جستجوی مقالات مرتبط با کلیدواژه "نشست سطح زمین" در نشریات گروه "مهندسی معدن"

Tunneling in urban areas by passing underneath several buildings causes subsidence due to stress relief and development of elastic and plastic deformations. If these subsidences are not controlled, the structures on the ground will be seriously damaged. Nowadays, several methods are used for tunnel analysis and design and for urban tunnels, which excavated in shallow and soft grounds, the best way is using numerical methods. Choosing the Appropriate behavioral model is one of the most basic steps in numerical analysis. tunnel excavation frequently uses the Mohr–Coulomb behavior model in numerical models.The Mohr-Coulomb elastic-plastic model is one of the most widely used models, used in cases evaluating the hardness of materials, independent of the surface tension. If the Mohr-Coulomb used for modeling of tunnel where in depth tunneling excavation is involved and where an increase in maximum ground surface settlement and decrease in the reliability of stability of tunnels can be seen, which may not be appropriate in some conditions. The more appropriate model should be used to solve this problem, one that can model the hardness of materials based on changes in the level of stress.In this study, the effect of different soil parameters on the ground surface settlement of Qom metro line A in Hardening Soil, Mohr–Coulomb and Drager Prager behavior models was investigated using the finite difference method. First, modeling of ground surface settlement was performed and the analysis results were compared with instrumentation data. Then, the effect of modulus of elasticity, friction angle, cohesion, Poisson's ratio and specific gravity parameters in different behavior models was investigated. The results of this research indicated that the Hardening Soil behavior model and the Drager Prager behavior model have the most and the least changes from the changes of soil parameters of Qom metro line A, respectively.

One of the problems with NATM tunneling in urban areas is the risk of excessive surface settlement during excavation operations. For real analysis and detailed study of surface settlement, it is necessary to pay attention to the real soil conditions. However, the conventional methods are always deterministic, rather than taking the natural spatial variability of soil properties into account. Therefore, in this study, an attempt has been made to model the real soil conditions by spatial variability of the soil young modulus based on a three-dimensional random field. By combining finite difference analysis with random field theory, a preliminary investigation has been performed into the surface settlement with spatially random Young modules. For this purpose, a combination of finite difference numerical method, random field, and Monte Carlo simulation is used which is known as the random finite difference method (RFDM). The procedure used is re-implemented by the authors in a MATLAB environment to combine it with The FLAC3D program and a series of parametric analyses were conducted to study the effects of uncertainty due to the variability of soil Young’s modulus on ground movements.

Excessive surface settlement is one of the major problems we encounter when constructing shallow tunnels in soft grounds. For the analytical study of surface settlement, it is necessary to consider soil properties in design calculations with high accuracy. In this research, the complex RFDM method is used to express the spatial variability of soil properties so that we can show its effects on surface settlement. The results demonstrate that soil variability exerts an influence both on the magnitude and distribution of surface settlement. In addition, it is concluded that negligence of the spatial variability of soil properties in surface settlement probability analysis can lead to underestimation of tunnel design parameters.

To create a random field, the values of SOF are determined first. Then, a three-dimensional random field is created by the random field generation functions. The random field created is assigned to the finite difference mesh by the embedded FISH language in FlAC3D.Finally, 1000 Monte Carlo simulations are performed and 1000 surface settlement curves for each SOF are generated. 

The mean values ​​of the Smax in numerical stochastic analysis when the SOF is 60 m is approximately equal to the obtained Smax from the numerical model because with increasing SOF the spatial correlation of the Young modulus parameter increases and is closer to the soil characteristics of the tunnel. In addition, the COV of the Smax tends to be 0.3 with increasing the SOF, but in general, it increases significantly (from 0.01 to 0.3), which causes changes in the magnitude of the Smax (between 5 and 80). Mm) becomes.The spatial variability of the Young modules causes the change in the magnitude of the surface settlement as well as a change in its location, so three-dimensional numerical analyzes can accurately display the maximum displacement of the Smax in both a vertical and longitudinal section of the tunnel.

Increasing urban development and social needs for transportation systems bring about construction and extension of urban transportation systems. Considering the fact that the important part of costs relates to excavation and maintenance of tunnels, choosing the single or double tube tunnels is one of the most important decisions in urban tunneling. In case of using single tube tunnel, it should be large enough to accommodate a pair of trains and their appurtenances. However, in case of using twin tunnels, considering that each tunnel is meant to be used for one train, the sections of the tunnels can be smaller. The aim of this paper is to use 3D numerical models for line 1 twin tube tunnels and line 2 single tube tunnel of Tabriz metro to study the various aspects of using twin or single tube tunnels in urban areas. Various criteria have been considered such as: stability of the single and twin tube tunnels, subsidence occurred on the surface and nearby buildings, forces and moments exerted on the twin and single tube tunnels and their factors of safety. In this paper finite difference numerical method (FLAC 3D) has been used to model the tunnels of both lines. The results show that when considering the viewpoint of displacements occurring on the walls of tunnels, using a single tube tunnel with big section will be recommended. However, when the viewpoint of subsidence control and forces and moments acting on segmental linings is taken into account, the use of the twin tube tunnels will be advantageous.

Evaluation of interaction between new and existing underground spaces is one of the important problems in tunneling in urban areas. In some cases it is necessary to excavate tunnels close to each other’s. This، in turn، will lead to important interaction between these tunnels. In this paper، using 3D numerical modeling of line 1 twin tunnels of Tabriz urban railway، excavation stability of these tunnels، using critical strain of Sakurai، have been studied. Also displacement pattern of lining in both twin tunnels (Sahand & Sabalan) have been investigated. In next step، effect of excavation of these tunnels on the subsidence of surface and adjacent buildings، using Cramer criteria and finite difference method (FLAC 3D)، have been studied. For the purpose of study of the interaction effects between these tunnels، forces and moments that act on the segmental lining of each tunnel and their safety factor have been verified. Eventually، stability of pillar that lies between two tunnels، have also been evaluated. The results show that: 1-twin tunnels of Tabriz metro will be stable during excavation. 2-Surface subsidence due to excavation of these tunnels will have no important effect on existing structures. 3-Safety factors varies between 5-10 on the different positions of segmental lining. 4- Pillar that lies between twin tunnels will be stable