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Investigating the Effect of Using Soil Bentonite Wall on Damage Mitigation of Steel Buried Pipelines Subjected To Reverse Fault Rupture

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As pipelines pass from large geographical regions, their passage through areas with active faults in seismic regions might be inevitable. On the other hand, map of active faults is faced with many uncertainties and it is not possible to estimate the precise place of fault, angle of fault and the fault line. Thus, as lifelines, pipelines are vulnerable to great dangers during an earthquake and resulting permanent ground deformations known as PGD. The previous earthquakes such as Chi-Chi (1999) and Wenchuan (2008) showed a wide ranges of damages caused to various structures subjected to reverse fault rupture. The aim of this study is to investigate the effect of using soft deformable wall (in order to diverting rupture path and absorbing the tectonic deformation) in the response of buried pipelines subjected to reverse fault rupture considering two cases: a) pipeline parallel to fault line b) pipeline perpendicular to fault line. In this method, a thick diaphragm-type soil bentonite wall (SBW) is used in the fault diversion path in order to absorb the fault movements. Three-dimensional finite element model including steel buried pipe in dense sand subjected to reverse fault rupture is considered. The results indicate that using soil bentonite wall can remarkably mitigate the damages caused to pipeline in parallel case. In perpendicular case, the location of damages on buried pipeline is confined in a small area around the SBW which is of great importance in quick discovery of pipeline's damaged section location in order to quick repair and return of pipeline to service.
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COMPDYN 2017
6th ECCOMAS Thematic Conference on
Computational Methods in Structural Dynamics and Earthquake Engineering
M. Papadrakakis, M. Fragiadakis (eds.)
Rhodes Island, Greece, 1517 June 2017
INVESTIGATING THE EFFECT OF USING SOIL BENTONITE WALL
ON DAMAGE MITIGATION OF STEEL BURIED PIPELINES
SUBJECTED TO REVERSE FAULT RUPTURE
Farnoud Farzanegan Pour1, Meysam Fadaee2
1 M.Sc. Student of Earthquake Engineering, Department of Civil Engineering, Science and Research
branch, Islamic Azad University, Tehran, Iran
Farnoud.Farzaneganpour@srbiau.ac.ir
2 Assistant Professor, Department of Civil Engineering, Science and Research branch, Islamic Azad
University, Tehran, Iran
Fadaee@srbiau.ac.ir
Keywords: Steel Buried Pipeline, Reverse Fault Rupture, Three Dimensional Finite Element
Model, Soil Bentonite Wall, Damage Mitigation
Abstract. As pipelines pass from large geographical regions, their passage through areas
with active faults in seismic regions might be inevitable. On the other hand, map of active
faults is faced with many uncertainties and it is not possible to estimate the precise place of
fault, angle of fault and the fault line. Thus, as lifelines, pipelines are vulnerable to great
dangers during an earthquake and resulting permanent ground deformations known as PGD.
The previous earthquakes such as Chi-Chi (1999) and Wenchuan (2008) showed a wide
ranges of damages caused to various structures subjected to reverse fault rupture. The aim of
this study is to investigate the effect of using soft deformable wall (in order to diverting
rupture path and absorbing the tectonic deformation) in the response of buried pipelines
subjected to reverse fault rupture considering two cases: a) pipeline parallel to fault line b)
pipeline perpendicular to fault line.
In this method, a thick diaphragm-type soil bentonite wall (SBW) is used in the fault diversion
path in order to absorb the fault movements. Three-dimensional finite element model
including steel buried pipe in dense sand subjected to reverse fault rupture is considered. The
results indicate that using soil bentonite wall can remarkably mitigate the damages caused to
pipeline in parallel case. In perpendicular case, the location of damages on buried pipeline is
confined in a small area around the SBW which is of great importance in quick discovery of
pipeline’s damaged section location in order to quick repair and return of pipeline to service.
