Rock Mechanics
Milad Manafi; Hamed Molladovoodi; Hamid Chakeri
Abstract
Tunneling in urban areas is associated with various challenges that must be carefully evaluated during pre-construction studies. Among these challenges, tunnel excavation through fault zones is particularly critical and has been widely investigated. Previous studies have primarily focused on the displacement ...
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Tunneling in urban areas is associated with various challenges that must be carefully evaluated during pre-construction studies. Among these challenges, tunnel excavation through fault zones is particularly critical and has been widely investigated. Previous studies have primarily focused on the displacement of tunnel linings under different fault movement conditions. In the present study, the effects of three key parameters, ground movement magnitude, grout layer thickness, and fault plane angle, on the induced bending moments and normal forces were examined. The numerical results indicate that ground movement magnitude has the most significant influence on induced stresses, whereas grout layer thickness and fault plane angle exhibit comparable effects. The analyses further show that a 100% increase in ground movement leads to a 60.67% rise in the induced normal force. Increasing the grout layer thickness reduces the induced forces by 32.9%, while a larger fault plane angle decreases the normal force by 34.52%. The modeling outcomes also reveal that grout layer thickness is the most influential factor effecting the induced bending moments. These findings provide valuable insights for evaluating the structural capacity and potential failure of tunnel lining crossing fault zones.
Leila Nikakhtar; Shokroallah Zare; Hossein Mirzaei
Abstract
Surface settlement induced by tunneling is one of the most crucial problems in urban environments. Hence, accurate prediction of soil geotechnical properties is an important prerequisite in the minimization of it. In this research work, the amount of surface settlement is predicted using three-dimensional ...
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Surface settlement induced by tunneling is one of the most crucial problems in urban environments. Hence, accurate prediction of soil geotechnical properties is an important prerequisite in the minimization of it. In this research work, the amount of surface settlement is predicted using three-dimensional numerical simulation in the finite difference method and Artificial Neural Network (ANN). In order to determine the real geotechnical properties of soil layers around the tunnel; back-analysis is carried out using the optimization algorithm and monitoring data. Among the different optimization methods, genetic algorithm (GA) and particle swarm optimization (PSO) are selected, and their performance is compared. The results obtained show that the artificial neural network has a high ability with the amounts of R=0.99, RMSE=0.0117, and MSE= 0.000138 in predicting the surface settlement obtained from 150 simulations from randomly generated data. Comparing the results of back-analysis using the optimization algorithm, the genetic algorithm shows less error than the particle swarm algorithm in different initial populations. In all cases of analysis, the calculation time for both algorithms lasts about 5 minutes, which indicates the applicability of both algorithms in optimizing the parameters in mechanized tunneling in a short time.
S. Akbari; Sh. Zare; H. Chakeri; H. Mirzaei Nasir Abad
Abstract
Evaluation of the interaction between a new and the existing underground structures is one of the important problems in urban tunneling. In this work, using FLAC3D, four numerical models of single- and twin-tube tunnels in urban areas are developed, where the horizontal distance between the single- and ...
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Evaluation of the interaction between a new and the existing underground structures is one of the important problems in urban tunneling. In this work, using FLAC3D, four numerical models of single- and twin-tube tunnels in urban areas are developed, where the horizontal distance between the single- and twin-tube tunnels are varied. The aim is to analyze the effects of the horizontal distances, considering various criteria such as the deformation of linings, the forces and moments exerted on the twin-tube tunnels and their safety factors, the subsidence that occur on the surface and the nearby buildings, the stability of the single-tube tunnel, and the stability of the pillar lying between the single- and twin-tube tunnels. Considering the above-mentioned criteria, the results obtained indicate that the interaction between the single- and twin-tube tunnels is virtually negligible in the distance more than three times the single-tube tunnel diameter. Also the stability of the pillar lying between the tunnels makes the distance to be chosen at least 1.5 times the single-tube tunnel diameter.
Rock Mechanics
L. Nikakhtar; Sh. Zare; H. Mirzaei Nasir Abad
Abstract
One of the main issues involved during tunnel construction with tunnel boring machines is the tail gap grouting. This gap is between the external diameter of tunnel lining and the excavation boundary that is filled with high-pressure grouting materials. In this work, three different approaches of gap ...
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One of the main issues involved during tunnel construction with tunnel boring machines is the tail gap grouting. This gap is between the external diameter of tunnel lining and the excavation boundary that is filled with high-pressure grouting materials. In this work, three different approaches of gap grouting modeling in the FLAC3D software are investigated with a special attention to the influence of the grout material hardening process. In the first approach, the grout is modeled as a liquid during injection, and considering the TBM advancement and its hardening time, the grout characteristics are changed to the properties of the solid grouting. In the second approach, the grouting material from the beginning of injection is considered with the properties of solid grouting in the model, and the liquid phase is ignored. In the third approach, without considering the back-filled grouting area in the model geometry, only the injection pressure is applied to the end of the shield and behind the installed segments. The validity of the approaches is evaluated with respect to the maximum ground surface settlement. All the three approaches estimate different surface settlement but the result of the first approach is closer to the monitoring data. Also as a sensitivity analysis, in this work, we investigate the effect of the elastic modulus of liquid and solid grouting materials on the amount of surface settlement that can help to gain a more accurate insight into the effect of grout mixture.
