جستجوی مقالات مرتبط با کلیدواژه « Numerical methods » در نشریات گروه « عمران »

The tunnel overburden height has considerable effect on stability or instability of surface tunnels. In this research, effects of overburden surface tunnel in strong rocks in both static and pseudo-static states investigated. In this paper, the results of pseudo-static analysis comparing to static state analysis are outstanding. Due to superficiality of tunnel, the water table line considered lower than tunnel bottom. The static analysis performed by Finite Element Method (FEM) and Finite Difference Method (FDM) and both results are close and acceptable. Results of static analysis indicated that by increasing in overburden height, horizontal displacement in sidewalls of tunnel and vertical deformation of tunnel crest would decrease. The stress amounts in sidewalls and crest of tunnel in pseudo-static state are higher than static condition.

In this paper, by using numerical method of half-plane boundary element which was previously proposed by the authors for single layer soil was applied for modeling embedded lined water transmission tunnels in the layered-soil medium. In the use of this method, only the boundary of lining and interfaces were required to be discretized. In addition to present the formulation of the mentioned method and verify the results in comparison of the literature, the behavior of a pressure tunnel embedded in two-layer soil was studied. In this regard, the effect of soil layers properties including Poisson ratio and elasticity modulus was investigated to obtain the stress distribution on the ground surface as well as around the tunnel. The results showed that half-plane boundary element method was a simple approach with high accuracy for modeling lined tunnel embedded in the layered soils. Use of this method was recommended for analyzing underground structures and presenting stress patterns in order to correct the existing codes.

When an underground space is drilled, the state of stresses is changed and a disturbance is created in the mechanical behavior of the surrounding Area. Stability of an underground space is provided by support systems. One of the most important loads in designing tunnel support system is environmental rock/soil loads. So far different methods have been represented to estimate the rock load such as empirical, analytical and numerical method that is based on engineering classification of rock. The aim of this study was to evaluate empirical and numerical methods of estimation of rock load on the segmental tunnel support system according to instrumentation data in the tunnel to transfer water from the Zayanderood dam to the city of Kashan. The results of numerical simulations, shows nearer results to field data.
In order to estimate the Rock load on tunnels, empirically, analytically or numerically methods those are useable for tunnel design engineers. Empirical methods are based on local observations, the required parameters in the project, comparing them with past experience and at last are based on the conclusions and determine the forces. In numerical method based on analysis stress, displacement and plastic zone is determined and rock load calculated. The most important advantage of this method for the simultaneous determination of the load on support system and deformation occurred in the rock mass. In estimating the Rock load for each of these methods sometimes large differences can be observed between the results from different methods.
Methodology and Approaches : In this research, all experimental methods available in the literature were evaluated. The SAP2000 and PLAXIS-2D software numerical modeling has been done. The results of empirical and numerical methods are compared with the results of field work and instrumentation and its results have been analyzed and interpreted. The results of the internal forces in the lining of software PLAXIS analysis and the results of the internal forces in the software SAP2000 (based on the rock of experimental methods) were compared and interpreted.
Results and Based on the results of numerical simulations, estimates of the analysis in Plaxis software for all host rock mass conditions, shows nearer results to field data. According to the analysis, the results of Goel & Jethwa and Goel et al. that based on RMR classification system using RMR Basic values as the closest approximation to field data to estimation of rock load have been introduced.

Technically speaking, there are different methods for modeling of the embedded water transmission pipes which include analytical, experimental and numerical ones. Although the responses of analytical as well as experimental methods have high accuracy, various types of arbitrarily shaped pipes cannot be applied for modeling in reality. It results in the development of numerical methods which have good flexibility. Generally, numerical methods can be divided into two categories of the volumetric and boundary methods. Despite the development of volumetric methods, such as finite element method (FEM) or finite difference method (FDM) and their simple formulations, the whole body including the inside and boundaries must be discretized in order to be modeled the embedded water transmission pipes. This process requires too much time and data. As a result, special attention has been given to the Boundary Element Method (BEM) among the various existing numerical methods during the recent two decades.