Farnoud Farzanegan Pour, Meysam Fadaee
1 INTRODUCTION
In today societies, While the distribution of vital material is developed, pipelines are
accounted as one of the most important and infra-structural facilities of every country. Water,
gas, oil and other liquids are remarkably transferred into the long distances path through
pipelines. Pipelines are installed in two forms of surface and buried which generally executed
buried due to the immunity to environmental hazards. But as buried pipelines encompassed
wide areas along its path, it fraught in various geotechnical dangers. One of the most
important of these dangers is earthquake and its consequences. During the investigation
carried out by O’Rourke and Liu, damages caused to pipelines mostly occurred by permanent
ground deformation (PGD) resulted from earthquakes [1]. This matter is of a great importance
regarding the fact that (PGD) happens in a short length of pipelines in comparison with
transient ground deformation (inferred of earthquake waves) and shows the importance of
pipeline behavior subjected to PGD. The PGD that caused by landslide, liquefaction or
surface rupture can remarkably apply damages on buried pipelines.
The report of the damages caused to water and gas pipelines in the past earthquakes of
Manjil (1990) [2], Northridge (1994) [3], Chi-Chi (1999) [4], Kokaeli (1999) [5] and Chili
(2010) [6], are shown the leakage and the stop of service of pipelines and in severe cases,
explosion and fire of gas pipelines.
Fault rupture is one of the most common types of PGD and can occur in various types.
Apparat from different types of fault rupture, Some of the important factors in the amount of
damages applied to pipelines are: The ratio of buried depth to pipe dimeter (H/D), ratio of
diameter to pipe thickness (D/t), soil types, fault angle ( figure 1) and pipe crossing angle
with respect to fault line ( β in figure 1).
The investigation carried out by Joshi et al on the effects of reverse fault rupture on buried
pipelines showed that the capacity of buried pipeline to accommodate the reverse fault rupture
could be increased if the pipe crossing angle with respect to fault line became near-parallel
[7]. On the other hand, with current knowledge, it is not always possible to determine the
precise place of fault and its path and therefore pipe crossing angle with respect to fault line
(β. Moreover, even the passage of buried pipeline parallel to fault line (figure 1a) which was
recommended by joshi et al [7], can cause severe damages to buried pipelines in some critical
conditions.
In this research, by inspiring from researches of Fadaee et al [8], [9] with using a thick
diaphragm-type soil bentonite wall (SBW) in a specific distance with buried pipelines which
is parallel with fault line (figure 1a), SBW absorbs the deformation resulted from any possible
reverse fault rupture and mitigates the damages caused to pipelines cross section (figure 2).
More details about the performance of SBW in reverse fault rupture are shown in [8], [9].
In this paper, the effect of using SBW on buried pipelines crossing fault line in normal
orientation (Figure 1b) in investigated.
Farnoud Farzanegan Pour, Meysam Fadaee
Figure 1. a schematic view of fault’s angle ( and pipeline crossing angle with fault line (β. a) Pipeline
parallel to fault line (β =180). b) Pipeline perpendicular to pipeline β)
Figure 2. a schematic view of SBW performance in case of reverse fault rupture
Farnoud Farzanegan Pour, Meysam Fadaee
2 NUMERICAL MODELING
A steel continuous buried pipeline was subjected to reverse fault rupture in two forms: a)
Pipeline parallel to fault line (figure 3). b) pipeline perpendicular to fault line (figure 4). To do
so, the finite element (FE) method was employed for numerical simulation of the problem.
Apart from some limits in exact simulation of shear band formation, FE modeling has been
shown to be able of competently reproducing fault rupture propagation in the free field [10],
as well as under shallow and deep foundations [11], and pipelines. An essential prerequisite is
the usage of a refined mesh and appropriate constitutive model for soil. Based on the findings
of previous studies [10], an elastoplastic constitutive model with Mohr Coulomb failure
criterion and isotropic strain softening are selected. the details of constitutive soil model are
shown in [10].
Figure 3. Details of FE model in parallel case a) The location of soil bentonite wall b) Pipe’s burial depth and
distance of SBW to pipe c) Details of pipe mesh d) Dimensions of soil blocks
Farnoud Farzanegan Pour, Meysam Fadaee
Figure 4. Details of FE model in perpendicular mode a) The location of soil bentonite wall b) Pipe’s burial depth
and distance of SBW to pipe c) Details of pipe mesh d) Dimensions of soil blocks
Dense sand was used in this research which was calibrated and verified in previous
research [9]. Table 1 shows the soil property.
