Fiber optic sensing and performance evaluation of a water conveyance tunnel with composite linings under super-high internal pressures

For long-distance water conveyance shield tunnels in operation,the high internal water pressure may cause excessive deformation of composite linings,affecting their structural integrity and serviceability.However,the deformation and failure characteristics of lining structures under internal water pressure are not well investigated in the literature,particularly for three-layer composite linings.This study presents an in situ experimental investigation on the response of two types of composite linings(i.e.separated and combined lining structures)subjected to internal pressures,in which a fiber optic nerve system(FONS)equipped with distributed strain and displacement sensing nerves was employed to monitor the performance of the two composite linings during testing.The experimental results clearly show that the damage of the tunnel lining under different internal pressures was mainly located in the self-compaction concrete layer.The separated lining structure responded more aggressively to the variations in internal pressures than the combined one.Moreover,two evaluation indices,i.e.radial displacement and effective stiffness coefficient,are proposed for describing the changes in the structural bearing performance.The effective stiffness coefficients of the two types of lining structures were reduced by 39.4%and 29.5%,respectively.Considering the convenience of field monitoring,it is suggested that the average strains at different layers can be used as characteristic parameters for estimating the health conditions of lining structures in service.The analysis results provide a practical reference for the design and health evaluation of water conveyance shield tunnels with composite linings.

A Discrete Element Analysis of the Sliding Friction Heat in High-Speed and Long-Runout Landslides

Earthquake is one of the main causes of high-speed and long-runout landslides.Generally,the heat generated in the sliding zone is significant in such devastating landslides.In this study,we establish a two dimensional slope model which includes 0.2 million elements to simulate the development of high speed and long-runout landslides using the discrete element software MatDEM.The model not only suggests that heat is produced by friction and fracturing,but also simulates the process of tension generation in cracks and the generation of a high heat zone near the sliding region.Besides,the heat field graph indicates a banded high heat belt that is related to the location of the thickest sliding body.The logarithms of the total calorific value and the highest value in the heat zone during the sliding process are linearly related to the logarithm of the landslide height.

Preface to the Special Issue on Earthquake-Induced Landslides

Earthquake-induced landslides are the most destructive secondary geological hazards following large earthquakes that can destroy infrastructures and cause loss of lives and properties(Marano K.D.et al.,2010;Xu Chong et al.,2018).In the past few decades,earthquake-induced landslides have captured growing interests of both scientific communities and the public;more and more studies have been carried out(Xu Chong et al.,2010;Xu Chong,2018;Fan Xuanmei et al.,2019).To demonstrate the state-of-the-art on related research,we presented a special issue on earthquake-induced landslides.This special issue includes six columns,including inventory and spatial distribution,hazard assessment,numerical calculation and simulation,shaking table test,early warning,and evolution of earthquake-induced landslides,as well as a few studies about nonseismic landslides.

Refractive index sensor based on tapered PCF in-line interferometer

A simple and compact refractive index sensor is demonstrated by tapering a photonic crystal fiber （PCF） in-line interferometer. The PCF is spliced between two single-mode fibers and tapered via hydrofluoric acid etching. Its sensitivity in liquid is more than an order of magnitude larger than the untapered one. By optimizing the etching process, we can fabricate more uniformly and thinly tapered PCF interferometers with higher sensitivity in the future.