The design and the manufacture of the oil and gas pipelines are being improved over the years in response to the observed damages and related disastrous effects. The improvements are possible, thanks to the increasing knowledge about pipeline performances in specific contexts. The seismic hazard on buried pipelines has always been of major concern, and the earthquake-induced soil liquefaction effects are among the most important issues to be accounted for in the design. Experiences based on case histories, experimental modelling, and numerical simulations represent the source of understanding of the involved mechanisms, the affecting parameters, and the structure response. Recently, all these aspects are becoming more accurate, thanks to the use of monitoring systems. The protection of pipelines from the seismic hazard is a crucial and challenging issue. This paper provides an overview of the research that has been conducted over the years in the specific framework of soil liquefaction phenomenon. Case histories on pipeline performances, commonly adopted analytical methods, and results of model tests and numerical simulations are summarized with main focus on the level of knowledge achieved up to date and the existing limitations that represent open issues for further development of the research. This study represents a useful background to be adopted from academics and practitioners in order to enhance the methods of analyses of the pipelines, thus improving their performances in the applications of the oil and gas industry.
Different scenarios need to be considered for pipeline design due to its deployment in large areas. If these structures cross regions of high seismicity, multiple serious problems might arise for these long-track buried structures and, among these, the soil liquefaction is of major interest. Several permanent ground movements are associated with liquefaction during earthquakes, such as ground oscillation, flow failure, loss of bearing capacity, lateral spreading, subsidence, and buoyancy. Buoyancy and lateral spreading are major critical effects for pipelines. A simplified scheme with possible induced mechanism is shown in Figure
Simplified scheme of liquefaction-induced effects on buried pipelines.
Thus, it is important to identify the liquefaction-prone areas for proper siting and design. The evidence of uplifted embedded structures induced by soil liquefaction was observed in numerous earthquakes, such as the 1964 Niigata Earthquake and the 1983 Nihonkai-Chubu Earthquake [
The uplift of buried pipelines induced by soil liquefaction was observed in several earthquakes such as the 1964 Niigata Earthquake, the 1983 Nihonkai-Chubu Earthquake [
The 1906 San Francisco and 1989 Loma Prieta earthquakes liquefaction observations are summarized by Holzer [
O’Rourke and Palmer [
With the 1971 San Fernando Earthquake, 11 pipelines were found to cross the areas involved in landsliding and lateral spreading. Moreover, two high-pressure natural gas transmission pipelines were severely damaged by the soil displacements. A specific study on the damage of transmission pipelines produced by liquefaction-induced soil displacements was conducted by O'Rourke and Tawfix [
The 1983 Nihonkai-Chubu Earthquake caused extensive destruction of lifeline facilities and, in Noshiro City, buried gas, water, and sewage pipelines suffered damages associated with ground displacements triggered by liquefaction [
The 1994 Northridge Earthquake induced permanent ground deformations that affected the Potrero Canyon characterized by the presence of alluvial deposits within a depth of 80 m. Sand boils and ground cracks were observed, and the latter were of both compressional and extensional types along the southern margin of the canyon, with few lateral displacements. In this scenario, pipelines experienced separations and cracks at the welds, most of them in correspondence to the ground cracks [
With the 1995 Kobe Earthquake, geotechnical failures were the main causes of damages including liquefaction effects. Two major and one small water treatment plants were damaged, and the distribution system was pulled away [
Ghayamghamian et al. [
The 2010-2011 Christchurch Earthquake sequence caused repeated liquefaction manifestations, and in areas close to the waterways, the liquefaction mainly caused lateral spreading. The widespread liquefaction in the suburbs of Christchurch, which interested almost one-thirds of the city area, shattered the lifelines to large areas resulting in numerous failures and reduction/loss of service for buried pipe networks [
In the occurrence of the 2010 Chile Earthquake, the GEER report [
From the real observations, it is possible to make guesses on the nature of the damage, but experimental modelling and numerical modelling are fundamental to understand the mechanisms and confirm or discard the hypotheses. On the other side, without real observations, it would not be possible to validate laboratory test performances or numerical simulation results. These considerations highlight the importance of all these three factors in the understanding process.
Case histories are very useful to observe the performances of the analysed structures in different scenarios; however, if the pipeline after the earthquake and related liquefaction event does not expose above the ground and if the network does seem to be working properly, then it may be possible not to detect deformations related to liquefaction effects at the moment. In this context, buoyancy and lateral spreading effects can also be detected after years, when the area will need to be inspected for maintenance, renewal, or other operations.