E (first layer, kPa)
12000
E (last layer, kPa)
50000
42

32
12

1
0.165
(t/)
1.8
Table 1- summary of soil property
Elastoplastic behavior for pipe was considered too. The pipe which used was constructed
from API/5L X65 which is commonly used in oil and gas industries. A large-strain J2 flow
(von Mises) plasticity model with isotropic hardening is employed for describing the
mechanical behavior of the steel pipe material.
Figure 4 shows the stress-strain curve obtained from uniaxial tensile test done by
Vazouras et al [13].
Farnoud Farzanegan Pour, Meysam Fadaee
Figure 4. Uniaxial nominal stress-engineering strain curve, APL-5L-X65 [13]
Soil block dimension as shown in figure 3&4 was chosen as below:
depth of 20 meters, length of 80 meters and the width of the model, based on the sensitive
analysis was considered as 10 meters.
A burial depth of 2.5 meters was chosen for steel pipe. For modeling of pipeline, four
node reduced-integration shell elements (type S4R) was used in order to observe the wrinkle,
local buckling and ovalization of pipe’s cross-section, whereas eight-node reduced-integration
“brick” elements (C3D8R) was used for simulation of surrounding soil.
The dimension of soil mesh was also considered equal to dFE=1 based on the
recommendations of Anastasopoulos in the rupture area [10]. The dimensions of SBW and its
distance from pipe (for parallel mode) was chosen equal to 3, 16 and 2 meters for width, depth
and distance from pipe, respectively based on sensitive analysis.
A contact algorithm was considered to simulate the interface between the outer surface of
the steel pipe and the surrounding soil. To this end, interface friction was taken into account
for the algorithm, using a coulomb friction criterion and also allows for the separation of the
soil medium and pipe surface. According to Yimsiri et al [14], The friction coefficient, μ ,was
computed based on the reduced interface friction angle between the soil and the pipe equal to
2/3, which is soil internal friction. So based on given soil property is table 1, for the
selected soil, μ, was set to 0.52.
The analysis was conducted in two consecutive steps:
a) Application of gravity loading to simulate the initial stress state in the soil
b) Application of reverse faulting motion
The bottom boundary of the model represents the interface between the soil and the
underlying bedrock. Therefore, it was divided in two parts, one on the right representing the
footwall which remains motionless, and the other on the left been subjected to the tectonic
movement of the hanging wall.
3 MODELLING RESULTS
3.1 Pipeline parallel to fault line
In this section, by using expressed numerical modeling, at first, the effects of reverse fault
rupture in the angles of    and  on buried pipelines in parallel case without
using SBW is investigated. Then, the effects of using SBW in reducing damages caused to
pipeline is examined. For this purpose, several analysis with different fault line distance from
pipeline in both angles of    and    performed and the most critical ones
selected. These sensitive analyses showed that the most critical situation happens when the
shear band formed in soil due to fault movement, is passed from pipe cross section. In fact,
Farnoud Farzanegan Pour, Meysam Fadaee
pipe section is placed between footwall and hanging wall. Figure 5 shows a schematic view of
critical situation.
Figure 5. schematic view of critical condition of pipeline parallel to reverse fault rupture.
The factor of ovalization and pipe movement is also investigated. The ovalization of pipe
section is of great importance from the standpoint of performance reduction. Moreover, in gas
pipeline which is undergone inside pressure, this ovilization can lead to severe dangers.
Finally, the influence of SBW in fault rupture deviation and its effects on pipeline movements
is examined.
3.1.1 Pipe strains
The figure 6 and 7 compares the maximum compressive and tensile strains in pipe cross
section under the fault angles of 30 & 45 in two modes of with SBW and without SBW. It
can be clearly seen that with using SBW, pipe’s strains are remarkably decreased. A closer
look at these two figures shows that using SBW can reduce tensile and compressive strains up
to 90%.
