• Tunnel and Underground Space
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• v.20 no.2
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• pp.73-81
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• 2010

The paper presents the application of FE simulations of NATM tunnel using different constitutive models. The results from a series of two dimensional plane strain finite element analyses of medium-liner interaction for NATM are presented. Four types of constitutive models are considered, namely, linear elastic, elasto-plastic Mohr-Coulomb, Hardening-Soil, Soft-Soil model. The design for tunnels requires a proper estimate of surface settlement and lining forces. It is shown that the advanced constitutive model gives better predictions for both ground movement and structural forces.

• Proceedings of the Korean Geotechical Society Conference
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• 1991.10a
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• pp.255-270
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• 1991

In recent years. finite element methods have been used with increasing effectiveness in analysis of displacements and stresses within soil masses. However, one of the weakest links in the analytical representations used in these methods is the models of the material behaviour. Herein is discribed a modification to the finite element methods that allows solution problems with realistic stress-strain relation for soils. A finite element program for the precision prediction of the stress distribution within foundation has been developed using the elasto-plastic Work-Hardening model. The developed program is verified by comparing the results of this study with the tested results for Sacramento river sand. The main results obtained from the numerical examples are as follows: The vertical total stress increments are insensitive to drainage and constitutive equation of materials. The horizontal total stress increments are considerably affected by the drainage and constitutive equation of materials. The maximum shear stresses are affected by the drainage only in elasto-ptastic meterirals. The excess pore water pressures and the volumetric strains not only are considerably affected by the constitutive equation of materials. but also have almost similar distribution.

• Journal of the Korean GEO-environmental Society
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• v.22 no.1
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• pp.13-20
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• 2021

A suite of 3D large deformation finite element (FE) analyses was performed to investigate the load transfer mechanism and penetration resistance of spudcan foundations in heterogeneous soil profile consisting of sand and clay. The Elasto-Plastic models following Mohr-Coulomb and Tresca failure criteria were adopted for sand and clay, respectively. The accuracy of the numerical model was validated against centrifuge test measurements. The dense sand behavior with dilation is modeled using the non-associated flow rule. An investigation study consisting of key parameters, which includes variation in soil stratigraphy (sand-clay, sand-clay-sand), strength parameters of sand and clay (��' and su) and normalized height ratio of the sand layer (Hs/D) was conducted to assess the penetration behavior of spudcan. Based on calculated outputs, it was demonstrated that these parameters have a significant influence on the penetration resistance of spudcan. The calculated penetration resistance profiles are compared with the published (sand overlying clay) analytical model. It is confirmed that for the case of two-layer soil, the available theoretical model provides an accurate estimate of peak penetration resistance (qpeak). In the case of three-layer soil, the presence of a third stiff layer affects the penetration resistance profile due to the squeezing of the soil.

• International conference on construction engineering and project management
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• 2009.05a
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• pp.432-439
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• 2009

This research project was carried out to develop the technique to assess quantitatively and rapidly the stability of a tunnel by using the measured displacement at the tunnel construction site under excavation. To achieve this purpose, a critical strain concept was introduced and applied to an assessment of a tunnel under construction. The new technique calculates numerically the strains of the surrounding ground by using the measured displacements during excavation. A numerical practical system was developed based on the proposed analysis technique in this study. The feasibility of the developed analysis module was verified by incorporating the analysis results obtained by commercial programs into the developed analysis module. To verify the feasibility of the developed analysis module, analysis results of models both elastic and elasto-plastic grounds were investigated for the circular tunnel design. Then the measured displacements obtained in the field are utilized practically to assess the safety of tunnels using critical strain concept. It was verified that stress conditions of in-situ ground and ground material properties were accurately assessed by inputting the calculated displacement obtained by commercial program into this module for the elastic ground. However for the elasto-plastic ground, analysis module can reproduce the initial conditions more closely for the soft rock ground than for the weathered soil ground. The stability of tunnels evaluated with two types of strains, that is, the strains obtained by dividing the crown displacement into a tunnel size and the strains obtained by using the analysis module. From this study, it is confirmed that the critical strain concept can be fully adopted within the engineering judgment in practical tunnel problems and the developed module can be used as a reasonable tool for the assessment of the tunnel stability in the field.

• Journal of the Korean Geotechnical Society
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• v.15 no.5
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• pp.81-98
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• 1999

The influence of tunnelling on buildings has become an important issue in urban areas. The problem is an interactive one: not only do tunnelling settlements affect existing structures, but existing structures affect tunnel-induced soil movements. In order to examine the constraint of surface settlement and the degradation of building damage parameters, 3-dimensional elasto-plastic finite element analyses are peformed. Also, in this paper, the results of the parametric studies for the variations of the damage parameters due to the ground movements are presented by utilizing 2-dimensional elasto-plastic finite element models, totally 162 models. The width of a structure, its bending and axial stiffness, its position relative to the tunnel and the depth of tunnel are considered. The interaction is shown by reference to commonly-used building damage parameters, namely angular distortion, deflection ratio, maximum building settlements, maximum differential settlements and horizontal strain. By introducing relative stiffness parameters which combine the bending and axial stiffness of the structure with its width and stiffness of soil, design curves are established. These give a guide as to the likely modification of the greenfield settlement trough caused by a surface structure. They can be used to give initial estimates of likely building damage.