In case histories, it is difficult to observe the subsurface deformation. This limitation can be overcome with experimental simulations and is nowadays solved, thanks to the monitoring that can provide data on soil deformation as well. In the latter case, it appears evident that the monitoring is going to be localized in specific areas, so again, it is not possible to have a complete overview of the situation in the soil deposit. Despite this, field monitoring is a very precious source of knowledge to provide quantitative measurements of real performances that were only qualitatively provided in past years.
Another limitation of the real observations is the difficulty in extracting information about the different parameters affecting the problem in hand. Indeed, it may take years to address the influence of one single parameter on the pipeline response. This limitation can be solved by using numerical simulations through parametric analyses that allow exploring a huge variety of cases.
Experimental modelling to study the response of buried pipelines to the liquefaction phenomenon is usually conducted by using the shaking table or centrifuge devices. In the following, some of the experimental tests that were conducted over the years to address the pipeline performances are presented, with main findings and with the limitations of the used approaches and the state of knowledge. All the studies recalled here refer to the displacements induced by soil liquefaction and to the pipelines or underground structures experiencing similar behaviour.
Yasuda et al. [
Exhaustive research on the uplift behaviour of underground structures induced by soil liquefaction was conducted by Koseki et al. [
Sasaki and Tamura [
Comparisons on uplift displacements for different test conditions (extracted from [
Case | Relative density (%) | Ratio W/D (−) | Wave type | Shaking acceleration (g) | Uplift (m) |
---|---|---|---|---|---|
97-02 | 80 | 1.33 | Sinusoidal | 0.294 | 0.23 |
98-02 | 80 | 1.33 | Sinusoidal | 0.785 | 0.72 |
98-04 | 80 | 1.33 | Kobe | 0.785 | 0.26 |
98-05 | 50 | 1.33 | Kobe | 0.785 | 0.60 |
01-03 | 50 | 0.80 | Sinusoidal | 0.294 | 1.32 |
01-05 | 50 | 1.33 | Sinusoidal | 0.294 | 1.21 |
The failure mechanism involved in the uplift of pipelines in liquefied soils was explained by Stringer and Madabhushi [
Ichii et al. [
Chian and Madabhushi [
Tests characteristics (extracted from [
Test | Pipe | Soil | Container | ||
---|---|---|---|---|---|
ID | Mass (kg) | Sand type | Pore fluid viscosity/centrifuge g-level (cSt/g) | Hydraulic conductivity (m/s) | Box type |
DC-02 | 5425 | Hostun | 1 | 4.37 × 10−4 | ESB box |
DC-03 | 5425 | Fraction E | 1 | 0.99 × 10−4 | ESB box |
DC-04 | 5425 | Hostun | 1/9 | 3.93 × 10−3 | ESB box |
DC-04b | 5425 & 438 | Hostun | 1/3 | 1.31 × 10−3 | Window box |
DC-07 | 5425 & 438 | Hostun | 1 | 4.37 × 10−4 | Window box |
DC-10 | 2411 & 195 | Hostun | 1 | 4.37 × 10−4 | Window box |
Experimental uplift displacement (extracted from [
Test | Earthquake | Pipe | |||
---|---|---|---|---|---|
ID | Peak bedrock acc. (g) | Duration (s) | Diameter (m) | Depth to axis/diameter (−) | Uplift (m) |
DC-02 | 0.22 | 25 | 5.00 | 1.5 | 0.676 |
DC-02 | 0.22 | 25 | 5.00 | 1.1 | 0.816 |
DC-02 | 0.23 | 40 | 5.00 | 1.5 | 0.754 |
DC-02 | 0.23 | 40 | 5.00 | 1.1 | 1.512 |
DC-03 | 0.22 | 25 | 5.00 | 1.5 | 0.337 |
DC-03 | 0.22 | 25 | 5.00 | 1.1 | 0.436 |
DC-03 | 0.23 | 40 | 5.00 | 1.5 | 0.264 |
DC-03 | 0.23 | 40 | 5.00 | 1.1 | 0.447 |
DC-04 | 0.21 | 25 | 5.00 | 1.5 | 0.559 |
DC-04 | 0.21 | 25 | 5.00 | 1.1 | 0.894 |
DC-04 | 0.22 | 40 | 5.00 | 1.5 | 0.286 |
DC-04 | 0.22 | 40 | 5.00 | 1.1 | 0.687 |
DC-04b | 0.08 | 25 | 5.00 | 1.5 | 0.143 |
DC-04b | 0.08 | 25 | 1.42 | 1.5 | 0.154 |
DC-04b | 0.09 | 40 | 5.00 | 1.5 | 0.018 |
DC-04b | 0.09 | 40 | 1.42 | 1.5 | 0.096 |
DC-04b | 0.09 | 50 | 5.00 | 1.5 | -0.022 |
DC-04b | 0.09 | 50 | 1.42 | 1.5 | 0.357 |
DC-07 | 0.09 | 25 | 5.00 | 2.0 | 0.025 |
DC-07 | 0.09 | 25 | 1.42 | 2.0 | 0.269 |
DC-07 | 0.10 | 40 | 5.00 | 2.0 | 0.027 |
DC-07 | 0.10 | 40 | 1.42 | 2.0 | 0.110 |