(a) (b)
Figure 6. comparison of maximum compressive strains. A)    B)   
Farnoud Farzanegan Pour, Meysam Fadaee
(a) (b)
Figure 7. comparison of maximum tensile strains. A)   B)   
3.1.2 Pipe’s cross-Section deformations
As pipes are modeled by using shell elements of S4R, the pipe’s cross-section
deformations can be seen. Also, factor of ovality which is defined in Eq. (1), [15] as a
representation of the degree of distortion of pipe’s cross-section can be monitored. fo, Dmax,
Dmin are factor of ovality, maximum diameter and minimum diameter of pipe cross section,
respectively.

 (1)
Figure 8 shows the changes of
by increasing fault offset for the fault angles of 30 and
45, respectively in two modes of with and without SBW.
As it is expected, using SBW has remarkable effects on the reduce of pipe’s cross-section
ovalization. The precise investigation shows that using SBW can lead to reduction of up to
90% in factor of ovality.
Figure 9 shows deformed shape of pipe cross-section for two modes of with and without
SBW after 2.8m fault offset for fault angles of 45 & 30. The results indicate that using SBW
is hugely effective in preventing pipe cross-section deforming.
(a) (b)
Figure 8. changes of fo A)    B) 
Farnoud Farzanegan Pour, Meysam Fadaee
(a) (b) (c) (d
Figure 9. pipe cross-section deformation at 2.8 m fault offset. a) Without SBW,   b) With SBW,  
c) Without SBW,    d) With SBW,  
3.1.3 Pipe movements
As discussed earlier, in parallel form, critical situation happens when the pipeline placed
between hanging wall and footwall (figure 5). So the pipeline movement in the direction of
soil movement is inevitable. These movements can lead to some issues in pipe joints and
welds as a result of fault offsets.
Figure 10 shows the pipe movements for different fault offsets for two fault angles of 30
and 45. In =30, until the fault offset of 0.5m, the movement of pipeline with and without
SBW is approximately equal, but after 0.5m fault offset, pipe movements increases with an
almost constant trend without using SBW and in the fault offset of 2.8m, pipe moves 1.8 m.
While by using SBW, the pipe almost remains stable. For comparison, at 2.8 m fault offset,
pipe movement reaches 0.4m which is less than 25% of pipe movement without using SBW.
The trend is almost the same For =45.
(a) (b)
Figure 10. Pipeline movement: A)  B)   
3.2 Pipeline perpendicular to fault line
In this section, another case is investigated where the pipe crosses fault line
perpendicularly (figure 4). In this case the fault angle is considered to be 45. SBW with the
same dimensions is used. In order to investigate the effect of SBW, like previous case, at first,
a model without SBW is subjected to reverse fault rupture and then, the response of pipeline
with SBW wall which is placed in fault dispersion path (X=37 to X=40) compares to each
other.
3.2.1 Localizing pipe damages
Figure 11 shows the location of pipe strains along the pipe length for different fault
movements away from the wall. As can be seen, the location of pipe damages is localized in
Farnoud Farzanegan Pour, Meysam Fadaee
2m from left side of the SBW to 3m from right side of the SBW for various fault lines away
from the SBW.
So considering existing uncertainties in the exact determination of fault line location and
Regarding the fact that the SBW absorbs deformations of reverse fault rupture, with using
SBW, the location of damages subjected to pipeline can be localized in a small area around
the SBW. So that in case of reverse fault rupture on buried pipelines and subsequent damages
(like pipe rupture and leakage which is inevitable in large fault offsets), the process of repair
and return of pipeline to service can be done more rapidly. It should be noted that in case of
not using SBW, the location of pipe damages is not clear and it may cause delays in repairing
the pipeline.
