Study on water inrush failure mode of karst tunnel based on three-dimensional discrete-continuous coupling

During the construction of karst tunnel, it is difficult to avoid approaching the cavern, even high pressure water cavern. Water inrush damage very easily causes safety accidents and would have irreversible impact on the tunnel. The study on damage mode is conducive to solving problems related to karst tunnel safety and has certain significance for the safety of route selection. In this study, the physical and mechanical parameters of micro-discrete particles are calibrated and verified by a three-dimensional discrete-continuous coupling numerical technology, and the important process of rock-burst collapse prevention between the underlying solution cavity and the tunnel invert under water pressure is simulated. The results show that the failure modes of outburst prevention rock mass are divided into three types: shear failure mode, bending failure mode, and composite failure mode. The bending failure mode indicates that the tensile cracks in the middle and both ends of the outburst prevention rock mass are in the form of penetration; the shear failure mode shows that the cracks at both ends of the outburst prevention rock mass are in the shear state; while the composite failure mode has the common characteristics of both. The fracture development rules caused by the three failure modes are similar and can be divided into three stages: initial development, rapid development, and gentle development. At the stage of initial development, the number of cracks in the rock body is small; the number of cracks in the rock mass maintaining water pressure and preventing outburst suddenly increases and enters the stage of rapid development; after that, the crack in the outburst prevention rock mass connect and then enter the stage of gentle development, ultimately, leading to the overall collapse of the outburst prevention rock mass. Thus, this study indicates that water inrush damage is a gradual process in karst tunnels, but it has an irreversible impact on the overall safety of karst tunnels

Seismic damage mechanism of slope and lining in the mountain tunnel portal section

A series of numerical simulations were conducted to study the seismic response in the mountain tunnel portal section. The seismic damage mechanism, including slope cracking and landslide, rockfalls and collapse, and lining cracking were analyzed based on the seismic damage characteristics of the Longxi tunnel during the 2008 Wenchuan earthquake in China. The results show that slope cracking due to the huge horizontal seismic inertial force which exceeds the strength of slope; landslide is caused by the connected cracks where the oblique component of horizontal seismic inertia force exceeds the shear strength of slope; rockfalls and collapse are caused by the cumulative tensile stress in loose soil and rock which exceed the strength of slope; the transverse lining cracks due to the alternate tensile and compressive action of the seismic load along the axial direction, which makes the lining tensile strain accumulates and exceeds the concrete ultimate strength. As for the longitudinal lining cracking, the transverse seismic load makes the bending moment direction in lining alternates, leading to the strength reduction of concrete. Moreover, the circumferential penetrating rupture zone is caused by the large shear force resulting from the slope sliding, which leads to the stress concentration at vault and when the tensile stress exceeds the concrete tensile strength, the vault begins to crack, and then the cracks extend from the arch shoulder to foot

Rapid Assessment and Classification for Seismic Damage of Mountain Tunnel Based on Concentric Circle Method

Concentric circle method (CCM), a new method based on analytic hierarchy process (AHP) and numerical discretization of 40 mountain tunnels damaged by Wenchuan earthquake in China, is proposed to rapidly assess the seismic damage level (SDL) of mountain tunnels. The new method consists of four components. First, according to the type and degree of seismic damage of tunnel, the whole tunnel is divided into a number of successive sections. Second, four factors (i.e., slope and portal damage, lining damage, pavement damage, and earthquake collapse) are selected as the main controlling factor set, and then multilevel factor sets are proposed to establish the assessment system. Third, the discretized assessment indexes and classification criteria are established for the rapid assessment of SDL of mountain tunnel. Finally, based on the comprehensive analysis on the SDL of each section, the SDL of the whole tunnel is calculated in terms of the seismic damage index and synthetic radius. With the assessment results shown on a straightforward concentric circle diagram, the proposed CCM method can rapidly and reliably assess the SDL of mountain tunnel to win over precious time for emergency rescue and provide references for the repair of damaged tunnel. In addition, the accuracy and applicability of the proposed method is verified by using a case study of Longxi tunnel located at the epicenter of the Wenchuan earthquake in China

Self-assembly and characterization of 2D plasmene nanosheets

Freestanding plasmonic nanoparticle (NP) superlattice sheets are novel 2D nanomaterials with tailorable properties that enable their use for broad applications in sensing, anticounterfeit measures, ionic gating, nanophotonics and flat lenses. We recently developed a robust, yet general, two-step drying-mediated approach to produce freestanding monolayer, plasmonic NP superlattice sheets, which are typically held together by holey grids with minimal solid support. Within these superlattices, NP building blocks are closely packed and have strong plasmonic coupling interactions; hence, we termed such freestanding materials plasmene nanosheets. Using the desired NP building blocks as starting material, we describe the detailed fabrication protocol, including NP surface functionalization by thiolated polystyrene and the self-assembly of NPs at the airwater interface. We also discuss various characterization approaches for checking the quality and optical properties of the as-obtained plasmene nanosheets: optical microscopy, spectrophotometry, transmission/scanning electron microscopy (TEM/SEM) and atomic force microscopy (AFM). With regard to different constituent building blocks, the key experimental parameters, including NP concentration and volume, are summarized to guide the successful fabrication of specific types of plasmene nanosheets. This protocol, from initial NP synthesis to the final fabrication and characterization, takes ~33.5 h