DC-10 | 0.17 | 18 | 3.33 | 1.5 | 0.182 |
DC-10 | 0.17 | 18 | 0.95 | 1.5 | 0.193 |
DC-10 | 0.18 | 25 | 3.33 | 1.5 | 0.058 |
DC-10 | 0.18 | 25 | 0.95 | 1.5 | 0.236 |
DC-10 | 0.18 | 36 | 3.33 | 1.5 | 0.013 |
DC-10 | 0.18 | 36 | 0.95 | 1.5 | 0.289 |
Chian et al. [
The first author of this review article [
Pipe vertical displacements summary (extracted from [
Shaking step (No.) | ||||||||||||
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | |
Base acceleration amplitude (g) | ||||||||||||
0.1 | 0.2 | 0.3 | 0.4 | 0.5 | 0.6 | 0.5 | 0.4 | 0.3 | 0.2 | 0.1 | 0.8 | |
# | Vertical displacement (mm) (−, uplift; +, settlement) | |||||||||||
1 | 0.3 | −1.8 | −10.5 | −6.6 | −4.7 | −7.6 | −6.2 | −5.1 | −1.5 | −2.5 | −0.7 | 4.0 |
2 | 1.0 | −1.0 | −3.8 | −1.1 | −0.6 | −2.3 | −0.7 | −0.4 | −0.1 | 0.1 | 0.1 | 2.2 |
3 | 0.9 | 0.7 | 2.7 | 4.0 | 4.0 | 4.2 | 3.1 | 2.2 | 0.9 | 0.5 | 0.0 | 0.3 |
Trautmann and O’Rourke [
Towhata et al. [
Ashford and Juirnarongrit [
Shimamura et al. [
Sarvanis et al. [
The pipeline floatation is experimentally well understood, thanks to the exhaustive model tests that have been conducted to address the specific issue. The pipeline performance in terms of uplift, within the framework of soil liquefaction phenomenon, is assessed in terms of both involved mechanisms and affecting parameters.
Different is the case of the lateral spreading phenomenon, for which experimental modelling on the specific matter is not directly available for the evaluation of pipeline performances. This means that, to account for the effects of possible permanent ground displacement on the pipeline caused by soil liquefaction induced lateral spreading, it is usually referred to (1) analyses conducted on piles; (2) pull-out tests with statically applied forces; or (3) permanent ground displacements induced by fault ruptures or landslides. In the latter point, the replication of the ground deformation effects on pipelines, which is similar to that induced by fault movement or landslide in terms of tensional state, other than the phenomenon itself, is commonly adopted. This is done due to the difficulties of reproducing the lateral spreading phenomenon with embedded structure interaction in model testing. It is clear, however, that the stress-strain behaviour of soil undergoing liquefaction process is completely different from the application of a force that can only simulate the direction and the entity of displacement.
The blasting in the full-scale testing site was proven to successfully liquefy the soil and induce lateral spreading; however, the movement produced by the blasting is not controlled and can lead to different distributions of displacements and strains. It should be carefully used to assess performances that are related to earthquake-induced effects due to the differences in the generation of waves. The explosive loadings are used to address different pipeline performances as well. For example, Zhang et al. [
The overall performances of buried pipelines are well caught from these model tests. However, being a reproduction in a laboratory of real mechanisms, some limitations can affect the results and impose restrictions on the extension of the achieved outcome to the real field. Moreover, it is worth considering that test results are dependent on the specific model test characteristics (e.g., model scale, similitude laws, geometries, model preparation, ground characteristics, and input motion characteristics) and, in most cases, it is difficult to generalize them, allowing quantitative comparisons.
Liquefaction is a very important issue but also challenging and still with open questions due to its complexity, mostly for the interaction with structures. In model tests, the liquefaction is one of the nonfully reproducible phenomena through the similitude theories. Big models should be used, to avoid scaling factors, but this would be very expensive. However, the possibility to use model tests depends on the specific results to be extracted from the experimental tests.