Figure 11. Location of crown strains for different fault lines away from SBW
4 CONCLUSION
In this research, the effect of using soil bentonite wall (SBW) on damage mitigation caused
to pipeline subjected to reverse fault rupture in two cases of pipeline parallel to fault line and
pipeline perpendicular to fault line by using 3D FE method is investigated. The analyses are
carried out on dense sand and steel pipeline. The results are as follows:
1- In parallel case, using SBW with the dimensions of 3*16m distanced 2m away from
pipe center, can remarkably reduce damages when subjected to reverse fault rupture. The
results of investigation show that using SBW with mentioned dimension, after low fault offset
(0.5m) with fault angles 30 and 45, the pipe cross-section strains, factor of ovality and pipe
movements remains minor and constant throw different fault offsets. The comparison of
pipeline responses with and without using SBW indicates the reduction of up to 90% in pipe
strains and factor of ovality and up to 70% reduction in pipe movements with/ using SBW.
2- Comparison of pipe responses with two fault angles of 30 and 45 shows with using
of SBW, the effect of fault angle eliminates and the pipe responses remains the same.
3- For perpendicular case, with a matter of fact that SBW absorbs the deformation of
reverse fault rupture and inevitable severe pipe damages subjected to large reverse fault
offsets, using SBW can confine the area of damages subjected to pipeline in a small zone
around the SBW. So in case of earthquake and subsequent reverse fault rupture, the location
of pipe which needs to be repaired is obvious. This is of great importance in terms of quick
repair and service of pipeline as lifelines.
Farnoud Farzanegan Pour, Meysam Fadaee
REFERENCES
[1] O’Rourke, M.J., and Liu, X. (2012). “Seismic Design of Buried and Offshore
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[2] Towhata I. Geotechnical earthquake engineering. Springer series in geomechanics and
geoengineering. 2010. p. 684.
[3] O’Rourke TD, Palmer MC. Earthquake performance of gas transmission pipelines.
Earthq Spectra 1996;12(3):493527.
[4] Earthquake Engineering Research Institute. The Chi Chi, Taiwan earthquake of
September 21, 1999. EERI special earthquake report; December 1999
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[6] Ayala AG, O’Rourke MJ. Effects of the 1985 Michoacán Earthquake on Water Systems
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[12] Bray JD (1990), “The Effects of Tectonic Movements on Stresses and Deformations in
Earth Embankments,” PhD Dissertation, University of California, Berkeley.
[13] Vazouras P, Karamanos SA, Dakoulas P. (2010) “Finite element analysis of buried steel
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Engineering,30 (11):136176.
[14] Yimsiri S, Soga K, Yoshiaki K, Dasari GR, O’Rourke TD. Lateral and upward soil
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Eng 2003;130(8):83041
[15] Hojat Jalali H, Rahimzadeh Rofooei F, Attari NKA, Samadian M. (2016),
“Experimental and finite element study of the reverse faulting effects on buried
Farnoud Farzanegan Pour, Meysam Fadaee
continuous steel gas pipelines,” Soil Dynamics and Earthquake Engineering, Vol.86,
pp.1-14
... The pipe element modeling will use the FEM shell element model in the analysis of the pipe crossing the fault area. The reason for using the shell element is because it can be used to observe wrinkle, local buckling, and ovalization of the pipe cross-section (Pour & Fadaee, 2017). The type of shell element used is S4R. ...
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The three notorious earthquakes of 1999 in Turkey (Kocaeli and Düzce) and Taiwan (Chi-Chi), having offered numerous examples of surface fault rupturing underneath civil engineering structures, prompted increased interest in the subject. This paper develops a nonlinear finite-element methodology to study dip-slip ("normal" and "reverse") fault rupture propagation through sand. The procedure is verified through successful Class A predictions of four centrifuge model tests. The validated methodology is then utilized in a parametric study of fault rupture propagation through sand. Emphasis is given to results of engineering significance, such as: (1) the location of fault outcropping; (2) the vertical displacement profile of the ground surface; and (3) the minimum fault offset at bedrock necessary for the rupture to reach the ground surface. The analysis shows that dip-slip faults refract at the soil-rock interface, initially increasing in dip. Normal faults may keep increasing their dip as they approach the ground surface, as a function of the peak friction angle φp and the angle of dilation ψp. In contrast, reverse faults tend to decrease in dip, as they emerge on the ground surface. For small values of the base fault offset, h, relative to the soil thickness, H, a dip-slip rupture cannot propagate all the way to the surface. The h/H ratio required for outcropping is an increasing function of soil "ductility." Reverse faults require significantly higher h/H to outcrop, compared to normal faults. When the rupture outcrops, the height of the fault scrap, s, also depends on soil ductility.
