Dynamic Analysis of a Deeply Buried Tunnel Influenced by a Newly-built Adjacent Cavity with a Special Emphasis on the Minimum Seismically Safe Tunnel Distance

Contemporary life streams, more often than ever, impose the necessity for construction of new underground structures in the vicinity of existing tunnels, with an aim to accommodate transportation systems and utility networks. A previously uninvestigated case, in which a newly-constructed tunnel opening is closely positioned behind an existing tunnel, referred to as the tunnel–cavity configuration, has been considered in this study. An exact analytical solution is derived considering a pair of parallel circular cylindrical structures of infinite length, with the horizontal alignment, embedded in a boundless homogeneous, isotropic, elastic medium and excited by time-harmonic plane SV-waves under the plane-strain conditions. The Helmholtz decomposition theorem, the wave functions expansion method, the translational addition theorem for bi-cylindrical coordinates, and the pertinent boundary conditions are jointly employed in order to develop a closed-form solution of the corresponding boundary value problem. The primary goal of the present study is to examine the increase in dynamic stresses at an existing tunnel structure due to the presence of a closely driven unlined cavity, as well as in a localized region around the tunnel (at the position of the cavity in close proximity), under incident SV-waves. A new quantity called dynamic stress alteration factor is introduced and the aspect of the minimum seismically safe distance between the two structures is particularly considered

Primerjava linearne in nelinearne seizmične interakcijske analize predor-tla

In order to study the effects of a seismically induced tunnel–ground interaction, two-dimensional numerical analyses are performed using the sofware ANSYS. The study employs a coupled beam–spring model subjected to earthquake loading that is simulated under pure shear conditions and determined by a free-field ground-response analysis using the code EERA. The properties of the soil material are considered as both linear and nonlinear. The results obtained by linear dynamic analyses are compared with state-of-practice analytical elastic solutions. A comparison of the results of both linear and nonlinear analyses is also performed, and significant differences, as well as important factors influencing the tunnel–ground interaction for both cases, are evaluated.Članek preučuje potresne učinke na interakcijo predor-tla. Za to so bile izvedene dvodimenzionalne numerične analize s pomočjo programa ANSYS. V študiji je uporabljen potresno obremenjen združeni model nosilec-vzmet, ki je simuliran pod čistimi strižnimi pogoji in določen z analizo odziva tal s prostim poljem z uporabo programske kode EERA. Lastnosti materiala tal so obravnavane tako linearno kot nelinearno. Rezultati, dobljeni z linearnimi dinamičnimi analizami so primerjani z v praksi znanimi analitičnimi elastičnimi rešitvami. Primerjani so tudi rezultati linearnih in nelinearnih analiz, za oba primera so ovrednotene pomembne razlike ter pomembni dejavniki, ki vplivajo na interakcijo predor-tla

Tunnel–ground interaction analysis: discrete beam–spring vs. continuous FE model

U cilju istraživanja interakcije tunela s okolnim tlom, provedene su dvodimenzijske linearne numeričke analize primjenom softvera ANSYS. Istraživanja su obuhvatila diskretni model s oprugama i kontinuirani model s konačnim elementima, kako bi se ispitala njihova sposobnost u simuliranju efekata interakcije konstrukcije i tla, s posebnim osvrtom na dinamičke analize, imajući u vidu da su ovi efekti posebice izraženi u seizmičkim uvjetima. Utjecaj potresa, simuliran u uvjetima čistog smika, određen je jednodimenzijskom analizom seizmičkog odgovora tla primjenom softvera EERA. Rezultati dobiveni pojednostavljenim dinamičkim analizama upoređeni su s najčešće primjenjivanim analitičkim rejšenjima, uz sagledavanje najznačajnijih faktora koji karakteriziraju interakciju tunelske konstrukcije s okolišem. U cilju razvoja što realnijih i relevantnijih modela, analizama su također obuhvaćeni i početni statički uvjeti.For the purpose of studying the soil–tunnel structure interaction, a number of two-dimensional linear numerical analyses has been performed with the aid of the software package ANSYS. The present study employs both discrete beam–spring and continuous FE models, in order to estimate their ability to simulate the soil–structure interaction effects. Since these effects are particularly pronounced during seismic events, the main attention has been focused on dynamic analyses. The earthquake loading is simulated under pure shear conditions and determined by the one-dimensional free-field ground response analysis using the code EERA. Results obtained by simplified dynamic analyses are compared with state-of-practice closed-form elastic solutions and significant factors influencing the tunnel–ground interaction are evaluated. In addition, with the author’s aim to develop more realistic and relevant models, effects of initial static conditions are also considered in the analyses

