A Review on Existing Methods to Assess Hydraulic Erodibility Downstream of Dam Spillways

In recent years, rock scouring or erosion downstream of dams has become an increasing dam safety concern. Several theoretical, semi-theoretical, semi-analytical and numerical methods can be used to assess the rock erosion in hydraulic structures. Semi-theoretical approaches determine the correlation between the erosive intensity of fluid flow and the resistive capacity of rock. Such approaches establish the scour thresholds as a function of erosive intensity of water and several rock mass indices by using in situ data and a curve-fitting approach. In some studies, the excavatability index, initially developed for rock mass stability analysis, was used to analyse the rock mass resistance in hydraulic erodibility analysis. The effectivity and weight of the geomechanical parameters used are yet to be determined on the basis of the erodibility phenomenon. The semi-analytical methods are developed on the basis of the mechanical and hydraulic interaction of rock mass and water. Four methods developed by Bollaert et al. are important in determining the erodibility in the plunge pool, but they are not applicable in the case of spillways. They used the comprehensive fracture mechanics for closed-end joints, quasi-steady impulsion, and dynamic impulsion (DI) for blocky rock erosion. The application of these methods to each site is necessary to identify constants that are difficult to determine. Few numerical methods are available to assess the rock mass erosion in hydraulic structures. In the case of numerical methods, the erosive agent is indistinct, and the hydraulic hazard parameter on the spillway surface is almost challenging to apply. This study comprehensively reviews the mechanism of erosion and the methods for assessing the risk of potential rock mass erosion downstream of dams and hydraulic structures. The advantages and disadvantages of all methods are discussed and the potential future research directions in this domain are proposed.

Causes and remedial measures for rockfall and landslides in Naini lake basin: Uttarakhand, India

The history of Naini Lake Basin reveals that this beautiful scenic natural surrounding has been a victim of landslides, mass erosion, rock-fall and slumping. Its location in highest rainfall zone, weak lithology and topography are the obvious reasons for these activities. Moreover the rising anthropogenic interferences like construction activities and deforestation on this geo-dynamically unstable zone has added more to the problem. The manuscript accounts of incidences of landslide and erosion activities, their causes and effects afterwards. An effort to stratify and to mark the comparatively lesser stable zones and patches in and around the lake basin has been made to demarcate the risk prone belt. Adequate measures for environmental planning and proper implementation of such plans are the utmost need of the hour to safeguard not only the beautiful basin but also the olives and property of population living under the continuous threat of disaster.

Investigation of the Influence of PLA Molecular and Supramolecular Structure on the Kinetics of Thermal-Supported Hydrolytic Degradation of Wet Spinning Fibres

In this study, differences in the kinetics of the thermal-supported hydrolytic degradation of polylactide (PLA) wet spinning fibres due to material variance in the initial molecular and supramolecular structure were analysed. The investigation was carried out at the microstructural and molecular levels by using readily available methods such as scanning electron microscopy, mass erosion measurement and estimation of intrinsic viscosity. The results show a varying degree of influence of the initial structure on the degradation rate of the studied PLA fibres. The experiment shows that hydrolytic degradation at a temperature close to the cold crystallization temperature is, on a macroscopic level, definitely more rapid for the amorphous material, while on a molecular scale it is similar to a semi-crystalline material. Furthermore, for the adopted degradation temperature of 90 °C, a marginal influence of the pH of the degradation medium on the degradation kinetics was also demonstrated.

Experimental Investigation on the cavitation erosion properties of concrete with different damage degrees under ultrasonic cavitation

<p>Cavitation erosion, widely existing in many flood discharge structures of concrete dams, has a direct impact on the performance of concrete. Understanding the cavitation erosion properties of concrete with different damage degrees is vital to the long-term operation safety of concrete dams. In this study, the cavitation erosion properties of concrete with different damage degrees under ultrasonic cavitation are systematically investigated in the laboratory, including three damage degrees and three ultrasonic cavitation intensities. Based on the stress-strain curve of concrete under uniaxial compression, the damage variable is defined and the corresponding concrete specimens are pre-treated. The experimental results reveal the influence of the damage degrees on the cavitation erosion properties of concrete, regarding the mass erosion characteristics, the predominant failure behaviour, and the coupling effect mechanism. Image analysis of the specimens shows some level of deterioration at the surface and inside the specimens. Under higher damage degree or cavitation intensity, the concrete is characterized by higher mass erosion rate, higher cumulative cavitation damage and worse surface smoothness. Furthermore, the micro-cracks caused by concrete damage aggravate the aggregate liberation of concrete under ultrasonic cavitation, and the crack propagation under coupling effect of damage and cavitation is most likely driven by the combination of fatigue-like crack growth and deformation, thereby reducing the service life of concrete.</p>

Smoke and Mirrors: The Bio-Con Documentary in the Age of Trump

Noting that popular film and television have answered the Trump era's mass erosion of truth and justice with narratives about powerful deceivers and sophists, Film Quarterly Assistant Editor Marc Francis argues that no fiction has yet to offer as cohesive and relevant a response to these times as the what he terms the “bio-con” (biographical con) documentary. The bio-con documentary zeroes in on one notorious figure—a fraud—the unveiling of whose scheme occupies multiple national news cycles and is therefore ready-made for an extended investigation. Citing well-known examples such as Fyre Fraud (Jenner Furst and Julia Willoughby Nason, 2019), The Inventor: Out for Blood in Silicon Valley (Alex Gibney, 2019), Divide and Conquer: The Story of Roger Ailes (Alexis Bloom, 2018), Where's My Roy Cohn? (Matt Tyrnauer, 2019), Francis probes these films for what insights they can offer about what is politically at stake in a postdemocracy United States and the connection between falsity and fascism.

The main influencing factors of soil mechanical characteristics of the gravity erosion environment in the dry-hot valley of Jinsha river

The dry-hot valley region counts as one of the most eco-sensitive zones in China, the issue of soil erosion is critical in regional ecological environment, soil mechanical property is one of the primary factors confining the occurrence of erosion, and it is attached crucial significance to in ascertaining the characteristics and principal factors of soil mechanics, and how to prevent and control soil erosion in arid red soil area of dry-hot valley. Through monitoring field location and directly shearing, the soil mechanical characteristics and the primary influencing factors of the mass erosion environment in the basin were ascertained. As the result indicates: (1) The soil moisture content, cohesion and internal friction angle are evidently correlated with each other abiding by power function, the relationship among soil cohesion, internal friction angle and volume moisture content goes as:$$\begin{array}{} \displaystyle c=80.107e^{-5.451\frac{{\it\omega}}{1.64\,+\,{\it\omega}}},\phi=65.646{\rm e}^{-3.325\frac{\omega}{1.64\,+\,\omega}}; \end{array}$$(2) The soil being large in pore radius vary in number and distribution evidently with structure and destruction degree (P<0.05). Soil aggregation was also significantly different (P<0.05), with the increasing of structural failure rate, the shear strength of soil decreased, and the probability of damage was increased as the external load increaseing. (3) The disintegration of soil can be effectively decelerated, and anti-disintegration ability of soil can be enhanced by the root system. The impact exerted by plant root system on shear strength of soil decreased as soil got deeper, more than a certain depth can be ignored; the impact exerted by plant root system on small-scale gravitational erosion was particularly evident, whereas the impact exerted by large-scale mass erosion was comparatively small. The ability of plant roots to optimize soil resistance was primarily through the roots shorter than 2 mm, the effective fibrous roots in the soil of the Leucaena Benth and the Dodonaea angustifolia were comparatively small, and the root of the herbaceous plants was comparatively large.