1-g shaking table tests are widely used to study the soil-structure interaction and liquefaction process development. However, the gravity field does not allow the reproduction of the confining pressure as in the real case. This stress level difference affects the strain level that alters the soil dynamic properties, and the reproduction of the stress-strain behaviour of sand is fundamental for describing the development of the liquefaction process. Moreover, there is often a difference related to the shaking frequency effects. These differences between the model and prototype also affect the similitude of residual displacements that govern the seismic damage in geotechnical structures, as it can be the case of pipeline residual displacements. Some scaling factors can be adopted to reduce the discrepancies, but the scaling factors cannot satisfy all the similarities with the real field.
Concerning, instead, the centrifuge devices, the centrifugal effect itself allows the respect of stress level even in a small-scale model, thus being able to reproduce the same stress-strain behaviour of soil in the real field. However, the limitation of this model testing can be found in the nonreproduction of geological history and ageing effects, as can be expected in model grounds prepared in the laboratory. Of course, in the real field, the soil deposit is affected, among others, by the geological history, the age, the soil grain packing, and the previous seismic shaking sequence.
Other than for the similarities, that would prefer the centrifuge device for the stress level correspondence, 1-g shaking table tests are usually adopted due to the easiness in preparing the models that have a smaller size than centrifuge models, other than smaller maintenance costs.
A deep analysis of the difference between 1-g shaking table tests and centrifuge modelling and the scaling factors to be adopted for the similitude law with the real field is provided by Towhata [
This section mainly refers to the numerical approaches adopted in the literature to investigate the response of embedded pipelines against liquefaction-induced displacements, focusing on the studies that addressed the problem from a computational point of view and analysing both the adopted strategies and solutions developed to overcome the difficulties linked to the modelling process. With reference to liquefaction-induced buoyancy and lateral spreading, an overview of the numerical simulations performed to assess the pipeline response against the abovementioned liquefaction effects is presented.
Pipelines need to be designed in order to guarantee their stability against both static and dynamic loads. Although the static calculation strategies are quite shared in the standard of practice, different approaches are used to evaluate the response of the embedded structures to dynamic excitations. The earthquake-induced effects along a pipeline can be modelled, applying to the structure a deformation pattern that is independent of the structural stiffness if the structure is softer than the soil. However, when the stiffness of both soil and structure is similar, great significance is assumed by the definition of the soil-structure interaction. The most convenient way to face this problem consists of avoiding to define the nondefinition of a proper interaction by imposing that pipeline moves in accordance with the surrounding soil [
Even if a wide research body was developed in order to analyse the behaviour of tunnels in liquefiable soils (see, for instance, Chang et al. [
Regarding the finite element strategy, Datta [
O’Rourke and Lane [
Takada et al. [
Shao [
Sahoo et al. [
A strong effort to simulate the pipeline response under seismic loads, with a specific focus on the crossing of active faults, was taken within the GIPIPE research project [
In the work proposed by Zou et al. [
Ling et al. [
Saeedzadeh and Hataf [
Chian et al. [
Sharafi and Parsafar [
In their work, Marinatou et al. [
Xia and Zhang [
An overview of computational methods adopted to evaluate the stability of onshore pipelines in liquefiable soils was also provided by Castiglia et al. [
In the case of liquefaction, soil stress-strain behaviour is very difficult to be modelled numerically. Moreover, the development of excess pore water pressure in undrained conditions is a crucial parameter to be simulated, the cause of the phenomenon being itself and extensive damage.
The replication of the in situ lateral spreading conditions through physical tests is extremely arduous. Consequently, the numerical models that aim at simulating this particular phenomenon cannot be easily developed because of the problems connected to the calibration procedure. Indeed, very often, the models to evaluate the response of pipelines crossing active faults are used in lateral spreading conditions as well. This can generate mispredictions linked, for example, to the unconsidered liquefaction of the surrounding soil.
Uplift problems appear easier to be modelled through physical tests, but the soil-pipe interaction in numerical simulations is generally difficult to be reproduced. As it was observed, there are always errors in the prediction of the response closer to the pipeline. This happens because the response is strongly affected by local mechanisms (e.g., local cracks in the soil overlying the pipeline due to the uplift) that are challenging to be simulated.
The modelling process is often very difficult to be attained because a reliable computational analysis needs a lot of parameters to be defined. Unfortunately, in the practice, there is a strong connection with the economic aspect, and for this reason, proper soil characterization is not always available.
