Study on Hydraulic Incipient Motion Model of Reinforced Tailings

Once the flood overtopping accident of a reinforced tailings dam occurs, it will cause great property losses and serious environmental pollution to the downstream residents. In order to further study the microscopic characteristics of the hydraulic erosion of reinforced tailings dams, considering that the beginning of reinforced tailings particles is the basis of flooding and erosion of reinforced tailings dams, in this paper, a reinforced tailings hydraulic erosion facility was used to carry out the tailings particle start-up test with reinforcement spacing of 5.0, 2.5, 1.7, 1.3, and 1.0 cm, and the influence the law of critical incipient velocity of tailings particles with different reinforcement spacing was revealed. The test results show that, the smaller the reinforcement spacing, the larger the incipient velocity of the reinforced tailings sample. Based on the sediment incipient motion theory, it is assumed that the resistance direction of particle incipient motion is opposite to the particle motion direction. A reinforcement coefficient is introduced to establish the incipient velocity formula of reinforced tailings particles. This model can provide theoretical support for the study of the hydraulic erosion rate of a reinforced tailings dam.

Incipient Motion of Gravel Bedload Considering the Secondary Flow in Bend

The transport of gravel bedload in river bend is one of the basic problems of river dynamics. However, both the complicated bend flow structure and the stochastic bedload transport make explaining the problem theoretically difficult. Flow is the power of the bedload transport, so obtaining the precise theoretical flow structure is fundamental. Through considering the velocity-dip phenomenon and giving the matched boundary conditions, we have obtained the completed three-dimensional bend flow structure in the previous study. Combining the flow structure and the influences of the two-way exposure, we did further research on the incipient motion of the gravel bedload in bend in this paper. It turns out that, because of the existence of the secondary flow, the particle in bend forced by both the longitude and the transverse velocities in the plane. The two-way velocities form an intersection angle which influences the incipient velocity and direction of the particle movement. Moreover, the non-uniform distribution of the bend flow structure along the cross-section decides the differences of the intersection angle, incipient velocity, transport speed of the bedload in the bed surface. Then, the above differences result in the change of the sediment gradation and partition behaviour of the bedload transport.

An Entropic Approach to Estimating the Instability Criterion of People in Floodwaters

People are always susceptible to a loss of stability in urban floodwaters that leads to serious casualties. Thus, the safety criterion for the instability of people in floodwaters must be determined. In this study, the hydrodynamic criterion of the instability of people in floodwaters in terms of the incipient velocity and water depth is derived using the probability method based on Shannon entropy theory. The derived model can characterize variations in the incipient velocity of people in floodwaters with respect to the inundating water depth. Furthermore, a comparison with seven experimental datasets available in the literature shows the validity of the proposed entropy-based model considering data scattering. A sensitivity analysis of the derived model to some of the incorporated parameters was performed, and the qualitative results are in accordance with our understanding of the physical mechanism of the instability of people in floodwaters. Taking the physical parameters (height and mass) of Chinese adults and children as a representative example, this study also showed the vulnerability degree of Chinese adults and children subject to floodwaters. These findings could provide a reference for administrators and stakeholders for flood hazard mitigation and flood strategy management. This study shows that an entropy-based method could be a valuable addition to existing deterministic models for characterizing the instability criterion of people in an urban flooding event.

Instability Criteria for Vehicles in Motion Exposed to Flood Risks

Flooded roads have somewhat become a norm to the society and among the damages that floods can pose, there are fatalities and harm caused to people. Floating debris such as vehicles, manipulated by floodwaters could potentially cause harm not only to the public safety but also towards the public and private-owned properties. In the past, research on vehicle’s instabilities have been solely dedicated to static vehicles which are normally translated as vehicles parked on road surface. A vehicle when exposed to floodwater get influenced by different hydrodynamic forces and becomes prone to different instability modes, namely sliding, floating and toppling. Outcomes on such modes are somehow recognised in the works on static vehicles, but the mechanics of a moving vehicle under such influences have not been studied. Herein the influence of floodwater flows on the vehicle attempting to cross a flooded path (partial submergence) is presented. With that regards, a non-stationary model vehicle with the scale ratio of 1:10 (Perodua Viva) was used and a series of experiments were conducted. Moreover, a new formula to estimate the incipient velocity for a moving vehicle has been introduced and the prediction accuracy of the proposed formula has been validated using experimental data. Measurements were taken including approaching velocities and water depths, through which the instability was computed.

Experimental Research on the Characteristics of Bamboo Powder Model Sediment

Physical characteristics (including unit weight, dry unit weight and submarine rest angle) and motion characteristics (including settlement characteristics, incipient velocity and resistance characteristics) of bamboo powder model sediment were studied by test in this paper. Experimental study on physical characteristics showed that particle size variation had little effect on unit weight, dry unit weight increased with the particle size,submarine rest angle increased with the decrease in particle size and an empirical formula for calculating submarine rest angle of bamboo powder model sediment was proposed. Experimental study on motion characteristics found that the single particle settling velocity of bamboo powder model sediment increased with particle size, the relative settling velocity initially increased and then decreased with sediment concentration, the incipient velocity increased with the particle size and water depth, the roughness decreased with water depth and increased with the flow velocity and an empirical formula for calculating the incipient velocity of bamboo powder model sediment is proposed.

Experimental Study on Low-Power Disturbing Sediment Dredging System

in the River, velocities of surface water flow typically are larger than the near-bottom flow. Combined with background of artificial disturbance sediment, surface water flows is taken to the river bottom to loose and raise sediment, dredge and so as to achieve the purpose of slowing river siltation. Preliminary tests showed that using low-power diversion disturbing sand dredging system, flow velocity of disturbing nozzle is larger than the incipient velocity of sediment, and the purpose of disturbing sediment and sediment transport can be obtained.