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Register a new userNumerical Analysis For Excavate Shallow Tunnel by T.B.M and its Impact on Settlement of the Soil Above the Tunnel
تحليل عددي لحفر نفق سطحي باستخدام TBM و أثرها على هبوط التربة فوق النفق
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Aِl-Baath University ورقة بحثية
Publication date
2017
fields
Geotechnical Engineering
and research's language is
العربية
Authors
إبراهيم حمود( باحث )
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Shamra Editor
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تم في هذا البحث دراسة مسألة حفر نفق مترو في ظروف تربة تشابه في توضعها و خواصها لتربة دمشق السطحية بالاعتماد على النمذجة ثنائية و ثلاثية الأبعاد و باستخدام برنامج العناصر المحدودة PLAXIS.
This paper presents and analyses the results of 2D and 3D numerical simulation conducted for the performance prediction of TBM tunneling in clay soil.
References used
Vermeer P.A.، Ruse N. (2000) Face stability when tunneling in soil and homogeneous rock. Proc. Developments in Theoretical Soil Mechanics – The John Booker Memorial Symposium. Sydney، 123- 138
Evert Hoek Big TunnelsIn Bad Rock2000 Terzaghi Lecture ASCE Journal of Geotechnical and Geoenvironmental Engineering Vol. 127، No. 9. September 2001، pages 726-740
Chambon، P. and J. F. Corte (1994) Shallow tunnels in cohesionless soil: stability of tunnel face. J. Geotech. Eng.، ASCE، 20(GT7)،1148-1165
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Supporting tunnel face by Fiber glass pipes technology is an effective method to
maintain the stability of tunnel face, thus reducing surface settlements, face deformation
and maintaining the safety of the workers and the mechanisms used in tunneli
ng.
This paper presents the results of finite-difference numerical analyses (FLAC3D program)
on the behavior of a shallow tunnel face reinforced by longitudinal fiber glass pipes. A 3D
numerical model has been calibrated and used to demonstrate the effectiveness of this
technique, and perform a parametric study to determine the critical reinforcements
parameters (the density (number of pipes)(A) and length (L)). The results indicate that the
face reinforcement technique using longitudinal fiber glass pipes can significantly reduce
the movements (face displacement and surface settlements), and thus improving the face
stability. These movements decrease by increasing the length of the pipes and increasing
the density of the pipes until reaching the critical density, and when we reach the critical
length, the pipes must be renewed to maintain the stability of the tunneling process.
The surrounding conditions of tunnel lining may change
during the investment period which leads to a redistribution of
forces acting on the tunnel lining and perhaps gives new forces are not taken into account during the design. The behavior of the
tunnel should be analyzed for the new conditions and assess its performance through the stages of investment.
In this paper, a case study of Alsafkon tunnel which is one of
the Syrian Railway deep tunnels is regarded. The lining of this
tunnel suffers from cracks, leakage, and other defects.
To analyze the behavior of the tunnel lining, it has been
modeled using the finite element method software Phase for five cases that represent the investment conditions experienced by the tunnel from its construction to date. It was found that the lining cracks appear from the third phase which represents the case of immersion of the tunnel by the underground water. The formation of a weak lens adjacent to the tunnel detected by geo radar plays also an important role in the cracking of the lining of the tunnel.
The results of numerical analysis were in correspondence with the current situation of the tunnel in terms of distributed cracks places in the concrete lining. The study showed also the improvement importance of the lens properties to avoid the total fall down of the tunnel.
In present investigation attempt has been made to study the bearing capacity and settlement
characteristics of footings subjected to central vertical load and resting on layered soil with
the help of model tests and with the application of finite e
lement method (FEM) to
calculate bearing capacity of a strip footing on one-layer and two-layer soil (Sand and
Clay). To investigate the effect of various parameters on soil bearing Capacity a
commercial finite element software, PLAXIS, has been used. Soil profile contains two soil
types including sand and clay. Soil behavior is represented by the elasto-plastic Mohrcoulomb
(MC) -model. For a one-layer case, the bearing capacity also is calculated which
has a good agreement with theoretical equations. For a layered soil, soft-over strong soil,
parametric study was carried out. It is concluded that the bearing capacity of footing
decreases as the height of clayey soil increases whilst the displacement under footing
increases. There is a critical depth where the stronger bottom layer does not affect ultimate
bearing capacity and failure mechanism of footing.
This research study aims at investigating the potential benefits of using the reinforcement
to improve the bearing capacity and reduce the settlement of strip footing on clay. To
implement this objective, many numerical 2D-analyses by finite elemen
t method / Plaxis
program were performed to study the behavior of reinforced soil foundation. And then we
carry out a parametric study of the most effective parameter on bearing capacity. The
results showed that the inclusion of reinforcement can significantly improve the bearing
capacity and reduce the footing settlement. The strain developed along the reinforcement is
directly related to the settlement. The results also showed that the inclusion of
reinforcement can redistribute the applied load to a wider area, thus minimizing stress
concentration and achieving a more uniform stress distribution. The redistribution of
stresses below the reinforced zone can result in reducing the settlement of the underlying
weak clayey soil.
In this paper, the modeling methods of tunneling and the surface subsidence induced by
that have been studied by using two-dimensional numerical analysis according to the FEM
method, assuming the green field condition، which means that there is no
load on the soil
surface above the tunnel. A FE study was conducted in which an elasto-plastic constitutive
model was adopted to model the soil behavior (HS, HSsmall).
This article includes a comparison between the results of numerical analysis and field
measurements to executed projects، and a suggested method for modeling tunnel
excavation and surface subsidence induced by that.
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