Regarding the soil definition, a lot of constitutive models capable to simulate liquefaction are available in the literature, even though being developed and calibrated for a specific material. Furthermore, some mispredictions for high strain levels can be generated; for this reason, the postliquefaction behaviour of the soils is very difficult to be evaluated, even applying very advanced constitutive models.
A key role is also played by the meshing technique. Indeed, a proper meshing procedure of the analysed dominion has to ensure that a high displacement field is allowed, and this can affect the computational time. In addition, the seepage is not often considered in the analyses and this can lead to misleading evaluation of the model response. Finally, in the real observations, there is a coupling between horizontal and vertical displacements, while in the analysis, this condition is difficult to reproduce.
The analytical methods presented here come from a geotechnical analysis of the phenomena without a focus on the stresses and strains imposed on the structure itself, which would need to account for structural characteristics as well and is out of the scope of this study. Moreover, among the analytical approaches available in the literature, only easily adopted simplified methods are mentioned in this paragraph, with relevance for practical applications. This means that additional research is available on the topic, but often the input data are unknown or of difficult determination, thus making the simplified procedure not worth using.
In the following, commonly used analytical approaches for the evaluation of vertical and horizontal forces acting on the pipe within liquefied soils are recalled, referring to the pipeline transverse cross section.
Regarding the uplift, the upward force exercised on the pipeline can be easily computed on the basis of a vertical equilibrium of forces acting on a transversal cross section (Figure
Simplified schemes of vertical equilibrium (a) and horizontal equilibrium (b).
Castiglia [
This conservative approach can be substituted by the procedure given by Huang et al. [
When structures are buried in saturated soils and subjected to horizontal earthquake vibrations, the lateral side of the pipe may be subjected to the combination of the dynamic water and dynamic effective soil pressure. Soil and water static pressures are applied on both sides of the embedded pipe and acting opposite to each other, thus making their contribution null and the dynamic pressure the only resultant on the buried structure. This cyclic component can be modelled by using the Westergaard [
In equation (2),
If the problem is extended from the pipe’s transversal cross section to the longitudinal development of the buried structure, additional elements need to be accounted for in the analytical solutions. The soil-pipe interaction can be modelled, in the simplest way, as a beam on elastic foundation, if it is within the range of elastic deformations. The interface between the pipe and soil is accounted for with elastic springs. The stiffness of the springs in liquefied soil can be computed using correction factors that can be applied to the stiffness of the spring for nonliquefied soils. Miyajima and Kitaura [
When a large buoyancy displacement is expected, the maximum pipe displacement to prevent its breakage can be computed by referring to a beam of length equal to the length of the liquefied area, constrained at the extremities in correspondence to the nonliquefied soils. Hou et al. [
In equation (3),
Even if the simplified methodologies represent a very useful tool to have a first assessment of the uplift or the permanent ground displacement related to lateral spreading, they are limited by the assumptions under which they are developed, their predictions becoming unreliable in case these conditions are not replicated. In some cases, caution is required not to oversimplify a complex problem through the use of correction factors or by neglecting some important contributions.
Even if the practical use of the abovementioned simplified methodologies is extremely advantageous for its timesaving, these methods often mispredict the displacements observed, carrying out physical tests, and for this reason, a more refined analysis is preferred. In this context, the computer analysis can decisively help the designer to test how the pipeline response is sensitive to the different parameters involved in the design process through, for example, parametric analysis.
Protection from pipeline failure is one of the main concerns in the oil and gas industry due to potential serious implications in terms of economic loss and environmental concerns if the damages of such lifeline systems occur. Interesting data are provided by Dai et al. [
In seismic areas, the principal effects of liquefaction-induced ground deformations on pipelines are recalled here, with a focus on buoyancy and lateral spreading. Case histories reporting pipelines damage in the occurrence of liquefaction manifestations with main earthquakes are listed and briefly described, emphasizing the experience of failure modes and associated geological contexts and earthquake characteristics. Methods for experimental and numerical modelling of soil-pipe interaction in the occurrence of liquefaction, referring to uplift and lateral movement, are reviewed. The achieved outcomes of the research and the main limitations are described because these represent the build-up of the current state of knowledge. Case histories of real observations and experimental and numerical modelling are a very important source of understanding, and they all contribute to the improvement of seismic hazard effect preventions. This current state of knowledge is important, indeed, in view of future improvements of the sources of knowledge that can become more accurate, faster, and more effective by reducing the limitations; of the response to seismic hazard effects of pipeline networks with more effective prevention systems; and of the pipeline performances, also through the technologies adopted for pipeline equipment.
The data used to support the findings of this study are from the existing literature.
The authors declare that there are no conflicts of interest regarding the publication of this paper.