems collect runoff water during rainfall; however, their malfunction or defective discharge systems may cause downslope soil erosion through scour and runoff. Under climate changes scenario it is expected the occurrence of intense rainfalls with high erosion potential, and therefore it is important to increase slope resilience against this. This study assesses the effectiveness of biocementation through enzymatically induced carbonate precipitation (EICP) technique to prevent ravine formation caused by this phenomenon. The effectiveness of the EICP treatment was evaluated by comparing the results of an erosion test performed on a small-scale laboratory slope with those found in tests where identical slopes were covered with calcareous riprap, or with mulch of pine bark, both traditional solutions adopted in Europe to solve this problem. For this purpose, five identical small-scale slopes (maximum height 15 cm, slope V:H = 1:2) were built with dry uniform grading size sand in the laboratory. The first slope was the reference case, where no treatment was applied. The second was treated by spraying with enzymes and a feeding solution, while the third was treated only with feeding solution to analyze the contribution of the soil native bacteria in carbonate precipitation. The fourth and fifth slopes were tested with the traditional cover solutions mentioned. All slopes were subjected to a water thread of 0.13 l/min simulating a culvert outflow. The untreated reference slope has developed a marked erosive channel along the entire length of the slope at the end of 9 min. Almost the same happened on the slope treated with feeding solution, showing that the amount of carbonate precipitated by soil native bacteria is not enough to prevent erosion. For the enzyme-treated slope no scour or runoff erosion have occurred, and the test was stopped only when the first signs of instability appeared, after complete saturation, at the end of 15 min. The slopes where the traditional solutions were applied exhibited resistance to runoff erosion but scour erosion has occurred. These tests ended also when the first signs of instability appeared also after saturation. Regardless of the erosion countermeasure adopted all have prevented runoff erosion of the slopes, but only EICP prevented scour erosion, proofing the efficiency of this treatment against ravine formation.