Hydraulic erosion is one of the main causes of failure within earth dams and embankments. Various methods are used to mitigate against such erosion, a common approach being grouting with cement, clay or chemical materials. Biogrouting using the microbial-induced carbonate precipitation technique is a relatively new, cost-effective, technically appropriate and environmentally friendly soil improvement method. Bacteria injected into the soil produce urease enzyme, which converts urea to ammonium and carbonate, causing calcite precipitation that binds soil grains together. In this study, the erodibility parameters of dense silica sand specimens treated with different injection strategies were investigated at bench scale. More effective treatment – in terms of greater and more uniform calcite precipitation over the test-specimen length, and hence greater erosion resistance – was achieved by aeration during solution injections and by incorporating a drained stage between injection cycles. With the latter, calcite precipitated as larger crystals, accumulating extensively over grain surfaces and also formed integrated in the pore voids. The best-performing treatment strategy produced a 95% reduction in erodibility and a five-fold increase in critical shear stress relative to untreated sand. These findings were confirmed by scanning electronic microscopy and calcium carbonate titration tests.

One of the most essential groundwater model components is accurate information about the recharge values within the input data, often introduced to a groundwater model as a percentage of rainfall on aquifers. Recharge values are influenced by many temporal and spatial factors. This paper suggests the use of a SWAT model for surface water simulation and the estimation of recharge rates. In this research, sensitivity analysis, calibration, validation and uncertainty analysis of results were performed by SWAT-CUP software. Due to the semi-distributed features of SWAT and the difficulty of calculating groundwater distributed parameters, recharge values estimated by SWAT were used in a MODFLOW model for groundwater simulation at steady and unsteady states. This method was applied in the Firoozabad basin, which is one of the most suitable agricultural basins for modeling surface water and groundwater in Iran. After MODFLOW model calibration, hydrodynamic coefficients of the aquifer were determined and the sensitivity of the model was checked for hydraulic conductivity and discharge rate of wells. In order to prove confidence, the model was validated. SWAT and MODFLOW models were successfully tested and the results of the combination of the two models were found to be acceptable.

Submerged vanes are small plate structures that create a secondary flow rotation to reduce scouring. This paper presents the results of laboratory experiments investigating how submerged vanes affect scouring around a vertical wall and spill-through abutments under clear water conditions. This study focused on vane distance from the abutment, lateral spacing of the vanes, number of vanes in a row, number of vane rows, the angle of attack with flow, the direction of the vanes, and the position of the first vane relative to the toe of the abutment. An angle of 30° was found to be the best angle of attack and lateral spacing of vanes obtained 2H_S - 3H_S. In addition the optimal distance of the first vane from the toe and wall of the abutment was L/3 and B/3.2, respectively (in which L is the abutment length and B is the channel width), and the number of vanes in a row was found to be 1 and 2. These results showed that, the maximum scour reduction in a vertical wall and spill-through abutments was 34.2% and 35.6%, respectively. Based on experimental results from changing the direction of the vanes and locating the first vane along the toe of the abutment, the depth of the scour was increased.

As a bio-inspired calcite precipitation method, bio-grouting via enzymatic-induced calcite precipitation (EICP) uses free urease enzyme to catalyze the urea hydrolysis reaction. This soil stabilization approach is relatively new and insufficiently investigated, especially for applications involving surface layer stabilization of sandy soil deposits for increasing hydraulic erosion resistance. This paper presents a laboratory investigation on the surface erosion resistance improvements for compacted medium-gradation quartz sand specimens mediated using 10 different EICP treatment protocols. They involved single- and two-cycle injections of the urease enzyme (activity of 2400 U/L) and 0.5, 0.75, or 1.0-M urea–CaCl₂ cementation solution reagents. The urease enzyme was extracted from watermelon seeds. Erosion rates were determined for various hydraulic shear stresses applied using the erosion function apparatus. The spatial distribution and morphology of precipitated calcite within the pore-void spaces of the crustal sand layer were investigated with a scanning electron microscope. Compared to untreated sand, all 10 investigated EICP treatment protocols produced substantially improved erosion resistance, especially for the higher cementation solution concentration (1.0 M). Of these 10 EICP protocols, a single cycle of enzyme–1.0-M-cementation solutions injections was identified as the more pragmatic option for achieving near-optimum erosion resistance improvements. Highest and lowest amounts (18.8 and 5.0 wt%) of precipitated calcite corresponded to the best and worst performing EICP-treated specimens, although the calcite’s spatial distribution in treated specimens is another important factor.

Scour is one of the main causes of hydraulic structural failures. The present experimental study examines the use of riprap, submerged vanes, and a combination of these for scour reduction around vertical walls and spill-through abutments under clear-water conditions. Specifically, the influence of placing riprap stones with different apron shapes (geometry) and/or a group of submerged vanes of constant height and length on abutment scour was examined. The main aim is to propose the optimum apron geometry and placement of submerged vanes to (1) reduce edge failure at vertical walls and spill-through abutments; and (2) prevent shear failure at the spill-through abutment (no shear failure is observed around the vertical wall abutment). The results show that using ripraps for scour protection is more effective than submerged vanes. However, the highest reduction in scour depth was achieved when a combination of riprap and submerged vanes was used together. This arrangement can reduce the maximum clear-water scour depth by up to 54% and 39% with vertical walls and spill-through abutments, respectively. Furthermore, selecting appropriate apron scale ratios reduces the required riprap volume by up to 46% and 31% for the vertical wall and spill-through abutment, respectively. In addition, the installation of vanes increased the riprap stability and reduced edge failure in both abutments tested. Finally, using riprap aprons with proper scales ratios at the downstream side of the spill-through abutment also prevents shear failure in this zone.

This briefing paper examines the improvement in the hydraulic erosion resistance of medium silica sand achieved using 1–4% nano-silica (NS) additive. The erodibility of the different soil blends (prepared by mixing NS solutions prepared at required concentrations with the dry test sand) was investigated at bench scale by testing compacted treated sand specimens using the erosion-function apparatus. The NS addition produced a viscous gel property for the soil mixtures, allowing the mobilisation of an effective cohesion (surface bond strength). A 1·5% NS addition was identified as the optimum amount in terms of the greatest erosion resistance for the particular sand investigated; that is, a 92% reduction in the erodibility coefficient value and an approximately six-fold increase in the critical shear stress value were achieved relative to the untreated sand. Further, these improvements in the erosion-resistance properties of the compacted sand–NS mixtures were achieved within a significantly shorter time period (i.e. 1 d specimen curing period adopted in the current investigation) when compared with that typically required for traditional cement and lime additives.