Stresses analysis using finite elements method around tunnels during construction stages

Dissertant

Shakir, Zaynab Hasan

Thesis advisor

Salim, Nahlah Muhammad Nuri
Shallash, Qays Taha

University

University of Technology

Faculty

-

Department

Department of Building and Construction Engineering

University Country

Iraq

Degree

Master

Degree Date

2013

English Abstract

The present research aims to study the stresses analysis through construction stages of the underground structures (Tunnels).

For this purpose, the finite element method (FEM) was adopted as an effective approach to analyze the test results using (SIGMA/W) program.

The research includes the study of the behavior of soil due to excavation of tunnel by calculating the displacements and stresses in the three positions of tunnel (crown, wall, and invert) during the various stages of construction.

The finite element analyses were carried out using (Elastic- plastic) and (linear elastic) models for the soil and the concrete liner respectively.

In this study, it can be noticed that the main reason for using an infinite element in the analysis is to extend the range of computed displacements that does not affect the boundary conditions.

Finally, the excavation process was done by excavating the tunnel in six stages instead of one stage because the latter causes high values of displacement.

In this study, different parameters are considered such as the effect of tunnel’s depth and tunnel’s diameter, soil properties, lining stiffness, surcharge value and surcharge position.

The effect of these parameters on the stresses and displacements is considered.

The results showed that there is a significant effect of tunnel’s depth on the vertical stresses and vertical displacements throughout all the tunnel positions where the increase of tunnel’s depth increases the vertical stresses and displacements, this is due to increase in the overburden pressure of the soil.

However, the excavation process led to move all the points surrounding the tunnel toward the center of the tunnel.

Moreover, when the diameter of tunnel increases the vertical displacement increases due to amount of soil removed in which the vertical stresses decreases due to distribution of the stress on larger area.

The results demonstrated that the soil cohesion (C) and the angle of internal friction (φ) have an inverse proportion to the vertical stresses and the vertical displacements, where as the soil properties (C, φ) increase, the vertical stresses reduce because the soil becomes more stable and the vertical displacements decrease due to increase in the modulus of elasticity of the soil.

It was also found that the increase in the stiffness of lining leads to decrease the vertical displacements which increase the vertical stresses.

Obviously, the values of displacements and stresses obtained from the analysis are affected by surcharge value, where the magnitude of stresses and displacements directly proportional to the magnitude of the surcharge.

Finally, the results displayed that the shifting of the surcharge position away from the center of the tunnel reduces the vertical stresses and vertical displacements.

Main Subjects

Engineering & Technology Sciences (Multidisciplinary)

Topics

• Tunnels

• APA
• MLA
• AMA

Language

English

Data Type

Arab Theses

Record ID

BIM-418560