A hydraulic-stepped spillway was designed using an aeration basin to provide the aerated flow to the stepped spillway utilizing a hydraulic jump. However, the flow through the entrance of the stepped spillway might separate from the first step top and impact the downstream steps at a large unit discharge, causing a so-called jet flow. A new experimental study was conducted to better understand the jet flow in the hydraulic-jump-stepped spillway with comparisons to coventional stepped spillways. The results showed that the critical condition required for the formation of the jet flow was close to the geometric parameters of the upstream aeration basin. Among these parameters, the height of the reverse step had a more significant effect on the local flow pattern, thus lowering the risk of jet flow. The relationships between the critical condition and the geometry of the aeration basin suggested that the Froude number at the entrance of the stepped spillway was the key parameter forming the jet flow. Compared with the conventional stepped spillways, the hydraulic-jump-stepped spillway could effectively extend the practical application for large unit discharges by providing a better understanding of jet flow conditions.

The ancient levees used for flood control generally exist in the rainy areas of southern China. After years of operation, the levees have lots of problems, such as leakage, swelling, and cracking, which need to be reinforced. In this paper, combined with the characteristics of river water level fluctuations, the effect of the upside-down hanging well and curtain grouting reinforcement of the ancient levee is analyzed by a numerical method, and the variation law of the levee’s stability in the flooding process before and after reinforcement is explored. The study results show that the flooding process significantly affects the pore water pressure of the filling soil between the ancient levee and the well, and has a weak impact on that behind the well, which is conducive to the levee’s stability. The horizontal displacements of the levee and the fill present the opposite change law before and after reinforcement. Before reinforcement, the maximum horizontal displacement reached 2.75 cm, and the displacement was toward the Lan River. This was caused by the deformation of the soil squeezing the levee after the water level rose, which was extremely unfavorable to the levee’s stability. After reinforcement, the levee and fill shifted away from the river, mainly due to the hydrostatic pressures caused by the rising water level. The change in the stability safety factors of the reinforced levee is basically consistent with the flood fluctuation. The minimum value of the safety factors is 1.727, the maximum value is 2.273, and the safety factor only decreases by 24.02%, which is half of the change range of the safety factors before reinforcement. The stability of the reinforced ancient levee is largely improved.

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Flood-controlled ancient dikes play a significant role in flood control and have received widespread attention as historical and cultural symbols. Flood-controlled ancient dikes often undergo disasters, and research on their repair is receiving increasing attention from experts and scholars. This article studies the control of seepage and bank slope instability in flood-controlled ancient dikes. Starting from the repair of ancient dike materials, three types of work are carried out: a test of soil’s mechanical properties, finite element numerical simulation, and repair technology research. The research results show that the soil of the ancient dike site has hardened after being contaminated with waste oil from catering. The strength index of the ancient dike soil decreases and shows brittleness when the water content is 15% and the oil content exceeds 6%. The strength index and permeability coefficient of oil-contaminated soil improved using modified lime mortar (MLM), which was achieved using the method of MLM to repair oil contaminated soil. When the MLM content was 10% and the oil content was 6%, the friction angle of the soil sample reached its maximum value. When the MLM content was the same, the higher the density of the soil sample, the greater the friction angle and cohesion and the smaller the permeability coefficient. Establishing a finite element numerical model, through comparative analysis, it was found that after MLM remediation of oil-contaminated soil, the extreme hydraulic gradient of the ancient dike decreased by 31.3%, and the extreme safety factor of the bank slope stability increased by 31.2%. MLM pressure grouting technology was used to improve the soil during the remediation of contaminated soil at the ancient dike site. Through on-site drilling inspection, the effective diffusion radius of MLM grouting was obtained, and the plane layout and grouting depth of MLM pressure grouting were determined. The on-site water injection permeability test showed that using MLM pressure grouting technology can effectively repair oil-contaminated soil in the ancient dike while reducing the permeability coefficient by 8–15%.