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An exploration of the plasma-sprayed abradable sealing coatings (ASCs) of a thick and porous LaMgAl11O19 topcoat onto SiC/SiC ceramic matrix composites (CMCs) is detailed in this study. Interlayers comprising Si/Si + Yb2Si2O7/Yb2SiO5 environmental barrier coatings (EBCs) were strategically employed, considering their function in protecting the SiC/SiC CMCs from recession and mitigating thermal expansivity misfit. An isothermal oxidation test was conducted at 1300 °C and resulted in the formation of bubble and glassy melt on the side surface of the coated sample, while a significant reaction layer emerged at the Yb2SiO5/LaMgAl11O19 interface near the edge. The localized temperature rise caused by the exothermic oxidation of the SiC/SiC substrate was determined to be the underlying factor for bubble generation. The temperature-dependent viscosity of the melt contributed to various bubble characteristics, and due to the enrichment of Al ions, the glassy melt exacerbated the degradation of the Yb2SiO5 layer. After a thermal shock test at 1300 °C, the substrate on the uncoated backside of the sample experienced fracture, while the front coating remained intact. However, due to the presence of a through-coating crack, an internal crack network also developed within the substrate. [ABSTRACT FROM AUTHOR]

The Winkler foundation modulus is key to evaluating the response of underground structures using the elastic foundation beam model. In this paper, an improved formula of the Winkler foundation modulus for a beam embedded in a full space is proposed to overcome the limitation of inconsistent assumptions in previous studies. To achieve this goal, the bending responses of the beam are obtained using the elastic foundation beam model and three-dimensional elastic continuum model, respectively, wherein a consistent assumption is proposed that tangential interactions at the beam–ground interface are ignored in the two models. In addition, as deformation of the site is an important source of the underground structure response, the beam is applied to standard soil displacement of the free field on the Winkler foundation to improve the accuracy of the Winkler modulus obtained by fitting solutions based on the concentrated force on the beam. The formula for the Winkler foundation is obtained by equating the first zero of the bending moment in the two models. The Winkler foundation modulus is verified by comparing the results with numerical solutions and previous studies. [ABSTRACT FROM AUTHOR]

Active faults pose significant threats to the structural integrity of mountain tunnels in seismic active zones. Post-earthquake reconnaissance revealed that numerous tunnels were damaged during past earthquakes, specifically those crossing active fault zones. In this study, the structural response and damage mechanism of a water conveyance tunnel subjected to reverse faulting was investigated. A three-dimensional finite element model incorporating the cohesive interface elements was developed to simulate the nonlinear process of the reverse fault rupture. The ground deformation and tunnel damage characteristics predicted by the numerical analysis were in good agreement with the field observations and experimental results, which proved the feasibility of the proposed simulation scheme. Moreover, a parametric study was conducted to estimate the effects of dip angle, surrounding rock property, tunnel rigidity, and friction coefficient between linings on tunnel performance. The results showed that the damage zone with softer rock masses of grade IV to V, based on the Chinese Guidelines for Design of Highway Tunnel, generally led to moderate structural damage to the tunnel. The tunnel's performance in the damage zone can be further enhanced by increasing tunnel rigidity and smoothness of the external surface of the secondary lining. [ABSTRACT FROM AUTHOR]

In this paper, the seismic reduction and isolation measures are first proposed by setting a segmented isolation layer between the diaphragm wall and the side wall of the station structure. Although the segmented isolation layer can effectively improve the stress state of the side wall and slabs, the seismic reduction effect of the middle column is not obvious. In order to improve the overall seismic performance of the station structure, the reduction measures by combining the segmented isolation layer and new type bearing of the middle column are then proposed. At the same time of inserting the isolation layer between the diaphragm wall and the structure, the sliding bearing at the top of the column is set up to reduce the vibration. The results show that the segmented isolation layer can significantly reduce the internal force and damage at the top, bottom and side wall joints. In addition, the combined measures of segmented isolation layer and sliding bearing at the top of the column can effectively reduce the seismic damage of the middle column. The damage of the connection between the top plate, the middle plate and the middle column can be significantly decreased. [ABSTRACT FROM AUTHOR]