The distribution of stresses and strains during the portal section excavation for the right tube of the Sleme Tunnel is analysed by the Finite Element Method (FEM). Results of analyses obtained using ...2D and 3D models have been compared to in-situ measurements of tunnel convergence and ground surface settlements. Multistage excavations with pipe roof support of the working face were modelled. The numerical models verified that for this particular case a sufficiently safe and cost-efficient construction technology was applied.Original Abstract: Analizirano je stanja naprezanja i deformacija tijekom iskopa portable dionice desne cijevi tunela "Sleme" primjenom metode konacnih elemenata. Napravljena je usporedba rezultata proracuna ravninskog (2D) i prostornog (3D) modela s rezultatima terenskih mjerenja konvergencija u tunelu i slijeganja povrsine terena. Modelirani su visefazni iskopi s ojacanjem cela cijevnim krovom. Proracunski model je pokazao da je u navedenom slucaju primijenjena dovoljno sigurna i ekonomicna tehnologija iskopa.
This paper discusses the pullout capacity of spatial anchors in soil under applied vertical force. In field tests, the pullout forces were gradually increased and the ground surface displacements ...measured in two profiles perpendicular to each other. The laboratory and field tests were performed for several embedment depths and anchor diameter ratios in the same sand and under the same conditions. The anchor pulling was also laboratory-tested so that the vertical anchor displacements were given and the corresponding force intensity measured. The finite element method was used for the pullout force computation in test cases. The relations between displacements and pullout forces obtained by the laboratory tests, field tests and numerical computations were statistically analysed. Owing to gradual convergence of pullout forces towards the limit value, the exponential function was adopted as an approximation curve. The two obtained constants of the function represent the significant mechanical characteristics. The first is limit pullout force and the second gives the total stiffness of the soil mechanical system.
The distribution of stresses and strains during the portal section excavation for the right tube of the Sleme Tunnel is analysed by the Finite Element Method (FEM). Results of analyses obtained using ...2D and 3D models have been compared to in-situ measurements of tunnel convergence and ground surface settlements. Multistage excavations with pipe roof support of the working face were modelled. The numerical models verified that for this particular case a sufficiently safe and cost-efficient construction technology was applied.
Foreseeing of the rock massif behaviour in tunnel breaking out is a complex engineering problem. In projecting it is important to evaluate the stability conditions in excavation and after the ...acceptance of suitable breaking out methods, the acceptance of supporting in order to stabilize the opening. The New Austrian Tunnel Method (NATM) is the excavation method adaptable to frequent changes of geological and geotechnical conditions at the working face. Beside the excavation of the whole profile, excavations in soft materials along the tunnel trace condition, so called profile development, i. e. the application of multi-phase excavation. The conditions of stresses and strains for the whole-profile excavation are compared with the conditions of stresses and strains for starting stages of multi-phase excavations with the New Austrian Tunnel Method (the paper is published in Croatian).
The most questionable are the values of pressures between rock and support resulting from common deformations on the contact area between rock and support. Therefore the modelling and design of the ...tunnel support is not reliable, if it is based on active rock pressure resulting from this common deformations. The inversion of the design procedure is proposed. Instead of the active extreme pressure of the rock on support, the influence of ultimate reaction of the support on the rock has to be analysed. This procedure can be performed using the ultimate load principle, as proposed by Eurocodc 7 (Geotechnies). Normally, the rock has the tendency to increase the common conver¬gence until the support reaches its ultimate state. So, loading of profile boundary with the ultimate possible reaction of the support is very plausible. The reactive support pressures have to be probable and itself in equilibrium. The ultimate reactive load has to be reduced by Euro-code safety factor for structural elements and applied on the rock with given properties, or alternatively (as proposed by Eurocode 7) the soil or rock properties have to be diminished and calculated with full ultimate support pressures. If the rock with given (or proposed) pro¬perties and loaded with ultimate reactive pressures resulting from supposed support, satisfy its failure criterion, then is the compound system support-rock verificatcd. By this procedure, the number of relevant material properties is reduce to the primary stress ratio and the constants defining the failure criterion. The verification can be performed by any of numerical methods, but we prefer here used boundary elements method (the paper is published in Croatian).
By excavation of opening in the rock, a stress concentration around the opening occurs. The state of stresses and strains around an opening is analysed by theory of elasticity and by Finite Element ...Method (FEM).The aim of the paper is to determine the dimension of the FEM model for the stress and strain analysis around an elliptical opening in rock massif. The numerical calculation have been performed for two different boundary conditions: with forces or with displacements. Boundary conditions given by displacements give better approximation in the state of stress and strains. An example of the excavation of a road tunnel is used to represent stress concentration at the opening and the places where the plastic zones occur. The computation has been done after FEM comprising the Hock-Brown criterion of failure. The results of stability analysis point to the zones where failure of the rock material may be anticipa¬ted. This is important when planning and designing the primary supp¬orts. The comparison of the results of numerical modelling and field recording during excavation is of particular significance (the paper is published in Croatian).
Analizirano je stanja naprezanja i deformacija tijekom iskopa portalne dionice desne cijevi tunela "Sleme" primjenom metode konačnih elemenata. Napravljena je usporedba rezultata proračuna ravninskog ...(2D) i prostornog (3D) modela s rezultatima terenskih mjerenja konvergencija u tunelu i slijeganja površine terena. Modelirani su višefazni iskopi s ojačanjem čela cijevnim krovom. Proračunski model je pokazao da je u navedenom slučaju primijenjena dovoljno sigurna i ekonomična tehnologija iskopa.
The data from the engineering geological measurements have to be adequate prepared for later use in the computer programs for examination of the underground rooms stability. The only mean values of ...the dip direction and dip angles are not relevant for later calculations, but rather the statistically defined area containing chosen percentage of the collected data. The main conclusions of the block theory are accepted for visual presentation of the relation between the rooms cross--sections and the planes of discontinuities so that the position and shape of critical (key) blocks can be easy recognized. The roof falls and side sidings volumes have to be tilled in the site with the expensive concrete, so the avoiding of falls is a challenge to the theory and tunnelling practice. The program based on the boundary elements is adapted so that it can calculate the failure criteria on the planes of weakness and compare this with the failure criteria through in the rock itself. The area with critical security factor will be displayed and so the numerically possible rock and block failure recognized (the paper is published in Croatian).
This paper includes main theses, proofs, and procedures of Boundary Element Method (BEM). The computer program. announced in 1981, for the calculation of stresses and strains around underground ...opening was used, comprising plane strain state for elastic continuum. Preprocessor with interactive input and postprocessor for graphic presentation of the results have been added to the program. In the main program the influences of various support systems for underground rooms were added, especially: shotcrete layers, steel arches and passive and prestressed bolts. This numerical method has been under current development, especially for materials with nonlinear behaviour The method is faster than other numerical methods and represents an efficient supplementation to them (the paper is published in Croatian).
U članku je, radi ocjene točnosti proračuna konstrukcije, prikazan sustavni niz primjera s analitičkim rješenjima koja se metodom konačnih elemenata mogu prikazati u obliku cijelih brojeva ili ...razlomaka. Kao primjer odabran je Lagrangeov trikubični element u obliku kvadra. Primjeri su riješeni numerički uporabom standardnog broja značajnih znamenaka. Na kraju je iz razlike točnog i numeričkog rješenja određen točan iznos pogreške. Cijeli je postupak proveden programom Mathematica.
PDF
