THE TECHNIQUE FOR EXTRAPOLATION OF ROCK MASS INITIAL PARAMETERS DURING THE CONSTRUCTION OF THE TUNNEL

It is important to perform research to the degree that it is adequate to identify the features of the terrain composition, before, during, and after the building of facilities since predicting the behaviour of rock mass during tunnel construction is a complicated engineering challenge. Engineering research works in laboratories and in the field are of different scope and methodology during testing. In this paper, the established interdependencies of some of the basic parameters obtained during the testing of rock mass are presented: Edyn = f(Vp), Edyn = f(RMR) i Edyn = f(Q). Also, the relations between the engineering systems of rock mass classification and seismic primary waves are derived. RMR = f(Vp), Q = f(Vp). The relations were based on the examination of the rock mass for the construction needs of the tunnel on the Nis-Merdare highway. The results obtained in this study can be applied in environments that have similar lithological and structural characteristics

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

COMPARATIVE ANALYSIS OF ATTERBERG’S LIMITS OF FINE-GRAINED SOIL DETERMINED BY VARIOUS METHODS

Determination of the Atterberg’s limits is necessary for the classification of fine-grained soil. That limits can be determined according to the valid standard SRPS EN ISO 17892-12. Two methods are prescribed by the standard for determining the liquid limit: the Casagrande cup and the Fall Cone test, and one method for determining the plasticity limit: the thread-rolling method. In this paper the Fall Cone method was also used as an alternative method to determine the plastic limit. Ten samples of various fine-grained materials, originating from the wider area of the city of Niš, were tested. The classification of all samples was performed based on the results obtained by the methods prescribed by the standard and alternative methods. Comparative analysis shows that the results obtained by applying standard and alternative methods are close, but also that the scattering of results obtained by the Fall Cone method is significantly less, whereas the reproducibility is higher

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

DEFINITION OF CRACKS FOR THE ULTIMATE DEGENERATION PROCESS OF REVOLVING ELLIPSOIDS

The state of stress around cavities of the revolving ellipsoidal shape (prolate or oblate) in the extreme cases of their degeneration is a very complex problem. Namely, the shape of cavities is defined by an appropriate curvilinear coordinate system, which contains hyperbolic and trigonometric functions. In this paper, the treatment of revolving ellipsoid coordinates has been presented, along with transformations of ellipsoids for corresponding limiting values of their coordinates. Various forms of cracking can be defined through the ellipsoid degeneration process. In addition, the paper is dealing with a definition of the stress state for the limiting cases of degeneration

REASONS TO CHANGE THE TENDER PROJECT OF A TUNNEL DURING CONSTRUCTION

During construction, especially of tunnels, very often there is a need to change the tender technicaldocuments, i.e. the documents upon which the construction permit is obtained and the tender isannounced. The main reason for the change of documentation is, above all, unsuficient geotechnicalinvestigations due to which technical solutions and calculations are inadequate. Very rearlydocumentation is changed due to errors in the calculation if the techncal review of documentation iscorrectly done. The paper presents an example of the change of documentation during construction andthe reasons for that

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

PREDLOG MODIFIKACIJE EVROKODA 2 U POGLEDU PRORAČUNA NOSIVOSTI AB TEMELJA SAMACA NA PROBIJANJE

The paper first presents the calculation of the punching shear capacity of concentrically loaded reinforced concrete column footings according to the current Eurocode 2, which can be carried out in two ways: by conducting an iterative procedure and by a simplified procedure applying the diagrams. By using these procedures, the punching shear capacity calculation was performed for the footings examined within the experimental research of the authors of this study, as well as for the footings that were considered by experiments conducted by other authors. Based on the conducted analysis of the calculation results and experimentally recorded results, a modification of the expression of the current Eurocode 2 with regard to the calculation of the punching shear capacity of concentrically loaded RC column footings is proposed. The proposed modification more realistically takes into account the influence of compressive strength of concrete and the reinforcement ratio  in the footing, so that its application provides the results of punching failure forces that are closer to the results recorded by experimental tests.U radu je najpre predstavljen proračun nosivosti centrično opterećenih armiranobetonskih temelja samaca na probijanje prema aktuelnom Evrokodu 2, koji se može sprovesti dvojako: sprovođenjem iterativnog postupka i primenom zamenjujućih dijagrama. Primenom ovih postupaka, urađen je proračun nosivosti pri probijanju za temelje ispitivane u okviru sopstvenih eksperimentalnih istraživanja, kao i za temelje koji su bili sagledani  eksperimentima sprovedenim od strane drugih autora. Na osnovu sprovedene analize rezultata proračuna i eksperimentalno registrovanih rezultata, predložena je modifikacija izraza aktuelnog Evrokoda 2 u pogledu proračuna nosivosti centrično opterećenih AB temelja samaca na probijanje. Predložena modifikacija realnije uzima u obzir uticaj čvrstoće na pritisak betona i procenta armiranja temelja, tako da se njenom primenom dobijaju rezultati sila probijanja koji su bliži rezultatima registrovanim tokom eksperimentalnih ispitivanja

Punching Behaviour of Reinforced Concrete Footings at Testing and According to Eurocode 2 and fib Model Code 2010

Abstract Punching shear resistance of column footings and foundation slabs varies significantly in different standards. The reason for this is because standards define differently the position of the critical perimeter in which the punching shear resistance should be determined, and quantify the influences of the main parameters like effective depth, shear slenderness, compressive strength of concrete, longitudinal reinforcement ratio and tension yield stress of reinforcement in different ways. In order to quantify the level of safety in Eurocode 2 and in fib MC 2010, their design results are compared with the test results of the series of footings tested in completely realistic boundary conditions in terms of the subgrade soil. Besides the performed tests results, the analysis of the other investigations of the footing punching rested on the real soil is also included. Thus was obtained the answer to the question how individual characteristics of the footings and of the soil affect the punching bearing resistance and how accurately Eurocode 2 and fib MC 2010 predict the bearing capacity of the tested column footings. At the end, based on the test results and on the tests of others, and on and performed numerical analyses, a possible modification of Eurocode 2 in the field of reinforced concrete footing was proposed