Εκτίμηση των γεωτεχνικών παραμέτρων της περιβάλλουσας βραχόμαζας από επί τόπου μετρήσεις και 3D αριθμητικές αναλύσεις- Εφαρμογή στην περιοχή Περιστερίου του Αττικό Μετρό.

Abstract

Εκτίμηση των γεωτεχνικών παραμέτρων της περιβάλλουσας βραχόμαζας από επί τόπου μετρήσεις και 3D αριθμητικές αναλύσεις - Εφαρμογή στην περιοχή Περιστερίου του Αττικό Μετρό.

Rapid growth rate of urban development has leαd to a continuously increasing need for new underground constructions that aim to further improve the living standards. Tunnels are a great example of such underground constructions. Often, tunneling takes place under severe geological and geotechnical conditions where engineering solutions must be found. Most recently, due to the improvement of design and construction equipment and due to the use of new excavation and support methods, tunneling has become feasible in geological formations and geotechnical conditions that used to be impossible in the past. The study of the pressure developed on the tunnel‟s temporary support is a complex issue that engineers are required to investigate early during the design phase of underground works. This is mostly because of the large scatter and uncertainty of the load from the surrounding geomaterial, estimated through the available empirical and analytical methods, which usually do not take into account the interaction of the system geomaterial - temporary support – final lining. This M.Sc. thesis presents the results of numerical analyses performed on the double-track tunnel located near Peristeri station of Attiko Metro. The results show the change of developed pressures on the shell of the temporary support measures of this cross section. Through the use of the 3-dimensional finite element code ABAQUS, a realistic simulation of the construction stages and the pressures on the shell in regards to the surrounding geomaterial was attempted. Therefore a numerical model was created that takes into account the stratigraphy and the laboratory results of the geotechnical evaluation, the actual construction conditions and the in-situ data of field measurements of pressure around the cross-section, finding the right balance between precision of results and calculation time of the analysis. The analyses obtained results on developing plastic deformations, the total and vertical displacements around the cross-section of the structure as well as the pressure distribution around the temporary support measures of the cross section. In order to achieve realistic estimation of the geotechnical parameters, wide parametric analyses, regarding the stress ratio Ko, the Young‟s modulus E, the thickness of the shotcrete and the cohesion of the formations encountered during the excavation process were carried out, aiming to quantify the sensitivity of the geotechnical problem. Furthermore, analyses were performed by sequential construction of shotcrete according to the tunnel advance rate and finally the effect of all these was studied in regards to the distributions and the values of the pressures on the shell of the temporary support. At this point it should be mentioned that in very good formations where subsidence and convergence measurements give low values as in the present thesis, the analysis of pressure cells results is an important instrument for the advancement of the project. Finally, after selecting appropriate geotechnical parameters for the geomaterial in which the tunneling was made and after using data about the pressures on the shell of the temporary support, a comparison was attempted between the in-situ measurements from the pressure cells in regards to the corresponding values of the mathematical model. That, in result, lead to the determination of the geotechnical strength parameters in regards to the formations of the area across and above the axis of tunneling construction.It should be underlined that the arguments and the conclusions which are included in this thesis are personal opinions of the authors and under no circumstances do they reflect the official opinion of Attiko Metro S.A.