An Empirical Shear Model of Interface Between the Loess and Hipparion Red Clay in a Loess Landslide

Quaternary loess is widely distributed over the tertiary Hipparion red clay on the Loess Plateau of China. Large-scale loess landslides often occur along the weak contact interface between these two sediment materials. To investigate the failure mode and shear strength characteristics of the loess–Hipparion red clay contact interface, a series of shearing experiments were performed on interface specimens using purpose-built shear equipment. In this article, the relationship between shear strength and interface morphology is discussed, and an empirical shear model of the interface is proposed based on the experimental results and theoretical work. The results indicate that discontinuities between the loess and the Hipparion red clay reduce the shear strength of specimens significantly. The contribution of the contact interface to shear performance including failure mode, shear deformation, and shear strength varies with the interface morphology and the applied normal stress. With low interface roughness or normal stress, sliding failure is likely to occur. With increasing interface roughness and normal stress, the peak strength increases rapidly. With further increase in the interface roughness and normal stress, the increment of peak strength decreases gradually as the failure mode transitions from sliding mode to cutoff mode. A staged shear model that takes the failure mode into consideration is developed to express the non-linear change in the interface shear strength. The shear model’s capability is validated by comparing model estimates with experimental data. This work improves our understanding of shear mechanisms and the importance of considering the effects of interfacial properties in the mechanical behavior of contact interfaces.

Bearing Capacity of Interfered Adjacent Strip Footings on Granular Bed Overlying Soft Clay: An Analytical Approach

In the present paper, the interference effects on bearing capacity of two and three closely spaced strip footings resting on granular bed overlying clay are being studied. A simple analytical model is proposed to predict the load-carrying capacity and the interference factor of an interfered footing, when adjacent strip footings are optimally placed on the surface of a Granular Bed (GB) overlying clay and both the footings are simultaneously loaded. A punching shear failure mechanism is envisaged in the analytical model. The load-carrying capacity of the footing is taken as the sum of total shearing resistances along the two vertical planes through the edges of the strip footing in the upper granular layer and the load-carrying capacity of the soft clay beneath the GB. Insights gained from finite element simulations are used to develop the new modified punching shear model for interfering footing. Bearing capacity can be easily calculated by using the proposed punching shear model for interfering footing. The analytical model is validated with numerical analyses and previous experimental results and found to be in reasonably good agreement. The influence of different parameters such as granular bed thickness, width of footing, number of footings are carried out in this study. Doi: 10.28991/cej-2021-03091723 Full Text: PDF

The Location of Magnetic Reconnection at Earth’s Magnetopause

One of the major questions about magnetic reconnection is how specific solar wind and interplanetary magnetic field conditions influence where reconnection occurs at the Earth’s magnetopause. There are two reconnection scenarios discussed in the literature: a) anti-parallel reconnection and b) component reconnection. Early spacecraft observations were limited to the detection of accelerated ion beams in the magnetopause boundary layer to determine the general direction of the reconnection X-line location with respect to the spacecraft. An improved view of the reconnection location at the magnetopause evolved from ionospheric emissions observed by polar-orbiting imagers. These observations and the observations of accelerated ion beams revealed that both scenarios occur at the magnetopause. Improved methodology using the time-of-flight effect of precipitating ions in the cusp regions and the cutoff velocity of the precipitating and mirroring ion populations was used to pinpoint magnetopause reconnection locations for a wide range of solar wind conditions. The results from these methodologies have been used to construct an empirical reconnection X-line model known as the Maximum Magnetic Shear model. Since this model’s inception, several tests have confirmed its validity and have resulted in modifications to the model for certain solar wind conditions. This review article summarizes the observational evidence for the location of magnetic reconnection at the Earth’s magnetopause, emphasizing the properties and efficacy of the Maximum Magnetic Shear Model.

Experimental Assessment of RANS Models for Wind Load Estimation over Solar-Panel Arrays

This paper reports a comparison between wind-tunnel measurements and numerical simulations to assess the capabilities of Reynolds-Averaged Navier-Stokes models to estimate the wind load over solar-panel arrays. The free airstream impinging on solar-panel arrays creates a complex separated flow at large Reynolds number, which is severely challenging for the current Reynolds-Averaged Navier-Stokes models. The Reynolds-Averaged Navier-Stokes models compared in this article are k-ϵ, Shear-Stress Transport k-ω, transition and Reynolds Shear Model. Particle Image Velocimetry measurements are performed to investigate the mean flow-velocity and turbulent-kinetic-energy fields. Pressure taps are located in the surface of the solar panel model in order to obtain static pressure measurements. All the Reynolds-Averaged Navier-Stokes models predict accurate average velocity fields when compared with the experimental ones. One of the challenging factor is to predict correctly the thickness of the turbulent wake. In this aspect, Reynolds Shear provides the best results, reproducing the wake shrink observed on the 3rd panel in the experiment. On the other hand, some other features, most notably the blockage encountered by the flow below the panels, are not correctly reproduced by any of the models. The pressure distributions over the 1st panel obtained from the different Reynolds-Averaged Navier-Stokes models show good agreement with the pressure measurements. However, for the rest of the panels Reynolds-Averaged Navier-Stokes fidelity is severely challenged. Overall, the Reynolds Shear model provides the best pressure estimation in terms of pressure difference between the front and back sides of the panels.