MATEMATIČKA INTERPRETACIJA RASIPANJA I REFRAKCIJE SEIZMIČKIH TALASA U PRISUSTVU TUNELSKIH OBJEKATA KRUŽNOG POPREČNOG PRESEKA

Mathematical interpretation of the elastic wave diffraction in circular cylinder coordinates is in the focus of this paper. Firstly, some of the most important properties of Bessel functions, pertinent to the elastic wave scattering problem, have been introduced. Afterwards, basic equations, upon which the method of wave function expansions is established, are given for cylindrical coordinates and for plane-wave representation. In addition, steady-state solutions for the cases of a single cavity and a single tunnel are presented, with respect to the wave scattering and refraction phenomena, considering both incident plane harmonic compressional and shear waves. The last part of the work is dealing with the translational addition theorems having an important role in the problems of diffraction of waves on a pair of circular cylinders.U fokusu ovog rada je interpretacija difrakcije i rasipanja seizmičkih talasa u polarno-cilindričnim koordinatama primenom odgovarajućeg matematičkog aparata. U radu je najpre dat pregled nekih od najznačajnijih svojstava cilindričnih Bessel-ovih funkcija, koje su podesne za matematičko opisivanje problema difrakcije i rasipanja seizmičkih talasa. Takođe, dat je prikaz jednačina koje predstavljaju osnovu tzv. metode ekspanzije talasnih funkcija (wave function expansion), u polarno-cilindričnim koordinatama i za slučaj seizmičkih talasa sa ravnim frontom. Prikazana su i rešenja primenom metode ekspanzije talasnih funkcija za slučaj nepodgrađenog tunelskog otvora i slučaj podgrađenog tunelskog objekta, sa aspekta fenomena rasipanja i refrakcije seizmičkih talasa, pod uticajem incidentnih harmonijskih P-talasa i S-talasa sa ravnim frontom. Na kraju rada prezentovane su i teoreme translatornog sabiranja (translational addition theorems), koje imaju važnu ulogu u matematičkom rešavanju problema difrakcije i rasipanja seizmičkih talasa u prisustvu dva blisko položena tunelska objekta

Flexible joints for seismic-resilient masonry-infilled RC frames: preliminary analyses for shaking table testing

Masonry infills are among the most vulnerable components of building frames, often undergoing severe damage even under minor or moderate seismic shaking. In recent years, flexible joints have emerged as a promising technique for protecting the infills from damage. To fully demonstrate the effectiveness of this technique, it is necessary to carry out full-scale tests on a structural prototype under realistic loading conditions, which can be simulated with shaking table testing. There is also a need to assess whether the joints can provide enough energy dissipation capabilities to enable a resilient-based design of infilled frames. The ERIES-FLEJOI project aims to address these gaps by investigating the performance of two promising systems based on flexible joints, one aimed at increasing the compliance of the infills, the other aimed at decoupling them from the frame. These systems, installed in two identical reinforced concrete (RC) frame prototypes, will be tested at the Dynamic Testing Laboratory of IZIIS (Skopje, N. Macedonia). This paper illustrates the two systems, the preliminary investigations, and the numerical analyses carried out to design the joint systems in order to meet the performance objectives and constraints posed by the shaking table capacity. The analyses involve two recently developed alternative modelling strategies, one based on a meso-scale description of the infill walls and the other on an equivalent discrete macro-element