Papers by Behzad Dastjerdy
Geomechanics and Geoengineering, 2019
This study presents the numerical modelling of tunnel segments under thrust loads of an EPB shiel... more This study presents the numerical modelling of tunnel segments under thrust loads of an EPB shielded TBM that utilised in Tabriz metro, Iran. Finite element analysis was used for 3D numerical investigations. Three different types of thrust jack configuration including French, German, and Japanese were applied to the segments and their results were compared. The numerical results indicate that the segment cracks are mainly concentrated in the circumferential joints in the French and Japanese configurations while the German configuration has the possibility of crushing in the longitudinal joints. By applying the maximum thrust load, the smallest tensile cracking area was observed in the Japanese configuration in comparison to the others. In the French and German configuration under the maximum thrust load, cracks were developed at the furthest point from the loading surface. Under the minimum thrust load, no crack appears in the Japanese configuration, while tensile cracks were initiated in the French and German configuration under the same load. Furthermore, the mechanical behaviour of the reinforced concrete (RC) was compared with plain concrete under various thrust loading configurations. Finally, the results of the numerical modelling are compared with the field observations for verifying of them.
Geotechnical and Geological Engineering, 2018
This paper presents numerical models of tunnel segments with respect to the steel rebars using a ... more This paper presents numerical models of tunnel segments with respect to the steel rebars using a finite element method under TBM thrust jack referring to the Tabriz metro line 2. The analyses have been carried out in five different steps. Numerical modellings have been done from the lowest ratio of reinforcement (the weakest case) to the highest ratio of it (the strongest case), which means that the curved longitudinal rebars were only placed within the concrete in the first step of the analysis, then other types of rebars are added gradually. The results indicated that stress contours in the z-direction (S33) of the model was approximately equal in all the steps. While distributed stress indicated more different behavior than the S33, which the maximum compressive and tensile distributed stresses are just applied on the reinforcement. The higher the reinforcement ratio, distributed stresses are increased step by step. So, it may be noticed that the reinforcement ratio was so crucial to the stresses which are needed to bear. A cracking form of the segment has been analyzed using different types of strains. The curved longitudinal rebars have a remarkable impact on cracking form in the z-direction in step 1, so that the magnitude of plastic strain in the z-direction (PE33) was remarkably decreased when they were placed within the concrete. Although adding the other main rebars has a negligible impact on the cracking form in z-direction whereas they can decline the plastic strain in the x-direction (PE11). The rebars which were added to the model in step 3, decrease the cracks around the shoulders of the segment. Nonetheless, all the rebars have not affected the segment behavior. Finally, in step 5, the cracking mechanism between the loading surfaces has completely changed. Also, displacement contours showed that the magnitude is decreased when the rebars are added to the reinforcement in every step.
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Papers by Behzad Dastjerdy