Numerical Investigation of Tunnel Face Sability using Forepoling or Fiberglass Nails

Abstract Pre-support of tunnel excavation faces using fiberglass nails or forepoling umbrellas aims to improve face stability in cases where an unsupported excavation face will develop uncontrollably large face extrusion, leading to face instability. The paper presents the results of a large set of parametric 3D numerical analyses of tunnel face excavation by the Finite Element Code Simulia Abaqus, using various degrees of reinforcement by fiberglass nails or forepoling umbrellas. The analyses use the average face extrusion as a measure of face stability, considering that face instability is associated with large face extrusions while the safety factor against face instability can be correlated with lower face extrusions in case of pre-supported tunnel faces. The results of the analyses are normalized and a set of semi-empirical formulae and design graphs are produced to calculate the safety factor of supported tunnel faces against instability and other useful quantities in tunnel design (average face extrusion, volume loss and deconfinement coefficient) as a function of ground strength, overburden depth and amount of face reinforcement. The analyses show that tunnel face reinforcement with FG nails is much more effective and less costly in securing face stability than the use of forepoling umbrellas. It is shown that even a coarse grid of FG nails can achieve better results than very heavy forepoling, and the difference in effectiveness is more pronounced in weaker ground and or deeper tunnels.

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Shallow tunnel face stability analysis using finite elements

Naukovyi Visnyk Natsionalnoho Hirnychoho Universytetu ◽

10.33271/nvngu/2021-1/091 ◽

2021 ◽

pp. 91-97

Author(s):

I. Kahoul ◽

S. Yahyaoui ◽

Y. Mehidi ◽

Y. Khadri

Keyword(s):

Shear Strength ◽

Safety Factor ◽

Reduction Method ◽

Plastic State ◽

Subway Tunnel ◽

Fe Modelling ◽

Tunnel Face ◽

Face Stability ◽

Tunnel Face Stability ◽

2D And 3D

Purpose. This work aims to study the tunnel face stability (Algiers subway Tunnel) and evaluate common numerical procedures that are used for analyzing the tunnel face stability. Two-dimensional (2D) and three-dimensional (3D) Finite Element (FE) modeling using PLAXIS programs. Methodology. Tunneling is executed by the NATM method; two types of calculations are used. The first one is done by reducing the applied face pressure until the face is collapsed. The second calculation method involves the Phi-c (the angle of internal friction and bonding) reduction method, which is based on calculating the safety factor of the shear strength of the soil. Both methods are applied for 2D and 3D FE-modelling. Findings. It is found that determining the applied face pressure is an important consideration to avoid face failure or excessive deformations with numerical methods resulting in more precise findings than analytical methods. Originality. The originality of this work is the use of both 2D and 3D modelling, combined with two approaches: structural analysis of plastic state and Phi-c reduction method based on calculating the safety factor of the shear strength of the soil. Practical value. This study illustrates that the reducing shear strength method is much better than the reducing applied face pressure method. Moreover, the result of 3D FE-modelling gives a better prediction comparing with the 2D FE-modelling results.

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3D Numerical Investigation of Face Stability in Tunnels with Unsupported Face

10.21203/rs.3.rs-397369/v1 ◽

2021 ◽

Author(s):

DIMITRIOS GEORGIOU ◽

ALEXANDROS KALOS ◽

MICHAEL KAVVADAS

Keyword(s):

Stability Parameter ◽

Volume Loss ◽

Tunnel Wall ◽

Tunnel Face ◽

Face Stability ◽

Ground Conditions ◽

The Face ◽

Suitable Combination ◽

Average Face ◽

The Stability

Abstract The paper studies the stability of unsupported tunnel faces by analyzing the results of a large number of 3D numerical analyses of tunnel faces, in various ground conditions and overburden depths. The analyses calculate the average face extrusion (Uh) by averaging the axial displacement over the tunnel face. Limiting face stability occurs when the average face extrusion becomes very large and algorithmic convergence becomes problematic. Using the results of the analyses, a dimensionless “face stability parameter” is defined, which depends on a suitable combination of ground strength, overburden depth and tunnel width. The face stability parameter correlates very well with many critical tunnel face parameters, like the safety factor of the tunnel against face instability, the average face extrusion, the radial convergence of the tunnel wall at the excavation face, the volume loss and the deconfinement ratio at the tunnel face. Thus, semi-empirical formulae are proposed for the calculation of these parameters in terms of the face stability parameter. Since the face stability parameter can be easily calculated from basic tunnel and ground parameters, the above critical tunnel parameters can be calculated, and conclusions can be drawn about tunnel face stability, volume loss and the deconfinement ratio at the excavation face which can be useful in preliminary tunnel designs.

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Analisis Stabilitas dan Deformasi Terowongan Kereta Cepat Indonesia dengan Pendekatan Numerik Tiga Dimensi

RekaRacana: Jurnal Teknil Sipil ◽

10.26760/rekaracana.v6i2.111 ◽

2021 ◽

Vol 6 (2) ◽

pp. 111

Author(s):

Rinaldi Alamsyah ◽

Indra Noer Hamdhan

Keyword(s):