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Observations after earthquakes where surface fault ruptures crossed engineering facilities reveal that some structures survived the rupture almost unscathed. In some cases, the rupture path appears to divert, "avoiding" the structure. Such observations point to an interaction between the propagating rupture, the soil, and the foundation. This paper (i) develops a two-step nonlinear finite-element methodology to study rupture propagation and its interaction with strip foundations; (ii) provides validation through successful Class "A" predictions of centrifuge model tests; and (iii) conducts a parameter study on the interaction of strip foundations with normal fault ruptures. It is shown that a heavily loaded foundation can substantially divert the rupture path, which may avoid outcropping underneath the foundation. The latter undergoes rigid body rotation, often detaching from the soil. Its distress arises mainly from the ensuing loss of support that takes place either at the edges or around its center. The average pressure q on the foundation largely dictates the width of such unsupported spans. Increasing q decreases the unsupported width, reducing foundation distress. The role of q is dual: (1) it compresses the soil, "flattening" fault-induced surface "anomalies" and (2) it changes the stress field underneath the foundation, facilitating rupture diversion. However, even if the rupture is diverted, the foundation may undergo significant stressing, depending on its position relative to the fault outcrop.
Article
The present paper investigates the mechanical behavior of buried steel pipelines, crossing an active strike-slip tectonic fault. The fault is normal to the pipeline direction and moves in the horizontal direction, causing stress and deformation in the pipeline. The interacting soil–pipeline system is modelled rigorously through finite elements, which account for large strains and displacements, nonlinear material behavior and special conditions of contact and friction on the soil–pipe interface. Considering steel pipelines of various diameter-to-thickness ratios, and typical steel material for pipeline applications (API 5L grades X65 and X80), the paper focuses on the effects of various soil and pipeline parameters on the structural response of the pipe, with particular emphasis on identifying pipeline failure (pipe wall wrinkling/local buckling or rupture). The effects of shear soil strength, soil stiffness, horizontal fault displacement, width of the fault slip zone are investigated. Furthermore, the influence of internal pressure on the structural response is examined. The results from the present investigation are aimed at determining the fault displacement at which the pipeline fails and can be used for pipeline design purposes. The results are presented in diagram form, which depicts the critical fault displacement, and the corresponding critical strain versus the pipe diameter-to-thickness ratio. A simplified analytical model is also developed to illustrate the counteracting effects of bending and axial stretching. The numerical results for the critical strain are also compared with the recent provisions of EN 1998-4 and ASCE MOP 119.
Article
Presently available simplified analytical methods and semi-empirical methods for the analysis of buried pipelines subjected to fault motion are suitable only for the strike-slip and the normal-slip type fault motions, and cannot be used for the reverse fault crossing case. A simple finite element model, which uses beam elements for the pipeline and discrete nonlinear springs for the soil, has been proposed to analyse buried pipeline subjected to reverse fault motion. The material nonlinearities associated with pipe-material and soil, and geometric nonlinearity associated with large deformations were incorporated in the analysis. Complex reverse fault motion was simulated using suitable constraints between pipe-nodes and ground ends of the soil spring. Results of the parametric study suggest that the pipeline's capacity to accommodate reverse fault offset can be increased significantly by choosing a near-parallel orientation in plan with respect to the fault line. Further improvement in the response of the pipeline is possible by adopting loose backfill, smooth and hard surface coating, and shallow burial depth in the fault crossing region. For normal or near normal orientations, pipeline is expected to fail due to beam buckling at very small fault offsets.
Seismic Design of Buried and Offshore Pipelines
  • M J O'rourke
  • X Liu
O'Rourke, M.J., and Liu, X. (2012). "Seismic Design of Buried and Offshore Pipelines," Monograph MCEER12-MN04, Buffalo, N.Y., USA.