Static Analysis ◽

Safety Factor ◽

Tunnel Face ◽

Face Stability ◽

Level Of Activity ◽

Tunnel Face Stability ◽

The Stability ◽

High Level ◽

Double Track ◽

Plaxis 3D

ABSTRAKWilayah perkotaan yang didalamnya terdapat perkantoran dan tempat yang memiliki tingkat kegiatan yang sangat tinggi, menjadikan struktur terowongan bawah tanah sebagai salah satu solusi untuk meningkatkan infrastruktur transportasi secara optimal. Terowongan kereta cepat Indonesia merupakan salah satu terowongan yang dibangun dan berlokasi di Halim, DKI Jakarta. Terowongan dengan panjang 1.885 m ini memiliki jalur ganda (Double Track Railway). Untuk mengetahui stabilitas dan deformasi terowongan pada saat konstuksi, dilakukan analisis geoteknik. Analisis yang dilakukan yaitu analisis statik dan kondisi longterm dengan analisis dinamik. Tunneling Bore Machine (TBM) dengan sistem perkuatan linning precast dan grouting dipilih sebagai metode konstruksi untuk membangun terowongan. Pemodelan analisis statik menghasilkan deformasi terbesar 0,03056 m dan nilai faktor keamanan 1,869.Kata kunci: terowongan kereta cepat Indonesia, stabilitas, deformasi, faktor keamanan, TBM, PLAXIS 3D, linning, grouting ABSTRACTUrban areas with offices and places that have a very high level of activity make underground tunnel structures one of the solutions to optimally improve transportation infrastructure. The Indonesian fast train tunnel is one of the tunnels built and located at Halim, DKI Jakarta. The tunnel with a length of 1,885 m has a double track (Double Track Railway). To determine the stability and deformation of the tunnel during construction, a geotechnical analysis was performed. The analysis performed is static analysis and longterm conditions with dynamic analysis. Tunneling Bore Machine (TBM) with precast linning reinforcement and grouting system was chosen as the construction method for tunneling. Static analysis modeling produces the largest deformation 0.03056 m and a safety factor value of 1.869.Keywords: tunnel, face stability, deformation, safety factor, TBM, numerical method, PLAXIS 3D, linning, grouting

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Determination of Force Coefficients for a Submerged Rigid Breakwater under the Action of Solitary Waves

Water ◽

10.3390/w13030315 ◽

2021 ◽

Vol 13 (3) ◽

pp. 315

Author(s):

Francesco Aristodemo ◽

Giuseppe Tripepi ◽

Luana Gurnari ◽

Pasquale Filianoti

Keyword(s):

Solitary Waves ◽

Pressure Sensors ◽

Wave Forces ◽

Wave Loads ◽

Force Coefficients ◽

Wave Flume ◽

Physical Tests ◽

The Difference ◽

The University ◽

Semi Empirical

We present an analysis related to the evaluation of Morison and transverse force coefficients in the case of a submerged square barrier subject to the action of solitary waves. To this purpose, two-dimensional experimental research was undertaken in the wave flume of the University of Calabria, in which a rigid square barrier was provided by a discrete battery of pressure sensors to determine the horizontal and vertical hydrodynamic forces. A total set of 18 laboratory tests was carried out by varying the motion law of a piston-type paddle. Owing to the low Keulegan–Carpenter numbers of the tests, the force regime of the physical tests was defined by the dominance of the inertia loads in the horizontal direction and of the lift loads in the vertical one. Through the use of the time series of wave forces and the undisturbed kinematics, drag, horizontal inertia, lift, and vertical inertia coefficients in the Morison and transverse semi-empirical schemes were calculated using time-domain approaches, adopting the WLS1 method for the minimization of the difference between the maximum forces and the linked phase shifts by comparing laboratory and calculated wave loads. Practical equations to calculate these coefficients as a function of the wave non-linearity were introduced. The obtained results highlighted the prevalence of the horizontal forces in comparison with the vertical ones which, however, prove to be fundamental for stability purposes of the barrier. An overall good agreement between the experimental forces and those calculated by the calibrated semi-empirical schemes was found, particularly for the positive horizontal and vertical loads. The analysis of the hydrodynamic coefficients showed a decreasing trend for the drag, horizontal inertia, and lift coefficients as a function of the wave non-linearity, while the vertical inertia coefficient underlined an initial increasing trend and a successive slight decreasing trend.

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Relation between Magnetic, Spectroscopic and Structural Properties of Binuclear Copper(II) Complexes of Pentadentate Schiff-base Ligand, Semi-empirical and ab-initio Calculations

Zeitschrift für Naturforschung A ◽

10.1515/zna-2003-5-620 ◽

2003 ◽

Vol 58 (5-6) ◽

pp. 363-372 ◽

Cited By ~ 12

Author(s):

Y. Elerman ◽

H. Kara ◽

A. Elmali

Keyword(s):

Ab Initio ◽

Coupling Constants ◽

Antiferromagnetic Coupling ◽

X Ray Diffraction ◽

Hartree Fock ◽

Ligand Orbital ◽

Rhf Calculations ◽

The Difference ◽

Semi Empirical

The synthesis and characterization of [Cu2(L1)(3,5 prz)] (L1=1,3-Bis(2-hydroxy-3,5-chlorosalicylideneamino) propan-2-ol) 1 and of [Cu2(L2)(3,5 prz)] (L2=1,3-Bis(2-hydroxy-bromosalicylideneamino) propan-2-ol) 2 are reported. The compounds were studied by elemental analysis, infrared and electronic spectra. The structure of the Cu2(L1)(3,5 prz)] complex was determined by x-ray diffraction. The magnetochemical characteristics of these compounds were determined by temperaturedependent magnetic susceptibility measurements, revealing their antiferromagnetic coupling. The superexchange coupling constants are 210 cm−1 for 1 and 440 cm−1 for 2. The difference in the magnitude of the coupling constants was explained by the metal-ligand orbital overlaps and confirmed by ab-initio restricted Hartree-Fock (RHF) calculations. In order to determine the nature of the frontier orbitals, Extended Hückel Molecular Orbital (EHMO) calculations are also reported.

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